Abstract
The Dohat Faishakh sabkha in Qatar is one of the rare modern environments where it is possible to study the formation of dolomite, a mineral whose origin has been long debated. In previous studies, dolomite formation in this area was considered to be the result of a penecontemporaneous replacement of aragonite, occurring in the presence of Mg-rich evaporated pore-waters. However, a re-investigation of the sabkha revealed that dolomite is not forming exclusively under the evaporitic conditions that characterize the supratidal zone, but also in microbial mats that colonize the lower intertidal zone, indicating that evaporated pore-waters are not a strict requirement for the mineralization process. Moreover, in the supratidal zone, portions of the sediment that are rich in dolomite are also relatively richer in organic material, which derives from partially degraded microbial mats buried in the sediments. Extracellular polymeric substances (EPS) that constitute microbial mats are recognized as an important component for the formation of Mg-rich carbonates. The presence of living and decaying microbial mats comprising EPS, rather than a replacement process, may be the key factor for dolomite formation in the Dohat Faishakh sabkha.
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Acknowledgments
We thank Jeremy Jameson for having guided us to the most interesting locations of the Qatari sabkhas, as well as for the numerous stimulating discussions. We also thank ExxonMobil Research Qatar and Qatar University for logistic support during the fieldwork. This study was supported by the Swiss National Science Foundation.
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Brauchli, M., McKenzie, J.A., Strohmenger, C.J. et al. The importance of microbial mats for dolomite formation in the Dohat Faishakh sabkha, Qatar. Carbonates Evaporites 31, 339–345 (2016). https://doi.org/10.1007/s13146-015-0275-0
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DOI: https://doi.org/10.1007/s13146-015-0275-0