Effects of thermal intrusion on biomarker distributions in the Alum Shale from south-central Sweden

The middle (Miaolingian) to upper (Furongian) Cambrian Alum Shale Formation in the DBH15/73 core from south-central Sweden was exposed to local heat from a diabase intrusion, providing an opportunity to investigate the molecular geochemical response to thermal stress. Organic petrological observatio...

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Published inInternational journal of coal geology Vol. 295; p. 104643
Main Authors Liu, Anji, Luo, Qingyong, Rudra, Arka, Schovsbo, Niels Hemmingsen, Zheng, Xiaowei, Zhou, Zhiheng, Sanei, Hamed
Format Journal Article
LanguageEnglish
Published Elsevier B.V 04.12.2024
Subjects
Bitumen
Lower Paleozoic
Maturation indicator
Molecular geochemistry
PAHs
Uranium
Maturation indicator
PAHs
Molecular geochemistry
Lower Paleozoic
Uranium
Bitumen
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Summary:The middle (Miaolingian) to upper (Furongian) Cambrian Alum Shale Formation in the DBH15/73 core from south-central Sweden was exposed to local heat from a diabase intrusion, providing an opportunity to investigate the molecular geochemical response to thermal stress. Organic petrological observations and biomarker analyses were conducted to study changes in maturity-indicating parameters and the distribution of high molecular weight polycyclic aromatic hydrocarbons (PAHs) during the maturation process. The DBH15/73 samples exhibit a maturity gradient, ranging from immature at the base to mature in the upper part of the Alum Shale Formation. Multiple maturity-based biomarker parameters were analyzed, and Ts/(Ts + Tm), M30/(M30 + H30), and Hopane H32: 22S/(22S + 22R) of saturated hydrocarbon parameters are found to be more reliable. Ratios of alkylnaphthalenes, alkylphenanthrenes, and alkyldibenzothiophenes (MNR, DNR, TMNr, TeMNr, MPI-1, MPR, MDR, and DMDR) also showed consistent correlations with thermal maturity. Thermal maturation impacted the macromolecular structure, resulting in the aromatization and demethylation, leading to MPy/Py, MChy/Chy, and the sum of unsubstituted 5-ring/4-ring PAH ratios changes with maturity. The influence of thermal maturation outweighs that of uranium radiation in this study, and maturity varies mainly with depth. •The behavior of saturated and aromatic maturity-dependent biomarkers within the maturity range of VReqv < 1.40 %•High molecular weight PAHs ratios in Alum Shale Formation under thermal intrusion•Influence of uranium radiation on biomarker distributions
ISSN:0166-5162
DOI:10.1016/j.coal.2024.104643