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 18 wt% TOC (total organic carbon), 8 wt% oil yield, a 8.35 MJ kg−1 calorific value, 400 kg t−1 hydrocarbon productivity and kerogen of type I–II1, showing a medium quality. On average, it comprises 49% clay minerals, 29% quartz, 16% feldspar and some iron oxides, which is close to the average mineral composition of global shale. The total SiO2 and Al2O3 comprise 63.69 wt% of the whole rock, indicating a medium ash type. The Sr/Ba is 0.33, the V/Ni is 7.8, the U/Th is 4.8 and the FeO/Fe2O3 is 0.5, indicating formation in a strongly reducing, freshwater or low-salinity sedimentary 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 northwards subduction of the Qinling oceanic plate during the Ladinian–Norian in a back-arc basin context. The oil shale of the Ordos Basin has a large potential for hydrocarbon generation. Supplementary material: Tables of oil-shale geochemical composition, proximate and organic matter analyses from the Chang 7 Member oil shale, the Ordos Basin, Central north China are available at https://doi.org/10.6084/m9.figshare.c.4411703
Highlights
Tectonic settingThe Ordos Lake was located in the SW part of the North China Plate and at the northern edge of the Qinling orogenic belt (Figs 1 and 3) (Yang 1991, 2002; Zhang et al 1995; Yang & Pei 1996; Bai et al 2006; Yang et al 2006; James 2012)
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 stratigraphic characteristics of the oil shales are clearly resolved in a well wireline logging; the oil shale being characterized by high natural gamma ray (GR) and resistivity of induction in lateral and deep (RILD) logs, low ρ, and spontaneous potential (SP) logs (Fig. 6) (Yang & Zhang 2005; Wang 2007)
Summary
The Ordos Lake was located in the SW part of the North China Plate and at the northern edge of the Qinling orogenic belt (Figs 1 and 3) (Yang 1991, 2002; Zhang et al 1995; Yang & Pei 1996; Bai et al 2006; Yang et al 2006; James 2012). Thick piedmont facies (up to 2400 m) are distributed in the SW Ordos Basin and are called the Kongtongshan conglomerates (the lower left part of Fig. 1 highlights their location). They are regarded as the remnants of the foredeep deposits of the back-arc foreland basin, most of which were destroyed subsequently. These suggest that the Ordos Lake environment was, a back-arc foreland basin, with a similar structural mechanism to the Karoo Basin in South Africa (Smith 1990)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
