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Early diagenetic constraints on Permian seawater chemistry from the Capitan Reef

Bryant, Roger N. and Present, Theodore M. and Ahm, Anne-Sofie C. and McClelland, Harry-Luke O. and Razionale, Dan and Blättler, Clara L. (2022) Early diagenetic constraints on Permian seawater chemistry from the Capitan Reef. Geochimica et Cosmochimica Acta, 328 . pp. 1-18. ISSN 0016-7037. doi:10.1016/j.gca.2022.04.027.

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The Capitan Reef Complex in West Texas is famous for its high prevalence of early marine cements, unusual for a Phanerozoic platform, leading some to suggest that Precambrian styles of carbonate sedimentation enjoyed a Permian encore. Here, we use patterns of stable Ca, Mg, C and S isotopes to better understand the environmental driver(s) of the enigmatic cementation. We find that calcite that is the most enriched in ⁴⁴Ca has δ³⁴S values that approach the inferred composition of Permian seawater sulfate. Microbial sulfate reduction in pore fluids must have been spatially and temporally coincident with recrystallization of primary carbonate phases, such that substantial ³⁴S-enriched sulfate was incorporated into diagenetic calcite under relatively closed-system conditions. Moreover, the magnitude of ³⁴S-enrichment of carbonates relative to seawater was strongly influenced by local diagenetic conditions, with fluid-buffered early marine cements, shelf, reef, and upper slope preserving more seawater-like S isotope ratios than the more sediment-buffered lower slope. Some samples are far more ³⁴S-enriched relative to seawater than those from modern sites in similar depositional environments, possibly responding to specific combinations of sedimentary parameters (e.g., grain size, porosity, organic matter rain rate). Additionally, the sulfate concentration in the Delaware Basin might have been slightly lower than modern levels, leading to more extensive isotopic evolution of sulfate in pore waters during carbonate recrystallization. Based on the data and a numerical model of carbonate recrystallization, we suggest that one driver of the extensive seafloor cement precipitation in the Capitan Reef Complex was a Permian water column [Ca²⁺]:[SO₄²⁻] ratio somewhere between 1 and modern seawater.

Item Type:Article
Related URLs:
URLURL TypeDescription data 1 data 2
Bryant, Roger N.0000-0001-7171-2070
Present, Theodore M.0000-0002-4747-2174
Ahm, Anne-Sofie C.0000-0002-5142-0326
McClelland, Harry-Luke O.0000-0001-5281-6915
Razionale, Dan0000-0002-9937-8497
Blättler, Clara L.0000-0003-4843-3625
Additional Information:© 2022 Elsevier. Received 3 September 2021, Accepted 25 April 2022, Available online 30 April 2022, Version of Record 13 May 2022. The authors thank two anonymous reviewers and the associate editor, Adrian Immenhauser, for their constructive and insightful comments, which greatly improved this manuscript. We thank the members of the Blättler group at the University of Chicago for their support and discussions during this project, particularly in the break enforced by the Covid-19 crisis. This work was supported by a grant from the Simons Foundation to ASCA (SCOL 611878). Samples from Guadalupe Mountains National Park were collected with permits GUMO-2012-SCI-0014, GUMO-2013-SCI-0016, and GUMO-2016-SCI-0010. Research Data. All data presented in this study can be found in the attached file named Research Data. The model code is available from the authors upon request. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Funding AgencyGrant Number
Simons FoundationSCOL 611878
Subject Keywords:Carbonate diagenesis; Ca isotopes; Mg isotopes; S isotopes; Sulfate reduction
Record Number:CaltechAUTHORS:20220513-557915000
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Official Citation:Roger N. Bryant, Theodore M. Present, Anne-Sofie C. Ahm, Harry-Luke O. McClelland, Dan Razionale, Clara L. Blättler, Early diagenetic constraints on Permian seawater chemistry from the Capitan Reef, Geochimica et Cosmochimica Acta, Volume 328, 2022, Pages 1-18, ISSN 0016-7037,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:114740
Deposited By: George Porter
Deposited On:16 May 2022 16:29
Last Modified:16 May 2022 16:29

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