T183 Excursions, Extinctions, and Environmental Change: New Advances in Geochemical Tools Linked to Critical Intervals of Environmental and Biotic Change in Earth History

Tuesday, 27 September 2016
8:00 AM - 12:00 PM
Room 404

A CARBON AND NITROGEN ISOTOPE PERSPECTIVE ON 13C EXCURSIONS AND EXTINCTIONS AT THE EDIACARAN/CAMBRIAN BOUNDARY

Paper number: T183-2
Program: Technical Sessions
Time: 8:15 AM – 8:30 AM

Authors

Abstract

The South Oman Salt Basin (SOSB) hosts one of the most complete and thermally best preserved Ediacaran sedimentary sequences that have recorded not only the globally-occurring Shuram 13C-isotope anomaly, but also a negative excursion in stable carbon isotopes that marks the Precambrian–Cambrian boundary and the extinction of the sessile benthic metazoans Cloudina and Namacalathus. We here report on bulk stable carbon isotopes and organic matter ‘quality’—as determined by elemental ratios of C, H and O—in synchronously deposited basin and platform carbonates of the SOSB, as well as on maleimide biomarkers that represent molecular fragments of porphyrins derived from photosynthetic pigments. While classic biomarkers indirectly indicative for euxinia are absent, carbon-isotopically heavy acyclic isoprenoids and higher alkylated maleimides point towards a strongly stratified and reducing system, where anoxygenic phototrophs thrived at a chemocline. Compound-specific nitrogen isotope analyses point to nitrogen assimilation from different pools in surface waters versus at the chemocline and suggest an indirect, nutrient-control on the terminal Ediacaran carbon cycle. We will discuss potentially causal connections between our observations, as well as the role of environmental redox by controlling nitrogen nutrient availability.

Geological Society of America Abstracts with Programs. Vol. 48, No. 7

doi: 10.1130/abs/2016AM-285292

© Copyright 2016 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.