Geochemistry of the Paleocene saline lake in the southwestern Jianghan Basin, Central China: implications for provenance, tectonic setting, and palaeoclimate

doi:10.21203/rs.3.rs-1525762/v1

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Geochemistry of the Paleocene saline lake in the southwestern Jianghan Basin, Central China: implications for provenance, tectonic setting, and palaeoclimate

https://doi.org/10.21203/rs.3.rs-1525762/v1

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As an important sedimentary area of mineral resources in central and eastern China, the Jianghan Basin has received more and more attention. In recent years, thick evaporites and potassium and lithium-rich brine ores have been discovered in the Paleocene strata in the southern Jianghan Basin, which provides a material basis for studying the genesis of evaporites in central and eastern China. This paper aims to further understand the provenance, tectonic setting and paleoenvironment of the Paleocene Shashi Formation in the south of Jianghan Basin through the study of whole-rock geochemistry, so as to provide theoretical basis for the formation of evaporite. The chondrite-normalized REE distribution pattern of the Shashi Formation’s siltstones are characterized by enriched LREE and flat HREE similar to those of UCC with negative Eu anomalies. Combined with the geochemical element ratio discriminant diagram, such as Al₂O₃-TiO₂, Zr/Sc-Th/Sc, Hf-La/Th, and La/Sc-Co/Th, these samples were sourced from felsic source rocks. Moreover, the discriminant diagrams of K₂O/Na₂O-SiO₂/Al₂O₃, La-Th-Sc, and Th-Co-Zr/10 suggest that the samples were formed under the tectonic settings of active continental margin and continental island arc. The discriminant diagrams of Zr/Sc-Th/Sc and Al₂O₃-Zr-TiO₂ show that all samples were not affected by recycling and hydraulic sorting. The weathering indices (CIA, CIW, PIA, and ICV) and the diagram of Al₂O₃-(CaO + Na₂O)-K₂O suggest that mild chemical weathering in the source area under arid climatic condition. And the palaeoclimatic indicators of Sr/Cu, Ga/Rb, and C-value indicate that the climate was cool and arid. According to the geochemical data and previous studies, the Paleocene sediments in the southwest of the Jianghan Basin were from felsic source rocks, and formed in the tectonic background of active continental margin and continental island arc, and the climate was mainly arid and cold.

The Jianghan Basin

Geochemistry

Provenance

Tectonic setting

Palaeoclimate

The Jianghan Basin is a Mesozoic-Cenozoic rift basin in central China, which has experienced multi-stage tectonic movement. In the Paleocene, the Jianghan Basin deposited abundant evaporites and potassium and lithium-rich brine ore (Wang et al. 2013, 2020; Liu 2013; Shen et al. 2014; Liu et al. 2015). Due to the complex tectonic movement, extremely arid paleoclimate type and various material sources in the Jianghan Basin, it is difficult for us to study the genesis of evaporite minerals. In view of the sedimentary characteristics of evaporite in a series of rifted basins in south China, Liu et al. (2013, 2016) proposed that the formation of evaporite deposits was controlled by tectonics, provenance and climate. Based on this view, a lot of studies on the origin of evaporites and deep brine have been carried out in recent years (Wang et al. 2016, 2021; Shen et al. 2014; Yu et al. 2018a, 2018b; Yan et al. 2018; Yu et al. 2020). And based on the analysis of geochemical data from the Paleocene Shashi Formation mudstone from Well ZK0303 in the southwestern Jianghan Basin, this paper reveals the provenance, tectonic setting and sedimentary environment of the clastic sediments in the saline lake.

After many years of development, geochemical parameters have been widely used in paleoenvironmental conditions, tectonic setting and clastic rock provenance (Nesbitt and Young 1982; Bhatia 1983; McLennan et al. 1995). And the composition of clastic sedimentary rocks is controlled by a combination of factors such as parent rock composition, weathering (physical and chemical), transport, sedimentation, and diagenesis. The formation of avaporite depends on the coupling of provenance, tectonic setting and climate, among which climate plays a decisive role (Liu 2013). Previous studies showed that the southwest of the Jianghan Basin had diverse provenance (Yu et al. 2018a), frequent tectonic activity (Wang 2006; Wang et al. 2018) and arid and hot climate (Sun and Wang 2005) during Paleocene. The geochemical characteristics of the sediments can reveal all these factors and provide reliable basis for the deposition of evaporite. And the latest geochemical data also provide new insights, such as that the climate was not hot at all.

Study area

The Jianghan Basin located in the Yangtze Block of central China, is a large Mesozoic-Cenozoic rift basin, with a total area of 36,360 km² (Gilder et sl. 1991; Teng et al. 2019). It is bordered by the Qinling orogen in the north, the Dabie Terrance in the northeast, the Edong fold-thrust belt in the east, the Jiangnan orogen in the south, and the Huangling massif and the Xiang’exi fold-thrust belt in the west (Fig. 1A; Hu et al. 2006a; Shen et al. 2012; Wu et al. 2017). The Presinian metamorphic basement of the Jianghan Basin was formed during the Late Proterozoic. The basement of the Jianghan Basin consists of two parts: the underlying crystalline basement and the overlying pre-rift strata. The crystalline basement of the Jianghan Basin mainly consists of Archean-Proterozoic metamorphic and metasedimentary rocks (HBGMR 1990). During the Ediacaran to the early Triassic, with the influence of the regional Indosinian movement spreading to this area, the Jianghan Basin uplifted to different degrees under the background of dramatic and rapid crustal rise, and the sea water slowly withdrew westward, forming a set of extensive coastal clastic rocks interbedded with marine carbonate rocks (Dai 1996; Yao et al. 2015). The middle Triassic to Jurassic sediments in the Jianghan Basin were mainly terrestrial conglomerate, sandstone and mudstone, and interbedded with coal seams formed from Carboniferous to early Triassic Period (HBGMR 1990; Shu et al. 2008). Under the influence of the Yanshanian movement, a NW-trending fault belt was formed in the Jianghan Basin from late Jurassic to early Cretaceous (Wang et al. 2006; Hu et al. 2006b). From the late Cretaceous to Paleogene, the Jianghan Basin experienced the active upwelling of the upper mantle induced by the rolling of the Pacific plate and the Indo-Asian collision, resulting in multi-stage rifting and the formation of extensive siliceous clasts, evaporites and a large number of basalts in the basin, and finally formed the present geographical characteristics (Liu et al. 2004; Li et al. 2015).

The Jianghan Basin is composed of several secondary structural units and depressions. The Jiangling depression is the largest secondary negative tectonic unit in Jianghan Basin, which was formed on the Yanshanian fold basement under the depression setting of late Cretaceous to Paleogene (Fig. 1B). The growth and development of Jiangling depression are controlled by Qingshuikou fault, Jishansi fault, Wen’ansi fault and Gong’an-Songzi fault, and divided into two independent units by Wancheng fault (Fig. 2; Yang et al. 2003; Wang et al. 2013; Yu et al. 2018b). In 2016, we obtained a 2,302.03 m long well (ZK0303) in the southwest of the Jiangling depression. The core is mainly composed of purplish pink siltstone and dark gray mudstone, interbedded with anhydrite, glauberite and halite.

A total of 35 siltstone samples were collected from Well ZK0303 based on the criteria of vertical differences (Fig. 2). We split the core ZK0303 into two halves in the longitudinal, and selected the fresh part that was not contaminated. All samples were stored in plastic bags to avoid secondary pollution and oxidation as much as possible. Under microscope, the clastic composition of these samples are composed of quartz, feldspar, and lithic. Among them, the lithic grains are subangular to subrounded, and lithic fragments are mainly sedimentary rock, with less volcanic and metamorphic rocks. Sedimentary lithic grains are mainly composed of chert (Fig. 3b, d, e, and f), mudstone and siltstone (Fig. 3a, c, e, and f), while the metamorphic grains are mainly quartzite (Fig. 3a, c, d). No significant volcanic debris are found in the samples. Feldspar grains are subangular, mainly plagioclase (Fig. 3a, b, f). Quartz grains are subrounded to angular, mainly monocrystalline quartz, visible polycrystalline quartz (Fig. 3). Most monocrystalline quartz is clear without inclusions. The individual crystals of the polycrystalline quartz grains have straight to slightly curved intercrystal boundaries. The matrixes and cements are dominated by mudstone, calcite, and anhydrite (Fig. 3).

Before the geochemical analysis all samples were air-dried, crushed to 200 mesh and thoroughly mixed. The major elements were analyzed by X-ray fluorescence spectrometer (XRF), and the trace and rare earth elements were tested by inductively coupled plasma mass spectrometry (ICP-MS). After that, the powdered samples were heated and poured into the mixture of anhydrous lithium tetraborate, lithium fluoride and ammonium nitrate to melt into glass sheets, which were continued to be heated in a muffle furnace to determine loss on ignition. Finally, the fused samples were heated to 800°C and analyzed using a sequential X-ray fluorescence spectrometer (AB104L, Axios-mAX). Calibrations of accuracy and reproducibility were conducted using the GB/T 14506.14–2010 and GB/T 14506.28–2010 standards. Precision for major elements are within 1%.

The content of trace and rare earth elements were measured by inductively coupled plasma mass spectrometer (ICP-MS, ELEMENT XR). Heat the powdered samples with HF and HNO₃. After evaporation to dryness, HNO₃ was added to dissolve the samples. Then, HNO₃ was added to samples again and heated to 130°C. Finally, the distilled water was added to the solution and the contents of trace elements were measured. Calibrations of accuracy and reproducibility were conducted using the GB/T 14506.30–2010 and HDB/T 3022 − 2018. Precision for trace and rare earth elements are within 5%. All geochemical analyses were carried out in the Analytical Laboratory Beijing Research Institute of Uranium Geology.

Among the major elements, the average contents of SiO₂ (48.27%), Al₂O₃ (14.01%) and CaO (8.00%) are the top three (Supplementary Table S1). And almost contents of SiO₂, Al₂O₃, TiO₂ and MnO show relative depletion after they are normalized to the Average Post-Archean Australian Shale (PAAS) (Fig. 4A). In contrast, the contents of all CaO and MgO were higher than those of PAAS and show strong enrichment (Fig. 4A).

The three elements with the highest average content are Sr, Ba and Rb, and their average contents are 2307.74 ppm, 393.60 ppm and 154.60 ppm, respectively (Supplementary Table S1). The preservation state of each element varies greatly if they are normalized to Average Upper Continental Crust (UCC) data. The contents of Cr and Cs are enriched relative to UC, the contents of Nb, Ta, Zr and Hf show strong depletion (Fig. 4B).

For REE, the Ce contents range from 47 to 88 ppm, averaging 64.07 ppm, the La contents range from 25.60 to 46.90 ppm, averaging 36.18 ppm, and the Nd contents range from 22.10 to 40.00 ppm, averaging 30.35 ppm (Supplementary Table S1). They are the three most abundant REEs. The LREE/HREE ratios range from 7.91 to 11.86, averaging 8.96 (Table 1). The Eu/Eu* ratios generally show negative anomalies, and they range from 0.62 to 0.83 (average = 0.70) (Table 1). In the chondrite-normalized diagram (Fig. 4C), the light REE (LREE) ratios show strong enrichment, while heavy REE (HREE) ratios show flat enrichment.

Table 1

Ratios of selected elements of the Paleocene siltstones in the Jianghan Basin
No.	LREE/HREE	Eu/Eu*	CIA	CIW	PIA	ICV	C-value	Sr/Cu	Ga/Rb
ZK1	9.06	0.68	55.33	63.50	57.17	1.63	0.31	40.00	0.13
ZK2	8.70	0.71	45.77	51.23	44.62	1.88	0.25	10.02	0.14
ZK3	8.36	0.76	48.03	53.51	47.53	1.83	0.25	14.63	0.15
ZK4	8.68	0.77	47.02	53.10	46.14	1.72	0.28	15.07	0.13
ZK5	8.04	0.79	59.06	69.46	62.93	1.30	0.46	15.04	0.14
ZK6	8.29	0.83	40.54	44.89	38.27	2.18	0.25	15.62	0.12
ZK7	8.33	0.68	56.03	65.34	58.44	1.67	0.31	83.85	0.12
ZK8	8.35	0.71	60.54	72.32	65.63	1.44	0.41	11.04	0.12
ZK9	11.86	0.66	59.99	70.51	64.23	1.32	0.40	10.35	0.12
ZK10	8.47	0.66	47.92	54.53	47.25	1.94	0.26	34.78	0.10
ZK11	13.83	0.62	61.51	73.11	66.86	1.44	0.38	23.13	0.09
ZK12	9.35	0.74	45.41	50.52	44.24	2.03	0.21	665.00	0.11
ZK13	8.48	0.64	62.38	74.40	68.29	1.32	0.46	10.30	0.11
ZK14	8.90	0.66	59.04	69.75	63.04	1.44	0.37	31.48	0.10
ZK15	9.58	0.72	65.46	78.08	72.84	1.27	0.44	36.14	0.11
ZK16	9.00	0.72	63.87	76.32	70.59	1.27	0.43	18.59	0.11
ZK17	8.58	0.77	48.06	54.35	47.47	1.78	0.27	14.17	0.12
ZK18	8.60	0.71	52.70	60.98	53.71	1.63	0.35	14.56	0.11
ZK19	8.37	0.69	53.24	60.86	54.32	1.70	0.25	79.48	0.11
ZK20	8.62	0.67	61.63	71.94	66.30	1.43	0.32	212.27	0.11
ZK21	8.71	0.73	54.25	62.35	55.74	1.58	0.35	134.67	0.12
ZK22	8.54	0.69	48.62	55.21	48.19	1.76	0.27	123.43	0.11
ZK23	10.23	0.68	36.79	40.23	34.05	2.39	0.15	840.48	0.11
ZK24	8.37	0.74	64.44	76.26	70.92	1.36	0.39	27.34	0.11
ZK25	8.88	0.66	46.88	52.21	46.08	1.86	0.28	15.53	0.13
ZK26	8.48	0.73	50.45	57.35	50.59	1.77	0.30	81.42	0.11
ZK27	9.21	0.62	38.44	42.49	35.72	2.34	0.18	59.03	0.10
ZK28	9.08	0.68	63.48	76.60	70.50	1.29	0.48	6.24	0.10
ZK29	8.98	0.66	58.35	68.58	61.90	1.35	0.36	38.67	0.09
ZK30	7.91	0.71	62.91	74.55	68.77	1.27	0.47	6.45	0.11
ZK31	7.97	0.68	55.78	64.18	57.83	1.45	0.34	9.53	0.12
ZK32	8.27	0.70	39.49	43.15	37.35	2.46	0.18	526.04	0.11
ZK33	8.33	0.77	43.93	49.31	42.24	2.03	0.27	7.07	0.10
ZK34	10.42	0.67	55.47	64.53	57.61	1.50	0.32	98.96	0.10
ZK35	8.83	0.70	52.63	60.44	53.55	1.63	0.31	9.23	0.10

Provenance

The geochemical data are often used to identify the provenance and reveal the characteristics of the source area (Roser and Korsch 1986; Cullers 1995; Armstrong-Altrin et al. 2013). As essential immobile elements, the ratios of of Al, Ti, and Zr can be used to reflect the type of the original rock (Stumm and Morgan 1981; Wesolowski 1992; Ayers and Watson 1993; Hayashi et al. 1997). In the plots of TiO₂ versus Al₂O₃, Hayashi et al. (1997) divided the provenance into three types: mafic igneous rocks, intermediate igneous rocks, and felsic igneous rocks. And the samples of the Shashi Formation mainly belong to the source area of intermediate and felsic igneous rocks (Fig. 5A). Apart from the major elements, some trace elements (La, Sc, Cr, Hf, Th, Zr, etc.) and REEs are of great significance in interpreting the provenance and composition of the source area because of their potential nature of low mobility during the post-depositional process (Bhatia and Crook 1986; Mclennan et al. 1993). On the diagram of Th/Sc versus Zr/Sc (McLennan et al. 1993), all samples were also concentrated near the felsic source rocks, and the trend for Zr enrichment indicates that the sediment compositions of all samples may be not affected by recycling (Fig. 5B). On the diagram of La/Th versus Hf (Floyd and Leveridge 1987), all of the samples fall around the felsic arc source region (Fig. 5C). And on the Co/Th versus La/Sc diagram proposed by McLennan et al. (1993), these samples are located between andesite and felsic source rocks (Fig. 5D). In addition, the REE distribution and Eu anomaly in the sediments can also provide clues for the research of the source characteristics (Cullers 1994). The high LREE/HREE ratios and negative Eu anomalies of the Shashi Formation show the characteristics of felsic source rocks (Table 1; Fig. 4C). And the siltstone samples are mainly quartz, followed by feldspar, without basic clasts, indicating felsic source rocks. In general, these samples have the characteristics of felsic source rocks.

Tectonic setting

Previous studies have showen that the bulk-rock geochemistry of siliciclastic sediments is affected by the tectonic movement of source rocks, so it is often used to distinguish the tectonic setting of sedimentary basins (Bhatia 1983; Roser and Korsch 1986; Bhatia and Crook 1986). Some trace elements (such as La, Th, Sc, and Zr) with relatively low mobility can not only be used to trace the source rock but also be an important basis to distinguish tectonic setting. The tectonic setting of sediment development can be roughly divided into four types (Taylor and McLennan 1985; Bhatia and Crook 1986): oceanic island arc (OA), continental island arc (CA), active continental margin (ACM), and passive margin (PM). On the diagram of Th-Co-Zr/10 (Fig. 6A), most samples of the Shashi Formation fall around the ACM field; on the diagram of La-Th-Sc (Fig. 6B), most of samples are located at the CA (Bhatia and Crook 1986). And on the diagram of SiO₂/Al₂O₃ versus K₂O/Na₂O (Roser and Korsch 1986) (Fig. 6C), almost all samples are located at ACM field.

Jianghan Basin is a rift basin in a composite basin-mountain system, and its sediments are provided by the erosion of elevated tectonic units that include various basement sequences. Yu et al. (2018a) identified four provenances with different orientations based on the U-Pb ages of zircons and bulk geochemical characteristics of clastic rocks of the Paleocene Shashi Formation. The oldest zircons are from Paleoproterozoic-Archean, and the geochemical data indicate that these samples are from the passive continental margin, characterized by recycled sedimentary, and are believed to have originated from the Huangling uplift in the northwest Jianghan Basin (Yu et al. 2018a). The second set of zircon ages are Neoproterozoic. During which magmatism associated with the Rodinian Supercontinent rupture was widespread in South China (Li et al. 2003a, 2003b; Zheng et al. 2004; Greentree et al. 2006), and Neoproterozoic volcanic rocks were also prevalent in the basement of the surrounding range systems of the Jianghan Basin, such as the South Qinling Belt, the Jiangnan Orogen, and Huangling uplift (Wang et al. 2007; Liu et al. 2008; Yao et al. 2013; Li and Zhao 2016). So, these samples of zircon are probably from basement of the ranges around the Jianghan Basin. The last set of zircons are from Ordovician-Triassic. The Ordovician zircons were derived from Caledonian magmatism in the Jiangnan Orogen (Shu et al. 1991; Ren 1991; Wang et al. 2011) and the North Dabashan zone of the South Qinling Belt (Chen et al. 2014; Cao et al. 2015; Wang et al. 2015), while the Triassic zircons were major derived from Indosinian magmatism in the Jiangnan Orogen (Yue et al. 1998; Wang et al. 2002, 2005). And the synthesis of geochemical data and petrographic results indicates felsic source rocks in the active continental margin and continental arc (Yu et al. 2018a). These indicate that the Jianghan Basin received detrital materials from the South Qinling Belt in the north and the Jiangnan Orogen in the south.

The siltstone samples of the Paleocene Shashi Formation in well ZK0303 also have the characteristics of felsic source rocks in the active continental margin and continental arc. According to the analysis of Yu et al. (2018), the provenance of the Paleocene in well ZK0303 should be mainly from the South Qinling Belt in the north and the Jiangnan Orogen in the south.

Palaeoweathering and palaeoclimate

In arid climate, the source rocks are mainly affected by physical weathering, in which they can only be mechanically broken down into smaller grain sizes without significant changes in mineralogical and chemical composition (Wanas and Assal 2020). And the chemical weathering plays a dominant role in humid climates and strongly controls the major and trace element composition of siliceous clastic sediments (Nesbitt and Young 1982; Harnois 1988; Middelburg et al.1988; McLennan et al. 1993; Fedo et al. 1995). It directly affects the removal of mobile elements (Na, K, Ca) and the enrichment of immobile elements (Al, Si) in the sediments (Nesbitt and Young 1982). The chemical index of alteration (CIA = Al₂O₃/(Al₂O₃ + CaO* + Na₂O + K₂O) × 100, Nesbitt and Young 1982; CaO*= CaO − 10/3 × P₂O₅, McLennan et al. 1993) and Al₂O₃-(CaO + Na₂O)-K₂O (A-CN-K) ternary diagram (Nesbitt and Young 1984) can determine the mobility of elements during chemical weathering and potassium metasomatism during diagenesis, and evaluate the weathering history and source rock composition. Besides, chemical index of weathering (CIW = Al₂O₃/(Al₂O₃ + CaO + Na₂O) × 100, Harnois 1988), plagioclase index of alteration (PIA = 100× (Al₂O₃ - K₂O)/(Al₂O₃ + CaO* + Na₂O - K₂O), Fedo et al. 1995), and index of compositional variability (ICV= (Fe₂O₃ + K₂O + Na₂O + CaO + MgO + TiO₂)/Al₂O₃, Cullers et al. 1995) are also important bases for assessing the source area palaeoweathering.

The ratios of CIA in the all samples vary from 36.79 to 65.46 (average = 53.30) (Table 1). In general, a CIA ratio of 55 or less represents unweathered, while 100 represents fully weathered (Nesbitt and Young 1982). The lower CIA ratio indicates that chemical weathering in the source area was less during the Paleocene. In the ternary diagram of A-CN-K (Fig. 7A), All the samples are near the boundary of A-CN and are distributed along the line between clinopyroxene and PAAS, away from the A-K boundary that represents high weathering. And the ratios of CIW range from 40.23 to 78.08 (average = 61.60), the ratios of PIA range from 34.05 to 72.84 (average = 55.17), the ratios of ICV range from 1.27 to 2.39 (average = 1.66) (Table 1), They all represent a low to moderate degree of weathering in the source area (Harnois 1988; Fedo et al. 1995). In addition, the ternary diagram of Al₂O₃-Zr-TiO₂ indicates that hydraulic sorting is not obvious (Fig. 7B, Garcia et al. 1991).

Worash (2002) believes that the distribution, composition and relative concentration of some trace elements in clastic rocks may indicate the palaeoclimate and palaeoenvironment. Zhao et al. (2007) and Cao et al. (2012) proposed using C-value as an indicator of palaeoclimate. The calculation formula of C-value is as follows: C-value = Σ(Fe + Mn + Cr + V + Ni + Co)/Σ(Ca + Mg + Sr + Ba + K + Na). This is because the Fe, Mn, Cr, V, Ni and Co elements are relatively enrich in humid conditions, while in arid conditions, evaporation precipitates saline minerals, resulting in the concentration of Ca, Mg, K, Na, Sr and Ba elements. And some current studies have shown that palaeoclimate conditions can impact the ratios of Ga/Rb, Rb/Sr and Sr/Cu in sediments (Jin and Zhang 2002; Bai et al. 2015). Gallium is related to kaolinite, suggesting strong chemical weathering associated with warm and humid climatic conditions (Roy and Roser 2013). Rubidium is enriched in illite, reflecting a dry and cold climate associated with weak chemical weathering (Beckmann et al. 2005). In the warm sedimentary environment, the ratio of Rb/Sr in sediments decreases, while the ratio of Sr/Cu increases (Lerman and Gat 1989; Cao et al. 2015). And the Sr/Cu ratio between 1.3 and 5.0 represents humid environments, while the Sr/Cu ratio is higher than 5.0 in arid climates (Lerman 1978).

On the major elements diagram (Suttner and Dutta 1986), all samples are located at arid field (Fig. 8A). And the C-value range from 0.15 to 0.48, Sr/Cu ratios range from 6.24 to 840.48, and Ga/Rb ratios range from 0.09 to 0.15 (Table 1). According to the C-value and Sr/Cu ratio (Zhao et al. 2007 and Cao et al. 2012), the climatic conditions of the Paleocene Shashi Formation were between arid and semi-arid/semi-humid (Fig. 8B). Moreover, the projection points in the Sr/Cu- Ga/Rb discriminant map indicate that the Jianghan Basin had a cold and arid climate during the Paleocene (Fig. 8C). Comprehensive geochemical indicators, climate of the Jianghan Basin was cold and arid during the Paleocene.

(1) The REE distribution and Al₂O₃-TiO₂, La/Sc-Co/Th, Hf-La/Th and Zr/Sc-Th/Sc ratios of the clastic rocks in Shashi Formation indicate that the southwestern Jianghan basin mainly received felsic source rocks during the Paleocene.

(2) Based on the analysis of the data of major and trace elements, the Paleocene clastic rocks in Jianghan Basin were formed under the tectonic background of active continental margin and continental island arc with frequent faulting activities.

(3) And the ratios of CIA, CIW, PIA, and ICV indicates low weathering in the source area. The ratios of Sr/Cu, Ga/Rb, and C-values reflect the cool and arid climate of the Paleocene in the Jianghan Basin.

Data Availability

Data is available based on request.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Author Contributions Statement

K.Y. and C.L.W. wrote the main manuscript text. J.Y.W., X.C.Y. and X.H.T. developed the idea for the study. R.Q.L. and L.H.L. analyzed the data. All authors reviewed the manuscript.

Acknowledgments

We appreciate the funding by grants from the Central Public Welfare Scientific Research Basic Scientific Research Business Expenses (No. KK2005), the National Natural Science Foundation of China (Nos. U20A2092, 42002106, 41907262 and 41502089), the Major State Basic Research Development Program of China (No. 2011CB403007) and the China Geological Survey (No. DD20190606).

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Geochemistry of the Paleocene saline lake in the southwestern Jianghan Basin, Central China: implications for provenance, tectonic setting, and palaeoclimate

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