Carbonate Sediments Microbially Induced by Anaerobic Oxidation of Methane in Hydrocarbon-Seeps

Abstract

Stromatolites, laminated benthic microbial deposits, and other microbialites have been known for more than three billion years since the very early periods of the history of life on Earth. Most of them are thought to have been formed as a result of photosynthetic processes. In contrast to such microbialites, chemo synthetically produced microbialites, mainly carbonate minerals, have been found in deep sea settings where active hydrocarbon seeps (synonymous with cold seeps and methane seeps) existed. Seep carbonates are formed under the influence of the anaerobic oxidation of methane (AOM) mediated by anaerobic methane-oxidizing archaea and sulfate-reducing bacteria. Some internal textures of these chemosynthetically mediated carbonates are similar to those of photosynthetically mediated microbialites. But the chemical signatures of the two types are different from each other. The most distinguishable signature is that the seep carbonate has 13 C-depleted carbonate cements and lipid biomarkers. Here, we show lithological and chemical features of Late Cretaceous hydrocarbon seep carbonates, which were found in fore-arc basin deposits in Hokkaido, Japan, as examples of chemo synthetically mediated microbialites.