TY - JOUR
T1 - Biogeochemical sulfur cycling during Cretaceous oceanic anoxic events
T2 - A comparison of OAE1a and OAE2
AU - Gomes, Maya L.
AU - Hurtgen, Matthew T.
AU - Sageman, Bradley B.
N1 - Funding Information:
The authors are grateful to Stuart Robinson, Gabriele Gambacorta, and Elisabetta Erba for help with site logistics, fieldwork, and helpful discussion. Our thanks also go to Jennifer Mills, Allegra Mayer, Laura Grace Beckerman, Kelly Peeler, and Koushik Dutta for help with isotope analyses. We thank Neal Blair, Brian Kristall, Benjamin Cowie, and Andrew Masterson for useful discussion. The manuscript was improved by thoughtful reviews by two anonymous reviewers and Editor Christopher Charles. This work was supported by NASA Earth and Space Science Fellowship Program grant Planet09F-0042 (Gomes), Northwestern University Graduate School Presidential Fellowship (Gomes), and National Science Foundation grant EAR-0955969 (Hurtgen). Data are included in the supporting information.
Publisher Copyright:
©2015. American Geophysical Union. All Rights Reserved.
PY - 2016/2/1
Y1 - 2016/2/1
N2 - Biogeochemical sulfur cycling has varied widely over geologic time, mainly in response to changes in primary productivity and organic carbon burial, volcanism, weathering, and evaporite deposition. Several of these processes are explicitly linked to discreet (<1.2 Ma) intervals of widespread organic carbon burial, termed oceanic anoxic events (OAEs). During the Cretaceous, there is a highly distinctive ~4‰ negative excursion in the sulfur isotope composition of seawater sulfate (δ34SSO4) that is bracketed by the two most prominent OAEs (OAE1a and OAE2). This excursion lasted for ~25 Ma and has been variously attributed to enhanced volcanism, changes in weathering, evaporite burial, and/or changes in modes of organic carbon remineralization. We present new high-resolution carbon and sulfur isotope records from carbonate-associated sulfate and pyrite for OAE1a and OAE2. OAE1a is characterized by a monotonic decrease in δ34SSO4 values. Both negative and positive δ34SSO4 excursions are associated with OAE2. To refine hypotheses for the observed changes in biogeochemical sulfur cycling associated with these events, we use a simple sulfur isotope box model. Both empirical and modeling results indicate that δ34SSO4 variability was dominated by input fluxes during OAE1a, whereas enhanced volcanism, weathering, and pyrite burial controlled δ34SSO4 records during OAE2. Our analysis supports the conclusion that Cretaceous marine sulfate concentrations were much lower than modern concentrations and indicates that increases in marine sulfate occurred at the onset of both events. We conclude that increases in marine sulfate from low background concentrations, in conjunction with other environmental characteristics, contributed to the development of OAEs.
AB - Biogeochemical sulfur cycling has varied widely over geologic time, mainly in response to changes in primary productivity and organic carbon burial, volcanism, weathering, and evaporite deposition. Several of these processes are explicitly linked to discreet (<1.2 Ma) intervals of widespread organic carbon burial, termed oceanic anoxic events (OAEs). During the Cretaceous, there is a highly distinctive ~4‰ negative excursion in the sulfur isotope composition of seawater sulfate (δ34SSO4) that is bracketed by the two most prominent OAEs (OAE1a and OAE2). This excursion lasted for ~25 Ma and has been variously attributed to enhanced volcanism, changes in weathering, evaporite burial, and/or changes in modes of organic carbon remineralization. We present new high-resolution carbon and sulfur isotope records from carbonate-associated sulfate and pyrite for OAE1a and OAE2. OAE1a is characterized by a monotonic decrease in δ34SSO4 values. Both negative and positive δ34SSO4 excursions are associated with OAE2. To refine hypotheses for the observed changes in biogeochemical sulfur cycling associated with these events, we use a simple sulfur isotope box model. Both empirical and modeling results indicate that δ34SSO4 variability was dominated by input fluxes during OAE1a, whereas enhanced volcanism, weathering, and pyrite burial controlled δ34SSO4 records during OAE2. Our analysis supports the conclusion that Cretaceous marine sulfate concentrations were much lower than modern concentrations and indicates that increases in marine sulfate occurred at the onset of both events. We conclude that increases in marine sulfate from low background concentrations, in conjunction with other environmental characteristics, contributed to the development of OAEs.
KW - Cretaceous
KW - biogeochemical cycling
KW - ocean anoxic events
KW - sulfur cycling
KW - sulfur isotopes
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U2 - 10.1002/2015PA002869
DO - 10.1002/2015PA002869
M3 - Article
AN - SCOPUS:84960807740
VL - 31
SP - 233
EP - 251
JO - Paleoceanography and Paleoclimatology
JF - Paleoceanography and Paleoclimatology
SN - 2572-4517
IS - 2
ER -