ON THE ORIGIN OF CHERT IN THE DEVONIAN NEW SCOTLAND AND KALKBERG FORMATIONS, ROSENDALE, NEW YORK

The New Scotland limestone (NSL) is an argillaceous, highly fossiliferous Lower Devonian limestone which contains bedded chert near the base of the formation. It is underlain by the Kalkberg limestone (KL) which is a 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 differentiate the chert found in the New Scotland limestone (NSL) from that found in the Kalkberg limestone (KL) and to determine the depositional environment for each of the formations as well. Representative chert samples collected from both formations, (NSL and KL), were analyzed by petrographic microscope for mineralogical and textural information. There is an apparent difference between the cherty horizons in these formations. Chert-bearing KL formation is mostly mixed with fine-grained carbonate (micrite), whereas, the NSL has both coarse crystalline calcite (sparite) and a micritic component. The NSL also contains of sparsely-distributed fine grained quartz. Preliminary field and petrographic data suggest that the KL was deposited in a restricted, low-energy, shallow marine to deep-water environment, as evidenced by the greater concentration of fine-grained carbonate mud; whereas, NSL was deposited in a shallow marine setting with intermittent influx of terrigenous materials.