16-3 Large Trace Fossil Trackways from the Upper Silurian Shawangunk Formation of Southeastern New York State

Session: From Thin Section to Outcrop: Exploration of Undergraduate Research (Posters)

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Abstract:

Large trace fossil trackways have recently been discovered in the Upper Silurian Shawangunk Formation of southeastern New York State. The Shawangunk Formation is a coarse-grained sandstone to conglomeratic unit that sits upon the Taconic Unconformity, recording depostion in a transitional marine-terrestrial system. Grain sizes range from medium-grained sand to coarse pebbles (up to 3cm), and the unit contains abundant crossbeds and channel forms. The depositional history of the Shawangunk Formation is poorly understood. The unit is known to preserve fossils of eurypterids from intercalted shale layers near Otisville to the south, but few if any body fossils are known from the sandy/conglomeratic units in NYS. A possible partial body fossil of a large trilobite has been discovered near Sam's Point to the notheast, but debate exists as to whether the structre preserved is actually a body fossil or a pseudofossil. Possible marine tracefossils have been recoreded from the unit in the region at various levels including Arthrophycus and Skolithos. 

The traces under investigation are exposed in steeply-dipping sand-dominated strata striking roughly south-southwest along an abandoned railroad grade proximal to the Ulster/Orange county boarder along the Rte. 209 corridor. The trackways are gently meandering to straight in shape, up to at least 1.5m in length and average about 10-15cm in width. The traces are preserved epichnially and are marked by ~0.5mm-wide ridges along the outer edge with gently arching transverse ridges in between. Scratches seem to indicate the traces were formed by an animal with articulated legs. Tracks have been discovered on multiple layers within the unit at the locality. Tracks show more of a cruziana-like morphology than distinctively separate repichnial-like traces. Comparison to roughly temporally equivalent traces show a greater resemblance to trackways attributed to trilobites more so than they do to those regarded as eurypterid tracks. 

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