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

Mike Rogerson, Ramon Mercedes-Martín, Alexander T Brasier, Rona A.R. McGill, Tim J. Prior, Hubert Vonhof, Simon M. Fellows, John J. G. Reijmer, Erin L. McClymont, Ian Billing, Anna Matthews, Martyn Pedley

Research output: Contribution to journalArticle

14 Citations (Scopus)
8 Downloads (Pure)

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.
Original languageEnglish
Pages (from-to)101-109
Number of pages9
JournalGondwana Research
Volume48
Early online date26 Apr 2017
DOIs
Publication statusPublished - Aug 2017

Keywords

  • Palaeozoic
  • magnesium silicate
  • calcite
  • hydrolysis
  • Pre-Salt
  • palaeogeography
  • lake
  • PHREEQC
  • Europe
  • sediment mineralogy

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