T234 Greenhouse to Icehouse Transition: Global Events of the Devonian, Carboniferous, and Early Permian I

Wednesday, 7 November 2018
8:00 AM - 12:00 PM
Room 140

SEAFLOOR OXYGENATION IN THE LATE DEVONIAN FRASNIAN-FAMENNIAN BOUNDARY EVENT

Paper number: T234-4
Program: Technical Sessions
Time: 8:45 AM – 9:00 AM

Authors

Abstract

Geochemical and sedimentological evidence indicates significant perturbations of marine carbon and sulfur cycle and the development of oceanic anoxia or euxinia in the Frasnian-Famennian (F-F) boundary (~372 Ma), suggesting the possible linkage between marine redox and the F-F mass extinction, one of the big five biological crises in Phanerozoic. In order to further explore the environmental background of the F-F mass extinction, we measured the elemental and isotopic compositions of carbonate samples collected from two sections, the Panlong and Baisha sections, which were deposited in a shallow marine carbonate platform and an intrashelf basin in South China Block. (1) Carbonate carbon isotope (δ13Ccarb) shows a positive excursion by +3‰ in the Baisha section, while δ13Ccarb of the Panlong section decreases by 1.6‰ followed by a 3‰ increase in the F-F boundary. (2) The Panlong section has more consistent and higher CAS sulfur isotopes (i.e. carbonate associated sulfate, δ34SCAS, Panlong: +22‰~+29‰, Baisha: +6‰~+26‰) and pyrite sulfur isotopes (δ34Spyrite, Panlong: +6‰~+26‰, Baisha: -30‰~+30‰). (3) There is a significant decrease of Fe content in carbonate (Fecarb) in the Baisha section, while Fecarb remains at low values in the Panlong section. (4) δ13Ccarb shows a negative correlation with Fecarb in the Baisha section. Because of predominant deposition in seafloor in late Paleozoic, benthic carbonate would be influenced by benthic flux from sediment porewater, which normally enriches in Fe2+, 13C-depleted HCO3- derived from organic carbon remineralization, and 34S-depleted sulfate derived from H2S oxidation. Thus, higher δ34SCAS and δ34Spyrite values of the Panlong section may indicate lower benthic flux, probably due to higher sedimentation rate and more oxygenated seafloor in shallow water platform, while the positive excursion of δ13Ccarb as well as negative correlation between δ13Ccarb and Fecarb may indicate seafloor oxygenation near the F-F boundary. Instead of oceanic anoxia, our study indicates the seafloor oxygenation in the F-F boundary, which is consistent with emergence of diverse brachiopods fauna in the F-F boundary.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-320205

© Copyright 2018 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.