DUKE GEOLOGICAL LABORATORY
COMPILED LIST OF 185 ON-THE-ROCKS FIELD TRIP STOPS
Dear friends of the On-The-Rocks Field Trip Series - Below, for educational interest, we provide an annotated On-The-Rocks field trip listing of all of the localities visited during the decade-long On-The-Rocks Field Trip Series conducted by Drs. Charles Merguerian and John E. Sanders. The OTR series consisted of forty-two all-day (and some two-day) geological field trips conducted to 24 regions between September 1988 and November 1998. The field trips were sponsored through June of 1996 by the New York Academy of Sciences. Later in 1997-98, a few trips were sponsored by the 92nd Street Y in Manhattan and by the Hofstra University College of Continuing Education in Hempstead.
With limited geographic overlap, the trips covered twenty-four specific destinations or regions within a radius of 150 miles of New York City. Because some trips were conducted more than once, the result of popular demand, trip dates are listed below under each trip heading. The trips and their individual localities ("stops") are organized under each region's Guidebook # (#1. through #24.) which are available once again for free download by popular request. UTM Grid coordinates and USGS quadrangle names are specified for each individual locality. In some cases, where "free-form" field trips or traverses were conducted, a central UTM position has been approximated or the end points are identified by their UTM grid. You might scroll through this entire document to visit all of the 185 localities covered by our On-The-Rocks Field guides, then click on the link at the top of each field trip listing to get road logs, regional background, a reference list, illustrations, and considerable more locality detail in fabulous two-color .pdf files (stunning black and glorious white).
Unfortunately, as time goes by more and more classical geological teaching localities have become overgrown, built upon, or removed from public access by land owners, entrepreneurs, (or as former Dukelabs consultant Ernest P. Worrell would have said, entremanures), and various legal departments. In the twenty+ years since our last "official" field trip, ownership and access conditions may have dramatically changed. Please be advised that permission must be sought in almost all of the areas visited on our trip series and that state and local law precludes stopping at interstate highway roadsides.
Our legal department, such as it is, forces us to state that: 1) "If you plan to visit any field locations, use your best judgement and always seek out appropriate permission", and, 2) "We do not endorse nor condone trespassing or unlawful activity of any kind by offering this compilation of specific localities but provide the listing, maps, and accompanying database for purposes of enlightened public education, as a teaching resource, and for purposes of continued scientific research".
References can be found by viewing our long-standing NYC/Appalachian/Cordilleran Reference Database. Indeed, detailed geological descriptions of OTR field-trip localities "stops", including driving directions and commentary, figures, maps, and orientation data can be found in each of the individual On-The-Rocks Field Guides which we once again provide for public download.
Other OTR goodies include a Geological Time Scale specific to the NYC region and a more comprehensive table outlining the details of the Developmental History of the NY-New England Appalachian region (suitable for download and large enough for effectively wrapping fish or soaking up oil spills), and a Classification Chart for Pleistocene Deposits of NYC and Vicinity.
Guidebook 1. Sedimentology of Robert Moses State Park, New York, 121 p.
Sunday, 25 September 1988
Sunday, 17 September 1989
OBJECTIVES:
1. To understand the general geologic relationships of Long Island and the occurrence of ground water in various geologic units.
2. To be duly impressed by the evidence for the rapid westward growth of the west end of Fire Island as a result of inlet migration (average rate of 1 meter per week in the interval 1834-1940).
3. To become familiar with the composition of the beach sediment (including at least three populations of particles: a. well-sorted white medium sand; b. well-sorted dark-colored, esp. dark reddish, medium sand; and c. poorly sorted coarse brown sand, gravel, and shell debris.
4. To recognize the various parts of an ocean beach, including the shore-parallel ridges of sand (are they dunes?), berm, beach face (and/or beach scarp), and the three morphodynamic zones of an ocean beach: supratidal, intertidal, and subtidal.
5. To study the relationship between deposition of new layers of sediment and sediment surfaces, including both small-scale bed forms and large-scale depositional "slopes;" and to recognize plane, parallel strata and cross strata.
6. To understand how distinctive sequences of strata are formed by shifting of depositional slopes and the significance of prograding parallel to shore and of prograding normal to shore.
7. To understand the dynamic effects of processes such as waves and tides at modern sea level and to consider the long-term history of sea-level changes, as related both to movements of the lithosphere and to world-wide (eustatic) effects, particularly with respect to climate.
8. To realize how the effects of the operation of the geologic cycle through time create a geologic record of sediments and of sedimentary bedrock.
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
As this field trip was to a single locality, detailed descriptions are in the guidebook. [UTM grid coordinates of the beach located just beyond the picnic pavilion at Parking Field 3, the starting point of our westward traverse to the jetty, is 646.85E / 4498.05N, Bay Shore West quadrangle.]
Guidebook 2. Geology of the Hudson Highlands and Bear Mountain, New York, 113 p.
Saturday, 22 October 1988
Sunday, 28 October 1990
Saturday, 21 May 1994
OBJECTIVES:
1. To get to our third "new" van rental garage before they go out of business.
2. To enjoy the spectacular scenery of the southern Hudson Valley, New York, during its finest viewing season.
3. To examine the geologic evidence which proves that the mafic- and ultramafic rocks, including cumulates, of the Cortlandt Complex, are parts of a pluton intruded into the continental crust as magma and later cooled in place, and were not thrust upon it (as are ophiolitic sequences from the deep-sea floor).
4. To study the contact between the Inwood Marble and the stratigraphically overlying pelitic unit (lower schist of CM's revisions of the geology of the Manhattan schist, and/or Annsville Phyllite) and the contact metamorphic effects on both within the contact metamorphic aureole of the Cortlandt plutons and in xenoliths within the pluton.
5. To examine the effects on the bedrock surface of glaciers that flowed across the region at different times and from different directions, with particular emphasis on the crescentic marks made on the Proterozoic granitoid rocks of Bear Mountain.
6. To compare the composition of the clasts from near the base of the Newark Supergroup with the composition of bedrock now exposed nearby.
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
STOP 1 - Igneous flow layering in norite, Pluton V of Cortlandt Complex. [UTM Coordinates: 588.94E / 4568.78N, Peekskill quadrangle.]
Situated at the western edge of the Central Funnel of Balk (1927), we here examine northeast-dipping coarse- to medium-grained norite with an igneous flow lamination composed of plagioclase laths (reddish tint) and hypersthene (an orthopyroxene).
STOP 2 - Glaciated Inwood Marble and Manhattan Schist? [UTM Coordinates: 587.29E / 4567.44N, Peekskill quadrangle.]
Low outcrop on the north side of 11th Street of dolomitic- and calcitic Cambro-Ordovician marble exhibiting glacial grooves and scratches. On the south side of the street occurs marble plus phyllite also showing glacial striae and grooves. We think it's the Annsville Phyllite.
STOP 3 - Glaciated Manhattan-Inwood contact and the Cortlandt Complex, Franklin Delano Roosevelt Veterans Hospital. [UTM Coordinates: Traverse from 589.55E / 4565.1N to 589.1E / 4565.1N, Haverstraw quadrangle.]
Four areas of interest are here covered in a traverse. The traverse starts with a rounded knoll has been sculpted by glacial ice coming from two directions. We then examine the Sauk/Tippecanoe unconformity at the edge of the Hudson River, contact metamorphic effects in the Manhattan Schist (Unit Om), and the pegmatitic Cortlandt diorite.
STOP 4 - Poikilitic, flow-layered Cortlandt norite (Pluton V) with spectacular xenolith of contact-metamorphosed Inwood Marble. [UTM Coordinates: 589.65E / 4570.3N, Peekskill quadrangle.]
Orthopyroxene-bearing gabbro (norite) of Pluton V of the Cortlandt Complex here exhibits poikiloblasts of primary igneous kaersutitic amphibole ranging from 1-4 cm and averaging 2 cm in size. Within the norite occurs an elongate xenolith of tightly folded, contact metamorphosed Inwood (Wappinger equivalent) Marble.
STOP 5 - Perkins Observatory, crest of Bear Mountain: Proterozoic granitic gneiss with crescentic glacial gouges. [UTM Coordinates: 583.15E / 4573.5N, Popolopen Lake quadrangle.]
Here, we examine glacial grooves and crescentic gouges on rounded knolls of Proterozoic gneiss that have been sculpted by glaciers that flowed across the Hudson Highlands. The usual two directions are indicated: from NNE to SSW and from NW to SE.
STOP 6 - Stony Point Battlefield and west edge of Cortlandt intrusives (Optional). [UTM Coordinates: 585.62E / 4565.8N, Haverstraw quadrangle.]
At this stop we make three small traverses at Stony Point State Park; one south of along the railroad cut to see conglomerate of the Newark Basin, one along the railroad cut that exposes intrusive rocks of the Stony Point-Cortlandt Complex and, a walk through the famous Stony Point battleground.
Guidebook 3. Geology of Manhattan and the Bronx, New York, 141 p.
Sunday, 20 November 1988
Sunday, 21 April 1991
OBJECTIVES:
1) To study the effects of extreme folding, faulting, and metamorphism of the Lower Paleozoic strata of New York City.
2) To examine lithologic variations in the three schist units of New York City formerly "lumped" together into the Manhattan Formation.
3) To examine the evidence for Cameron's Line and the St. Nicholas thrust.
4) To get up close and personal with mylonitic rocks.
5) To examine the effects of multiple glaciations.
6) To get in the groove, glacial-, that is!
7) To find sufficient restrooms to keep field trip participants happy, and,
8) To try to visit all of our planned stops (Fat Chance!)
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
STOP 1 - Hartland exposures near West 90th to 91st streets [UTM Coordinates: 586.22E / 4516.00N, Central Park quadrangle] and between West 82nd to 85th streets [UTM Coordinates: 585.95E / 4515.50N, Central Park quadrangle], Riverside Park, Manhattan.
The Hartland Formation or upper schist unit (C-Oh) crops out in Riverside Park from West 116th Street southward to West 75th Street. Exposures near West 90-91st Streets and from West 82-85 Streets are examined for metamorphic and glacial features.
STOP 2 - Middle schist unit (C-Om) exposed at West 165th Street, Manhattan. [UTM Coordinates: 588.78E / 4521.44N, Central Park quadrangle.]
The middle schist unit (C-Om), is here exposed in a large outcrop west of Riverside Drive. We describe the structural and metamorphic geology of the rusty- to gray-weathering, coarse,biotite-muscovite-plagioclase-quartz-kyanite-sillimanite-garnet-tourmaline gneiss and schist with 2-15 cm interlayers of quartz-biotite-garnet-kyanite-sillimanite granofels. Several types of glacial features are also found here.
STOP 3 - Inwood Marble and Inwood-Manhattan contact, Isham and Inwood Hill Parks, Inwood section of Manhattan. [UTM Coordinates: 590.97E / 4524.72N, Central Park quadrangle and 590.66E / 4525.40N, Yonkers quadrangle, respectively.]
A few areas are examined in the traverse including facies of the Inwood Marble (C-Oi; originally called the Inwood Limestone by Merrill l890) in Isham Park. In entering Inwood Hill Park , the first prominent ridge is composed of kyanite gneiss and schist of the middle schist unit (C-Om). From there we examine a south-plunging F3 antiform which exposes tan weathering, gray-white Inwood Marble.
The contact between the middle and lower schist units (the St. Nicholas thrust) is exposed in a 20 m zone from beneath the Henry Hudson Bridge abutment to river level. Directly beneath the bridge, where a dirt trail leads down to the river, a coarse-grained gray-white calcite marble with differentially eroded calc-silicate nodules is exposed at low tide. It is unknown whether the marble exposed at the low-tide mark is an interlayer in the lower schist unit (Om) or the Inwood Marble.
STOP 4 - St. Nicholas Park, west of St. Nicholas Avenue between West 129th and West 141st Streets. [UTM Coordinates centered on: 588.58E / 4518.74N, Central Park quadrangle.]
The St. Nicholas thrust here separates the middle schist unit from the Inwood Marble along the east edge of St. Nicholas Park. Excellent outcrops of the schist form the steep ridge of the park. The Inwood Marble is not exposed but, based on drill core data, underlies the lowland immediately east of the park.
STOP 5 - Mount Morris Park at West 122nd Street and Fifth Avenue. [UTM Coordinates centered on: 589.15E / 4517.28N, Central Park quadrangle.]
Another traverse stop to examine the mylonitic contact of the middle schist unit (C-Om) from the Inwood Marble (C-Oi) and overlying lower schist unit (Om).
STOP 6 - Grand Concourse and the Cross Bronx Expressway, The Bronx. [UTM Coordinates: 591.70E / 4521.95N, Central Park quadrangle.]
An excellent exposure of the lower schist unit (Om) occurs west of the Grand Concourse in an overpass above the Cross Bronx Expressway (I-95). Massive Inwood Marble occurs in the roadcut forming the south wall of I-95 beneath the overpass. This locality, together with exposures described earlier in Inwood Hill Park (STOP 3) are interpreted as the autochthonous essentially in place) portions of the Manhattan Schist.
STOP 7 - St. Nicholas thrust and Cameron's Line, Cross Bronx Expressway, The Bronx. [UTM Coordinates: 592.94E / 4521.75N, Central Park quadrangle.]
Most of the Paleozoic rock units of the NYC area converge in and around Boro Hall and Crotona Parks in The Bronx according to our previous and ongoing research efforts. In these small parks, separated by I-95, marble, calc-schist, granofels, gneiss, and mica schist are all exposed from west to east in NE-striking, imbricated ductile-fault bounded tectonostratigraphic units.
Guidebook 4. Geology of Staten Island and Vicinity, New York, 152 p.
Saturday, 15 April 1989
Sunday, 29 September 1991
Sunday, 16 October 1994
OBJECTIVES:
1) To study the four major units that are in contact on Staten Island (from the top downward, Layer VII, Quaternary sediments; Layer VI, Coastal-plain strata; Layer V, Newark strata; and IIAE, Paleozoic deep-water metamorphosed strata, and included Staten Island serpentinite). We will start with the oldest unit and study progressively younger units.
2) To examine the serpentinite of Todt Hill in light of W. O. Crosby's (1914) idea that the serpentinite body which we see now has resulted from two notable modifications to the original rock, or protolith. As a second topic, we shall consider the possible age and origin of the associated breccia that contains clasts of both serpentinite (and relatated talc "schist") and red siltstones from the Newark Supergroup.
3) To examine the petrologic relationships in the Palisades intrusive sheet; to see the effects of high-temperature reaction between the mafic magma of the sill and a xenolith of Lockatong Argillite of the Newark Supergroup, which forms the country rock into which the "city rock" of the Palisades was intruded. The argillite that became engulfed in the mafic magma was not only heated, it actually was melted and the small bit of felsic magma that formed did not mix into the mafic magma, but cooled to form a felsic igneous rock unlike that formed by solidification of the mafic magma. We shall also study the morphologic relationships of the sill and discuss our new model designating Staten Island as a potential magma feeder for the Palisades intrusive sheet.
4) To see what happens to a beach when its supply of sand is cut off.
5) To study Pleistocene sediments (tills and outwash); soil-forming reactions; mineralogic immaturity; provenance of erratics; sedimentary characteristics of braided-stream deposits; state of decomposition/preservation of stones as basis for relative ages of units; hematite-cemented sandstones and /or conglomerates.
6) To find out the current status of the continuous interaction between the beach whose predominant direction of longshore transport is toward the SW and the mouth of a small stream.
7) To examine a stratigraphic succession (possibly not needing to be converted by us into an SSF) in which a much-decayed immature Quaternary braided-stream outwash deposit rests unconformably on mineralogically mature Upper Cretaceous sands and clays.
8) To examine the contrasting kinds of strata in the coastal-plain Cretaceous, notably the effects of marine transgression whereby open-shelf sediments came to overlie sediments deposited on an intertidal flat.
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
STOP 1 - The Staten Island serpentinite, local serpentinite-clast breccia, and the scarce mineral artinite, east side of Todt Hill. [UTM Coordinates: 576.35E / 4495.10N, The Narrows quadrangle.] Note: This exposure is on private property owned by the homeowners association consisting of local residents. Permission may or may not be available.
The glaciated knoll forming the south part of Emerson juts up from street level roughly 10 m and displays classic roche moutonée structure with a steep, plucked southern margin. This serpentinite is one of a large number of similar bodies scattered along the entire length of the deeply eroded core zone of the Appalachian mountain range. The oval-shaped Staten Island body is about 11 km long and about 5 km in maximum width and underlies a prominent northeast-trending ridge (locally called Todt Hill) through the center of Staten Island. The top of Todt Hill, altitude 540 feet, is the highest natural point in New York City.
The weathered knoll at Stop 1 is known to mineral collectors as the "Spring Street" locality, famed for its artinite, a hydrated alteration product of serpentinite. First described in 1902, the rare hydrated mineral artinite forms pure white- to transparent needle-like monoclinic crystals. After we have examined the serpentinite, we shall study the associated breccia, a small body of Lafayette Gravel, a post-Miocene formation on the Atlantic Coastal Plain.
STOP 2 - Palisades Intrusive Sheet in the old "Graniteville" quarry (a misnamed place; had a knowledgeable geologist given the name it might have been Doleriteville or even "Diabaseville". [UTM Coordinates: 571.60E / 4497.72N, Elizabeth quadrangle boundary.]
Walk south on trail for the locality studied by Benimoff and Sclar (1984). We shall go to the exact spot where their specimens came from and to study the effects of the interaction between the xenolith of argillite from the Lockatong Formation (formerly considered to be a small dike intruding the dolerite) and the mafic magma of the sill. Proof exists here that a chunk of the Lockatong Formation was not only internally altered by the heat from the surrounding magma, but that some of the Lockatong actually melted to form a felsic magma (magma rich in sodium/potassium feldspars). The rock which crystallized from this small amount of magma has been identified by Benimoff and Sclar (1984) as a trondhjemite.
Examination of the orientations- and marginal relationships of xenoliths in the Palisades intrusive sheet of New York and New Jersey suggests that one of the feeder areas for the intrusive sheet was in the vicinity of Graniteville, Staten Island because of the orientation of the xenolith and other features. By contrast to the gentle dips of all other xenoliths in the New York City are where xenoliths are parallel to the gently-dipping contact of the Palisades intrusive sheet, we contend that this unique vertical xenolith and the annular cooling fractures imply upward flow of the magma and thus proximity to the feeder channel.
The Pleistocene geology includes a place where red-brown till rests on the mafic bedrock along a sharp contact. On the surface of the bedrock in the quarry area, numerous ice-sculpted features are present. These include shallow trough-like grooves, striae, and crescentic marks. Crossing sets of features eroded by the ice on the mafic bedrock confirm the effects of at least two glaciers.
STOP 3 - Great Kills (Oakwood Beach) Park - Modern beach rapidly advancing landward by marine erosion. [UTM Coordinates: 574.15E / 4488.30N, The Narrows quadrangle.]
The Oakwood Beach is undergoing rapid erosion that has intensified during the last 14 years. In 1989, the year of our first trip to this area, the main bathhouse and building that is the office for the Park Police were in great jeopardy. A scarp, 2 to 3 meters high, had formed by the undercutting action at water level. This edge is an active slope subject to collapse and is marked by a snow/sand fence. Only a few years ago, the water's edge was 100 feet or more from this building and in April 1989 the water's edge was beneath the building (which is built on piles). By 1994, the building was condemned and by the late 1990's had collapsed.
This area is the only place on Staten Island underlain by a large body of outwash. Elsewhere, the Pleistocene deposits consist mainly of till. (This is the opposite of the relationships on Long Island, where outwash predominates and till is very localized.)
STOP 4 - Cliffs of deformed and overthrust Pleistocene and Cretaceous strata along Princes Bay. [UTM coordinates: 566.7E / 4484.2N, Arthur Kill quadrangle.]
The traverse at this stop includes a dig to expose several tills and interbedded outwash. In the face closest to the creek, the sequence from beach upward is red-brown till, red-brown outwash, and red-brown till, capped by what may be about a half meter of loess and the modern soil. Near the navigation tower, a considerable body of yellowish and whitish sands and light-colored clays [some layers containing bits of charcoal that Hollick (1906d) inferred came from ancient forest fires]. Included are firmly cemented quartz-rich sandstones and -conglomerates. Evidence found in the 1987 borings for the sewer line now recently completed along Hylan Boulevard (See Figures 38-41) show the same relationships as seen here: till at the surface, outwash below, and at still-greater depth, the presumably in-situ Cretaceous.
Our subsequent studies indicate that the Cretaceous surrounded by Pleistocene sediments is part of a gigantic glacial erratic that the ice tore loose and incorporated in the till (Sanders, Merguerian, and Okulewicz, 1995a, b). The geometry of folds bounding the Cretaceous slab indicate ice-shove deformation from NW to SE. Keep in mind that such Pleistocene thrusting took place under permafrost conditions when the Cretaceous sequence was undoubtedly still frozen! Here, the displaced Cretaceous is encased in outwash, which implies that the dislocation involved ice rafting of a frozen slab in a shallow stream.
STOP 5 - AKR Excavating Co., 4288 Arthur Kill Road, Kreischerville, Staten Island, about 1 mile N of Outerbridge Crossing. Red-brown till overlying decayed-pebble outwash, which rests on white, charcoal-bearing Cretaceous micaceous sands and gray clays. [UTM coordinates: 564.68E / 4487.42N, Arthur Kill quadrangle.]
At this stop we examine geologic relationships that are nowhere else exposed in the New York metropolitan area. These include Pleistocene outwash with spectacular examples of trough cross strata. Among the clasts in this outwash are abundant recycled sedimentary strata including many Newark red-brown siltstones, white quartz, and pieces of the Cretaceous ironstone sandstone and -conglomerate; and rare granitic rocks. The siltstones have been decomposed; they can be easily broken by hand and the feldspars in the granites have been completely decomposed. This decayed-pebble outwash overlies light gray- to white, cross-stratified sand containing lignitic plant debris and interbedded layers of light gray clay (Raritan Formation, Upper Cretaceous, the oldest exposed part of the coastal-plain succession).
STOP 6 - Park at Atlantic Highlands, New Jersey, with view into Lower New York Bay from a local park. [UTM Coordinates: 581.75E / 4474.31N, Sandy Hook quadrangle.]
Cross-stratified Cretaceous sands are exposed near the parking lot. Depending on the time situation, we may carry out a short dig to show the cross strata.
STOP 7 - Cretaceous sand pits behind new furniture store south of Matawan, New Jersey. [UTM Coordinates: 566.38E / 4470.91N, Keyport quadrangle.]
The upper parts of the face consist of marine sands, and the lower parts, of sediments from intertidal flats. In the coarse debris at the base of the marine strata are pebbles of ironstone conglomerate.
Guidebook 5. Geology of the Palisades and the Newark Basin, New Jersey, 120 p.
Sunday, 21 May 1989
Saturday, 26 October 1991
Saturday, 29 April 1995
OBJECTIVES:
1) To study the minerals-, structure, and contact relationships of the Palisades Intrusive Sheet and the Lockatong Formation it has intruded.
2) To learn to distinguish an intrusive sheet from sheet of extrusive igneous rock solidified from an ancient lava flow.
3) To examine the evidence indicating that the paleoflow direction of the Palisades magma was from SW to NE and not from NW to SE.
4) To evaluate the evidence bearing on the state of lithification (or lack of it!) of the sandstones in the Lockatong Formation at the time the Palisades sheet was intruded and from this evidence to estimate the depth of intrusion.
5) To examine pillows--the products of the extrusion of hot lava under a cover of water.
6) To examine the characteristics of the Newark sedimentary strata and to notice the contrast between sediments deposited well away from the Ramapo fault at the northwest basin margin and those deposited close to this basin-marginal fault.
7) To study the composition of boulders in the basin-marginal rudites (general name for any coarse sediment composed chiefly of gravel-size debris, i. e., coarser than 2 mm).
8) To study the evidence for postdepositional faults.
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
STOP 1 - Palisades Intrusive Sheet, Olivine Zone, and Lockatong Formation at Fort Lee in Palisades Interstate Park, New Jersey branch. [UTM Coordinates: 587.58E / 4522.67N, Central Park quadrangle.]
Exposures along the Palisades Interstate Park access road beneath the George Washington Bridge feature the lower contact of the Palisades intrusive sheet above contact metamorphosed sedimentary rocks of the Lockatong Formation, former lake deposits in the lower part of the Newark Supergroup. The Palisades Intrusive Sheet is one of the world's premier examples of a large sheet of mafic intrusive igneous rock. The tilted- and eroded edge of the mafic rock is expressed in the landscape as the Palisades ridge along the west side of the Hudson River.
Immediately north of the George Washington Bridge is a spectacular exposure of the basal contact of the Palisades intrusive sheet. As originally diagrammed by Olson (1980c), and reexamined by your heroes, JES and CM, the Palisades is in discordant contact relationship with a deformed slab of the Lockatong Formation. Above the Lockatong, at the south end of the xenolith, note the chilled aphanitic (very fine) texture in the Palisades at the contact with the metamorphosed sedimentary rock. Microscopic vesicles occur in the chilled-contact basalt suggesting the presence of pore water in the sediments prior to intrusion. What is more, the sandy sediments are chaotic near the contact and have "intruded" upward into the Palisades as "sedimentary apophyses" and clastic dikes.
Ramping contacts and folds (Merguerian and Sanders, 1995a, b) indicate that paleoflow of the Palisades magma was from SW to NE, not from NW to SE as had been previously thought.
STOP 2 - Pillow basalt of Orange Mountain Formation ("First Watchung Basalt"). East side of McBride Avenue ~0.7 mile NE of intersection of Glover Avenue and McBride Avenue. [UTM Coordinates: 568.1E / 4528.9N, Paterson quadrangle.]
The McBride Avenue exposures are about in the middle of the outcrop belt of the Orange Mountain Formation here. Geologists exploring the sea floor in research submarines been photographed modern pillows forming where lava oozing out of a fissure reacts with the water in such a way that individual pillows are squeezed out, expand, and then separate. The large pillowed part of the Orange Mountain Formation is inferred to have resulted from the extrusion of lava on the bottom of a large lake.
STOP 3 - Lower contact of the Orange Mountain Formation ("First Watchung Basalt") and underlying sedimentary strata of the Passaic Formation. [UTM Coordinates: 569.00E / 4529.45N, Paterson quadrangle.]
In the low cuts in the parking lot one can see the contact between an overlying mafic extrusive igneous rock (Orange Mountain Formation) and a sedimentary rock (top of Passaic Formation). The contact is not a planar surface but displays considerable irregularity. The direction of in which a sheet of ancient lava flowed can be determined from cylindrical (="pipe") vesicles and -amygdales. Typically these are bent over in the direction toward which the lava flowed. According to Manspeizer (1980), pipe amgydales here are bent over toward the NE. (See Figure 38.) This is the opposite to the direction inferred for the paleoslope of the land surface (based on directions of flow of streams that deposited the cross strata). As a result, the lava here onlapped the regional paleoslope.
STOP 4 - The Great Falls of Paterson, Orange Mountain and Passaic formations. [UTM Coordinates: 568.9E / 4529.5N, hillside exposures E and N of stadium: 569.05E / 4529.75N for contact and 569.15E / 4529.85N for cliff face near dog pound, glacial erratic at 568.95E / 4529.65 N, Paterson quadrangle.]
The waterfall here drops about 75 feet (from the 120-ft contour at the lip to about 45 ft below). The Passaic River, flowing northeastward (more or less parallel to the strike of the tilted strata), pours into a fracture that trends N-S. The water tumbles over the lip on the rock forming the W side of the fracture, and then flows southward along the fracture, then makes a U-turn and continues flowing NE. No gorge has formed downstream, as has been eroded, for example, by the upstream retreat of the lip of Niagara Falls. In its flow along a fracture and absence of a gorge, Great Falls are a miniature version of the mighty Victoria Falls on the Zambezi River in southeastern Africa (Zambia/Zimbabwe).
This stop includes a walk northward beyond the falls to examine sandstones of the Passaic Formation and a large glacial erratic.
STOP 5 - Upper, glaciated contact of the Orange Mountain Formation ("First Watchung basalt") at Garrett Mountain Reservation. [UTM Coordinates of old house: 569.50E / 4577.75N, Paterson quadrangle, altitude: 500 feet.]
From the crest of the ridge enjoy the splendid view eastward toward Manhattan (atmospheric conditions permitting). Notice the two clusters of skyscrapers: at the Battery and in midtown Manhattan. This is a function of the depth of bedrock. Where the tall buildings have been built, solid bedrock is close to the surface. In between, where no tall buildings have been built, the depth to bedrock becomes several hundred feet.
Along the trail, look for vesicles in the basalt (we are near the top of a flow unit where vesicles are to be expected) and the glacial features. Present here are glacial grooves trending NE-SW, about parallel to the trend of Garrett Mountain, and a miniature roche moutonée structure.
STOP 6 - Upper- and lower contacts of the Hook Mountain Formation ("Third Watchung Basalt"). Near parking lot for shopping center at junction of Paterson-Hamburg Turnpike and Oakland Road, Pompton, in gap cut through Packanack Mountain by Ramapo River where U. S. 202 makes a 90-degree corner at the S end of Pompton Lake. [UTM Coordinates: 560.7E / 4537.8N, Pompton Plains quadrangle.]
The top of the Hook Mountain Formation is not visible at Stop 6, but on the basis of the amygdaloidal-vesicular structure of the igneous rock exposed at the edge of the parking lot one can infer that the top is not far away. The strata here strike NW and dip SW (a result of being on the SW limb of a transverse anticline whose axis strikes NW-SE). The highland about one mile due W of us is underlain by Proterozoic rocks of the Ramapo block; the Ramapo fault, the basin-marginal fault at the NW edge of the Newark basin, lies along the foot of the steep slope. The Ramapo River flows southwestward along the trace of the Ramapo fault.
The contact at the base of the Hook Mountain Formation is exposed in the cuts along the east side of US Route 202 (if we go there, be careful of the traffic). Notice the sequence of the columnar joints in the basalt and the coarse particles in the basin-marginal rudites of the underlying Towaco Formation.
STOP 7 - Basin-marginal rudites of Feltville Formation [sedimentary strata underlying the Preakness Formation ("Second Watchung basalt")]. Behind Oakland Diner. [UTM Coordinates: 562.2E / 4540.5N, Wanaque quadrangle.]
This locality is situated close to the Ramapo fault (buried beneath sediments of Ramapo River at foot of escarpment) near the NW end of Preakness Mountain, the type locality of the Preakness Formation ("Second Watchung Basalt"). The strike of the strata is NW-SE and the dip is to the SW. The sedimentary strata are from near the top of the Feltville Formation. What can be seen here, however, is an abundance of boulders of Cambro-Ordovician carbonates (mostly dolostones, not metamorphosed, and some limestones), vesicular basalt (presumably derived by eroding the Orange Mountain Formation), and Green Pond Conglomerate; and medium-rare boulders of Proterozoic gneiss (hold the steak sauce, please!). The predominance of pieces from the Paleozoic sedimentary formations indicates that the main body of the Proterozoic rocks forming the Ramapo block in today's landscape had not yet been exposed during the early part of the Jurassic Period when the Feltville Formation was being deposited.
At Oakland, we have ended a traverse downsection that began at the top of the Hook Mountain Basalt. We have cut through the entire Towaco Formation and the Preakness Formation and are in the topmost part of the Feltville Formation. Despite this change in stratigraphic position, the kind of rock (rudite) has remained about the same. Put another way this means that in localities within about a mile or so of the Ramapo fault, nearly all sedimentary formations consist of basin-marginal rudites. The total stratigraphic range of such rudites has not been determined, but it might come close to equaling the entire thickness of the Newark basin-filling strata. Why do you suppose that all the boulders are cut by fractures? (Are they really what they are cracked up to be?)
Guidebook 6. Western Connecticut Mines and Minerals, 46 p.
Saturday, 03 June 1989
OBJECTIVES:
1) To examine the Hartland Formation of western Connecticut.
2) To locate and discuss glacial features.
3) To discuss the history of mining in western Connecticut.
4) To collect minerals and rocks from famous localities in western Connecticut.
5) Not to get bitten by ticks or mosquitos.
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
STOP 1 - Hartland Formation (upper member), Route 8 cuts, Torrington, Connecticut. [UTM Coordinates: 657.0E / 4624.9N, Torrington quadrangle.]
The outcrops forming the cliffs across from the commuter lot were originally described by Martin (1970) and subsequently detailed by Merguerian (1985). Here, 2-15 cm-scale very well-layered muscovite-biotite-plagioclase-quartz-(hornblende)-garnet) granofels occurs with interlayered schist of similar mineral composition. The abundance of muscovite in the rocks creates a lustrous sheen from foliation surfaces reflecting sunlight, a hallmark of aluminous Hartland lithologies. The pervasive interlayering of granofels and schist, high muscovite and plagioclase content, and presence of amphibolite suggests that protoliths of these rocks were volcaniclastic graywackes and interlayered shale with subordinate basalt flows.
STOP 2 - Harwinton Pegmatite, Harwinton, Connecticut. [UTM Coordinates: 659.1E / 4625.2N, Torrington quadrangle.]
Back from the road a quarry was opened in a pegmatite in order to mine for feldspar. Luckily for mineral collectors, the quarry operators selected pure specimens of feldspar and left behind minerals that would interfere with the processing of feldspar. Here, these minerals include whitish to greenish beryl forming six-sided prismatic crystals and groupings up to 20 cm long and 30 cm long black tourmaline (schorl). Permission to collect must be sought from local landowners. Happy hunting !
STOP 3 - Thomaston Dam Site, Thomaston, Connecticut. [UTM Coordinates: 660.4E / 4617.4N, Thomaston quadrangle.]
The Thomaston dam, a dry dam to hold back flood waters, was built by the U.S. Army Corps of Engineers in 1957 in the aftermath of disastrous flooding of the Naugatuck River valley in 1955. Fractured granite pegmatites and mica schist were exposed in a new railroad cut was made to relocate the rail line west of it's former location. Mineral collectors try to identify veins peripheral to the granite that cut, commonly along joints or faults, across the foliation of the Hartland. During the late stages of magmatic crystallization, large, typically incompatible elements complex with the fluoride and chloride ions and, driven by high vapor pressure, purge through the surrounding country rock leaving well-crystallized mineral samples as vug- and fracture fillings. The common minerals found at Thomaston include fluorite (in various colors), quartz, kyanite, galena, pyromorphite, wulfenite, pyrite, wurtzite (a polymorph of sphalerite), and a host of zeolite minerals including stilbite, harmotone, heulandite, and chabazite. This site is closed to collectors!
STOP 4 - Roxbury Iron Mine, Roxbury, Connecticut. [UTM Coordinates: 638.71E / 4601.90N, Roxbury quadrangle.]
Originally opened as a silver mine in roughly 1750, iron ore was ultimately discovered (probably much to the surprise and chagrin of investors!) and, later (by 1800), mined for iron ore. Forming an important deposit of "spathic" or "sparry" ore, to use the old vernacular, the iron ore occurs as siderite, an iron carbonate. The siderite occurs with quartz, pyrite, black sphalerite, chalcopyrite, galena, limonite, and arsenopyrite (rare). The ore formed in a 2-3 m wide subvertical vein cutting the Hartland strata at a high angle. Here, the mine occurs along a fault at the contact of the Mine Hill granite gneiss and mica quartzite, schist, and feldspathic mica quartzite and schist. Mineralization may have occurred here due to hydrothermal activity peripheral to the Mine Hill granite gneiss, a buried pluton, or be due to metamorphic melting at depth of carbonate-rich strata. Interesting reading on this mine can be found in Shepard (1837), Schairer (1931), Gates (1959), and Januzzi (1972, especially pp. 194-203). Now run by the Roxbury Land Trust, this site is closed to collectors but not to visitors!
STOP 5 - Roxbury Garnet Mine, Roxbury Falls, Connecticut. [UTM Coordinates: 641.62E / 4595.95N, Roxbury quadrangle.]
The Roxbury garnet mines were operated as small prospect pits in the 1800s(?) and were a major source of garnet abrasive material until the huge discoveries in the Adirondacks near North Creek, New York. The garnets occur as perfect 1-3 cm dodecahedral (twelve-sided) crystals embedded in a crumbly, muscovite-quartz schist and granofels of the Hartland Formation. In some rocks, 1-2 cm tabular brown staurolite crystals coexist with garnet. Mapping by Gates (1959) indicates that the mines occur along the west edge of 1.5-mile lense of similar porphyritic rocks within more typical Hartland occurring on Mine Hill (Stop 4). This site is closed to collectors!
STOP 6 - Tungsten Mines, Old Mine Park, Trumbull, Connecticut. [UTM Coordinates: 648.48E / 4572.08N, Long Hill quadrangle.] Note: Non-residents must obtain permission to park from the Trumbull Police Department. No collecting allowed!
Originally inhabited by Indians, the present site of Old Mine Park in Trumbull, Connecticut, is an area of historic and mineralogic interest. The Indian name Saganawamps (meaning "on the side of the hill") was derived from accounts of early English-speaking settlers in the area. Clearly, the Indian interest in the mine area was in the manufacture of arrow points from a pure quartz vein (currently fenced in). By the early 1800s, Ephraim Lane was selling mineral specimens of tungsten, tellurium, topaz, and fluorite from Saganawamps.
Up to the mid 1800s, tungsten ores and minerals were of interest to mineral collectors only as no commercial uses for these minerals were known. By 1855, however, the strength of tungsten-steel had been discovered and the search for tungsten ores became a priority. Mining rights were purchased by the American Tungsten Mining and Milling Company of of West Virginia by 1899 and construction of mine buildings began with the issue of $100,000 in bonds. The plant was shut down due to separation problems between pyrite and tungsten ore (wolframite) and by 1906, the American Tungsten Mining and Milling Company was declared bankrupt!
Crowley (1968) mapped the Long Hill quadrangle and shows the Trumbull Tungsten mine located in the Hartland Formation in a thin marble layer sandwiched between two layers of amphibolite. The presence of marble to the east of Cameron's Line is rare but according to CM, can easily be explained as a slide block (olistolith) formed within the trench sequence. Mineralization occurs at the contact between the amphibolite and marble in a typical contact-metamorphic environment with epidote, scheelite, and pyrite occurring as replacement minerals. Locally, the scheelite has been replaced by wolframite (pseudomorph) which retains the crystal shape of scheelite.
Of particular interest here is the mineral fluorite which occurs in its reddish-brown variety exhibiting fluorescence, phosphorescence, and thermoluminescence. Try this experiment at home. Boil some water on the stove then turn out the flame, turn out the lights, and drop the reddish-brown fluorite into the hot water. Voila -- thermoluminescence! Have fun collecting here and plan to return someday on your own. Remember to register your car with the Trumbull Police as Old Mine Park is intended for residents only.
Guidebook 7. Taconic Range of Eastern New York and Massachusetts, 107 p.
Saturday+Sunday, 21+22 October 1989
Saturday+Sunday, 09+10 May 1992
OBJECTIVES:
1) Examine the stratigraphy of southeastern New York.
2) Understand the complex structure and history of faulting in southeastern New York.
3) Discuss the "Taconic controversy".
4) Examine and compare correlative bedrock units northward from New York City.
5) Discuss olistostromes, mélanges, and turbidites with particular reference to the Poughkeepsie mélange.
6) Identify and examine the Taconic unconformity.
7) To appreciate the change in metamorphic grade across the Taconide zone.
8) To discuss plate models for the development of the Taconic range, and identify the probable source area of the Taconic strata.
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
STOP 1a - Proterozoic metasedimentary, granitic-, and dioritic gneiss of the Hudson Highlands, Sloatsburg Service area, I-87N. [UTM Coordinates: 568.1E / 4556.05N, Sloatsburg quadrangle.]
Behind the Thruway rest facilities and OTR pit stop, Grenville-aged (1.1 billion year old) granitic gneisses of the Hudson Highlands complex crop out. Here, the Grenville basement is well-exposed along the east wall of the Sloatsburg Service area of I-87N as hornblende-bearing granitic gneisses that are locally migmatitic (show evidence of partial melting) and cut by numerous faults (with at least three different orientations), as well as a series of joints. The intersection of joints and faults create blocs that are generally rust colored because of the weathering of iron-bearing sulphide minerals such as pyrite. The faults are distinguished from joints in that they show visible offset and often show slickensides (mineralized gouge developed along the bounding rock surfaces). The joints are often tight (and, by definition, show little or no displacement) but are commonly mineralized by fine intergrowths of mica, zeolite minerals, epidote, calcite, quartz, and pyrite, or mixtures of the above.
Interlayered within the main mass of the granitic gneiss are layers and lenses of dark-colored amphibolite and light green diopsidic calc-silicate rock. The probable parent rock (protolith) of the granitic gneisses are granite plutons, and/or quite possibly volcanic ash deposits and/or feldspar-rich greywackes. The calc-silicate rocks began life as carbonate-rich sediments and amphibolites are probably metamorphosed basaltic extrusives or calcareous, iron-rich (ferruginous) shales. As such, the overall stratigraphic sequence idealizes our concept of pre-metamorphic continental crustal rock and overlying shallow- water sediment of the cratonic realm.
In the center of the exposure note the steep post-Grenville mafic dike that contains no vestige of metamorphic fabric but is cut by the same brittle features found throughout. Based on regional mapping, these mafic dikes are either lamprophyres of Ordovician age (related to the Taconic Orogeny) or basaltic dikes of Mesozoic age (related to rifting and development of the Newark Basin).
Pull-Over STOP 1b - Carbonate rocks of the Sauk Sequence cut by mafic dikes on Route I-87N (10.2 miles north of STOP 1). [UTM Coordinates: 571.8E / 4570.3N, Monroe quadrangle.]
State law precludes stopping to look at rocks on I-87 so this pull-over stop will be discussed in the van - eyes right! After numerous miles of Proterozoic gneiss exposure on I-87N we have now passed into a major graben that exposes Cambrian to Ordovician limestone and dolostone. Here the well-layered, whitish to tan-weathering dolostone dips to the east with a strike parallel to the highway. Of additional interest here is the tan-weathering ferroan dolomite, algal laminae, and a mafic dikes that cut angularly across the bedding of the carbonate rock and in places include angular xenoliths of the carbonate host rock.
Pull-Over STOP 1c - Route I-84E, just off exit ramp from I-87N. Nonconformable contact between Proterozoic gneiss and overlying Cambrian Lowerre quartzite. [UTM Coordinates: N/A, Newburgh quadrangle.]
The geology of this area was mapped by Holzwasser in 1926. This site is famous for its rare glimpse at the basal contact of the Paleozoic shelf sequence where it rests depositionally upon the eroded Proterozoic in spectacular angular unconformity. Note how the layering in the Grenville gneiss is truncated at an acute angle against the surface of nonconformity (conveniently marked by the east-dipping poplar tree root), whereas the layering (bedding) in the massive quartzite is parallel to the surface of nonconformity. Across I-84 (eyes left!) the outcrop is also composed of graphite-bearing Proterozoic gneiss which dips gently toward and beneath us. Here, the Proterozoic is faulted against the Middle Ordovician Martinsburg Formation. Up the hill and to the east, are Sauk Sequence (Cambrian to Ordovician) carbonates.
STOP 2 - Sauk Sequence of central shelf: Wappinger Group (Cambrian - Ordovician) carbonates. [UTM Coordinates: N/A, Newburgh quadrangle.]
Across from the parking areas of Perkins and Burger King occur large cuts of Wappinger carbonates of Cambrian to Ordovician age. These essentially non-metamorphosed rocks are similar to age equivalent rocks of the Inwood Marble of New York City, the Woodville Marble belt of western Connecticut, and the Stockbridge Marble of western Massachusetts. Taken together, these carbonate units constitute the shallow-water Cambrian to Ordovician North American passive-margin carbonate-shelf strata that overlie the Lower Cambrian clastics. Here, the Wappinger carbonates form a well-layered, east-dipping sequence with meter-scale interbedding of dolostone, oolite, and chert with dark-colored ribbony solution residue (stylolites) generally parallel to bedding.
STOP 3 - Varigated red and green to gray Taconic slates on Route I-84E, Fishkill, New York. [UTM Coordinates: N/A, Newburgh quadrangle.]
In the only known (at least to JES and CM) occurrence of Taconic slates found to the west of the Hudson River in New York State, the outcrops exposed here show rocks typical of the Taconic allochthon. The slates at the extreme west end of the outcrop are dominantly red colored indicating a large amount of hematite (ferric iron, Fe3+). The interlayered greenish slate contains ferrous iron (Fe++). The greenish slate is similar in texture and color and possibly in composition to volcaniclastic rocks mapped by many farther north as the Mettawee Slates of the central Taconic range. As such, these rocks may represent volcanic-ash deposits which were interbedded with iron-rich oceanic mudstones.
We identify and discuss structural features and walk farther east along the exposure where the color changes to dominantly grey slates and siltstones which are representative of carbonate muds, poor in iron. Close examination indicates that truncated ripples occur in the silty layers from which we can interpret stratigraphic top directions. Intercalated with the grey slate occurs cm-scale layers and lenses of hemipelagic limestone and 10 cm by 40 cm limestone blocks. Close examination indicates that the larger limestone blocks are actually fragmental and contain angular to sub-rounded clasts of limestone. That is, they are actually carbonate conglomerates.
STOP 4 - Sauk Sequence: Pine Plains Formation on Lime Kiln Road. [UTM Coordinates: 598.88E / 4500.13N, Hopewell Junction quadrangle.]
The Pine Plains Formation was named by E. B. Knopf (1946) when she subdivided the Wappinger Group. Here, the cyclicity of alternating A-B-A-B facies patterns shows up as light- and dark layers(s) which strike NE and dip NW. Similar to Stop 2 (earlier today), the light-colored layers were carbonate sand and the darker layers consisted of carbonate mud. Layers of chert (siliceous ooze), sandstone, and intraformational breccia are common along the length of the exposure. Symmetrical wave-generated ripples occur with ripple crests roughly parallel to the strike direction. Finely laminated layers are the result of carbonate deposition during the formation of algal stromatolites. In addition, evaporite nodules have dissolved to form micro-geodes now filled with calcite, silica, pyrite, and chalcopyrite (the result of burial and dissolution). Burial has also prompted the development of stylolites as branching layer-parallel dark "injections" (cross-cutting dissolution residues) at all scales.
STOP 5 - Tippecanoe Sequence: black shale and interbedded graywacke in Mesier Park, Route 9D, Wappingers Falls, New York. [UTM Coordinates: 590.17E / 4605.48N, Wappingers Falls quadrangle.]
This will be a brief stop at a convenient place for viewing the weathered massive graywacke layers in the Tippecanoe Sequence (M. Ord.). Here, the graywackes form highly jointed, massive outcrops with approximately north-south strikes and steep easterly to vertical dips. Sedimentary structures include local shaly interbeds, large-scale cross beds, rolling ripple laminae, and amalgamated ripple bedding. These rocks were deposited in the foreland basin that replaced the shallow-water carbonate shelf on which the Sauk Sequence was deposited.
STOP 6 - Tippecanoe Sequence: black shale and interbedded graywacke exposed in Wappinger Creek, beneath bridge on Route 9D, Wappingers Falls, New York. [UTM Coordinates: 589.94E / 4605.67N, Wappingers Falls quadrangle.]
A short stop (time permitting) to look over the edge of the bridge and examine graywackes differentially eroded by Wappinger Creek. Here, the creek has deeply eroded the shaly interbeds and the massive graywackes form prominent outcrops in the creek bed. Note the potholes formed by swirling waters. With a strike essentially parallel to the south-flowing creek, these beds are oriented steeply eastward to vertical in dip and control the orientation of Wappinger Creek. Also note the building stones used along the bridge. These are potassium feldspar-rich sandstones (arkose) probably from the Newark Basin.
STOP 7 - Sauk Sequence: Pine Plains Formation (Upper Cambrian), Wappinger Group, at entrance to South Hills Mall. [UTM Coordinates: 590.16E / 4607.52N, Wappingers Falls quadrangle.]
The roadcuts directly north of the parking lot opposite the entrance to the mall expose thick bedded hummocky dolostones showing alternating A-B-A-B lithologic layering. Here, as in Stops 2 and 4, the light-colored layers were originally massive, coarse-textured carbonate sands and the darker layers are finely laminated carbonate muds. Stylolites are developed in two directions, one set parallel to bedding (often with branching forms) and the other set at a high angle to bedding. The presence of the secondary high-angle set is evidence that layer-parallel shortening here was greater than in the exposures of these carbonates we have seen previously. Structurally, the rocks of this stop dip beneath the graywackes exposed at Mesier Park and Wappinger Falls thus forming the northern limb of a syncline. Of further geological interest here, note the diagenetic bedding (dark streaks), burrow mottles resulting from bioturbation of soft sediment by burrowing creatures, micro-geodes filled with carbonate, and high-angle brittle faults.
STOP 8 - Poughkeepsie Olistostrome(?) or Mélange(?) Unit, Kaal Park, under the east footing of the Mid-Hudson Bridge. [UTM Coordinates: 588.00E / 4617.15N, Poughkeepsie quadrangle.]
One of the perplexing problems facing geologists in studying rocks associated with subduction zones, forearc and backarc basins, and in this case, arc-continent collisional orogens, is the identification of pre-tectonic soft-sedimentary slump deposits (called olistostromes) from tectonically deformed packages of incipiently lithified sediment (mélange) formed penecontemporaneous with the emplacement of thrust sheets. Here, in spectacular poison-ivy-covered exposures beneath the bridge, we will attempt to make observations and discuss this problem in order to decide, in a living laboratory - "Well Mabel, is it sedimentary, tectonic, or a combination of the two?". Because of the fact that your trip leaders are in partial disagreement over this matter, with JES supporting a soft-sediment slump model (naturally) and CM (of course) supporting the tectonic model, perhaps your observations can settle this once and for all without the need for fisticuffs, late in the day, on raw rock, in the poison ivy.
Let's turn to the videotape (exposure) and collect the facts as we see them:
Fact 1 - The rocks are indeed black argillite in which numerous blocks of quartzose arenite in variable orientation exist. The arenite blocks range from cobble- to boulder size, show internal grading (tops indicators), laminated upper portions, and glazed bottoms (a result of sedimentary loading). The blocks are surrounded by a shaly- to slaty black matrix. In addition, larger, 2-3 m thick, internally bedded masses are surrounded by shaly- to slaty sheared margins and found rotated into various attitudes. The interbeds of arenite are separated by the same black shale (slate?) found elsewhere in the exposure. Taken together, we see what most geologists would argue is a "broken formation". But a broken formation of what? Interbedded shales and arenites which could be none other than the Tippecanoe Sequence (Middle Ordovician) flysch part of the filling of the foreland basin (great exposures to be seen at Stop 9 (tomorrow morning)). By contrast, Fisher, and others, say these rocks belong in the Taconic Sequence and are related to a subduction zone.
Fact 2 - The unit is strongly deformed; the outlines of the arenite blocks are rounded to angular. Typically, arenite masses are flattened parallel to the sub-horizontal slaty cleavage which forms a crude clast shape-fabric to the outcrop.
Fact 3 - Many of the blocks are elliptical in shape showing flattening in the subhorizontal dimension and linear elongation (within the plane of flattening) toward the east.
Fact 4 - The slaty- to shaly matrix anastomoses around the blocks of arenite (not through them) and the outlines of the blocks are sharp, not wispy or gradational.
In the light of these facts, CM argues (without significant hesitation) that the unit represents a ductile tectonic mélange but leaves open the possibility that limited internal soft-sediment deformation in the autochthon preceded the effects of low-angle thrusting. CM argues that the dominantly pelitic matrix, monomict clast population, pervasive shearing of the matrix, and sharp clast outlines all argue for a ductile mélange call on this one (JES note: based on the rules outlined by CM!). CM views the overall crude shape fabric and rounding of the clasts as tectonic in nature and the strong alignment of elliptical clasts vectorally pointing toward the direction of overthrusting. In most thrust zones, strong down-dip alignment of linear elements is taken to indicate the tectonic-transport direction, an observation that would certainly "fit the model" of Taconian continentward advancement of allochthons here, or, for that matter, post-Taconic low-angle faulting. The lack of soft, wispy outlines, the lack of injection of mud into the "non-lithified" arenite blocks, and the lack of polymict clasts argue against a pure olistostrome model for the exposure in his view. CM is not opposed to the concept of early, limited soft-sediment deformation but would tend to interpret this exposure the result of incipient subduction of the medial Ordovician foreland basin beneath the advancing active overthrust toe of the Taconic subduction complex. Implicit in this idea is that the foreland basin fill (the Tippecanoe Sequence, here) was dragged down into the trench for hundreds of meters or more, with mélange formation and subsequent shearing related to subduction. As these rocks are considered part of the autochthon, they may have been involved in incipient subduction during the final stages of Taconian arc-continental margin convergence! Deformation of the Poughkeepsie Mélange may also be the result of post-Taconic (post Medial Ordovician = Acadian or Appalachian) low-angle faulting or shearing.
JES points out that the terms used by Fisher and Warthin are not synonymous, and that clarity will be improved by using them as originally defined. Fisher has expressed his interpretation by applying "mélange" as a formational designation. But a mélange is not the same thing as an olistostrome, a wildflysch, or a chaos, which are clearly products of subaqueous, gravity-driven "mass-wasting" activities. JES argues that exposed here is an olistostrome because "blocks" are the shallow-water type and argues that the arenites (now quartzites) are possibly topset beds of a delta. He views the imbrication of the blocks as being a result of gravity slippage which caused them to become bent before cementation. According to JES, the pieces of the arenites moved downslope to deeper water where pelites were being deposited as the large slabs are parallel to the depositional surface (i.e. - bedding). JES suggests that the pieces are too small to have been pried loose by an overriding overthrust sheet and that deep burial and deformation occurred later, resulting in the cleavage. CM asserts that JES may have slumped on this interpretation! What do you think? Can they both be right? Of course! -- This is the appeal of academia.
Remarks about the "mélange," as seen when leaves are absent.
1. The only kind of material forming the blocks is coarse quartzose arenite (quartzite? as contrasted with Austin Glen graywacke). Discrete bits and pieces of arenite are scattered at random everywhere within the cleaved black-shale matrix, in all possible orientations. Some clearly show sole marks that indicate original bottoms. Some that have been folded are completely upside down. At N end, the large continuous layers may be part of an isoclinal anticline, with tops both directions away from the shale in the middle.
2. What age are the disrupted arenites? To JES they look most like the so-called Quissaic Quartzite, DWF's Upper Ordovician molasse present on W side of Hudson River. An age as late as Late Ordovician for the disrupted arenite would scuttle the DWF idea of a Taconic mélange here. Is Quissaic the top of the Austin Glen (poss. Ramseyburg member of Martinsburg) or even younger than the upper shale member (=Penn Argyl member)? If so, then syndepositional faulting in the foreland basin during deposition of the Penn Argyl member could be an explanation for simultaneous deposition of the matrix here and the disruption of the arenite. This assignment eliminates any "Normanskill" age even if one accepts the Late Trentonian assignment of Ruedemann and WNB Berry).
If the breaking of the arenites is not syndepositional but is tectonic, then when was the deformation and tectonic mixing? Acadian? CM suggests that is possible. Or even Appalachian? Both would be in a backarc setting, not within the main subduction zone. Similar relationships are described by Vollmer and Bosworth (1984) for other localities west of the Taconic range.
JES afterthought: what about this as one of the Queenston deltas? The big news on "deep-water" (> 20 m) modern deltas from the NW Gulf of Mexico is that the sand brought to the ends of the distributary channels during floods founders into the thick hydroplastic muds (the H. N. Fisk "bar-finger sands") and all manner of slumping takes place even on very low slopes. The fact that no other kinds of coarse arenites are present or other kinds of rocks (carbonates, granites, etc. - despite Fisher's pronouncement on a variety of blocks) is consistent with a deltaic interpretation. Also, the matrix interbedded with arenites in large, multi-bed masses is the same as the general matrix (the suspended load of the river?). This delta idea needs checking. If correct, it completely revises the interpretation here and the tectonic significance of the old Poughkeepsie Mélange goes slumping into the scrap heap.
STOP 9 - Tippecanoe Sequence: flysch of foreland-basin filling, west footing of Mid-Hudson Bridge, NY Route 44 (old and new) and Johnson Iorio Town Park, Highland, New York. [UTM Coordinates: 587.11E / 4617.22N, Poughkeepsie quadrangle.]
The rocks magnificently exposed on the west end of the Mid-Hudson Bridge are part of the Tippecanoe Sequence (Middle Ordovician) flysch deposits, the bulk of the filling of the foreland basin that supplanted the carbonate shelf when the passive-margin plate setting became convergent. The new location of US Route 44 going west from the Mid-Hudson bridge has involved making splendid deep cuts through the coarser member of the Middle Ordovician flysch (possibly the Ramseyburg Member of the Martinsburg Formation, but use of that name here is not a matter of general agreement; others would opt for Austin Glen). We plan to spend much of our time in the cuts along the former location of Route 44, now a town park and thus not subject to the problems of fast-moving vehicles and anxious Bridge Authority patrols, who seem determined to keep geologists from looking at these splendid strata. We may try to look at the new cuts on the N side of the new location of US Route 44; to do so we shall park along the old Route 44 and climb up a hill to the new cuts.
The fine-grained, brown-weathering sandstones display a complete set of primary structures formed by deposition of fine sand from currents moving fast enough to create "normal" ripples, to cause these ripples to migrate downcurrent, and in some instances, to cause the ripple laminae to be oversteepened, even overturned, and convoluted. Examples can be found of climbing ripple-drift ripples, of climbing partial-drift ripples, of climbing oversteepened ripples, and of climbing sets of convoluted laminae.
In general, the coarse graywacke beds display few internal sedimentary structures. Along the basis of many, one can see evidence that the newly deposited coarse sediment foundered into what must have been a hydroplastic (Shrock, 1948) substratum.
STOP 10a - Taconic Sequence/Tippecanoe Sequence contact: The Taconic thrust (?) or post-thrust normal fault (?), Duchess County Road 21, Noxon, New York. [UTM Coordinates: 599.41E / 4610.87N, Pleasant Valley quadrangle.]
This exposure was described by Fisher and Warthin (1976; Stop 3 NYSGA Trip) and Bence and McLelland (1976; Stop 1 NYSGA Trip) and we borrow from their discussion but differ from their interpretation. Firstly, the rocks exposed in the large roadcuts are slates (metamorphic rocks) not shales as reported by Fisher and Warthin. We here argue that the eastern end of the exposure consists of variegated slates of the Taconic Sequence (thus, part of the Taconic allochthon) but that based largely on physical stratigraphic grounds, the western part, indeed, consists of black slates of the Tippecanoe Sequence (which also includes such formations as the Martinsburg, Normanskill, and Walloomsac). If we are correct, then within these roadcuts is a major tectonic boundary between the two so-called "pelitic" sequences! One possibility is that the tectonic boundary is none other than the Taconic overthrust itself.
Starting at the east end of the exposure (north side of Route 21) one finds pale green to red to maroon slate with cm-scale interlayers of nonfossiliferous, gray hemipelagic limestone. These strata are similar to the Taconic slates of Stop 3 (yesterday); we would correlate these units directly and argue that the depositional environment is that of the outermost continental rise or deep ocean. The west end of the exposure consists of tan-weathering black slates that are typical of the Tippecanoe Sequence (Middle Ordovician) foreland-basin flysch deposits witnessed yesterday (Stop 8) and earlier today at Stop 9.
Structurally, the rocks have experienced a number of folding events, the oldest of which resulted in long-limbed recumbent isoclinal folds with subhorizontal axial surfaces. The penetrative slaty cleavage in the slates is parallel to, and believed to be contemporaneous with, the sub-horizontal fabric. Throughout most of its extent, the map pattern indicates that the Taconic thrust dips at a low angle. These shallow-dipping recumbent structures, which are typical of the sole thrust areas of the Taconic allochthon, have been refolded by north-plunging folds with westward-dipping axial surfaces as well as by refolded drag folds. The multitude of refolded drag folds may have formed during an episode of steep faulting as argued above.
Pull-over STOP 10b - Spectacular westward view of Catskill Mountains and Hudson Valley. [UTM Coordinates: 605.40E / 4657.90N, Ancram quadrangle.]
Title says it all!
Pull-over STOP 10c - Thinly layered Taconian grayish green slate and hemipelagic limestone. [UTM Coordinates: 600.71E / 4672.72N, Hudson South quadrangle.]
The road cut exposes Taconic slate and interbedded light-gray-weathering hemipelagic limestone similar to Stops 3 and 10 seen earlier. Here, the limestone is very well layered, not metamorphosed, and forms a distinctive Taconic lithology.
STOP 11 - Taconic unconformity, bedding thrusts, and late faults, south end of Becraft Mountain. [UTM Coordinates: 599.75E / 4673.42N, Hudson South quadrangle.]
Only a few places exist where budding geologists can place their fingers on the pulse of a former orogeny. In this exposure, the Silurian Rondout Formation rests with angular unconformity on cherts of the Mount Merino Formation (Middle Ordovician Tippecanoe Sequence). The surface of unconformity is quite irregular and the angular discordance between beds above and below is small, perhaps as a result of minor thrust faulting at the Rondout-Mount Merino contact. Within the base of the brown-weathering Roundout (a silty dolostone), however, clasts of black Mount Merino chert and quartz occur. This would be expected if the contact is indeed one of unconformity!
The Rondout is overlain by highly laminated, whitish rocks of the Manlius Formation, but the Rondout appears again above the Manlius. What gives? Bedding thrusts occur within the Rondout and overlying Manlius. The field exposure shows the bedding thrusts (the lower one outlined by a calcite vein) which imbricate the Siluro-Devonian carbonates above the surface of unconformity with local folding ("rolling") of the Rondout. Again, clear evidence for significant post-Taconic, low-angle thrusting! Toward the south, the Manlius dips below the calc-arenites of the overlying Coeymans Formation and possibly massive limestones of the Kalkberg and New Scotland formations but significant complications are present.
STOP 12 - Taconic unconformity and other goodies, east side of Becraft Mountain. [UTM Coordinates: 602.53E / 4674.95N, Hudson South quadrangle.]
At the south end of this exposure on the east side of Becraft Mountain, we find support for our previous interpretations at Stop 11 and find the Rondout in profound angular unconformity with older strata below. But here, the older strata do not belong to the Tippecanoe Sequence, as at Stop 11, but consist of typical variegated red- and green allochthonous Taconic slates. Here, we are on the eastern limb of a syncline (which underlies Becraft Mountain) with the Rondout bedding parallel to the surface of unconformity.
Northward along the road note the change in orientation of the Taconic slaty cleavage beneath the surface of unconformity and the fact that the Manlius begins to crop out in the hillside above the Rondout. Farther north the dip of the bedding steepens and the stratigraphic relationships have been complicated by low-angle bedding-plane thrusts and high-angle solution cleavage. These exposures support our contention that two significant episodes of low-angle thrusting occurred before high-angle faulting and gentle folding of the Helderbergian strata. The relative ages of these events are known (post-Middle Ordovician low-angle Taconic thrusts, followed by post-Taconic low-angle thrusts, followed by high-angle faulting) but the absolute ages await further investigation.
STOP 13 - Evidence of progressive metamorphism in the Paleozoic Everett Phyllite, Bashbish Falls, Copake, New York and Massachusetts. [UTM Coordinates: N/A, Bashbish Falls quadrangle.]
Be prepared for a half-hour eastward stroll along the north side of Bashbish Creek. Note the nature of the rocks on the trail. These are Taconic slates and phyllites described by Zen and Hartshorn (1966). Near the trailhead the rocks are greenish slates and phyllites rich in chlorite mica. Near Bashbish Falls, the rocks are decidedly of higher metamorphic grade with porphyroblasts of garnet and staurolite sticking up out of the foliation surface and forming a spotted schist. Thus the complete metamorphic lithologic transition from slate to phyllite to schist can be observed along our walk.
By the time you reach Bashbish Falls, you have crossed the New York-Massachusetts state line. At the falls, note the foliation on the steeply dipping Everett Schist. The Everett is considered to be of Cambrian to Ordovician age and part of the Taconic allochthon. It rests structurally upon the bedrock of the autochthon consisting of the Walloomsac (=Egremont Phyllite), and underlying Stockbridge Marble.
STOP 14 - The Walloomsac Formation (Tippecanoe Sequence, mid Ordovician), NY Route 55. [UTM Coordinates: 613.40E / 4602.51N, Poughquag quadrangle.]
The rocks in these long roadcuts have been mapped as Walloomsac Schist by Bence and McLelland (1976; Stop 6 NYSGA) but in their own words, "whether they are, or not, is open to question." The rocks include quartzite, quartz-feldspar gneiss, and biotite-rich schist which contain garnet and kyanite, indicators of amphibolite-facies metamorphism. The kyanite occurs as bluish blades, 3 mm to 2 cm long, particularly concentrated within more-micaceous layers.
STOP 15 - Metamorphosed Briarcliff Dolostone (Sauk Sequence, Cambrian to Ordovician), NY Route 55. [UTM Coordinates: 616.07E / 4600.79N, Pawling quadrangle.]
This stop focuses on how the effects of metamorphism increase rapidly from northwest to southeast across the Taconide zone. Note that we are less than 15 miles (9 km) from our easternmost stop (Stop 4) in the Wappinger Group. Here, in an outcrop described by Bence and McLelland (1976; Stop 7 NYSGA) and McLelland and Fisher (1976; Stop 7 NYSGA) metamorphosed equivalents of the Sauk Sequence (Layer IIA(W) are exposed in cuts on either side of the road.
Along either side of Route 55, large cuts show gray-weathering, light-colored Briarcliff Dolostone with yellow, white, and black chert layers up to 5 cm thick. Accessory minerals include quartz, phlogopite, tremolite, diopside, and local serpentine. Structurally, tight to isoclinal folds, which occur in the dolostone with generally shallow axial surfaces, refold an earlier phlogopite foliation. These early fabrics are refolded by NNE-trending folds with steep plunges and a younger set of N-S-trending upright, dominantly open folds. Note disharmonic folds develped because of the profound differences in mechanical behavior between the ductile marble and brittle siliceous layers.
Petrologically, this stop is of interest because it affords the opportunity to examine the development of calc-silicates at grades approaching the first sillimanite isograd. Throughout the roadcut diopside, tremolite, and phlogopite are abundantly developed in the appropriate lithologies and are best seen on the weathered surface at the top of the roadcut. Recrystallization from progressive metamorphism, of original carbonate-rich sediments has resulted in a major change in the minerals.
Regionally, these relationships indicate that in a very short distance metamorphic grade increases rapidly from west to east. Ratcliffe (1984) argues that steepened metamorphic isograds in this region are the result of tight, asymmetric folding of the isograds along steeply dipping limbs. In concert, or perhaps alternatively, the data could be interpreted to indicate more uplift to the east, with originally deeper rocks now exposed at the surface, perhaps in response to high-angle brittle faulting.
Guidebook 8. Geology of Bellvale Mountain and Vicinity, New York, 111 p.
Saturday, 11 November 1989
Sunday, 24 September 1995
OBJECTIVES:
1) To study the four major bedrock units exposed in the trip area. From top downward, these are: Layer V, Newark strata; Layer III, Silurian and Devonian; Layer II, where not metamorphosed; and Layer I, Proterozoic of the Ramapo block-Reading Prong. We will start with the oldest unit and study progressively younger units, but see Layer V only in passing.
2) To study the geologic structure, on scales both large and small, with particular emphasis on features found in the post-Taconian strata.
3) To examine the geologic relationships of the local valley-and-ridge type morphology associated with the downdropped Silurian and Devonian strata of the Green Pond-Bellvale-Schunnemunk belt.
4) To understand the relationship between slaty cleavage and bedding in folds.
5) To learn how to use slickensides to infer direction of relative movement on faults.
6) To note any flow-direction features made by glaciers or left in the glacial sediments.
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
STOP 1- Proterozoic Gneiss Exposures on NY Route 17A, Tuxedo, New York. [UTM Coordinates: 567.8E / 4564.6N, Sloatsburg quadrangle.]
Our first stop today is just a quick stop to examine Proterozoic gneiss of the Hudson Highlands. These gneisses are predominantly felsic; their layering and foliation are distinct and they contain variable percentages of the mafic minerals pyroxene, amphibole, and biotite. Other rock types include thin, dark layers of amphibolite gneiss and discordant bodies of granitic pegmatite. Locally, the pegmatite is internally foliated as well. This indicates that the granitic magma was emplaced before a phase of penetrative deformation had been completed. Ample evidence for granitization comes in the form of wispy pegmatite-felsic gneiss contacts, and partly digested gneissic xenoliths.
Here, the gneissic layers are subvertical and they have been cut by numerous brittle faults. Although CM and JES were not able to determine the relative ages of the faults (at 40 mph), we are convinced that both high-angle- and low-angle faults exist in this exposure. Both of these sets of structures dip eastward. As argued later, and on other On-The-Rocks field trips, the significance of low-angle faults within the Proterozoic rock is that they may be related to major dislocations within the basement. The absolute age(s) of such displacement(s) is (are) unknown.
Alternatively, according to JES, these northwest-trending cross structures might possibly be mid-Jurassic strike-slip faults. In the vicinity of New York City, CM has found ample evidence for northwest-trending faults. The movement histories of these faults are complex and include an early component of strike-slip movement. CM suggests that these faults, which are on line with transcurrent faults of the Atlantic Ocean basin, are active today because of readjustments of the oceanic lithosphere during contemporary sea-floor spreading and, therefore, are potential seismically active faults.
STOP 2 - Middle Devonian Strata, eastern crest of Bellvale Mountain. [UTM Coordinates: 560.2E / 4566.3N, Greenwood Lake quadrangle].
Our interpretation of the relationships at STOP 2 are based on the results of the 1981 "ad-hoc" Barnard summer geologic "field camp," during which JES instructed a hardy band of 6 (including 3 Barnard junior geology majors) in the fundamentals of field observations and geologic mapping and an advanced undergraduate mapping course in 1997 at Hofstra University conducted by JES and CM. The mapping projects started at STOP 2 and progressed northeastward along the crest of Bellvale Mountain, with emphasis on three units: the graded graywackes of the lower Bellvale, the coarsely cross-bedded graywackes of the Upper Bellvale, and the quartzose, pebbly Schunnemunk Conglomerate.
Topics discussed in the guidebook include characteristics of steeply dipping graywackes of the lower Bellvale and coarse, quartzose Schunnemunk Conglomerate; plant debris in the graywackes; upward-fining cycles in the Schunnemunk; evidence for original top direction of steeply dipping strata; "technicolor" slickensides; and inferred direction of fault movement.
STOP 3 - Schunnemunk Conglomertae and Upper Bellvale Formation, NY 17A, western crest of Bellvale Mountain. [UTM Coordinates: 559.6E / 4565.9N, Greenwood Lake quadrangle.]
In view of the scenic panorama to the NW are isolated knobs composed of Proterozoic rocks (klippen), the Appalachian Great Valley, Schunnemunk Mountain (to the NE), and the Shawangunk-Kittatinny ridge in the far distance. In exposures behind us the rocks here are typical Schunnemunk, with upward-fining cycles starting with pebbles at the base and grading up into shale. Notice the irregular bases of the pebbly layers, the clasts of red slate (as well as of white quartz), and the cross strata. Two cleavages are present here. As usual, the slaty cleavage is best developed in the fine-textured strata. Notice what becomes of the cleavage in the coarser layers.
STOP 4 - Tippecanoe Sequence (Martinsburg Slate), County Route 1, west of Warwick, New York. [UTM Coordinates: 592.8E / 4568.3N, Warwick quadrangle.]
The purpose of this stop is to demonstrate the relationship between slaty cleavage that is parallel to the axial plane of a fold and the bedding, and also to examine the Bushkill Member of the Martinsburg Formation. Notice that in the axial part of the fold (crest of an anticline or trough of a syncline), the slaty cleavage cuts the bedding at a high angle.
STOP 5 - Franklin Marble (Grenville Proterozoic), Orange County Route 1A, between Warwick and Pine Island, New York. [UTM Coordinates: 551.2E / 4569.1N, Pine Island quadrangle.]
In sharp contrast to the felsic Proterozoic gneisses exposed at Stop 1, the Grenville here consists of massive graphite-bearing carbonate rocks. In fact, this entire exposure might be considered a single crystal of calcite but we suspect that significant heating and recrystallization have taken place. In fact, CM and JES are of the opinion that we are looking at "igneous" carbonate here that was thoroughly molten and then crystallized at depth to form such large crystals (more than 5- to 10 cm in size). At this stop, mineral enthusiasts will be happy to collect beautifully twinned calcite, graphite, quartz, calcic plagioclase, amphibole, diopsidic pyroxene, phlogopite, muscovite, idocrase(?), and a few specimens of red-colored idontknowite and leverite. These minerals are typical of skarn deposits (contact-metamorphic rocks). If the skarn interpretation is correct, then a buried intrusive lurks in the vicinity.
These massive carbonate rocks lie along strike with and thus are considered to be correlative with the massive Franklin Marble and identical marbles exposed at Sparta, New Jersey. Likewise, their mineralogic composition is identical with Grenville-aged Proterozoic marbles mapped throughout the Adirondack massif of northern New York State. Many of you apply lime to your lawns from the Limecrest Quarry which is located in this marble belt (look for the Limecrest trademark next time you shop!).
STOP 6 - Coarse-textured Tippecanoe Sequence - either the Ramseyburg (M. Ord.) or the High Point (U. Ord.) Members of the Martinsburg Formation. Cuts in Ramps at I-84 interchange at Mountain Road and Smith Corners. [UTM Coordinates: 532.3E / 4579.1N, Unionville quadrangle.]
Here we approach the NW side of the Appalachian Great Valley and its bounding strike ridge underlain by NW-dipping Lower Silurian conglomerate/sandstone. Along this side of the Great Valley, the dips of Ordovician and Silurian strata typically are the same; we are outside the belt of Taconian folds. The coarse Martinsburg strata here display the features of what geologists refer to as a "flysch." The coarse layers commonly show grading; their bases are sharp and may display indications that the current which deposited the coarse sediment interacted with the muddy bottom over which it flowed. See how many features you can find that were made by currents, either now preserved as counterparts on the bases of the sandstone beds or within them, and what conclusions you can draw about the direction of flow of the currents on the Ordovician sea floor.
STOP 7 - Shawangunk Formation, High Point State Park, New Jersey. [UTM Coordinates: 528.35E / 4574.25N, Port Jervis quadrangle.]
STOP 7 is another rocks-plus-scenic-vista locality. The Shawangunk and underlying Martinsburg here have been closely folded together, an arrangement that is not typical of the monoclinal strike ridge to the NE and SW. Our purpose is to examine the massive sandstone/conglomerate, look for sedimentary structures to indicate tops, and to relate this resistant formation to its topographic expression.
STOP 8 - Upper Cambrian part of the Sauk Sequence (Cambro-Ordovician carbonates). Roadcut along NJ Route 94, Hamburg, New Jersey. [UTM Coordinates: 534.30E / 4455.45N, Hamburg quadrangle.]
The features to see here include the alternating coarse-fine layers and the characteristics of each, plus their mutual interpenetration along stylolite seams and the chert. Layers that consist of original sand-size sediment contain quartz, intraclasts of the former lime mud, and ooids. Cross laminae are common. The finer-textured layers are well laminated. Algal stromatolites characterize certain layers. The repeated pattern of couplets of coarse- and fine layers has been interpreted as being the result of upward shoaling from a subtidal environment to an intertidal/supratidal environment.
STOP 9 - SE-vergent anticline in the Green Pond Formation, SE of Newfoundland, NJ. Roadcut in the median of NJ Route 23. [UTM Coordinates: 547.4E / 4542.7N, Newfoundland quadrangle.]
This splendid exposure enables one to examine the crest of an anticline that is totally accessible. Trace the layers carefully and see if they are as continuous as they might seem to be. Notice the direction of asymmetry of the folds; the steep limbs are on the SE and the gentler limbs on the NW, just the opposite of most Appalachian folds. This area is part of the Green Pond outlier where the width of the outcrop of the Green Pond belt increases so that all the strata from the Green Pond to the Schunnemunk are present. The wider outcrop belt also coincides with the localities in which the basal Silurian cuts across the older Paleozoic strata to rest on the basement.
Guidebook 9. Geology of Croton Point and Peekskill Hollow, New York 109 p.
Saturday, 12 May 1990
Saturday, 21 November 1992
OBJECTIVES:
1) To examine the depositional features in the deltaic sediments at Croton Point Park.
2) To compare and contrast the red-brown tills with those having colors other than red-brown.
3) To study the gray varved clays that were deposited in the same lake into which the delta grew, but that were protected by higher-standing parts of the former lake bottom (underlain by till) from the influx of sand from the east.
4) To relate the modern depositional setting (intertidal marsh, beach, and boulder-strewn flats) to the Pleistocene sediments.
5) To infer a chronology of events that took place during the Pleistocene glacial age(s) and the Holocene.
6) To study the boulders washed out of the till(s) as indicators of provenance. In this respect, we will concentrate on the kinds of mafic rocks derived from the Cortlandt Complex, a pluton near Peekskill, and the surrounding country rocks, and,
7) To examine the bedrock geology in the vicinity of Peekskill Hollow, a source for many of the boulders in the NNE-derived tills exposed to the south.
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
STOP 1 - Pleistocene deltaic sediments along cliff face and SST (Sanders Scientific Trench) in beach sands. [UTM Coordinates: 592.8E / 4560.0N, Haverstraw quadrangle.]
Walk northward beyond the Park Office then turn right along the beach at opening in fence. A couple of hundred yards along the shore look up (to right) to find the preliminary dig site. We have four stops at Croton Point Park as shown on the location map in our guide. Note the view to the north of the Hudson Highlands and electric power-generating plants (including Indian Point nuclear reactors). To the west note the north end of the Palisades at High Tor where this sheet of igneous rock swings inland away from the Hudson River. The undulating lowlands to the east and northeast are underlain by metamorphic rocks of the Manhattan Prong that project upward from beneath the water of the Hudson River.
The dig site will expose the lower part of the deltaic sands of the Croton River delta. The delta was built into Lake Albany that formed when the Woodfordian glacier retreated northward past Croton Point Park. This lake persisted until roughly 12,000 years ago (based on radiocarbon date published by Newman and others, 1969). Glacial Lake Albany drained abruptly when a glacial moraine dam at the Narrows broke and water surged out across the shelf, eroding the Hudson Shelf Valley. Then a very rapid submergence took place, and the Hudson estuary formed and has stayed that way ever since.
STOP 2 - Cliffs at Teller's Point to examine oyster middens, red-brown till overlying gray till containing decayed granite boulders and erratics from Cortlandt Complex and boulder-residue "beach". [UTM Coordinates: 592.38E / 4557.81N, Haverstraw quadrangle.]
The cliffs at Teller's Point are immediately across (about 2 km or 1.2 miles) the Hudson River from the Palisades intrusive just south of Haverstraw, New York. At the left of the path just before the steep descent to the river are some oyster shells from an Indian midden. Walk down the path to the water's edge and begin by scraping off loose sediment from the cliff face. Note that two tills are present here. A red-brown till caps the cliff; at a level of about 3 m above the water can be seen the top of a gray-brown till that persists down to water level. We know that the red-brown till is associated with a glacial advance from New Jersey (from NW to SE): it contains boulders and pebbles of various facies of the Palisades trap rock, red-colored sedimentary rocks from the Newark Supergroup, the Green Pond Conglomerate, and chips of anthracitic coal.
The lower gray-tan till contains rocks not found west of the Hudson River. Rather, the distinctive rocks eroding out of the lower till consist of igneous- and metamorphic lithologies which crop out to the east of the Hudson, mostly from regions due north of us. The feldspars in the dark, smaller stones in the lower part of the cliff face have totally decayed.
A list of boulders averaging from 2 m to pebbles in size observed at our pre-trip investigation follows. See if you can find these distinctive rock types and perhaps identify some odd lithogies that we've missed. Boulder bashing is an acceptable method of investigation here.
Boulders, boulders everywhere------
IGNEOUS
Diabase showing fine, medium, and coarse textures
Hornblende diorite
Poikilitic pyroxenite
Pyroxenite
Gabbro, norite, and poikilitic norite
Granite and granite pegmatite
Red-orange granite
METAMORPHIC
Granite gneiss +/- garnet, epidote
Hornblende gneiss
Mica schist
Phyllite
Amphibolite
Foliated granite
Hematitic quartzite
Clean quartzite
Greenstone
Folded, foliated rocks
Red jasper
SEDIMENTARY
Limestone
Dolostone
Arkose
Siltstone
Graywacke
STOP 3 - Squaw Cove beach: Gray varved clay overlying red-brown till overlain by fluffy brownish sand and boulder-residue "beach." [UTM Coordinates: 592.27E / 4558.37N, Haverstraw quadrangle.]
Walk through wooded area to the beach for Stop 3. At the beach, gray varved clay is exposed at the top of a low bluff. A dig a few meters to the N from where the pat ends shows that this same gray clay overlies the red-brown till. We note many more reddish Newark sandstone boulders here plus mafic rocks of the Palisades intrusive sheet (in comparison to Stop 2) and lesser mafic- and ultramafic rocks of the Cortlandt intrusive suite.
On our pre-trip investigation on 21 October 1992, we found a large dropstone in the clay. (A dropstone is a stone that started its career by being incorporated into a glacier. At the terminus, the glacier calved into the water of a lake, and the ice+stone became an iceberg. The iceberg drifted out into the middle of the lake. When the iceberg melted, the stone to the bottom, coming to rest in a quiet environment where otherwise only clay was being deposited.) On trip day, we plan to clean up a face to show the relationship between this dropstone and the laminae in the clay.
STOP 4 - Enoch's Nose: Drumlin, red-brown till, red-brown outwash, upper yellow-brown till, oyster middens, and boulder-residue "beach". [UTM Coordinates: 592.1E / 4559.9N, Haverstraw quadrangle.]
Walk along the trail to the large erratic boulder marked by two smaller rocks. The elongate shape of the promontory suggests that it is a drumlin, shaped by the advance of glacial ice. The bluffs here consist of two red-brown tills with local reddish outwash between two units of till. Note that no gray-tan till as observed at Stop 2 is exposed here. However, boulders of the Cortlandt Complex suggest that some gray till or other must have been eroded. Possibly the older such till is present exposed at or below river level. Possibly these boulders came from the upper yellow-brown till that caps the hill.
Walk along the boulder beach. Notice the large erratics from the Cortlandt Complex and a few Newark sandstone boulders. Dig at the NW end of the promontory and, depending on time, we'll look at the large cliff at the north end of the drumlin. Note the oyster middens on the terrace level at the boundary between the youngest yellow-brown till (capping the drumlin) and the older red-brown till(s) exposed in the eroding bluffs.
STOP 5 - Igneous flow layering in norite, Pluton V of Cortlandt Complex. [UTM Coordinates: 588.94E / 4568.78N, Peekskill quadrangle.]
The purpose of this stop is to examine flow layering in igneous rocks of Pluton V (norite) of the Cortlandt Complex. We are situated at the western edge of the Central Basin of Balk (1927). Here notice the well-developed, northeast-dipping coarse- to medium-textured norite with an igneous flow layering. The layers consist of plagioclase laths (reddish tint) and hypersthene (an orthopyroxene). Note the northeast-dipping lithologic contact between texturally and mineralogically different phases within the igneous rock, the presence of schlieren (mafic clots), and the compact, dense mafic rock here. Are you convinced that bedrock such as some of the coarse layers exposed here could have supplied some of boulders we have just examined at Croton Point?
STOP 6 - Glaciated Inwood Marble and Manhattan Schist? [UTM Coordinates: 587.29E / 4567.44N, Peekskill quadrangle.]
Low outcrop on the north side of 11th Street of dolomitic- and calcitic Cambro-Ordovician marble exhibiting glacial grooves and scratches. On the south side of the street occurs marble plus phyllite also showing glacial striae and grooves. We think it's the Annsville Phyllite.
STOP 7 - Poikilitic flow-layered norite (Pluton V) with xenolith of isoclinally folded, contact-metamorphosed Inwood marble. [UTM Coordinates: 589.65E / 4570.3N, Peekskill quadrangle.]
Orthopyroxene-bearing gabbro (norite) of Pluton V of the Cortlandt Complex here exhibits poikiloblasts of primary igneous kaersutitic amphibole ranging from 1-4 cm and averaging 2 cm in size. Within the norite occurs an elongate xenolith of tightly folded, contact metamorphosed Inwood (Wappinger equivalent) Marble.
STOP 8 - Type locality of Annsville Phyllite, Annsville, NY. [UTM Coordinates: 590.00E / 4573.19N, Peekskill quadrangle.]
This large roadcut exposes the Annsville Phyllite of Medial Ordovician age. We are in the town of Annsville and you are therefore in the type locality of this distinctive, black to dark-gray carbonaceous rock unit. Here, the lithology holds up a ridge bifurcated by Sprout Brook to the west and Peekskill Hollow Creek to the east. The cut exposes a rather monotonous, steeply dipping and highly cleaved sequence of uniform micaceous slate and lustrous, flaggy phyllite that extends northeastward toward Gallows Hill. CM argues that the presence of a steep down-dip intersection lineation and mineral streaking within the slaty cleavage indicates the presence of non-obvious intrafolial F1 isoclinal folds that are probably best observed on top of the outcrop. In a few places isoclinal folds (probably F2 or second generation) of thin quartz veins occur showing SE plunges. There is a sub-horizontal rock cleavage that is axial planar to kink bands and crenulations of the slaty cleavage and late joints that trend N28°E, 32°NW. The overall structure of the ridge is probably that of a synform overturned to the northwest.
STOP 9 - Poughquag Quartzite. (Optional, time permitting). [UTM Coordinates: 589.82E / 4559.9N, Peekskill quadrangle.]
Here, hopefully up-wind from the sewage treatment plant on the day of our trip, note the gently east-dipping thinly laminated bedding and sub-parallel foliation of the Poughquag Quartzite. The quartzite is of Early Cambrian age; it represents the basal part of the Sauk Sequence (deposits of former Early Paleozoic shelf). The Poughquag is a dense, hard, fine- to medium-textured quartzite that ranges in color from white to tan and brown to reddish (Schaffel, 1958). Local conglomeratic facies contain distinctive bluish quartz pebbles. As such, this outcrop belt of the Poughquag (and perhaps its northern correlative--the Cheshire Quartzite) are the probable parents for many of the resistant quartzite (+/- hematite stained) boulders that we found had been eroded from the tills at Croton Point Park.
Guidebook 10. Geology of the Little Appalachians and the Catskills, New York, 103 p.
Saturday+Sunday, 26+27 May 1990
Saturday+Sunday, 24+25 September 1994
OBJECTIVES:
1) To familiarize you with the variety and depositional history of the Silurian and Devonian strata of Layer III in New York State.
2) To examine and understand the northeasterly stratigraphic thinning and ultimate pinchout of these units in comparison to their temporal equivalents toward the southwest.
3) To get close and personal with anticlines, synclines, faults, and other geologic structures.
4) To examine and use in the determination of topping direction, sedimentary structures such as graded beds, ripple marks, cross beds, etc.
5) To examine and marvel at the Taconic unconformity at a number of places.
6) To observe and hopefully, collect fossils from the Siluro-Devonian strata.
7) To perform a series of exercises in geologic mapping and compass techniques.
8) To test, in the field, the application of the PAC hypothesis in understanding sedimentation.
9) To witness, in a 350-million-year flashback, the depositional history of the Lower Paleozoic strata and to note the change from marine- to non-marine sedimentary successions, and,
10) To visit all of our intended field trip stops (Fat Chance! But 9 out of 10 isn't bad).
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
STOP 1a - Proterozoic metasedimentary, granitic-, and dioritic gneiss of the Hudson Highlands, Sloatsburg Service area, I-87N. [UTM Coordinates: 568.1E / 4556.05N, Sloatsburg quadrangle.]
Behind the Thruway rest facilities and OTR pit stop, Grenville-aged (1.1 billion year old) granitic gneisses of the Hudson Highlands complex crop out. Here, the Grenville basement is well-exposed along the east wall of the Sloatsburg Service area of I-87N as hornblende-bearing granitic gneisses that are locally migmatitic (show evidence of partial melting) and cut by numerous faults (with at least three different orientations), as well as a series of joints. The intersection of joints and faults create blocs that are generally rust colored because of the weathering of iron-bearing sulphide minerals such as pyrite. The faults are distinguished from joints in that they show visible offset and often show slickensides (mineralized gouge developed along the bounding rock surfaces). The joints are often tight (and, by definition, show little or no displacement) but are commonly mineralized by fine intergrowths of mica, zeolite minerals, epidote, calcite, quartz, and pyrite, or mixtures of the above.
Interlayered within the main mass of the granitic gneiss are layers and lenses of dark-colored amphibolite and light green diopsidic calc-silicate rock. The probable parent rock (protolith) of the granitic gneisses are granite plutons, and/or quite possibly volcanic ash deposits and/or feldspar-rich greywackes. The calc-silicate rocks began life as carbonate-rich sediments and amphibolites are probably metamorphosed basaltic extrusives or calcareous, iron-rich (ferruginous) shales. As such, the overall stratigraphic sequence idealizes our concept of pre-metamorphic continental crustal rock and overlying shallow- water sediment of the cratonic realm.
In the center of the exposure note the steep post-Grenville mafic dike that contains no vestige of metamorphic fabric but is cut by the same brittle features found throughout. Based on regional mapping, these mafic dikes are either lamprophyres of Ordovician age (related to the Taconic Orogeny) or basaltic dikes of Mesozoic age (related to rifting and development of the Newark Basin).
Pull-Over STOP 1b - Carbonate rocks of the Sauk Sequence cut by mafic dikes on Route I-87N (10.2 miles north of STOP 1). [UTM Coordinates: 571.8E / 4570.3N, Monroe quadrangle.]
State law precludes stopping to look at rocks on I-87 so this pull-over stop will be discussed in the van - eyes right! After numerous miles of Proterozoic gneiss exposure on I-87N we have now passed into a major graben that exposes Cambrian to Ordovician limestone and dolostone. Here the well-layered, whitish to tan-weathering dolostone dips to the east with a strike parallel to the highway. Of additional interest here is the tan-weathering ferroan dolomite, algal laminae, and a mafic dikes that cut angularly across the bedding of the carbonate rock and in places include angular xenoliths of the carbonate host rock.
STOP 2 - Devonian Sandstones at Highland Mills (former) Railroad Station. [UTM Coordinates: 573.5E / 4577.3N, Popolopen Lake quadrangle.]
Watch for trains here as they do come by! The belt of outcrop here is the NW-dipping southeast limb of a syncline consisting of steeply dipping Devonian clastic strata of the Highland Mills Member of the Esopus Formation. Note the view to the north of Schunnemunk Mountain which occupies the core of a large synclinal structure. The topographic map shows evidence of strike ridge with a NE strike and vertical to very steep NW dip. The ridge is underlain by lower Silurian, here the Green Pond Conglomerate, overlain by redbeds (Longwood Shale = equivalent of High Falls Shale to be seen later). The things we would like to do here is show you how to measure strike and dip, identify tops and bottoms of beds, hummocky strata, and to find some representative Devonian fossils.
The rocks here consist of interbedded highly laminated sandstones and shales with individual layers 0.5 to 1.0 m thick. Local 3-4 cm layers of black shale are present. The laminated texture of the sandstones suggest that deposition took place under the influence of moderate to strong currents. The interbedded shales indicate periods of quiescent deposition. The fossils found here include various types of brachiopods, gastropods, pelecypods, and trilobites, preserved as molds and casts; original skeletal carbonate has generally been dissolved. The layers show shell hash, probably concentrated during storms. Loose slab shows symmetrical wave-generated ripples; look to see if these can be found in situ. At the N end of exposure, where the burrow marks are so prominent, the overlying massive sandstone shows spheroidal weathering as a result of weathering along right-angle corners of joint intersections.
STOP 3 - Ordovician graywackes of the Tippecanoe Sequence under Thruway Bridge. [UTM Coordinates: 578.21E / 4629.7N, Rosendale quadrangle.]
Exposed under the Thruway overpass are interbedded, cross laminated Ordovician graywacke and black shale and siltstone exposed in an open syncline. Beneath the Thruway bridge, strata are nearly horizontal and wacke layers are over a meter thick. West of the bridge, the average thickness of the wacke layers are 5 to 15 cm and they are internally laminated indicating deposition during strong currents. They exhibit graded bedding, irregular bases, rip-up clasts, flame structure, and sole marks that together indicate that tops are up. Cross strata indicate current flow towards the SW. Locally the wackes contain pebbles of Sauk carbonate and black chert, black argillite, and brachiopod fossils. The brachiopods show up as "holes" in the graywacke layers and as these are grain-flow deposits, the fossils have been transported and would give a maximum age for the layer.
Time permitting, we may continue eastward on Route 213 to examine a thick-bedded portion of the Tippecanoe sequence exposed on the above the Dashville hydroelectric plant along the Wallkill river. Here, many spectacular anticlines and synclines expose Tippecanoe rocks. Faulting and imbrication and minor folding of the wacke layers was produced by layer-parallel shortening during large-scale folding when the incompetent shaly interbeds flowed and the sandy beds broke. A steep fault is exposed at the east end of the exposure. Note the calcite and quartz veining and the abrupt change in orientation east of the fault. Glacial scratches here are oriented N5°W and an erratic of Helderbergian limestone looms on the hillside above the fault.
STOP 4 - Siluro-Devonian Section and Rosendale Quarry at Tillson. [UTM Coordinates: 576.7E / 4631.7N, Rosendale quadrangle.]
The strata exposed here are quite thin but consist of a northward-topping sequence of Shawangunk Conglomerate (L. Sil.), overlain by the High Falls Shale, Binnewater Sandstone, and overlying cementstone carbonates. Farther ahead in the woods, the Siluro-Devonian succession crops out.
From the base upward, the units include the Shawangunk Conglomerate near the Taconic unconformity. The actual contact is not visible here (we might dig a little during the trip). The Shawangunk Conglomerate is in sharp contact at top with an overlying silty unit, the High Falls "Shale". The High Falls is not too well exposed and is about 6 m thick behind the bushes. Some reddish layers occur but bedding is obscure as the siltstone breaks into irregular chips. Farther along the road, is a good exposure of the top of the High Falls and base of the overlying Binnewater Sandstone. The Binnewater consists of interlayerd dolomitic carbonates and gray quartzose sandstones, in layers 10 to 15 cm thick. In the sandstones, are wave-generated oscillatory ripples, ripple cross strata, and possible hummocks.
Walk to end of exposure; find trail on R at start of metal guard rail. Continue along trail to exposure in woods to R and beware of poison ivy. Look for two pillars and entrance to former cement mine, now flooded. It is possible that the Wilbur Limestone occurs in this covered interval. The next rock unit exposed is the Rosendale Dolostone, the brownish-weathering rock found in the bottoms of the pillars. Cementstones were quarried because the dolomitic layers contain just the right amount of quartz silt to make a cement when roasted. These formed the basis of the Rosendale cement business of the 19th century (see historical marker in village of Rosendale).
STOP 5 - Faulted Shawangunk Conglomerate in High Falls village. [UTM Coordinates: 572.6E / 4630.65N, Rosendale quadrangle.]
This stop is in two parts separated by a buried (inferred) fault. Part 1 is found to the E, opposite the High Falls Motel (CM, but not George Washington, slept here on the eve of his first undergraduate field trip with Drs. Jack Fagan and Sy Schaffel of CCNY in 1968). Here occurs Shawangunk, about 6 m thick, with no top or bottom exposed. The conglomerate and silica-cemented sandstone dips 13°E and exhibits planar cross strata that show updip transport direction. Two sets of slickensides are found at the western edge of the exposure: (1) parallel to bedding, and (2) steep, with sense of motion E side up.
Part 2 to the W is across a fault with overlying red High Falls Shale preserved on top of the Shawangunk. The conglomerate here is about 8 to 10 m thick with base not exposed, in the crest of a broad anticline that trends N-S. The features here include shaly interbeds, possible hummocks, and cross beds. It is unusual to find this much Shawangunk without high relief. A possible explanation is that this is the crest of an anticline only recently exposed and not yet elevated with respect to surrounding rocks. Between the two outcrops is a fault, trending NS and with E side up to bring Shawangunk up to level of High Falls Shale Formation. In the covered interval, Ordovician shale may be faulted against High Falls Formation.
STOP 6 - Binnewater Sandstone and High Falls Shale in east-vergent monoclinal flexure, High Falls hydroelectric station. [UTM Coordinates: 571.91E / 4630.95N, Mohonk Lake quadrangle.]
Walk through fence maze to the fence nearest the falls. This area has been restored and made available by Central Hudson Gas and Electric Corp and the High Falls Civic Association. At the upper Falls, the lip is composed of the Rosendale Dolostone with Binnewater Sandstone just below, both dipping NW (upstream). Beneath the Binnewater is the High Falls Shale with cuts here on the N side of creek marking the type locality. Walk down blacktop path to lower level. Exposed on R is cliff of Binnewater Sandstone, with dip to NW. Near the bottom is the contact with the High Falls Shale.
A noteworthy feature of the asymmetric fold on opposite bank of creek is that the fold axial surface dips NW (opposite to the SE dip of most Appalachian folds). CM and JES suggest that this anticline has developed over a ramp up to a bedding-plane thrust that duplicates the Rosendale-Binnewater-High Falls succession here.
STOP 7 - Williams Lake Hotel transect through plunging folds. [UTM Coordinates: 576.3E / 4535.0N, Rosendale quadrangle.]
This is a free-form stop with no notes, but we will traverse the old railroad bed to map the lithology and structure of the rocks exposed here. The section starts with Shawangunk Conglomerate and proceeds upward through the High Falls Shale, Binnewater Sandstone, Rosendale Dolostone, Glasco Limestone, Whiteport Dolostone, and Manlius Formation. Note that this area marks the northernmost exposure of the Shawangunk which pinches out somewhere between the Fifth and Fourth Binnewater Lakes. We will examine many geologic features, including sedimentary structures, bedding-plane thrusts, bedding-cleavage relationships, and folds and you will be rewarded with a lovely trip through the plunging folds (literally). We will walk up section into the Helderbergian limestones which you will see in more detail tomorrow. This site is currently private property though the public Rail Trail will take you through the area.
STOP 8 - Mount Marion Formation on US Route 209, near Sawkill Road. [UTM Coordinates: 581.25E / 4647.15N, Kingston West quadrangle.]
The Mount Marion Formation is exposed here and consists of turbidites with individual beds 20 to 30 cm thick. They are interspersed in a predominantly black siltstone/shale succession. A spectacular repetition of an individual bed, over 30 times, in slices 2 m long, occurs as stacked, imbricate slices, sandwiched between horizontal beds. CM noticed this at 55 MPH! Let's pace the current horizontal distance between the 30 slices and calculate the percent of layer-parallel shortening. We estimate roughly 300% shortening just within this one obvious thrust zone.
The main slip surface is subhorizontal and disappears within bedding. Slabs are sheared along individual imbricate thrusts. Many of the slabs terminate in lenticular tips which we view as "tectonic" with a capital T. Earlier investigators have suggested soft-sediment deformation for this exposure. Rather we view the lenticular ends the result of mechanical slivering. Many angular shards of wacke floating in the weaker shaly matrix originated from the larger slabs of wacke. Overall, the movement sense is right-lateral slip with travel toward the west. As such, this small exposure is a microcosm of the entire Valley and Ridge Province as deformed during the terminal stage of the Appalachian orogeny.
The Mount Marion is equivalent to the Lower Bellvale Formation of the Monroe area of New York. It is the highest marine unit in the Appalachian Devonian and also the highest marine formation in Devonian. From here on up section there are no more carbonates. You might say we have just made a sudden withdrawal from the carbonate bank.
STOP 9 - Taconic Unconformity with Silurian Rondout Formation on Ordovician (Tippecanoe) Siltsone, NY 32, East Kingston. [UTM Coordinates: 585.1E / 4646.2N, Kingston East quadrangle.]
The two main features to be seen here are the Taconian unconformity and the Binnewater and Rondout strata that immediately overlie it. Notice the characteristics and attitude of the Ordovician strata (dominantly siltstones) which dip more gently than the overlying Rondout strata. Here the Binnewater is only 0.25 m thick and the High Falls and Shawangunk formations are totally missing.
The rocks are tilted due to folding and although we do not see obvious folds a prominent pressure solution cleavage is developed in the Silurian strata. It passes through and beneath the unconformity and is sub-parallel to the Ordovician slaty cleavage. Thus, the Ordovician strata are cut by two cleavages (note the wedge-like appearance of the cleavage fragments) but the Silurian only possesses one obvious deformational fabric. If the Rondout strata are rotated back to their initial horizontal positions, the attitude of the Ordovician strata would be subhorizontal. Note that the pre-Silurian (Taconic) Ordovician cleavage (after unfolding of the Silurian strata) would dip moderately steep toward the SW! Thus, we must be at the hinge area of an eroded Ordovician fold and, as such, the unconformity here might be a disconformity.
STOP 10 - Taconic Unconformity and bedding-plane thrusts in Helderbergian carbonates, NY 32, East Kingston. [UTM Coordinates: 585.1E / 4646.82N, Kingston East quadrangle.]
At Stop 10, we see all parts of the Rondout Formation, with base resting on the Taconian unconformity, as at Stop 9, but with the added factor of repetition of the Siluro-Devonian strata along a number of bedding-plane thrusts. We will work our way along the large rock face beginning at the N end with the Ordovician strata. Steeply north-dipping extension fractures (related to the ramp-like thrusts) are lined with calcite. We note minor normal reactivation of some of the bedding plane thrusts based on left-lateral offset of steep, post-thrust calcite veins.
STOP 11 - Helderberg Strata on N side NY Route 199, on W approach to Kingston-Rhinecliff Bridge. [UTM Coordinates: 585.05E / 4647.5N, Kingston East quadrangle.]
At this stop, the bottom of the Helderberg carbonates is not visible, but we can see the upper part of the Manlius (Thacher Member) and all three units of the lower fining-upward cycle of Coeymans (Ravena Member)-Kalkberg (lower Hannacroix and upper Broncks Lake members)-New Scotland. See what you can find in the way of fossils here. The best specimens may not be in the fresh bedrock, that breaks so irregularly, but in the weathered blocks at the top of the ridge. Study of the molds and casts in fine-textured rocks can yield nearly as much detail as study of fossils in which the original skeletal material is intact.
STOP 12 - Anticlinal Fold of Helderberg Strata, on N side of NY Route 199, W approach to Kingston-Rhinecliff Bridge. [UTM Coordinates: 584.75E / 4647.38N, Kingston East quadrangle.]
This small anticline brings up the strata of the upper fining-upward cycle, the Becraft-Alsen-Port Ewen beds. The anticline is separated from the strata at Stop 11 by a fault that follows the low covered interval between the two ridges where rock is exposed along the highway. Notice the comparable relationships of a coarse, gray, skeletal limestone without much silt and lacking chert in the basal unit (Coeymans and Becraft). This grades upward into a siltier rock containing chert (Kalkberg and Alsen). At the top, the chert vanishes and the rock is a shaly calcareous siltstone (New Scotland-Port Ewen).
STOP 13 - Mount Marion Formation, New Cut on NY Route 32, Quarryville (N of Mt. Airy). [UTM Coordinates: 584.0E / 4363.15N, Saugerties quadrangle.]
This cut exposes the same formation we examined at Stop 8, a deep-water marine deposit consisting of dark gray to black shale, siltstone, and sandstone somewhat resembling the Ordovician flysch. Very little shale is exposed at the W end of the exposure. Rather, non-graded and non-laminated massive sandstone and siltstone occurs. Note the rounded, dense concretions which consist of pyrite, siderite, and possibly barite. Look for Devonian brachiopods in the sandy layers. Check closely to see if any bedding-plane thrust faults repeat any layers, as observed at Stop 8.
STOP 14 - Ashokan Formation, NY Route 32, W of Quarryville. [UTM Coordinates: 583.13E / 4663.6N, Saugerties quadrangle.]
The Ashokan Formation is the formation quarried as New York blue stone and is used for paving slabs on sidewalks. Notice the well-developed large-scale cross strata that show stream flow toward the west. JES thinks that the Mount Marion-Ashokan combination is equivalent to the Bellvale Formation of the Schunnemunk-Green Pond belt, with lower Bellvale equal to Mount Marion and upper Bellvale, to the Ashokan.
STOP 15a - Catskill Redbeds and Conglomerate along North Lake Escarpment, Haines Falls, New York. [UTM Coordinates: 580.02E / 4672.92N, Kaaterskill quadrangle.]
The Catskills are a thick sequence of fan- and delta deposits that show sedimentary structures indicating an eastward source. The horizontal layering of the Catskills are quite obvious (even from a distance) and the rocks vary from red shales to siltstones and sandstones to very coarse conglomerates. The red color may make you think of the Newark Series but, in fact, these rocks are much older (middle Devonian) despite the fact that they appear similar. We hope you noted the impressive thickness of the Catskill sequence as we drove up the Catskill Front from Stop 14.
The Catskill Mountains are mountains because they are composed of resistant strata containing sandstone and conglomerate. These are much more difficult to erode than the soft shales and limestones in the Hudson Valley. The section of strata along Route 23A consists of 2,000 feet of coarse river deposits and also contains successive intervals of fine grained floodplain deposits (red siltstone and mudstone) - all characteristics of the non-marine portion of the Catskill Delta. The source area for the cobbles is clearly toward the east - any ideas on where they came from? Try to imagine the ancient landscape as mirror image of the modern Rockies and Great Plains with mountains to the east (now eroded hills of the Taconics and Berkshires) with an alluvial apron sloping westward as far as present day Ohio. The continentally-derived fans gave way westward to shallow marine seas into western Pennsylvania and Ohio where thinner Devonian marine facies are found. The shoreline prograded toward the west as the abundance of sediment pushed the seas toward the interior of Devonian North America.
Pull-Over STOP 15b. [UTM Coordinates: 589.27E / 4672.20N, Cementon quadrangle.]
Note the open anticline on the right (south) side of the road at the end of the unfinished (abandoned?) Thruway exit ramp. Here, The sequence, from top to bottom, is the Esopus Shale, Glenarie Limestone, and Port Ewen Limestone. Note the well developed subvertical slaty cleavage in the Esopus and the intricate folds in the Glenarie within the disrupted bedding. Note the contrast in structural style of the three units, a function of their composition and layering characteristics.
STOP 16 - Taconic Unconformity and overlying Rondout and Helderbergian carbonates, N side of exit ramp from new location of NY Route 23 from Rip Van Winkle Bridge to old NY Route 23, Jefferson Heights, Catskill. [UTM Coordinates: 591.9E / 4676.6N, Cementon quadrangle.]
Here, the Rondout Formation and Helderbergian carbonate succession are in marked steeply-dipping unconformity with underlying Ordovician graywackes. The Rondout Formation consists of about 1 m of Rosendale Dolostone with a thin basal sandstone (Binnewater?) resting on the steeply dipping Ordovician Tippecanoe sequence. Overlying the Rosendale is roughly 10 cm of limestone that is probably the feather edge of the Glasco Limestone, followed by the Whiteport Dolostone. Thrust faults occur above the Whiteport in a chaotic zone with right-lateral shear sense, characterized by intrafolial isoclinal folds and then the chaotic sequence is capped by the highly laminated Manlius (Helderbergian) Limestone follwed by the Coeymans and Kalkberg limestones. Note that the Shawangunk, High Falls, Binnewater, Wilbur sequence is absent and that what is left of the Silurian is exceedingly thin.
STOP 17 - Taconic Unconformity at SW corner of Becraft Mountain, S of Hudson, NY. [UTM Coordinates: 599.75E / 4673.42N, Hudson South quadrangle.]
Only a few places exist where budding geologists can place their fingers on the pulse of a former orogeny. In this exposure, the Silurian Rondout Formation rests with angular unconformity on cherts of the Mount Merino Formation (Middle Ordovician Tippecanoe Sequence). The surface of unconformity is quite irregular and the angular discordance between beds above and below is small, perhaps as a result of minor thrust faulting at the Rondout-Mount Merino contact. Within the base of the brown-weathering Roundout (a silty dolostone), however, clasts of black Mount Merino chert and quartz occur. This would be expected if the contact is indeed one of unconformity!
The Rondout is overlain by highly laminated, whitish rocks of the Manlius Formation, but the Rondout appears again above the Manlius. What gives? Bedding thrusts occur within the Rondout and overlying Manlius. The field exposure shows the bedding thrusts (the lower one outlined by a calcite vein) which imbricate the Siluro-Devonian carbonates above the surface of unconformity with local folding ("rolling") of the Rondout. Again, clear evidence for significant post-Taconic, low-angle thrusting! Toward the south, the Manlius dips below the calc-arenites of the overlying Coeymans Formation and possibly massive limestones of the Kalkberg and New Scotland formations but significant complications are present.
Guidebook 11. Geology of Franklin Furnace, New Jersey, 139 p.
Sunday, 17 June 1990
Sunday, 29 October 1995
OBJECTIVES:
1) To drive across and observe the Mesozoic rocks of the Newark Basin at 55 mph.
2) To examine the Cambro-Ordovician shelf deposits Kittitinny dolomitic carbonates of Passive Margin I.
3) To examine evidence for glaciation and glacial deposition in the Wallkill valley and discuss the drainage history of the region.
4) To contrast and compare the Paleozoic and Proterozoic marble units and to discuss their paleoenvironments.
5) To examine the Proterozoic rocks paying particular attention to the host rock for the Franklin-Sterling Hill orebodies and to discuss their genesis.
6) To visit the world-famous Sterling Hill Mine site and the Franklin Mineral Museum for guided tours and, time permitting collecting, and,
7) To get close and personal with folds, faults, and surfaces of unconformity.
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
STOP 1 - Folded- and Faulted Sauk Sequence Carbonates (Cambro-Ordovician) in new cuts on NJ Route 15. [UTM Coordinates: 530.7E / 4544.5N, Newton East quadrangle.]
New road cuts are the stuff geologist's dreams are made of. Here, in freshly opened roadcuts for new ramps on NJ 15, Paleozoic carbonate rocks (the blue limestone of the older literature or Kittatinny Dolostone and Limestone of modern usage) are exposed. At the extreme south end of the exposure note the well-bedded nearly vertical layers with discontinuous black chert seams 3- to 4 cm thick. The bedding is subparallel to subvertical dissolution cleavage (stylolites) that indicate, along with the steep orientation, that some degree of deformation has affected these strata. These features are cut by subhorizontal cross fractures filled with calcite.
Grading northward, underneath the overpass, the carbonates are more massive. Here, crenulate folds with subhorizontal axial surfaces deform the dissolution cleavage and sedimentary layering. These second-generation (F2) folds are geometrically, and possibly temporally, related to the calcite-filled fractures noted above. North of the overpass significant zones of breccia are present; clast sizes range from l cm to 1 m and many show significant internal cracking suggesting high pore pressures during brecciation of consolidated rock. In addition, some of the boulders are breccias within themselves! We interpret that most of the brecciation was stratigraphic (sinkhole- and collapse breccias) and compare them to the breccia zones found within the Pine Plains Formation of the Wappinger Group of New York State.
STOP 2 - Pleistocene Till and Gravel Body of Ogdensburg Moraine. [UTM Coordinates: 533.4E / 4548.0N, Franklin quadrangle.]
The Ogdensburg Moraine occurs in a lowland east of the Sterling Hill Mine, New Jersey. This is an old gravel pit from which extensive amounts of outwash sand and gravel have been removed. Till forms the west wall. This locality has furnished erratics from the Franklin ore deposit to the north. As noted on a foregoing page, such erratics are easily to identify because of their fluorescence in ultraviolet light. Mineral collectors are well aware of this and use it to look for specimens at night among the stones. A considerable hole has been excavated in the gravel in search of Franklin erratics. According to Bob Metsger, part of the Sterling Mine lies 2000 feet beneath the small hole dug in the gravel.
Another feature of interest here is the precipitation by circulating ground water of a white calcite cement. Evidence of this cement consists of coarse sand-size particles attached to larger cobbles and of a thin, discontinuous white coating on the surfaces of cobbles and -boulders. If conditions are conducive to digging, we might scrape away at the face of till with the idea of exposing some fluorescent erratics that have not been spotted by zealous collectors.
STOP 3 - Sterling Hill Mine, Ogdensburg. [UTM Coordinates: 532.9E / 4547.9N, Franklin quadrangle.]
Mr. Richard Houck, owner of the Sterling Hill Mining Company and tour guide/lecturer, re-opened the mine as a tourist attraction on 01 July 1990, about two years after it was closed in September of 1988. Of further benefit, Dr. Bob Metsger, former Chief Geologist (in the years 1949 to 1988) for the New Jersey Zinc Company at Sterling Hill and currently geologist for the New Jersey Geological Survey, has agreed to meet us at the mine and provide a guided tour of the mine area. As such, CM and JES have little to say here and will allow the area experts to provide the details. This is a great place for an outing with family and friends where a world-class mineral deposit is on display!
STOP 4 - Rutherford Cross Fault, Franklin. [UTM Coordinates: 535.5E / 4551.4N, Franklin quadrangle.]
In the large rock face in front of you, massive Cambro-Ordovician carbonates (to the right - SE) are in fault contact with mylonitic Grenville Marble (to the left - NW) along the Rutherford cross fault of Metsger. This area is actively being cleared by developers and as such the rock face may be unstable and may not last forever. The Paleozoic rocks are massive dark gray dolostones with black chert stringers on the SE side of the fault. Slickensides in the fault zone are marked by graphite smears in the Grenville Marble and indicate dominantly dip-slip normal motion (hanging wall down to SE) with some component of oblique slip. The fault zone is extremely sharp and marked by a clay- rich gouge zone 10 cm thick. Weathering of the clay gouge creates a recess that makes the fault all the more visible.
Even without the marked gouge zone, the difference in lithology across the fault is striking. Here, the footwall is composed of highly laminated graphitic marble with tight isoclinal and rootless folds of a well-developed mylonitic foliation in the marble defined by smeared graphitic lamellae. The folds of the mylonitic foliation (which may be related to faulting) plunge steeply toward the NE. The Grenvillian marble grades into iron-stained quartzo-feldspathic gneiss and a massive quartz-feldspar alaskitic intrusive away from the fault.
STOP 5 - Proterozoic-Cambrian surface of nonconformity and camptonite dike in Franklin Marble. [UTM Coordinates: 534.65E / 4551.0N, Franklin quadrangle.]
Climb up on steep slope to R beside Franklin Revolver and Rifle Club building and note, where the rock was not quarried, the presence of a 1.5-m-thick camptonite dike. The dike, which is an alkalic igneous rock similar to the Beemerville intrusives to the west, is intruded into the Franklin Marble and contains a thin vein of quartz along its SE side. The quarrying removed marble for lime.
Of further interest here, note the crack filling of quartzite of overlying Lower Cambrian Hardyston Formation. Look closely at the iron-stained quartzite and note the presence of detrital franklinite and graphite. This simple observation proves the Proterozoic age of ore formation and you've just sampled across the Proterozoic-Cambrian nonconformity at no extra charge. CM notes that the thin veneer of iron-stained quartzite here may be older than Cambrian as the lithology fits descriptions presented earlier for the Proterozoic Z Chestnut Hill Formation which rests nonconformably above the Grenvillian Franklin Marble. More work needs to be done here to prove or disprove this idea.
STOP 6 - Franklin Mineral Museum Lecture, Tour, and (Time-Permitting) Collecting at Buckwheat Dump. [UTM Coordinates: 534.58E / 4551.26N, Franklin quadrangle.]
We have made an arrangement with Mrs. Carol Hunsinger (Manager) and Steve Sanford, curator of the Franklin Mineral Museum, to enjoy a guided tour and lecture of the museum. There are specimens for sale in his shop and a phenomenal collection of Franklin/Sterling Hill mineral specimens on view in the museum including the Bill Welsh collection. Time permitting (and for a $3.00 fee) you will be permitted to collect fluorescent minerals from the Buckwheat Dump immediately west of the museum.
Just behind here is the old open pit of the Franklin Mine. The underground workings of the mine (which form a labyrinth beneath the town of Franklin) were closed in 1954. In the distance is a narrow cut beyond which occurs a subvertical lamprophyre dike 20 ft thick, which encloses xenoliths of Franklin ore. Strangely, the willemite-bearing xenoliths still fluoresce despite the fact that high heat typically destroys the fluoresence of willemite.
STOP 7 - Anticline and syncline in Lower Silurian Green Pond Formation, Newfoundland. [UTM Coordinates: 547.4E, 4542.7N, Newfoundland quadrangle.]
We have just come out of a continuous belt of Proterozoic gneisses and have passed over a fault that separates the older gneisses from an inlier of Silurian- and Devonian strata. Presumably the Siluro-Devonian strata have been downdropped against the in-situ Proterozoic but modern interpretations, involving significant basement-over-basement overthrusting, allow for the possibility that the Proterozoic and Paleozoic rocks may have been downdropped from the upper plate. As such, this may be a down and in-lier (a new term not to be confused with down and out-lier).
The cuts on the SW side of NJ 23 expose a distinctive fine-pebble conglomerate with uniformly sized white quartz pebbles in a purplish fine-textured matrix interbedded with sandstone and siltstone. This distinctive rock forms erratics found on the beach at Princes Bay, Staten Island and thus provide a direct line provenance point-source that is a glacial- flow-direction indicator. After seeing such erratics, the late Professor Emeritus of Biology from Barnard College, Donald Ritchie, dubbed them "Braunschweiger-sausage" rocks. Once you have seen this rock, you will understand why he gave it this name.
Exposed in the roadcut are an asymmetric anticline and -syncline couple of sandstones with interbedded siltstones and shales. Compared to the sandstones, the shales are differentially strongly cleaved; cleavage has been "refracted" across bedding surfaces. The bedding/cleavage relationships indicate that the folds are upright. Slickensides within the more-competant sandstones indicate that they were lithified at the time of deformation with the axes of small folds parallel to the regional "Appalachian" trends. Take note, however, that the axial surfaces of the folds dip toward the northwest, a reversal of the typical southeast dip of most Appalachian folds in this area.
STOP 8 - Ramapo Border Fault, Exposed in New Cuts, I-287. [UTM Coordinates: 558.0E / 4537.6N, Pompton Plains quadrangle.]
This is a free-form stop where we will examine new exposures of the Ramapo Fault. Here, the Proterozoic gneisses consist of quarto-feldspathic, amphibolitic, and granitoid gneisses that are strongly retrograded to epidote-rich rocks. The exposure is cut by surprisingly few brittle faults. Thus, despite the fact that we are within the Ramapo fault zone only a few faults have been observed. These faults dip steeply toward the east and contain slickensides that plunge toward the northeast. We have not examined these rocks in detail, however, and will discover and discuss our findings On-The-Rocks.
Guidebook 12. Cameron's Line and the Hodges Complex, West Torrington, Connecticut, 115 p.
Saturday, 23 September 1990
OBJECTIVES:
1) To examine the Hartland and Waramaug formations of western Connecticut.
2) To study mafic- and ultramafic rocks of the Hodges Complex and the younger Tyler Lake Granite.
3) To establish the contact relationships of these plutons to each other and to Cameron's Line.
4) To identify slivers of ophiolite and to compare them to the mafic- to ultramafic igneous rocks of the plutons.
5) To illustrate methods of analyzing geologic structures in rock that have been complexly deformed.
6) To locate and discuss glacial features.
7) Not to get bitten by ticks or mosquitos, and,
8) To visit all of our field trip stops (Fat Chance!).
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
STOP 1 - Hartland Formation (upper member) granofels, schist, and amphibolite. [UTM Coordinates: 656.80E / 4624.88N, Torrington quadrangle.]
The outcrops forming the cliffs across from the commuter lot were originally described by Martin (1970) and subsequently detailed by Merguerian (1985). Here, 2-15 cm-scale very well-layered muscovite-biotite-plagioclase-quartz-(hornblende)-garnet) granofels occurs with interlayered schist of similar mineral composition. The abundance of muscovite in the rocks creates a lustrous sheen from foliation surfaces reflecting sunlight, a hallmark of aluminous Hartland lithologies. The pervasive interlayering of granofels and schist, high muscovite and plagioclase content, and presence of amphibolite suggests that protoliths of these rocks were volcaniclastic graywackes and interlayered shale with subordinate basalt flows.
STOP 2 - Hartland Formation (lower member) amphibolite and subsidiary D2 shear zone. [UTM Coordinates: 651.75E / 4629.13N, West Torrington quadrangle.]
The roadside exposures consist of fine- to medium-textured, dark-green hornblende-plagioclase-biotite-(quartz)-(epidote)-(chlorite)-(garnet) amphibolite with lineated prismatic hornblende. Elliptical quartz segregations up to 4 cm thick lie within the S2 foliation. Elsewhere, felsic granofelsñhornblende, +/- biotite, +/- chlorite in layers 1 to 2 m thick, are interlayered with the amphibolite and the muscovitic schist.
Walk 110 m west on Soapstone Hill Road where amphibolite exposures exhibit S2 mylonitic layering. Between these exposures, the muscovite schist is phyllonitic and thin. The mylonitic textures may mark a subsidiary D2 shear zone that imbricates the Hartland amphibolite. Alternatively, shearing could simply have been the result of ductility contrasts developed across the amphibolite-schist contact.
STOP 2a (Optional) - Soapstone Quarry. [UTM Coordinates: 653.63E / 4629.55N, West Torrington quadrangle.]
Walk north on a dirt trail immediately west of the parking area for Stop 2. Along the way, ridges are composed of amphibolite and the intervening valleys are underlain by muscovitic schist. Roughly 700 m north, the trail ends at a pit, of a former soapstone quarry, that is 90 m long by 20 m wide. (They don't call it Soapstone Hill Road for nothing, you know!). The excavation, which is oriented parallel to S2 in the bounding muscovite-chlorite schist, produced commercial quantities of soapstone. Blocks from the tailings pile include talc-tremolite schist, chlorite schist, and very coarse amphibolite rich in opaque minerals.
STOP 3 - Hartland Formation (lower member) muscovite-kyanite-staurolite schist. [UTM Coordinates: 651.10E / 4629.12N, West Torrington quadrangle.]
The lower-member Hartland schist crops out less than 50 m north of the road. The rocks are highly lustrous, gray-weathering, medium- to coarse quartz-muscovite-plagioclase-biotite-opaque-(garnet)-(chlorite)-(apatite) schists often containing 1-to 10-cm porphyroblasts of kyanite, staurolite, and garnet, and more rarely, plagioclase and biotite. The proportions of quartz and muscovite are roughly equal. Together, these two minerals constitute more than half the rock. Granular, clear- to smoky-gray quartz pods are conspicuous and have been flattened into S2. The rocks are lithically correlative with the Rowe Schist of western Massachusetts.
STOP 4 - Cameron's Line and dismembered ophiolite. [UTM Coordinates: 653.70E / 4629.30N, West Torrington quadrangle.]
The mylonitic amphibolite (Ohau) exposure on the dirt road occurs within Cameron's Line, a zone 90 m thick consisting of highly sheared, tectonically intercalated units of the Hartland (upper member) and the Waramaug formations. In the amphibolite, an S2 mylonitic foliation is parallel to the axial surfaces of F2 folds with sheared-out limbs. In the hinge areas of F2 folds, one finds an S1 foliation composed of aligned hornblende. A specimen collected from this exposure after blasting in 1973 shows an F1 isocline refolded by F2 with significant shearing and recrystallization parallel to S2. The Hartland crops out to the north, west, and south. The Waramaug crops out to the south and north. As such, Cameron's Line is situated between these exposures and the cars.
As we walk north, adjacent to the small creek, note the overturned F3 fold with pegmatite intruded along S3. The small hill to the west is underlain by southwest-dipping Waramaug gneiss. Trace the creek to where a 10-m isoclinally folded serpentinite body separates Waramaug rocks to the southeast from Hartland rocks to the west and northwest. Folded by F2 folds, the serpentinite is zoned and highly altered and contains relict olivine and orthopyroxene. The zoning (compositional? or tectonic?) has resulted from relative enrichment of greenish, intergrown cummingtonite and tremolite in the upper part of the body compared to the dense, black serpentine- and anthophyllite-enriched lower part.
In mineral composition and texture, this body differs from ultramafic rocks of the Hodges Complex. The overall eugeoclinal nature of the Hartland and the features resulting from D2 (and possibly D1) deformation in the serpentinite suggest that the body represents dismembered ophiolite (Merguerian, 1979).
STOP 5- Waramaug Formation and contact relationships of Hodges diorite sill. [UTM Coordinates: 652.38E / 4633.12N, West Torrington quadrangle.]
Walk roughly 60 m south on the dirt trail to an exposure of massive but internally laminated, gray-weathering quartz-plagioclase-biotite-sillimanite-muscovite-garnet gneiss. The rocks at this exposure are similar to those of the Waramaug at Stop 4. Because of differential erosion of quartz and sillimanite, the weathered surface is nubby.
At the southern margin of the gneiss, note the abundance of garnet. The enrichment marks the contact effects of adjacent flow-layered diorite of the Hodges Complex. The diorite forms a small sill intruded parallel to S2 in the Waramaug. The microscope shows that in the Waramaug wall rocks, the contact garnets (up to 1 cm) have grown across S2. Garnet has also been enriched in the diorite. This enrichment suggests that limited alumina metasomatism from the wallrocks took place. In the woods to the east and west, Hodges diorites were intruded as sills and lit-par-lit injection bodies (typically less than 10 m thick) along S2 in the Waramaug. Flow layering, defined by oriented hornblende and biotite set in a matrix composed of plagioclase, is regionally parallel to S2.
STOP 6 (Optional) - Mafic and ultramafic rocks of the Hodges Complex. [UTM Coordinates: 652.15E / 4632.64N, West Torrington quadrangle.]
As we walk up the overgrown trail westward from Weed Road, notice that the hill to the west is primarily composed of hornblende gabbro. Locally, this rock is melanocratic and its texture, porphyritic. Concentrations of mafic minerals and oriented hornblendes define a west-dipping flow layering. Near the top of the hill and in a small pod to the south, coarse pyroxenite and hornblendite crop out. Here, the intrusives mask Cameron's Line. But based on detailed tracing of screens and xenoliths, CM infers that Cameron's Line crosses the top of the hill in a SSW direction. The Hodges rocks are in contact with both the Waramaug and Hartland to the west and east, respectively.
To the west, near exposures of the Waramaug, flow-layered diorite trends NE and dips vertical to steep. The Waramaug consists of a dense hornfels peppered with garnet. Despite these contact-mineral changes, the characteristic nubby weathering is still preserved. Along the western slope of the 1320' hill, the Waramaug contains white tremolitic calc-silicate layers.
STOP 7 - Mafic- and ultramafic rocks of the Hodges Complex. [UTM Coordinates: 651.80E / 4632.11N, West Torrington quadrangle.]
Walk from the barn northwestward onto a ridge where flow-layered diorites grade westward into gabbroic rocks. The diorites were multiply intruded as thin sill-like masses parallel to S2 in the Harland Formation. In the contact zone, both the Hartland and the diorites have been strongly enriched in garnet. Near the top of the ridge, massive gabbroic rocks are present; they extend toward the northeast. To the west, beyond the ridgecrest, a large NE-trending mass of pyroxenite and hornblendite crops out. The ultramafic mass, which crosscuts the diorite-gabbro contact and truncates flow layering in the diorite, is interpreted as the youngest intrusive in the Hodges Complex. Locally, the ultramafic rocks have been strongly sheared and transformed into laminated serpentinite. The shear zone cuts across the central part of the Hodges. It has resulted from shearing along the axial surface of the major dextral F4 fold which deformed Cameron's Line, the Hodges Complex, and the Tyler Lake Granite into a broad dextral flexure. In fact, the plutons may have acted as immobile plugs localizing the F4 hinge area.
STOP 8 - Tyler Lake Granite. [UTM Coordinates: 653.00E / 4631.34N, West Torrington quadrangle.]
Near the creek bed is exposed tan-weathering, medium-grained, foliated quartz-microcline-plagioclase-muscovite-biotite-garnet-(chlorite)-(apatite) granite. An X-ray- fluorescence analysis by Dr. D. Radcliffe of Hofstra University produced the following result: SiO2 = 73.0, Al2O3 = 14.2, Fe2O3 = 1.4, MgO = 0.6, CaO = 0.8, K2O = 5.5, Na2O = 3.1, TiO2 = 0.2, MnO = 0.1, loss on ignition = 0.7 (total = 99.6). The granite has been foliated by cm-spaced micaceous layering (S4).
The Tyler Lake Granite contains xenoliths of the Hodges rocks and is in direct contact with all major metamorphic units in the area (except C-Ohmk and C-Oha). This suggests a young intrusive age. Widely separated sample suites from the granite yield a well defined 466 +/- 12 Ma Rb-Sr isochron with initial Sr 87/86 = 0.7082 +/- 0.0011 (Merguerian and others, 1984). Because the Hodges was intruded following or nearly synchronously with D2, this mid-Ordovician age is proof of a Taconian or possibly older age for Cameron's Line.
Guidebook 13. Glacial Geology of Long Island, 133 p.
Saturday+Sunday, 17+18 November 1990
Saturday+Sunday, 01+02 June 1996
OBJECTIVES:
1) To examine the Cretaceous strata of northern Long Island.
- To study the relationships of the Quaternary sediments to the modern landscape.
3) To study the provenance of glacial erratics, especially of stones found on Long Island's north-shore beaches and facies changes in the Quaternary sediments.
4) To demonstrate the importance of lacustrine-deltaic strata in Fuller's Manhasset Formation.
5) To emphasize the general correctness of Fuller's interpretation of the stratigraphy compared with those who have cast Fuller aside, and,
6) To understand the general geologic relationships of the geologic units on Long Island and the occurrence of ground water in various geologic units.
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
STOP 1 - Outwash, till, and loess in beach cliffs at Sands Point Museum and Preserve, Sands Point. [UTM Coordinates: 609.9E / 4524.3N, Sea Cliff quadrangle.]
We are indebted to Herb Mills, County Parks Naturalist, who will accompany us to Stops 1 and 2 and who has been helpful in arranging permissions for us to visit these localities. Take trail #3 (green markers) to beach past kettle lake. We shall examine the cliff to the W of the end of the trail (on L as we approach) first and then spend most of our time examining the cliffs to the E of the trail's end.
Cliff to W end of trail:
The cliff W of the end of the trail displays three contrasting materials: (1) Cretaceous(?) black- and deep reddish-brown sandstone (recently exposed at base of bluff just W of stairs); (2) Quaternary outwash (predominates to the W); and (3) Quaternary red-brown till (exposed close to the trail). The newly exposed dark-colored sandstone, stained with probable manganese oxides and hematite, may be the Upper Cretaceous. Previously, we had noticed a similar manganese-oxide-stained sandstone E of the trail, but not enough of it was exposed to enable us to make any decision about it. The new exposures resemble the dark-stained Upper Cretaceous sands at the AKR exposure, SW Staten Island.
Cliff E of trail:
On the beach, note the abundant erratics including possible blueschist boulders. Also present here are the ubiquitous Cretaceous "ironstone" conglomerates with well-rounded white quartz pebbles, and small pieces of light-gray fossiliferous Devonian chert containing straight-hinged spiriferid brachiopods (probably from the Onondaga Limestone). Beneath the slope-wash cover (whose thickness is up to 0.5 m), the upper part of the cliff face consists of horizontally stratified outwash sand- and -gravel with mafic minerals, and rounded white quartz pebbles, as in the exposure W of the stairs. Toward the top of the cliff, the outwash is overlain by a thin till that probably qualifies as being the Montauk Till Member of the Manhasset Formation of Fuller (1914). Overlying this till is a layer of coarse reddish loess, 1 m thick, which undoubtedly was derived from a reddish-brown till.
STOP 2 - Glacial chaos in the Sand Pits, Port Washington. [UTM Coordinates: 612.0E / 4521.0N, Sea Cliff quadrangle.]
The overall relationships here were determined by the ice-push deformation of the last glacier to invade Long Island, which (Mills and Wells, 1975; Sirkin and Mills, 1975) infer came from the NW and which they have classified as Woodfordian. We agree with the first two points about its being the "last glacier to invade Long Island" and that it came from the NW, but we reject their Woodfordian age assignment; we prefer Fuller's Early Wisconsinan. Be that as it may, this "last glacier" did a number on the Cretaceous, bringing it up from several hundred feet below sea level, carving it into slices, and placing them above the Quaternary sediments, as a series of ice-thrust "allochthons." These Cretaceous-over-Quaternary features are confined to the northern half of the former face that extended in a N-S direction for about 2.5 mi when the sand pits were still active. In the southern half of the face, the Quaternary strata are in normal order: from base upward, outwash, till, outwash, till.
The first major trail to the left leads to a small pit where black Cretaceous clay is exposed. Notable features of this clay are its concretions, pyrite, and "lignite" [all examples of which we think are not lignite but rather charcoal, which Hollick (1906) inferred are remnants of ancient forest fires]. In the "Death Valley"-like landscape visible at the end of the trail (trailbiker's "heaven"), several protruding parts of the Montauk Till are surrounded by light-colored Cretaceous kaolitic sands and -conglomerates. On 01 June 1996, we dug out the thrust contact at the top of this till and found, as Mills indicated, a thin zone of clay along the thrust surface.
STOP 3 - Outwash, till, and loess at Garvies Point Museum and Preserve, Glen Cove. [UTM Coordinates: 613.5E / 4523.7N, Sea Cliff quadrangle.]
Assemble outside the museum by the large erratic for a walk down to the beach. At the bottom of the bluff, Cretaceous strata are exposed. Units visible are variegated clays and -sands with lignite seams. The stratigraphic succession as found in a slump block to the south of the wooden stairs (from the top down) is:
Yellow-brown sand with local cross strata, underlain by
Whitish clay,
Red-purple clay with local lignite at base, and
Gray clay.
The slump block implies that these strata have been gravity displaced downslope from an original position higher up the slope. Given the normal relationship that the top of the Cretaceous lies below sea level, the pre-slump situation here probably involved upward displacement of the Cretaceous on glacio-tectonic thrusts, as in the northern end of the Port Washington pits at Stop 02. We have not seen any evidence at Garvies Point that Cretaceous has been thrust over Pleistocene, but it would not surprise us to find such a relationship.
About 150 m S of the stairs, whitish Cretaceous clay of the slump block, at beach level, is overlain by a reddish-brown till, about 1 m thick, consisting of deeply weathered granitic- and other stones, and Cretaceous ironstones; a manganiferous residue is present at the contact with underlying outwash. Other dark-reddish-brown outwash, ca 1.5 m thick, overlies the thin till. The till occupies channels in the white clay; the orientation of the long axes of the channels is NW-SE. The till also fills a crack that extends down into the white clay.
The beach is littered with a great variety of distinctive kinds of erratics, some of bouder size, including plagioclase-phyric gabbro with xenoliths, pyroxene-phyric lamprophyre, potash-feldspar phyric granitic gneiss, mylonitic granitoid gneiss, augen gneiss, epidote amphibolite, potash-feldspar pegmatite, mica-rich red shale (Cretaceous), Cretaceous "ironstone" conglomerate, and many others.
STOP 4 - Caumsett State Park, West Neck Road, Lloyd Neck. [UTM Coordinates: 628E / 4533N, Lloyd Harbor quadrangle.]
We have obtained permission to enter the Park and to drive our vehicle to the fishermen's landing at the beach. The bluff is being eroding by gullying, slumping, and various debris flows. Root balls of trees from above are being undermined and the trees are in various stages of falling down. The same general situation applies to the boulders in the overlying till. Based on our reconnaissance to the shore cliffs on 08 Nov 1990 and our previous trip, we saw the following: At the base of the section in draw at the E end are Cretaceous sands and -gravels characterized by a kaolinitic clay matrix and iron seams. Cross strata in sets of 10 cm to 15 cm dip to SSW with roughly 5 m aggrgate thickness.
The storms of December 1992 uncovered S-dipping Gilbert-delta-type foresets, as at Sands Point, but with several important differences. Here, gravel is very abundant in the dipping layers and many of the stones show evidence of decomposition, implying considerable antiquity. We infer that most of the bluff consists of deltaic foresets belonging to Fuller's Herod Gravel Member of the Manhasset Formation. Higher up, the relationships are not too clear at a distance (we did not climb nor dig). Above the Cretaceous is a red-brown till that we sampled. Above it is outwash (yellowish) and clearly deformed judging by variation in dip as well as fault offset. Higher-still seems to be another brownish till, probably the Montauk, of Fuller, and at top, loess.
STOP 5 - Target Rock National Wildlife Refuge, West Neck Road, Lloyd Neck. [UTM Coordinates: 632.0E / 4531.8N, Lloyd Harbor quadrangle.]
En route, the trail crosses the loess, which forms the topmost layer of the cliff exposures (as seen at the N end of the Preserve). The Target Rock exposures were described in Sirkin and Mills (1975, p. 319-323), who illustrated two tills and some laminated silts/clays in between. We have interpreted these laminated fine sediments as deposits of Lake Long Island (Sanders and Merguerian, 1994a; Sanders, Merguerian, and Mills, 1993). The beach here contains abundant green pebbles featuring porphyritic volcanic rocks that we think came from W of New Haven, CT (Maltby volcanics). They are definitely not trap rocks from the Palisades, as suggested by Sirkin and Mills. They imply glacial flow from NNE to SSW, not NNW to SSE.
The lower half of the cliff exposed after the storms of December 1992 consists of till containing green porphyritic mafic erratics, so common on the beach. We correlate this till with the oldest till at Croton Point Park (the gray till containing decayed granite stones; Merguerian and Sanders, 1992b; Sanders and Merguerian, 1994b).
STOP 6 - Roanoke Landing Beach, Riverhead. [UTM Coordinates: 692.8E / 4538.3N, Riverhead quadrangle.]
According to Sirkin (notes on June 1990 trip for Long Island Association of Geologists), the exposures here are a recessional moraine of the Connecticut lobe of the Woodfordian glacier (not much moraine left because of erosion). In the territory between the moraine ridges, vegetable farms are numerous. The moraine is capped by a diamictite that is overlain by loess (at top of cliff).
The results of our shovel action diclosed pebbly outwash in the lower bluffs, with mature composition (derived from the mature Upper Cretaceous). Higher up is a till; above it another outwash, then another till, and finally the loess at the top. We have not yet determined the proper age assignments for these units. However, after re-reading Fuller (1914, p. 139), we agree with his assignment of the beds here to the Manhasset Formation, including all three members, the basal Herod Gravel, the middle Montauk Till, and upper Hempstead Gravel. Fuller did not mention the loess at the top, but did mention "dune sand" 10 ft thick. The upper till may be his Early Wisconsinan Till (associated with the terminal-moraine ridges).
STOP 7 - Jacobs Hill, Southold. [UTM Coordinates: 702.2E / 4540.5N, Mattituck quadrangle.]
Assemble at the SE corner of the parking lot for a walk down the trail to the beach. Assemble by the van for a brief look at the topographic map of the Mattituck- and Mattituck Hills quadrangles. Notice that the houses shown on the Mattituck quadrangle map dated 1955? are no longer present. They probably disappeared during the big storms of December 1992, but we do not know this for certain. Geologic descriptions of the locality referred to simply as "Jacob Hill" have been published by Fuller (1914) and by J. E. Upson (1970) of the U. S. Geological Survey. Fuller made this the type locality of the Jacob Sand, which overlies the Gardiners Clay. (Both of these formations underlie the Manhasset Formation.) A notable feature of the cliff here is the till at the top that contains large boulders, many of which now litter the beach. This is the Montauk Till of Fuller's Manhasset Formation. This till is overlain by the ubiquitous loess.
Guidebook 14. Geology of Stokes State Forest, New Jersey, 118 p.
Sunday, 21 May 1991
Saturday, 20 May 1995
OBJECTIVES:
1) Examining the regional stratigraphy and structure of the Appalachians in the vicinity of northwestern New Jersey.
2) Identifying evidence for Late Paleozoic (terminal-stage Appalachian) deformation in both the Great Valley and Valley and Ridge Province.
3) Taking a leisurely walk through a part of Stokes State Forest for a detailed look at folds, faults, and superposed cleavage.
4) Pointing out evidence for large-scale overthrusts of Paleozoic and older strata during protracted Phanerozoic orogeny.
5) Looking for glacial features and indicator stones to develop ideas on superposed glaciation for this part of northwestern New Jersey, and,
6) To get to all of our intended stops for the day (we think we have a good chance at this one, for a change!)
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
STOP 1 - Scenic overlook from Kittatinny Mountain westward to the strike ridges and Pocono/Catskill Plateau. [UTM Coordinates: 522.19E / 4562.00N, Branchville quadrangle.]
The strike valley underlain by the Devonian shales and Helderberg limestones here lies northwest of Kittatinny Mountain. Prevailing wisdom suggests that strata are dipping NW but ending downward against horizontal strata below (proof of bedding-type thrust in which the beds on the upper block are dipping back down to intersect the fault surface, maintaining the same angle with the fault as deeper down where the steep fault cuts horizontal beds. Now the result is a horizontal fault and dipping beds).
Depending upon time and interest level, we may opt to take a short walk down Tinsley Trail (note trailhead above at 68.9) for about a mile or so in search of an unusual glacial boulder of nepheline syenite on the way to a boulder field. Our reputations as "Pleistocene Boulder Chasers" precedes us so keep an open mind for a possible "fabulous discovery" of a potentially important indicator stone. Because Upper Ordovician carbonatite-alkalic rocks of the Beemerville Complex (Ratcliffe, 1981) crop out to the northeast of this area, the identification of nepheline syenite and related rocks may provide much-needed evidence for SSW-directed (meaning originally from the NNE) glacial flow.
STOP 2 - Sunrise Mountain. [UTM Coordinates: 523.35E / 4562.77N, Branchville quadrangle.]
At the breathtaking elevation of 1653' above sea level, we here stand on the Shawangunk-Kittatinny Conglomerate near a portion of the Appalachian Trail. Look out toward the east for a panoramic vista of the Great Valley (underlain by slates and carbonates) and the Proterozoic crystalline massifs of the Reading-Hudson Highlands of New Jersey and New York. We wonder, upon looking at the Proterozoic massifs in the distance, how many of them were "punched up" through the Paleozoic cover as horsts, or "dropped down" from above as grabens. High Point State Park, the highest elevation in New Jersey, may be seen toward the north depending on the amount of vegetation in the way. Note that the local mountain peaks are all approximately the same height. Such summit accordance is indicative of prolonged erosion and development of a planation surface. Sunrise Mountain is a natural drainage divide where rainfall on the east side flows toward the Hudson River and rain falling to the west works its way into the Delaware River.
According to a 31-page booklet entitled "A Guide to Stokes State Forest", published by the New Jersey Department of Environmental Protection, Division of Parks and Forestry, State Park Service, CN 404, Trenton, NJ 08625, we are standing on a ridge of great natural significance. The harsh climate and thin soil promote the growth of hardy (and laurel?) strains of vegetation, including scrub oak, pitch pine, wild blueberry, and, you guessed it, mountain laurel. Monarch butterflies and hawks use the Shawangunk-Kittatinny Ridge as a part of their seasonal migratory flight by utilizing warm-air updrafts against the eastern edge.
STOP 3 - Tillman Ravine, Stokes State Forest. [UTM Coordinates: 511.40E / 4556.03N, Culver's Gap quadrangle.]
The rocks exposed in Tillman Brook are reddish sandstones, shales, and siltstones of the Silurian Bloomsburg Formation (equivalent to the High Falls Formation of previous On-The-Rocks trips). These sediments were deposited roughly 400 Ma (million years ago) in a broad fan-delta complex and are essentially non-fossiliferous excepting a few preserved remains of fish and plant fossils. The strata have been folded and display many aspects of cleavage.
Tillman ravine is a youthful feature illustrating the erosive effects of rapid downcutting by post-glacial streams. Just before the lower falls a tributary enters; from the trail, one gets a clear view of its V-shaped cross-valley (or transverse) profile indicating a youthful stream. Such a profile is indicative of stream action and not glaciation. Here, the course of the main stream is controlled by the steep fracture cleavage, a structural weakness in the rocks.
At the Lower Falls-Teacup area (the Teacup is a large pothole), red siltstones are exposed. In the red siltstones, it is not easy to ascertain the attitude of the bedding but greenish-gray interlayers of siltstone give a faint hint of the orientation. Here, the intersection of the cleavages forms splinter-like wedges in the siltstone.
STOP 4 - Martinsburg slates, Hampton Township. [UTM Coordinates: 523.05E / 4550.55N, Newton East quadrangle.]
Before you is a marvelous example of an anticline in dark- colored slates of the Martinbsburg Formation. Note the very prominent "pencil" structure here because the bedding and the cleavages break the rock into extremely long pieces. Let's look for evidence for another (third?) slaty cleavage or two and try to find some nice slate specimens showing a high angle bedding/cleavage relationship.
STOP 5 - Sauk Sequence (Cambro-Ordovician) carbonates thrust over Martinsburg slates ("Jenny Jump thrust"), Newton County Mall. [UTM Coordinates: 521.60E / 4546.60N, Newton East quadrangle.]
The area of this stop was described in detail by Drake and Lyttle (1980; Stop 9) and we borrow liberally from their discussion. Here a small slab of Allentown Dolostone (Upper Cambrian part of the Sauk Sequence) lies structurally above slates of the Tippecanoe Sequence [Ramseyburg Member of the Martinsburg Formation (part of our Layer IIB)]. The contact is a thrust fault (the Jenny Jump thrust of Lewis and Kummel (1915), and Kummel (1940), and renamed the Grand Union thrust by Drake and Lyttle 1980). This marvelous, but somewhat non-picturesque, exposure was created during excavation for the shopping center. The thrust is marked by 2 to 8 cm of gouge consisting of crushed, slickensided dolostone.
Guidebook 15. Connecticut Mines and Dinosaurs, 111 p.
Sunday, 16 June 1991
Sunday, 18 June 1994
OBJECTIVES:
1) To collect minerals from the Case beryl prospects in Portland, Connecticut.
2) To examine the stratigraphy of the Hartford Basin of central Connecticut.
3) To discuss the structure of the Hartford Basin.
4) To locate and discuss glacial features, and,
5) To avoid being bitten by ticks or mosquitos.
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
STOP 1 - Case Quarries. [UTM Coordinates: 701.4E / 4610.2N, Middle Haddam quadrangle.]
The Case quarries were owned by Myron N. Case of Rose Hill, Portland Connecticut according to Cameron and others (1954). From 1933 to 1935, the Worth Spar Company, Inc., of Cobalt, Connecticut, quarried the three pegmatites for feldspar. The quarries were last worked in 1942. The workings are open cuts that range from 20 to 40 meters in length, 2 to 15 meters in width, and 3 to 8 meters in depth. The three pegmatites of the Case quarry lie within 160 m of one another. They strike north to northeast with variable dip and cross cut their host rock, the Monson Gneiss that strikes northward and dips gently west.
According to estimates by Cameron and others (1954), the Case No. 2 and 3 quarries contained slightly more than 100 tons of beryl, mostly in small crystals. Much of this material was left by the Worth Spar Company in mine dumps around the area. So, get comfortable and begin scratching around and most importantly, down, for some nice specimens of beryl, tourmaline, and columbite-tantalite. Other minerals found here, but not mentioned above, include: albite, almandite, autunite, biotite, bismite, bismuthinite, bismutite, chalcopyrite, cyrtolite, epidote, fluorapatite, goethite, hornblende, limonite, microcline, muscovite, opal, pyrite, pyrolusite, spessartite, torbernite, uraninite, and uranophane according to Januzzi (1972). During a visit by CM in April of 1984, bluish beryl crystals were observed in Case Quarry No. 3 grown in quartz, perpendicular to the contact between the Monson Gneiss and adjacent quartz vein. Pickings were scarce during a CM field trip in July of 1990 but the "Connecticut quarry fairies" may have restocked the tailings pile since. In the mine-dump area, the best matrix-specimen beryl occurs in the feldspathic pegmatite material. Uranium minerals are found in association with smoky quartz. Happy hunting.
STOP 2 - Dinosaur State Park at Rocky Hill. [UTM Coordinates: 695.3E / 4613.6N, Hartford South quadrangle.]
During the Jurassic Period, roughly 185 Ma, mudflats extended over much of the flat floor of the Hartford basin. Fault-related uplifts along the eastern basin-marginal fault of this basin provided intermittent supplies of coarse clastic sediments eroded from the pre-Triassic crystalline rocks of the persistently elevated Eastern Highland block. Into the Hartford basin poured many sediments that we now see as interbedded red sandstones, shales, conglomerates and non-red-colored lacustrine deposits. Many dinosaurs traversed these muddy plains searching for food (not mineral specimens as had been commonly thought!) and left tracks in their wake. Fossil bones of these dinosaurs have never been found as the conditions that preserve tracks are not the best for preserving bone, but the search continues. The geodesic dome constructed here preserves a multitude of tracks for the public to see and admire. We will stop here for lunch and, time permitting a brief visit to the dinosaur footprint area where you may create a plaster cast of a Eubrontes footprint.
STOP 3 - Hampden Basalt and East Berlin Formation, Cromwell. [UTM Coordinates: 692.0E / 4610.8N, Hartford South quadrangle.]
Many geologists have published descriptions of the East Berlin formation exposed here during the "Texas" time period. All of these authors have emphasized the cyclicity of these sediments, which were deposited in lakes of varying water depth and along the margins of lakes. The most-comprehensive interpretation of these Newark ancient lake deposits in terms of changing water levels has been presented by P. E. Olsen (1986) for the Lockatong Formation in New Jersey. Olsen has set forth the details of what he named a Van Houten cycle, that is the sediments deposited during a change from a deep-water lake (typical deposit, a black shale) to a shallow-water lake (red mudstone) to an alluvial plain (sandstone) and back again to a deep-water lake. Olsen's chronologic reconstruction connects these changes in level of the Mesozoic lakes with periods that are the same as those calculated by Milankovitch for the Pleistocene changes of climate associated with astronomic factors that cause the Earth's orbit and axial tilt to change.
One thing we would particularly like to do here is see if we can find the layers that contain the dinosaur trackways seen at Stop 2. Other things to notice are the conditions associated with the contact between the basalt and the sedimentary layers. Notice the chilled margin in the basalt and the effects of the heat from the lava on the underlying sedimentary strata.
STOP 4 - Hampden Basalt and East Berlin Formation, East Berlin. [UTM Coordinates: 688.5E/ 4610.2N, Middletown quadrangle.]
Exposed here are the upper layers of the East Berlin Formation (this is the type locality so designated by E. P. Lehmann in 1959) and contact with overlying Hampden Basalt (the same units as at Stop 3, but repeated here by being relatively downdropped about 2000 feet on a normal fault). Some large and splendid glacial grooves are visible at top of knoll on NE side of the road. The lower part of the Hampden Basalt contains bent-over pipestem vesicles that indicate the direction of flow of the lava before final cooling. We will use a compass to record the direction implied. Notice the "vesicles" in the underlying siltstone!
Guidebook 16. Cameron's Line and the Bronx Parks, 126 p.
Sunday, 24 November 1991
Saturday, 08 May 1993
OBJECTIVES:
1) To study the effects of extreme folding, faulting and metamorphism of the Lower Paleozoic strata of the Bronx.
2) To examine lithologic variations in the three schist units of the Bronx formerly "lumped" together into the Manhattan Formation.
3) To examine the evidence for Cameron's Line.
4) To get up close and personal with mylonitic rocks.
5) To examine the effects of multiple glaciations.
6) To get in the groove, glacial-, that is!
7) To find sufficient restrooms to keep field trip participants happy, and,
8) To try to visit all of our planned stops.
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
STOP 1 - Fordham Gneiss on the Cross Bronx Expressway, The Bronx. [UTM Coordinates: 590.9E / 4521.9N, Central Park quadrangle.]
We would like to begin today's field trip with a short stop to view the "Grand-daddy" bedrock unit of the Bronx. Here in spectacular vertical exposures that Robert Moses' busy work crews blasted away to make room for the Cross Bronx Expressway (CM laments - What a waste of rock!), the Proterozoic Y Fordham Gneiss Member B is exposed. The Fordham consists of a steep, west-dipping, highly folded- and faulted sequence of garnetiferous quartzofeldspathic gneiss and migmatite, biotite schist, and amphibolite. Elsewhere, greenish calc-silicate layers are present. Of interest here are the obvious asymmetric Z-folds of the older foliation with steep- to subvertical axial surfaces and with a gentle horizontal plunge. The obvious folds are probably correlative with the F3 folds found elsewhere in the Bronx and Manhattan.
We will walk along the length of the outcrop until carbon monoxide poisoning begins to set in. You will know this has happened when CM begins waving his arms, talking about superposed deformation, migmatites, and ductile shear zones. We have not examined these exposures in great detail but in passing them at 55 MPH, we have noticed brittle- and ductile faults as well as a multitude of faults. Keep you eyes peeled for spare car parts and "previously owned, partly used" major appliances.
STOP 2 - Cameron's Line or the St. Nicholas Thrust - Boro Hall and Crotona Parks, Cross Bronx Expressway, The Bronx. [UTM Coordinates: 592.94E / 4521.75N, Central Park quadrangle.]
Most of the Paleozoic rock units of the NYC area converge in and around Boro Hall and Crotona Parks in The Bronx according to our previous and ongoing research efforts. In these small parks, separated by I-95, marble, calc-schist, granofels, gneiss, and mica schist are all exposed from west to east in NE-striking, imbricated ductile-fault bounded tectonostratigraphic units.
STOP 3 - New York Botanical Garden. [UTM Coordinates centered on: 594.7E / 4523.6N, Central Park quadrangle. Detailed trail maps in guidebook.]
The structural geology of the New York Botanical Garden was the subject of investigations by Langer (1966) and Bowes and Langer (1969). The rocks exposed in this area of the Bronx Botanical Garden and eastward are in a key position with respect to CM's interpretation of the schists of Manhattan. He and Baskerville (1987) have independently mapped the rocks here as belonging to the Hartland Formation. The Hartland Formation consists of a vast succession of metasedimentary rocks (that is, metamorphic rocks formed from protoliths that were sedimentary rocks). One of the diagnostic characteristics of the Hartland Formation is well-developed layering and overall aluminous composition. Various kinds of metamorphic rocks are present: muscovite schist and -gneiss with interlayers of mica granofels, quartz-feldspar gneiss, and amphibolite. The schistose- and gneissic members of the Hartland Formation contain minerals rich in aluminum. This implies that in the sedimentary protolith, clay minerals were abundant. The inferred abundance of clay implies further that the original sediments consisted of extremely fine size fractions.
The Hartland's interlayers of mica granofels and quartz-feldspar gneiss on the one hand, and of amphibolite, on the other, are inferred to have resulted from the metamorphism of turbidites and of basaltic extrusive rocks, respectively. In total, the Hartland Formation is thought to represent the products of metamorphism of a sequence of Lower Paleozoic rocks deposited in deep water adjacent to and east of the early Paleozoic shelf edge of the eastern North American continent (Merguerian, 1983b).
Glacial features noted in the Botanical Gardens include polished bedrock surfaces, roche-moutonée structure, and glacial grooves, indicating at least three major glacial episodes: (1) earliest movement from NNE to SSW; (2) movement from the NNW to SSE, and (3) movement from NNE to SSW. These are in keeping with our results from studies of glaciation in the region.
The following stops are all within the confines of the New York Botanical Gardens in the Bronx (Stop 3) and are numbered 3.1 through 3.12. The twelve sub-stops of Stop 3 are described separately in our guidebook on the area.
STOP 3.1 - Hartland Formation on the east side of Bronx River beneath Hester Bridge.
STOP 3.2 - Migmatitic Hartland Formation on east side of Bronx River at waterfall area.
STOP 3.3 - Roche-moutonée structure in the Hartland Formation.
STOP 3.4 - Stratigraphy of the Hartland Formation and evidence for glaciation.
STOP 3.5 - Shallow early structures in the Hartland Formation and evidence for two glaciations.
STOP 3.6 - Elephant Rock--a trunkful of crescentic- and lunate gouges, erratics, and striae in deformed Hartland rocks.
STOP 3.7 - Lincoln Rock - Two glacial directions and local flow divergence.
STOP 3.8 - Well layered (mylonitic?) Hartland cut by a prominent joint set.
STOP 3.9 - Dolerite erratics.
STOP 3.10 - Manhattan Schist Formation.
STOP 3.11 - Hartland Formation and amphibolite float.
STOP 3.12 - Mylonitic Manhattan Formation and the elusive Inwood Marble.
STOP 4 - Hutchinson River Group of North and South Twin Islands, near Orchard Beach, Pelham Bay Park. [UTM Coordinates: 602.4E / 4525.0N, Flushing quadrangle.]
Orchard Beach is one of Robert Moses' grand designs. The sand forming the crescentic beach was barged here from Rockaway Inlet. The bathhouse was built as elegantly as possible following the guidelines limiting the uses of the federal money that largely paid for the construction costs. Interested readers should consult Robert Caro's (1972) book for a description of the pre-Moses land use and of a field "brainstorming" session held here by Moses and his staff.
Rocks of the Hutchinson River Group are fully displayed on glaciated pavements (look for glacial features) on South and North Twin Islands to the north of Orchard Beach in Pelham Bay Park in the Bronx. Described by Leveson and Seyfert (1969), and Seyfert and Leveson (1968, 1969), these high- to medium- grade metamorphic rocks include gneiss, schist, and amphibolite all showing ample evidence for partial melting (fusion) forming mixed igneous- and metamorphic rocks known as migmatites. Of additional geologic interest, many pegmatites and veins of quartz occur.
The glacial features of South Twin Island are remarkable and take the form of glacial striae oriented NW, glacial polish, and roche-moutonée structure. A boulder of ultramafic rock from the Cortlandt Complex in Peekskill, New York can be found at the southern end of the South Twin Island exposure near Orchard Beach. This discovery mandates glacial advance from the NNE. In addition to these features, a thin red-brown till, consisting of rounded boulders set in a reddish-brown matrix of poorly sorted sand, silt, and clay, was extensively exposed as a byproduct of the erosion of a wave-cut scarp during the higher-than-normal spring tides accompanying the perigee-syzygy Full Moon of Passover (06 April 1993). Judging from the newly visible features in the bedrock, we estimate that scarp retreat during the storm ranged from 3 to 5 m.
The Hutchinson River Group, which is correlative with the Hartland Formation of western Connecticut and southeastern New York, has been intensely deformed under high- to medium-grade metamorphic conditions. Mapping by C. Merguerian in 1981-83 showed the presence of at least four sets of superposed folds, two early stages of isoclinal folds, followed by tight F3 folds, that were gently warped by open F4 folds. Based on similarities in structural style and -orientation compared to sequences mapped in New York City and western Connecticut on either side of Cameron's Line (Merguerian, 1985a, 1986b), the F1 and F2 fold phases are superposed and probably progressive. Significant shearing parallel to the axial surfaces of F1 and F2 folds has resulted in folds with sheared-out limbs and has created beautiful interference patterns. In addition, pegmatitic sweat-outs and bull-quartz veins injected parallel to S2 are omnipresent. Together these create local migmatite.
Guidebook 17. Geology of the Delaware Water Gap and Vicinity, New Jersey and Pennsylvania, 109 p.
Saturday, 20 June 1992
OBJECTIVES:
1) Examining the regional stratigraphy and structure of the Appalachians in the vicinity of northwestern New Jersey.
2) Identify evidence for Late Paleozoic (terminal-stage Appalachian) deformation in the Great Valley and Valley and Ridge Province.
3) Taking a leisurely walk through a part of the Delaware Water Gap National Recreation Area for a detailed look at folds and superposed cleavage.
4) Pointing out evidence for large-scale overthrusts of Paleozoic and older strata during protracted Phanerozoic orogeny.
5) Looking for glacial features along the walls of the Delaware Water Gap, and,
6) To get to all of our intended stops for the day.
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
STOP 1 - Proterozoic rock cuts on exit ramp from rest area/truck-parking area on I-80 westbound, Town of Allamuchy, NJ. [UTM Coordinates: 518.0E / 4530.3N, Tranquility quadrangle.]
The rocks here are part of the Allamuchy nappe of Drake and Lyttle (1980, p. 98), of which they wrote: "The Allamuchy nappe is typical of the other crystalline-cored nappes de recouvrement of the Reading Prong nappe megasystem as described to the west. Exposed here is a coarse felsic gneiss displaying effects of extensive brittle deformation. Almost all rock faces are limonite-lined fractures (probably a result of oxidation of original pyrite films). Near the E end of the cuts are steep normal faults, that strike parallel to I-80 (NE-SW) and dip steeply SE on which dip-slip slickensides are well developed. By the guard rail, the gneissic foliation is clear; its strike is roughly perpendicular to I-80 and its dip is to the NE. Near the drain pipe at the end of the cut is a splendid example of a fault-mirror slickenside displaying right-lateral strike slip offset.
STOP 2 (Optional) - Scenic Overlook on I-80 westbound. [UTM Coordinates: 516.0E / 4530.2N, Town of Allamuchy, NJ, Tranquility quadrangle.]
At the breathtaking elevation of 1100' above sea level, we may be able see through gaps in the trees a panoramic vista toward the NW across the Great Valley (here named the Kittatinny Valley; it is underlain by the Sauk Sequence carbonates and limestones/slates of the Tippecanoe Sequence) to the Delaware Water Gap, which cuts through the otherwise-unbroken ridge along the NW side of the Appalachian Great Valley. This ridge is underlain by massive Lower Silurian conglomerate and sandstone units that generally dip to the NW. Note that the elevations of the tops of the local mountain ridges are all approximately the same height. Such summit accordance is indicative of prolonged erosion and development of a planation surface.
STOP 3 - Cuts on County Route 519, NE of Hope, Warren Co., NJ (carbonate-pebble conglomerate (the Jacksonburg Limestone) at base of Tippecanoe Sequence, beneath the Jenny Jump thrust. [UTM Coordinates: 504.0E / 4529.3N, Blairstown quadrangle.]
Exposed on L is limestone-pebble conglomerate at base of Tippecanoe Sequence (Jacksonburg Limestone in these parts; the rocks here are equivalent to the Balmville of the central Hudson Valley, New York). We have crossed the Jenny Jump thrust and these are the rocks below this fault.
STOP 4 (Optional): Scenic Overlook, I-80, Columbia, NJ. [UTM Coordinates: N/A, Portland quadrangle.]
We quote the following from the caption of a photograph taken from this spot (Epstein, 1980, fig. 4, p. 77):
"...Kittatinny Mountain underlain by resistant quartzite and lesser siltstone and shale of the Shawangunk Formation. The Shawangunk generally dips moderately to the northwest, such as at Delaware Water Gap (2), but is overturned to the southeast in places. The dark laminated slates exposed along Interstate 80 below (3) are in the lower (Bushkill) member of the Martinsburg Formation. Paulins Kill Valley (4) is underlain by carbonate rocks of the Allentown Dolomite, Beekmantown Group, and Jacksonburg Limestone that are in a window and are separated from the Martisnburg by the Portland Fault. The hills in the middleground (sic) beyond the Paulins Kill (5) are underlain by the Bushkill and Ramseyburg Members of the Martinsburg Formation. The upper (Pen Argyl) Member of the Martinsburg first appears across the Delaware River in Pennsylvania, coming out from under the Taconic unconformity with the overlying Shawangunk Formation (6)..."
STOP 5 - Northwest slope of Delaware Water Gap (Lower Silurian red quartzites and siltstones) under I-80 bridge. [UTM Coordinates: 488.4E / 4535.9N, Stroudsburg quadrangle.]
The rocks exposed alongside I-80 consist of reddish sandstones, shales, and siltstones of the Silurian Bloomsburg Formation (equivalent to the High Falls Formation of previous On-The-Rocks trips). The sediments composing these rocks were deposited roughly 400 Ma (million years ago) in a broad deltaic fan complex; they are essentially non-fossiliferous excepting a few preserved remains of fish and plant fossils. The strata have been folded and display many aspects of cleavage.
The features to see in the bedrock include gentle upright folds, inclined regional cleavage, and refracted cleavage. Before we leave this place, would you believe your eyes and that you can see glacial striae(!) parallel to the road (i.e., NW to SE)? These striae indicate that the Delaware Water Gap is as least as old as the last glacier from the NW. (Compare this situation with the lack of glacial striae in the Bronx River gorge.)
STOP 6 - Cuts on PA Route 191, valley of Broadhead Creek, N of Stroudsburg, PA. [UTM Coordinates: 482.4E / 4541.8N, East Stroudsburg quadrangle.]
Be prepared to make withdrawals from a Devonian bank (bioherm). Fossils are plentiful in the siltstone here. Where original skeletal calcite remains in the fresh rock, its color is white. The best collecting is in rust-colored pieces that are full of holes where the calcite has been dissolved away, leaving external- and/or internal molds. We found many bryozoa, corals, brachiopods, and champion critter collector CM found a coiled trilobite, pygidium and all. Novice collector Christopher (Vern) Merguerian made a fabulous brachiopod discovery on our pre-trip runthrough.
STOP 7 - Cross-bedded Devonian sandstone cuts on PA 191, valley of Broadhead Creek, between Analomink and Henryville, N of Stroudsburg, PA. [UTM Coordinates: 480.6E / 4547.2N, East Stroudsburg quadrangle.]
These sandstones, which prominently display large-scale cross strata, are probably equivalent to the Ashokan Flags of New York State. The cross strata imply that these are fluvial deposits. As such, they are the lowest of the thick Devonian strata that are mostly of nonmarine origin. The siltstones below are the youngest marine Devonian hereabouts.
STOP 8 - Cuts on Cherry Valley Road, near boundary between Hamilton Township (Monroe Co.) and Stroud Township (Northampton Co.), S of Stroudsburg, PA. [UTM Coordinates: 480.3E / 4533.5N, Stroudsburg quadrangle.]
These rocks are approximately equivalent to the New York "Manlius" Limestone. The polygons here have long been pointed out to geology students as examples of polygons formed by superimposed mudcracks. Yet, the dissolution residues along the sides of the polygons show that polygons have resulted from dissolution cleavage and are comparable to stylolites, the other geologic feature formed as a result of high pore pressure dissolution.
STOP 9 - Resort Point Overlook, Stroudsburg, PA. [UTM Coordinates: 488.2E / 4536.2N, Stroudsburg quadrangle.]
Get out of vans, fast! Scenic view. General discussion. The rocks in the large cuts directly opposite are the same rocks as at STOP 5. They show steep cleavage, refraction of cleavage, and thrust faults. We will not try to examine them here with a large group.
STOP 10 - Cuts on PA 611, Point of Gap Overlook S of Stroudsburg, PA. [UTM Coordinates: 489.8E / 4535.9N, Portland quadrangle.]
The rocks in the cut belong to the Lower Silurian Tuscarora Formation (equivalent of Shawangunk in New York). The strike is NE and the dip NW. Massive- to cross-stratified sandstone in layers 1 to 2 m thick are interbedded with slaty cleaved siltstones 5 cm to 0.5 m thick. The bases of some sandstones are channel fills; some beds pinch out; quartz pebbles are present in some beds. The talus slope on hillside on NE side of Delaware River covers the Martinsburg Formation.
STOP 11 - Cuts on complex cloverleaf at junction of NJ 94, I-80, and US Route 46, Town of Columbia, NJ. [UTM Coordinates: 492.5E / 4530.5N, Portland quadrangle.]
The complex of cuts in this cloverleaf complex expose Sauk Sequence carbonates (the Upper Cambrian Allentown Formation)in the Ackerman anticline that Drake (1978) and Drake and Lyttle (1980) infer form a part of the Paulins Kill window beneath the Portland thrust. We have not made a careful study of the contacts, but from the general relationships merely raise the question of whether or not this belt of carbonate rocks could be a klippe of a thrust sheet of older carbonates thrust above younger slates that possibly has been faulted down into the slates, as at Hope, rather than a folded overthrust of younger slates over older carbonates.
STOP 12 - Cuts on US Route 46, Manunka Chunk, New Jersey (slates of Bushkill Member of Martinsburg Formation). [UTM Coordinates: 495.2E / 4522.0N, Belvidere quadrangle.]
Before you is a marvelous example of slaty cleavage that is not parallel to the bedding in the dark-colored slates of the Bushkill Member of the Martinsburg Formation. This is the locality that John C. Maxwell (1962) made famous in his classic paper on the origin of slaty cleavage in the Delaware Water Gap area. Maxwell notes that the slaty cleavage in the water gap area is restricted to the Ordovician Martinsburg slates and antedates the overlying Lower Silurian to Devonian clastic and carbonate strata that rest unconformably above the Martinsburg. Thus, a Taconian (Ordovician) age for the slaty cleavage has been well documented in northwestern New Jersey.
As noted by Maxwell, the slaty cleavage in the Martinsburg is axial planar to northwest-vergent folds of bedding and is characterized by a flow foliation consisting of oriented illite (mica) and quartz. At this locality, the prominent slaty cleavage strikes NE and dips SE. The bedding trends NE and is clearly defined by a deformed, subvertical calcareous siltstone layer (15 to 20 cm thick) and adjacent color bands in the slate produced by subtle compositional variations. Mechanical differences between the slate and calcareous siltstone have resulted in the relative brittle offset of the siltstone, local transposition of bedding into parallelism with cleavage, and development of quartz-calcite veining.
Rumor has it that a few geologists have interpreted this classic exposure the result of "intrusion" of a clastic dike into the dark muds of the Martinsburg followed by flattening and deformation of the dike into a sinuous form. Implied in this interpretation is the notion that the true bedding and the cleavage are parallel and that the clastic dike cut across the original bedding. In trying to trace down the source of this clastic-dike rumor we have found the following passage in the second edition of L. U. DeSitter's widely used textbook on structural geology (1964, p. 276): "It [meaning the roadcut] shows a slate with almost horizontal cleavage crossed vertically by a folded sandstone." We suspect that Maxwell showed DeSitter the roadcut and that DeSitter understood the relationships. His use of the verb crossed in the statement quoted above may have confused a few geologists into thinking that that the calcareous siltstone layer is indeed a clastic dike but we, of course, disagree strongly with the clastic-dike interpretation. Rather, we agree with Maxwell that the supposed "dike" is normal compositional layering (stratification) and that the subhorizontal deformational fabric is related to the development of a pre-Silurian Taconian slaty cleavage.
Guidebook 18. Beach at Robert Moses State Park, Long Island, 103 p.
Saturday, 26 September 1992
OBJECTIVES:
1) To discuss the topics: "What is a beach?" and what are smaller "Sons of Beaches".
2) To compare a narrow beach subject to chronic erosion with a wide beach subject to deposition.
3) To become familiar with the three sediment populations found at RMSP:
a. well-sorted white medium sand;
b. well-sorted dark-colored, esp. dark reddish, medium sand; and,
c. poorly sorted coarse brown sand, gravel, and shell debris.
4) To recognize the various parts of an ocean beach, including the shore-parallel ridges of sand (are they dunes?), berm, beach face (and/or beach scarp), and the three morphodynamic zones of an ocean beach: supratidal, intertidal, and subtidal.
5) To study the relationship between deposition of new layers of sediment and sediment surfaces, including both small-scale bed forms and large-scale depositional "slopes;" and to recognize plane-, parallel-, and cross strata.
6) The understand the general geologic relationships of Long Island and the occurrence of ground water in various geologic units.
7) To be duly impressed by the evidence for the rapid westward growth of the west end of Fire Island as a result of inlet migration (average rate of 1 meter per week in the interval 1834-1940).
8) To realize how the effects of the operation of the geologic cycle through time create a geologic record of sediments and of sedimentary rock.
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
As this field trip was to a single locality, detailed descriptions are in the guidebook. [UTM grid coordinates of the beach located just beyond the picnic pavilion at Parking Field 3, the starting point of our westward traverse to the jetty, is 646.85E / 4498.05N, Bay Shore West quadrangle.]
Guidebook 19. Geology of the Newark Basin, Delaware River Valley, New Jersey, 90 p.
Saturday, 19 June 1993
OBJECTIVES:
1) Study type sections of Stockton and Lockatong formations in the south-central part of the Newark Basin.
2) Observe facies changes between basin-marginal rudites and finer-textured strata away from the basin margin.
3) Examine evidence for lake-level control on sediments in the Lockatong Formation.
4) Study the effects of mid-Jurassic deformation, notably the evidence that significant strike-slip faults are present, and,
5) Try to avoid eating the hot dogs at Stop 5.
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
STOP 1 - Dolerite quarry, Belle Mountain. [UTM Coordinates: 506.4E / 4464.6N, Lambertville quadrangle.]
The mafic igneous rock exposed here is a deeply iron-stained diabase (medium-textured gabbro) with significant K-feldspar in the form of orthoclase and/or anorthoclase based on our hammer and hand-lens investigation. Because of their tan color, the feldspars are obvious in weathered specimens. Petrologists call such rocks granophyres which are known to be present in small amounts at all levels in mafic sills and can constitute up to 25% volume in thick sills.
Cutting through the diabase are prominent fractures spaced roughly 10 cm apart. We suspect they are not columnar cooling joints but structural fabrics related to faulting. These fractures cut an older set of healed microfaults characterized by roughly 1-mm thick, dark-green- to black, chloritized gouge zones oriented NE with steep SE dips. These older, fault-related gouge zones exhibit subhorizontal slickensides with a gentle pitch. Locally, these surfaces have been overprinted by steep, dip-slip slickensides indicating that the tectonic displacement changed from strike slip to dip slip. We will observe this same relationship again at Stop 2.
STOP 2 - Superposed faults in deformed Lockatong Formation (Lower Jurassic part of Newark Supergroup) along cuts for new US Route 202. [UTM Coordinates starting at 504.7E / 4470.0N, Stockton quadrangle.]
According to some geologists, the rocks filling the Newark basin have been subjected only to regional tension. Accordingly, deformation should consist of simple block faults. We plan to visit several localities along these US Route 202 cuts, where the road cuts across a significant fault zone that affects gently dipping Newark strata.
The first thing we shall examine is a fault that has made a gouge zone about 0.5 m thick. Present within the fault zone are beautifully transluscent, greenish fault-mirror slickensides (called "slickentite" by California geologists) with local white zeolite minerals on the faces. This fault strikes NE and dips NW. Steep dip-slip slickensides locally overprint these chloritized subhorizontal slickensides and are related to small faults varying in orientation. Large-scale "corrugations" or undulations in the rock faces plunge gently into the SE. We infer that these are related to the older, strike-slip teconic episode. Farther down the ramp, low-dipping strata are evident.
STOP 3 - Conglomerate and interbedded sandstone in Solebury Member of Stockton Formation exposed in woods adjacent to the Stockton Borough School. [UTM Coordinates: 502.1E / 4472.5N, Stockton quadrangle.]
Essentially monomict quartz-pebble rudites with intercalated coarse, cross-bedded sandstones are exposed at this locality. Marlene Leeb, Chief School Administrator, who was nice enough to permit access to this exposure, has asked us not to remove samples. Rounded, ellipsoidal pebbles of quartz (quartzite?) are up to 8 cm in long dimension in a matrix-supported conglomerate. Note the lack of carbonate clasts (compared with Stop 6, later today). The pebbles are aligned with their widest dimension lying flat within the layering of the enclosing sands with bedding. Large-scale cross beds are evident in the sandy matrix. Measurements of cross beds suggest a component of flow in the SW direction. Elsewhere channels at the base of the rudites are oriented NW.
STOP 4 - Lockatong Formation. [UTM Coordinates: 495.0E / 4475.8N, Lumberville quadrangle.]
We will try to follow what Van Houten described from his Stop 2, 1969 GSA trip, p. 33, mile 22.9 to 23.1:
Items:
1. Vague cyclic pattern of major ledges of albite-biotite hornfels; Nepheline occurs about 100 ft below sill.
2. Lower contact of chilled border of diabase with sheared, weathered Lockatong pelitic hornfels.
3. Coarse-grained diabase, extensively fractured. Joint minerals include calcite, epidote, prehnite, tourmaline and amphibole. Conspicuous lineations expressed in concentration of joint minerals have no apparent relationship to compositional layering in the diabase.
4. Complex upper contact (enlargement), essentually undisturbed along curved contact; faulted and sheared diabase and hornfels on north side. Nepheline, cancrinite, pyroxene and amphibole presesnt in both blocks of Locaktong albite-biotite hornfels.
5. Relationship of 70-foot sequence from fault to outcrops north of creek is obscure. Isolated exposures and sheared zones at roadside topographically below position of northern lobe of diabase.
6. O marks beginning of undisturbed, continuous sequence of Lockatong Formation, estimated to be about 70 feet above the faulted contact with diabase. Nepheline absent above the 11-foot mark (81 ft above diabase); cancrinite and albite diminish and analcime and thomsonite increase out to the 370-foot mark. Analcime and albite present above this level. Analcime and thomsonite also occur as joint minerals.
STOP 5 - Passaic Formation (formerly Brunswick Redbeds - only the name has changed, not the color!) [UTM Coordinates: 494.0E / 4488.5N, Frenchtown quadrangle.]
Here, next to the dilapidated hot dog van, note red siltstones, very fine sandstones, and shale. The bedding surfaces are very gently dipping and display mudcracks, raindrop-impact pits, tiny ripples, and possible dinosaur tracks. Joints are spaced about a meter apart. Grab a hot dog, if you dare!
STOP 6 - Basin-marginal rudites in Passaic Formation, S end of Gravel Hill. [UTM Coordinates: 488.5 E / 4491.5N, Riegelsville quadrangle.]
Those of you who have been to Oakland, New Jersey, on our Palisades Newark Basin trip, will find this exposure looks somewhat familiar. Discrete layers containing rounded boulders of Paleozoic rocks, most of which are quartzites, but with the light-colored ones carbonates, are interbedded with layers composed of sand-size sediment. In some of the fine layers are scattered rounded boulders. According to Bradford Willard (1956), the limestones are fossiliferous Decker Limestone (Silurian?) and the quartzites are from the Green Pond Formation (Lower Silurian). This location is about 1 mile SE of the basin-marginal fault.
Guidebook 20. Geology of Southern Central Park, New York, 143 p.
Sunday, 26 September 1993
OBJECTIVES:
1) To show you some of the stratigraphic- and structural evidence upon which CM has proposed his far-reaching re-interpretation of the "Manhattan Schist."
2) To study features eroded on the bedrock by glaciers and try to convince participants that the dominant direction of glacier flow that can be reconstructed in Central Park is from NW to SE (from across the Hudson Valley) rather than from NNE to SSW (the direction of the most-recent glacier; which was down the Hudson Valley).
3) To become aware of all the improvements Robert Moses made to Central Park in 1934 and especially to follow Moses' first principle, namely that a visit to the Park should be the occasion for having a good time.
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
STOP 1 - SE of Zoo work shed, Hartland formation and an obscene roche moutonée. [UTM Coordinates: 586.75E / 4513.10N, Central Park quadrangle.]
The exposure consists of gray- and locally brown-weathering muscovite-biotite schist and thin interlayers of biotite granofels, rocks typical of the Hartland Formation (C-Oh) in New York City. The S2 foliation consists of parallel thin laminae and local syntectonic granitoid veins, predominates at this exposure. Abundant pegmatite veins (some with large books of muscovite) and veinlets create a nubby weathering appearance, but should not be confused with the aluminosilicate-induced nubby weathering of the C-Om unit of the Manhattan Schist.
Evidence for SE-directed glacial flow is obvious in the glacially sculpted exposure in the form of large- and small grooves at the south end of the exposure. A fake roche moutonée is the product of drill-and-blast work of Obscene age (the period of geologic time stratigraphically above the Holocene) on the eastern edge of the exposure. Luckily, our glacial hypotheses are not drilled full of holes as the glacial grooves are real.
STOP 2 - E of walkway just N of 65th Street Transverse Road; mylonitic Hartland formation cut by glacial grooves. [UTM Coordinates: 586.85E / 4513.32N, Central Park quadrangle.]
The exposures of Hartland here consist of slabby, gray-weathering vitreous quartzite, granofels, minor schist and amphibolite with a laminated fabric developed parallel to a composite S2 foliation. S2, subparallel S1 and bedding (S0), are strongly transposed because of the effects of F3 Z-folds and associated lineations plunging SW. Vertical healed joints cut the exposures at a high angle and show positive relief producing a reticulate pattern with the dominant lithologic layering and subparallel metamorphic fabrics. All of the scattered outcrops show the effects of glacial rounding and -polish.
STOP 3 - E of walkway near "X" crossing of paths S of "The Dene;" mylonitic Hartland formation and glacial grooves. [UTM Coordinates: 586.90E / 4513.40N, Central Park quadrangle.]
Similar to the last exposure (still in view toward the S), here the Hartland possesses a pronounced mylonitic fabric suggesting that we are approaching Cameron's Line. The composite S2 + S3 foliation is transposed by F3 folding and has been intruded by numerous foliated lit-par-lit granitoids. In fact, two generations of granitoids cut the bedrock: 1) an older foliated generation, as mentioned above, and 2) a younger sinuous granitoid that cuts across the metamorphic layers. Glacial grooves are here products of a glacier that flowed SE.
STOP 4 - Outcrop W of "The Dene"; two sets of cross-cutting glacial features on polydeformed Hartland formation. [UTM Coordinates: 586.83E / 4513.40N, Central Park quadrangle.]
This large polished exposure contains rocks similar to the last three stops and shows the effects of superposed F2 and F3 folds. The composite S2 + S3 foliation is oriented NE and is vertical or dips steeply SE. We will examine the rocks for structural features on the trip day and concentrate here on glacial features.
Obscured by post-glacial weathering on the E end of the exposure a partial pothole greets the observant student of geology. Nearby, glacial grooves are oriented NW again, supporting our earlier observations, indicating a SE-directed glacial ice-flow direction. At the NE end of the exposure a glacial treat awaits our eyes. Here, a subdued roche-moutonée structure oriented N37°E is cut by N36°W-trending glacial grooves. Thus, one of our older glacial advances has left its indelible mark on the bedrock.
STOP 5 - By "Platform" (outcrop E of "The Dene" and N of playground); beginning of the Cameron's Line thrust zone, glacial features, and outdoorsmen. [UTM Coordinates: 586.92E / 4513.43N, Central Park quadrangle.]
At this exposure, we will try to convince you that deep-seated mylonitic faults such as Cameron's Line are not unique single surfaces of dislocation but rather zones of imbricated lithologies (termed mélange) bearing mylonitic fabrics. Here, we see comingled gray-weathering quartzite- and granofels-bearing schist of the Hartland (C-Oh) and rusty-weathering schist and gneiss of the Manhattan (C-Om) formations. At the north end of the large exposure, where rusty-weathering C-Om predominates, C-Oh granofels layers, 30 to 50 cm thick, can be seen "floating" in a schistose matrix. Such intermixing is perhaps the product of shearing and imbrication related to the formation of mélange within the Cameron's Line thrust zone. The folds- and fabrics related to the F2- and older folds are strongly reoriented by F3 folds. Tight- to isoclinal F3 folds gently plunge SW with axial surfaces oriented NE. Beautiful examples of F2 X F3 interference patterns are found in this exposure - be on the lookout.
Glacial plucking (excuse the expression!) has here been facilitated by joints. A broad roche-moutonée structure oriented NE occurs at the north end of the exposure and glacial grooves and troughs are found elsewhere oriented NW. Based on what we saw at Stop 4, we suspect that the NW-trending grooves are younger than the roche-moutonée structure. No evidence was found at this exposure.
STOP 6 - At USGS bench mark S of The Pond; typical Hartland Formation away from the Cameron's Line thrust zone. [UTM Coordinates: 586.58E / 4512.93N, Central Park quadrangle.]
Rocks of the Hartland Formation here consist of their typical gray-weathering, highly muscovitic schist and massive, structureless granofels in an exposure at the SE corner of "The Pond", across from the Plaza Hotel. The granofels layers are quite numerous; their thickness varies from 3 cm to 50 cm and they are separated by schistose layers, 3 cm to 4 cm thick, that are exceedingly rich in muscovite (only about 5% biotite). Muscovite-rich pegmatites locally have been intruded parallel to the S3 foliation. Near their contacts with the metamorphic strata one can find a veritable "library" of muscovite "books." Glacial grooves indicate SE-directed glacial-ice flow.
STOP 7 - W of the Pond, opposite Avenue of the Americas access to Park; folded and glacially polished Hartland formation. [UTM Coordinates: 586.39E / 4513.05N, Central Park quadrangle.]
Muscovite schist and interlayered granofels of the Hartland are cut by open warps of the composite S2 + S3 foliation. These folds, which must postdate the F3 folds, plunge southward with NE-trending axial surfaces. A minor shear zone in the center of the exposure cuts through a 10-cm-thick layer of amphibolite and an F2 reclined fold refolded by F3 occurs on the south end of the exposure.
Glacial grooves are here oriented NW and a subdued roche moutonée structure is oriented NE. On our pre-trip visit, we were not able to establish any cross-cutting relationships. We observed SSW-oriented chattermarks on the northward-sloping surface of the roche moutonée.
STOP 8 - On S side of West Drive, near SW boundary of Park; Hartland rocks sheared along F3 limbs and glacial features. [UTM Coordinates: 586.32E / 4513.04N, Central Park quadrangle.]
The effects of shearing along the limbs of F3 folds here produce a penetrative foliation in highly muscovitic rocks of the Hartland Formation. The effects of rounding and smoothing of the bedrock surface here are quite obvious as are glacial grooves.
STOP 9 - On N side of West Drive near bridge over walkway from 7th Avenue; Hartland rocks showing bedding. [UTM Coordinates: 586.27E / 4513.20N, Central Park quadrangle.]
Pronounced interbedding of granofels and muscovite schist here typify the Hartland formation. We are near the vicinity of an F3 antiformal hinge area (CM's 7th Avenue Antiform). The F2 folds here show Z-fold symmetry indicating we are on the eastern side of the south-plunging antiform.
STOP 10 - Umpire Rock; Hartland rocks "safe at home". [UTM Coordinates: 586.27E / 4513.37N, Central Park quadrangle.]
Umpire Rock is the most-spectacular natural exposure in the southern part of Central Park. Here, rocks of the Hartland Formation show the superposed effects of F2 and F3 folds, abundant syn- and post-tectonic pegmatite intrusives, brittle faults, and numerous glacial features. The rocks consist of interlayered muscovite schist and granofels that have been cut by numerous granitoids. Beautiful interference patterns result from the superposition of F2 and F3 folds. Late-stage open warps with southward plunges are locally developed (similar to Stop 7 but with kinder, gentler plunges as first described by former President George Bush). At least two NE-trending brittle faults cut the exposure; the one on the eastern edge of the outcrop shows a crumbly gouge zone roughly 3 m thick.
Perhaps the most-obvious geologic features here are of glacial origin. At the NW edge of the exposure, glacial meltwaters have modified spectacular glacial troughs oriented NW. These troughs are related to the overall SE-directed roche-moutonée shape of the exposure with its steep dropoff toward the playground area. A potpourri of glacial erratics can be found on this outcrop. On our brief pre-trip visit, we identified erratics of Palisades diabase and hornfelsic Lockatong Formation from the Newark basin W of the Hudson River, Hartland Formation, granite, and diorite. Of additional structural interest, the north-facing wall offers a rare glimpse at the shallow dip of the S2 foliation and a sub-parallel granitoid sill, all folded by F3? or younger open warps.
STOP 11 - E side of walk E of Heckshcer Playground; pegmatite erratic on glacially polished Hartland rocks. [UTM Coordinates: 586.39E / 4513.38N, Central Park quadrangle.]
The most-obvious feature of this stop is the 2m-high K-feldspar megacrystic pegmatite erratic. The erratic rests on rocks of the Hartland that have been scored by NW glacial grooves. F3 S-folds are locally found in the exposure.
STOP 12 - E of junction of walks N of Stop 11; mildly mylonitic Hartland rocks. [UTM Coordinates: 586.39E / 4513.39N, Central Park quadrangle.]
The Hartland Formation here shows some evidence for lithologic mixing; rocks of the "middle unit of the Manhattan formation," are present in the form of inclusions consisting of wisps- and shreds of aluminosilicate-bearing, rusty- to maroon-weathering schist. The outlines of the wisps and shreds are probably masked by shearing along S2 and S3 (a convenient circumstance that requires little leg-to-leg hopping by CM). F3 folds are not hard to spot with their typical southward plunges and steep NE-trending axial surfaces.
STOP 13 - By the Carousel; the "middle unit" of the Manhattan Formation. [UTM Coordinates: 586.45E / 4513.43N, Central Park quadrangle.]
The exposure of rocks immediately west of The Carousel show the rusty- to maroon-weathering typical of CM's "middle unit of the Manhattan Formation" (Unit C-Om). Layers- and lenses of kyanite+sillimanite+magnetite weather in positive relief and outline the S2 foliation which is largely mylonitic. CM maps this area as the beginning of the Cameron's Line thrust zone and links these exposures to those found at our earlier Stop 5.
From here, after a brief interlude on The Carousel, we will begin a freeform mapping exercise to regions of the park north of Stop 13, hoping to further support our visions of the structural- and glacial history of the park. We plan to end somewhere near the American Museum of Natural History and then walk back to the Academy.
Guidebook 21. Geology of the Northeastern Newark Basin, New York and New Jersey, 114 p.
Sunday, 14 November 1993
OBJECTIVES:
1) Evaluate the "shelving-basin" interpretation and the "transverse anticline" viewpoint.
2) Study an example of the Lockatong Formation that all previous workers evidently have overlooked.
3) Evaluate the significance of the curvature of the Palisades sheet in Rockland County, NY: is it a folded intrusive sheet or a steeply cross-cutting dike?
4) Briefly examine the pre-Newark rocks and the basal conglomeratic Newark strata near Stony Point State Park.
5) Look at the nearly horizontal strata in the Ladentown-Wesley Chapel area and try to figure out if they are anomalous with respect to the rest of the Newark strata in Rockland County, NY.
6) Compare weathered- with fresh rock in the Ramapo fault zone and record the orientations of the numerous fracture surfaces.
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
STOP 1 - Palisades igneous rock, Stockton and Lockatong formations of Newark Supergroup. Center of old quarry - [UTM Coordinates: 591.6E / 4554.8N.] Sandstone exposures along Hudson River at Upper Nyack - [UTM Coordinates: 591.80E / 4554.15N, Haverstraw quadrangle.]
The first thing visible is the massive igneous rock and its sets of regular intersecting joints. The joint surfaces are perpendicular to the surface of cooling. The color of the fresh igneous rock is bluish gray, but on most visible surfaces (weathered) is yellowish brown. This brownish color results from the presence of the iron-oxide mineral limonite, which coats most joint faces.
On the E side of the Hudson River, opposite us, one can see several noteworthy features. At left is Croton Point Park; the S end of the wooded ridge at water's edge is Teller's Point at Croton Point Park. To the right of Croton Point is a complex of large buildings, Sing Sing, the notorious destination of prisoners sent "up the river" (from New York City), which is in the Town of Ossining. The wide expanse of wooded countryside between Ossining and Tarrytown, near the Tappan Zee Bridge, is the Rockefeller family preserve, much of which has become Rockefeller State Park.
We plan to study sedimentology of Stockton sandstones and evidence for possible fault contact with Palisades sheet and to view a long-overlooked exposure of the Lockatong Formation. The most-persistent unit along the trail is a reddish-brown siltstone, 2 to 2.5 m thick, which is overlain- and underlain by various sandstones. At the N end of the exposure, which we shall see first, only the sandstones are present. JES infers that the strata here exemplify an upward-fining succession of the kind formed by the migration of an ancient point bar deposited on the inside of meander bends of a river meandering across a flat floodplain.
STOP 2 - Non-marine lacustrine facies in lower part of Newark Supergroup (Stockton? or Passaic? Formation), Lowland Park, Stony Point. [UTM Coordinates: 585.05E / 4564.2N, Haverstraw quadrangle.]
The objective of this stop is to examine at close range the strata exposed on the S bank of the creek and beneath the bridge for Route 9 (overhead). This can best be done by driving the vans down to the area of the picnic tables and then crossing the creek. Whether we do that or not will depend on the amount of rain that has fallen lately.
Reddish-brown siltstones and associated gray carbonate rocks about 1250 ft. above base of Newark succession and 3 miles SE of Ramapo fault. Lithologically, these strata are ancient mudstones and nonmarine limestones that were deposited in the offshore parts of a lake. We assign them to the Brunswick (on the presumption that we are above the level of the Lockatong Formation; if they are below the Lockatong, then they belong in the Stockton). The greenish nodules are composed of calcite; they are caliche--the products of upward movement- and evaporation at the surface of water in the ancient soil in a semi-arid climate zone. The NW trend of the bedding can be measured on several of the limestone beds.
STOP 3 - Newark Conglomerate, pre-Newark metamorphic- and igneous rocks, and west edge of Cortlandt intrusives at Stony Point State Park, Stony Point, NY. [UTM Coordinates: 585.62E / 4565.8N, Haverstraw quadrangle.]
At this stop we make three small traverses at Stony Point State Park; one south of along the railroad cut to see conglomerate of the Newark Basin, one along the railroad cut that exposes intrusive rocks of the Stony Point-Cortlandt Complex and, a walk through the famous Stony Point battleground.
STOP 4 - Vesicular- and amygdaloidal basalt of the Ladentown Basalt of Kummel (1900) on Limekiln Road. [UTM Coordinates: 576.3E / 4557.1N, Theills quadrangle.]
When construction was underway for these houses, pillowed basalt was exposed at the top of the knoll. We'll discuss the geologic relationships inferred by Ratcliffe (1988) in connection with the Spook Rock core site.
STOP 5 - Near-horizontal sedimentary strata near Ramapo fault: rudites and well-laminated to cross-stratified sandstone. [UTM Coordinates: 575.25E / 4555.9N, Theills quadrangle.]
The conventional wisdom about these coarse basin-marginal rudites is that they were deposited on fans at the toe of the steep fault scarp. Indeed, these rudites are commonly designated as "fanglomerates." We have deliberately avoided using the term "fanglomerate," because the sedimentary characteristics of these strata do not match those of subaerial fans.
The key points we discuss: conglomerate at far SW end along US Route 202; well-bedded and horizontally laminated sandstones near the intersection of US Route 202 and Spook Rock Road; and along Spook Rock Road, cross strata showing water movement from NE to SW, nearly at right angles to the direction from that traveled by the boulders from the elevated Ramapo Mountains block into the subsiding Newark basin.
The stratigraphic position of these strata is not known. Because we are adjacent to the Ramapo fault, a common opinion is that these strata should be from high in the Newark Supergroup, say from the Boonton Formation. Some insight into the subject may come from a final decision about the relationship between the Ladentown Basalt and the Watchung extrusives. If the Ladentown equals Orange Mountain (First Watchung), and these strata underlie the Ladentown Basalt, then they could be from the top of the Passaic Formation. Stay tuned.
STOP 6 - Proterozoic rocks in Ramapo fault at Pavilion Road and newly excavated exposure on I-87. [UTM Coordinates: 571.6E / 4552.3N, Ramsey quadrangle.]
This area allows an interesting view of the rocks in the Ramapo fault zone in both weathered- and fresh exposure. We prefer weathered rock for the analysis of fault motion and fresh rock for samples of cataclasite. As such let's begin at the weathered zone and examine the steeply dipping fault surface. CM has brought a number of advanced classes from Hofstra University to this locality. The slickensides vary from large-scale corrugations to minor streaks and, given proper lighting conditions, as you step away from the exposure, are very obvious.
The asymmetry of steps on the slickensides indicate that during the latest motion, hanging wall (the missing block) moved up the fault surface away from the SW. Hidden beneath the obvious slickensided fault surface are traces of subhorizontal slickensides that suggest an episode of horizontally directed motion antedated the more-obvious SW-raking slickensides. Thus, the movement history along the Ramapo fault has been complex. We would define the last (most-obvious) motion sense on the Ramapo fault as being oblique slip with composite left-lateral strike-slip and reverse dip-slip movement.
After we have walked over to the fresh cuts on the shoulder of I-87, note the variation in lithology of the Proterozoic orthogneisses (meaning metamorphosed plutonic rocks) that include granitoid-, dioritic-, and gabbroic rocks. The thin seams of blackish material cutting through the rocks are cataclasite (finely granulated pre-existing fault rocks and new minerals produced by fault motions in the brittle zone (upper 10 km) of the crust). Slickensides are common and where faults cut through the more-mafic lithologies some serpentine-group minerals have developed. Numerous fault orientations are measureable here and as an On-The-Rocks exercise we will measure as many as we can and see if the results make sense with what we just observed at the weathered area near the vans. To most of you, the contrast between fresh- and weathered rock may be astounding as they look like totally different rocks.
Guidebook 22. Geology of New Haven, Connecticut and Vicinity, 113 p.
Saturday, 27 April 1996
OBJECTIVES:
1) To study the basal contact of the New Haven Arkose and the kinds of metamorphic rocks forming the floor of the Hartford Basin.
2) To examine paleosol caliche in the New Haven Arkose and study the contact-metamorphic effects on the caliche along the walls of mafic dikes.
3) To examine pillows--the products of the extrusion of hot lava under a cover of water.
4) To examine the characteristics of the Newark sedimentary strata and to notice the contrast between sediments deposited well away from the basin-marginal fault along the SE basin margin and those deposited close to this basin-marginal fault.
5) To study the composition of boulders in the basin-marginal rudites (general name for any coarse sediment composed chiefly of gravel-size debris, i. e., coarser than 2 mm).
6) To study the evidence for postdepositional faults and the relationship between some of these faults and gaps in Saltonstall Ridge.
7) To examine the evidence for the presence of the Talcott Formation along the basin-marginal fault and to observe a distinctive volcanic breccia.
8) To visit the Eastern Uplands and examine the pink granitic rocks at Stony Creek and the light gray granitic rocks at Lighthouse Point.
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
STOP 1 - Base of Newark Supergroup in contact with Milford Chlorite Schist, Amity Shopping Center. [UTM Coordinates: 668.55E / 4577.83N, New Haven quadrangle.]
You're on your own.
STOP 2 - New Haven Arkose and caliche carbonate (green) cut on Wilbur Cross Parkway at Interchange 60. [UTM Coordinates: 673.81E / 4581.02N, New Haven quadrangle.]
Krynine (1950) measured a section here when the cut on the Parkway was fresh. In 1958, JES spotted the green calcareous nodules and interpreted them as probable caliche. Hubert (1977, 1978) has published the results of his careful petrographic examination of the caliche/calcrete. We will forego an opportunity to see spectacular exposure of caliche carbonates, etc., in the New Haven Arkose on Mt. Carmel Connector Road. Pedogenic carbonates are important indicators of a former semiarid climate.
STOP 3 - New Haven Arkose in contact with N wall of Mill Rock dike. [UTM Coordinates: 674.35E / 4578.07N, New Haven quadrangle.]
You're on your own.
STOP 4 - Top of East Rock. On a clear day, the view from up here is spectacular. [UTM Coordinates: 675.19E / 4577.09N, New Haven quadrangle.]
You're on your own.
STOP 5 - New Haven Arkose in contact with one of the Foxon dikes. [UTM Coordinates: 678.07E / 4576.29N, Branford quadrangle.]
You're on your own.
STOP 6 - Pillowed Talcott basalt, hillside E of what formerly was the Weeping Willows Restaurant, E of Laurel Street, East Haven. [UTM Coordinates: 678.11E / 4574.60N, Branford quadrangle.]
At this locality, the distance from the basin-marginal fault is 2 miles. (3.2 km). The strata strike NE and dip gently SE on a limb of the Saltonstall syncline. The part of the Talcott exposed here is the base of the pillowed- and brecciated member. The correct classification of the underlying pebbly coarse sandstone is still a puzzle. The answer depends on whether other Talcott flow units are present below the sandstone. If so, then these strata belong in the middle sedimentary member. If not, then these strata presumably belong at the top of the New Haven Arkose. The effect of a Pleistocene glacier on the pebbly sandstone is also well displayed here. This is a good spot for comparing the scratches and striae created by a glacier with the marks made by the large power shovel used in excavating the till.
STOP 7A - Cut on N side of US Route 1, East Haven, at junction with western end of loop made by CT Route 142. This is the southern of two large gaps in Saltonstall Ridge. [UTM Coordinates: 679.10E / 4571.51N, Branford quadrangle.]
A tape-and-compass traverse of this cut in the Shuttle Meadow indicates that about 190 ft of strata are present; there are numerous small faults, but nevertheless the succession seems to be fairly straightforward. The lower 80 ft are interbedded sandstone and siltstone with a few pebbly layers. Two prominent conglomerates are present: a unit 20 ft thick at 80 ft above the base of the exposure, and a unit 18 ft thick at 130 ft above base of the exposure. The sandstones at the top of the exposure may correlate with those exposed north of the New Haven Railway tracks in the next gap to the north, but this is not certain.
STOP 7B - Cuts on AMTRAK Railway and Connecticut Turnpike, East Haven, in an artificial gap west of Saltonstall Lake, the northernmost of the two large gaps in Saltonstall Ridge. [UTM Coordinates: 679.06E / 4571.95N, Branford quadrangle.]
To begin with, the Shuttle Meadow strata in the railway cut consist largely of sandstone and siltstone in beds 1 to 3 ft thick; a tape-and-compass traverse indicates 174 feet of strata are present from the bridge abutment on the north side of the tracks to the western limit of the exposure. The contact between Shuttle Meadow sandstone and Holyoke basalt was exposed during construction of the bridge in the middle of the nineteenth century; the stones of the bridge pier conceal it now.
The top of the Holyoke is present just east of this bridge, on both the N side and S side of the tracks. The horizontal distance between the base of the Holyoke and the top of the sheet is 110 ft; assuming a dip of 45° this indicates a vertical component of slip equal to about 700 ft. About 1 ft above the base of the overlying East Berlin Formation is a limestone bed 1 ft thick; it is visible in the cut on the south side of the railway and east of the bridge.
STOP 8 - Roadcuts in Branford, along Connecticut Turnpike W of Todds (Cherry) Hill Road overpass and at Interchange 54. [UTM Coordinates: 681.92E / 4572.54N, Branford quadrangle.]
From the bridge carrying Todds Hill Road over the Connecticut Turnpike three rock faces are visible. These three rock faces expose volcanic rocks belonging to a linear belt of extrusive rocks paralleling the basin-marginal fault and extending NNE for 0.95 mi. (1.55 km), from the basin-marginal fault at the intersection of US Routes 1 and 1A, west of Branford Center (16.53 N - 57.84 E) to a point 0.07 mi. (0.1 km) N of the intersection of Todds Hill Road and a short road leading to Brush Plain Road (16.65 N - 57.97 E).
Percival (1842, p. 325) designated this belt as the "Second Posterior Range" (p. 2 of his map). Since the time of W. M. Davis (1898, p. 128; fig. 31) most geologists (exception Rodgers 1985, following Sanders' results) have assigned the volcanic rocks of this belt to the upper extrusive sheet (Hampden Formation of modern terminology). Davis inferred that the volcanic rocks had been dragged upward by movement along several smaller faults paralleling the basin-marginal fault. In the absence of any other compelling evidence to the contrary, this interpretation satisfied the dictates of the rule of simplicity: if there must be a fault, prefer the alternative that requires the least displacement. The Davis cross section of the 1898 report was not drawn to scale; I have tried to re-create it along a profile based on the modern topographic map of the Branford quadrangle (lower part of Figure 31). Davis' geologic map did not show as many faults as he sketched on his cross section.
STOP 9 - Proterozoic Stony Creek Granite at Stony Creek, remobilization rather than classical intrusion? [UTM Coordinates: ~688.25E / 4570.82N, Branford quadrangle.]
You're on your own.
STOP 10 - Lighthouse granite-gneiss, Lighthouse Point Park, New Haven, CT. [UTM Coordinates of BM @ +31': 675.75E / 4568.52, Branford quadrangle.]
You're on your own.
Guidebook 23. Geologic Setting of the Lower Hudson River, New York Harbor, 148 p.
Monday, June 30, 1997
During a dinner cruise "up the Hudson River" from the mouth of the East River to the George Washington Bridge, observant passengers with excellent night vision can see shorelines composed of four of the major components of New York City's geologic record. In order of increasing ages, these are: (1) Pleistocene glacial sediments produced by as many as five separate glacial advances into the New York City area (700,000 to 10,000 years old); (2) the coastal plain (65 to 15 million years old); (3) Newark basin-filling strata and the Palisades intrusive sheet of igneous rock (220 to 170 million years old); and (4) "stumps" of the central part of the much-eroded Appalachian Mountains, a complex of metamorphic rocks deformed several times during plate convergence at a former continental margin (materials 450 to 1350 million years old deformed at 1100, 440, 365, and possibly also at 260 million years ago).
Despite the fact that this cruise does not include any stops ashore to look at rocks, nevertheless, the view of the shoreline from out in the water provides interested participants with the opportunity to observe several large-scale morphologic features that are surface expressions of the four major components of the geologic record of the New York City region. We plan to point out many of the large-scale geologic features of the New York City region and also to marvel at the numerous engineering structures that have yielded so much information about the subsurface geologic relationships. This guidebook reviews the major components of the local geologic record and relates these to the waterways and shorelines of the cruise route.
Guidebook 24. Geology of the Great Falls, Watchung- and Palisades Ridges, New Jersey, 165 p.
Sunday, 14 September 1997
BRIEF DESCRIPTIONS OF INDIVIDUAL LOCALITIES ("STOPS")
STOP 1 - Palisades Intrusive Sheet, Olivine Zone, and Lockatong Formation at Fort Lee in Palisades Interstate Park, New Jersey branch. [UTM Coordinates: 587.58E / 4522.67N, Central Park quadrangle.]
Exposures along the Palisades Interstate Park access road beneath the George Washington Bridge feature the lower contact of the Palisades intrusive sheet above contact metamorphosed sedimentary rocks of the Lockatong Formation, former lake deposits in the lower part of the Newark Supergroup. The Palisades Intrusive Sheet is one of the world's premier examples of a large sheet of mafic intrusive igneous rock. The tilted- and eroded edge of the mafic rock is expressed in the landscape as the Palisades ridge along the west side of the Hudson River.
Immediately north of the George Washington Bridge is a spectacular exposure of the basal contact of the Palisades intrusive sheet. As originally diagrammed by Olson (1980c), and reexamined by your heroes, JES and CM, the Palisades is in discordant contact relationship with a deformed slab of the Lockatong Formation. Above the Lockatong, at the south end of the xenolith, note the chilled aphanitic (very fine) texture in the Palisades at the contact with the metamorphosed sedimentary rock. Microscopic vesicles occur in the chilled-contact basalt suggesting the presence of pore water in the sediments prior to intrusion. What is more, the sandy sediments are chaotic near the contact and have "intruded" upward into the Palisades as "sedimentary apophyses" and clastic dikes.
Ramping contacts and folds (Merguerian and Sanders, 1995a, b) indicate that paleoflow of the Palisades magma was from SW to NE, not from NW to SE as had been previously thought.
STOP 2 - Pillow basalt of Orange Mountain Formation ("First Watchung Basalt"). East side of McBride Avenue ~0.7 mile NE of intersection of Glover Avenue and McBride Avenue. [UTM Coordinates: 568.1E / 4528.9N, Paterson quadrangle.]
The McBride Avenue exposures are about in the middle of the outcrop belt of the Orange Mountain Formation here. Geologists exploring the sea floor in research submarines been photographed modern pillows forming where lava oozing out of a fissure reacts with the water in such a way that individual pillows are squeezed out, expand, and then separate. The large pillowed part of the Orange Mountain Formation is inferred to have resulted from the extrusion of lava on the bottom of a large lake.
STOP 3 - Lower contact of the Orange Mountain Formation ("First Watchung Basalt") and underlying sedimentary strata of the Passaic Formation. [UTM Coordinates: 569.00E / 4529.45N, Paterson quadrangle.]
In the low cuts in the parking lot one can see the contact between an overlying mafic extrusive igneous rock (Orange Mountain Formation) and a sedimentary rock (top of Passaic Formation). The contact is not a planar surface but displays considerable irregularity. The direction of in which a sheet of ancient lava flowed can be determined from cylindrical (="pipe") vesicles and -amygdales. Typically these are bent over in the direction toward which the lava flowed. According to Manspeizer (1980), pipe amgydales here are bent over toward the NE. (See Figure 38.) This is the opposite to the direction inferred for the paleoslope of the land surface (based on directions of flow of streams that deposited the cross strata). As a result, the lava here onlapped the regional paleoslope.
STOP 4 - The Great Falls of Paterson, Orange Mountain and Passaic formations. [UTM Coordinates: 568.9E / 4529.5N, hillside exposures E and N of stadium: 569.05E / 4529.75N for contact and 569.15E / 4529.85N for cliff face near dog pound, glacial erratic at 568.95E / 4529.65 N, Paterson quadrangle.]
The waterfall here drops about 75 feet (from the 120-ft contour at the lip to about 45 ft below). The Passaic River, flowing northeastward (more or less parallel to the strike of the tilted strata), pours into a fracture that trends N-S. The water tumbles over the lip on the rock forming the W side of the fracture, and then flows southward along the fracture, then makes a U-turn and continues flowing NE. No gorge has formed downstream, as has been eroded, for example, by the upstream retreat of the lip of Niagara Falls. In its flow along a fracture and absence of a gorge, Great Falls are a miniature version of the mighty Victoria Falls on the Zambezi River in southeastern Africa (Zambia/Zimbabwe).
This stop includes a walk northward beyond the falls to examine sandstones of the Passaic Formation and a large glacial erratic.
STOP 5 - Upper, glaciated contact of the Orange Mountain Formation ("First Watchung basalt") at Garrett Mountain Reservation. [UTM Coordinates of old house: 569.50E / 4577.75N, Paterson quadrangle, altitude: 500 feet.]
From the crest of the ridge enjoy the splendid view eastward toward Manhattan (atmospheric conditions permitting). Notice the two clusters of skyscrapers: at the Battery and in midtown Manhattan. This is a function of the depth of bedrock. Where the tall buildings have been built, solid bedrock is close to the surface. In between, where no tall buildings have been built, the depth to bedrock becomes several hundred feet.
Along the trail, look for vesicles in the basalt (we are near the top of a flow unit where vesicles are to be expected) and the glacial features. Present here are glacial grooves trending NE-SW, about parallel to the trend of Garrett Mountain, and a miniature roche moutonée structure.
STOP 6 - Upper- and lower contacts of the Hook Mountain Formation ("Third Watchung Basalt"). Near parking lot for shopping center at junction of Paterson-Hamburg Turnpike and Oakland Road, Pompton, in gap cut through Packanack Mountain by Ramapo River where U. S. 202 makes a 90-degree corner at the S end of Pompton Lake. [UTM Coordinates: 560.7E / 4537.8N, Pompton Plains quadrangle.]
The top of the Hook Mountain Formation is not visible at Stop 6, but on the basis of the amygdaloidal-vesicular structure of the igneous rock exposed at the edge of the parking lot one can infer that the top is not far away. The strata here strike NW and dip SW (a result of being on the SW limb of a transverse anticline whose axis strikes NW-SE). The highland about one mile due W of us is underlain by Proterozoic rocks of the Ramapo block; the Ramapo fault, the basin-marginal fault at the NW edge of the Newark basin, lies along the foot of the steep slope. The Ramapo River flows southwestward along the trace of the Ramapo fault.
The contact at the base of the Hook Mountain Formation is exposed in the cuts along the east side of US Route 202 (if we go there, be careful of the traffic). Notice the sequence of the columnar joints in the basalt and the coarse particles in the basin-marginal rudites of the underlying Towaco Formation.
STOP 7 - Basin-marginal rudites of Feltville Formation [sedimentary strata underlying the Preakness Formation ("Second Watchung basalt")]. Behind Oakland Diner. [UTM Coordinates: 562.2E / 4540.5N, Wanaque quadrangle.]
This locality is situated close to the Ramapo fault (buried beneath sediments of Ramapo River at foot of escarpment) near the NW end of Preakness Mountain, the type locality of the Preakness Formation ("Second Watchung Basalt"). The strike of the strata is NW-SE and the dip is to the SW. The sedimentary strata are from near the top of the Feltville Formation. What can be seen here, however, is an abundance of boulders of Cambro-Ordovician carbonates (mostly dolostones, not metamorphosed, and some limestones), vesicular basalt (presumably derived by eroding the Orange Mountain Formation), and Green Pond Conglomerate; and medium-rare boulders of Proterozoic gneiss (hold the steak sauce, please!). The predominance of pieces from the Paleozoic sedimentary formations indicates that the main body of the Proterozoic rocks forming the Ramapo block in today's landscape had not yet been exposed during the early part of the Jurassic Period when the Feltville Formation was being deposited.
At Oakland, we have ended a traverse downsection that began at the top of the Hook Mountain Basalt. We have cut through the entire Towaco Formation and the Preakness Formation and are in the topmost part of the Feltville Formation. Despite this change in stratigraphic position, the kind of rock (rudite) has remained about the same. Put another way this means that in localities within about a mile or so of the Ramapo fault, nearly all sedimentary formations consist of basin-marginal rudites. The total stratigraphic range of such rudites has not been determined, but it might come close to equaling the entire thickness of the Newark basin-filling strata. Why do you suppose that all the boulders are cut by fractures? (Are they really what they are cracked up to be?)
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