Geological Society of America

T247 Volcanism, Impacts, and Phanerozoic Mass Extinctions: Discovering a Common Cause and Planning for the 6th Mass Extinction I

Wednesday, 25 September 2019
8:00 AM - 12:00 PM
Room 227ABC, North Building

THE RECORD OF ENVIRONMENTAL CHANGE IN NORTHEASTERN PANTHALASSA DIRECTLY PRECEDING THE END-TRIASSIC MASS EXTINCTION EVENT

Paper number: T247-6
Program: Technical Sessions
Time: 9:15 AM – 9:30 AM

Authors

Ekaterina Larina Presenting Author
University of Southern California, Los Angeles, CA
David Bottjer
Univ Southern CaliforniaDept Earth Sciences, ZHS 117, Los Angeles, CA
Frank Corsetti
University of Southern California, Los Angeles, CA
Will Berelson
USCEarth Sciences, Los Angeles, CA
John-Paul Zonneveld
University of Alberta, Edmonton, AB
Aaron J. Celestian
Natural History Museum of Los Angeles, Los Angeles, CA
Jake V. Bailey
University of Minnesota - Twin Cities, Minneapolis, MN
A. Joshua West
University of Southern California, Los Angeles, CA
Joyce A. Yager
University of Southern California, Los Angeles, CA

Abstract

A compilation of environmental information across the end-Triassic mass extinction (ETE) from Nevada to British Columbia reveals potentially stressed environmental/dysoxic conditions preceding the ETE in northeastern Panthalassa. The Ferguson Hill locality, central Nevada, records the initial negative carbon isotope excursion (INIE) of 1.7‰ found worldwide along with the highest occurrence of Choristoceras crickmayi,and presence of elevated Hg indicating the onset of CAMP volcanism. A precursor negative carbon isotope excursion (PCIE) of 1.6‰ is documented 7m below the extinction horizon. Macrofaunal and petrographic analyses show a lack of bioclasts within the precursor and INIE intervals, which suggests the cause of the carbon isotope shift may be connected to deleterious environmental effects. An identical PCIE documented in Tethys and the Germanic basin, which predates the ETE by ~100,000 k.y., suggests that observed shifts in the carbon cycle occurred worldwide. At Ferguson Hill, an elevated amount of sulphide pseudomorphs (goethite framboids after pyrite) was identified within the PCIE interval followed by episodic re-occurrence up-section and then by steady increase starting 2m below the extinction horizon. The presence of sulphide pseudomorphs suggests episodic dysoxic conditions within the sediment and potentially within the water column preceding the ETE. The upper part of the section starting 3m below the extinction horizon is characterized by the appearance of chemosymbiotic bivalves and low oxygen tolerant taxa illustrating a gradual change to tolerance of dysoxic conditions by benthic fauna.

We also investigated three sites at Williston Lake, British Columbia, which document occurrence of multiple phosphorite deposits in the interval preceding the ETE. The genesis of modern phosphorites in similar environments requires fluctuating redox conditions, from oxic to euxinic, linked to organic matter delivery in upwelling zones. Thus, phosphorite deposits may provide direct biosedimentary evidence that episodic shelf euxinia existed at the Williston Lake site leading up to the ETE. Both sites record stressed conditions before the ETE, which possibly were precursors for reduced environmental stability during initial CAMP volcanism in northeastern Panthalassa.

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

doi: 10.1130/abs/2019AM-340665

© 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.