Microbial role in dolomite formation in hypersaline sabkha and Miocene mud volcano outcrop in Kuwait

The origin of dolomite has remained the subject of an ongoing debate for over a century and is known as “the dolomite problem”. The essence of this problem is the inability to explain the disparity of dolomite abundance in sedimentary carbonate records and in modern depositional environments. Previously conducted laboratory experiments have demonstrated the ability of microbes to mediate dolomite formation; yet microbial involvement in large scale worldwide dolomitization is poorly understood. This dissertation attempts to expand the knowledge on the microbial role in dolomite formation by investigating modern and paleo environments in Kuwait where dolomite exists. Microbes live in interactive communities where ecological interactions can possess properties of positive cooperation or negative antagonism, thereby affecting microbial composition. In Chapter 2, proto-dolomite was formed by microbial consortia dominated by Halomonas strains alongside a considerable increase in pH which is required for increasing the dolomite saturation index. Although microbes are important to overcome the dolomite kinetic barrier, Chapter 3 showed that aerobic halophilic heterotrophic microbial consortia enriched from Al-Subiya sabkha in Kuwait were unable to replace calcium carbonate by magnesium carbonate to form any of dolomite’s metastable phases. This inability suggests that dolomitization is a lengthy process at Earth’s surface temperature and the factors controlling microbial ability to precipitate dolomite from saturated solutions are dissimilar to microbial ability to dolomitize precursor calcium carbonate. In Chapter 4, crustacean burrows in Early-Middle Miocene coastal mud volcano outcrop provided channels for the mixing of the seeped methane and the downward seawater flux. The anoxic channels provided the preferential conditions for dolomite formation carried by consortia of methanotrophic archaea and sulphate reducing bacteria. In Chapter 5, organic microanalysis of microbial signatures in the mud volcano showed the immediate proximity of methanotrophic archaea and sulphate reducing bacteria to dolomite in contrast to calcite. This observation is in agreement with microbes as a nucleation site for dolomite to overcome the dolomite kinetic barrier as opposed to calcite formation.Ph.D