Comparison of Geochemical and Mineralogical Characteristics of Palaeogene Oil Shales and Coals from the Huangxian Basin, Shandong Province, East China

: Coal and oil shale are both organic matter-rich sedimentary rocks. However, their sources of organic matter and their depositional environments are di ﬀ erent. The present study focuses on the Palaeogene Lijiaya Formation sequence in the Huangxian Basin, Shandong Province, East China, which has oil shales showing marine geochemical indicators overlain by coals indicating marine regression. We investigated the C1 coal seam and underlying OS2 oil shale layers, compared their geochemical and mineralogical characteristics, clariﬁed the details of their constituents, in order to elucidate the features of their sources, their depositional environments, and the post depositional processes in the context of the geological evolution of the basin. The Al 2 O 3 / TiO 2 (18.1–64.9) and TiO 2 / Zr ratios (28.2–66.5) in the C1 coals and OS2 oil shales, respectively, suggest a felsic to intermediate source, and the Mesozoic granite on the South of Huangxian Fault may be one of the provenances of these sediments. The low sulphur content (0.53–0.59%) and low Sr / Ba ratios (0.32–0.67) suggest a freshwater depositional environment for the C1 coals. In contrast, the higher total sulphur contents (0.60–1.44%), the higher Sr / Ba ratios (0.31–1.11%), and the occurrence of calcareous shells, indicate seawater intrusions during deposition of the oil shales. The V / Ni, V / (V + Ni), and V / Cr ratios of the OS2 oil shale suggest oxic to suboxic conditions with a distinct change in palaeo-redox between the lower and upper parts of OS2 seam. The high boron contents in C1 coals (average, 504 ppm) is related to the high content of analcime (with the correlation coe ﬃ cient of 0.96), and the high concentration of boron was attributed to a secondary enrichment by epigenetic hydrothermal solutions. The occurrence of idiomorphic-authigenic albite in association with analcime and quartz in veins in the coals suggests that albite is a product of a reaction between analcime and silica, both of volcanic origin. The reaction takes place at about 190 ◦ C, indicating that the area was a ﬀ ected by hydrothermal ﬂuids. and the record of the geological evolution of the basin. we the results of our study of the geochemical and characteristics of to discuss and and the of and


Introduction
Oil shale is defined as organic matter-rich sedimentary rock, which can be distilled to yield oil or gas [1,2]. Oil shale usually has a lower content of organic matter, with higher hydrogen and lower oxygen contents than coal [2]. The significant difference in the maceral composition between oil shale focuses on the coals of C1, the oil shales of OS2, and their host rock samples (roof and floor samples). They were deposited in a lacustrine environment as indicated by drill hole data, fauna, and geological setting [18].

Sampling and Analytical Techniques
A total of 18 samples were investigated, including four coal samples of C1, 12 oil shale samples of OS2, one roof sample of C1, and one floor sample of OS2 ( Figure 1C). These samples were collected from the underground working faces of the Liangjia Coal Mine, Huangxian Basin.
A sub-sample of each sample was ground to <200 mesh with a mill made of chromium-free steel and split into representative portions for the mineralogical and the chemical analyses. The ash yields, moisture, and volatile matter of coal samples were determined by a thermogravimetric analyser (LECO, TGA 801). One empty crucible and one certified coal standard (Leco coal standard LCRM reference 502-682) were analysed with no more than 18 samples in each run (there are 20 positions in the ceramic carousel). The calorific values of coals and oil shales were determined by LECO AC600. Two certified coal standards (GBW11101F and GBW11104L) were analysed along with every 10-15 samples to control the quality of the results. The total sulphur content was analysed by an automatic sulphur analyser (LECO SC832). The analyser was calibrated with certified coal standards (GBW11101f, GBW11104L, and GBW11110p) to cover a range of S concentrations 0.47% to 4.11% sulphur contents. Ultimate analysis, including carbon, hydrogen, and nitrogen content, were performed using a Vario Macro Elemental Analyzer. Vitrinite random reflectance was determined using a Leica DM4 P LED microscope equipped with a Fossil spectrophotometer, using incident light passing through a 546-nm band filter on the path to the photomultiplier.
Concentrations of trace elements in the coal, oil shale, roof, and floor samples were determined by inductively coupled plasma-mass spectrometry (ICP-MS), except B and Hg. Prior to ICP-MS analysis, the coal, oil shale, and host rock powder samples were subjected to microwave dissolution in a mixed HNO 3 + HF acid. The digestion reagent was a mixture of 5 mL HNO 3 and 2 mL HF for coal and low-ash oil shale (ash yield <50%) samples, and a mixture of 2 ml HNO 3 and 5 mL HF for each 50 mg host rock and high-ash oil shale (ash yield >50%) samples [20]. The procedures of digestion and ICP-MS analyses are more fully described by Dai et al. [20]. For boron analysis, the addition of H 3 PO 4 to the HNO 3 and HF aims to diminish boron volatilisation during acid-drying after sample digestion [21]. The concentrations of boron in the samples were determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The mercury contents of the samples were determined using the Direct Mercury Analyser (Milestone DMA-80), and the detection limit of Hg is 0.005 ng. Mineralogical compositions were determined using a Rigaku D/ max-2500/PC X-ray powder diffractometer (XRD) with Ni-filtered Cu-Kα radiation and a scintillation detector. Before XRD analysis, low-temperature ashing (LTA, <150 • C) of the coal samples and oil shale samples with low ash yield (<50%) was carried out using an EMITECH K1050X plasma asher. XRD analysis was carried out on the low-temperature ashes of the coals and low ash oil shales, and powdered samples of the high ash oil shale and host rock samples. Each XRD pattern was recorded over a 2θ interval of 2-70 • with 0.02 • steps. The Rietveld-based Siroquant™ commercial interpretation software was used to determine the mineral percentages from the X-ray diffractograms [22]. A field emission scanning electron microscope (FE SEM) in conjunction with an EDAX energy-dispersive X-ray spectrometer (Genesis Apex 4) was used to observe and record the morphological features and modes of occurrence of the minerals, and also to determine the distribution of selected elements in polished pellets of the coal and oil shale samples. Table 1 presents the proximate and ultimate analyses, thickness, total sulphur, and gross calorific value of individual coal and oil shale benches of C1 and OS2. The coals of C1 are classified as ultra-low ash (A d ≤ 10%) and low ash (10% < A d ≤ 20%) coals according to the Chinese Standard GB/T 15224.1-2018 [23] (coals with ash yields of no more than 10% and 10-20% are considered as ultra-low-ash coals and low-ash coals, respectively), and low-sulphur coals (S t,d < 1%) according to [24]. The GCV im, MMF values, varying from 24.545 MJ/kg to 26.324 MJ/kg, is in the range of subbituminous A coal (24.418-26.743 MJ/kg) according to ASTM D 388-18 [25].  On a whole-coal basis, the concentrations of most of the major-element oxides in C1 coals are lower than those of the average Chinese coals [26], but CaO and Na 2 O are enriched.

Trace Elements
Compared with the average values for world low-rank coals [27], trace elements of C1 coals in Liangjia Coal Mine are depleted, except for B and Ba. Boron is highly enriched, with a concentration coefficient (CC, the ratio of element concentrations in investigated samples vs. corresponding averages for world low-rank coals) of 9.0 [28]. The concentration of Ba is slightly higher than the average values for world low-rank coals [27] (CC = 1.1) ( Table 3).  Ave-C1, the average value of C1 coals; Ave-OS2, the average value of OS2 oil shales; R, correlation coefficient between concentrations of elements and ash yield of the studied samples; Ave-C, average value of world low-rank coal by Ketris and Yudovich [27]; Ave-S, average values for world terrigenous and volcanic-sedimentary shales reported by Ketris and Yudovich [27]; CC-C1, concentration coefficient of trace element in C1 coals, the ratio of the element concentration in C1 coals vs. Ave-C; CC-OS2, concentration coefficient of trace element in OS2 oil shales, the ratio of the element concentration in OS2 oil shales vs. Ave-S; nd, not detected; bdl, below detection limit.
Compared with the average values for world terrigenous and volcanic-sedimentary shales reported by Ketris and Yudovich [27], the concentrations of Sr and B in OS2 oil shales are slightly enriched (CC values of 1.47, 1.06), and other trace elements are depleted.
A strong positive correlation exists between concentrations of most trace elements and ash yields in all coal, oil shale, roof, and floor samples ( Table 3). The correlation coefficients (r) of concentrations of Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Cd, Sn, Cs, REE and yttrium and ash yield are higher than 0.9. However, boron is negatively correlated with ash yield, with a correlation coefficient of −0.86 (Table 3). In order to show the inorganic matter affinity of these elements, X-Y plots of the concentrations and ash yields of these elements are shown in Figure A1 [29].
The total concentrations of rare earth elements and yttrium (REY) in coals range from 11.8 to 31.7 ppm, with an average of 17.1 ppm (  [32]. In the C1 coals, OS2 oil shales and the host rock samples, the Ba/Eu ratios have an average of 748, most coals and some oil shales have Ba/Eu ratios of more than 1000 (Table 3). Therefore, the positive Eu anomalies in the studied samples are due to Ba interference, and therefore the Eu values interfered by Ba are not interpreted in this study.

Minerals in the C1 Coals
The main minerals of the C1 coals are quartz, kaolinite, mixed-layer I/S, anorthite, analcime, calcite, and bassanite. The minerals of the roof sample are mainly quartz, mixed-layer I/S, muscovite, kaolinite, albite, orthoclase, calcite, pyrite, and apatite (Table 4). In order to show more directly the distribution of the main minerals among coal, oil shales, roof, and floor, we divided the minerals into six groups: quartz, clay minerals (kaolinite, mixed-layer I/S, illite, muscovite, and chamosite), feldspar (anorthite, albite, and orthoclase), analcime, carbonate minerals (calcite, high-Mg calcite, siderite, and ankerite), and pyrite ( Figure 2). Sample LJ1-3 is unique in its high content of calcite (40.7%, on a low-temperature ash basis), corresponding to the high concentration of CaO (39.36%, on ash basis). Compared with the OS2 oil shales, the C1 coals have high contents of analcime, especially LJ1-4 (46.2%, on a low-temperature ash basis). Bassanite is identified by XRD in most LTA residues of C1 coals. However, we could not detect bassanite in C1 coals under the analytical SEM, and no bassanite was identified in raw oil shale, roof, and floor samples by XRD. Moreover, we detected sulphur in organic matter using a SEM-EDS, so bassanite may represent an artifact derived from the interaction of non-mineral Ca with organic S during plasma ashing [7]. Quartz occurs as fine particles in the crack in organic matter, or as grains scattered in the organic matter ( Figure 3A,B), as large discrete grains indicating terrigenous origin, as fracture fillings with calcite indicating epigenetic origin (Figure 3).
Albite occurs as a fracture filling across the coal bedding, indicating deposition from epigenetic solutions ( Figure 4A,B). Albite also occurs as irregular polygons in the cement of calcite ( Figure 4C). The albite particle along the bedding plane indicates the syngenetic detrital origin ( Figure 4D). SEM-EDS analysis reveals that the albite of different occurrences in C1 coals does not contain detectable concentrations of potassium or calcium, indicating that it is a pure end member.  Calcite in C1 coals commonly occurs as filling cracks of organic matter, indicating an epigenetic origin ( Figure 3A), fracture filling with quartz cement (Figure 3D), and cement around albite and organic matter ( Figure 4C).

Minerals in the OS2 Oil Shales
The main minerals of OS2 oil shales are quartz, kaolinite, mixed-layer I/S, illite, anorthite, analcime, pyrite, calcite, high-Mg calcite, and siderite. Clay minerals in OS2 oil shales identified by XRD include kaolinite, mixed-layer I/S, and illite. Compared with clay minerals in C1 coals, the average concentration of illite in the OS2 oil shales is high, and that of kaolinite is low. Anorthite is the most common feldspar in OS2 oil shales like in C1 coals, and albite was also identified in U2-1-2 and U2-1-3 oil shales by XRD. The carbonate minerals in OS2 oil shales include high-Mg calcite, siderite, and ankerite identified by XRD. Pyrite is common in OS2 oil shales, but it was not detected by XRD in the C1 coals, in agreement with the relatively low sulphur content in C1 coals ( Table 1).
The SEM results indicate the following features: Quartz in the OS2 oil shales from the Liangjia deposit occurs as cell filling ( Figure 5A), fine grains scattered in the organic matter matrix ( Figure 5B), detrital particles in illite matrix ( Figure 5C), and also intergrown with albite, K-feldspar, and calcite ( Figure 5D). Broom-like kaolinite in the illite matrix occurs with the edge altered to chlorite ( Figure 5C). The feldspars in OS2 oil shale vary in their proportions ( Figure 5E-G). Crystals of pure albite are intergrown with those of ankerite ( Figure 5H). Chloritized feldspar occurs as detrital grains in the matrix of organic matter, indicating its syngenetic origin ( Figure 5G). Feldspars are also intergrown with apatite ( Figure 5I). The upper part of the OS2 seam (OS2-2) has a higher content of carbonate minerals than the lower part (OS2-1), with calcite as the dominant component (Table 4). U2-2-4 has a high content of calcite (42.7%, on low-temperature ash basis), unlike the massive or fracture-filling occurrence in C1 coals, calcite mainly occurs as laminae in organic matter, with the long-axes of the laminae aligned along the bedding, indicating its syngenetic and biogenic origin, and the calcareous shells may be their potential precursors ( Figure 5E, and Figure 6A,B) [7]. To a lesser extent, calcite also occurs as large grains surrounded by calcite laminae (Figure 6A,B). In some cases, calcite replaces the biological cell wall ( Figure 6C). High-Mg calcite was only detected by XRD in the lower part of the OS2. High-Mg calcite was also imaged using a SEM in U2-1-1 ( Figure 6D). Pyrite mainly occurs as framboids and euhedral crystals ( Figure 7A-D). Two types of framboidal pyrite were identified using a SEM: one with massive mineralisation (Figure 7A), another type consists of euhedral pyrite crystals [24,33] (Figure 7A,B). Framboidal pyrite is assumed to have two kinds of origin: biogenetic and inorganic origin. To test the different origins, experiments were performed under different conditions. Kizilstein and Minaeva performed the laboratory experiments in the presence of multiple types of bacteria [34]; Farrand performed the experiments using mineral solutions with organics, but without any bacteria [35]. The massive mineralisation having globular texture is supposed to be of bacterial origin, and the well-shaped crystals in the framboids are considered to be the crystallisation from mineralising solutions in the organic matter [33]. The bacterial pyrite framboids usually occur as aggregates of small or large globules, irregular in shape. In contrast, inorganic framboidal pyrite exhibits a relatively uniform mineralisation, and the pyrite crystals in individual framboidal bodies are usually equal in size [33]. In this study, the framboidal pyrite with massive mineralisation is supposed to be of bacterial origin (Figure 7A), and the framboids consist of euhedral pyrite crystals are likely to be of inorganic origin ( Figure 7B). Euhedral pyrite crystals dispersed in the organic matrix or occur as aggregates bounded by calcite laminae (Figure 7C,D). Pyrite also occurs in dense radial forms in the organic matter matrix, and clusters of nodular pyrite ( Figure 7E,F). The modes of occurrence of pyrite in OS2 oil shales are closely related to apatite and calcite. Pyrite occurs as filling the cavities in apatite ( Figure 8A) and scattered among the apatite particles ( Figure 8B). Small pyrite grains dispersed over a large apatite grain, indicating that the pyrite formed later than the apatite ( Figure 8C). Pyrite in the calcite matrix occurs as fine particles or thin crystals ( Figure 8D).
Apatite occurs in various forms in the OS2 oil shales, including a rod-like shape ( Figure 9A), the aggregations of subrounded particles ( Figure 8B), lens-shaped aggregate ( Figure 9B), jagged-shape bands associated with biogenetic calcite laminae along bedding planes ( Figure 9C), the dense arrangement of apatite grains with anorthite inclusions (Figure 9D), and intergrown with feldspar with frost boundaries ( Figure 5I). The jagged-shape apatite ( Figure 9C) may represent a cell wall and biogenic origin.

Provenance
Although Ti and Al, as reported, are mobile in acidic conditions [36][37][38], they are relatively immobile in supergene environments. Therefore, the Al 2 O 3 /TiO 2 ratio has been effectively used as an indicator of the provenance of sedimentary rock [39], including coals [40], and oil shales [11]. Typical Al 2 O 3 /TiO 2 ratios are 3-8, 8-21, and 21-70 for sedimentary rocks derived from mafic, intermediate, and felsic dominated sediment source regions, respectively [39]. The high values of Al 2 O 3 /TiO 2 ratios of the C1 coals and OS2 oil shales (18.1-64.9) are indicative of a felsic to intermediate sediment source (Figure 10.). The TiO 2 /Zr ratio range from 28.2 to 66.5, which is in agreement with felsic to intermediate source rock [39]. In the diagram of Nb/Y versus Zr/TiO 2 ( Figure 11) [41], the C1 coals, OS2 oils shales and their host rocks fall into the andesite, dacite and trachyandsite categories also suggest that the source magmas had a felsic to intermediate composition.  The angular shapes of detrital quartz grains and their greatly varying sizes ( Figure 3C, Figure 4D, and Figure 9A,B) indicate that they were deposited a short distance from their source. The Huangxian Basin is fault controlled, and the Mesozoic granite on the South of Huangxian Fault may be a major source provenance of the sediments (Figure 1).

Depositional Environment
The concentrations of several indicative elements and/or their ratios, such as sulphur, boron, Sr/Ba, V/Cr, V/Ni, V/(V + Ni), have been used as indicators for the depositional environments of coal [6,42] and oil shale [2,11,43].

Palaeosalinity
The sulphur contents in coal and oil shales have been widely used as indicators for freshwaterand seawater-influenced depositional environments [6,24,[43][44][45][46][47][48][49][50]. The concentrations of total sulphur in CI coals is 0.53% to 0.59% (Table 1), indicating freshwater environments [24]. However, in the OS2 oil shales, the total sulphur varies from 0.60% to 1.44% (Table 1). These values may indicate a higher proportion of seawater in the depositional environment of the oil shales than in that of the coal. Moreover, the occurrence of pyrite as euhedral crystal and framboids ( Figure 6) and the widespread occurrence of organic sulphur ( Figure 5B) indicate the syngenetic origin of sulphur bearing phases and varying degrees of seawater inputs during depositions [24], although framboidal pyrite could be derived from epithermal solutions [51], but the organic sulphur is generally low [24]. The calcitic shells in oil shale (U2-2-4) probably indicate a lacustrine environment, and the shell-rich band may indicate the deepening of the water and a deeper-water faunal accumulation [7].
In summary, the calcareous shells that contribute calcite, together with the relatively higher total sulphur concentrations and higher Sr/Ba ratios of the oil shales, are interpreted as indications for a higher contribution of seawater during the deposition of the oil shales in comparison with a lesser effect associated with the deposition of the overlying coals. Therefore the transition from oil shale to coal observed in the Liangija Coal Mine indicates a marine regression.

Palaeoredox
The V/Ni, V/(V + Ni), and V/Cr ratios are widely used as geochemical indexes of palaeoredox in sedimentary rocks [6,[52][53][54]. Vanadium and Ni occur in tetrapyrrole structures, which are highly stable under reducing conditions. Furthermore, when the organic matter is exposed to oxic conditions, the tetrapyrrole content will decrease, resulting in low contents of V and Ni [53]. Thermodynamics predict that V/Ni in bitumens and oils will increase when the depositional conditions become reducing due to the preferential removal of Ni as sulfide under anoxic conditions [52]. Galarraga et al. [55] suggested V/Ni ratios of 1.9-3 and >3, represent suboxic and anoxic conditions, respectively. Hatch and Leventhal [56] related V/(V + Ni) ratios to depositional conditions, the high V/(V + Ni) ratios (0.84-0.89) represent a strongly stratified water body and anoxic conditions, the intermediate V/(V + Ni) ratios (054-0.82) represent less strongly stratified and anoxic conditions, and the low ratios (0.46-0.60) indicate a weakly stratified and dysoxic condition. Chromium can substitute for Al in clay, and can be absorbed by clay or occur as chromite [52], and is not affected by redox condition [54]. Jones and Manning [52] suggested that V/Cr ratios of >2 indicate anoxic condition, and the lower values indicate more oxidising conditions.
In the present study, the concentrations of V, Ni and Cr show positive correlations with the ash yields (with correlation coefficients of 0.90, 0.95 and 0.95, Figure A1), indicating inorganic affinities. V, Cr, and Ni are associated with silicates, most likely the clay minerals [57].

Analcime and Albite
Analcime, a type of Na-rich zeolite, was detected by XRD in all C1 coals and most OS2 oil shales (Table 4, Figure 2). The contents of analcime in C1 coals range from 12.8% to 46.2% on a mineral basis. The high zeolite concentrations in coal can be related to the volcanic activity [58]. When the original volcanic glass is Na-rich, the Na-rich solution will cause alkaline activation of the aluminosilicate glass, and produce Na-rich zeolite, like analcime [58]. Volcanic glass is the primary precursor for zeolites, and zeolites can alter to feldspar when the physicochemical environment changes or time is sufficient for transformation to a stable phase [59]. Campbell and Fyfe [60] suggested the reaction analcime + quartz = albite + liquid water is in equilibrium near 190 • C or possibly at even lower temperatures. This mineral assemblage may, therefore, indicate the ambient temperature of the coal at the time of the formation of the idiomorphic albite. Effects of high temperatures were reported from Palaeogene reservoir rocks in boreholes the Bohai Bay area and were related to volcanic activity in this area [61,62].
In general, the reported occurrences of albite in coal are of detrital origin [7,63,64]. In some cases, albite is derived from epigenetic hydrothermal solutions [65,66], and some occurrences characterised by sharp edges are of pyrogenic origin [40,67]. Albite in the C1 coals mainly occurs as fracture filling ( Figure 4A,B), indicating an epigenetic origin.
The occurrence of quartz ( Figure 3A,B) and albite ( Figure 4A), the last being of pure chemical composition in the form of large crystals filling cracks in the organic matter in coals ( Figure 4A,B), raises the possibility that the fracture-filling albite is a product of alteration of analcime, the precursor was volcanic glass and formed analcime through a dissolution and precipitation process [58,59]. The transformation of analcime to albite takes place at a high temperature of around 190 • C [60]. It thus provides an indication of the thermal regime in the Huangxian Basin.

Analcime and Boron
The average concentration of B in the C1 coals is 504 ppm on a whole-rock basis, which is much higher than the average in world low-rank coals (56 ppm) [27]. The OS2 oil shales have an average B concentration of 86.1 ppm, which is near the average value of terrigenous and volcanic-sedimentary shales (81 ppm) [27]. Boron concentration is used as an indicator of the palaeosalinity of the depositional environment of coals or other sedimentary rocks [2,[68][69][70]. Concentrations of B of <50, 50-110, and >110 ppm in coal are interpreted as indicative of freshwater, mildly brackish water, and brackish water, respectively [70]. Successful applications of this method were reported from the Hongmao and Luocheng deposits in Jiangxi Province, China [71], Datanhao deposit in Inner Mongolia, China [72], and lacustrine Big Marsh oil shale from Nova Scotia, Canada [2]. However, the use of boron concentration as a palaeosalinity indicator remains controversial [6,73] because increased B contents in coal may be the result of secondary enrichment [6], caused by hydrothermal activity [74], acid water [75,76], volcanic activity [73,77], or climatic variations [77]. Even some seawater-influenced coals have low B concentrations [78,79], and this was explained by the screening of the coal seam overlain by a clay layer, insulating peat from the seawater effects during the accumulation of the overlying limestone [78]. The concentrations of boron in the C1 coals and OS2 oil shales show positive correlations with analcime (with the correlation coefficient of 0.96 and 0.71, respectively) ( Figure 13A), indicating that the increased B contents due to their secondary enrichment by epigenetic hydrothermal solutions. Furthermore, analcime shows positive correlations with ash yield, with correlation coefficient values of 0.87 and 0.93 for C1 coals and OS2 oil shales, respectively ( Figure 13B). This may illustrate that epigenetic fracturing is common in the organic matter. The higher the concentration of organic matter is, the more fractures may be generated for potential analcime filling.

Mineralogical and Geochemical Characteristics of An Example "Marine Oil Shales" for Comparison with Those from the Huanxian Basin
The present study of oil shales from the Huagxian Basin revealed mineralogical and geochemical features indicative of a diminishing influence of sea water on the environment of deposition. It may be interesting to compare them with an example of "marine oil shale", showing clear indication of their marine origin. An example of such "oil shales" of marine origin is the Campanian-Maastrichtian (Upper Cretaceous) calcareous bituminous rocks of the Ghareb Formation, which extend over large areas around the eastern Mediterranean. Several occurrences in Israel have the following general characteristics. The dominant mineral is calcite occurring in various forms, including well-preserved planktonic foraminifera. Other minerals are scarce; low contents of clay minerals, gypsum and pyrite-around 1%. The total organic matter content is up to 19% and it shows a large compositional variation [80]. The kerogen (non extractable fraction) is characterized by H/C atomic ratios of 1.2-1.5, and S/C atomic ratios (after removal of pyrite) of 0.045-0.063 [80].
The occurrence of idiomorphic calcite crystals adjacent to gypsum which shows textures of dissolution, all within a foraminiferal chamber indicate the process of sulphate reduction and calcite precipitation [81]. This observation is supported by the presence organo-geochemical indicators for sulphate-reducing bacteria [80]. It is interesting that idiomorphic crystals of microcline of various habits, and also idiomorphic heulandite and anatase, were observed in these calcareous bituminous rocks (similar to Huangxian). Upon burial in the Dead Sea graben, these bituminous rocks produced asphalt and oil, as indicated by their high S content and biomarker compounds [82].
It might be of interest to explore whether there are organo-geochemical indicators in oil occurrences in the Huangxian basin that can be related to these oil shales.

Conclusions
The geochemical and mineralogical features of the C1 coals and OS2 oil shales in the Linagjia Coal Mine of the Huangxian Basin provide clear indications about their composition, their environment of deposition, and the post-depositional processes: (1) The C1 coals from the Liangjia Coal Mine are subbituminous A coals with ultra-low to low ash yield, and low-sulphur contents.
(2) The Al 2 O 3 /TiO 2 ratio and TiO 2 /Zr ratio suggest a felsic to intermediate sediment source, and the Mesozoic granite on the South of Huangxian Fault may be the source of the inorganic components of the Palaeogene coals and oil shales.
(3) The OS2 oil shales were influenced by seawater intrusion to the lake, which caused high values of total sulphur contents and Sr/Ba ratios, brought about the appearance of the calcareous-calcitic shells and syngenetic pyrite. However, The C1 coals were deposited in a freshwater-dominated lacustrine environment. The marine regression seems to be the factor that transformed the deposition of oil shale to coal in the Huangxian Basin.
(4) The OS2 oil shales were deposited under anoxic to suboxic conditions with a palaeo-redox change between the lower and upper parts of the OS2 section.
(5) The high boron contents in C1 coals (average, 504 ppm) are related to the high content of analcime (with a correlation coefficient of 0.96), and they have an epigenetic origin. (6) The albite in the form of large crystals filling cracks in the organic matter of coal and their pure chemical composition raises the possibility that the albite was produced by the reaction of analcime and quartz. This reaction takes place at over 190 • C and thus provides an indication of the effects of hydrothermal fluids on the Palaeogene coal beds investigated.