Five series of benzohopanes in early Cretaceous sediments from the Chaoyang Basin, NE China

Five series of benzohopanes were identified in a set of immature to early-oil-window early Cretaceous sediments from the ZK1006 well, Chaoyang Basin, NE China. Series a (C₃₁-C₃₅), b (C₃₃-C₃₅), and c (C₃₁-C₃₅) benzohopanes form by different pathways, while the newly-found series d (C₃₁-C₃₄, maybe to C₃₅?) and e (C₃₁-C₃₂, maybe to C₃₅?) benzohopanes have similar formation mechanisms. Series a is usually the predominant benzohopane series, but occasionally samples are dominated by series c benzohopanes. Series b benzohopanes may be associated with terrigenous organic matter. Series a and b benzohopanes are possibly influenced by redox properties, while paleosalinity more likely controls the formation and enrichment of series c benzohopanes. Two novel parameters (a benzohopane index, and the C₃₅/C₃₄ benzohopane ratio) are proposed to be useful paleoenvironmental proxies in the study area. A high benzohopane index and C₃₅/C₃₄ benzohopane ratio may indicate an anoxic environment.