A novel redox indicator based on relative abundances of C31 and C32 homohopanes in the Eocene lacustrine Dongying Depression, East China

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