Acta Geochim (2018) 37(2):228–243 https://doi.org/10.1007/s11631-017-0206-y

ORIGINAL ARTICLE

Elemental characteristics of lacustrine and its controlling factors of palaeo-sedimentary environment on oil yield: a case from Chang 7 oil layer of Triassic Yanchang Formation in southern Ordos Basin

1 1 2 2 Delu Li • Rongxi Li • Zengwu Zhu • Feng Xu

Received: 27 April 2017 / Revised: 4 July 2017 / Accepted: 20 July 2017 / Published online: 27 July 2017 Ó Science Press, Institute of Geochemistry, CAS and Springer-Verlag GmbH Germany 2017

Abstract As an important unconventional resource, oil Paleosalinity and paleohydrodynamics have an inconspic- shale has received widespread attention. The oil shale of uous influence on oil yield. the Chang 7 oil layer from Triassic Yanchang Formation in Ordos Basin represents the typical lacustrine oil shale in Keywords Elemental geochemistry Á Palaeosedimentary Á China. Based on analyzing trace elements and oil yield Main controlling factors Á Lacustrine oil shale Á Triassic Á from boreholes samples, characteristics and paleo-sedi- Ordos Basin mentary environments of oil shale and relationship between paleo-sedimentary environment and oil yield were studied. With favorable quality, oil yield of oil shale varies 1 Introduction from 1.4% to 9.1%. Geochemical data indicate that the paleo-redox condition of oil shale’s reducing condition Regarded as one of the important unconventional from analyses of V/Cr, V/(V ? Ni), U/Th, dU, and authi- resources, oil shale is a solid organic genic uranium. Equivalent Boron, Sp, and Sr/Ba illustrate (Liu et al. 2015). After being combusted by low-tem- that paleosalinity of oil shale is dominated by fresh water. perature carbonization, it can produce (Liu et al. The paleoclimate of oil shale is warm and humid by cal- 2009). The ratio of shale oil to oil shale in unit mass is oil culating the chemical index of alteration and Sr/Cu. Fe/Ti yield. In petroleum reserve assessments, oil yield, as a and (Fe ? Mn)/Ti all explain that there were hot water key evaluation index, has a direct influence on evaluation activities during the sedimentary period of oil shale. In results (Li et al. 2014). Therefore, the research on con- terms of Zr/Rb, paleohydrodynamics of oil shale is weak. trolling factors of oil yield becomes more and more sig- By means of Co abundance and U/Th, paleo-water-depth of nificant, especially in the lack of conventional resources oil shale is from 17.30 to 157.26 m, reflecting sedimentary nowadays. environment which is mainly in semi deep–deep lake There are many factors affecting oil yield of lacustrine facies. Correlation analyses between oil yield and six oil shale, primarily including: the foundation of hydrocar- paleoenvironmental factors show that the oil yield of oil bon generation (Fahmi et al. 2008), the control action of shale is mainly controlled by paleo-redox conditions, palaeosedimentary environment (Han et al. 2014), later paleoclimate, hot water activities, and depth of water. preservation condition (Brumsack 1988; Dean and Arthur 1989), etc. And the degree of effect of different factors are also various. Considering that many factors are hardly & Delu Li quantified, the study on controlling factors of oil yield is [email protected] still in a qualitative stage (Chang et al. 2012). However, & Rongxi Li with the development of elemental geochemistry, the [email protected] abundant palaeosedimentary environment can be well 1 School of Earth Sciences and Resources, Chang’an expressed by some parameters, which can help researchers University, Xi’an 710054, China explore their correlations more accurately (Chermak and 2 Shaanxi Center of Geological Survey, Xi’an 710068, China Schreiber 2014; Mapoma et al. 2014). 123 Acta Geochim (2018) 37(2):228–243 229

With superior oil yield, oil shale from Triassic Yan- regressive cycle and early Chang 7 oil layer is regarded as chang Formation in Ordos Basin has the typical lacustrine the most developmental period of the lake (He 2003). Pre- characteristics in China. Previous studies mainly concen- vious studies indicated that Chang 7 oil layer in the north of trate on organic geochemistry and sedimentary facies Weibei Uplift deposited in semi deep–deep lake facies (Jiang et al. 2013; et al. 2015), and the research on (Yang et al. 2016) and the lithologies at the bottom are inorganic geochemistry, especially elemental geochem- mainly oil shale and silty mudstone with a deep lake envi- istry, are seldom seen before, leading to incomplete ronment (Fig. 1b). Modified after Qiu et al. (2014). recognition. In addition, the relationships between oil yield and palaeosedimentary environment are still uncertain. So, it is vital to make an investigation on elemental geo- 3 Samples and analysis methods chemistry so as to further make palaeosedimentary envi- ronment clear on one hand, and to find out main controlling Attaching to Weibei Uplift, the studied area is located in factors of palaeosedimentary environment on oil yield on southern Ordos Basin (Fig. 1a). A total of 25 oil shale the other hand. samples from four drillings were collected (Fig. 3). In this paper, the characteristics of oil yield and For oil yield of oil shale analysis, samples are ground till palaeosedimentary environment, including paleo-redox particle size is under 3 mm, then 50 g of them is enclosed condition, paleosalinity, paleoclimate, hydrothermal depo- into aluminum retort with low-temperature carbonization sitional condition, paleo-hydrodynamics, and paleo-water- method. The procedures follow the Chinese standard depth are discussed. Then, main controlling factors of methods SH/T 0508-1992. The analytical error is within palaeosedimentary environment on oil yield are found 5%. The experiment is conducted at Shaanxi Geo- using statistical methods. This contribution fills in gaps of logical Laboratory Co., Ltd. study on main controlling factors of oil yield in lacustrine The samples for element analysis were all crushed and oil shale and has significance in guiding future exploration. ground to less than 200 mesh, using X-ray fluorescence spectrometry (XRF) and inductively-coupled plasma mass spectrometer with AA-6800 atomic absorption spec- 2 Geological settings troscopy, UV-2600 ultraviolet–visible spectrophotometer and Perkin Elmer SciexElan 6000. The analytical proce- Located in central China, Ordos Basin is a Mesozoic dures follow Chinese National Standard GB/ depressed basin on a Paleozoic Craton with a Proterozoic T14506.1*14-2010 and GB/T14506.30-2010. The ana- crystalline basement (Wan et al. 2013; Li et al. 2013) lytical uncertainty is within 5%. The analyses are at Ana- (Fig. 1a). According to tectonic characteristics, the basin is lytical Center, No. 203 Research Institute of Nuclear classified to six first order tectonic units, Yimeng Uplift, Industry. Yishan Slope, Weibei Uplift, Tianhuan Depression, Western Thrusted Zone, and Jinxi Flexure Zone. By Permian-Car- boniferous, Ordos Basin belonged to the marine basin of 4 Results North China Block. After Middle Triassic, the initial appearance of basin gradually formed. During Indosinian 4.1 Oil shale and its oil yield characteristics Orogeny, the whole basin was in stable condition mostly. In Upper Triassic and Early-Middle Jurassic, the basin entered Oil shale from Chang 7 oil layer in the study area is a period of prosperous development. Then, the basin grad- characterized by black and brown color and lamina shape ually uplifted and subducted in Early Cretaceous and Weibei with greasy luster and jagged fracture. The oil shale Uplift deposited mainly in receiving sediments. After that, thickness is generally over 10 meters with fossils of fish tectonic orogenies developed variably and Ordos Basin scale and plant stems. The oil yields of 21 oil shale samples underwent reformation (Li et al. 2011, 2013; Yang et al. from Chang 7 oil layer range from 1.40% to 9.10% with an 2016; Qiu et al. 2014, 2015). Since the epoch, the average of 5.01% (Table 1). According to National lifting of Weibei Uplift gradually increased until now resource assessment (Zhao et al. 1991), the oil shale quality (Fig. 2) (Wang et al. 2010). The Triassic Upper Yanchang is classified to middle-grade criterion. Formation from the southern basin is dominated by the fluvial-lacustrine depositional system with a thickness of 4.2 Major element geochemistry 1000–1300 m (Qiu et al. 2015) and divided into 10 oil layers

(Chang 10- Chang 1 from the bottom to the top in order) Major oxides data show that SiO2 content ranks the most according to the sedimentary cycle. The whole formation abundant content (36.42%–64.70%) in all oxides. Al2O3 represents an integrated lacustrine transgressive-lacustrine (10.69%–20.15%), TFe2O3 (total iron) (3.61%–11.27%) 123 230 Acta Geochim (2018) 37(2):228–243

Fig. 1 The tectonic map of Ordos Basin and stratigraphic column of the Upper Triassic Yanchang Formation. a The tectonic map of Ordos Basin and location of studied section, b stratigraphic column of Upper Triassic Yanchang formation and K2O (1.49%–4.11%) are the second most abundant abundant bivalve and gastropod fossil remains and low oxides. The rest of the oxides (MgO, Na2O, P2O5, MnO, concentration may refer to fossil remains in oil shale and TiO2) have a concentration of less than 4%. SiO2 (Mukhopadhyay et al. 1998; Fu et al. 2010a, b). The con- mainly occurs in quartz and clay minerals (Fu et al. tent of CaO is relatively low (0.39%–3.59%), elucidating 2010a, b). The Al/Si ratio of shale samples is from 0.25 to that Ca possibly exists in organic matter partially. The

0.42 (Table 1), indicating that SiO2 is primarily related fossils of fish scale in oil shale bedding can also demon- with quartz. The correlation coefficient (r = 0.47) between strate this. A mass of framboids of pyrite in oil shale

SiO2 and Al2O3 further support the recognition. The ele- samples in SEM analyses can support that Fe is mainly ment Al is usually from clay minerals (Fu et al. 2010a, b) associated with pyrite (Fig. 4b). and the relatively high content of Al2O3 manifest that clay minerals commonly occurs in oil shale samples (Fig. 4a). 4.3 Trace element geochemistry MgO concentration holds a positive correlation (r = 0.72) with Al2O3, implying Mg is also from clay minerals. Table 2 shows the results of trace elements of 21 oil shale Generally, a high concentration of CaO is related with samples from Chang 7 oil layer. The relatively high

123 Acta Geochim (2018) 37(2):228–243 231

Fig. 2 Simplified geological map of study area, showing the location of drill holes. Modified after Ma et al. (2016) average concentrations of trace elements in oil shale enrich, while in reducing environment, U shows ?4 samples are Ba (622.35 lg/g), Sr (241.70 lg/g), V valence, leading to enrichment (Fan et al. 2012). The (192.87 lg/g), Zr (145.69 lg/g), Rb (120.93 lg/g), and Zn extreme concentration of U suggests that oil shale may (101.79 lg/g), whereas all the other elements occur in deposit in reducing environment. Element Ba is more prone amounts smaller than 100 lg/g. Enrichment factor (EF) is to subside after entering the lake (Sun et al. 1997), so its always calculated to evaluate the element enrichment content gradually decreases along with the increase of degree (Patterson et al.1986), which was defined as the distance from the lakeshore. The average EF of Ba shows a ratio of the concentration of an element in samples to the little deficit, indicating that oil shale deposit away from the corresponding value of Upper Continental Crust (UCC) lakeshore and more in depocenter. In addition, the content (Rudnick and Gao 2003). As seen from Table 3 and Fig. 5, of Sr has a close relationship with Ca because of adsorption trace elements can be classified into three types, according from biogenic shells. The average EF of Sr is a deficit, to enrichment state. (1) Extremely concentrated type (av- which is in accordance with low CaO concentration. erage EF [ 5): As, U, Cd, and Mo. (2) Concentrated type (1 \ average EF \ 5): V, Cu, Zn, Ga, Pb, Rb, Cs, Th, Nb, Hf, Ta, Li, Be, In, Bi, and B. (3) Depleted type (average 5 Discussions EF \ 1): Cr, Sr, Zr, Ba, Sc, Co, and Ni. As a whole, oil shale from Chang 7 oil layer is characterized by enrichment 5.1 Paleo-environment analysis of metallic elements. Usually, Cu concerns biological growth and Mo is 5.1.1 Paleo-redox condition chalcophile elements (Sun et al. 2015). Their concentra- tions in oil shale samples represent the prosperity of living Paleo-redox condition plays an important role in the substance during sedimentation. Element U shows ?6 preservation of organic matter. Some redox-sensitive trace valence under the oxidizing condition and can hardly elements can reconstruct it well. In this study, in view of

123 232 Acta Geochim (2018) 37(2):228–243

Fig. 3 Oil shale drill sections from the bottom of Chang 7 oil layer, showing sampling locations

Table 1 Concentrations of oil yield, major elements and parameter of samples from Chang 7 oil layer (units in %)

Sample no. Tad SiO2 Al2O3 TFe2O3 MgO CaO Na2OK2OP2O5 MnO TiO2 Al/Si

ZK702H6 4.30 55.73 13.54 6.95 0.75 0.42 0.98 3.61 0.24 0.09 0.29 0.28 ZK702H14 7.20 40.61 13.37 10.52 0.97 0.97 0.91 2.25 0.28 0.05 0.40 0.37 ZK702H18 9.10 46.90 10.69 9.48 0.86 1.61 1.30 1.85 0.45 0.06 0.36 0.26 ZK702H24 8.10 43.33 12.50 8.85 0.98 1.67 1.49 1.49 0.35 0.07 0.33 0.33 ZK702H32 7.70 44.26 12.66 9.62 0.93 1.25 1.00 2.37 0.29 0.09 0.34 0.32 ZK1501H3 5.70 45.36 11.45 9.57 1.06 1.62 1.45 2.12 0.36 0.11 0.39 0.29 ZK1501H6 6.80 36.42 11.37 11.27 1.45 2.19 0.74 1.90 0.26 0.08 0.35 0.35 ZK1501H11 6.00 43.58 12.96 9.87 1.16 2.36 1.43 2.03 0.41 0.21 0.45 0.34 ZK1501H13 2.30 56.52 14.20 5.48 2.31 3.48 1.92 2.09 0.23 0.10 0.42 0.29 ZK1501H15 5.40 48.09 14.00 7.97 1.22 1.98 1.30 2.36 0.46 0.25 0.39 0.33 ZK1501H17 1.50 59.95 13.61 4.86 2.13 3.59 2.25 4.11 0.15 0.13 0.51 0.26 ZK2709H1 1.80 53.80 20.15 7.28 2.08 0.94 1.17 3.02 0.23 0.23 0.77 0.42 ZK2709H3 7.40 44.44 14.15 8.03 1.71 1.59 1.29 2.53 0.39 0.19 0.51 0.36 ZK2709H5 2.40 64.70 14.00 3.61 1.19 1.24 1.73 2.43 0.12 0.14 0.42 0.25 ZK2709H6 6.80 46.51 13.44 7.46 1.76 2.09 1.39 2.23 0.38 0.19 0.52 0.33 ZK2709H8 5.10 50.17 15.92 7.61 2.01 1.17 1.14 2.80 0.27 0.16 0.63 0.36 ZK2709H11 5.00 49.72 16.53 7.54 2.06 1.02 1.03 2.74 0.23 0.13 0.61 0.38 ZK2709H12 1.40 62.40 16.97 5.80 2.09 0.39 2.05 3.10 0.13 0.06 0.78 0.31 ZK719H7 1.40 52.60 17.95 7.16 2.39 1.39 0.78 2.18 0.15 0.14 0.64 0.39 ZK719H13 7.20 47.03 17.07 6.21 1.74 0.73 0.76 2.54 0.24 0.15 0.54 0.41 ZK719H16 2.70 56.23 18.72 6.14 2.08 1.92 0.82 2.22 0.14 0.09 0.73 0.38 Average 5.01 49.92 14.54 7.68 1.57 1.60 1.28 2.47 0.27 0.13 0.49 0.33

Tad, oil yield

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Fig. 4 a Clay minerals of oil shale sample (ZK702) and b framboids of pyrite of oil shale sample (ZK2709) in SEM elements sensibility, V/Cr, V/(V ? Ni), U/Th, (Zheng et al. 2016). Therefore, the content of boron can be dU[dU = 2U/(U ? Th/3)], and AU(AU = U - Th/3) are used to analyze paleosalinity (Xiao et al. 1999; Lendergren applied to judge redox condition comprehensively. and Carvajal 1969). Walker (1963) calculated Equivalent

Generally, V/Cr [ 4.25 indicates a strong reducing Boron through the content of boron and K2O to judge condition, and V/Cr with 2–4.25 shows reducing condition, paleosalinity. The formula is Equivalent Bor- and V/Cr \ 2.00 implies oxidation environment (Teng on = 11.8 9 (B 9 8.5/K2O %)/[1.70 9 (11.8-K2O %)]. et al. 2004). V/(V ? Ni) [ 0.5 shows reducing condition. B represents the content of boron. Degens et al. (1958) and On the contrary, it shows oxidation condition (Tribovillard Keith and Bystrom (1959) proposed the scope of sea water et al. 2006). U/Th [ 1.25 elucidates strong reducing con- and fresh water by Equivalent Boron. When Equivalent dition and U/Th in 0.75–1.25 represents the reducing Boron is in the range of 300–400, 200–300 and\200 ppm, condition, while U/Th \ 0.75 means oxidation condition it means sea water, brackish water, and fresh water deposit. (Ernst 1970; Jones and Manning 1994). dU \ 1 suggests As calculated in Table 4, the content of Equivalent Boron strong reducing environment, and dU [ 1 implies oxida- in oil shale samples is from 39.90 to 234.70 with an tion condition (Zhao et al. 2016). AU [ 12 ppm means a average of 100.89, indicating that the sedimentary water is strong reducing condition, and when it is below 5 ppm, it mainly fresh water. Adams et al. (1965) put forward to an means oxidation condition (Teng et al. 2005; Deng and equation to calculate paleosalinity. The equation is Qian 1993). Sp = 0.0977x - 7.043. Sp represents paleosalinity (%) All kinds of parameters showing paleo-environment are and x represents Equivalent Boron. Previous study classi- all listed in Table 4. The averages of V/Cr, V/(V ? Ni), fied water by paleosalinity (Qin 2005), however, in order to U/Th, dU and AU in oil shale samples are 2.90, 0.85, 1.50, unify standard of above salinity, we reconsider the classi- 2.24, and 24.21 (Table 4). All parameters of oil shale fication and regard \5%, 5–18%, and [18% as fresh samples show reducing-strong reducing environment dur- water, brackish water, and sea water. The result of Sp is ing sedimentation. As can be seen from Table 4, the 0.21%–15.89% (average 6.21%), showing the character of parameters of oil shale samples from ZK2709 and ZK719 fresh water and brackish water sedimentation (Table 5). are lower than the parameters from ZK702 and ZK1501 in Sr/Ba ratio can also be used to reconstruct paleosalinity. varying degrees, implying the paleo-redox condition in the After counting Sr/Ba of samples in 13 sea floors, Sr/Ba eastern area is more reducing than in the western area from 0.8 to 1.0 is regarded as marine deposit and below 0.6 (Table 5). is regarded as a lacustrine deposit (Wang and Wu 1983). Thus, Sr/Ba ratio with [1, 0.6–1, and \0.6 are treated as 5.1.2 Paleosalinity sea water, brackish water, and fresh water. The Sr/Ba in oil shale samples from Chang 7 oil layer is in the range of Boron is a diffluent element, being in sedimentary rocks of 0.23–0.69 (average 0.38), suggesting mainly fresh water hydrosphere or upper crust and it can be easily adsorbed by deposition (Table 5). In summary, the paleosalinity of clay minerals. Once fixed in clay minerals, boron can water during oil shale sedimentation could be mainly fresh hardly redissolve when the solubility of boron decreases water and brackish water.

123 234 123 Table 2 Trace elements concentrations of oil shale samples from Chang 7 oil layer (units in ppm) Sample no. Cr Sr Zr Ba Sc V Cu Zn Ga As Pb Rb Cs Th U Co

ZK702H6 38.90 110.40 138.70 380.90 10.80 123.80 90.30 98.00 22.10 82.40 51.90 215.30 8.33 22.20 28.50 13.30 ZK702H14 80.40 162.00 120.40 515.70 12.70 282.80 139.20 117.90 23.70 101.60 45.90 107.60 9.72 14.90 54.10 21.60 ZK702H18 60.20 229.80 135.50 463.40 13.90 235.30 144.50 107.00 19.20 80.10 35.40 88.90 7.88 10.80 61.30 15.10 ZK702H24 58.10 384.90 132.60 774.60 16.50 305.90 142.10 116.70 22.10 104.40 47.00 82.90 7.56 9.56 61.10 14.60 ZK702H32 68.40 328.20 146.80 792.60 13.10 316.80 132.30 122.10 24.10 153.30 37.90 117.30 11.30 12.70 47.00 14.70 ZK1501H3 56.10 185.00 120.30 562.40 10.10 255.50 139.30 99.80 21.00 81.80 43.80 85.30 10.20 15.80 68.20 15.80 ZK1501H6 78.60 151.70 116.90 438.50 13.20 286.70 150.10 101.20 22.00 109.20 47.70 81.90 8.57 12.60 61.70 18.90 ZK1501H11 71.30 438.80 127.20 765.10 16.90 299.70 141.90 121.90 22.50 84.50 48.00 88.70 8.14 9.96 51.10 17.70 ZK1501H13 44.40 436.80 148.80 631.70 12.50 114.90 49.40 69.70 19.00 30.30 33.70 99.20 5.74 19.60 20.00 12.00 ZK1501H15 55.50 425.00 146.30 849.80 11.60 249.20 123.10 117.80 22.70 113.20 52.80 114.00 9.69 15.10 47.30 17.40 ZK1501H17 53.30 375.80 168.00 838.90 9.10 80.60 30.90 77.10 19.30 12.90 30.30 136.10 4.29 11.60 6.82 8.57 ZK2709H1 90.50 160.50 197.30 513.60 18.70 135.00 41.00 120.70 25.30 10.00 42.50 139.80 9.12 17.60 4.21 15.90 ZK2709H3 68.60 192.40 127.90 649.50 16.20 189.50 97.50 100.50 19.00 65.60 31.90 115.70 7.70 13.10 17.70 17.80 ZK2709H5 41.20 236.10 183.30 680.40 11.10 69.10 31.20 74.90 16.80 11.70 32.80 124.80 8.41 16.60 6.41 7.93 ZK2709H6 76.30 182.00 134.00 612.00 14.50 179.00 95.90 95.10 17.90 44.30 29.70 105.00 7.24 12.00 21.60 17.50 ZK2709H8 78.10 177.70 132.80 662.00 16.60 170.00 64.20 101.00 20.50 37.90 33.60 122.90 8.23 14.00 12.70 17.10 ZK2709H11 83.60 159.30 129.70 692.70 16.00 153.00 66.60 102.50 22.60 53.10 35.80 124.80 8.56 14.40 12.40 18.30 ZK2709H12 83.40 245.50 209.90 635.40 16.00 116.10 40.10 105.00 22.50 126.10 31.10 128.60 7.80 12.10 2.94 15.80 ZK719H7 86.20 133.30 149.10 486.20 14.40 158.10 42.40 90.90 24.00 12.80 27.20 141.10 8.42 14.50 5.90 14.80 ZK719H13 85.90 155.40 130.90 584.00 16.90 196.30 53.20 96.80 24.50 27.90 31.30 163.70 9.92 15.00 14.00 15.50 ZK719H16 86.80 205.00 163.00 540.00 15.40 133.00 43.00 101.00 23.60 6.30 30.40 156.00 9.99 14.60 3.07 16.70 Sample no. Ni Nb Cd Hf Ta Li Be In Bi Mo B La

ZK702H6 22.00 21.70 0.79 7.08 0.97 35.60 3.17 0.0840 0.89 44.97 22.81 33.2 ZK702H14 34.20 13.80 0.87 5.17 0.78 43.20 2.47 0.0700 0.80 52.32 32.08 29.9 ZK702H18 29.10 9.20 0.78 4.44 0.86 25.30 1.93 0.0600 0.56 76.38 15.51 37.6 ZK702H24 26.90 7.86 0.75 4.57 0.57 26.70 1.82 0.0630 0.48 76.81 14.70 40.4 37(2):228–243 (2018) Geochim Acta ZK702H32 28.30 12.50 0.90 4.84 0.81 25.00 2.56 0.0740 0.63 74.14 19.57 35.8 ZK1501H3 27.70 12.30 0.93 4.98 0.72 23.80 2.16 0.0590 1.16 52.65 18.44 36.1 ZK1501H6 31.20 20.00 0.92 4.15 0.52 24.70 1.91 0.0620 0.75 24.64 20.86 34.0 ZK1501H11 30.00 6.69 1.08 3.90 0.54 26.10 2.00 0.0600 0.52 58.32 20.00 32.7 ZK1501H13 17.40 9.02 0.36 4.26 0.46 23.50 2.23 0.0530 0.79 27.56 33.73 30.2 ZK1501H15 31.00 20.00 1.12 6.00 0.66 28.20 2.56 0.0760 0.62 62.02 26.56 35.6 ZK1501H17 14.70 14.50 0.22 3.08 0.36 20.00 1.94 0.0490 0.30 4.08 21.37 31.9 ZK2709H1 37.00 30.60 0.53 7.60 2.28 57.50 3.00 0.0950 0.55 3.51 93.40 49.7 ZK2709H3 36.80 19.90 0.60 5.86 2.11 34.60 2.45 0.0810 0.59 14.40 29.50 39.3 Acta Geochim (2018) 37(2):228–243 235

5.1.3 Paleoclimate

Paleoclimate can usually affect weathering, transportation, and composition of source rocks (Zhang et al. 2011). The chemical index of alteration (CIA) can reflect the paleo- climatic conditions and has gained favorable application effect (Bai et al. 2015). The CIA expression is * CIA = 100 9 [Al2O3/(Al2O3 ? CaO ? Na2O ? K2O)]. CaO* refers to CaO in silicate and is calculated using the * expression CaO = CaO - (10/3 9 P2O5) to amend the content of apatite (Cox et al. 1995). The CaO* result is chosen as the minimum between calculated result and the

content of Na2O (Nesbitt and Young 1982). All oxide concentrations are given in molecular proportions. When the value of CIA is 50–65, it reflects cold and dry climate during sedimentation. The value being 65–85 marks a warm and humid climate. When the value is between 85 and 100, it indicates hot and humid climate. The CIA of oil shale samples is from 53.92 to 78.95 with an average of 69.74 (Table 5), indicating that the integral paleoclimate is a warm and humid climate. Meanwhile, Sr/Cu ratio can also be well applied in judging paleoclimate widely (Liang et al. 2015). If Sr/Cu ratio is 1.3–5.0, it means that the paleoclimate is warm and humid. If it is over 5, it means the paleoclimate is dry and hot. The Sr/Cu of oil shale samples ranges in 1.01–12.16 with an average of 3.64, also implying that the integral paleoclimate is warm and humid. So in summary, the paleoclimate of oil shale sedimentation is warm and humid (Table 5).

5.1.4 Hydrothermal depositional condition

Sediments concerning hydrothermal fluid are called hydrothermal deposition (Zhong et al. 2015). The activities of hydrothermal fluid are widespread and can obviously affect the concentration of trace elements and organic matter in sedimentary rocks (Chu et al. 2016). Previous studies show that Fe/Ti and (Fe ? Mn)/Ti ratios can be indexes of hydrothermal sediments. When Fe/Ti is above 20 or (Fe ? Mn)/Ti is above 20 ± 5, sediments are considered going through a hydrothermal fluid (Bostro¨m 1983). The average of Fe/Ti and (Fe ? Mn)/Ti in eastern area (ZK702 and ZK1501) are 26.87 and 27.25, indicating there are obvious hydrothermal fluid events. However, the average of Fe/Ti and (Fe ? Mn)/Ti in western area (ZK2709 and ZK719) are 12.96 and 13.29 (Table 5), indicating there are inconspicuous hydrothermal fluid events.

5.1.5 Paleo-hydrodynamics continued

Occurring in zircon, element Zr is a typical continental

Table 2 Sample no.ZK2709H5ZK2709H6 NiZK2709H8 20.10ZK2709H11 36.90ZK2709H12 36.70ZK719H7 Nb 20.30 40.70ZK719H13 18.10 41.00ZK719H16 17.40 0.27 16.80 33.00 Cd 37.30 0.68 22.60 34.00 0.51 7.07 0.58 17.00 Hf 16.10 5.90 0.33 17.90 5.51 1.13 5.82 0.21 0.34 1.76 7.64 Ta 0.28 1.52 24.30 1.19 6.60inert 6.15 35.30 1.39 Li 7.20 40.60 element 2.23 42.40 1.23 1.69 2.25 33.40 1.53 2.47 and Be 0.0640 2.73 50.00 48.00 0.0710 2.53deposits 48.80 0.0785 0.48 0.0810 2.49 In 2.61 0.55 0.0760 in 2.44 0.53 shallow 0.55 0.0890 4.07 0.0890 23.00 0.43 Bi 0.0920 25.00 water 22.60 0.62 31.40 0.84 43.80 2.18 sections. 0.61 51.00 Mo 35.70 39.8 6.38 38.90 35.4 57.40 Due 40.9 2.76 B 43.3 75.00 72.20 36.7 84.60 46.4 48.0 La 47.7 123 236 123

Table 3 Enrichment factors of trace elements of oil shale samples from Chang 7 oil layer

Sample no. Cr Sr Zr Ba Sc V Cu Zn Ga As Pb Rb Cs Th U Co Ni Nb Cd Hf Ta Li Be In Bi Mo B

ZK702H1 0.20 0.51 0.65 0.87 0.56 0.45 0.81 0.87 1.07 3.73 2.15 2.01 4.14 2.71 4.81 0.36 0.25 1.92 4.89 1.91 1.04 1.54 1.43 1.34 4.94 9.18 1.24 ZK702H6 0.42 0.35 0.72 0.61 0.77 1.28 3.23 1.46 1.26 17.17 3.05 2.56 1.70 2.11 10.56 0.77 0.47 1.30 8.78 1.34 1.08 1.48 1.51 1.50 5.56 40.88 1.34 ZK702H8 0.20 0.37 0.58 0.85 0.36 0.41 0.75 0.72 1.01 3.94 1.91 2.25 2.16 3.00 6.00 0.25 0.17 1.53 2.33 1.16 1.04 1.28 1.90 1.05 5.69 7.30 0.89 ZK702H14 0.87 0.51 0.62 0.82 0.91 2.92 4.97 1.76 1.35 21.17 2.70 1.28 1.98 1.42 20.04 1.25 0.73 0.83 9.67 0.98 0.87 1.80 1.18 1.25 5.00 47.56 1.89 ZK702H18 0.65 0.72 0.70 0.74 0.99 2.43 5.16 1.60 1.10 16.69 2.08 1.06 1.61 1.03 22.70 0.87 0.62 0.55 8.67 0.84 0.96 1.05 0.92 1.07 3.50 69.43 0.91 ZK702H24 0.63 1.20 0.69 1.23 1.18 3.15 5.08 1.74 1.26 21.75 2.76 0.99 1.54 0.91 22.63 0.84 0.57 0.47 8.33 0.86 0.63 1.11 0.87 1.13 3.00 69.83 0.86 ZK702H32 0.74 1.03 0.76 1.26 0.94 3.27 4.73 1.82 1.38 31.94 2.23 1.40 2.31 1.21 17.41 0.85 0.60 0.75 10.00 0.91 0.90 1.04 1.22 1.32 3.94 67.40 1.15 ZK702H35 0.55 1.58 0.83 1.32 0.81 0.85 1.03 0.98 1.06 5.17 1.51 1.70 0.77 1.00 2.52 0.41 0.32 0.66 2.00 0.58 0.42 0.67 0.95 0.88 2.00 9.21 1.11 ZK1501H1 0.18 0.43 0.71 0.74 0.52 0.50 0.92 0.85 0.98 4.46 2.13 2.28 3.88 3.03 6.11 0.29 0.21 1.06 4.89 1.11 1.00 1.18 1.55 0.89 4.63 11.55 0.85 ZK1501H3 0.61 0.58 0.62 0.90 0.72 2.63 4.98 1.49 1.20 17.04 2.58 1.02 2.08 1.50 25.26 0.91 0.59 0.74 10.33 0.94 0.80 0.99 1.03 1.05 7.25 47.86 1.08 ZK1501H6 0.85 0.47 0.61 0.70 0.94 2.96 5.36 1.51 1.26 22.75 2.81 0.98 1.75 1.20 22.85 1.09 0.66 1.20 10.22 0.78 0.58 1.03 0.91 1.11 4.69 22.40 1.23 ZK1501H11 0.78 1.37 0.66 1.22 1.21 3.09 5.07 1.82 1.29 17.60 2.82 1.06 1.66 0.95 18.93 1.02 0.64 0.40 12.00 0.74 0.60 1.09 0.95 1.07 3.25 53.02 1.18 ZK1501H13 0.48 1.37 0.77 1.01 0.89 1.18 1.76 1.04 1.09 6.31 1.98 1.18 1.17 1.87 7.41 0.69 0.37 0.54 4.00 0.80 0.51 0.98 1.06 0.95 4.94 25.06 1.98 ZK1501H15 0.60 1.33 0.76 1.35 0.83 2.57 4.40 1.76 1.30 23.58 3.11 1.36 1.98 1.44 17.52 1.01 0.66 1.20 12.44 1.13 0.73 1.18 1.22 1.36 3.88 56.38 1.56 ZK1501H17 0.58 1.17 0.87 1.34 0.65 0.83 1.10 1.15 1.10 2.69 1.78 1.62 0.88 1.10 2.53 0.50 0.31 0.87 2.44 0.58 0.40 0.83 0.92 0.88 1.88 3.71 1.26 ZK2709H1 0.98 0.50 1.02 0.82 1.34 1.39 1.46 1.80 1.45 2.08 2.50 1.66 1.86 1.68 1.56 0.92 0.79 1.83 5.89 1.43 2.53 2.40 1.43 1.70 3.44 3.19 5.49 ZK2709H3 0.75 0.60 0.66 1.03 1.16 1.95 3.48 1.50 1.09 13.67 1.88 1.38 1.57 1.25 6.56 1.03 0.78 1.19 6.67 1.11 2.34 1.44 1.17 1.45 3.69 13.09 1.74 ZK2709H5 0.45 0.74 0.95 1.08 0.79 0.71 1.11 1.12 0.96 2.44 1.93 1.49 1.72 1.58 2.37 0.46 0.43 1.22 3.00 1.33 1.26 1.01 1.06 1.14 3.00 3.70 1.85 ZK2709H6 0.83 0.57 0.69 0.97 1.04 1.85 3.43 1.42 1.02 9.23 1.75 1.25 1.48 1.14 8.00 1.01 0.79 1.08 7.56 1.11 1.96 1.47 1.07 1.27 3.44 20.91 2.58 ZK2709H8 0.85 0.56 0.69 1.05 1.19 1.75 2.29 1.51 1.17 7.90 1.98 1.46 1.68 1.33 4.70 0.99 0.78 1.04 5.67 1.04 1.69 1.69 1.18 1.40 3.31 22.73 3.00 ZK2709H11 0.91 0.50 0.67 1.10 1.14 1.58 2.38 1.53 1.29 11.06 2.11 1.49 1.75 1.37 4.59 1.06 0.87 1.01 6.44 1.10 1.32 1.77 1.30 1.45 3.44 20.55 2.10 ZK2709H12 0.91 0.77 1.09 1.01 1.14 1.20 1.43 1.57 1.29 26.27 1.83 1.53 1.59 1.15 1.09 0.91 0.87 1.35 3.67 1.44 1.54 1.39 1.20 1.36 2.69 1.98 3.38 caGohm(08 37(2):228–243 (2018) Geochim Acta ZK719H7 0.94 0.42 0.77 0.77 1.03 1.63 1.51 1.36 1.37 2.67 1.60 1.68 1.72 1.38 2.19 0.86 0.70 1.02 2.33 1.25 1.37 2.08 1.19 1.59 3.88 5.80 4.41 ZK719H13 0.93 0.49 0.68 0.93 1.21 2.02 1.90 1.44 1.40 5.81 1.84 1.95 2.02 1.43 5.19 0.90 0.79 0.96 3.78 1.16 1.88 2.00 1.24 1.59 5.25 35.36 4.25 ZK719H16 0.94 0.64 0.84 0.86 1.10 1.37 1.54 1.51 1.35 1.31 1.79 1.86 2.04 1.39 1.14 0.97 0.72 1.07 3.08 1.36 1.70 2.03 1.16 1.64 3.79 2.51 4.98

Enrichment factor (EF) = Xsample /XUCC Acta Geochim (2018) 37(2):228–243 237

Fig. 5 Spider diagram of trace elements of oil shale from Chang 7 oil layer

Table 4 Parameters of the palaeosedimentary environment of oil shale samples from Chang 7 oil layer

Sample no. V/Cr V/(V ? Ni) U/Th dU AU EB (ppm) Sp (%) Sr/Ba CIA Sr/Cu Fe/Ti (Fe ? Mn)/Ti Zr/Rb H (m)

ZK702H6 3.18 0.85 1.28 1.59 21.10 45.51 / 0.29 71.10 1.22 27.96 28.36 0.64 34.28 ZK702H14 3.52 0.89 3.63 1.83 49.13 88.07 1.56 0.31 73.61 1.16 30.68 30.85 1.12 92.16 ZK702H18 3.91 0.89 5.68 1.89 57.70 49.72 / 0.50 65.54 1.59 30.72 30.94 1.52 41.53 ZK702H24 5.27 0.92 6.39 1.90 57.91 56.47 / 0.50 67.75 2.71 31.29 31.56 1.60 36.71 ZK702H32 4.63 0.92 3.70 1.83 42.77 51.66 / 0.41 69.54 2.48 33.01 33.35 1.25 40.45 ZK1501H3 4.55 0.90 4.32 1.86 62.93 53.01 / 0.33 63.97 1.33 28.63 28.99 1.41 46.81 ZK1501H6 3.65 0.90 4.90 1.87 57.50 65.42 / 0.35 72.01 1.01 37.57 37.86 1.43 68.78 ZK1501H11 4.20 0.91 5.13 1.88 47.78 59.50 / 0.57 65.72 3.09 25.59 26.19 1.43 61.64 ZK1501H13 2.59 0.87 1.02 1.51 13.47 98.05 2.54 0.69 62.87 8.84 15.22 15.53 1.50 29.22 ZK1501H15 4.49 0.89 3.13 1.81 42.27 70.33 / 0.50 67.62 3.45 23.84 24.67 1.28 57.34 ZK1501H17 1.51 0.85 0.59 1.28 2.95 39.90 / 0.45 53.92 12.16 11.12 11.45 1.23 12.45 ZK2709H1 1.49 0.78 0.24 0.84 -1.66 207.82 13.26 0.31 76.64 3.91 11.03 11.42 1.41 37.75 ZK2709H3 2.76 0.84 1.35 1.60 13.33 74.21 0.21 0.30 68.55 1.97 18.37 18.85 1.11 57.05 ZK2709H5 1.68 0.77 0.39 1.07 0.88 81.36 0.91 0.35 65.78 7.57 10.03 10.46 1.47 6.75 ZK2709H6 2.35 0.83 1.80 1.69 17.60 121.09 4.79 0.30 66.24 1.90 16.74 17.21 1.28 58.15 ZK2709H8 2.18 0.82 0.91 1.46 8.03 119.40 4.62 0.27 72.13 2.77 14.09 14.42 1.08 51.32 ZK2709H11 1.83 0.79 0.86 1.44 7.60 84.85 1.25 0.23 74.15 2.39 14.42 14.70 1.04 57.18 ZK2709H12 1.39 0.74 0.24 0.84 -1.09 125.57 5.23 0.39 70.98 6.12 8.68 8.77 1.63 46.37 ZK719H7 1.83 0.83 0.41 1.10 1.07 211.00 13.57 0.27 78.72 3.14 13.05 13.34 1.06 33.81 ZK719H13 2.29 0.84 0.93 1.47 9.00 181.11 10.65 0.27 78.94 2.92 13.42 13.78 0.80 36.64 ZK719H16 1.53 0.80 0.21 0.77 -1.80 234.70 15.89 0.38 78.85 4.77 9.81 9.97 1.04 43.83 Average 2.90 0.85 1.50 2.24 24.21 100.89 6.21 0.38 69.74 3.64 20.25 20.60 1.25 45.25

EB, equivalent Boron; H, Paleo-water-depth to its active chemical property, element Rb tends to migrate Formation Profile of Lower Ordovician in Ordos Basin and and deposit in deep water with high energy (Teng et al. found that the average of Zr/Rb is 0.92, reflecting weak 2005). Therefore, Zr/Rb ratio can be applied to response hydrodynamic force. The Zr/Rb of oil shale samples from the variation of depth of water. The smaller Zr/Rb ratio Upper Paleozoic Shanxi Formation in Ordos Basin ranges turns, the deeper sedimentary water is and the weaker from 1.25 to 4.76 (average 2.12), showing relatively strong hydrodynamic force is. Teng (2004) studied Zhuozishan paleo-hydrodynamics (Zhao et al. 2016) (Table 5). The Zr/

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Table 5 Geochemical index of sedimentary environment and geochemical parameters of oil shale from Chang 7 oil layer Paleo-environments Judging criterion Oil shale from Chang 7 Conclusions oil layer (average)

Paleo-redox condition Strong reducing condition 4.25 \ V/Cr V/Cr:2.90; Dominated by reducing 1.25 \ U/Th V/(V ? Ni):0.85 condtion 12 \ AU U/Th:1.50 Reducing condition 2 \ V/Cr \ 4.25 dU:2.24 0.5 \ V/(V ? Ni) AU:24.21 ppm 0.75 \ U/Th \ 1.25 1 \ dU 5 \ AU \ 12 Oxidation condition V/Cr \ 2.00 V/(V ? Ni) \ 0.5 U/Th \ 0.75 dU \ 1 AU \ 5 Paleosalinity Fresh water EB \ 200 ppm EB:100.89 Dominated by fresh water Sp \ 5% Sp:2.81% sedimentation Sr/Ba \ 0.6 Sr/Ba:0.38 Brackish water 200 ppm \ EB \ 300 ppm 5% \ Sp \ 18% 0.6 \ Sr/Ba \ 1.0 Sea water 300 ppm \ EB \ 400 ppm 5% \ Sp 1.0 \ Sr/Ba Paleoclimate Cold and dry 50 \ CIA \ 65 CIA:69.74 Dominated by warm and Warm and humid 65 \ CIA \ 85 Sr/Cu:3.64 humid 1.5 \ Sr/Cu \ 5 Hot and humid 85 \ CIA \ 100 Dry and hot 5 \ Sr/Cu Hydrothermal Fe/Ti [ 20 East:26.87 East: existence depositional condition West:12.96 West: no existence (Fe ? Mn)/Ti [ 20 ± 5 East: 27.25 West:13.29 Paleo-hydrodynamics Strong Zr/Rb turns big Zr/Rb:1.25 Weak hydrodynamic force Weak Zr/Rb turns small Paleo-water-depth Semi deep–deep lake 20 m \ H H:45.25 m Semi deep–deep lake Shallow lake 10 m \ H \ 20 m

Rb ratio of oil shale samples is from 0.64 to 1.63 with an lacustrine sediments (20 ppm); Tco: Co abundance of average of 1.25, showing a weak hydrodynamic force. provenance (4.68 ppm) t: contribution values of Co from provenance to samples [can be replaced by (La from 5.1.6 Paleo-water-depth samples)/(La from terrigenous detrital) ratio and La from terrigenous detrital is 38.99 ppm] (Wu and Zhou 2000). The content of element Co can be applied to calculate The depositional rate of sediments of normal lake ranges paleo-water-depth quantitatively (Wu and Zhou 2000). from 150 to 300 m/Ma. Considering study location in the 5 The calculation is H = 3.05 9 10 /[Vo 9 Nco/(Sco- lake and previous researches (Zhang and Zhao 2002), we 1.5 t 9 Tco)] (Wu and Zhou 2000). H: paleo-water-depth set Vo as 200 m/Ma. (m); Vo: deposition rate of sediments (m/Ma); Sco:Co The calculated results indicate that paleo-water-depth abundance of samples; Nco: Co abundance of normal during sedimentation of oil shale samples is from 6.75 to

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Fig. 6 Correlations diagram of oil yield versus parameters of palaeosedimentary environment of oil shale from Chang 7 oil layer

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Fig. 6 continued

92.16 (average 45.25) (Table 5). Usually, the depth above are interrelated. So, in order to discuss their controlling 20 meters is defined as semi deep–deep lake and the depth degree on oil yield of oil shale, here we separate the above from 10 to 20 m is set as a shallow lake, so the oil shale six factors factitiously and suppose they are independent. samples from Chang 7 oil layer deposit in semi deep–deep Meanwhile, we assume all parameters can represent their lake (Table 5), which is in accordance with sedimentary corresponding sedimentary factors accurately. Then we facies. focus on the individual factors to be discussed. Different degree of correlation between oil yield and 5.2 Paleo-environment controlling factors on oil palaeoenvironment parameters can be seen from Fig. 4. yield Five parameters (V/Cr, V/(V ? Ni), U/Th, dUand AU) can all indicate that paleo-redox condition has an obvious Paleo-environment can influence oil yield of oil shale. influence on oil yield and high oil yield is closely related to However, there are so many factors to consider when the reducing condition (Fig. 6a–e). For paleosalinity, the referring to the sedimentary environment and the factors parameter Sp is more sensitive to oil yield than Sr/Ba and

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Table 6 Results of correlation analysis between oil yield and parameters of oil shale from Chang 7 oil layer

Factors Paleo-redox condition Paleosalinity Paleoclimate HDC PH PWD

Parameters V/(V ? Ni) V/Cr U/Th dU AU Sr/Ba Sp CIA Sr/Cu Fe/Ti (Fe ? Mn)/Ti Zr/Rb H

P value 0.001 0.001 0.000 0.000 0.000 0.978 0.42 0.938 0.001 0.000 0.000 0.935 0.018 R2 0.4456 0.5198 0.5611 0.691 0.5401 0.00004 0.2001 0.0003 0.4722 0.5403 0.5418 0.0004 0.2598

HDC hydrothermal depositional condition, PH Paleo-hydrodynamics, PWD Paleo-water-depth

Table 7 Results of homogeneity test of variance model between oil for sure that there are impacts of paleoclimate on oil yield. yield and parameters of oil shale from Chang 7 oil layer P values of two parameters in hydrothermal depositional Parameters dU Sr/Cu (Fe ? Mn)/Ti H condition are below 0.05, implying obvious influence on oil yield. Parameters of paleo-hydrodynamics conduct high P 0.003 0.023 0.501 0.751 P value (P = 0.935) on oil yield. So, it is considered not to affect oil yield. The P value of paleo-water-depth is 0.018, fresh water, compared with brackish water, is good for high indicating that oil yield of oil shale is influenced by paleo- oil yield (Fig. 6f–g). Two parameters concerning paleo- water-depth. In summary, paleo-redox condition, paleo- climate all explain that warm and humid climate is of great climate, paleo-water-depth, and hydrothermal depositional benefit to oil yield (Fig. 6h–i) and in Sr/Cu–Tad diagram condition affect oil yield of oil shale obviously, while the (Fig. 6i) it seems that the more humid the climate becomes, influences of paleosalinity and paleo-hydrodynamics are the bigger oil yield turns. For the judgment of hydrother- inconspicuous. mal deposition, the hydrothermal fluid has a positive After analyzing single factors, relevant multi-factors are influence on oil yield (Fig. 6j–k). Paleo-hydrodynamics discussed to identify different effective proportion on oil parameter shows a negligible relationship with oil yield, yield by Homogeneity test of variance. In 4 factors, indicating the effect of paleo-hydrodynamics may be parameters having the highest R2 are chosen to represent inconspicuous (Fig. 6l). In addition, paleo-water-depth has corresponding factors. For example, dU is selected to stand certain control effect on oil yield of oil shale obviously for the paleo-redox condition due to its highest R2 value (Fig. 6m). (0.691). Then, dU, Sr/Cu, (Fe ? Mn)/Ti, and H are cal- To further determine to influence degree of six factors culated to build correlation model with oil yield. The on oil yield, Student’s t test here is used to make sure P value of linear regression model is 0.000, illustrating that which factors do affect oil yield and which factors doesn’t. the model can well express oil yield. P values of individual Then Homogeneity test of the variance in statistics is factors are shown in Table 7. As explained above, the applied to decide which factors impact more and which smaller P value is, the bigger contribution degree is. factors impact less (Feng et al. 2006). Statistically speak- Therefore, the paleo-redox condition represented by dU ing, the P value is a declining indicator of confidence level, effect oil yield of oil shale most. Paleoclimate represented representing error probability of whole samples. If the by Sr/Cu ranks second. The third and the fourth factors are P value is equal to 0.05, it means that 5% of samples is a hydrothermal depositional condition, represented by caused by contingency. So, samples are considered rele- (Fe ? Mn)/Ti, and paleo-water-depth represented by H. vant when P is below 0.05. Otherwise, samples are not Through statistical analysis can provide a theoretical relevant. Meanwhile, that P value approaches to 0 indicates foundation, theory results still need to accord with geo- correlation is favorable (Feng et al. 2006). logical regularity. Obvious relations have been seen from In 5, parameters of the paleo-redox condition, P values scatter diagram and correlation analysis, indicating that of the parameters are all below 0.05, indicating that the main controlling factors of oil yield in oil shale from parameters can well reflect changes of oil yield (Table 6) Chang7 oil layer in Ordos Basin are a paleo-redox condi- and the paleo-redox condition has a positive correlation tion, paleoclimate, hydrothermal depositional condition, with oil yield. Two parameters of paleosalinity all show and paleo-water-depth. low correlations (R2 = 0.00004; 0.2001) with oil yield and However, the paleosalinity and paleo-hydrodynamics P value are all below 0.05 (P = 0.978; 0.42), which showing no obvious correlations with oil yield in numeri- illustrates that effect of paleosalinity on oil yield can be cally doesn’t mean they have no impact on oil yield. ignored. Maybe due to different methods, CIA of paleo- Actually, lacustrine oil shale usually deposits in fresh water climate shows low correlation and high P value with oil and weak hydrodynamic condition (Fan et al. 2012; Zhang yield, while P value of Sr/Cu is below 0.05. Therefore, it is et al. 2004) so that oil shale can form favorably. Hence,

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