Microbial dolomite in fresh water carbonate deposits

Abstract

This article reports evidence for biologically mediated precipitation of dolomite in a fresh water spring in the south‐east of Spain. Build‐ups in the spring consisted of calcite, minor dolomite, barite and gypsum crystals formed by the mineralisation of microbial biofilms and bryophytes. A detailed microscopic study, coupled with geochemical analysis of the dolomite‐precipitating biofilms, showed that dolomite crystals occurred in association with living coccoid micro‐organisms, providing strong evidence that micro‐organisms play a fundamental role in the precipitation of this mineral. Many of the calcite crystals observed were associated with extracellular polymeric substances. Moreover, microbial involvement in the precipitation of calcite was further supported by the presence of living cyanobacteria within the calcite crystals. Two different types of build‐up were found in the spring: soft spongy moss tufa and laminated crusts. Two types of crusts were identified as follows: simple pink crusts and laminated crusts, the latter forming in both sub‐aquatic and sub‐aerial environments. Sub‐aquatic accumulation of simple detached pink crust fragments occurred sporadically. Both tufa and the carbonate crusts hosted cyanobacterial‐dominated biofilms with different bacteria and diatoms and their extracellular polymeric substances. The δ13C values of calcite showed some biogenic involvement in the origin of this mineral. The δ18O values were similar in the tufa and carbonate crusts and corresponded to current climatological characteristics. The occurrence of different groups of minerals (carbonates and sulphates) in close spatial association with micro‐organisms suggests the presence of different macro‐environmental and micro‐environmental conditions that facilitate mineral precipitation within biofilms. These findings extend the known range of aerobic microbial dolomites to include springs, and show that the precipitation of both dolomite and calcite carbonates occurs while organisms are alive.

Origin and palaeo-environmental significance of the Berrazales carbonate spring deposit, North of Gran Canaria Island, Spain

“…These deposits can be classified as thermogene deposits following Pentecost (2005) classification. δ 13 C values in hot-water travertine deposits are mainly controlled by physical (CO 2 degassing or water temperature) and microbial processes (Kele et al, 2008;García-del-Cura et al, 2014). On the other hand, changes in δ 18 O values can also reflect the effect of evaporation, temperature of water and, at the time of precipitation, degassing of CO 2 and/or groundwater inflow (Chafetz and Lawrence, 1994;Valero-Garcés et al, 2001;Kele et al, 2008).…”

“…In Berrazales deposit changes in evaporation, water temperature or degassing were probably not significant because the small size of the deposit did not allow water to reequilibrate. CO 2 removal and subsequent variations in δ 13 C values in Berrazales travertine could occur due to biological processes, such as respiration or microbial photosynthesis (García-del-Cura et al, 2014). Microbes consumed preferably the lighter carbon isotope, enriching water and the precipitated calcite in the heaviest isotope, as shown by heavy δ 13 C values and high Mg content on micrite/microsparite, precipitated under the influence of EPS.…”

Sedimentological perspectives on climatic, atmospheric and environmental change in the Neoproterozoic Era

“…Hence, in modern and experimental studies disordered (proto)dolomite formation has been observed, in various contexts, in waters from fresh to saline. Examples include: (i) actively photosynthesizing microbial mats (García‐del‐Cura et al ., ); (ii) in association with extracellular polymeric substances with living or dead microbiotas (Bontognali et al ., ); and (iii) in artificial analogues containing carboxyl groups (Roberts et al ., ). Dolomite can form in sulphate‐rich water (Sánchez‐Román et al ., ), although its formation can be enhanced by sulphate‐reducing bacteria (Wacey et al ., ; Krause et al ., ), and is promoted by the presence of sulphide ions (Zhang et al ., ).…”

Variations of fluvial tufa sub-environments in a tectonically active basin, Pleistocene Teruel Basin, NE Spain

“…Several studies have recorded an increase in the carbon isotopic signal linked to photosynthetic effects (Pentecost and Spiro, 1990;Lojen et al, 2004;García-del-Cura et al, 2014), but other studies have not observed this relation (Shiraishi et al, 2008). In this study, framestone of bryophyte (moss) facies present the lightest δ 13 C values, which could be related to purely physicochemical precipitation.…”