oa Chemosedimentary Sequence Analysis using Biomarkers in Miocene Turbiditic Sediments of South-Central Hokkaido, Japan

Recently, geochemical investigations of sedimentary sequences were performed at single bed units in the sedimentary event beds, especially turbiditic sediments deposited by flood, to evaluate sedimentary processes and early diagenesis after deposition. Such geochemical data profiles such as carbon isotope ratios in sedimentary sequence configuring for the investigations of sedimentary systems and the related phenomena are suggested to be called ‘Chemosedimentary sequence’. In this analysis, biomarker data can be essentially useful for analyzing the turbiditic sequences deposited during the ages older than the Pleistocene. In the present study, we report the analytical results of Miocene turbiditic sediments of south-central Hokkaido, Japan. The concentrations of diterpenoids (DTs) and triterpenoids (TTs) increase, especially TTs are remarkably higher, in Tc (or Td) unit. The profile of the concentrations of DTs and TTs are almost similar to those of the wax-derived n-alkanes, which are mainly derived from leaves. Hence, it is presumed that the leaves, barks, and wood fragments were deposited through the same sedimentary processes in the case of the high density turbidity current forming a typical Bouma sequence. A-ring degraded triterpenoids (des-A TTs), which are generated by microbial degradation during early diagenesis, can be used as the chemosedimentary sequence indicators.