Geological Society of America

T76 Co-Evolution of Earth’s Surface Environment and Eukaryotic Life from the Mid-Proterozoic to Early Paleozoic

Tuesday, 27 October 2020
1:30 PM - 5:30 PM
Meeting Rooms

AN EXCEPTIONAL RECORD OF EARLY TO MID-PALEOZOIC REDOX CHANGE FROM THE ROAD RIVER GROUP, YUKON, CANADA

Paper number: T76-13
Program: Technical Sessions
Time: 3:55 PM – 4:10 PM

Authors

Erik Sperling Presenting Author
Stanford University, Stanford, CA
Alfred Lenz
University of Western Ontario, London, ON
David K. Loydell
University of Portsmouth, Portsmouth
Joseph Malinowski
Dartmouth College, Hanover, NH
Austin Miller
Stanford University, Stanford, CA
Stephanie Plaza-Torres
University of Colorado Boulder, Boulder, CO
Beatrice M. Rodewald
Vanderbilt University, Nashville, TN
Alan Rooney
Yale University, New Haven, CT
Sabrina Tecklenburg
Stanford University, Stanford, CA
Jacqueline Vogel
Stanford University, Stanford, CA
Noah Planavsky
Yale University, New Haven, CT
Michael Melchin
St. Francis Xavier Univ, Antigonish, NS
Justin Strauss
Dartmouth College, Hanover, NH
Tiffani Fraser
Yukon Geological Survey, Whitehorse, YT
Richard Stockey
Geological Sciences Department, Stanford, CA
Úna C. Farrell
Stanford University, Stanford, CA
Liam Bhajan
Stanford, CA
Tessa N. Browne
Stanford University, Stanford, CA
Devon B. Cole
Georgia Institute of Technology, Atlanta, GA
Benjamin Gill
Virginia Polytechnic Institute and State University, Blacksburg, VA

Abstract

The extent to which Paleozoic oceans differed from Neoproterozoic oceans, and the causal relationship (if any) between biological evolution and changing environmental conditions, is heavily debated. Here we report an expansive record of Paleozoic seafloor redox change from the upper Cambrian to Middle Devonian Road River Group of Yukon, Canada. This represents an ideal sedimentary succession to investigate long-term redox change, as it provides a nearly continuous record of deep-water marine sedimentation over ~110 million years of Paleozoic history. More than 1,100 shale samples from the Road River Group and other Paleozoic shale units worldwide were analyzed for major- and trace-element geochemistry, iron speciation, and total organic carbon content. Redox geochemical data indicate that bottom waters were broadly anoxic during the entirety of Road River Group deposition, but independent evidence from iron speciation and Mo/U ratios suggests that the biogeochemical nature of anoxia changed through time. Both in Yukon and in a global dataset, Ordovician through Early Devonian anoxic water columns were broadly ferruginous (non-sulfidic), with a transition towards more euxinic (sulfidic) water columns in the mid-Early Devonian (Pragian), coincident with the disappearance of graptolites. Thus, an ~80 million-year interval of the early Paleozoic was characterized by ferruginous bottom waters, similar to the Neoproterozoic redox geochemical record. Utilizing this new global shale compilation, trace metal-based inferences of the global extent of reducing conditions suggest that dynamic redox conditions characterized the Paleozoic, with relatively more oxygenated conditions in the late Cambrian-Early Ordovician and Mid-Late Devonian.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-357561

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