A3: EARLY PALEOZOIC CONTINENTAL SHELF TO BASIN TRANSITION ROCKS: SELECTED CLASSIC LOCALITIES IN THE LAKE CHAMPLAIN VALLEY OF NEW YORK STATE
James C. Dawson
Distinguished Service Professor
Center for Earth and Environmental Science
State University of New York
Plattsburgh, NY, 12901
james.dawson@plattsburgh.edu
TRIP ABSTRACT
Well-exposed classic localities in the Lake Champlain Valley of New York provide opportunities to examine the transition from Early Cambrian to Early and Medial Ordovician continental clastic and carbonate shelf sequences (e.g. Upper Cambrian Potsdam Group, Lower Ordovician Theresa Formation and Beekmantown Group, and Middle Ordovician Chazy Group) to the Medial Ordovician foreland basin carbonates and calcareous shales (Middle Ordovician Trenton Group).
INTRODUCTION
This field trip is designed to begin at the SUNY Plattsburgh campus at 8:00 a.m., and end near Plattsburgh, NY about 4;00 p.m., in time for participants to drive to Lake George, NY to make their lodging arrangements, have dinner, and attend the conference welcoming party. This trip visits many of the localities that are commonly visited in the introductory geology classes at SUNY Plattsburgh. The field trip description is largely based on the work of Fisher (1968) and Isachsen, et al. (2000) and is not based on any significant research by this author. The trip is included among the package of four trips originating in Plattsburgh, NY, in order to round out the offerings so that they include an opportunity to see a portion of the Lower Paleozoic section. Other faculty at SUNY Plattsburgh are involved in offering opportunities to see Adirondack bedrock geology, glacial geology, and hydrology and geomorphology localities in the area.

A3: EARLY PALEOZOIC CONTINENTAL SHELF TO BASIN TRANSITION ROCKS: SELECTED CLASSIC LOCALITIES IN THE LAKE CHAMPLAIN VALLEY OF NEW YORK STATE

Note the 'old base' stone buildings
Note the 'old base' stone buildings constructed in the 19th century of Potsdam Sandstone.

STOP 1. Montreal Member of the Glens Falls Limestone and Dike
Montreal Member of the Glens Falls Limestone of the Trenton Group and Lamprophyre (Monchiquite Dike). You are parked on the apron of the former Plattsburgh Air Force Base marina and boat launch. To reach the outcrop hike, approximately 2000' north, along the cobble beach shore of Lake Champlain. The Pleistocene sediments forming the bluff between the railroad track and Lake Champlain along the way include a contact between earlier Lake Vermont varved and later Champlain Sea sediments. The Montreal Member and a cross cutting Lamprophyre Dike are exposed to varying degrees depending on the water level of Lake Champlain. The Montreal Member is a medium-bedded limestone with some shale partings, that weathers to medium dark gray. Crab Island (the smaller island that can be seen in Lake Champlain two miles southeast of this stop) takes its name from the trilobite, Isotelus, that is commonly found in exposures of the the Montreal Member on the island. Fisher (1968) maps the Lamprophyre Dike as a monchiquite dike, containing phenocrysts of titan augite with some biotite and barkevikite (a monoclinic amphibole), phenocrysts of olivine and titanomagnetite.

Pass the Fort Brown historic site markers on your left/west.
Pass the Fort Brown historic site markers on your left/west. Fort Brown was the left/west flank of the American defense during the land portion of the Battle of Plattsburgh on September 6 - 11th, 1814.

STOP 2. Cumberland Head Argillite of the Trenton Group.
The Cumberland Head Argillite is exposed in this road cut on both sides of Route 9, although the exposures are better on the left/west side. The roadcut (Fisher, 1968 - Figure 27) is typical of the Cumberland Head Argillite. The thin bedding (it looks like varves) of fairly distal turbidite deposition can clearly be seen as more calcareous layers alternate with the thinner, pale buff-colored quartz-silt bearing layers being slightly more resistant to erosion. Fresh surfaces of the rock are uniformly black; however, the thin layers can still be distinguished. The rocks in the vicinity are folded; but, the strike is generally N35E with a dip of 23 degrees N. Be sure to look north along Route 9 and see the slight dip that the highway makes north of the road cut. STOP 3 is just beyond the dip.

STOP 3. Providence Island Dolostone of the Beekmantown Group.
The Providence Island Dolostone is exposed in this road cut on both sides of Route 9, although the exposures are better on the right/east side (Fisher, 1968 - Figure 17). Before examining the outcrop, be sure to look south along Route 9 and recognize that you can see Stop 2. The Rocks at STOP 3 are nearly horizontal, compared to the steeper dips at STOP 2 and the entire Chazy Group and lower portion of the Trenton Group (some 400' or more of rock section) are missing. Fisher (1968) has mapped the edge of the Cumberland Head Allochthon, a Taconic thrust fault, as passing between these two trip stops on the basis of missing section at both the surface and in a 200' deep water well on Cumberland Head. The Providence Island Dolostone is a thick bedded, massive unit that weathers to the buff color characteristic of dolostones. With careful examination, horizons that display significant soft sediment rip ups and other features characteristic of supra-tidal environments. The dolostone is sometime vuggy and fracture zones that have been filled with secondary crystalline calcite are common.

STOP 4. Cumberland Head Argillite at Point au Roche State Park.
Walk the short distance from the parking lot to Lake Champlain and examine the large outcrop of Cumberland Head Argillite along the shore. The folding and jointing associated with the Taconic thrusting is very obvious. The rock is essentially the same as that seen at Stop 2 and again the thinning bedding of the fairly distal turbidite deposition can be seen as the more calcareous layers alternate with the thinner, pale buff-colored, quartz silt bearing layers being more resistant to erosion.

A hump in the road will indicate that you are crossing the Ingraham Esker (Denny. 1972).

A series of sand pits can be seen to the right/east
A series of sand pits can be seen to the right/east after you first cross the Esker. Route 9 crosses the Ingraham Esker again, just before the hamlet of Ingraham on the left/west.

STOP 5. Day Point Limestone of the Chazy Group.
(THIS IS NOT A HAMMER STOP.)
This road cut is part of the upper part of The Day Point Limeston, probably the Fleury Member of Oxley and Kay (1959). It is a medium gray calcarenite that is both cross bedded and regular bedded in this small exposure. Fisher (1968) mentions this outcrop as containing pelmatozoan debris.

STOP 6. Valcour Limestone of the Chazy Group at Sheldon Lane.
(THIS IS NOT A HAMMER STOP.)
This is the first of two opportunities that we will have (see also STOP 10) to see the bioherms in the Valcour Limestone.

Road to old Quarry
Just past a red barn on your right/east there is an amateurish 'stone henge' and an old road. The road leads to the abandoned International Lime and Stone quarry where the Pamelia Dolostone, the Lowville Limestone and the Isle LaMotte Limestone formations of the Black River Group (Fisher 1968 - Figure 25) were once exposed. A few years ago the remainder of this outcrop was mined and the quarry floor today consists of Valcour Limestone. None of the Black River Group remains.

STOP 7. Crown Point Limestone of the Chazy Group at the Northway in Chazy
Maclurites magnus Le Sueur, Death Assemblage
(THIS IS NOT A HAMMER STOP.)
To reach the outcrop cross the open area and enter the woods on a vague trail behind and to the right of the obvious transmission pole. The vague trail heads north a few yards in a white cedar forest and then bends left/west toward the Northway. The outcrop is close to the Northway, a short distance north of the Fiske Road Bridge and is illustrated in Fisher. 1968 (Figure 20).

STOP 8. Lacolle Melange at the Chazy Railroad Bridge.
The road cut is located along the west side of Route 9 as you walk toward the railroad bridge and is figured in Fisher, 1968 (Figure 30). Fisher, 1968 maps this locality and the STOP 9 locality as part of the Tracy Brook (normal) Fault. The wide range of angular clasts are composed of angular sandstone fragments in a sandstone matrix, presumably a tectonically crushed portion of the Keeseville Sandstone.

Cross Corbeau Creek.
Corbeau Creek was studied, as a monitored watershed, by a succession of students at SUNY Plattsburgh in the 1970s and early 1980s. In recent years SUNY Plattsburgh students have been engaged in watershed studies on the Altona 'Flat Rock' lands owned by the William H. Miner Institute and some of this work is described in Field Trip A6 of this field conference.

STOP 9. Lacolle Melange at Coopersville.
The small outcrop is located adjacent to the south side of Route 9B and is figured in Fisher, 1968 (Figure 29). The breccia clasts include a wide range of sizes and the lithology of the clasts is predominately made of carbonate fragments that appear to be of Black River group and Trenton Group origin.

STOP 10. Valcour Limestone at the Bechard Quarry, Near Kings Bay.
To reach the quarry walk across the agricultural field to the higher vegetated are that is visible to the west. Once you reach the top of the vegetated mound the quarry can be seen as illustrated in Fisher, 1968 (Figure 22). The bioherms consist intertidal stromatolites (algae), stromatoporoids, and bryozoans with the various colonies being completely compatible (Pitcher, 1964b) and building their colonies on top of one another.

STOP 11. Keeseville ss of the Potsdam ss at the Clinton Farm Supply, Champlain.
The outcrop is exposed along the north side of the northernmost of the two driveways and in the flat area behind the Farm Supply building. In a series of articles (Erickson, 1993a. Erickson, 1993b. Erickson and Bjerstdt, 1993. Erickson. Connett, and Fetterman, 1993) the stratigraphy and trace fossils of the Keeseville Sandstone and Theresa Dolostone/Sandstone have been described. STOP 11 (Erickson, 19938, and Erickson, Connett and Fetterman, 1993) consists of medium bedded, cream colored Keeseville Sandstone. At this locality large scale ripple marks, and an unusual abundance of trace fossils can be seen.

STOP 12. Theresa Dolostone/Sandstone at Champlain.
The Theresa Dolostone/Sandstone consists of an inter-layered, medium and thick bedded, quartz dolostone. Bjerstedt and Erickson (1989) and Erickson and Bjerstedt (1993) have described the trace fossils of the Theresa in detail and Skolithos can be located on the south wall of this quarry.

STOP 13. Keeseville ss of the Potsdam ss at the Gadway Preserve.
This stop requires driving in to the Gadway Preserve of the Adirondack Nature Conservancy and consists of three short STOPS within the STOP. Vehicles with low clearance should not attempt this and we will consolidate riders at the entrance.

STOP 13a. Large scale ripples
Continue west on the Gadway Road and stop and park at a bare rock rock wash. Carefully cross over a barbed wire fence to examine a pavement of large scale ripples in the Keeseville Sandstone.

STOP 13b.
Continue west on the Gadway Road and STOP and park at the next significant open area on the right/north and stop and park. At the north end of the open area near a red posted sign there is a 4 meter long (10 cm wide) Climachtichnites track. Yochelson and Fedonkin (1993) illustrate several similar examples of this trace fossil in the Keeseville Sandstone of northern New York. Additional trace fossils can be seen near the Adirondack Nature Conservancy sign.

STOP 13c.
Continue west on the Gadway Road and STOP and park at the next significant open area on the right/north and stop and park. At the north end of the open area near a red posted sign there is a 4 meter long (10 cm wide) Climachtichnites track. Yochelson and Fedonkin (1993) illustrate several similar examples of this trace fossil in the Keeseville Sandstone of northern New York. Additional trace fossils can be seen near the Adirondack Nature Conservancy sign.

STOP 14. Trough Cross Stratification in the Keeseville ss of the Potsdam ss
The trough cross stratification is located on the east side of the road, within what goes for a right of way. It is a small outcrop of well exposed cross stratification in the Keeseville Sandstone

Pass the historic Robinson Tavern on the left/east.

STOP 15. Ausable Arkose of the Potsdam ss on the Military Turnpike.
Cross to the ditch on the west side of Route 190 Military Turnpike and walk north. Excellent examples of the 'Basal' Member of the Potsdam Sandstone, a hematitic, feldspathic and micaceous sandstone can be found over much of the distance to the Blue Chip Farm driveway.

Pass the Rand Hill dikes on both sides of the road
Pass the Rand Hill dikes on both sides of the road with the best exposure on the left/east side of Route 190.

STOP 16. Crown Point ls with Lamprophyre Dikes
This extensive road cut along both sides of Route 374/Cadyville expressway contains two lamprophyre dikes on the south side of the road that intrude the Crown point Limestone with a strike of N70W and a dip 85 degrees N. Only the easternmost of the two dikes appears on the north side of the road. Interesting features, including baked zones, xenoliths and partial xenoliths, can be seen associated with the intrusions. The Crown Point Limestone is mainly a medium to dark gray calcilutite. Some of the large planispiral gastropod, Maculurites magnus Le Sueur are present along with trilobite and brachiopod fragments.