Influence of diagenesis on the stable isotopic composition of biogenic carbonates from the Gulf of Tehuantepec oxygen minimum zone

Blanchet, Cécile L., Kasten, S., Vidal, L., Poulton, S. W., Ganeshram, R. and Thouveny, N. (2012) Influence of diagenesis on the stable isotopic composition of biogenic carbonates from the Gulf of Tehuantepec oxygen minimum zone Geochemistry Geophysics Geosystems, 13 (4). Q04003. DOI 10.1029/2011GC003800.

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Abstract

In order to evaluate the influence of diagenetic and post-sampling processes on the stable oxygen and
carbon isotope compositions of biogenic carbonates, we conducted a multiproxy study of organic-rich sediments
from the eastern Pacific oxygen minimum zone. Core MD02-2520, which was retrieved from the
Gulf of Tehuantepec (Mexico), has seasonal laminations and covers the last 40 kyr. Together with the presence
of gypsum crystals and inorganic calcite aggregates, the occurrence of large excursions in the stable
oxygen and carbon isotope records of both planktonic and benthic foraminifera (as large as +3‰ in d18O
and -5‰ in d13C) point to significant secondary transformations. Storage-related gypsum precipitation
was ruled out since it implies sulfide reoxidation by oxygen that triggers biogenic calcite dissolution, which
proved to be of minor importance here. Instead, precipitation of authigenic calcite during early diagenesis
appears to be the most likely process responsible for the observed isotopic excursions. The d13C composition
for inorganic calcite aggregates (-5 to -7‰) suggests a major contribution from anaerobic oxidation
of organic matter. The d34S composition for gypsum crystals (-10 to +15‰) suggests a major contribution
from anaerobic reoxidation of authigenic sulfides, potentially involving reactions with metal oxides and sulfur
disproportionation. A minor part of the gypsum might possibly have formed as a result of local pore
water salinity increases induced by gas hydrate formation.

Document Type: Article
Keywords: diagenesis; gypsum; inorganic calcite; laminations; oxygen minimum zone; sulfur reoxidation
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
Refereed: Yes
DOI etc.: 10.1029/2011GC003800
ISSN: 1525-2027
Date Deposited: 07 Jan 2013 10:40
Last Modified: 28 Feb 2018 14:27
URI: http://eprints.uni-kiel.de/id/eprint/19920

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