Compound specific sulfur isotopes of saline lacustrine oils from the Dongpu Depression, Bohai Bay Basin, NE China

Abstract Lacustrine oils from type I-II kerogen from the Dongpu Depression of Bohai Bay Basin have been characterised by compound specific sulfur isotope and hydrocarbon biomarker analyses. The sample suite included sixteen saline lacustrine oils from the northern part of the Dongpu Depression, most of which (i.e., all but two interbedded samples) could be separated into four tectonically aligned oil families (OF1-4) on the basis of differences in their hydrocarbon composition (e.g. high MW n-alkanes, isoprenoids, polycyclic terpenoids). The other two oils studied were freshwater lacustrine oils from the south of the Dongpu Depression, the hydrocarbon composition of which indicated a fifth oil family (OF5). The δ34S values of organic sulfur compounds (δ34SOSCs) in the oils showed several general differences consistent with the five hydrocarbon biomarker defined oil families, including the relative magnitude of their δ34S values: Ave δ34SOSCs values: OF1 = 19‰ (relatively depleted δ34S); OF2 = 28‰ (enriched δ34S); OF3 = 24‰ (intermediate δ34S); OF4 = 25‰ (intermediate δ34S); and OF5 = 18‰ (depleted δ34S); and the respective δ34SOSCs profiles of the oils, e.g., the intermediate δ34S values of the LT oils (OF3) showed little variance with alkylation (