Organic matter remains in the laminated microfabrics of the Kess-Kess mounds (Hamar Laghdad, Lower Devonian, Morocco)

The Lower Devonian Kess-Kess mounds of the Hamar Laghdad Ridge, SE Morocco, are one of the most spectacular carbonate buildups of the world. The differential erosion highlighted their original shapes and the relationships with associated beds. The origin of these buildups is still under debate and the most consistent hypothesis is related to submarine hydrothermal vents in which bacteria and/or archaea played a prominent role in the carbonate biomineralization.The research was focused on micro-nanomorphology and biogeochemistry of the very fine dark and white wrinkled laminated microbialites to investigate the traces of prokaryotic metabolic activity, which possibly induced their precipitation. Epifluorescence observations put in evidence a high organic matter content mainly in the dark laminae. The geochemical characterization of extracted organic matter was performed through the functional group analyses by FT-IR Spectroscopy. FT-IR parameters indicate a marine origin and low thermal evolution for these organic compounds. The organic matter, which is characterized by the presence of stretching νCC vibrations attributable to alkene and/or unsaturated carboxylic acids, is likely to have been synthesized by bacteria and/or archaea communities.