Gypsum and dolomite biomineralization in endoevaporitic microbial niche, EMISAL, Fayium, Egypt

Biogenic gypsum in the form of microbialite and potential domal stromatolite as well as endoevaporitic dolomite are deposited in a perennial saline basin characterized by microbial bloom. Deposition environment, mode of occurrence, and microscopic investigation including SEM of these precipitates are discussed in conjunction with XRD, XRF, and FTIR data. Combined effects of salinity gradient and the wind action on the maturity of gypsum outcrop are evident. A characteristic multi-color vertical gypsum profile reflects steep gradient of oxi-anoxic microenvironments and encodes diverse seasonal microbial communities. Direct impact of microbial signature in gypsum crystal habit is conspicuous. Endoevaporitic authigenic dolomite is recorded in specific horizons in interstices of selenite layers.