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

Changwei Ke, Sumei Li, Hongan Zhang, Nannan He, Kliti Grice, Tianwu Xu, Paul Greenwood

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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 (<4‰), whereas the intermediate δ34S values of the higher maturity Wenliu oils (OF4) showed 34S enriched alkylated DBTs compared to base DBT (Δδ34SalkylDBT-DBT = +7‰). This demonstrates the potential of δ34SOSC s data assisting the genetic correlation of S-rich saline lacustrine oils. However, separate correlations between some of the δ34SOSCs data and hydrocarbon indicators of paleo-environmental (C35-/C34-hopanes), thermal maturity (C29 sterane and MDBT parameters) and TSR (Δδ34SBTs–DBTs = 6–12‰) impacts suggest each of these factors also influenced the δ34S character of the Dongpu oils. Therefore, δ34SOSCs data should be used cautiously in correlation of oils from complex petroleum systems and where possible integrated with other complimentary analytical information.

Original languageEnglish
Article number104361
JournalJournal of Asian Earth Sciences
Volume195
DOIs
Publication statusPublished - 15 Jun 2020

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