Organic petrology and geochemistry of mudstones from the lower Shahejie Formation in the Tanggu area of eastern China : evidence for the presence of an ancient saline lake
Li, L. (Sinopec Jianghan Oilfield Companye (Wuhan, Xina))
Yao, G. Q. (Ministry of Education of China. Key Laboratory of Tectonics & Petroleum Resources)
Cai, M. J. (PetroChina Dagang Oilfield Company)
Liu, Y. H. (PetroChina Dagang Oilfield Company)

Fecha:	2018
Resumen:	Mudstones in the lower Shahejie Formation, in the Tanggu area of the Huanghua Depression, have been found to contain analcime and ankerite. Hydrothermal sedimentation has been invoked to explain the origin of these two minerals, raising the question of whether hydrothermal activity occurred at a sufficient scale to significantly raise the salinity of the depositional environment. We applied a suite of organic petrological and geochemical methods to directly address this question. Maceral composition, kerogen type, and the distribution of n-alkanes, hopanes, and steranes indicate that the organic matter contained in these mudstones and dolomitic mudstones is mainly derived from algae and bacteria. The dominant acritarch genera, C31R/C30 hopane ratio, gammacerane index, Pr/Ph ratio, and the relationship between Pr/n-C17 and Ph/n-C18 suggest that the mudstones and dolomitic mudstones were deposited in an anoxic, saline lacustrine environment. Tmax, biomarker maturity indices, the thermal alteration index (TAI) and acritarch alteration index (AAI), and vitrinite reflectance all indicate that the organic matter is at an immature to early mature stage. The estimated maximum paleotemperature is close to the present-day burial temperature, and much lower than the homogenization temperature of the analcime veins. Combined with the absence of unresolved complex mixtures on the n-alkane pattern, this suggests that hydrothermal activity had a negligible impact on the salinity and alkalinity of the depositional lake.
Derechos:	Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, la comunicació pública de l'obra i la creació d'obres derivades, fins i tot amb finalitats comercials, sempre i quan aquestes es distribueixin sota la mateixa llicència que regula l'obra original i es reconegui l'autoria de l'obra original.
Lengua:	Anglès
Documento:	Article ; recerca ; Versió publicada
Materia:	N-alkanes ; Burial temperature ; Organic matter ; Salinity ; Hydrothermal activity ; Stratification
Publicado en:	Geologica acta, Vol. 16 Núm. 1 (March 2018) , p. 45-64 (Articles) , ISSN 1696-5728

Adreça alternativa: https://raco.cat/index.php/GeologicaActa/article/view/335935
Adreça alternativa: https://revistes.ub.edu/index.php/GEOACTA/article/view/GeologicaActa2018.16.1.3
DOI: 10.1344/GeologicaActa2018.16.1.3

20 p, 3.4 MB

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