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Article

Sedimentary Environment and Organic Matter Enrichment Model of Saline Lake Source Rock in the Linhe Depression, Hetao Basin, China

by
Xiaoyan Fu
1,
Jungang Lu
1,*,
Yulei Shi
2,
Ranran Zhou
2,
Shijia Chen
1 and
Man Yuan
1
1
School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, China
2
ChinaPetroChina North China Oilfield Branch, Renqiu 062550, China
*
Author to whom correspondence should be addressed.
Processes 2023, 11(7), 2114; https://doi.org/10.3390/pr11072114
Submission received: 16 June 2023 / Revised: 8 July 2023 / Accepted: 12 July 2023 / Published: 15 July 2023
(This article belongs to the Special Issue Latest Advances in Petroleum Exploration and Development)
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Abstract

:
The well-developed mudstone and gypsum mudstone in the Oligocene Linhe Formation (E3l) in the Hetao Basin are the main source rocks for gypsum. However, the sedimentary environment and organic matter (OM) enrichment factors of E3l are not clear, and this inhibits the prediction of hydrocarbon source rock distribution and resource calculation. Major and trace elements, total organic carbon (TOC), pyrolysis using the Rock-Eval II, and saturated hydrocarbon gas chromatography–mass spectrometry (GC–MS) analyses were performed in this study. The results show that E3l was deposited in brackish water and saline–ultrasaline water, with weak oxidation reduction in an arid and hot environment. Terrestrial input inhibits OM enrichment, while the redox, paleosalinity, paleoclimate, and paleoproductivity play a catalytic role. The main controlling factors of the same lithologic source rocks are different: terrestrial input and paleoclimate have a greater impact on mudstone, and the redox and paleosalinity were more favorable to gypsum mudstone. Although the main controlling factors are different for different lithologies, their OM enrichment characteristics are still consistent. The E3l water body was deep, and the contribution of nutrients from terrigenous debris to OM enrichment was less. In addition, the water retention environment changed significantly during the E3l sedimentary period, resulting in fewer nutrients, which limited the improvement of surface water paleoproductivity. The arid climate increased water evaporation and salinity, which to some extent prevented consumption and decomposition. Weak oxidation-reduction fluctuations and the stratification of the water body were obvious, and this was not only conducive to the enrichment of OM but also to its preservation.

1. Introduction

Many large terrestrial oil and gas fields have been developed in saline lake basins [1,2,3,4]. The characteristics of the paleo-sedimentary environment and the development model of source rocks in saline lake facies are important scientific issues in petroleum geology, geochemistry, and lacustrine sedimentology. Compared with freshwater lake basins, the biological development characteristics, sedimentary environment, and organic matter (OM) development models of source rocks in saline lake basins are special [5,6,7]. First, changes in water salinity affect the development of microorganisms and algae [8,9]. Secondly, the special stratification of sedimentary water in the saline lake basin will lead to corresponding changes in the temperature, light transmittance, and redox properties of sedimentary water with depth, which is more conducive to the production and preservation of OM [9,10]. Finally, saltwater lake basins have obtained abundant hydrocarbon production [11,12], confirming good research prospects.
Typical paleo-sedimentary environments and development models of lacustrine source rocks include the large-scale deep-water anoxic lake basin model, the high-salinity enclosed lake basin model, the medium-deep tropical lake basin model, and the oligotrophic lake basin model [13,14,15,16,17]. Based on the sedimentary theory and previous research experience, the study of the paleo-sedimentary environment mainly includes terrestrial input [18], redox conditions [19], paleosalinity [20], paleoclimate [21], paleoproductivity [22], sedimentation rate, paleowater depth [23], etc. Terrestrial inputs introduce plant detritus but also dilute OM availability [18]. Reducing the environment reduces consumption and contributes to OM enrichment [13,14,15,16,17,18,19]. Adequate salinity is more conducive to biogenesis [8]. Climate affects water evaporation and is closely related to conservation [24]. Paleoproductivity directly affects the hydrocarbon generation capacity [25]. The sedimentation rate and paleowater depth affect water redox and productivity, and they further affect OM development [23,26].
At present, there are few studies on the source rocks of the Linhe Formation (E3l) in the Linhe Depression of Hetao Basin. Seismic facies are studied for their source rock distribution [27], organic geochemistry [28], oil source correlation [29], structural prediction of exploration prospects [30], etc. Ancient sedimentary environment characteristics of E3l mudstone and gypsum mudstone have not been systematically studied. There is no distinction between their sedimentary environments. This is not conducive to the correct assessment of hydrocarbon generation capacity and distribution characteristics. In addition, the ancient sedimentary environment and development model of saline lake source rocks in E3l are clarified. This can not only enrich the theoretical research of saline lake source rocks but also enrich the content of sedimentology, environmental chemistry, and petroleum geology.
Based on the characteristics of organic geochemistry and the inorganic elements of source rocks, this study will discuss the effects of terrestrial input, redox, paleosalinity, paleoclimate, sedimentation rate, and paleowater depth on organic matter enrichment in mudstone and gypsum-bearing mudstone. It will present an innovative discussion on organic matter enrichment factors in the source rocks of mudstone and gypsum mudstone, and this will also provide a good guiding role in the exploration and development of source rocks in saline lake basins.

2. Geological Setting

The Hetao Basin has an area of approximately 40,000 square kilometers, between the Yinshan and Helan Mountains, and it is adjacent to the Ordos Basin (Figure 1a) [28]. In the regional tectonic position, the basin is sandwiched between the North China plate, the Alxa plate, and the Central Asian orogenic belt [30,31]. The Linhe depression is located in the western part of the basin and has the largest area of 2.43 × 104 km2, which is the main sedimentary depression and oil-bearing area (Figure 1a,b) [32,33,34]. It can be divided into the Jilantai sag in the south and the Bayannaoer sag in the north. It has the structural characteristics of east–west zoning and north–south zoning [35]. Among them, the east–west direction of the Bayannaoer sag can be divided into the central fault belt and the Huanghe depression (Figure 1b). The Jilantai sag is divided into the Jixi depression and the Jibei uplift. The basement of the basin is the metamorphic rock series of the Paleoproterozoic–Archaean Wulashan Group. Its stratigraphic distribution is shown in Figure 1c. The Linhe Formation is a better source rock, while the Wuyuan formation is a better cap rock [28].

3. Materials and Methods

A total of 78 core samples were collected for experiments. A total of 42 samples (23 mudstones and 19 gypsum mudstones) were used for total organic carbon (TOC), Rock-Eval pyrolysis and saturated hydrocarbon gas chromatography—mass spectrometry (GC–MS). We collected 36 core data (10 mudstones, 11 sandstones, and 15 gypsum mudstones) from the Linhe Formation of well H6 for major and trace element analysis experiments. The sampling location is shown in Figure 1b. The main trace element sampling diagram and core photos are shown in Figure 2. Because the cores shown in both Figure 2a,b are sandstones, this section was not continuously sampled. Lithology of LH-13, LH-14 and LH-15 is a gypsum-bearing argillaceous siltstone, which is summarized as gypsum mudstone in data processing.
Before analysis, the samples were washed and dried with methanol/dichloromethane (1/9) solution and ground to powder. Total organic carbon (TOC) analysis was conducted using a LECO CS-125 carbon sulfur analyzer. Specific analysis steps can be found in Xiao et al. [36]. After the air in the instrument was removed by helium, it was analyzed by a Rock-Eval II instrument and heated to 600 °C. The pyrolysis parameters were recorded according to the analysis steps of Su et al. [37].
GC–MS analysis was performed on Agilent 6890 chromatographic column with Agilent 5975 mass spectrometer detector. The saturated hydrocarbon was separated on a 30 m-long HP-5MS elastic silica capillary column (0.25 mm in diameter and 0.25 μm in wall thickness). The gas chromatography heating program was 50 °C constant temperature for 1 min, then 3 °C/min to 310 °C, and a constant temperature of 30 min. Its carrier gas was at a constant current mode, with a flow rate of 1.0 mL/min.
Major and trace elements have been mentioned many times in the literatures, and the experimental procedures of this current experiment mainly refer to the experimental methods of Wang et al. [38] and Li et al. [27].
Analysis of trace boron was carried out with sodium hydroxide melt on an inductively coupled plasma mass spectrometer (Model 7900). The sample was weighed in a nickel crucible, and the sodium hydroxide flux was added to the sample. After fully mixing, it melted at a high temperature. After cooling, the melt was dissolved and diluted in 100 mL deionized water. An equal amount of HCl was added to the solution, fully mixed, and analyzed by inductively coupled plasma mass spectrometry. After the spectral interference between the elements was corrected, the final analysis result was obtained.

4. Results

4.1. Organic Geochemistry

Table 1 summarizes the geochemical data of source rocks.
TOC represents the total amount of all organic matter in the rock [39,40]. The S1 represents free hydrocarbon (mg/g), i.e., liquid hydrocarbon content per unit mass of source rock detected at 300 °C. The S2 (mg/g) represents the amount of kerogen cracked by heating in source rocks from 300 to 600 °C [41,42]. The hydrogen index (HI) is S2/TOC × 100% [40,41]. The pyrolyzed hydrocarbon (Tmax) maximum temperature represents the temperature corresponding to the highest point of peak S2, which can be used to indicate OM maturity [43].
The TOC values of mudstone samples in the study area were 0.11–2.97%, with an average of 0.95%. The S1 value was between 0.04 mg/g and 0.89 mg/g, averaging 0.31 mg/g. The content of S2 was from 0.11 mg/g to 18.76 mg/g, averaging 3.76 mg/g. The Tmax values were between 416 °C and 435 °C, with an average of 423 °C. The average HI value was 293 mg HC/g TOC. The parameters of gypsum mudstone were similar to mudstone.
Source rock quality can be assessed by TOC and S2 [40]. The quality of E3l source rock mudstone and gypsum mudstone in the Hetao Basin was the same, which is distributed from Poor to Very Good (see Figure 3a). OM types are mainly II2 and III, and some are I and II1 (Figure 3b). Most source rock samples are distributed between immature and mature (Figure 3b).
In the m/z 85 mass chromatogram of the study area, the peak of pristane (Pr) is lower than that of phytane (Ph). The Pr/Ph ratio of mudstone is 0.14–0.87 (average 0.36), and the parameter of gypsum mudstone is 0.20–0.59 (0.36). In addition, γ and β-carotene are detected in the gypsum mudstone (Figure 4). The source rocks in the study area have high gammacerane. The gammacerane index (gammacerane/C30 hopane) (GI) in mudstones is 0.29–1.86 (average 0.97), and the GI ratio in gypsum mudstones is 0.16–1.23 (average 0.77). They all have the ‘tail up’ phenomenon of C31–C35 hopane (Figure 4).

4.2. Geochemistry of Elements

4.2.1. Major Elements

SiO2 content in the main elements is high, averaging 50.11%, followed by Al2O3 and CaO. The Al2O3 content is 3.40–18.29%, with an average of 10.89%, and CaO content is 1.25–27.00%, averaging 8.39%. Compared to Union Carbide Corporation (UCC) elements, SiO2 in sandstone is relatively enriched while other major elements are relatively depleted. The variation trend of elements in mudstone and gypsum mudstone is similar. However, P2O5 in mudstone is relatively enriched, and in gypsum mudstone it is relatively depleted (Figure 5, Table 2).

4.2.2. Trace Elements

Table 3 summarizes the trace elements content. Enrichment factor (EF) is often used to evaluate the trace elements enrichment [44,45]. The formula is XEF = (X/Al) sample/(X/Al) UCC, where X and Al represent element content. The enrichment degree of elements is divided into slight enrichment (EF > 1), moderate enrichment (EF > 3) and strong enrichment (EF > 10), and EF < 1 indicates depleted [44,45]. The calculated trace element enrichment factor profile of the Linhe Formation in the study area is shown in Figure 6. The EF of trace elements obviously changes with lithology and can be divided into four cases, which are represented by four colors in Figure 6.
(1) BaEF, NaEF and KEF have little difference in mudstone and gypsum mudstone, but they are relatively enriched in sandstone. NaEF is relatively depleted in mudstone and gypsum mudstone (EF < 1), and it is slightly enriched in sandstone (1 < EF < 3). (2) CoEF, CrEF, CuEF, FeEF, ThEF, NiEF and VEF show the opposite characteristics. They are relatively high in mudstone and gypsum mudstone, and they are depleted in sandstone (EF < 1). (3) PEF, MnEF, MoEF, MgEF, CaEF and UEF are characterized by moderate enrichment and strong enrichment in lithologic transition areas. (4) RbEF and TiEF do not change with lithology. RbEF is slightly enriched and TiEF is relatively depleted.

4.2.3. Rare Earth Elements

Rare Earth Elements (REEs) are generally divided into light rare earth elements (LREEs) and heavy rare earth elements (HREEs). LREEs include La~Eu, while HREEs include Gd~Lu [46,47,48]. Due to the strong stability of REEs, they are often used in paleo-sedimentary environment analysis [48,49]. The average ∑REEs is 134.6 μg/g in mudstone, 47.7 μg/g in sandstone and 149.4 μg/g in gypsum mudstone. The average value of ∑REEs in UCC is 146.4 μg/g, and the gypsum mudstone is higher than the Union Carbide Corporation (UCC), while the mudstone is lower. The differentiation degree of ∑REEs can be reflected by the ratio of LREEs to HREEs ∑LREEs/∑HREEs [50,51,52,53]. The average value of ∑LREEs /∑HREEs in mudstone is 10.32, in sandstone 9.63, and in gypsum mudstone 10.65. The ratio of mudstone and gypsum mudstone is similar, which is higher than UCC (average 9.54) (Table 4), indicating that the differentiation is large, the LREEs are enriched and the HREEs are depleted. The mean slope ((La/Yb)N) of the UCC-normalized REE distribution pattern in mudstone is 1.28, and that in gypsum mudstone is 1.33 (Figure 7), indicating weak LREEs. Values less than 1 in Figure 7 are all sandstone samples.

5. Discussion

Table 5 summarizes the data for all the elements discussed in this section. The distribution of these elements on the profile is shown in Figure 8. Table 6 shows the range of some parameters and the reference information.

5.1. Terrigenous Input

Input from terrestrial debris can have multiple effects on OM enrichment [54,55]. As a diluent, it directly reduces OM content, or carries terrigenous OM into the lake bottom, increasing sediment abundance. Preservation of underwater sediments can also be disrupted by affecting burial rates [39,56]. Al and Ti are the main components of the continental crust. Due to the low Ti content in the samples, Al2O3 and TiO2 are used to characterize the terrestrial input (Table 6). Depending on the profile changes, the terrigenous input in mudstone and gypsiferous mudstone is similar, while that in sandstone is significantly lower (Figure 8). By analyzing the correlation between Al2O3, TiO2 and TOC, the Hetao Basin terrestrial input is used as a diluent to reduce the content of OM, which is not conducive to the enrichment (Figure 9a,b). The influence of terrestrial input on mudstone is greater than that of gypsum mudstone.

5.2. Redox

Biomarker complex parameters Pr/Ph, Gammacerane index (GI) (Gammacerane/C30hopane), Pr/nC17 and Ph/nC18 may reflect redox and stratification of water bodies [57,58,59]. The Pr/Ph ratio of less than 1.0 indicates a strong reducing environment [58], and a high GI indicates water stratification and salinity [60]. Through the intersection diagram of Pr/nC17 and Ph/nC18 parameters (Figure 10a), it is observed that the source rocks in the whole study area are in a strong reducing environment. At the same time, Pr/Ph is less than 1, with a high GI value (Figure 10b), which proves that the E3l source rocks have strong reduction and water stratification characteristics.
The concentrations of U and Mo in the continental crust are low (U = 2.8 μg/g, Mo = 1.5 μg/g), which are mainly transported to the ocean through rivers [61]. The concentrations of U and Mo in marine plankton are also low, but the residence time is long. Increased absorption by sediments under anoxic conditions results in better water redox characteristics [61]. Other elements, such as V, Ni, Ce, La and Th, are also sensitive to redox changes. The parameters used in this study were δU (δU = 2 × U/(Th/3 + U), V/(V + Ni) and Ce/La (Table 6) [19].
Based on the results of previous studies, 0.3SW < MoEF/UEF < SW, SW < MoEF/UEF < 3SW, 3SW < MoEF/UEF < 10SW indicate suboxic, anoxic, and euxinic environments (SW is modern seawater), respectively [61]. Source rock samples in the study area are basically located in the purple area in Figure 10c (representing an ‘unrestricted ocean’ (UM) trend, which is characteristic of the eastern tropical Pacific), and they have an increasing trend with the increase in enrichment coefficient. Other redox parameters showed weak oxidation-reduction changes in the profile (Figure 8), indicating that the water body fluctuated during deposition and that there was obvious stratification. The value of δU in the oxidation parameter changes obviously, and the correlation between this parameter and TOC is selected (Figure 10d). It was found that the source rocks in the study area are enriched with OM with the increase in water reduction, and that gypsum mudstone is more affected than mudstone.
Multiple well data were selected for biomarker parameters, indicating that the Linhe Formation was deposited in a reduced environment. Inorganic elements were analyzed from longitudinal data of a single well. Through comprehensive analysis, the following conclusions can be drawn, the source rocks of E3l in the Hetao Basin were in a reduced environment as a whole, but the vertical stratification of water bodies was obvious, and there was a weak alternating oxidationreduction transformation phenomenon.

5.3. Paleosalinity

Water salinity is an important indicator of sedimentary environment. This study characterizes paleosalinity from a qualitative and quantitative perspective. The parameters of Sr/Ba, CaO/(CaO + Fe) and MgO/Al2O3 × 100, which are sensitive to the change in water salinity, were selected. Their parameter indication ranges are shown in Table 6. The Sr/Ba parameters of the source rocks in the study area are 0.41–4.48 (1.35), and the CaO/(CaO + Fe) ratio is between 0.21 and 0.96, with an average value of 0.66. MgO/Al2O3 × 100 is 17.35–336.57 (69.66). According to the changes in the profile in Figure 8, these parameters all have interbedding changes, which reflect that the water body has both brackish water and salt water characteristics during deposition.
Boron (B) is a reliable indicator of salinity in muddy sediments [62,63]. This study measured 23 B elements in mudstone and gypsum mudstone. The formula is established by Li et al., 2003 [64] according to the formula of saline lake basin in China: LgS = (LgB−2.0272)/0.2428. Among them, B is the measured element, S is the ancient salinity (‰), and the use range is 0–40‰. The calculation results are shown in Table 5. Adams (1965) pointed out that the water salinity division standard is S < 10‰ for brackish water–freshwater environment, 10~25‰ for brackish water, 25~35‰ for salty water, and S > 35‰ for ultra-saline water. The paleosalinity of E3l ranges from 15.46‰ to 38.31‰, with an average value of 23.27‰. There is a change in backwatersaline-ultrasaline water. It shows that there was also stratification of water salinity.
Crossplots of Sr/Ba, CaO/(CaO + Fe), B, and GI parameters characterizing salinity with TOC showed that OM abundance increased with salinity (Figure 11a–c). The correlation between B element and TOC in gypsum mudstone was the best (Figure 11c), indicating that changes in water salinity have the greatest influence on OM enrichment in gypsum mudstone. It is worth noting that TOC increases first and then decreases with the index of GI (Figure 11d). This shows that for the source rocks in the whole study area, TOC increases with the increase in salinity within a certain range, but if salinity is higher, OM abundance may decrease with the increase in salinity. This is consistent with previous conclusions that high salinity is not conducive to biological life [9].

5.4. Paleoclimate

The paleoclimate parameters selected in this study include Sr/Cu, Mg/Ca, Rb/Sr, chemical alteration index (CIA) and C, and their parameter indication ranges are shown in Table 6. CIA = 100 × Al2O3 × (Al2O3 + NaO + K2O + CaO *), CaO * = CaO − (3 × P2O5/10) [54]. C = ∑(Fe + Mn + Cr + V + Co + Ni)/∑(Ca + Mg + Sr + Ba + K + Na) [24].
Changes in the profile occur through each indicator (Figure 8). The E3l is in a cold and dry environment as a whole, but the parameters on the profile change, indicating that the climate changes with deposition. Figure 12 shows the correlation between each paleoclimatic index and TOC. Overall, the arid climate is conducive to the enrichment of OM. The TOC correlation between CIA and mudstone and gypsum mudstone is weak (Figure 12a). Mg/Ca, Rb/Sr and C values have a large influence on the abundance of OM in mudstone, but have little influence on gypsum mudstone (Figure 12b–d).

5.5. Paleoproductivity and Water Body Limitation

Paleoproductivity is the basis for the formation of organic-rich sediments [65]. Phosphorus (P) is an important nutrient in the process of biological metabolism. It is also an integral part of the skeleton of many marine organisms and can enter sediments after the organism decomposes [66]. Ni content indicates organic carbon input and also reflects higher paleontological productivity. Ratios of P to Ni and Al to Ti eliminate the effects of P and Ni from land [66]. The increase in paleoproductivity should be conducive to OM enrichment and increased TOC, but the P/Ti and P/Al of mudstone in Figure 13 are inversely proportional to mudstone (Figure 13b,c). The reason may be that the terrestrial input studied in 5.1 has a greater impact on the mudstone, resulting in the ancient productivity shown by the parameters is inversely proportional. If these three abnormal values are ignored, ancient mudstone productivity is positively correlated with TOC.
The connection between basin water and the open sea has an influence on the nutrient supply of surface water in the basin. As the degree of water limitation increases, the exchange between water bodies weakens, and the supply of reducing element Mo from the open sea decreases. According to the restricted degree chart of anoxic water body established by Algeo [66] (Figure 13d), the sample data in the study area are scattered, from weak to strong retention, which is consistent with the conclusion of stratification and fluctuation of the water body.

5.6. Sedimentation Rate and Paleowater Depth

(La/Yb)N (UCC normalized) is considered to be an effective indicator of REE differentiation. When the value of (La/Yb)N is close to 1, it indicates that the degree of REE differentiation is weak or there is almost no differentiation, indicating a high deposition rate. If the (La/Yb) N value is significantly higher or lower than 1, it reflects a low deposition rate [26]. The (La/Yb)N ratios of the source rocks in the study area are 0.83–1.58, with an average of 1.22, indicating that the E3l source rocks have a high deposition rate during deposition.
The Co element method is a commonly used quantitative index of paleowater depth. It mainly uses Co element and deposition rate to restore paleowater depth. The calculation formula of the deposition rate with Co is based on Wu and Zhou, 2000 [67]: Vs = Vo × Nco/(Sco-t × Tco). Vs is the deposition rate of the sample; Vo is the deposition rate of normal lakes, 300m/Ma; Nco is the mass fraction of Co in normal lake sediments, 20 ppm; Sco is the abundance of Co in the sample μg/g, and t is the ratio of La abundance in the test sample to the average value of La in the terrigenous clastic rock (31 μg/g). Tco represents the abundance of Co in terrigenous clastic rocks (4.68 μg/g). The calculation formula of ancient water depth is H = 3.05 × 105/(Vs1.5) [67]. The calculation results are shown in Table 5. The deposition rate ratio is between 306.90 and 1877.35 μg/g, with an average of 666.58 μg/g, indicating that the E3l had a high deposition rate. The ancient water depth range is 3.75–56.73 m, with an average of 23.82 m, indicating that the water body was relatively deep.
Sedimentation rate and paleowater depth vary significantly in the profile (Figure 8). However, there is no correlation with TOC change, which has little effect on OM enrichment in the Linhe Formation source rocks.

5.7. Enrichment Model

The environmental control factors of mudstone and gypsum mudstone in E3l of Hetao Basin are different. Terrestrial input has a stronger inhibitory effect on the enrichment of mudstone OM, and the arid paleoclimate is more favorable. Reducing the environment and salinity of water are more conducive to promoting OM enrichment of gypsum mudstone. For the sampled well H6, the gypsum mudstone deposited earlier than the mudstone, and the main controlling factors of the environment were different in different periods, but for the whole Hetao Basin, the main controlling factors of OM enrichment were unchanged.
There was evidence from the northwest and southeast of the study area [68]. Although the provenance was abundant, the nutrient content was low due to the deep-water body and less input of terrigenous clastic material, which was not conducive to the enrichment of OM in the study area. In addition, the water retention environment changed significantly during the E3l sedimentary period, resulting in less nutrients, which limited the improvement of surface water paleoproductivity. The above reasons may explain the low TOC in the study area. The arid climate increased water evaporation and salinity, which to some extent prevented the consumption and decomposition of OM. The source rocks in the study area are in a low oxidation-reduction fluctuation environment, and the stratification of the water body is obvious, which is not only conducive to enrichment, but also conducive to preservation (Figure 14).
Both mudstone and gypsum-bearing mudstone can be used as good source rocks, but the environment has different effects on them, which can provide a basis for studying the hydrocarbon generation potential of source rocks. In addition, clarifying the influencing factors of organic matter enrichment can also explain the generally low abundance of organic matter in the saline lake basin.

6. Conclusions

There are two types of source rocks, mudstone and gypsum mudstone, in E3l of the Hetao Basin, but their hydrocarbon generation potential is the same. By analyzing the characteristics of their sedimentary environment, the following conclusions can be drawn:
  • The correlation between Al2O3 and TiO2 and TOC shows that terrestrial input is used as a diluent to reduce OM content, which is not conducive to enrichment. The effect of terrestrial input on mudstone dilution is greater than that of gypsum mudstone.
  • Pr/Ph, Pr/nC17, Ph/nC18, δU, V/(V + Ni), Ce/La, UEF and MoEF represent redox. The source rocks of E3l were in a reduced environment, and there were weak changes in oxidation-reduction in the vertical direction. The more reducing the environment, the more conducive OM enrichment.
  • GI, Sr/Ba, CaO/(CaO + Fe) and MgO/Al2O3 × 100 are used to qualitatively characterize paleosalinity, and B is used for quantitative calculation. Analysis results show that E3l was in a saline water environment, and there was water stratification on the profile. Paleosalinity promotes OM enrichment, which has a greater impact on gypsum mudstone.
  • The paleoclimatic parameters of Sr/Cu, Mg/Ca, Rb/Sr, CIA and C indicate that the E3l was in a cold and dry environment, and the arid environment promotes the enrichment of OM, especially for mudstone.
  • Paleoproductivity, water restriction and deposition rate are weakly correlated with TOC, and the water body is deeper.
In this study, good preservation conditions, including reduction conditions, water stratification, and hot and dry climate, were the main controlling factors for OM enrichment. On the basis of clarifying the main controlling factors of organic matter enrichment, further research will be carried out in the future on the hydrocarbon generation mechanism of source rocks and oil and gas resources in the basin.

Author Contributions

X.F.: conceptualization, methodology, writing, and editing. J.L. and S.C.: conceptualization and review. Y.S. and R.Z.: materials provided, project administration. M.Y.: draw and translation. All authors have read and agreed to the published version of the manuscript.

Funding

Funding for this research comes from the “Science and Technology Cooperation Project of the CNPC-SWPU Innovation Alliance” (Nos. 2020CX030000 and 2020CX050000), and “Study on the Control Mechanism of Early Product of Source Rock on Tight Oil Accumulation” (No. 42072185).

Data Availability Statement

All data used to support the findings of this study are included within the article.

Acknowledgments

The authors acknowledge the funding provided, as well as previous research findings related to the study.

Conflicts of Interest

The authors declare that there is no conflict of interest.

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Figure 1. Geographical location map (a), tectonic unit division map (b), and stratigraphic column map (c) of Hetao Basin.
Figure 1. Geographical location map (a), tectonic unit division map (b), and stratigraphic column map (c) of Hetao Basin.
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Figure 2. (a) Core photos and microelement experimental sampling location map of upper Linhe Formation in well H6. (b) Core photos and microelement experimental sampling location map of lower Linhe Formation in well H6.
Figure 2. (a) Core photos and microelement experimental sampling location map of upper Linhe Formation in well H6. (b) Core photos and microelement experimental sampling location map of lower Linhe Formation in well H6.
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Figure 3. TOC and S2 cross plot (a), the quality classification of source rocks, Tmax and HI cross plot (b), and the type classification.
Figure 3. TOC and S2 cross plot (a), the quality classification of source rocks, Tmax and HI cross plot (b), and the type classification.
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Figure 4. Mass chromatogram of saturated hydrocarbon m/z 85 and m/z 191 of E3l source rocks in the Linhe Depression, Hetao Basin.
Figure 4. Mass chromatogram of saturated hydrocarbon m/z 85 and m/z 191 of E3l source rocks in the Linhe Depression, Hetao Basin.
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Figure 5. The mean value line chart of major elements/UCC of different lithology in E3l of H6 well.
Figure 5. The mean value line chart of major elements/UCC of different lithology in E3l of H6 well.
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Figure 6. (a) Profile of trace element enrichment factor in the upper Linhe Formation of well H6. (b) Profile of trace element enrichment factor in the lower Linhe Formation of well H6.
Figure 6. (a) Profile of trace element enrichment factor in the upper Linhe Formation of well H6. (b) Profile of trace element enrichment factor in the lower Linhe Formation of well H6.
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Figure 7. UCC normalized distribution curve of rare earth elements in the Linhe Formation.
Figure 7. UCC normalized distribution curve of rare earth elements in the Linhe Formation.
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Figure 8. (a) Profile of parameter distribution with environmental indication in the upper Linhe Formation of well H6. (b) Profile of parameter distribution with environmental indication in the lower Linhe Formation of well H6.
Figure 8. (a) Profile of parameter distribution with environmental indication in the upper Linhe Formation of well H6. (b) Profile of parameter distribution with environmental indication in the lower Linhe Formation of well H6.
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Figure 9. The correlation between elements Al2O3 (a) and TiO2 (b) and TOC.
Figure 9. The correlation between elements Al2O3 (a) and TiO2 (b) and TOC.
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Figure 10. The Pr/nC17 and Ph/nC18 parameter crossplot (a) reflecting the sedimentary environment, and the Pr/Ph and Gammacerane /C30hopane crossplot (b). Crossplot of UEF and MoEF (c), and correlation of δU and TOC. SW: modern seawater (d).
Figure 10. The Pr/nC17 and Ph/nC18 parameter crossplot (a) reflecting the sedimentary environment, and the Pr/Ph and Gammacerane /C30hopane crossplot (b). Crossplot of UEF and MoEF (c), and correlation of δU and TOC. SW: modern seawater (d).
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Figure 11. Correlation between paleosalinity parameters and TOC in mudstone and gypsum mudstone. (a) Sr/Ba with TOC, (b) CaO/(CaO+Fe) with TOC, (c) B with TOC, (d) Gamma cerane index with TOC.
Figure 11. Correlation between paleosalinity parameters and TOC in mudstone and gypsum mudstone. (a) Sr/Ba with TOC, (b) CaO/(CaO+Fe) with TOC, (c) B with TOC, (d) Gamma cerane index with TOC.
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Figure 12. Correlation between paleoclimatic parameters and TOC of mudstone and gypsum mudstone. (a) CIA with TOC, (b) Mg/Ca with TOC, (c) Rb/Sr with TOC, (d) C with TOC.
Figure 12. Correlation between paleoclimatic parameters and TOC of mudstone and gypsum mudstone. (a) CIA with TOC, (b) Mg/Ca with TOC, (c) Rb/Sr with TOC, (d) C with TOC.
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Figure 13. Correlation between Ni/Al (a), P/Ti (b), P/Al (c), Mo (d) and TOC in mudstone and p gypsum mudstone.
Figure 13. Correlation between Ni/Al (a), P/Ti (b), P/Al (c), Mo (d) and TOC in mudstone and p gypsum mudstone.
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Figure 14. Organic matter enrichment model of E3l in the Linhe Depression, Hetao Basin.
Figure 14. Organic matter enrichment model of E3l in the Linhe Depression, Hetao Basin.
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Table
Table 1. Statistical table of geochemical data of source rocks in the Linhe Depression, Hetao Basin.
Table 1. Statistical table of geochemical data of source rocks in the Linhe Depression, Hetao Basin.
WellLithologyDepth (m)Pr/PhPr/nC17Ph/nC18GIS1 (mg/g)S2 (mg/g)Tmax (°C)TOC (%)HI (mg HC/g TOC)
H1mudstone33400.230.313.791.220.312.134240.79269.62
H1mudstone33620.260.131.520.840.7514.634162.97492.59
H1mudstone33650.300.451.381.360.7512.104181.201008.33
H1mudstone33690.140.826.281.270.3810.014201.90526.84
H1mudstone33710.190.503.381.350.281.824270.74245.95
H1mudstone34720.340.481.501.820.611.524270.80190.00
H1gypsum mudstone34500.230.694.631.010.161.054241.5268.90
H1gypsum mudstone34620.380.492.860.950.090.514161.9825.76
H1gypsum mudstone35800.200.414.291.101.000.864260.63136.51
H1gypsum mudstone37100.230.434.180.990.131.264280.64196.88
H2mudstone36350.200.265.190.590.100.974190.51189.51
H2mudstone37580.200.264.800.870.172.664230.81328.65
H2mudstone38550.300.532.780.910.364.254191.18360.25
H2gypsum mudstone39300.250.433.050.900.172.084290.69301.74
H2gypsum mudstone40150.270.653.181.140.171.714250.55311.67
H2gypsum mudstone41300.340.532.380.930.201.984281.58125.41
H3mudstone41970.310.321.960.570.080.264220.11232.61
H3mudstone42150.210.273.500.540.130.924240.44206.31
H3mudstone42360.660.391.680.290.040.114320.2251.06
H3mudstone4238.20.870.661.430.600.081.644350.61269.38
H3gypsum mudstone4238.40.520.320.520.280.100.864170.44196.99
H3gypsum mudstone4238.80.420.421.420.160.110.274120.23119.39
H3gypsum mudstone4242.90.260.350.891.070.270.324210.14228.43
H3gypsum mudstone42430.460.280.560.550.211.204260.49243.46
H3gypsum mudstone43280.450.350.810.230.534.624241.43323.35
H3mudstone43800.370.501.420.910.733.914211.65236.93
H3mudstone44700.380.661.810.940.271.334180.69191.62
H3mudstone45350.380.541.511.860.190.604170.35172.31
H3mudstone46000.480.731.601.510.150.684180.46147.83
H3mudstone46700.470.661.401.080.170.784190.48162.50
H4mudstone44550.640.420.940.300.080.384220.6161.37
H4mudstone45800.500.501.280.330.110.484210.5291.87
H4gypsum mudstone46550.420.752.040.571.3513.244343.02438.30
H4gypsum mudstone47500.340.391.111.231.259.204321.29712.97
H4gypsum mudstone48150.590.841.480.730.091.244340.56222.97
H5mudstone40270.310.242.350.710.8918.764312.91644.54
H5mudstone42720.320.462.980.630.162.394270.88270.77
H5gypsum mudstone43970.310.652.380.670.5210.294292.08494.61
H5gypsum mudstone44450.230.642.660.800.141.194250.67178.89
H5gypsum mudstone44970.410.691.940.900.070.554270.42131.81
H5gypsum mudstone45530.350.702.000.880.101.264270.64197.21
H5mudstone46500.430.751.821.240.111.004180.53187.18
Table
Table 2. Statistical table of TOC and major elements in the Linhe Formation of well H6.
Table 2. Statistical table of TOC and major elements in the Linhe Formation of well H6.
Number of samplesDepth
(m)		LithologyTOC
(%)		SiO2
(%)		Al2O3
(%)		CaO
(%)		MgO
(%)		TFe2O
3(%)		K2O
(%)		Na2O
(%)		TiO2
(%)		P2O5
(%)		Al2O3 + K2O + Na2O
(%)
LH-14999.8mudstone0.21951.3815.127.263.725.413.451.600.670.3520.17
LH-25000.33mudstone0.18656.2315.545.502.845.253.521.660.710.1420.72
LH-35000.8mudstone0.2153.6715.105.992.666.213.281.940.680.1420.32
LH-45001.13mudstone0.1753.9716.484.892.866.053.671.920.690.1422.07
LH-55001.87mudstone0.1838.4711.5910.907.964.932.581.620.470.1515.79
LH-65002.5mudstone0.9533.9010.3213.409.054.472.361.340.400.2314.02
LH-75002.9mudstone1.8143.2112.8611.603.935.222.821.860.530.1417.54
LH-85003.57mudstone0.58313.333.4027.08.811.710.730.650.140.094.78
LH-95004.15sandstone 62.214.8911.000.381.241.661.420.080.017.97
LH-105004.68sandstone 77.296.772.700.742.041.992.160.230.0210.92
LH-115005.35sandstone 78.697.012.531.231.881.992.250.230.0211.25
LH-125006.25sandstone 79.476.922.101.092.132.072.290.200.0211.28
LH-135233.06gypsum-bearing argillaceous siltstone2.3646.3313.216.374.775.703.071.430.540.1717.71
LH-145233.2gypsum-bearing argillaceous siltstone1.8629.548.5113.6511.503.612.000.950.360.1111.46
LH-155233.6gypsum-bearing argillaceous siltstone0.21337.538.2416.353.603.291.781.360.420.1011.38
LH-165234.1gypsum mudstone0.16654.8018.291.254.316.814.761.240.710.1224.29
LH-175234.5gypsum mudstone2.0152.6416.962.455.316.623.881.350.700.1822.19
LH-185234.8gypsum mudstone0.15145.8114.685.746.166.553.491.180.610.1619.35
LH-195235.5sandstone 61.604.789.484.021.521.341.440.110.027.56
LH-205236.17gypsum mudstone0.22817.645.6613.6519.053.291.300.570.220.097.53
LH-215236.73gypsum mudstone0.16149.5817.143.485.296.923.961.280.670.1622.38
LH-225237.2gypsum mudstone0.16934.0711.3514.754.634.292.630.890.480.1114.87
LH-235237.82gypsum mudstone0.076346.1815.045.867.095.893.461.200.590.1619.70
LH-245238.1gypsum mudstone0.11146.6015.974.776.176.413.691.210.640.1620.87
LH-255238.55gypsum mudstone0.089549.0116.454.055.886.003.911.160.650.1521.52
LH-265239.1gypsum mudstone0.11945.5415.196.526.175.533.531.110.600.1519.83
LH-275239.48gypsum mudstone0.25443.0613.519.066.395.283.081.100.570.1417.69
LH-285239.9sandstone 35.0310.6114.156.734.442.390.870.440.1213.87
LH-295240.45sandstone 65.406.527.692.181.551.481.700.250.039.70
LH-305241.19gypsum mudstone3.9723.787.3818.6011.803.071.760.640.300.099.78
LH-315241.6sandstone 52.435.1013.153.161.591.551.160.220.037.81
LH-325242.37sandy mudstone2.9863.1610.034.394.703.432.361.710.460.1014.10
LH-335243.5mudstone1.4735.8211.5610.809.424.542.890.990.460.1015.44
LH-345244.1sandstone 77.155.184.400.231.671.871.330.410.028.38
LH-355244.5sandstone 72.286.914.453.161.782.241.680.210.0310.83
LH-365246.1sandstone 77.027.892.191.142.082.561.890.260.0312.34
UCC 66.0015.204.202.205.083.403.900.650.1522.50
Table
Table 3. Statistical table of trace elements in the Linhe Formation of well H6.
Table 3. Statistical table of trace elements in the Linhe Formation of well H6.
Number of samplesLithologyDepth (m)VCrCoNiCuSrMoThUBaAlMgFePRbCaMnKNaTi
μg/gμg/gμg/gμg/gμg/gμg/gμg/gμg/gμg/gμg/g%%%μg/gμg/g%μg/g%%%
LH-1mudstone4999.81127816.2039.2029.802220.9613.653.505407.532.133.781530130.505.208992.911.180.37
LH-2mudstone5000.331027517.6039.5036.001840.4213.352.304007.541.583.51580125.003.854442.881.190.39
LH-3mudstone5000.81067618.3042.7038.901931.2313.352.804207.521.504.29610123.004.304432.741.390.38
LH-4mudstone5001.131147818.4043.0042.001660.7313.352.504007.911.554.04590124.503.423863.011.360.37
LH-5mudstone5001.871026015.0031.0037.5034910.759.939.203705.744.663.3867099.507.726682.171.170.27
LH-6mudstone5002.51035714.4033.9036.4026733.409.2311.006005.345.503.17105095.209.537592.061.010.23
LH-7mudstone5002.91066517.1040.4053.7064114.1511.5512.205706.512.273.67600115.508.275822.401.390.30
LH-8mudstone5003.5730274.6010.2010.8010007.272.786.603001.785.291.2541028.8019.355350.630.530.08
LH-9sandstone5004.158101.403.304.0013605.161.420.604402.500.220.864046.908.17871.411.070.05
LH-10sandstone5004.6818312.606.906.003351.512.480.806603.420.411.5010054.302.032131.671.610.13
LH-11sandstone5005.3519242.506.306.002290.812.630.906303.520.711.2710053.301.902591.671.700.13
LH-12sandstone5006.2517242.306.106.202050.732.390.707303.460.631.467055.601.552381.711.680.12
LH-13gypsum-bearing argillaceous siltstone5233.061507321.0046.5053.8082048.8010.2022.908606.632.763.98690118.004.624362.571.060.30
LH-14gypsum-bearing argillaceous siltstone5233.2644110.0024.4020.0013452.737.264.103904.346.932.5648076.309.715151.710.710.21
LH-15gypsum-bearing argillaceous siltstone5233.652418.7021.3017.0013003.737.562.902904.182.042.2844063.1011.404261.491.020.23
LH-16gypsum mudstone5234.11188018.6045.5036.501681.0613.652.303609.112.484.66520158.500.922823.920.920.39
LH-17gypsum mudstone5234.51217718.1044.5036.803051.1614.452.304608.633.144.65770139.001.824713.311.000.39
LH-18gypsum mudstone5234.81166525.0048.0037.6093711.9012.809.405207.553.694.58730134.004.215402.990.900.35
LH-19sandstone5235.511161.704.304.8016100.991.600.708402.452.341.018037.006.823411.131.090.07
LH-20gypsum mudstone5236.1761308.1018.8018.40126018.604.8810.806002.9111.452.2736048.509.538891.110.420.13
LH-21gypsum mudstone5236.731187016.2041.4032.702271.0314.152.303408.413.014.70700140.002.464393.220.920.37
LH-22gypsum mudstone5237.2815214.1030.9029.7010300.939.172.205605.642.642.9548092.6010.204562.180.680.27
LH-23gypsum mudstone5237.821056515.1037.5029.202011.6512.203.303007.484.144.07670124.004.197272.880.870.33
LH-24gypsum mudstone5238.11137021.7047.9036.102991.2414.053.304007.993.604.43660135.503.425463.070.890.36
LH-25gypsum mudstone5238.551187116.4042.5032.502403.7613.803.903708.253.464.15660140.502.924843.200.880.37
LH-26gypsum mudstone5239.11106215.8037.3032.603746.4312.705.103507.573.603.85630128.004.665312.940.810.34
LH-27gypsum mudstone5239.48975412.2030.9020.109040.5711.151.706606.853.773.69620114.006.555192.610.850.32
LH-28sandstone5239.9774310.6026.9022.2010602.129.002.403905.313.973.1151083.8010.006602.010.650.25
LH-29sandstone5240.4518173.106.606.6013951.033.680.803603.171.221.0115043.205.411981.191.230.14
LH-30gypsum mudstone5241.1958389.6023.3023.4012008.786.719.203503.747.052.0341068.4012.655421.460.500.17
LH-31sandstone5241.616212.906.506.8054200.953.330.901002.561.801.0314047.609.183251.270.870.12
LH-32sandy mudstone5242.3753469.0023.7020.8010901.267.991.908004.992.792.2746080.503.123721.961.270.26
LH-33mudstone5243.51006217.4042.2038.5035632.909.7312.206605.815.723.00450112.007.574922.400.730.27
LH-34sandstone5244.112182.504.508.109712.783.132.605002.570.131.097051.003.201271.530.990.22
LH-35sandstone5244.518173.006.908.401991.162.981.006803.371.801.1612063.003.153051.841.220.12
LH-36sandstone5246.120233.408.407.504431.213.950.8011203.850.651.4215071.001.602032.091.380.15
UCC 1078317.0044.0025.003501.5010.702.805508.041.333.50700112.003.006002.802.890.41
Table
Table 4. Statistical table of rare earth elements in the Linhe Formation of well H6.
Table 4. Statistical table of rare earth elements in the Linhe Formation of well H6.
Number of SamplesLithologyDepth
m		La
μg/g		Ce
μg/g		Pr
μg/g		Nd
μg/g		Sm
μg/g		Eu
μg/g		Gd
μg/g		Tb
μg/g		Dy
μg/g		Ho
μg/g		Er
μg/g		Tm
μg/g		Yb
μg/g		Lu
μg/g		∑REE∑LREE∑HREE∑ LREE/∑ HREE(La/Yb)N
LH-1mudstone4999.833.1067.107.8629.705.831.174.390.673.980.742.250.311.980.32159.40144.7614.649.891.23
LH-2mudstone5000.3335.7074.108.2731.206.281.254.670.693.910.752.100.311.900.31171.44156.8014.6410.711.38
LH-3mudstone5000.837.1072.108.3230.906.191.244.690.713.930.762.130.311.940.32170.64155.8514.7910.541.40
LH-4mudstone5001.1333.4070.308.2231.405.981.204.460.663.800.722.030.301.870.30164.64150.5014.1410.641.31
LH-5mudstone5001.8726.6053.906.0723.204.520.873.340.512.940.571.610.241.540.25126.16115.1611.0010.471.27
LH-6mudstone5002.527.1052.606.1123.504.640.903.450.533.050.591.680.241.520.26126.17114.8511.3210.151.31
LH-7mudstone5002.933.2066.707.4928.405.641.084.120.633.550.712.070.291.840.30156.02142.5113.5110.551.32
LH-8mudstone5003.579.3018.952.258.601.660.331.280.191.160.220.630.090.550.0945.3041.094.219.761.24
LH-9sandstone5004.154.708.771.104.100.740.230.520.070.490.100.300.040.280.0521.4919.641.8510.621.23
LH-10sandstone5004.688.3016.352.047.601.500.391.120.161.020.210.590.090.650.1040.1236.183.949.180.94
LH-11sandstone5005.358.6017.002.118.001.570.421.240.181.120.220.670.100.640.1141.9837.704.288.810.99
LH-12sandstone5006.258.0015.801.947.101.300.350.960.141.280.190.570.080.590.0938.3934.493.908.840.99
LH-13gypsum-bearing argillaceous siltstone5233.0629.7061.307.1226.705.361.083.970.603.390.661.850.271.680.28143.96131.2612.7010.341.30
LH-14gypsum-bearing argillaceous siltstone5233.221.3042.505.0519.103.790.722.850.412.460.481.360.201.280.21101.7192.469.2510.001.22
LH-15gypsum-bearing argillaceous siltstone5233.621.1043.705.1119.603.810.732.690.402.400.451.240.181.190.19102.7994.058.7410.761.30
LH-16gypsum mudstone5234.138.0078.208.7133.406.521.314.860.744.190.832.290.342.110.34181.84166.1415.7010.581.32
LH-17gypsum mudstone5234.540.9083.409.3835.206.951.425.420.774.400.862.380.342.110.36193.89177.2516.6410.651.42
LH-18gypsum mudstone5234.836.1073.108.2431.206.221.234.620.724.240.832.390.372.300.38171.94156.0915.859.851.15
LH-19sandstone5235.56.7012.151.535.701.120.340.920.140.850.170.500.080.480.0830.7627.543.228.551.02
LH-20gypsum mudstone5236.1715.2030.703.6013.902.740.521.980.291.740.340.950.140.860.1473.1066.666.4410.351.30
LH-21gypsum mudstone5236.7340.6084.109.3935.606.851.395.230.794.450.862.470.352.260.37194.71177.9316.7810.601.32
LH-22gypsum mudstone5237.226.4055.006.1824.104.590.913.210.472.660.501.400.211.220.20127.05117.189.8711.871.59
LH-23gypsum mudstone5237.8235.7074.608.3531.606.011.214.560.693.880.762.270.322.030.32172.30157.4714.8310.621.29
LH-24gypsum mudstone5238.138.3080.208.8033.406.381.304.930.744.130.832.270.342.040.34184.00168.3815.6210.781.38
LH-25gypsum mudstone5238.5537.9078.708.9833.506.491.335.100.764.280.852.360.352.220.39183.21166.9016.3110.231.25
LH-26gypsum mudstone5239.135.0071.208.1130.905.941.164.440.673.880.762.140.321.960.32166.80152.3114.4910.511.31
LH-27gypsum mudstone5239.4834.0069.307.7729.205.611.094.170.633.420.681.880.271.700.28160.00146.9713.0311.281.47
LH-28sandstone5239.924.4050.105.4621.204.200.843.200.472.710.551.510.221.600.23116.69106.2010.4910.121.12
LH-29sandstone5240.458.0019.602.509.601.780.391.280.191.010.200.580.090.570.1045.8941.874.0210.421.03
LH-30gypsum mudstone5241.1916.2036.504.2715.802.950.522.120.321.730.351.020.140.910.1582.9876.246.7411.311.31
LH-31sandstone5241.66.7017.952.349.101.830.371.380.211.140.220.670.100.590.0942.6938.294.408.700.83
LH-32sandy mudstone5242.3722.1046.405.7322.004.150.763.230.482.590.501.520.211.340.22111.23101.1410.0910.021.21
LH-33mudstone5243.522.8049.805.8421.504.170.693.050.462.580.511.530.221.420.23114.80104.8010.0010.481.18
LH-34sandstone5244.17.2017.602.278.601.440.311.010.150.900.180.610.090.630.0941.0837.423.6610.220.84
LH-35sandstone5244.58.2018.552.398.801.740.471.400.221.200.230.690.100.640.1044.7340.154.588.770.94
LH-36sandstone5246.112.4025.903.2111.802.120.441.460.211.390.230.660.100.650.1060.6755.874.8011.641.40
UCC 30.0064.007.1026.004.500.883.800.643.500.802.300.332.200.32146.37132.4813.899.541.40
Table
Table 5. Statistical table of parameters indicating environmental significance of inorganic elements in riverfront formation.
Table 5. Statistical table of parameters indicating environmental significance of inorganic elements in riverfront formation.
Number of SamplesDepth (m)LithologyTOC (%)Terrigenous InputRedoxPaleosalinity
Al2O3 (%)TiO2 (%)δUV/(V+Ni)Ce/LaU-EFMo-EFSr/BaCaO/(CaO+Fe)MgO/Al2O3 × 100B(μg/g)S(‰)
LH-14999.8mudstone0.2215.120.670.870.742.031.330.680.410.6624.6024832.55
LH-25000.33mudstone0.1915.540.710.680.722.080.880.300.460.6118.2824229.43
LH-35000.8mudstone0.2115.100.680.770.711.941.070.880.460.5817.6223526.08
LH-45001.13mudstone0.1716.480.690.720.732.100.910.490.410.5517.3521317.40
LH-55001.87mudstone0.1811.590.471.470.772.034.6010.040.940.7668.6820916.09
LH-65002.5mudstone0.9510.320.401.560.751.945.9133.530.450.8187.6921819.14
LH-75002.9mudstone1.8112.860.531.520.722.015.3811.651.120.7630.5624329.93
LH-85003.57mudstone0.583.400.141.750.752.0410.6521.893.300.96259.1223325.18
LH-95004.15sandstone 4.890.081.120.711.870.6911.063.090.937.77
LH-105004.68sandstone 6.770.230.980.721.970.672.370.510.6410.93
LH-115005.35sandstone 7.010.231.010.751.980.731.230.360.6717.55
LH-125006.25sandstone 6.920.200.940.741.981.302.140.280.5915.75
LH-135233.06gypsum-bearing argillaceous siltstone2.3613.210.541.740.762.060.721.740.950.6236.1125838.31
LH-145233.2gypsum-bearing argillaceous siltstone1.868.510.361.260.722.001.011.993.450.84135.1424631.48
LH-155233.6gypsum-bearing argillaceous siltstone0.218.240.421.070.712.072.905.804.480.8843.6922622.20
LH-165234.1gypsum mudstone0.1718.290.710.670.722.060.851.840.470.2123.5620715.46
LH-175234.5gypsum mudstone2.0116.960.701.260.732.040.601.680.660.3531.3122521.80
LH-185234.8gypsum mudstone0.1514.680.611.380.712.020.581.131.800.5641.9621518.08
LH-195235.5sandstone 4.780.111.140.721.819.9239.451.920.9084.10
LH-205236.17gypsum mudstone0.235.660.221.230.762.022.713.372.100.86336.5721718.78
LH-215236.73gypsum mudstone0.1617.140.670.660.742.071.994.780.670.4330.8621016.41
LH-225237.2gypsum mudstone0.1711.350.480.840.722.080.720.621.840.8340.7922321.01
LH-235237.82gypsum mudstone0.0815.040.590.900.742.090.770.720.670.5947.1422421.40
LH-245238.1gypsum mudstone0.1115.970.640.830.702.093.588.450.750.5238.6321618.43
LH-255238.55gypsum mudstone0.0916.450.650.920.742.080.822.170.650.4935.7421518.08
LH-265239.1gypsum mudstone0.1215.190.601.090.752.0310.6634.261.070.6340.6222321.01
LH-275239.48gypsum mudstone0.2513.510.570.630.762.040.790.661.370.7147.3022019.87
LH-285239.9sandstone 10.610.440.890.742.051.120.882.720.8263.43
LH-295240.45sandstone 6.520.250.790.732.451.271.183.880.8833.44
LH-305241.19gypsum mudstone3.977.380.301.610.712.251.190.833.430.90159.8925637.10
LH-315241.6sandstone 5.100.220.900.712.681.362.4454.200.9361.96
LH-325242.37sandy mudstone2.9810.030.460.830.692.101.934.551.360.6646.86
LH-335243.5mudstone1.4711.560.461.580.702.180.710.450.540.7881.49
LH-345244.1sandstone 5.180.411.430.732.447.0612.581.940.804.44
LH-355244.5sandstone 6.910.211.000.722.261.091.350.290.7945.73
LH-365246.1sandstone 7.890.260.760.702.096.0330.350.400.6114.45
Number of SamplesDepth (m)LithologyTOC (%)PaleoclimatePaleoproductivitySedimentation Rate and Paleowater depth
Sr/CuCIAMg/CaRb/SrCNi/AlP/TiP/AlVsH(m)
LH-14999.8mudstone0.227.4555.330.410.591.345.214146.34203.19535.5724.61
LH-25000.33mudstone0.195.1159.360.410.680.985.241506.4976.92491.3828.00
LH-35000.8mudstone0.214.9657.480.350.640.945.681618.0481.12472.4729.70
LH-45001.13mudstone0.173.9461.220.450.750.935.441577.5474.59449.1832.04
LH-55001.87mudstone0.189.3143.500.600.291.075.402518.80116.72546.2423.89
LH-65002.5mudstone0.957.3437.730.580.360.996.354487.18196.63582.0321.72
LH-75002.9mudstone1.8111.9444.200.270.180.596.212033.9092.17496.3727.58
LH-85003.57mudstone0.589.2610.710.270.000.065.735256.41230.341877.353.75
LH-95004.15sandstone 340.0025.780.030.030.061.32784.3116.00
LH-105004.68sandstone 55.8349.730.200.160.262.02757.5829.24
LH-115005.35sandstone 38.1750.890.370.230.341.79757.5828.41
LH-125006.25sandstone 33.0651.740.410.270.291.76608.7020.23
LH-135233.06gypsum-bearing argillaceous siltstone2.3615.2454.980.600.140.367.012300.00104.07363.2844.05
LH-145233.2gypsum-bearing argillaceous siltstone1.8667.2533.940.710.060.345.622296.65110.60884.3811.60
LH-155233.6gypsum-bearing argillaceous siltstone0.2176.4729.750.180.050.315.101938.33105.261088.028.50
LH-165234.1gypsum mudstone0.174.6071.712.700.940.814.991326.5357.08466.4530.28
LH-175234.5gypsum mudstone2.018.2968.981.730.460.805.161984.5489.22503.1327.03
LH-185234.8gypsum mudstone0.1524.9258.620.880.140.476.362091.6996.69306.9056.73
LH-195235.5sandstone 335.4228.060.340.020.151.761230.7732.65
LH-205236.17gypsum mudstone0.2368.4826.761.200.040.516.462769.23123.711033.549.18
LH-215236.73gypsum mudstone0.166.9466.401.220.620.994.921902.1783.23595.7920.97
LH-225237.2gypsum mudstone0.1734.6838.360.260.090.355.481804.5185.11593.2121.11
LH-235237.82gypsum mudstone0.086.8858.950.990.621.665.012030.3089.57617.8919.86
LH-245238.1gypsum mudstone0.118.2862.401.050.450.985.991848.7482.60376.9341.68
LH-255238.55gypsum mudstone0.097.3864.451.180.591.005.151803.2880.00561.8922.90
LH-265239.1gypsum mudstone0.1211.4757.750.770.340.894.931863.9183.22570.5522.38
LH-275239.48gypsum mudstone0.2544.9850.580.580.130.394.511937.5090.51849.0012.33
LH-285239.9sandstone 47.7537.910.400.080.515.072056.4596.05
LH-295240.45sandstone 211.3637.510.230.030.132.081102.9447.32
LH-305241.19gypsum mudstone3.9751.2826.031.230.060.406.232356.32109.63838.6512.56
LH-315241.6sandstone 797.0624.340.200.010.062.541176.4754.69
LH-325242.37sandy mudstone2.985.2454.330.890.070.244.751755.7392.181059.398.85
LH-335243.5mudstone1.479.2544.110.760.310.617.261679.1077.45429.8634.22
LH-345244.1sandstone 119.8840.550.040.050.111.75324.0727.24
LH-355244.5sandstone 23.6345.250.570.320.382.051043.4835.61
LH-365246.1sandstone 59.0754.340.410.160.152.181027.4038.96
Table
Table 6. Scope of some parameters and references.
Table 6. Scope of some parameters and references.
Meaning of IndicationParameterContentReferences
Terrigenous inputAl2O3The greater the ratio, the greater the terrestrial input[27,44]
TiO2
OxidationWeak oxidationReducingReferences
RedoxδU<1 >1[33]
V/(V + Ni)<0.460.46–0.57>0.57[50]
Pr/Ph>31–3<1[40]
Fresh waterBrackish waterSalt waterReferences
PaleosalinitySr/Ba<0.50.5–1.0>1.0[51]
CaO/(CaO + Fe)<0.20.2–0.5>0.5[52]
MgO/Al2O3 × 100<11~10>10[30]
Paleoclimate Warm and humidCold and dry
Sr/Cu1.3~5.0>5 [53]
Mg/CaHigh values indicate dry and low values indicate moist [46]
Rb/SrHigh values indicate moist, low values indicate dry
Cold and dryWarm and humidHot humid
CIA50~7070~8080~100[54]
Arid climateSemi-arid to semi-moist climateHot humid
C<0.20.2~0.8>0.8[24]
PaleoproductivityNi/AlThe greater the ratio, the greater the ancient productivity[3,12]
P/Ti
P/Al
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Fu, X.; Lu, J.; Shi, Y.; Zhou, R.; Chen, S.; Yuan, M. Sedimentary Environment and Organic Matter Enrichment Model of Saline Lake Source Rock in the Linhe Depression, Hetao Basin, China. Processes 2023, 11, 2114. https://doi.org/10.3390/pr11072114

AMA Style

Fu X, Lu J, Shi Y, Zhou R, Chen S, Yuan M. Sedimentary Environment and Organic Matter Enrichment Model of Saline Lake Source Rock in the Linhe Depression, Hetao Basin, China. Processes. 2023; 11(7):2114. https://doi.org/10.3390/pr11072114

Chicago/Turabian Style

Fu, Xiaoyan, Jungang Lu, Yulei Shi, Ranran Zhou, Shijia Chen, and Man Yuan. 2023. "Sedimentary Environment and Organic Matter Enrichment Model of Saline Lake Source Rock in the Linhe Depression, Hetao Basin, China" Processes 11, no. 7: 2114. https://doi.org/10.3390/pr11072114

APA Style

Fu, X., Lu, J., Shi, Y., Zhou, R., Chen, S., & Yuan, M. (2023). Sedimentary Environment and Organic Matter Enrichment Model of Saline Lake Source Rock in the Linhe Depression, Hetao Basin, China. Processes, 11(7), 2114. https://doi.org/10.3390/pr11072114

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