PREDOMINANCE OF TERRIGENOUS ORGANIC MATTER IN CRETACEOUS MARINE FORE-ARC SEDIMENTS, JAPAN AND FAR EAST RUSSIA

Abstract

Marine Cretaceous sequences of the eastern margin of northeast Asia show remarkable predominance of terrestrial woody kerogens over marine algal ones. Microscopic study on 18 hemipelagic mudstones collected from three dated Albian-Santonian sections in Far East Asia established that inertinite (especially semifusinite) and vitrinite were predominant macerals in all samples. Rare (#1%) liptinite detected by fluorescence indicates little contribution from marine organic matter to the total maceral composition. The predominance of semifusinite over vitrinite suggests that occasional wildfire played a primary role in supplying resistant organic matter to the sedimentary basin during the Late Cretaceous. Polycyclic aromatic hydrocarbons (PAHs) of pyrolytic origin from all selected horizons also support paleo-wildfires. Non-alkylated benzo[a]pyrene, benzo[e]pyrene, benzo[g,h,i]perylene and coronene predominate over alkylated ones. Vitrinite reflectance that exhibits large intra-sample variation up to 2.0% may indicate various oxidation levels for the precursor of vitrinite (wood fragments) during biodegradation, transportation and early diagenesis before reaching the depositional site in the basin. Similar vitrinite reflectance populations between the three sections studied suggest similar oxidation processes and transportation mechanisms for non-pyrolysed portion of organic matter around these depositional sites. The kerogen from the studied marine sections offers a unique opportunity for paleoenvironmental research and understanding land-sourced environments.