Geological Society of America

T81 Deep-Time Carbon Cycles, Redox Changes, and the Evolution of the Biosphere I

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

SHALLOW WATER ANOXIA PRECEDING THE RISE OF EUKARYOTES

Paper number: T81-3
Program: Technical Sessions
Time: 1:50 PM – 2:05 PM

Authors

Feifei Zhang Presenting Author
Nanjing University, Nanjing
Noah Planavsky
Yale University, New Haven, CT
Richard Stockey
Geological Sciences Department, Stanford, CA
Shuhai Xiao
Virginia Tech, Blacksburg, VA
Shuzhong Shen
Nanjing University, Nanjing
Ying Cui
Montclair State University: Department of Earth and Environmental Studies, Montclair, NJ
A.D. Anbar
Arizona State University, Tempe, AZ

Abstract

Earth’s redox evolution has been commonly assumed to have shaped the course of biological evolution. However, whether and how shifts in marine redox conditions are linked to key biotic innovations–foremost the rise and diversification of animals in the late Proterozoic oceans–remains heavily debated. Our current picture of global marine redox evolution during this critical interval is incomplete fostering debate. This is particularly the case for the Tonian Period (~1.0 to ~0.717 Ga), where molecular clock data suggest animals may have emerged and where biomarker and planetological data indicate there was a significant increase in the abundance and diversity of eukaryotic algae. Here, we present >140 new uranium isotope (δ²³⁸U) measurements from Tonian carbonate rocks to fill this outstanding gap. Tonian carbonates from 1000-800 Ma are characterized by anomalously negative δ²³⁸U values—we report the most negative stratigraphically continuous observations to date. These low δ²³⁸U values can only be explained by an interval of intensive and widespread marine euxinia, including prevalent photic zone anoxic conditions.

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

doi: 10.1130/abs/2020AM-355564

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