CARBON ISOTOPE STRATIGRAPHY OF DEVONIAN (EMSIAN-EIFELIAN) LIMESTONES OF NEW YORK AND NEVADA

Carbon isotope stratigraphy for the Emsian-Eifelian (Lower-Middle Devonian) of New York State is poorly defined. We determined d¹³C_carb values in carbonate deposits of the Onondaga Formation for comparison to global isotopic trends. Values in the lower part of the Onondaga (Edgecliff Member) sampled at the LeRoy Quarry in New York are compared to values we obtained from shelf deposits preserved in the Northern Antelope Range, Nevada, and trends from central and southern European sections published by Buggisch and Mann (2004).

The d¹³C_carb trend through the late patulus-early partitus zones in the LeRoy Quarry of New York shows a small negative shift from +1.5‰ to +1‰, which fits with composite European values of this time interval. Although we have not yet sampled the early costatus-late australis zones in the upper part of the Onondaga in New York, this same interval in the Northern Antelope Range, Nevada shows a baseline shift from –0.5‰ to +1.6‰ while the composite European trend remains steady at about +1.7‰.

As a result of the closing of the Rheic Ocean between the colliding Laurentian and Baltic land masses, exchange with the open ocean (Panthalassa) was likely restricted in the New York and European sections. The relative geographic proximity of New York and European sections during Emsian-Eifelian time and their similar exposure to somewhat reduced ocean circulation may explain why the two d¹³C_carb curves correspond. In constrast, our Nevada section was situated off the open Panthalassa-coast of Euramerica, and was directly influenced by global ocean circulation, which may be reflected in the different d¹³C_carb trends compared to European sections of the same time interval.