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

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 (δ³⁴S_OSCs) 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 δ³⁴S_OSCs 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 δ³⁴S_OSCs profiles of the oils, e.g., the intermediate δ³⁴S values of the LT oils (OF3) showed little variance with alkylation (<4‰), whereas the intermediate δ³⁴S values of the higher maturity Wenliu oils (OF4) showed ³⁴S enriched alkylated DBTs compared to base DBT (Δδ³⁴S_alkylDBT-_DBT = +7‰). This demonstrates the potential of δ³⁴S_{OSC s} data assisting the genetic correlation of S-rich saline lacustrine oils. However, separate correlations between some of the δ³⁴S_OSCs data and hydrocarbon indicators of paleo-environmental (C₃₅-/C₃₄-hopanes), thermal maturity (C₂₉ sterane and MDBT parameters) and TSR (Δδ³⁴S_BTs–DBTs = 6–12‰) impacts suggest each of these factors also influenced the δ³⁴S character of the Dongpu oils. Therefore, δ³⁴S_OSCs data should be used cautiously in correlation of oils from complex petroleum systems and where possible integrated with other complimentary analytical information.