Downloaded from http://pg.lyellcollection.org/ by guest on September 28, 2021

Review article Petroleum Geoscience Published online April 24, 2019 https://doi.org/10.1144/petgeo2018-091 | Vol. 26 | 2020 | pp. 355–371

Geology of the Chang 7 Member oil shale of the Yanchang Formation of the Ordos Basin in central north China

Bai Yunlai & Ma Yuhu* Northwest Branch of Research Institute of Petroleum Exploration and Development (NWGI), PetroChina, Lanzhou 730020, Gansu, China * Correspondence: [email protected]

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 Received 28 July 2018; revised 23 December 2018; accepted 17 February 2019

In addition to oil, natural gas, coal, coal-seam gas, uranium and including grey or green sandstone and shale (Fuller & Clapp 1926; groundwater resources, a large tonnage of oil shale is also present in Pan 1934; Yang 2002). Its reservoirs produce 90% of the oil in the the Ordos Basin (Fig. 1) , which is one of the largest oil- and gas- Ordos Basin. It is a group of terrestrial sequences of middle–late bearing basins, ranked second in oil and gas resources, and first in Triassic age, and is composed of fluvial, delta plain and lake facies. annual production, in China (Pan 1934; Yang 1991, 2002; Wang The overlying strata of theYanchang Formation are the Wayaobao et al. 1992; Guan et al. 1995; Zhang et al. 1995; Yang & Pei 1996; Formation, which was a set of coal-bearing strata that originally Li 2000; Chen 2002; Liu & Liu 2005; Lu et al. 2006; Yang et al. belonged to the upper Yanchang Formation but was later separated 2006, 2016a, b; Bai et al. 2006, 2009, 2010a, b, 2011; Liu et al. from the Yanchang Formation.They contain 10 reservoir members, 2009; Qian 2009; Wang et al. 2016; Deng et al. 2017). The oil shale each including both reservoir sands and (oil) shales (Fig. 2). The has attracted considerable interest in recent years in the context of units are numbered 1–10 from the top of the Wayaobao Formation to global oil depletion and the search for unconventional energy the bottom of the Yanchang Formation (i.e. opposite to the normal resources. The commercial potential of the oil shale has been geological convention). Chang 1 is now contained in the Wayaobao assessed and the resource may become more important as other Formation, but it is still called Chang 1 rather than the customary energy reserves decline. Recent research undertaken by the ‘Wa1’. Among them, the Chang 6 and 8 members are the two main Northwest Branch of the Research Institute of Petroleum oil reservoirs. Exploration and Development (NWGI), PetroChina, and others, The Chang 7 Member oil shale is a high-quality source rock has shown that the Ordos Basin contains more than 2000 × which supplies oil for the reservoirs of the Yanchang Formation, 108 tonnes (t) of ‘shale oil’ predicted resources, of which the Chang especially the Chang 6 Member and Chang 8 Member reservoirs, 7 Member shale oil comprises more than 1000 × 108 t: that is, 50% and it even supplies oil to reservoirs of the younger middle Jurassic of that occurring at depths of 0–2000 m in the entire basin. The Yanan Formation (Fig. 2). Yang et al. (2016a, b) discovered that the Chang 7 Member oil shale, also called ‘the Zhangjiatan shale’ in the oil derived from the Chang 7 Member oil shale also fills internal northern Ordos Basin, has an area of around 30 000 km2, an average nano-sized pores and pore throats to form ‘shale oil’, equivalent to thickness of 28 m and an average oil yield of 8 wt%. It is both a tight oil occurring naturally in oil-bearing shales, which is is high-quality source rock and an oil shale with a high residual different to ‘oil-shale-derived oils’ (‘oil shale’ is an organic-rich organic matter content, and is the most important oil-shale seam in fine-grained sedimentary rock containing immature kerogen, a solid the basin (Yang 2002; Duan et al. 2004; Bai et al. 2006; Yang et al. mixture of organic chemical compounds, from which liquid 2006, 2016a, b; Zhang et al. 2008b). It is located in the Yanchang hydrocarbons, can be produced by low-temperature pyrolysis). Formation (Fig. 2), which was originally deposited over an area The Chang 7 Member oil shale and its host stratum, the Yanchang of c. 400 000 km2 during the middle–late Triassic, with a current Formation, have been investigated by the drilling of at least 57 area of 250 000 km2 and current thicknesses of 184–2060 m boreholes in the basin interior (Fig. 1). Early in the last century, (Yang 2002; Bai et al. 2009). outcrops of the Chang 7 Member oil shale were investigated by Pan The Yanchang Formation is a well-documented lithostratigraphic Zhongxiang (Pan 1934), who studied its distribution, occurrence unit, first discovered in the northern Shaanxi in 1926 by M.L. Fuller and quality. In the 1960s, the Shaanxi Industrial Bureau and F.G. Clapp, who described it as a set of stratigraphic units commenced open-cast mining of the oil shale which outcrops in

© 2019 The Author(s). This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License (http://creativecommons.org/ licenses/by/4.0/). Published by The Geological Society of London for GSL and EAGE. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics Downloaded from http://pg.lyellcollection.org/ by guest on September 28, 2021

356 Y. L. Bai & Y. H. Ma

Fig. 1. (a) Location map showing two cross-sections through the Ordos Basin X–X and Y–Y, together with outcrops of the middle–late Triassic and the oil shale. (i) Location map of the Ordos Basin in China and (ii) the location map for Figure 5.(b) Cross-sections X–X and (c)Y–Y through the Ordos Basin showing the spatial distribution of the Chang 7 Member oil shale and its host strata (modified and supplemented after Bai et al. 2009, 2010a, b)Key:Q, Quaternary System; N, Neogene System; E, Paleogene System; Mz, Mesozoic; K, Cretaceous System; J, Jurassic System; T, Triassic System; C-P Carboniferous–Permian systems; ∈-O Cambrian–Ordovician systems; Pt, Proterozoic; Ar, Archean. Downloaded from http://pg.lyellcollection.org/ by guest on September 28, 2021

Ordos oil shale 357

Fig. 2. Strtigraphic chart summarizing the history of the Ordos Basin which is divided into five phases including the Meso-Neo Proterozoic, the early Paleozoic, the late Paleozoic, the middle–late Triassic and the Jurassic–early Cretaceous (modified and supplemented after Bai et al. 2009, 2010b). (The width of the bars in the far-right column represents the importance of the resource.)

the Tongchuan area in the southern margin of the basin. They to initiate oil shale production using the Fushun Furnace, a small, refined the oil shale using a cracking process but the annual shale oil low-temperature, pyrolysis furnace, but all of them failed. Since production was only 80–90 t, and production was terminated 2005, given the heightened imperative for seeking alternative because of water shortages and technological shortcomings (Bai energy sources, outcrops and drilling data for the oil shales in et al. 2009). During 2000–08, several private enterprises attempted the region were reinvestigated (Liu & Liu 2005; Lu et al. 2006; Downloaded from http://pg.lyellcollection.org/ by guest on September 28, 2021

358 Y. L. Bai & Y. H. Ma

Liu et al. 2006, 2009; Qian 2009; Shu 2012; Bai et al. 2009, 2010a, Triassic, forming a volcanic–magmatic arc and back-arc basin on b, 2011). Supported by PetroChina, Professor Bai Yunlai conducted the northern side of the volcanic–magmatic arc (Fig. 3)(Wan 2004; a high-quality study (Bai et al. 2010b). However, in general, Chen 2010). Thick piedmont facies (up to 2400 m) are distributed in research on the oil shale of the region remains sporadic and the SW Ordos Basin and are called the Kongtongshan conglom- unsystematic. This has hindered further exploration and exploitation erates (the lower left part of Fig. 1 highlights their location). They of the oil shale resource; moreover, most of the research has been are regarded as the remnants of the foredeep deposits of the back-arc published in Chinese, making comparisons with comparable foreland basin, most of which were destroyed subsequently. These deposits elsewhere more difficult. suggest that the Ordos Lake environment was, in fact, a back-arc Previous research focused primarily on the characteristics of the foreland basin, with a similar structural mechanism to the Karoo oil shale, especially its occurrence, volume and quality. However, Basin in South Africa (Smith 1990). little research has been conducted to address such key questions as: – How and when did the oil shale form? Is it Triassic or middle late Sedimentary fill Triassic in age? How did the basin accumulate such abundant oil and oil shale resources? What was the tectonic setting? What are the The Ordos Basin has a sedimentary fill with a maximum thickness of properties of the basin? Is it marine? Is it an intracratonic basin or a about 12 800 m, which has accumulated in varying tectonic settings foreland basin (Li 2000; Yang 2002; Yang & Zhang 2005; Bai et al. and different climatic regimes since the Proterozoic era (Fig. 2). 2006; Wang et al. 2017)? The present review seeks to address these Broadly, the Ordos area has experienced five sedimentary cycles, questions. including: (1) the Meso-Neo Proterozoic; (2) the early Paleozoic; (3) The structure of the present study is to summarize pre-existing the late Paleozoic; (4) the middle–late Triassic; and (5) the Jurassic– research, describe the characteristics of the Chang 7 Member oil early Cretaceous, and in only the last three phases was the oil shale shale, and to discuss the environment and processes of formation. formed. In the Meso-Neo Proterozoic and the early Paleozoic, The overall aim is to provide a basis for future investigations of the the marine facies carbonate sedimentary rocks accumulated on the Ordos Basin oil shale and to facilitate comparisons with similar Ordos area. In the late Paleozoic, 600–1400 m-thick deltaic and deposits elsewhere. fluvial facies sandstone, mudstone, and coal and oil-shale seams formed in a paralic environment at first under humid, and later under dry and hot, conditions (Fig. 2). From the middle Triassic to the Geological context Jurassic, fluvial, deltaic and lacustrine facies sandstone, mudstone Tectonic setting and oil shale accumulated in terrestrial environments in a damp hot phase, in general attaining 20–3000 m in thickness in the middle– The Ordos Lake was located in the SW part of the North China Plate late Triassic and 184–2060 m in the Jurassic. There is also an and at the northern edge of the Qinling orogenic belt (Figs 1 and 3) unconformable blanket of Cretaceous sandstone and mudstone (Yang 1991, 2002; Zhang et al. 1995; Yang & Pei 1996; Bai et al. (terrestrial facies) that covers the entire basin, varying from 600 to 2006; Yang et al. 2006; James 2012). The Qinling Ocean Plate 3000 m in thickness (Fig. 2). Present day, the southern Ordos area is subducted beneath the North China Plate in the middle–late covered by nearly 100 m of Quaternary loess and the northern area is

Fig. 3. Tectonic profiles and background during the middle–late Triassic (Ladinian–Norian) in the Ordos areas. The top sketch shows a back-arc foreland basin resulting from subduction of the Qinling oceanic plate and the bottom sketch shows the location of the Ordos Basin in the regional structure (after Wan 2004; Chen 2010; James 2012). Downloaded from http://pg.lyellcollection.org/ by guest on September 28, 2021

Ordos oil shale 359 beneath the Mu Us Desert (Fig. 2)(Liu 1986; Bureau of Geology & of accumulation of the Chang 9 Member, which was supplied with Mineral Resources of Shaanxi Province (BGMRSP) 1989, 1998; large amounts of terrigenous material and a small amount of algal Yang 1991, 2002; Yang & Pei 1996; Zhang et al. 2005; Yang & parent material. The framboidal pyrite content is low. Although Zhang 2005; Bai et al. 2006, 2013, 2014; Yang & Liu 2006; Yang indicating an overall euxinic environment, the low framboidal pyrite et al. 2006, 2016a, b). Based on analyses of previous works on content in the Chang 9 Member oil shale indicates a weakly vitrinite reflectance, fluid inclusions and apatite fission tracks in the oxidizing–reducing environment. basin, Ren (1991) reconstructed the thermal history of the Ordos The Chang 7 Member oil shale is widely distributed in the region, Basin, depicting a temperature gradient of 2.2–3.0°C/100 m from with an area of around 30 000 km2 and a thickness of 28 m (average the Paleozoic to the early Mesozoic, which increased to 3.3–4.5°C/ thickness). It developed in an anoxic, deep-lake environment (about 100 m in the late Mesozoic, gradually decreasing to 2.8°C/100 m 60 m depth: Yang et al. 2016a) and is rich in framboidal pyrite; during the Cenozoic. Research on the relationship between the there is a relatively small amount of clay minerals and abundant thermal history and oil-gas accumulation of the Ordos Basin algal material (Ji et al. 2007). Although some of the oil from the oil suggests that: (1) the low temperature gradient and low thermal shales have been migrated into oil reservoirs of the oilfields, the maturation of gas resource rocks were favourable for the preservation residual organic matter content is still very high, about 18 wt% TOC of organic matter from the Paleozoic to the early Mesozoic; (2) the (see below), and the in situ oil shale resources account for more than higher temperature gradient in the Cretaceous (150−125 Ma) was 50% of the total oil shale resources of the basin (Wang et al. 1992; responsible for generating and migrating gas from the Paleozoic coal Guan et al. 1995; Liu & Liu 2005; Liu et al. 2006, 2009; Lu et al. series and carbonates (Jia et al. 2006); (3) the higher temperature 2006; Bai et al. 2009, 2010a, b, 2011). gradient during the Cretaceous was also responsible for maturing In addition to the Chang 7 and 9 Member oil shales, a shale seam and migrating Triassic and Jurassic oils; and (4) the decrease in is present in the Chang 4 + 5 Member of the Yanchang Formation temperature gradient during the Cenozoic was favourable to the with a wide distribution and a distinct response in wireline logs, and preservation of oil-gas fields. Both the late generation of is known as the ‘thin neck section’, forming a regional marker. It hydrocarbons and the lack of faults in the Ordos Basin are key was deposited in a shallow lake-delta environment and there is no factors in preserving the hydrocarbon accumulations. kerogen in the shales, and therefore lacks the basic conditions for Burial history analysis show that the strongest uplift and erosion forming oil shale or hydrocarbon source rocks (Fu et al. 2012). event took place at the end of the later Cretaceous, and three weaker A thin oil-shale seam is present in the Chang 1 Member of the uplift and erosion events took place at the end of the late Triassic, the Wayaobao Formation, formed in the limnic and delta environment, middle Jurassic and the late Jurassic (Chen et al. 2006). and interbedded with coal seams; it covers a limited area and is thin (Wang et al. 2007). The oil shale with coal had been mined, mainly Characteristics of the oil shales and shale in different strata used as fuel. In summary, the Chang 7 Member oil shale has a real in the Ordos Basin significance for exploration and is quite different to the others.

Since the late Paleozoic, multiple oil-shale (shale) seams developed The Yanchang Formation: host rock of the Chang 7 – in different strata of the Ordos Basin, in the late Carboniferous early Member oil shale Permian Taiyuan Formation, the middle–late Triassic (Ladinian– Norian) Yanchang Formation, the late Triassic (Rhaetian) The middle–late Triassic Yanchang Formation (Ty) mainly Wayaobao Formation, the middle Jurassic (Aalenian–Bajocian) comprises carnation and celadon fine–coarse grain arkose, with Yanan Formation and the middle Jurassic (Bathonian–Callovian) interbeds of black shale, oil shale and andesitic to dacitic tuff Anding Formation (Bai et al. 2009, 2010b). (Fig. 4). It is an important oil-bearing formation. The oil shales of the Taiyuan Formation were formed in a paralic The lower part of the Yanchang Formation consists of carnation environment. Because of deep burial, it is mature to overmature, and celadon medium–coarse grain arkose, fine sandstone, sand- with the vitrinite reflectance of the shale verying from 0.9–2.5% Ro, wiched with siltite, argillaceous siltite, mudstone, oil shale (Chang 9 most of the kerogen was converted to gas.The oil shales and coals Member oil shale) and tuff; followed by oil shale (Change 7 mainly crop out along the edge of the basin, with a burial depth Member oil shale), black shale, interbeded with argillaceous siltite greater than 600 m in the eastern part, near Hancheng, and attain a and tuff (Fig. 4). maximum burial depth of c. 3000 m in the mid-western part The upper part of the Yanchang Formation is grey, celadon fine– (Qingshen-2 well) (Fig. 1). The oil shale generally has a low oil medium grain arkose, black shale, mudstone, siltite, and interbed- yield (only 2.8 wt%) and thin seams (c. 2 m), forming a relatively ding of celadon sandstone and black silty mudstone (Fig. 4). low-grade resource (Bai et al. 2009). The Yanchang Formation has conformable contacts with the The Jurassic oil-shale seams were mainly formed in a lake-delta overlying stratum (the Wayaobao Formation) and underlying environment, and are interbedded with coal seams. The oil-shale stratum (the Ermaying Formation), and can be readily distinguished seams are thin and local, and therefore are of low economic value by its celadon, grey, black colour. The base of the Yanchang (Bai et al. 2009). Formation is marked by the disappearance of the crimson mudstone, The Chang 9, 7, 4 + 5 and 1 Member oil shale (shale) occurred in which located the top of the Ermaying Formation, also known as the the Yanchang Formation and the Wayaobao Formation. Zhifang Formation (T2). The top of the Yanchang Formation, or the The Chang 9 Member oil shale, also called ‘the Lijiapan shale’ in base of the Wayaobo Formation, is marked by the occurrence of the Ordos Basin, is present at the top of the Chang 9 Member of the rhythmic layers of sandstone and mudstone containing coal seams Yanchang Formation. The oil shale is mainly distributed in the or very thin coal seams (Fig. 4). north-central basin, in Yanan, Zhidan and Ansai counties. It has an The Yanchang Formation contains abundant fossils (e.g. area of 4336 km2, about one-seventh of the Chang 7 Member oil phytoliths, palynoflora, estheria, bivalves, insect, acritarchs and shale, with a limited thickness of about 6 m. It is characterized by a fish) and framboidal pyrite (Liu 1986; Bai et al. 2006), and formed relatively large burial depth and a relatively low abundance of in fluviatile delta lake facies during the middle–late Triassic organic matter (c. 4.5 wt%, on average) (Zhang et al. 2008a; Zhou (BGMRSP 1998; Bai et al. 2006, 2009; Deng et al. 2017). The age et al. 2008). Its organic matter type is different to that of the Chang 7 of the Yanchang Formation, which was regarded as Late Triassic Member oil shale: the sapropel content of the former is less than in (Yang 2002; Bai et al. 2006; Wang et al. 2017), has recently been the latter. A deep or semi-deep lake was formed during the interval determined to be middle–late Triassic (Deng et al. 2017). Downloaded from http://pg.lyellcollection.org/ by guest on September 28, 2021

360 Y. L. Bai & Y. H. Ma

Fig. 4. Stratigraphic column indicating the position of the oil-shale-rich seams within the Triassic section.

The Yanchang Formation is a lithostratigraphic unit. According developed again. In the Chang 3 and Chang 2 Member sedimentary to the formal definition, it lacks coals. The coal-bearing section of intervals, the lake remained narrow and the deeper lake facies began the Chang 1 Member is therefore assigned to the Wayaobao to disappear. This represents the third lake transgressive–regressive Formation (BGMRSP 1998). cycle (Ty3)(Deng et al. 2011). The Yanchang Formation experienced three lake transgressions, In the Wayaobao Formation, or the Chang 1 Member, the lake corresponding, respectively, to the Chang 9, Chang 7 and Chang 4 disappeared completely and there was extensive swamp develop- + 5 members (in terms of sedimentary cycles Ty1,Ty2,Ty3, ment, with the deposition of some coal seams, some interbedding of respectively) (Figs 2 and 4). oil shale, large amounts of charcoal debris and numerous plant fossils. In the Chang 10 Member, deposition comprised alluvial plain, deltaic plain and shallow lake facies. The lake facies covers a relatively small area. During deposition of the Chang 9 Member, the Geological and geochemical characteristics of the Chang lacustrine area was significantly enlarged, with development of 7 Member oil shale shallow lake and delta facies, while in some regions a deeper lake Spatial distribution facies formed. The alluvial plain and alluvial fan facies became restricted. The Chang 9 Member represents the first lake The Chang 7 Member oil shale is present on a large scale, with an transgression in the area. In the Chang 8 Member, although the almost north–south-orientated asymmetrical syncline (Figs 1 and 5). lake area was wide, it was narrower and shallower than that of the The oil shales with the Yanchang Formation have been uplifted Chang 9 Member. The deltaic sandstone deposited during this stage and eroded in the eastern, southern and western parts (arc is one of the main reservoirs in the basin. This completes the first distribution), and have subsided in the mid-western parts (including lake transgressive–regressive cycle (Ty1)(Deng et al. 2011). the Qingshen-2 well, Huangxian, Huachi and Qingyang counties, In the Chang 7 Member, lacustrine facies dominated, and the and Xifeng city: Figs 1 and 5). The deepest burial is in Huanxian deeper lake facies reached its maximum extent of c. 30 000 km2 and County in Gansu Province (Fig. 5). In the western part of the Ordos possible water depth of about 60 m, representing a major lacustrine Basin (including the Tiantan-1 well, west Huanxian County, transgression. This was fellowed by the Chang 6 Member, where the Zhenyuan County and the Qingshen-2 well) (Figs 1 and 5), the lake shallowed and deltaic sand bodies developed to form another oil-shale seams and its host rock are steeply uplifted and dip to the main reservoir. This represents the second lake transgressive– east, while in the eastern part (including Zhidan, Fuxian and regressive cycle (Ty2)(Deng et al. 2011). Yanchang counties, and Yanan city) is gently uplifted and dips to In the early stages of Chang 4 + 5 Member, the lake began to the west (Figs 1 and 5). The structural contours in Figure 5 indicate narrow considerably but was extended again in the middle of the the burial depth of the oil shales, which also reflects the structural interval. A mudstone-rich lake facies developed that formed characteristics of the oil-shale layers. Outcrops of both the oil shale the regional cap rocks. Subsequently, deltaic plain sand bodies and strata are mainly distributed in the east and south, in Yijun Downloaded from http://pg.lyellcollection.org/ by guest on September 28, 2021

Ordos oil shale 361

Fig. 5. Thickness distribution and burial depth of the Chang 7 Member oil shale; the location is shown in Figure 1a (modified and supplemented after Yang & Zhang 2005; Bai et al. 2009, 2010b).

County, Tongchuan city, Yaoqu town and Binxian County in Formation, suggesting the upper part of the Yanchang Formation northern Shaanxi (Fig. 1). is of late Triassic (Carnian–Norian) age. The Annalepis– Tongchuanophyllum assemblage, with a Ladinian age (Si 1956), Basic sequence of the Chang 7 Member occurring in the lower part of the Yanchang Formation below the Chang 7 Member indicates an middle Triassic age for the lower part The basic sequence of the Chang 7 Member consists of three parts: of the Yanchang Formation. The Chang 7 Member oil shale is (1) oil shale, shale and mudstone; (2) sandstone and siltite; and (3) therefore of Ladinian (i.e. middle Triassic) age. tuff (Fig. 4). The lower part of the Chang 7 Member consists of oil shale and tuff, with interbeded fine sandstone and siltite. The upper part consists of mudstone, shale and tuff, sandwiched with siltite Zircon SHRIMP U–Pb ages and fine sandstone. The stratigraphic characteristics of the oil shales Zircon SHRIMP U–Pb ages have recently been published for the are clearly resolved in a well wireline logging; the oil shale being lowermost tuff units (K0) of the Chang 7 Member oil shale characterized by high natural gamma ray (GR) and resistivity of (stratigraphic horizon K0, see Fig. 4)(Xie 2007; Wang et al. 2014). induction in lateral and deep (RILD) logs, low ρ (density), and These ages range from 239.7 to 241.3 Ma, which are equivalent to spontaneous potential (SP) logs (Fig. 6)(Yang & Zhang 2005; the Ladinian age as indicated by the phytoliths. Wang 2007). In summary, the Yanchang Formation is middle–late Triassic (Ladinian–Norian) age, not just late Triassic age (Wang et al. 2017). Age The Chang 7 Member oil shale is of middle Triassic (Ladinian) age. Biostratigraphic age Thickness The biostratigraphy is based on phytoliths. The Danaeopsis– Bernoullia assemblage, with a Carnian–Norian age (Si 1956; Based on outcrops (Fig. 1) and logging data (Fig. 6), the thickness BGMRSP 1989, 1998), occurs in the upper part of the Yanchang of the oil shale ranges from 0 to 61 m, with an average of c. 28 m Downloaded from http://pg.lyellcollection.org/ by guest on September 28, 2021

362 Y. L. Bai & Y. H. Ma

Fig. 6. Logging and organic geochemical profile of the Chang 7 Member oil shale in the Li 57 well, which is located in the mid-west in Figure 1a, in the SE of Huanxian County (after Yang & Zhang 2005; Wang 2007). The legend is the same as in Figure 4.

(Fig. 5). The areas with a thickness greater than 20 m are elongated relatively high, if primary, indicating that the nutrient content of the approximately NW–SE, and include Huanxian, Huchi, Qingyang lake water was relatively high, which may have been associated with and Zhengning counties and Tongchuan city (Fig. 5). The oil shale volcanism to the south of the lake: numerous tuff layers are present is thin at the edge of the basin and thickest in the central part where it in the oil-shale seams. is more than 40 m in thickness near Huanxian County and more than M (M = 100 × MgO/Al2O3) values of the shale could reflect the 20 m thick to the NW of Tongchuan city (Fig. 5). salinity of the lake water and the provenance; in general, M < 1 for freshwater environments, 1 < M < 10 for transitional environments, 10 < M < 500 for marine environments and M > 500 for epicontin- Petrological and geochemical characteristics ental seas or lagoons (Liu 1984). M = 6.1 for the oil shale indicates Petrological characteristics a transitional brackish water environment. However, numerous specimens of Leiosphaeridia and Micrhystridium are preserved, The oil shales have a dark, greasy lustre with a maroon-coloured which indicates that the lake was primarily freshwater (Ji et al. surface resulting from oxidation (Fig. 7). The fresh oil shales have a 2006). The Sr/Ba ratios cited below also support this conclusion. flakey, banded structure, uneven conchoidal fractures, low hardness The sum of SiO and Al O reaches 63.69% of the whole-rock and light brown streak. 2 2 3 chemical composition, indicating a continental deposition. This The main components of the oil shale, by average, are 49% clays, corresponds to a siliceous ash on combustion (the criteria for siliceous 29% quartz, 16% feldspars and iron oxides. The composition falls ash-type oil shale are SiO (40–70 wt%), Al O (8–50 wt%), Fe O within the muddy shale area in the shale classification scheme of 2 2 3 2 3 (<20 wt%) and CaO (1.20 wt%), (Zhao et al. 1991). The oil shales Kuila & Prasad 2012 (Fig. 8). Carbonate minerals are rare. Clay are slightly lower in SiO and Al O than that of the Tertiary oil minerals comprise mainly mixed-layer illite and smectite, followed 2 2 3 shales of the Fushun Basin, which consist of 61.59 wt% SiO and by illite and chlorite, and are partially affected by sericitization. The 2 23.36 wt% Al O (Yuan et al. 1979; The Office of the National clastic minerals are mainly quartz, followed by feldspars (Bai et al. 2 3 Committee of Mineral Reserves 1987), indicating that the latter have 2009, 2010b). Iron oxides and organic matter fill the pore spaces a more obvious continental deposition (Zhao et al. 1991). between the clay minerals (Fig. 9a). The diameters of the detrital Oil-shale fusibility can be expressed by (SiO +Al O )/(Fe O + mineral grains vary from 0.03 to 0.06 mm (i.e. silt), occasionally up 2 2 3 2 3 CaO + MgO) values, which are <5 for fusible ash, 5–9 for medium to 0.15 mm, Sand-size mineral grains are angular, subangular and fusion ash and >9 for refractory ash (Zhao et al. 1991). Because the rounded, and consist of quartz and feldspar (Fig. 9b); indicating a (SiO +Al O )/(Fe O + CaO + MgO) value for the oil shales is proximal provenance trait. 2 2 3 2 3 5.87, it belongs to a medium fusion ash.

Chemical composition characteristics The average chemical composition of the oil shale is shown in Trace element characteristics Table 1. Compared with ‘North American shale composite’ The average trace element concentrations of the oil shale are given (NASC) (Gromet et al. 1984), the oil shale has higher P2O5 and in Table 1. Both Mn and Ni have enrichment coefficients (relative to Fe2O3; lower CaO, SiO2 and MgO; slightly lower Na2O and K2O; NASC according to Gromet et al. 1984; see below) of less than 0.5; and similar Al2O3 and TiO2. Ba, Zr, Rb, Cr, Co and Th have coefficients ranging from 0.5 to 1; The concentrations of CaO, SiO2 and MgO in the oil shale are Sr, V and Zn have coefficients ranging from 1 to 1.5; Pb has a relatively low, which indicates limited terrigenous matter input into coefficient of 1.7; and Cu has a coefficient 3.02. Both Mo and U are the lake. The concentrations of P2O5 and Fe2O3 in the oil shale is very strongly enriched. The strong enrichment of U, Mo, Cu and Pb, Downloaded from http://pg.lyellcollection.org/ by guest on September 28, 2021

Ordos oil shale 363

Fig. 7. Examples of outcrops and specimens of the Chang 7 Member oil shale in the Ordos Basin: (a) Hejafang village oil shale (mining face of oil shale in 1960); (b) Bawangzhuang village oil shale (note the layer structure); (c) Jinsuoguan town oil shale (note the oil-shale layers interbedded with a thin layer of greyish-buff tuff); and (d) Bawangzhuang oil-shale specimen (note the maroon colour of the surface of oil shale after weathering). The locations of these outcrops are shown in Figure 1a. if primary, shows that the lake was rich in organic nutrients. sedimentary rocks. Thus, their concentration could be used to The eutrophic lake water would have enhanced the productivity, reconstruct the redox of the original water (Liu 1984; Tribovillard promoting algal booms and, at the same time, resulting in anoxia et al. 2006). Because of fine particles, compacting construction and of the water. The enrichment of U, Mo, Pb and Cu is a positive very low porosity of the oil shale, the concentration and ratios of relationship with TOC (Zhang et al. 2008b). some major and trace elements are very small change in the The Sr/Ba ratio of a shale, if primary, is proportional to the diagenetic alteration, and could be used to indicating sedimentary salinity of water; Sr/Ba >1 indicates a marine or saline lake environment (Liu 1984). environment, 0.5 < Sr/Ba < 1 indicates brackish water and Sr/Ba < 0.5 indicates freshwater (Liu 1984). The Sr/Ba ratio of 0.33 in the oil shale indicates that the lake was a freshwater environment. Rare earth element characteristics The Mn content of lake water is positively correlated with water The amount of REE in the oil shales is slightly higher than the depth. The Mn abundance is about 10 ppm for lake shore, about average amount of REE (146.4 ppm) in the upper crust and slightly 60 ppm for shallow lakes and about 400 ppm for semi-deep lakes to lower than that (197 ppm) in NASC (Gromet et al. 1984) deep lakes (Liu 1984). The 313 ppm Mn of the Chang 7 Member oil (cf.Table 1; Figure 10). Fu & Qi (1995) showed that the amount shale indicates a semi-deep to deep lake environment. of both REE and TOC in the deposits of the warm, damp, climate The geochemical behaviour of the variable valence elements V environments is, generally, higher than that in arid and cold climate and U is closely related to the sedimentary redox environment. In a environments. The amount of REE is relatively high in the oil shale, reducing environment, V and U have a low valency, are less soluble which shows that the warm and damp climate prevailed during the and are readily enriched, so that the ratios of V/Ni, V/Cr and U/Th middle Triassic, favouring biological productivity. are often used as redox indicators (Lewan & Maynard 1982). The oil The REE distribution patterns of the oil shales are characteris- shale has a V/Ni ratio of 7.8 and a U/Th ratio of 4.8, indicating a tically rich in LREEs (light REE) and have a weakly negative Eu strongly reducing environment. anomaly, similar to that of the upper crust (Fu & Qi 1995), which The Sr/Cu ratio is climatically related. A Sr/Cu ratio of 1.3–5.0 suggests the degree of differentiation of REE is relatively high and indicates a warm and humid climate; a ratio value of >5 indicates a the deposition rate is relatively low in the lake, which favoured hot, dry climate; and a ratio of <1.3 indicates a cold, humid climate enrichment in organic matter (Fu & Qi 1995). (Liu 1984). The Sr/Cu ratio of the oil shale is about 2, indicating a In sedimentary systems, the Ce anomaly may reflect changes in warm, humid climate. the redox conditions in water, Ceanom = lg [3Cen/(2Lan +Ndn)] (the Redox conditions in the original water settings controlled the subscript n is standardized values for NASC). Ceanom > −0.1 concentrations of some major and trace elements in sediments and reflects a reducing water body and Ceanom < −0.1 reflects an Downloaded from http://pg.lyellcollection.org/ by guest on September 28, 2021

364 Y. L. Bai & Y. H. Ma

Fig. 8. Shale mineral composition triangular diagram showing the Chang 7 Member oil shale characteristic composition (modified and supplemented after Kuila & Prasad 2012). The square symbol shows the location of the average mineral composition of global shale regardless of the content of organic matter, which indicates that the global shale generally has a higher clay mineral content, but less quartz and feldspar content, and almost no calcite and dolomite content. The two ellipses indicate the range of the Green River oil shale: the right ellipse is the distribution area of the Parachute Greek oil shale, which is shown as black squares; and the left ellipse is the distribution area of the Garden Gulch oil shale, which is shown as circles. The black rhombus is the location of the shales coming from all around the world and the triangle is the location of the Ordos Triassic oil shale. oxidized water body (Fu & Qi 1995). The oil shale has Ce anomaly composed of saturated hydrocarbon, aromatic hydrocarbon, gum greater than −0.1 (Ma et al. 2016). and asphaltene; generally, chloroform bitumen ‘A’ is the ratio of the The oil shales have very similar REE characteristics to chondrite extracted bitumen mass to the mass of rock sample), a hydrocarbons distribution patterns among the different samples (Fig. 10). The content of 0.3–0.6 wt% and a pyrolytic hydrocarbon-generation coherence of the REE distribution patterns indicates a consistent potertial (S1 +S2) content of about 70 mg HC/g rock (Table 2). The provenance. yield of the oil shale is up to 400 mg HC/g rock. IH has two interval values (bimodal) of 200–300 and 600–650 mg HC/g TOC, and IO Organic geochemistry characteristics also has two interval values, <5 and 50–100 mg CO2/g TOC (Yang The oil shale has a high residual organic matter content, with an & Zhang 2005; Ma et al. 2016), which suggest that the kerogens average TOC content of 18 wt% (Table 2). The main component come from a variety of sources.The residual ‘chloroform bitumen (kerogen) of the organic matter has reached maturity, with a Ro A’ conversion rates (A/TOC) are 3.14–9.84 and the hydrocarbon value of 0. 9−1.15% (Tmax = 445–455°C), a residual chloroform conversion rates (HC/TOC) are 2.11–5.77 (Yang & Zhang 2005). bitumen ‘A’ content of 0.1–0.4 wt% (chloroform bitumen is a The hydrocarbon-expulsion efficiency reaches an average of 72% soluble organic matter in rocks that can be dissolved in chloroform, (Mu et al. 2001; Yang & Zhang 2005; Zhang et al. 2006, 2008b).

Fig. 9. The characteristics of the oil shale under a light microscope (after Bai et al. 2009, 2010b). (a) Remaining argillaceous texture, slab structure, weak sericitization (perpendicular polarized light). (b) Angular, subangular and rounded silt-sized mineral grains (feldspars) (perpendicular polarized light). Downloaded from http://pg.lyellcollection.org/ by guest on September 28, 2021

Ordos oil shale 365

Table 1. Major, trace and rare-earth element analyses from the Chang 7 Member oil shale

Chang 7 Member Trace Chang 7 Member Oxide oil shale (average, elements oil shale (average, Rare-earth Chang 7 Member oil (wt%) N = 54)1 NASC2 (ppm) N = 43)3 NASC4 elements (ppm) shale (average, N =8)5 Chondrite6 NASC7

SiO2 48.69 58.10 Mn 313.0 922.0 La 31.0 0.3 32.0 Al2O3 14.40 15.40 Sr 197.0 142.0 Ce 56.0 1.0 73.0 TiO2 0.51 0.65 Ba 593.0 636.0 Pr 6.5 0.1 7.9 Fe2O3 8.54 4.02 V 176.0 130.0 Nd 24.0 0.7 33.0 MgO 0.97 3.44 Zr 132.0 200.0 Sm 4.4 0.2 5.7 CaO 1.14 3.11 Rb 121.0 125.0 Eu 0.9 0.1 1.2

Na2O 0.96 1.30 Cu 98.0 32.4 Gd 3.9 0.3 5.2 K2O 2.72 3.24 Pb 34.5 20.0 Tb 0.6 0.1 0.85 FeO 4.00 3.24 Zn 74.5 70.0 Dy 3.6 0.9 5.8

P2O5 0.30 0.17 Cr 65.2 125.0 Ho 0.8 0.1 1.0 Ni 22.5 58.0 Er 2.3 0.3 3.4 Co 17.1 26.0 Tm 0.4 0.1 0.5 Mo 59.1 3.1 Yb 2.5 0.2 3.1 U 31.9 3.0 Lu 0.4 0.1 0.48 Th 6.6 12.3 Y 23.0 1.9 24.0 ∑REE 160.5 160.5 197.0

N, number of samples. 1Chang 7 Member oil shale (N = 54) data were compiled from Miao et al. (2005), Changqing Oilfield Company, PetroChina (2008), Bai et al. (2009), Zhang et al. (2013), Sun et al. (2015) and Wang et al. (2016). 2NASC according to Gromet et al. (1984). 3Chang 7 Member oil shale (N = 43) data were compiled from Miao et al. (2005), Zhang et al. (2008a, b), Bai et al. (2009), Zhang et al. (2013), Sun et al. (2015) and Ma et al. (2016). 4NASC according to Gromet et al. (1984). 5Chang 7 Member oil shale (N = 8) data were compiled from Bai et al. (2009) and Ma et al. (2016). 6Chondrite according to Taylor & Melennan (1985). 7NASC according to Gromet et al. (1984).Analytical methods: the analytical method for major elements uses X-ray fluorescence (XRF) in different laboratories following Chinese standards GB/T 14506.14-2010 (AQSIQ & SAC 2010c) and GB/T 14506.28-2010 (AQSIQ & SAC 2010b); the analytical method for microelements uses XRF and inductively coupled plasma mass spectrometry (ICP-MS) following Chinese standard GB/T 14506.30-2010 (AQSIQ & SAC 2010a); and the analytical method for rare earth elements uses XRF and ICP-MS in different laboratories following Chinese standard GB/T 14506.30-2010 (AQSIQ & SAC 2010a).

The kerogens mainly consist of amorphous lipids, with a few & Zhang 2005; Ji et al. 2007; Ma et al. 2016). The high residual Hystrichosphaera and spores, and are characterized by a uniform, organic matter content, good-quality kerogens with 0.9–1.05% Ro monotonous biological component (Mu et al. 2001; Yang & Zhang but low (S1 +S2) values (Table 2) indicate that the oil shales (source 2005; Ji et al. 2007). They lack aryl isoprenoid alkane complexes, rocks) underwent strong hydrocarbon expulsion, and a low ratio of which shows that the kerogens are mainly derived from algal saturated hydrocarbon/aromatic hydrocarbon (SH/AH of 0.86–3.0) material of lacustrine origin, of the I–II1 type (Mu et al. 2001; Yang also suggests this (Yang & Zhang 2005).

Fig. 10. Chondrite-normalized REE distribution patterns of the Chang 7 Member oil shale. Downloaded from http://pg.lyellcollection.org/ by guest on September 28, 2021

366 Y. L. Bai & Y. H. Ma

Table 2. Proximate and organic matter analysis from the Chang 7 Member oil shale

Proximate analysis1 items Chang 7 Member oil shale2 (average, N = 35) Organic matter abundance analysis items3 Chang 7 Member oil shale4 (average) Oil yield (wt%)/ 8.00 TOC (wt%) 17.76 (N = 72) −1 – Qnet,v,ar (MJ kg ) 8.35 Chloroform bitumen A (wt%) 0.4 1 Ad (wt%) 69.24 S1 (mg HC/g rock) 3.06 (N = 41) St,d (wt%) 4.69 S2 (mg HC/g rock) 60.51 (N = 40) Mt (wt%) 3.37 S3 (mg CO2/g rock) 7.78 (N = 41) Vdaf (wt%) 68.16 S1 +S2 (HC/g rock) 70.00 (N = 76) Cad (wt%) 19.08 IH (mg/g) 407.80 (N = 434) Had (wt%) 2.13 IO (mg/g) 63.39 (N = 19) − ARD (g cm 3) 1.77

N, number of samples. 1 Proximate analysis: Qnet,v,ar, net calorific value at constant volume; Ad, ash content (dry basis); St,d, sulphur content(dry basis); Mt, total moisture; Vdaf, volatile (dry ash-free basis); Cad, carbon (air dry basis); Had, hydrogen (air dry basis); ARD, apparent density. 2Chang 7 Member oil shale data were compiled from Lu et al. (2006), Zhang et al. (2006), Ren (2007), Changqing Oilfield Company, PetroChina (2008), Bai et al. (2009) and Zhang et al. (2013).Analytical methods: the analytical method for the oil yield uses Gray–King low-temperature distillation in different laboratories following Chinese standard GB-T 1341- 2007 (AQSIQ & SAC 2007); the analytical method for ash yield uses the fast ashing method in different laboratories following Chinese standard GB/T 212-2008 (AQSIQ & SAC 2008a); and the analytical method for calorific value uses the environmental isothermal automatic oxygen bomb calorimeter in different laboratories following Chinese standard GB/T 213-2008 (AQSIQ & SAC 2008b).3Organic matter abundance analysis: TOC (total organic carbon) is the content of residual organic matter in oil shale (%); chloroform bitumen ‘A’

(%) is the ratio of the extracted bitumen mass to the mass of rock sample; S1 is the content of soluble hydrocarbon in oil shale (mg HC/g rock); S2 is the content of pyrolytic hydrocarbon in oil shale (mg HC/g rock); S3 is the content of pyrolytic carbon dioxide in oil shale (mg CO2/g rock); S1 +S2 is the potential amount of hydrocarbon generation (mg HC/g rock); ¼ = IH =QHC/COT × 100 and IO QCO2 COT 100 (where QHC is hydrocarbon from kerogen pyrolysis and extractable hydrocarbon components; COT is total organic carbon; and

QCO2 is the amount of CO2).Analytical methods: the analytical method for total organic carbon (TOC) uses the Carbon/Sulfur Determinator in different laboratories following Chinese standards GB/T 19145-2003 (AQSIQ & SAC 2003); the analytical method for chloroform bitumen A analysis uses Soxhlet extraction equipment in different laboratories following the enterprise standard of CN-PC SY/T5118-2005 (NDRC 2005); and the analytical method for rock pyrolysis analysis uses Rock-Eval pyrolysis apparatus in different laboratories – 4 following Chinese standard GB/T 18602-2012 (Tmax = 425 450°C) (AQSIQ & SAC 2012). Chang 7 Member oil shale data were compiled from Yang & Zhang (2005), Ren (2007), Changqing Oilfield Company, PetroChina (2008), Bai et al. (2009), Zhang et al. (2013), Ma et al. (2016) and Yang et al. (2016b).

The Chang 7 Member oil shale kerogen and ‘chloroform calorific value at constant volume) and an apparent specific gravity bitumen’ are enriched in the light carbon isotope 12C. The of 1.79 (Table 2). kerogen and ‘chloroform bitumen’ have a limited range of δ13C The grade of oil shale can be divided into three types by oil yield values, which are −30.00 to −28.5 and −33.00 to 32.2‰ (Yang & of oil shale (dry basis), which is, respectively, low (3.5 wt% < oil Zhang 2005), respectively, which shows that the kerogen formed in yield ≤ 5 wt%), medium (5 wt% < oil yield ≧ 10%), and high a terrestrial, freshwater to low-salinity water body. grades (oil yield >10 wt%) (Liu et al. 2009). The oil shale is Gas chromatography shows that the saturated hydrocarbon medium quality. chromatogram is of unimodal type, and the main carbon peak is The calorific value is useful for determining the quality of oil nC16–nC19, showing an odd–even equilibrium with an OEP (odd– shale that is burned directly in a power plant to produce electricity. even performance) of 0.95–1.21. Pr/Ph is 0.56–1.17, Pr/nC17 is The calorific value of a given oil shale is a useful and fundamental 0.11–0.33 and Pr/nC18 is 0.16–0.40, which also indicates a reducing property of the rock, although it does not provide information environment. The low Pr/Ph, lower Pr/nC17 and Pr/nC18 ratios on the amounts of shale oil or combustible gas that would be indicate that the sedimentary environment was a deep reducing yielded by retorting (destructive distillation). The oil shale is water body, and the source of the organic material was primarily high grade compared with other Chinese oil-shale deposits, lower aquatic organisms; in addition, it has reached the peak of the which have average calorific values of 5.7 MJ kg−1 (Fushun), oil source mature phase (Yang & Zhang 2005; Zhang et al. 2006; 7.3 MJ kg−1 (Maoming), 7.0 MJ kg−1 (Yaojie), 3.6 MJ kg−1 Ji & Xu 2007; Ji et al. 2007). (Nongan), 4.2 MJ kg−1 (Dongsheng), 6.6 MJ kg−1 (Huadian) and −1 Hopane is composed primarily of C30αβ. The content of 4.2–5.0 MJ kg (Guyang), respectively (Zhao et al. 1991; Liu gammacerane and tricyclic terpane is low, and the content of Ts et al. 2009), but it is low grade compared with the high-grade is high. Sterane is given priority to with regular Sterane, with kukersite oil shale of Estonia, which fuels several electric power −1 preponderant C29, slightly low C28,lowC22, and a high content of plants and has a calorific value of about 10.03–12.62 MJ kg on a diasteranes. Both a low content of gammacerane and a high content dry-weight basis (Dyni 2006a, b). The higher calorific value are of diasteranes indicate that the oil shale formed in a low salinity linked to the higher oil yields, TOC and lower Ad (ash content, dry sedimentary environment (Yang & Zhang 2005). basis) in the oil shale (Fig. 11a–c). The oil shale averages 69 wt% ash yield (dry basis): a high ash Quality type (Zhao et al. 1991; Liu et al. 2009). The higher ash yield is linked to the lower calorific value and oil yield (Fig. 11b and d). Oil yield and calorific value are the most common parameters for Considering the above data of the oil shale fusibility, it is a medium evaluating oil shales (Yuan et al. 1979; Smith 1980; The Office of fusion, high ash type. the National Committee of Mineral Reserves 1987; Zhao et al. The data analysis indicates that there is an obvious positive 1991; Zhao & Liu 1992; Guan et al. 1995; Dyni 2006a, b; Liu et al. correlation between the oil yields and Cad (carbon, air dry basis) 2006, 2009). The oil yield of the oil shale was measured by the (Fig. 10e). The higher the total sulphur content, the greater the Gray–King low-temperature dry distillation assay method following potential environmental pollution in oil-shale utilization. Oil shale Chinese standard methods (GB/T 1341-2007) (AQSIQ & SAC can be divided into five levels: ultra-low sulphur (≤1.0 wt%), low 2007), and the calorific value of the oil shale was measured by sulphur oil shale (1.0−1.5 wt%), medium sulphur (1.5–2.5 wt%), isothermal oxidation bomb calorimetry following Chinese standard rich sulphur (2.5–4.0 wt%) and high sulphur (>4.0 wt%) methods GB/T 213-2008 (AQSIQ & SAC 2008a, b). (The Office of the National Committee of Mineral Reserves Based on our own and previously published data, the oil shale has 1987). The total sulphur is 4.69 wt%: indicating a high sulphur an average oil yield of 8 wt%, a calorific value of 8.35 MJ kg−1 (net oil shale. Downloaded from http://pg.lyellcollection.org/ by guest on September 28, 2021

Ordos oil shale 367

Fig. 11. The relationships between key parameters of the Chang 7 Member oil shale. Qnet, v, ar, net calorific value at constant volume; Ad, ash content, dry basis; Cad, carbon, air dry basis.

Oil shale can be divided on moisture content into high samples is very obvious (Fig. 11f), but there is no obvious moisture content (Mt of 20–30 wt%), medium moisture content correlation between TOC and (S1 +S2). (Mt of 10–20 wt%), low moisture content (Mt of less than 10 wt%) The average content of Cad (carbon, air dry basis) and Had (The Office of the National Committee of Mineral Reserves (hydrogen, air dry basis) in the oil shale are, respectively, 19.08 and 1987).The oil shale has Mt of 3.37 wt%: a low moisture content 2.13 wt% (Table 2), so an average H/C ratio of 1.4 is obtained. Ma oil shale. et al. (2016) pointed out that the oil shale has average H/C and O/C The oil shale has an average density of 1.77 kg m−3, which is ratios of 1.34 and 0.1, respectively. Therefore, the organic matter of quite high, related to the higher silicon and aluminum components; the oil shale belongs to Type I and II1. Tissot & Welte (1978) stated this means a lower oil yield per tonne. that the Type I kerogen has a H/C ratio of >1.5, a O/C ratio of <0.1. The oil shale has an average Vdaf (volatile, dry ash-free basis) of and the precursors of the kerogen are mainly from marine or 68 wt%, which is also quite high, reflecting the relatively high continental deep-water lake algae and bacteria; the Type II kerogen metamorphic grade and relatively high organic matter content of has a H/C ratio of 1.0–1.5, a O/C ratio of 0.1–0.2, and the precursors the shale (Liu et al. 2009). of the kerogen are mainly from continental deep-bathyal lake spores The average TOC of the oil shale is high (Table 2). The and pollen, plankton, micro-organisms, and other mixed organic correlation between the TOC and oil yield in the outcrop oil shale matter; and the Type III kerogen has has a H/C ratio of <1.0, a O/C Downloaded from http://pg.lyellcollection.org/ by guest on September 28, 2021

368 Y. L. Bai & Y. H. Ma ratio of >0.2 and the precursors of the kerogen are mainly from and Pr/nC18 also indicate that the lake was a strongly reducing terrestrial higher plants. Based on content of Cad and Had, and the environment. H/C and O/C ratios in the oil shale, the organic matter is mainly The lake where the oil shale formed may have been a freshwater derived from lacustrine algae, spores and pollen. Thus, ‘carbon’ in to brackish water environment. The Sr/Ba ratio indicates that the the organic matter of the oil shale is unlikely to have been derived lake was a freshwater lake, but the M value of the oil shale indicates from seawater or carbonate minerals, with a probable lake water a transitional brackish water environment. Both the low content of origin. gammacerane and high content of diasteranes also indicates that the oil shale formed in a low-salinity sedimentary environment (Yang Origin & Zhang 2005). The Sr/Cu ratio indicates a warm, humid climate. Classification of the Ordos Basin oil shale Recent research shows that the sapropel group in the kerogens in Oil shales can be classified by their depositional environment (e.g. the Chang 7 Member oil shale contains abundant Leiosphaeridia, large lake, shallow marine, deltaic and lagoonal/small lake settings) which is multicellular macro red algae and/or chlorophytes, rooted (Carman & Bayes 1961; Surdam & Wolfbauer 1975; Yuan et al. in the lacustrine macroscopic algae, fomed in a freshwater 1979; Macauley 1981; Boyer 1982; Francis & Miknis 1983; Hutton environment, different to the Proterozoic and Paleozoic 1987; Brendow 2003; Altun et al. 2006; Dyni 2006a, b; Ots 2007; Leiosphaeridia which is commonly thought as a marine unicellular Lu et al. 2006; Durham 2010). Oil shales of great lakes have large phytoplankton (Ji & Xu 2007; Ji et al. 2007). Although thicknesses and areas, and are of good quality. A typical example is Leiosphaeridia is abundant in the area, it is not only monotone in the Green River oil shale in the NW USA, which is black in colour species but also conspicuous in echinulate process, suggesting that with a thickness of several hundred metres, and with an oil yield of some marine acanthomorphic acritarches survived in freshwater and generally <15 wt% (Surdam & Wolfbauer 1975; Smith 1980; Boyer had experienced long-term evolution. Therefore, the sedimentary 1982; Dyni 2006a, b). environment of the Chang 7 Member oil shale is a lacustrine Shallow sea and continental shelf oil shales are generally much environment, which turned into the climax of lake transgression in thinner than the large lake deposits, and are associated with the Chang 7 sedimentary interval, indicating the supply of a large- carbonates, siliceous and phosphatic facies. They do not exceed scale lake water body that came from rivers rather than from a rise in 2–3 m in thickness and are distributed over very large areas, up to sea level (Ji & Xu 2007; Ji et al. 2007). thousands of square kilometres (Hutton 1987). They are black to The limited range of δ13C values of ‘chloroform bitumen’ shows light brown in colour with a high oil yield (c. 20 wt%). A typical that the kerogen formed in a deep, reducing, low-salinity water body. example is the Kukersite oil shale of Ordovician age in Estonia, Considering that the composition of the kerogen is monotonous, it is which is in a single calcareous layer, 2.5–3 m in thickness, with an conjectured that the water body of the Ordos Basin was indistinctly average oil yield of 20 wt%. Most of the organic matter is derived stratified (Yang & Zhang 2005). A low gammacerane content and from green algae (Hutton 1987). the absence of aryl isoprenoid compounds in the kerogen structure of Oil shales deposited in lagoonal or small lake environments are the oil shale also indicate that the lake basin was not significantly rarely extensive and are often associated. Despite having a high oil delaminated (Zhang et al. 2008b). Both the low content of yield, they are thin and are unlikely candidates for commercial gammacerane and the high content of diasteranes indicate that the exploitation. A typical example is the Yaojie oil shale of Jurassic oil shale formed in a low-salinity sedimentary environment (Yang & age in NW China, which is black in colour, 4–11 m thick, with an Zhang 2005). The Pr/Ph, Pr/nC17 and Pr/nC18 ratios also indicate a oil yield of 4.6–8.9 wt%, and most of the organic matter is derived reducing deep-water environment within which the biological from macrophytes (Bai et al. 2010b). source material was dominated by lower aquatic organisms (Yang The Chang 7 Member oil shale formed in a larger-scale lake & Zhang 2005; Ji & Xu 2007; Ji et al. 2007). setting. The ‘Ordos Lake’ itself covers an area of 400 000 km2 with To sum up, the Ordos Basin oil shale formed in a deep-water a maximum water depth of about 60 m (Yang et al. 2016a) during reducing environment with a warm, humid climate context. The lake the middle Triassic, resembling the Green River oil shale (Surdam may have been freshwater or brackish water and was indistinctly & Wolfbauer 1975; Smith 1980; Boyer 1982; Dyni 2006a, b). The stratified. The biological source material was dominated by lower oil shale covers an area of around 30 000 km2, has an average aquatic organisms. thickness of 28 m and an average oil yield of 8 wt%. The Chang 7 Member oil-shale clay mineral content of 49% is Volcanism in the Ordos area similar to the composition of the Darden Gulch oil-shale seam of the Green River, which has a clay mineral content of 40–70%. The andesitic–dacitic tuff interbeds in the Chang 7 Member oil- However, it differs from the Kukersite oil shale in Estonia, which shale seams and the Yanchang Formation (Fig. 7c) indicate its has a clay mineral content of only 13.9% and a carbonate mineral formation close to a volcanic arc, and that the lake was a relatively content of 56.1% (Hutton 1987). high-energy environment. In addition, the sandstone types in the The relatively low concentration of CaO, SiO2 and MgO, and upper and lower host layers of the oil-shale seams are mostly the relatively high concentration of P2O5 and Fe2O3 and MgO/ feldspar quartz sandstone and arkose, also indicating a relatively Al2O3 ratio show that the lake was a coastal lake, lacked high-energy environment. The Ordos Basin was not a stable significant terrigenous matter inputs and that the lake water had intracratonic basin (Yang 2002), and was subject to relatively a high nutrient content. The coherence of the REE distribution energetic sedimentary processes. Moreover, the angular sandy patterns among the different samples indicates a consistent debris grains suggest a proximal provenance (Fig. 9b). provenance. The Pr/Ph, Pr/nC17 and Pr/nC18 ratios also As stated above, the Ordos Lake was a reducing sedimentary indicate that the biological source material is dominated by environment; however, the atmospheric oxygen level was not low at lower aquatic organisms (Yang & Zhang 2005; Ji & Xu 2007; the time of the oil-shale formation and questions arise regarding the Ji et al. 2007). origin of the reducing lake environment. Multiple layers of andesitic The oil shale formed in a reducing environment. Its surface is acid tuff (Figs 4 and 7c) are present in the Yanchang Formation and maroon after oxidation, indicating enrichment in Fe2+, and thus a the oil-shale seams; therefore, it is possible that their deposition was deep-water reducing environment. Pb, Cu, Mo and U are stronly to some extent responsible for the reducing conditions in the lake enriched, the the ratios of V/Ni, U/Th, FeO/Fe2O3, Pr/Ph, Pr/nC17 basin. There may have been a catastrophic death of organisms due to Downloaded from http://pg.lyellcollection.org/ by guest on September 28, 2021

Ordos oil shale 369 ash falls, which may be the main reason why organic matter was AQSIQ & SAC. 2003. Determination of Total Organic Carbon in Sedimentary enriched in the lake. At the same time, the tuff layers also provided Rock. GB/T 19145-2003. General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China (AQSIQ) & nutrients for the next cycle of oil-shale formation (Yang & Zhang China Standardization Administration Commission, Standardization 2005). Administration of the People’s Republic of China (SAC). Standards Press of China, Beijing. AQSIQ & SAC. 2007. Gray–King Assay of Coal. GB/T1341-2007. General Marine facies or lacustrine facies? Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China (AQSIQ) & China Standardization It is problematic that recently one paper proposed that the Chang 7 Administration Commission, Standardization Administration of the People’s Member oil shale in the Ordos Basin was deposited in a marine Republic of China (SAC). Standards Press of China, Beijing. AQSIQ & SAC. 2008a. Proximate Analysis of Coal. GB/T212-2008. General intrusion (Wang et al. 2017). Their evidence is a typical marine Administration of Quality Supervision, Inspection and Quarantine of the coelacanth fossil with a rounded tail that was found in the late People’s Republic of China (AQSIQ) & China Standardization Triassic stratum in the Huachi County area; a broken marine Administration Commission, Standardization Administration of the People’s coelacanth fossil was discovered in Tongchuan city area about Republic of China (SAC). Standards Press of China, Beijing. AQSIQ & SAC. 2008b. Analytical Method for Calorific Value of Coal. GB/T213- 20 years ago by Liu et al. (1999). The research shows that these 2008. General Administration of Quality Supervision, Inspection and marine organisms actually belong to a ‘terrestrial organism with sea Quarantine of the People’s Republic of China (AQSIQ) & China origin’ rather than a marine organism (Liu et al. 1999; Wang 1995), Standardization Administration Commission, Standardization Administration of the People’s Republic of China (SAC). Standards Press of China, Beijing. and the terrestrial organism with a sea origin represents the survival AQSIQ & SAC. 2010a. Methods for Chemical Analysis of Rocks – Part 30: of early marine creatures in the lake and does not represent a Determination of 44 Elements. GB/T14506.30-2010. General Administration seawater intrusion. In combination with the geochemical evidence of Quality Supervision, Inspection and Quarantine of the People’s Republic of described above (Sr/Ba ratio of 0.33), it is proposed that the Chang 7 China (AQSIQ) & China Standardization Administration Commission, Standardization Administration of the People’s Republic of China (SAC). Member oil shale in the Ordos Basin was principally deposited in a Standards Press of China, Beijing. freshwater or brackish water body, neither marine environment nor AQSIQ & SAC. 2010b. Methods for Chemical Analysis of Rocks – Part 28: salinized lake. Determination of 16 Major and Minor Elements Content. GB/T14506.28- 2010. General Administration of Quality Supervision, Inspection and In fact, the North China Plate, including the Ordos Basin, suffered Quarantine of the People’s Republic of China (AQSIQ) & China the subduction of the Qinling oceanic plate in the middle–late Standardization Administration Commission, Standardization Administration Triassic, resulting in a decline in sea level; in such a tectonic setting, of the People’s Republic of China (SAC). Standards Press of China, Beijing. AQSIQ & SAC. 2010c. Methods for Chemical Analysis of Silicate Rocks – Part how did seawater rise over the island arc belt and invade the area? 14: Determination of Ferrous Oxide Content. GB/T 14506.14-2010. General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China (AQSIQ) & China Standardization Conclusion Administration Commission, Standardization Administration of the People’s Republic of China (SAC). Standards Press of China, Beijing. Oil-shale resources are abundant in the Ordos Basin in central north AQSIQ & SAC. 2012. Rock Pyrolysis Analysis. GB/T 18602-2012. General China. There are multiple oil-shale seams in the basin, but the Administration of Quality Supervision, Inspection and Quarantine of the Chang 7 Member oil-shale seam is the main oil shale seam (MOSS), People’s Republic of China (AQSIQ) & China Standardization Administration ’ with a thickness of 28 m and an area of around 30 000 km2. The oil Commission, Standardization Administration of the People s Republic of China (SAC).Standards Press of China, Beijing. shale is usually found in layers developed at the top of the lower part Bai, Y.L., Wang, X.M., Liu, H.Q. & Li, T.S. 2006. Determination of the of the Yanchang Formation of middle Triassic (Ladinian) age. The borderline of the western Ordos Basin and its geodynamics background. Acta Yanchang Formation was deposited in a great lake in the middle– Geolodica Sinica, 80, 702–813 [in Chinese with English abstract], http:// – www.geojournals.cn/dzxb/ch/index.aspx late Triassic (Ladinian Norian). The oil shale is mainly brown- Bai, Y.L., Ma, L. & Wu, W.J. 2009. Geological characteristics and resource black to black in colour, of a medium ash type with a TOC of 18 wt potential of oil shale in the Ordos Basin. Geology in China, 36, 1123–1137 [in %, an oil yield of 8 wt%, a calorific value of 8.35 MJ kg−1, and a Chinese with English abstract], http://geochina.cgs.gov.cn/geochina/ch/ reader/create_pdf.aspx?file_no=20090516&flag=1&year_id=2009&quarter_ relatively high P2O5 and Fe2O3 content. It is strongly enriched in – id=5 Mo, U and LREE, and is kerogen type I II1. Volcanism may have Bai, Y.L., Zhao, Y.C., Ma, L., Wu, W.J & Ma, Y.H. 2010a. Geological favoured the formation of the oil shale. The oil shale formed in a Characteristics and Resource potentials of Oil Shale in Ordos Basin, Center large, deep to moderately deep lake, the Ordos Lake, with a China. In: In: World Energy Congress 2010, Montreal, Quebec, Canada 12– 16 September 2010. World Energy Council (WEC), London. low input of terrigenous material but abundant algal growth. The Bai, Y.L., Zhao, Y.C. & Xu, D. 2010b. Geological characteristics and developing water is freshwater or brackish and strongly reducing. The tectonic prospecting of oil shale in Tongchuan–Huangling district, Shaanxi Province, context of the lake is a back-arc basin which was formed by the China. Geoscience, 24, 158–165 [in Chinese with English abstract]. Bai, Y.L., Tang, H. & Yan, K. 2011. Geological characteristics and some northwards subduction of the Qinling oceanic lithosphere beneath problems in development for oil shale in northwest China. Oil Shale, 28, the southern margin of the Ordos Kratogen during the middle–late 380–397, https://doi.org/10.3176/oil.2011.3.03 Triassic (T2–3). Bai, Y.L., Ma, Y.H., Huang, Y., Liao, J.B. & Liu, X.G. 2013. Properties of continental margin and its hydrocarbon exploration significance in Cambrian in the southern Ordos kratogen of north China. Acta Geologica Sinica (English Acknowledgements We thank Mr Yang Jie (Dean of NWGI), Prof. Edition), 87, 777–803, https://doi.org/10.1111/1755-6724.12089 Yang Hua, Prof. Wang Daxing, and senior engineers Sun Liuyi, Mao Minglu, Bai, Y.L., Ma, Y.H., Huang, Y. & Liu, X.G. 2014. On the Cambian aulacogen of Bao Hongping and Ren Junfeng for their help in this work. We thank Dr P.A.F. the southern Ordos continental margin and its hydrocarbon exploration Christie for his valuable modification advice and Professor Jan Bloemendal for implications. Natural Gas Geosciences, 25, 1706–1717 [in Chinese with his polishing of this paper. We also thank Bruce Levell, Co-Editor of Petroleum English abstract], https://doi.org/10.11764/j.issn.1672-1926.2014.11.1706 Geoscience, and two experts in the field for many good revision suggestions. Boyer, B.W. 1982. Green River laminites: Does the playa -lake model really invalidate the stratified-lake model? Geology, 10, 321–324, https://doi.org/10. 1130/0091-7613(1982)10<321:GRLDTP>2.0.CO;2 Funding This work was funded by the PetroChina Company Limited (serial Brendow, K. 2003. Global oil shale issues and perspective-Synthesis of grant number 20160821). the Symposium on Oil Shale held in Tallinn (Estonia) on 18 and 19 November 2002. Oil Shale, 20,81–92, http://www.doc88.com/ Correction notice: The spelling of Ma Yuhu's name has been corrected. p-9052394455179.html Bureau of Geology and Mineral Resources of Shaanxi Province (BGMRSP). 1989. Regional Geology in Shaanxi Province. Geological Publishing House, References Beijing [in Chinese with English abstract]. Altun, N.E., Hiçyilmaz, C., Hwang, J.Y., Suat, B.A. & Kök M.V., 2006. Oil Bureau of Geology and Mineral Resources of Shaanxi Province (BGMRSP). shales in the world and Turkey; reserves, current situation and future 1998. Multiple Classification and Correlation of the Stratigraphy of China prospects: a review. Oil Shale, 23, 211–227 https://doi.org/10.2516/ (61) – Stratigraphy (lithostratic) of Shaanxi Province. China University of ogst:2006011x Geosciences Press, Wuhan [in Chinese]. Downloaded from http://pg.lyellcollection.org/ by guest on September 28, 2021

370 Y. L. Bai & Y. H. Ma

Carman,E.P.&Bayes,F.S.1961.Occurrence, properties, and uses of some natural Liu, G.B., Zhou, Z.X. & Zhang, X.L. 1999. A coelacanthid fossil from Huach bitumens, information circular 7997. U.S. Dept. of the Interior, Bureau of Mines, area, Gansu Province. Geological Journal of China University, 5, 474–480 [in Washington, pp. 18–20. http://www.doc88. com/p-7304586824313.html Chinese with English abstract], http://geology.nju.edu.cn/CN/abstract/ Changqing Oilfield Company, PetroChina. 2008. Oil Shale in the Ordos Basin. abstract9063.shtml Changqing Institute, Xian, China [in Chinese]. Liu, S.L. 1986. The existence of a large-scale Trassic sedimentary basin in north Chen, F.Z. 2002. Metallogenic geologic prerequisites of sandstone-type China. Acta Geologic Sinica, 60, 128–138 [in Chinese with English abstract], uranium deposits and target area election: Taking Erlian and Ordos basins http://www.geojournals.cn/dzxb/ch/reader/create_pdf.aspx?file_no=19860212 as example. Uranium Geology, 18, 138–143 [in Chinese with English &flag=1&journal_id=dzxb&year_id=1986 abstract], https://wenku.baidu.com/view/f125afa433687e21ae45a948.html Liu, Y.J. 1984. Element Geochemistry. Science and Technology Press, Bejing [in Chen, Y.J. 2010. Indosinian tectionic setting, magmatism and metallogenesis in Chinese]. Qinling orogen, central China. Geology in China, 37, 854–865 [in Chinese Liu, Z.J. & Liu, R. 2005. Oil shale character and exploitation and utilization with English abstract], http://www.doc88.com/p-2963493801439.html prospect. Earth Science Frontiers, 12, 315–323 [in Chinese with English Chen, R.L., Luo, X.R., Chen, Z.K., Yu, J. & Yang, Y. 2006. Restoration of burial abstract], http://www.earthsciencefrontiers.net.cn/CN/ history of four periods in Ordos Basin. Acta Petrolei Sinica, 27,43–47 [in Liu, Z.J., Dong, Q.S. et al. 2006. The situation of oil shale resources in China. Chinese with English abstract], http://www.syxb-cps.com.cn/CN/abstract/ Journal of Jilin University (Earth Science Edition), 36, 869–876 [in Chinese abstract183.shtml with English abstract], http://xuebao.jlu.edu.cn/dxb/CN/ Deng, X.Q., Fu, J.H., Yao, J.L., Peng, J.L. & Sun, B. 2011. Sedimentary facies of Liu, Z.J., Yang, H.L. & Dong, Q.S. 2009. Oil Shale in China. Petroleum Industry the middle–upper Triassic Yanchang Formation in Ordos Basin Press, Beijing [in Chinese]. and breakthrough in petroleum exploration. Journal of Palaeogeography, Lu, J.C., Li, Y.H. & Wei, X.X. 2006. Research on the depositional environment 13, 443–456 [in Chinese with English abstract], http://manu22.magtech.com. and resources potential of the oil shale in the Chang 7 Member, Triassic cn/gdlxb/CN/abstract/abstract9145.shtml Yanchang Formation in the Ordos Basin. Journal of Jilin University (Earth Deng, S.H., Lu, Y.Z. et al. 2017. Subdivision and age of the Yanchang Formation Science Edition), 36, 928–932 [in Chinese with English abstract], http:// and the Middle/Upper Triassic boundary in Ordos Basin, North China. Science xuebao.jlu.edu.cn/dxb/CN/ China Earth Sciences, 61,1–21. https://doi.org./10.1007/s11430-017-9215-3 Ma, Z.H., Chen, Q.S., Zhong, W., Wang, C., Du, W.G. & Zhao, C.Y. 2016. Duan, Y., Zhang, H., Wu, B.X., Zheng, C.Y. & Wang, C.Y. 2004. Distribution of Geochemistry of oil shale from Chang-7 reservoir of Yanchang Formation in nitrogen compounds and migration of the oils in the Xifeng Oilfield, Ordos South Ordos Basin and its geogical significance. Geological Bulletin of Basin, NW China. Petroleum Exploration and Development, 31,17–20 [in China, 35, 1550–1558 [in Chinese with English abstract], http://dzhtb.cgs.cn/ Chinese with English abstract], http://www.cpedm.com/CN/article/open gbc/ch/reader/view_abstract.aspx?file_no=20160921&flag=1 ArticlePDF.jsp?id=905 Macauley, G. 1981. Geology of the Oil Shale Deposits Canada. Geological Durham, L.S. 2010. Bakken fractures yield the goods; oil shale takes turn in Survey of Canada, Ontario, Canada, 26–36. spotlight. AAPG Explorer, 31,34–36, http://www.aapg.Org/explorer/2010/ Miao, J.Y., Zhao, J.S., Li, W.H., Han, Z.Y. & Ma, J. 2005. Research on the 10oct/bakken1010.cfm. deposit environments about source rocks in South Ordos Basin. Journal of Dyni, J.R. 2006a. Geology and Resources of Some World Oil-Shale Deposits. Northwest University (Natural Science Edition), 35, 771–777 [in Chinese with Scientific Investigations Report 2005-5294. United States Department of the English abstract], http://mall.cnki.net/onlineview/MagaView.aspx?fn=xbdz Interior, United States Geological Survey, Reston, VA, http://pubs.usgs.gov/ 200506*1* sir/2005/5294/pdf/sir5294_508.pdf [accessed 9 July 2007]. Mu, Z.H., Zhu, H.H. & Zhang, K.Y. 2001. The Oil-Forming System of Mesozoic Dyni, J.R. 2006b. Oil shale developments in the United States. Oil Shale, 23, in South Ordos Basin. Petroleum Industry Press, Beijing, 1–10 [in Chinese] 97–98, https://doi.org/10.2516/ogst:2006011x National Development and Reform Commission (NDRC). 2005. Oil and gas Francis, P. & Miknis, J.F. 1983. Geochemistry and Chemistry of Oil Shales. industry standard of the People’s Republic of China (SY/5118-2005): American Chemical Society, Washington, DC. Determination of bitumen from rocks by chloroform extraction. Fu, J.M. & Qi, K.Z. 1995. Geochemistry of Kerogen. Guangdong Science and Ots, A. 2007. Estonian oil shale properties and utilization in power plants. Technology Publishing House, Guangzhou, DC, 28–74 [in Chinese]. Energetika, 53,8–18, https://doi.org/10.1007/978-1-4757-9223-2_24 Fu, J.M., Li, S., Liu, X. & Deng, X.Q. 2012. Sedimentary facies and its evolution Pan, Z. X. 1934. Oil shale in northern Shaanxi. In: The Geological Survey, Front of the Chang 9 interval of Upper Triassic Yanchang Formation in Ordos Basin. Ministry of Industry. Memoirs of the Geological Survey of China, 24,10–56 Journal of Palaeogeography, 14, 269–284, https://doi.org/10.7605/gdlxb. [in Chinese]. 2012.03.001 Qian, X.L. 2009. Chinese oil shale business is still going on. Oil Shale, Fuller, M.L. & Clapp, F.G. 1926. Formation of the North Shensi Basin, China. 26,97–98, https://doi.org/10.3176/oil.2009.2.01 The Journal of Geology, 34, 434–440, https://doi.org/10.1086/623330 Ren, L. 2007. Characteristics and resource evaluation of Mesozoic oil shales in Gromet, L.P., Dymek, R.F. & Haskin, L.A. 1984. The ‘North American shale Binxian–Tongchuan, Ordos Basin. PhD thesis, Jilin University, Changchun, composite’: Its composition, major and trace element characteristics. China. Geochimica et Cosmochimica Acta, 48, 2469–2482, https://doi.org/10.1016/ Ren, Z.L. 1991. Research on the relations between geothermal history and oil-gas 0016-7037(84)90298-9 accumulation. Acta Petrolei Sinica, 17,17–24 [in Chinese with English Guan, D.S., Niu, J.Y. & Guo, L. 1995. Unconventionality Oil and Gas Geology in abstract], https://doi.org/10.7623/syxb199601003 China. Petroleum Industry Press, Beijing 228–287 [in Chinese]. Shu, Y. 2012. The developments of Chinese oil shale activitie. Oil Shale, 29, Hutton, A.C. 1987. Petrographic classification of oil shales. International Journal 101–102, https://doi.org/10.3176/oil.2012.2.01 of Coal Geology, 8,203–231, https://doi.org/10.1016/0166-5162(87)90032-2 Si, X.J. 1956. Floral in the Northern Shaanxi. Science and Technology Press, James, G.O. 2012. Triassic. In: F. M. Gradstein et al. (eds), The Geologic Time Beijing [in Chinese with English abstract]. Scale. Elsevier, Amsterdam, Holland, https://doi.org/10.1016/B978-0-444- Smith, J.W. 1980. Oil shale resources of the United States. Mineral and Energy 59425-9.00025-1 Resources5, 23,1–23, http://xueshu.baidu.com/usercenter/paper/show? Ji, L.M. & Xu, J.L. 2007. Triassic acritarchs and its relation to hydrocarbon paperid=79785876241a952512ee83e9a082e563&site=xueshu_se source rock in Ordos Basin. Acta Petrolei Sinica, 28,40–43 [in Chinese with Smith, R.M.H. 1990. A review of stratigraphy and sedimentary environments of English abstract], https://doi.org/10.7623/syxb200206007 the Karoo Basin of South Africa. Journal of African Earth Sciences, 10, Ji, L.M., Wang, S.F. & Xu, J.L. 2006. Acritarch assemblage in Yanchang 117–137, https://doi.org/10.1016/0899-5362(90)90050-O Formation in eastern Gansu province and its environmental implications. Earth Sun, S.S., Yao, Y.B. & Lin, W. 2015. Elemental geochemical characteristics of Science – Journal of China University of Geosciences, 31,789–807 [in Chinese the oil shale and the paleo-lake environment of the Tongchuan area, southern with English abstract], http://www.doc88.com/p-6971874998149.html Ordos Basin. Bulletin of Mineralogy, Petrology and Geochemistry, 34, Ji, L.M., Wu, T. & Li, L. 2007. Geochemical characteristics of kerogen in 642–645 [in Chinese with English abstract], https://doi.org/10.3969/j.issn. Yanchang Formation source rocks, Xifeng area, Ordos Basin. Petroleum 1007-2802.2015.03.021 Exploration and Development, 34, 424–429 [in Chinese with English abstract]. Surdam, R.C. & Wolfbauer, C.A. 1975. Green River oil shale play – a pattern. Jia, C.Z., He, D.F., Shi, X. & Yang, G. 2006. Characters of late-stage formation Bulletin of Geological Society of America, 86, 335–345, https://doi.org/10. reservoirs of China. Science in China Series D: Earth Sciences, 36, 412–420 1130/0016-7606(1975)86<335:GRFWAP>2.0.CO;2 [in Chinese], http://kns.cnki.net/kcms/detail/detail.aspx?dbcode=CJFD&file Taylor, S.R. & Melennan, S.M. 1985. The Continental Crust: Its Composition name=JDXK200605001&dbname=CJFD2006 and Evolution. Blackwell, Oxford, UK. Kuila U & Prasad M. 2012. Compositional controls on mud rock pore-size The Office of the National Committee of Mineral Reserves. 1987. Reference distribution: an example from Niobrara Formation. Paper presented at the Manual of Mineral Industrial. Geological Publishing House, Beijing [in Society of Petroleum Engineers Annual Technical Conference and Exhibition, Chinese]. 8–10 October 2012, San Antonio, Texas, USA. Tissot, B.P. & Welte, D.H. 1978. Petroleum Formation and Occurrence – ANew Lewan, M.D. & Maynard, J.B. 1982. Factor controlling the enrichment of Approach to Oil and Gas Exploration. Springer, Berlin, 67–94. vanadium and nickel in the bitumen of organic sedimentary rock. Geohimica Tribovillard, N., Algeo, T.J. & Riboulleau, A. 2006. Trace metals as paleo redox et Cosmochimica Acta, 46, 2547–2560, https://doi.org/10.1016/0016-7037 and paleoproductivity proxies: An update. Chemical Geology, 232,12–32, (82)90377-5 https://doi.org/10.1016/j.chemgeo.2006.02.012 Li, S.T. 2000. The dynamics of sedimentary basins and energy resources – Wan, T.F. 2004. China Tectonics Outline. Geological Publishing House, Beijing retrospective and prospects at the turn of the century. Earth Science Frontiers, [in Chinese]. 7,1–8 [in Chinese with English abstract], http://www.earthsciencefrontiers. Wang, C., Wang, Q. X., Chen, G. J., He, L., Xu, Y., Chen L & Chen, D. F. 2017. net.cn/CN/ Petrographic and geochemical characteristics of the lacustrine balck shale from Downloaded from http://pg.lyellcollection.org/ by guest on September 28, 2021

Ordos oil shale 371

the Upper Triassic Yanchang Formation of Ordos Basin, China: Implication Yang, J.J. 2002. Geotectonic Evolution and Hydrocarbon Distribution for the organic matter accumulation. Marine and Petroleum Geology, 86, Regularities. Petroleum Industry Press, Beijing [in Chinese], http://www. 52–65, https://doi.org/10.1016/j.marpetgeo.2017.05.016 doc88.com/p-95727915621.html Wang, D.Y., Xin, B.S. & Yang, H. 2014. Zircon SHRIMP U–Pb age and Yang, J.J. & Pei, X. 1996. Natural Gas Geology of China, Volume 4. Petroleum geological implications of tuff at the bottom of Chang-7 Member of Yanchang Industry Press, Beijing [in Chinese]. Formation in the Ordos Basin. Science China: Earth Sciences, 44, 2160–2171, Yang, M. & Liu, C.Y. 2006. Sequence stratigraphic framework and its control on https://doi.org/10.1007/s11430-014-4979-0 [in Chinese with English accumulation of various energy resources in the Mesozoic continental basins abstract]. in Ordos. Oil & Gas Geology, 27, 563–570 [in Chinese with English abstract], Wang, P.X. 1995. Talassogenous fauna and ‘Cenosoic transgressions’ in China. https://doi.org/10.11743/ogg20060419 Journal of Tongji University (Natural Science), 23, 129–135 [in Chinese with Yuan, J.Q., Zhu, S.Q. & Zhai, Y.S. 1979. Mineral Deposits. Geological English abstract]. Publishing House, Beijing, 327–329 [in Chinese]. Wang, S.Y., Xu, J.M. & Wang, Z.H. 1992. Present state of China oil shale Zhang, H., Bai, Q.Z. & Zhang, X.W. 1995. Formation and Evolution of the development and utilization. Geological Economy of China, 5,16–19 [in Ordos Coal-Forming Basin. Shaanxi Science and Technology Press, Xian, Chinese with English abstract], https://www.doc88.com/p-7843590321056.html China [in Chinese]. Wang, Y.M. 2007. Geophysical logging of oil shale in exploration of the Triassic Zhang, H., He, Z. L & Jin, X. L. 2005. Tectonic evolution and coal accumulation coal-fields in northern Shaanxi. Geology of Shaanxi, 26,59–72 [in Chinese of the Ordos Basin. In: A Brief Explanation of the Geological Tectonic Map of with English abstract], http://www.doc88.com/p-113710777424.html the Ordos Coal Basin (with a Scale of 1:500 000). Geological Publishing Wang, Z., Chen, Q.M., Yang, W.B. & Yao, X.B. 2016. Characteristics and House, Beijing [in Chinese with English abstract], pp. 3–31. resources evaluation for oil shale in Tongchuan area of Ordos Basin. Zhang, Q.C., Wang, K.M., Luo, S.S. & Wu, X.Z. 2013. Study on the Unconventional Oil & Gas, 3,32–39 [in Chinese with English abstract], http:// characteristics and origin of the oil shale in the Chang 7 Member, Yanchang www.docin.com/p-1750919340.html Formation in Ordos Basin. Advances in Geosciences, 2013, 197–209, https:// Xie, X.Y. 2007. Sedimentary record of Mesozoic intracontinental deformation in doi.org/10.12677/AG.2013.34028 [in Chinese with English abstract]. the South Ordos Basin, China. PhD thesis, University of Wyoming, Laramie, Zhang, W.Z., Yang, H., Li, J.F. & Ma, J. 2006. Leading effect of high-class WY, USA. source rock of Chang 7 in Ordos Basin on enrichment of low permeability oil- Yang, H. & Zhang, W.Z. 2005. Leading effect of the Seventh Member gas accumulation – hydrocarbon generation and expulsion mechanism. high-quality source rock of Yanchang Formation in Ordos Basin during the Petroleum Exploration and Development, 33, 289–294, http://www.doc88. enrichment of low-penetrating oil-gas accumulation: geology and geochem- com/p-7813707435776.html istry. Geochimica, 34, 147–154 [in Chinese with English abstract], https://doi. Zhang, W.Z., Yang, H. & Li, S.P. 2008a. Hydrocarbon accumulation significance org/10.3321/j.issn:0379-1726.2005.02.007 of Chang 91 high-quality lacustrine source eocks of Yanchang Formation Yang, H., Xi, S.L., Wei, X.S. & Li, Z.H. 2006. Evolution and natural gas Ordos Basin. Petroleum Exploration and Development, 35, 557–561, https:// enrichment of multi cycle superimposed basin in the Ordos Basin. China doi.org/10.1016/S1876-3804(09)60088-4 Petroleum Exploration, 1,17–25 [in Chinese with English abstract], https:// Zhang, W.Z., Yang, H., Yang, Y.H. & Kong, Q.F. 2008b . Petrology and element doi.org/10.3969/j.issn.1672-7703.2006.01.004 geochemistry and development of Yanchang Formation Chang-7 high quality Yang, H., Fu, Q., Qi, Y.L., Zhou, X.P., Gong, N. & Huang, S.X. 2016a. The source rock in Ordos basin. Geochimica, 37,59–64 [in Chinese with English geological significance on the late Triassic Yanchang stage palaeo-lacustrine abstract], http://www.docin.com/p-1185993616.html Ordos Basin. Acta Sedimentologica Sinica, 34, 688–694 [in Chinese with Zhao, L.Y., Chen, J.N. & Wang, T.S. 1991. Grade dividing and composition of English abstract], https://doi.org/10.14027/j.cnki.cjxb.2016.04.009 shale in China. Geoscience, 5, 423–429 [in Chinese with English abstract]. Yang, H., Niu, X.B. et al. 2016b. Exploration potential of shale oil in Chang 7 Zhao, Y.T. & Liu, W.B. 1992. Advance in synthesized usage of oil shale in Member, Upper Triassic Yanchang Formation, Ordos Basin, NW China. foreign Countries. Advance in Earth Science, 7,49–50 [in Chinese with Petroleum Exploration and Development, 43, 560–569, https://doi.org/10. English abstract], https://doi.org/10.11867/j.issn.1001-8166.1992.02.0048 1016/S1876-3804(16)30066-0 [in Chinese with English abstract]. Zhou, J.G., Yao, G.S., Deng, H.Y., Xin, Y.G., Hu, H., Zheng, X.P. & Gong, Q.S. Yang, J.J. 1991. Discover for gas of Lower Palaeozoic in Shanganning Basin. 2008. Exploration potential of Chang 9 member, Yanchang Formation, Ordos Gas Industry, 11,1–6 [in Chinese with English abstract], http://www.doc88. Basin. Petroleum Exploration and Development, 35, 289–293, https://doi.org/ com/p-95727915621.html 10.1016/S1876-3804(08)60074-9