High Resolution Stratigraphic Analysis of Upper Ordovician to Lower Silurian (Katian to Telychian) Neritic Carbonates from Anticosti Island, Eastern Canada

Posted on 2017-12-22 in Events
Jan 4, 2018

Please join us for a special graduate student presentation on Thursday January 4 at 3:30 pm in rm 265 Geology presented by Matthew Braun, MSc Candidate at University of Ottawa:

High Resolution Stratigraphic Analysis of Upper Ordovician to Lower Silurian (Katian to Telychian) Neritic Carbonates from Anticosti Island, Eastern Canada

Matthew Braun, Pascale Daoust, Alain Mauviel, and André Desrochers

University of Ottawa, Department of Earth and Environmental Sciences

The storm-dominated paleotropical carbonate succession superbly exposed on Anticosti Island in Eastern Canada represents one of the most complete, thickest, and well-preserved successions in the world spanning the Ordovician-Silurian (O/S) boundary. As part of a large research program, a series of continuous costal outcrops and drill cores in the western part of the island were sampled for high resolution δ13C and δ18O chemostratigraphy, multi-order cyclostratigraphic patterns, and chitinozoan biostratigraphy. Once completed, our δ13C and δ18O chemostratigraphy will comprise over 1000 data points spaced at 0.5-1.0m intervals, spanning the entire upper Katian to Telychian succession (~900 m) exposed on Anticosti Island. Four distinct positive δ13C excursions are recognized in the Anticosti succession; the Hirnantian (+5‰), lower Aeronian (+2‰), upper Aeronian (+5‰), and the lower Telychian (+3.5‰) excursions. These positive excursions provide an isotopic carbon signature useful for local, regional, and global correlations with other O/S sections. Like the Quaternary δ18O marine signal, our δ18O record is locally coupled with multi-order cyclic facies changes. The tightly coupled lithologic and oxygen isotopic data suggests the Anticosti succession was influenced by glacio-eustatic fluctuations prior, during and following the end-Ordovician glacial maximum. Furthermore, the estimated duration of these cycles supports an astronomical forcing as the primary driver of the stratigraphic architecture in the deep geological time. Primary isotopic signal preservation is supported by the lack of significant covariance between δ13C and δ18O, by microfabric preservation of both macro and microfossils in petrographic, cathodoluminescence, and SEM microscopy, and by little or no diagenetic resetting as suggested by the trace element geochemistry.