T282 Chemostratigraphy: Physical and Temporal Applications (Posters)

Wednesday, 25 September 2019
9:00 AM - 6:30 PM
Hall AB, North Building

A CHEMOSTRATIGRAPHIC ANALYSIS OF THE ORDOVICIAN AND SILURIAN BOUNDARY IN THE APPALACHIAN BASIN

Paper number: T282-3
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

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.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-338055

© Copyright 2019 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.