Abstract

Microbially induced carbonate precipitation (MICP) plays an important role in the formation and stabilization of carbonate sediments and lithified structures in shallow marine environments. Despite its significance, the occurrence, environmental controls, and microbial mechanisms driving carbonate precipitation in the Red Sea remain poorly understood. This thesis investigates microbial-induced and microbially enhanced carbonate precipitation across multiple coastal and shallow marine environments of the Saudi Arabian Red Sea, focusing on beachrock, stromatolites, and ooid-forming systems. 

The study aims to identify the environmental settings in which microbial carbonate precipitation occurs, determine characteristic geological and microbial signatures of these systems, and evaluate how environmental conditions influence microbial communities and carbonate formation processes. To address these objectives, extensive field campaigns were conducted over a period of more than three years, integrating geological, ecological, microbiological, and geospatial approaches. 

Beachrock formation was investigated on Um al Misk Island near Thuwal, where microbial community analysis, permanent temperature and pH loggers, combined with monthly field sampling, were used to monitor seasonal seawater variability and lithification conditions. Stromatolite formation on Sheybarah Island was studied through seasonal sampling, microbial characterization, high-resolution drone mapping, and tidal-zone analysis supported by pressure logger deployments. Ooid formation was examined on Abu Laheq Island within Al Wajh Lagoon using hydrodynamic monitoring, sedimentological analyses, seasonal biological sampling, and radiocarbon dating to constrain formation timescales. 

To compare microbial precipitation signatures across environments, samples collected during the field campaigns were integrated with carbonate platform cores and remotely operated vehicle (ROV) samples from platform flanks and deeper seafloor environments. Geological textures, cement fabrics, microbial communities, and environmental datasets were analyzed alongside published literature to identify common indicators of microbial carbonate precipitation. 

This thesis provides one of the first integrated regional assessments of microbial carbonate precipitation systems in the Saudi Arabian Red Sea. The results improve the understanding of interactions between microbial communities, environmental forcing, and carbonate formation processes in modern tropical carbonate systems and contribute to broader interpretations of microbial signatures in both modern and ancient carbonate platforms.