Abstract

We present a review of the Chang 7 Member oil shale, which occurs in the middle –late Triassic Yanchang Formation of the Ordos Basin in central north China. The oil shale has a thickness of 28 m (average), an area of around 30,000 km2 and a Ladinian age. It is mainly brown-black to black in colour with a laminar structure. It is characterized by average values of 18wt% TOC (total organic carbon), 8wt% oil yield, and 8.35 MJ/kg calorific value, 400kg/t hydrocarbon productivity, and kerogen of type I-II1, showing a medium quality. On average it comprises 49% clay minerals, 29% quartz, 16% feldspar, and iron oxides, closed to the average mineral composition of global shale. The total SiO2 and Al2O3 comprise 63.69wt% of the whole rock, indicating a medium ash type. The Sr/Ba is 0.33, V/Ni is 7.8, U/Th is 4.8, and the FeO/Fe2O3 is 0.5, indicating formation in a strongly reducing, fresh water or low salinity environment. Multilayered intermediate acid tuff is developed in the basin, which may have promoted the formation of the oil shale. The Ordos Basin was formed during the northward subduction of the Qinling oceanic plate during Ladinian to Norian in a back-arc basin context.

Supplementary material:https://doi.org/10.6084/m9.figshare.c.4411703

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