Geochemical characteristics and sedimentary environment differences of Paleogene source rocks in lacustrine basins with different salinities

Abstract

Geochemical characteristics and sedimentary environment of source rocks in the Paleogene Wenchang Formation (E2W) of the Pearl River Mouth Basin (PRMB) and the Linhe Formation (E3L) of the Hetao Basin are studied. Geochemical experiments were carried out, and the results shows: (1) E2W source rocks have a high abundance of organic matter (OM) and, are in the mature stage with good hydrocarbon generation potential. The paleoclimate was warm and humid, and was oxidative freshwater. (2) The hydrocarbon generating OM of E2W and E3L were mainly aquatic organisms, while E1W was mainly terrestrial organisms. Compared with the E2W source rocks, the abundance and maturity of OM in the E3L are lower. The E3L source rocks is in a reducing environment, the salinity of the water body is relatively high, and there are obvious vertical stratification phenomena. (3) OM in freshwater basins is less affected by paleoclimate, paleoredox, and paleosalinity, while in the saline lake basins is greatly affected by paleosalinity. Low salinity (Sr/Ba < 1.5, Cl < 400 ppm) and high salinity (Sr/Ba > 2.0) are not conducive to organic enrichment, and abundance is also positively correlated with reduction.