GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 282-3
Presentation Time: 9:00 AM-6:30 PM


FARNAM, Cole, Department of Geology, University of Cincinnati, 345 Clifton Court, Cincinnati, OH 45221, BRETT, Carlton E., Department of Geology, University of Cincinnati, 500 Geology/Physics Building, Cincinnati, OH 45221-0013, HUFF, Warren D., Dept. of Geology, Univ of Cincinnati, Cincinnati, OH 45221, STURMER, Daniel M., Department of Geology, University of Cincinnati, Cincinnati, OH 45221-0013 and PATON, Timothy, Department of Earth & Planetary Sciences, University of Tennessee, 1621 Cumberland Av., Knoxville, TN 37996

The position of the Ordovician/Silurian boundary in the strata of the Appalachian basin had been questioned by Bergström and colleagues, with their discovery of elevated δC13 values (probable HICE) suggesting a Hirnantian age for the presumed Silurian, Manitoulin Fm. This study investigated this controversy through detailed fieldwork and analysis of δC13 values from bulk carbonate samples that were collected from outcrops and cores in Ontario, New York, and to determine a tentative age of debated Ordovician and Silurian units.

Fieldwork in southern Ontario and Ohio, led to new hypotheses about the depositional history of the Manitoulin Fm. and adjacent Whirlpool Sandstone. First, the marine sandstones of the upper Whirlpool grade laterally into the type, or upper, Manitoulin Fm found in southern Ontario through Manitoulin island, while the non-marine to marginal marine lower Whirlpool, which shows high δC13 values in basal samples at Niagara, may transition into the lower Manitoulin of the Bruce Peninsula, which contains the HICE. The hypotheses were first tested through the sampling of the Manitoulin Fm. near Hamilton, Ontario, which is apparently transitional into upper Whirlpool Fm. The HICE was not found in these samples, which is consistent with correlation into the upper Manitoulin Fm. farther northwest. Efforts were directed toward testing the complimentary hypothesis that the lower Whirlpool grades laterally in to the HICE bearing lower Manitoulin. Locations near Hornings Mill, Ontario, show upward gradation of lower Whirlpool sandstones and shale into the lower Manitoulin; this section was sampled for δC13 values.

A second hypothesis that in Ohio, the lower Manitoulin Fm/lower Whirlpool grades into a calcareous siltstone, termed the Centerville Fm., was tested by sampling within both outcrop and core for the presence/absence of an excursion. Documentation of a +1‰ δC13 excursion in the Centerville Fm. of West Union, Ohio is consistent with this hypothesis.

Based on preliminary observations, both the Manitoulin and Whirlpool are, at least in part, of potential Hirnantian age and appear to be intergradational. The results of this study could prove groundbreaking for Paleozoic research in the Appalachian basin since it would be evidence for Hirnantian strata above the widespread Cherokee Unconformity.