明珠国际足

Abstract: A suite of oils and bitumens from the Eocene Shahejie Formation (Es) in Dongying Depression was geochemically characterized to illustrate impact of source input and redox conditions on distributions of pentacyclic terpanes. The Es4 developed under highly reducing, sulfidic hypersaline conditions, while Es3 formed under dysoxic, brackish to freshwater conditions. Oils derived from Es4 are enriched in C32 homohopanes (C32H), while those from Es3 are prominently enriched in C31 homohopanes (C31H). The C32H/C31H ratio shows positive correlation with homohopane index (HHI), gammacerane index, and negative correlation with pristane/phytane ratio, and can be used to evaluate oxic/anoxic conditions during deposition. High C32H/C31H ratio (> 0.8) is an important characteristic of oils derived from anoxic environments, while low values (< 0.8) indicate dysoxic conditions and extremely low values (< 0.4) indicate strong oxic conditions. The C32H/C31H ratio can be applied for deposition condition diagnosis because carboxyl group of C32 hopanoic acids might be reduced to C32 homohopanes under anoxic conditions, and oxidized to C31 homohopane under oxic conditions. Advantages to use C32H/C31H ratio as redox condition proxy compared to the HHI and gammacerane indexes are wider valid maturity range, less sensitive to biodegradation influence and better differentiating reducing from oxic environments.