Geological Society of America

29 D22. Sediments, Carbonates

Monday, 26 October 2020
5:30 PM - 8:00 PM
Meeting Rooms

A HYDROTHERMAL ORIGIN OF THE STRONTIUM ISOTOPE ANOMALIES IN EDIACARAN CARBONATES OF SAUDI ARABIA

Paper number: 29-2
Program: Technical Sessions
Time: 5:45 PM – 6:00 PM

Authors

Huan Cui Presenting Author
Mississippi State University, Mississippi State, MS
Abdullah Yazedi
Saudi Geological Survey, Jiddah
Xiao-Ming Liu
University of North Carolina, Chapel Hill, Chapel Hill, NC
Peter R. Johnson
Portland, OR
Steven Goderis
Vrije Universiteit Brussel, Brussels
Philippe Claeys
Vrije Universiteit Brussel, Brussels
Patricia Vickers-Rich
Monash University, Melbourne
Patricia Vickers-Rich
Swinburne University of Technology, Melbourne
Alan Kaufman
University of Maryland, College Park, MD
Haibo Zou
Auburn University, Auburn, AL
Fayek H. Kattan
Saudi Geological Survey, Jiddah
Peter Trusler
Queen's University, Kingston, ON
Jeff Smith
Monash University, Melbourne
Andrey Yu Ivantsov
Paleontological Institute, Russian Academy of Sciences, Moscow, N/A
Thomas H. Rich
Museum of Victoria, Melbourne
Ashraf Al Qubsani
Saudi Geological Survey, Jiddah

Abstract

Secular variation of ⁸⁷Sr/⁸⁶Sr in carbonate strata has been widely used in regional and global chemostratigraphic correlations. Typically, diagenesis results in higher ⁸⁷Sr/⁸⁶Sr signals relative to their primary composition due to the alteration by Rb-rich fluids and radiogenic decay of ⁸⁷Rb to ⁸⁷Sr. Surprisingly, ⁸⁷Sr/⁸⁶Sr values in the Ediacaran limestones from Saudi Arabia (from 0.7029 to 0.7059) are significantly lower than typical Ediacaran seawater values (mostly from 0.7080 to 0.7090) based on a global compilation. Understanding the origin of these anomalies is important insofar as early macrofossils are preserved in these strata. Two hypotheses have been independently evaluated in this study. The first hypothesis shows a low temperature scenario with isolated oceans or lakes in proximity to a mafic source. The second hypothesis is characterized by a high temperature scenario with profound overprints by juvenile hydrothermal fluids. Integrated Sr and Nd isotope data reveal that the ⁸⁷Sr/⁸⁶Sr anomalies are closely coupled with positive εNd(t = 560 Ma) values (up to +4.1). Covariations between ⁸⁷Sr/⁸⁶Sr, εNd, TOC, δ¹³C_carb, δ¹³C_org, and δ¹⁸O_carb were found. Based on multiple lines of petrographic, field, and geochemical evidence, the second hypothesis (i.e., hydrothermal alteration by juvenile fluids) is preferred in this study. We argue that the concept that the Ediacaran biotic radiation took place in an isolated lake environment should be treated with caution. These remarkably low ⁸⁷Sr/⁸⁶Sr signals have neither temporal nor biogeochemical significance. Sr isotope chemostratigraphy in this particular region may not be a reliable tool for stratigraphic correlations.

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

doi: 10.1130/abs/2020AM-350815

© 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.