Abstract:

Molar-tooth carbonates (briefly called MT or microsparite carbonates) are characterized by early diagenetic sedimentary features. The term of ‘Molar-tooth’ is named after their tapered, ptygmatically folded texture which are mainly developed in Mesoproterozoic and Neoproterozoic carbonates. The origin of these enigmatic structures have been argued. The authors investigated the MT carbonates from Simian (0.65-0.81 Ga) of Neoproterozoic Era in Liaoning and Jilin Provinces of China. A series of biomarkers found from the extracted bitumens of MT carbonates include n-alkanes, alkyl cyclohexanes, acyclic isoprenoids alkanes, extended tricyclic trepans, hopanes, gammacerane, steranes. Furthermore, their biological precursors of these hydrocarbon class are discussed particularly based on the distribution of boilipids in extant organisms. The results show that MT carbonates contain a lot of Prokaryote bacteria (oxygenic photosynthesis cyanobacteria), Archaebacteria (sulfur bacteria, methanotroph), Eukaryote algae (Cyanophyta, Chlorophyta, Rhodophyta, Phaeophyta), Fungi and Protozoa. Therefore, the origin of MT carbonates should be acompanied by these early organisms. The existence of diverse biomarkers indicates that early organisms of Neoproterozoic era reached a certain extent grade in evolution and prepared ready for the great breakthrough of Edicaran life.

Key words: Cryogenian, Neoproterozoic, molar-tooth(MT) structure, Liaoning and Jilin Provinces, biomarkers, biological precursor