%0 Journal Article
%A García del Cura, María Ángeles
%A Sanz Montero, María Esther
%A De los Ríos, Asunción
%A Ascaso, Carmen
%T Microbial dolomite in fresh water carbonate deposits
%D 2014
%@ 1365-3091
%U https://hdl.handle.net/20.500.14352/87908
%X This article reports evidence for biologically mediated precipitation of dolomitein a fresh water spring in the south-east of Spain. Build-ups in the springconsisted of calcite, minor dolomite, barite and gypsum crystals formed by themineralisation of microbial biofilms and bryophytes. A detailed microscopicstudy, coupled with geochemical analysis of the dolomite-precipitatingbiofilms, showed that dolomite crystals occurred in association with livingcoccoid micro-organisms, providing strong evidence that micro-organismsplay a fundamental role in the precipitation of this mineral. Many of thecalcite crystals observed were associated with extracellular polymeric substances.Moreover, microbial involvement in the precipitation of calcite wasfurther supported by the presence of living cyanobacteria within the calcitecrystals. Two different types of build-up were found in the spring: soft spongymoss tufa and laminated crusts. Two types of crusts were identified as follows:simple pink crusts and laminated crusts, the latter forming in both sub-aquaticand sub-aerial environments. Sub-aquatic accumulation of simple detachedpink crust fragments occurred sporadically. Both tufa and the carbonate crustshosted cyanobacterial-dominated biofilms with different bacteria and diatomsand their extracellular polymeric substances. The d13C values of calciteshowed some biogenic involvement in the origin of this mineral. The d18Ovalues were similar in the tufa and carbonate crusts and corresponded tocurrent climatological characteristics. The occurrence of different groups ofminerals (carbonates and sulphates) in close spatial association with microorganismssuggests the presence of different macro-environmental and microenvironmentalconditions that facilitate mineral precipitation within biofilms.These findings extend the known range of aerobic microbial dolomites toinclude springs, and show that the precipitation of both dolomite and calcitecarbonates occurs while organisms are alive.
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