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Geochemical constraints on the origin of Marinoan cap dolostones from Nuccaleena Formation, South Australia

Liu, Chao and Wang, Zhengrong and Raub, Timothy D. (2013) Geochemical constraints on the origin of Marinoan cap dolostones from Nuccaleena Formation, South Australia. Chemical Geology, 351 . pp. 95-104. ISSN 0009-2541. doi:10.1016/j.chemgeo.2013.05.012.

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The geochemistry (including Sr isotope and trace element ratios) of “Snowball Earth” terminal deglacial cap-dolostone from the Nuccaleena Formation, South Australia, is studied. An incremental leaching approach was applied in order to extract the nearest-to-primary chemical composition. Based on the relationship between ^(87)Sr/^(86)Sr and Rb/Sr ratios of the leachates, the samples can be categorized into two groups: 1) Group-I dolostones are located 9 cm below to 1.1 m above, and again 4–6 m above a lithologic contact within Nuccaleena Formation marking the end of diamictite (dominantly siliciclastic sediments) and the onset of solid dolostone deposition (“meters above solid dolostones”, MASD). In each of these intervals, ^(87)Sr/^(86)Sr and Rb/Sr ratios of leachates mostly define a binary mixing relationship and the leaching-sequence-minimum, Rb-corrected ^(87)Sr/^(86)Sr ratio is ~ 0.7077 on average (± 0.0003, 1σ, with a minimum value of 0.7073 among all samples); 2) Group-II dolostones define an interval between 1.7 and 4.0 MASD, in which the leaching-sequence-minimum, Rb-corrected ^(87)Sr/^(86)Sr ratio is ~ 0.7092 on average (± 0.0004, 1σ). We interpret these minimum ^(87)Sr/^(86)Sr ratios in Group-I dolostones to represent Sr isotope compositions of penecontemporaneous seawater, similar to values previously reported for high-Sr limestones under- and over-lying “Marinoan” cap dolostones around the world and permitting an interpretation of no significant long-term seawater ^(87)Sr/^(86)Sr variation during Marinoan deglaciation. In contrast, elevated ^(87)Sr/^(86)Sr ratios of Group-II cap dolostones indicate later alteration events or formation of samples in a non-marine environment (e.g., the ‘glacial lake Harland’, Hoffman, 2011). Negative correlation between ^(87)Sr/^(86)Sr ratios and δ^(18)O values can be explained by fluid–rock interaction, either with brine/saline groundwater, ice melt seeps, or hydrothermal fluids as possible alteration fluids, leading to the elevated ^(87)Sr/^(86)Sr ratios. Alternatively, the elevated ^(87)Sr/^(86)Sr ratios may record the values of ‘glacial lake Harland’.

Item Type:Article
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URLURL TypeDescription
Liu, Chao0000-0001-7049-493X
Wang, Zhengrong0000-0003-3149-0236
Raub, Timothy D.0000-0002-7471-0246
Additional Information:© 2013 Elsevier B.V. Received 3 October 2012. Received in revised form 2 May 2013. Accepted 15 May 2013. Available online 25 May 2013. C.L. and Z.W.would like to thank Jerzy Blusztajn at WHOI, Zhanxiong Peng and Ping Hu at Yale University for all the help to conduct the analyses, Karl Turekian, Danny Rye, Jay Ague, Mark Pagani, and Hagit Affek for the comments and suggestions, and David Evans for the help with sample collections and comments on an early draft of the manuscript. This research is funded by a Yale Start-Up Grant to Z.W.
Funding AgencyGrant Number
Yale Start-Up GrantUNSPECIFIED
Subject Keywords:Cap dolostone; Nuccaleena Formation; Elatina Creek; Step-leaching; Sr isotopes
Record Number:CaltechAUTHORS:20130906-143418561
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Official Citation:Chao Liu, Zhengrong Wang, Timothy D. Raub, Geochemical constraints on the origin of Marinoan cap dolostones from Nuccaleena Formation, South Australia, Chemical Geology, Volume 351, 2 August 2013, Pages 95-104, ISSN 0009-2541, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:41149
Deposited By: Ruth Sustaita
Deposited On:06 Sep 2013 21:53
Last Modified:10 Nov 2021 04:26

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