Petrology, Elemental and Isotope Geochemistry and Geomicrobiology of Carbonate Infillings and Biofilms Lining Cracks Below the Neoproterozoic (Sturtian) Cap Carbonate in the Mirbat Inlier, Southernmost Oman

Abstract

Cryptic biofilms line cracks in granite basement below a Neoproterozoic cap carbonate in southern Oman. Their depth in the narrow cracks indicates that they grew in a dark non-photic environment, and signs of upward flow within the cracks suggest that they may have grown in waters expelled from depth, which may not have been in isotopic equilibrium with contemporary ocean waters. This study tested this hypothesis and disproved it. The biofilms and associated detrital carbonate were precipitated in isotopic equilibrium with contemporary seawater. The study also confirms the C-13 secular trends previously observed and attributed to seawater changes during post-glacial transgression and accumulation of the cap carbonate.