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Dolomite formation within microbial mats in the coastal sabkha of Abu Dhabi (United Arab Emirates)

Bontognali, Tomaso R. R. and Vasconcelos, Crisόgono and Warthmann, Rolf J. and Bernasconi, Stefano M. and Dupraz, Christophe and Strohmenger, Christian J. and McKenzie, Judith A. (2010) Dolomite formation within microbial mats in the coastal sabkha of Abu Dhabi (United Arab Emirates). Sedimentology, 57 (3). pp. 824-844. ISSN 0037-0746.

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Microbial mediation is the only demonstrated mechanism to precipitate dolomite under Earth surface conditions. A link between microbial activity and dolomite formation in the sabkha of Abu Dhabi has, until now, not been evaluated, even though this environment is cited frequently as the type analogue for many ancient evaporitic sequences. Such an evaluation is the purpose of this study, which is based on a geochemical and petrographic investigation of three sites located on the coastal sabkha of Abu Dhabi, along a transect from the intertidal to the supratidal zone. This investigation revealed a close association between microbial mats and dolomite, suggesting that microbes are involved in the mineralization process. Observations using scanning electron microscopy equipped with a cryotransfer system indicate that authigenic dolomite precipitates within the exopolymeric substances constituting the microbial mats. In current models, microbial dolomite precipitation is linked to an active microbial activity that sustains high pH and alkalinity and decreased sulphate concentrations in pore waters. Such models can be applied to the sabkha environment to explain dolomite formation within microbial mats present at the surface of the intertidal zone. By contrast, these models cannot be applied to the supratidal zone, where abundant dolomite is present within buried mats that no longer show signs of intensive microbial activity. As no abiotic mechanism is known to form dolomite at Earth surface conditions, two different hypotheses can reconcile this result. In a first scenario, all of the dolomite present in the supratidal zone formed in the past, when the mats were active at the surface. In a second scenario, dolomite formation continues within the buried and inactive mats. In order to explain dolomite formation in the absence of active microbial metabolisms, a revised microbial model is proposed in which the mineral-template properties of exopolymeric substances play a crucial role.

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Additional Information: © 2009 The Authors. Journal compilation © 2009 International Association of Sedimentologists. Manuscript received 4 February 2009; revision accepted 14 October 2009. Published Online: 8 Dec 2009. We thank Abdulla Al-Mansoori, Ali Al-Shamry, Omar Jeelani, Ismail Al-Hosani (ADCO), Hesham Shebl (ZADCO) and Khalil Al-Mehsin (ADNOC) for discussions and help during the field campaigns in Abu Dhabi, Anne Greet Bittermann for her assistance with the microscopy investigation, and Virginie Matera for carrying out ICP-MS analysis. This work was supported by Swiss National Science Foundation grant 200020-105149/-113590.
Funding AgencyGrant Number
Swiss National Science Foundation200020-105149/-113590
Subject Keywords:Biomineral, biosignatures, dolomite, evaporites, exopolymeric substances, sabkha.
Issue or Number:3
Record Number:CaltechAUTHORS:20100408-112958709
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:17904
Deposited By: Ruth Sustaita
Deposited On:08 Apr 2010 21:39
Last Modified:03 Oct 2019 01:35

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