Comparison of Organic Matter Origin and Source Rock Potential Between Cretaceous Gyeongsang Basin in Jinju and Tertiary Taishu Group in Tsushima Islands
Ji-Hoon Kim1, Tae-Jin Cheong1, Myong-Ho Park2, Jae-Ho Oh1, and Young-Joo Lee1
1Petroleum and Marine Resources Research Division, Korea Institute of Geoscience and Mineral Resources, Daejeon, South Korea
2Petroleum Technology Institute, Korea National Oil Corporation, Anyang, South Korea
Black shales were observed in the outcrops of Cretaceous Gyeongsang Basin in Jinju and Tertiary Taishu Group in Tsushima Islands. Rock-Eval pyrolysis, elemental and isotopic analyses were performed to compare the geochemical characteristics and source rock potential of organic matters between them. The results of Rock-Eval pyrolysis showed similarities in both black shales; organic matters are mostly higher than 0.5 wt%, and do not have any meaningful S2 peak and then Tmax values implying that they could be overmatured. Accordingly, both black shales do not have a good potential as source rock even though high TOC content.
Elemental and isotopic results of black shales in both showed somewhat differences compared to Rock-Eval pyrolysis. TN is slightly higher in Taishu Group while TS, δ13Corg and δ15Norg have higher value in Gyeongsang Basin, which can be used as possible geochemical proxies to distinguish organic matter source, depositional environments and/or diagenetic processes between them. Based on the analyzed results, TOC/TN and δ13Corg have the ranges of 1.9 to 37.6 and of -24.6 ‰ to -21.2‰ for
Gyeongsang Basin, while 1.7 to 9.1 and -28.7 to -26.2‰ for Taishu Group, respectively. These indicate that the organic matter has a different origin between them. In the former, organic matter predominantly derived from the C3 land plant, which is very consistent with the results of previous studies. On the contrary, organic matter of the latter mainly originated from the freshwater algae. Thus, there is a very discrepancy between the results: e.g., the Taishu Group in Tsushima Islands was dominantly deposited in marine environment according to the sedimentologic and paleontological studies. Hence, the studies for identifying the reason to cause this discrepancy in Taishu Group are required in the future.
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