Asaphoides Florentinensis Trilobite

FIGURE 4.7. New York in the Cambrian. A. New York in the Upper Cambrian, showing the carbonate bank over much of the state. B. Cross section of the plate movement during the Upper Cambrian. C. Stratigraphic chart of the Cambrian exposures in New York. From Isachsen et al. (1991). Printed with permission of the New York State Museum, Albany, N.Y.

FIGURE 4.8. Close-up of Upper Cambrian Potsdam Sandstone showing sets of cross-bedded quartz-rich sandstone. Cut along Street, Whitehall, Washington County.

The coarser sands derived from this erosion accumulated in nearshore areas to form the Potsdam Sandstone facies (Figures 4.8 to 4.10). However, substantially larger amounts of finegrained sediment (clay minerals) were either carried in dilute suspensions to offshore areas, where they settled out as hemipelagic "rain" of mud, or perhaps were blown offshore during dust storms, eventually to settle out and accumulate as deep-water deposits.

The rocks that were deposited in the continental slope and rise belt are no longer found in their area of original accumulation. Rather, they are found as a series of thrust sheets that lie east of the Hudson River Valley in present eastern New York, referred to as the Taconic Mountains (see under Ordovician). The earliest, pretrilobite, portion of the Cambrian is poorly recorded in New York. However, some of the thick, muddy sandstones and silt-stones of the high Taconic Mountains may represent this time interval.

The low or western portions of the Taconics display well-preserved successions of Cambrian-Early Ordovician strata that comprise a series of alternating green to purple or black slaty shales (Truthville, Browns Pond, Middle Granville). The alternation between purple, green, and black mudrocks indicates differ ing redox (oxidation states) conditions on the seafloor. At certain intervals, the bottom water seems to have been better oxygenated, leading to the development of reddish or green slates with little or no accumulated organic matter (Figure 4.10).

Cambrian Trilobite-Bearing Allochthonous Rocks

The green and purple Early Cambrian shales or slates of the Taconic Mountains (up to 600 m thick) are commonly quarried as roofing slates in eastern New York and Vermont, but these quarries are not major fossil localities. In general, it appears that relatively few organisms inhabited the deep sea during the Cambrian time, and most slates are barren, even as life was just bursting forth in shallow-shelf settings. Very few fossils have been found within these beds, although an unusual branching trace fossil, Oldhamia, is abundant in some of the purple shales low in the Taconic succession. These very small trace fossils may represent some of the earliest deep-water grazing animals. A few localities have yielded trilobites. The Lower Cambrian Middle Granville or Nassau Formation, in the vicinity of Troy, Rensselaer. County, has yielded articulated remains of Elliptocephala asaphoides as well as a fairly complete growth series of this trilo-bite. The Lower Cambrian trilobites found are:

FIGURE 4.9. Upper Cambrian limestones. A. Upper Cambrian limestone, Whitehall Formation. Note the darker gray oolitic limestone (a) in sharp contact with fine-grained "ribbon limestone" (b). Also note the small stromatolite (c) attached to the Upper contact of the oolitic limestone. Warner Hill Cuarry, Whitehall, Washington County. B. Domal stromatolites ("cryptozoan") in upper Cambrian Hoyt Formation. Cryptozoan ledge, Petrified Gardens Road, Lester Park, Saratoga County.

FIGURE 4.9. Upper Cambrian limestones. A. Upper Cambrian limestone, Whitehall Formation. Note the darker gray oolitic limestone (a) in sharp contact with fine-grained "ribbon limestone" (b). Also note the small stromatolite (c) attached to the Upper contact of the oolitic limestone. Warner Hill Cuarry, Whitehall, Washington County. B. Domal stromatolites ("cryptozoan") in upper Cambrian Hoyt Formation. Cryptozoan ledge, Petrified Gardens Road, Lester Park, Saratoga County.

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