Benthic microbial mats: a possible major component of organic matter accumulation in the Lower Aptian oceanic anoxic event


Georges Gorin, Department of Geology and Paleontology, Unviersity of Geneva, 13 Rue des Manaichers, Geneva CH-1205, Switzerland. E-mail:


Oceanic anoxic events (OAEs) throughout the Cretaceous were periods of high organic carbon burial leading to drawdown of atmospheric carbon dioxide and lowering of bottom-water oxygen concentration, thereby enhancing the preservation of organic matter (OM). Two dynamic depositional models have been proposed for these events in the Tethyan domain: one is based on strong thermohaline stratification and low surface productivity, the other on high surface productivity with intensified deep-water circulation. Here, we propose another explanation for the concentration of OM, derived essentially from microscopical observations (scanning electron microscope and transmission electron microscope) in the organic-richest interval of an Early Aptian OAE in central Italy (OAE1a or Selli level, 116 Ma). This high-resolution microscopical study of OM highlights benthic microbial mats as the possible source of organic-rich samples where amorphous OM is the major organic constituent. These mats could be more common in OAE black shales than previously thought.