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Implications for Neoarchaean ocean chemistry from primary carbonate mineralogy of the Campbellrand-Malmani Platform, South Africa

Sumner, Dawn Y. and Grotzinger, John P. (2004) Implications for Neoarchaean ocean chemistry from primary carbonate mineralogy of the Campbellrand-Malmani Platform, South Africa. Sedimentology, 51 (6). pp. 1273-1299. ISSN 0037-0746. doi:10.1111/j.1365-3091.2004.00670.x.

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The precipitation of calcite and aragonite as encrustations directly on the seafloor was an important platform‐building process during deposition of the 2560–2520 Ma Campbellrand‐Malmani carbonate platform, South Africa. Aragonite fans and fibrous coatings are common in unrestricted, shallow subtidal to intertidal facies. They are also present in restricted facies, but are absent from deep subtidal facies. Decimetre‐thick fibrous calcite encrustations are present to abundant in all depositional environments except the deepest slope and basinal facies. The proportion of the rock composed of carbonate that precipitated as encrustations or in primary voids ranges from 0% to > 65% depending on the facies. Subtidal facies commonly contain 20–35%in situ precipitated carbonate, demonstrating that Neoarchaean sea water was supersaturated with respect to aragonite, carbonate crystal growth rates were rapid compared with sediment influx rates, and the dynamics of carbonate precipitation were different from those in younger carbonate platforms. The abundance of aragonite pseudomorphs suggests that sea‐water pH was neutral to alkaline, whereas the paucity of micrite suggests the presence of inhibitors to calcite and aragonite nucleation in the mixed zone of the oceans.

Item Type:Article
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URLURL TypeDescription
Sumner, Dawn Y.0000-0002-7343-2061
Grotzinger, John P.0000-0001-9324-1257
Additional Information:© 2004 International Association of Sedimentologists. Manuscript received 20 May 2003; revision accepted 18 November 2003. Many thanks go to Nicolas J. Beukes, who provided extensive field support and many insightful discussions. Thanks also to Andrey Bekker and Bruce Simonson for helpful reviews. Financial support during collection of field data was provided by an NSF Graduate Fellowship and the Gretchen L. Blechschmidt Fund of GSA to D.Y.S., and by NASA grant NAGW‐2795 and NSF grant EAR‐9058199 to J.P.G. D.Y.S. was supported by NASA grant NAG5‐10591 during compilation and writing of the manuscript.
Funding AgencyGrant Number
NSF Graduate Research FellowshipUNSPECIFIED
Geological Society of AmericaUNSPECIFIED
Subject Keywords:Aragonite; atmospheric carbon dioxide; calcite; carbonate saturation state; microbialites; siderite; stromatolites
Issue or Number:6
Record Number:CaltechAUTHORS:20181127-132400776
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Official Citation:Sumner, D. Y. and Grotzinger, J. P. (2004), Implications for Neoarchaean ocean chemistry from primary carbonate mineralogy of the Campbellrand‐Malmani Platform, South Africa. Sedimentology, 51: 1273-1299. doi:10.1111/j.1365-3091.2004.00670.x
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:91230
Deposited By: Tony Diaz
Deposited On:27 Nov 2018 21:43
Last Modified:16 Nov 2021 03:39

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