Geochemical Characterization, Depositional Environment, and Controlling Factors of β-Carotene—A Case Study of Jimsar Depression, Junggar Basin of China

Abstract

Relatively high abundance of β-carotane has been detected in some source rock extracts from Lucaogou Formation(LCG) of Jimsar Depression, Eastern Junggar Basin. A combined investigation of bulk geochemical study and molecular geochemical observation on 31 source rocks samples from LCG were carried out. The LCG is defined as good source rock with high hydrocarbon generation potential, indicated by high TOC (0.27%-13.90%), high hydrocarbon potential index (S1+S2, 0.15–109.01 mg HC/g) and low-maturity to maturity. The biomarkers of LCG source rocks extracts are characterized by short to long chain n-alkanes, a wide range of Pr/Ph (0.74-1.42) and β-Carotane (β-Carotane/Maximum Carbon, 0.16-1.92), high concentrations of C29 sterane, the presence of relatively low tricyclic terpanes and middle gammacerane index values (0.14-0.29). These are consistent with a relatively low oxidizing to low reducing depositional environment of fresh to brackish water conditions, with a major contribution of terrigenous organic matter input and a low contribution of aquatic algal-bacterial organic matter. Based on the correlation relationship between β-Carotane abundance and depositional environment and thermal maturity, it can be concluded that the β-Carotane of LCG is mainly derived from terrigenous organic matter and distributed in the brackish water conditions, low reducing depositional environment, but not affected by thermal maturity. However, β-carotane is mostly associated primarily with anoxic, saline lacustrine environment, and its biological origin was cyanobacteria and algae, historically. This study could provide a new research perspective for geological and geochemical significance of β-carotane and its application in oil-source correlation.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017