Enrichment Characteristics of Organic Matter of Shale Series in He-3 Member of Paleogene Hetaoyuan Formation,Biyang Depression

The shales in He-3Member of Paleogene Hetaoyuan Formation in the Biyang Depression mainly consists of hydrocarbon source rocks,and can be divided into five organic-matter-rich intervals(ORIs),where organic matter(OM)is distributed regularly in the sequence stratigraphic framework.The present work addresses the distribution of major elements,trace elements and biomarker parameters of shales from5 th and 3rd ORIs for discussion of the relationships between the enrichment of organic matter and the changes of climate,salinity,redox condition,productivity,and identification of the mechanism of OM accumulation in the sequence stratigraphic framework.The results show that OM of 5th and 3rd ORI is mainly enriched in the middle and lower of expanding system tract,and near the maximum flooding surface,respectively.The total organic carbon content(TOC)varied widely and frequently in periphery of deep depression due to dilution of organic matter by turbidity flow,and had a slight change in the center of the deepest sag.The linear relationship between TOC and paleoredox coefficient of V/Cr and Pr/Ph is observed in 5th and 3rd ORI.TOC in the 3rd ORI shows a positive correlation well with the paleoproductivity coefficient of Cu and Ni contents.The evidence indicates that stratified water column with high salinity and anoxic conditions under arid climate enhanced OM storage in 5th ORI,and the conjunction of high productivity following phytoplankton bloom coupled with oxygen-depleted bottom water in the relatively deep basin are favorable for OM preservation and accumulation in 3rd ORI.