New Geochemical Data on the Organic Matter in Rocks of the Lower and Middle Cambrian Kuonamka Complex, the Lena–Amga Interfluve Area, Southeastern Siberian Platform

Abstract

Saturated hydrocarbon biomarkers were studied in bitumens from organic matter (OM) in the Lower and Middle Cambrian Kuonamka Complex in the Lena–Amga interfluve of East Siberia. Their contents and distribution were analyzed. It was established that OM of siliceous and carbonate rocks from the lower part of the sequence differs from OM of overlying mainly mixed siliceous–carbonate rocks in terms of distribution of alkanes, steranes, tricyclanes, hopanes, and ratios of their homologs. It was concluded that the peculiarities of molecular composition of OM in the rocks are related to the biochemistry of microorganism communities, the remains of which were accumulated in sediments of Cambrian sea. It is possible that the microbiota changed its composition in response to a sharp change of sedimentation settings, which follows from biomarker proxies. It is suggested that sediments in the lower part of the sequence were formed under conditions of H₂S contamination. Catagenesis of OM and contribution of the Lower and Middle Cambrian potentially oil-generating rocks in naphthide generation on the northern slope of the Aldan anteclise are discussed.