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

THE MEANING OF DOLOMITE IN THE DEEP-SEA SEDIMENTARY RECORD: IMPLICATIONS FOR GLOBAL CARBON CYCLE

Paper number: T81-13
Program: Technical Sessions
Time: 4:20 PM – 4:35 PM

Authors

  • Peter Swart Presenting Author
    Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL
  • Amanda M. Oehlert
    Rosenstiel School of Marine and Atmospheric Sciences, Miami, FL

Abstract

Although dolomite is not abundant in the Modern, it is a minor and persistent component (< 1 to 20%) of many deep-sea sediments. In this presentation we show data on dolomite abundance and δ13C values from sediments deposited in deep water (> 500 m) adjacent to several carbonate platforms (Bahamas, Maldives, Great Barrier Reef, and Great Australian Bight) that suggest that higher concentrations of dolomites generally are associated with periods of low rates of deposition. The low rate of deposition is critical as it provides time for the diffusion of Mg2+ and SO42- from the over lying seawater. Magnesium is necessary for the process of dolomitization while SO42- is needed to oxidize organic material and thereby raise the alkalinity to promote the dolomitization process. In turn the oxidation of organic material alters the carbon isotope balance and, depending upon the amount of SO42- supplied, the organic content, and the carbonate content of the sediments, can produce a negative δ13C value in the bulk sediments. Such changes in the δ13C values do not represent a global signal and the extent to which they develop is very much dependent upon local sedimentary conditions, such as sediment supply, insoluble content, and slope geometry. A typical dolomite profile beneath a hardground might show a low concentrations immediately at the hardground surface (representing a more open system), but increase with depth, reaching a maximum at a distance dependent upon the time period represented by the hiatus (thus controlling the supply of Mg2+ and SO42-) and the amount of organic material available for oxidation (closed system). An interval of reduced sedimentation may show a similar profile, although the maximum concentration of dolomite and influence on the δ13C values would be reduced. Further support for these processes is provided by additional geochemical tracers such as δ34S values of the carbonate associated sulfate, δ18O, δ44Ca, and δ26Mg values, and concentrations of strontium in the dolomite.

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

doi: 10.1130/abs/2020AM-355256

© 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.