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Biosedimentary and geochemical constraints on the precipitation of mineral crusts in shallow sulphate lakes

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Cabestrero, Óscar and Buey, Pablo del and Sanz Montero, M. Esther (2018) Biosedimentary and geochemical constraints on the precipitation of mineral crusts in shallow sulphate lakes. Sedimentary Geology, 366 . pp. 32-46. ISSN 0037-0738

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Official URL: https://www.sciencedirect.com/science/article/pii/S0037073818300149


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Abstract

Seasonal desiccation of Mg2+–(Na+)–(Ca2+)–SO42−–(Cl−) saline lakes in La Mancha (Central Spain) that host microbial mats led to the precipitation of hydrated Na-Mg sulphates and gypsum. Sulphates precipitated in the submerged conditions form extensive biolaminites, whilst in marginal areas they produce thin crusts. Sedimentological, mineralogical, petrographic and high resolution textural studies reveal that the crusts were formed within the benthic microbial mats that thrive at salinities ranging from 160 to 340 g·L−1. The minerals of the crusts are primary bloedite (Na2Mg(SO4)2·4H2O), epsomite (MgSO4·7H2O), gypsum (CaSO4·2H2O) and mirabilite (Na2SO4·10H2O), as well as secondary hexahydrite (MgSO4·6H2O) and thenardite (Na2SO4). Primary bloedite crystals, which form the framework of surficial and submerged crusts are seen to nucleate subaqueously and grow incorporatively within the matgrounds. Displacive and incorporative epsomite grows on previous bloedite crystals and also on the ground. Mirabilite is precipitated rapidly at the brine-air interface over bloedite and epsomite. Hexahydrite and thenardite are formed due to dehydration of epsomite and mirabilite, respectively.


Item Type:Article
Uncontrolled Keywords:Playa lakes, Hypersaline, Desiccation, Microbial mats, Hydrated sulphates
Subjects:Sciences > Geology > Geochemistry
Sciences > Geology > Mineralogy
Sciences > Geology > Petrology
ID Code:47448
Deposited On:09 May 2018 16:35
Last Modified:07 Jun 2019 08:19

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