Geochemical Investigations of the Chert-Bearing Units Associated with the New Scotland and Kalkberg Limestones (Devonian), Rosendale, New York

The Lower Devonian carbonates and associated siliceous sedimentary rocks exposed in Rosendale, upstate New York, exhibit distinctive sedimentological features and warrant detailed field-based geological and laboratory investigations. Of particular interest is the New Scotland limestone (NSL), which is gray colored, argillaceous, highly fossiliferous limestone and contains bedded chert near the base of the formation. It is underlain by Kalkberg limestone (KL) and consists of fine-grained, dark gray, fossiliferous limestone containing cherty layers from a few inches to a few feet apart. The objective of this research is to analyze any differences in the chert from each of these formations and determine the respective depositional environments, as well. Representative chert samples collected from both formations (NSL and KL) were analyzed by petrographic microscope for mineralogical information. There is an apparent difference between the cherty horizons (NSL and KL). Chert-bearing KL formation is mostly mixed with fine-grained carbonate (micritic), whereas, the NSL has both coarsely crystalline calcite (sparite) and micritic component. The NSL also consists of sparsely-distributed fine grained quartz. Field, petrological, and preliminary bulk chemical and trace-element data suggest that KL was deposited in a restricted, low-energy, shallow marine to deep-water environment, as evidenced by the greater concentration of fine-grained carbonate muds; whereas, NSL was deposited in a shallow marine setting with intermittent influx of terrigenous materials. The bulk silica concentration in the cherts units ranges from 94 to 98%; whereas, the distribution of Ba, Sr, Zr, Ce, Cu, and Mn, among the chert units can be used as a discriminating factor and, suggests variable water-depth conditions, clastic input, and distinctive diagenetic pathways constraining the occurrences of these cherty units.

** Current research was supported by a LSAMP (The New York City Louis Stokes Alliance For Minority Participation)scholarship awarded to Charren Cabaroy