32 Chemostratigraphic, Biotic, and Sedimentologic Changes through Earth History

Saturday, 21 March 2020
8:00 AM - 12:00 PM
Lake Audubon

INVESTIGATING THE ROLE OF MARINE REDOX CONDITIONS IN AN EARLY SILURIAN MASS EXTINCTION (IREVIKEN EVENT): A DEEPER WATER PERSPECTIVE

Paper number: 32-4
Program: Theme Sessions
Time: 9:00 AM – 9:20 AM

Authors

Abstract

The Ireviken carbon isotope excursion (CIE) was a large-magnitude positive shift in δ13C values that is recorded in early Silurian (~432 Ma; Llandovery-Wenlock boundary) strata globally. Associated with this CIE is a marine mass extinction, the Ireviken Event (murchisoni Event in graptolites), approximately 80% of conodont and graptolite fauna went extinct, along with a ~50% reductions in trilobites and brachiopods, as well as a decline in chitinozoans and acritarchs. Previous paleoredox studies of carbonate sequences throughout the Ireviken CIE and extinction event have shown evidence for widespread euxinic (anoxic + sulfidic) conditions in the Silurian oceans as a causal mechanism. This study investigates two localities that preserve deeper basinal mudstone/shale sequences to further test this redox-based hypothesis: the Baltic Basin (Latvia) and the Cape Phillips Basin (Bathurst Island, Arctic Canada). The Ireviken CIE has been previously documented at both localities. We utilized a set of local paleoredox proxies for both sites (δ34Spyr, [Mo, V, U, Mn], Fe-speciation) to constrain local marine water column conditions. Additionally, we analyzed samples from both sections for ε205Tl, a global paleoredox proxy for Mn-oxide burial. Our local proxy records indicate both deeper water sections were reducing throughout the Ireviken CIE interval. Our new Tl isotope data suggest the global oceans were more reducing prior to the CIE, followed by a brief oxic event during the rising limb of the CIE, and then a return to more reducing conditions globally during peak CIE and falling limb values. This study presents new insights and constraints on paleoredox conditions during this interval of the early Silurian suggesting a more complex marine redox history associated with the Ireviken extinction event and CIE.

Geological Society of America Abstracts with Programs. Vol. 52, No. 2

doi: 10.1130/abs/2020SE-344788

© Copyright 2020 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.