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Are spherulitic lacustrine carbonates an expression of large-scale mineral carbonation? A case study from the East Kirkton Limestone, Scotland

Rogerson, Mike; Mercedes Martín, Ramón; Brasier, Alexander T.; McGill, Rona A. R.; Prior, Timothy J.; Vonhof, Hubert; Fellows, Simon M.; Reijmer, John J. G.; McClymont, Erin; Billing, Ian; Matthews, Anna; Pedley, H. Martyn

Abstract

Lacustrine carbonate deposits with spherulitic facies are poorly understood, but are key to understanding the economically important “Pre-Salt” Mesozoic strata of the South Atlantic. A major barrier to research into these unique and spectacular facies is the lack of good lacustrine spherulite-dominated deposits which are known in outcrop. Stratigraphy and petrography suggest one of the best analogue systems is found in the Carboniferous of Scotland: the East Kirkton Limestone. Here we propose a hydrogeochemical model that explains why the CaCO₃, SiO₂, Mg-Si-Al mineral suite associated with spherular radial calcite facies forms in alkaline lakes above basaltic bedrock. Demonstrating links between igneous bedrock chemistry, lake and spring water chemistry and mineral precipitation, this model has implications for studies of lacustrine sediments in rift basins of all ages. Using empirical and theoretical approaches, we analyze the relationship between metal mobilization from sub-surface volcaniclastic rocks and the potential for precipitation of carbonate minerals, various Mg-bearing minerals and chalcedony in a lacustrine spherulitic carbonate setting. This suite of minerals is most likely formed by in-gassing of CO₂ to a carbon-limited alkaline spring water, consistent with the reaction of alkali igneous rocks in the subsurface with meteoric groundwater. We suggest that an analogous system to that at East Kirkton caused development of the ‘Pre-Salt’ spherulitic carbonate deposits.

Journal Article Type Article
Publication Date 2017-08
Journal Gondwana research
Print ISSN 1342-937X
Electronic ISSN 1878-0571
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 48
Pages 101-109
DOI https://doi.org/10.1016/j.gr.2017.04.007
Keywords Palaeozoic; Magnesium silicate; Calcite; Hydrolysis; Pre-Salt; Palaeogeography; Lake; PHREEQC; Europe; Sediment mineralogy
Publisher URL http://www.sciencedirect.com/science/article/pii/S1342937X17301235
Copyright Statement ©2018, Elsevier. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/
Additional Information This is the accepted manuscript of an article published in Gondwana research, 2017. The version of record is available at the DOI link in this record.

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