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A 1.25 Ga depositional age for the “Paleoproterozoic” Mapedi red beds, Kalahari manganese field, South Africa: New constraints on the timing of oxidative weathering and hematite mineralization

Rasmussen, Birger and Muhling, Janet R. and Zi, Jian-Wei and Tsikos, Harilaos and Fischer, Woodward W. (2020) A 1.25 Ga depositional age for the “Paleoproterozoic” Mapedi red beds, Kalahari manganese field, South Africa: New constraints on the timing of oxidative weathering and hematite mineralization. Geology, 48 (1). pp. 44-48. ISSN 0091-7613. https://resolver.caltech.edu/CaltechAUTHORS:20191030-095359299

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Abstract

The Great Oxidation Event (GOE) is marked by the loss of readily oxidizable detrital minerals and the onset of oxidative weathering. One of the oldest post-GOE weathering surfaces, which extends for almost 350 km along strike, occurs in Griqualand West, South Africa. It is best preserved east of the Blackridge thrust, where oxidized paleoweathering profiles are developed below the unconformity at the base of Mapedi-Gamagara red beds. In the Maremane Dome, the red beds preserve pisolitic hematite laterites, which indicate a highly oxygenated atmosphere and suggest hot and humid climatic conditions. The Mapedi and Gamagara Formations are undated east of the Blackridge thrust but were thought to be lithological correlatives of the ≥1.91 Ga Mapedi red bed sequence to the west. Here, we report a U-Pb zircon age of 1.25 Ga for a felsic tuff in red beds of the Mapedi Formation in the Kalahari manganese field. The new tuff age shows that the Mapedi red beds east of the thrust were deposited >650 m.y. after the Mapedi Formation to the west, and therefore they are part of a distinct Mesoproterozoic sequence. Based on lithologic and sedimentological similarities, the Mapedi-east and Gamagara formations are likely to be correlatives that were deposited on an ancient weathering surface at ca. 1.25 Ga. Our findings suggest that key evidence for a highly oxygenated atmosphere during the early Paleoproterozoic actually formed at ca. 1.25 Ga during a major episode of Mesoproterozoic oxidative weathering.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1130/g46707.1DOIArticle
ORCID:
AuthorORCID
Rasmussen, Birger0000-0001-5052-6797
Tsikos, Harilaos0000-0002-1352-2655
Fischer, Woodward W.0000-0002-8836-3054
Additional Information:© 2019 Geological Society of America. Manuscript received 30 June 2019; Revised manuscript received 16 September 2019; Manuscript accepted 18 September 2019. Rasmussen acknowledges support from the State Key Laboratory of Geological Processes and Mineral Resources Open Research Grant GPMR201802 and Australian Research Council grants (DP140100512 and DP190102237). J.-W. Zi appreciates support from the National Natural Science Foundation of China, grant 41873062. Tsikos thanks ASSMANG, Proprietary Ltd. (South Africa), for support and South32 (Perth, Australia) for access to the drill core. Fischer acknowledges support of the Simons Foundation Collaboration on the Origins of Life (New York, USA). Scanning electron microscope analyses were performed at the Centre for Microscopy, Characterization and Analysis at the University of Western Australia, a node of Microscopy Australia funded from university and government sources. Sensitive high-resolution ion microprobe analyses were done at the John de Laeter Centre, Curtin University, Australia. We thank A. Gumsley, D.A.D. Evans, and an anonymous reviewer for their helpful comments.
Funders:
Funding AgencyGrant Number
State Key Laboratory of Geological Processes and Mineral ResourcesGPMR201802
Australian Research CouncilDP140100512
Australian Research CouncilDP190102237
National Natural Science Foundation of China41873062
Simons FoundationUNSPECIFIED
Issue or Number:1
Record Number:CaltechAUTHORS:20191030-095359299
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20191030-095359299
Official Citation:Birger Rasmussen, Janet R. Muhling, Jian-Wei Zi, Harilaos Tsikos, Woodward W. Fischer; A 1.25 Ga depositional age for the “Paleoproterozoic” Mapedi red beds, Kalahari manganese field, South Africa: New constraints on the timing of oxidative weathering and hematite mineralization. Geology ; 48 (1): 44–48. doi: https://doi.org/10.1130/G46707.1
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:99555
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:30 Oct 2019 17:19
Last Modified:07 Jan 2020 19:29

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