Gypsum Microbial Sediments: Neogene and Modern Examples

Abstract

Neogene gypsum deposits provide good examples of microbially induced structures (planar laminites, columnar buildups) whose study elucidates the intimate relations between microbial components and gypsum crystallization. This study closely links petrography and comparisons with modern settings. All the examples studied in both modern and ancient gypsum deposits show that the microbial features in gypsum result from periodically controlled phases of microbial mat development and gypsum precipitation. Although most of the traces of microbial communities proliferating in the evaporitic settings are poorly preserved or absent in the fossil record, the relations between microbial remains and gypsum seems to be controlled by three main processes: (1) interstitial precipitation of gypsum within microbial mats, (2) incorporation of organic material within crystals during gypsum precipitation, and (3) organic material deposited on the surface of gypsum crystals during interruption of crystal growth.