Paleoclimate Transition Recorded by Palynological and Clay Mineral Evidence in the Santanghu Basin during the Middle Jurassic

Paleoclimate Transition Recorded by Palynological and Clay Mineral Evidence in the Santanghu Basin during the Middle Jurassic | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Paleoclimate Transition Recorded by Palynological and Clay Mineral Evidence in the Santanghu Basin during the Middle Jurassic Bing Yang, Di Zhang, Xinzhi Zhang, Siyuan Sun, Weitong Li This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5779811/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The arid event that began in the Middle Jurassic Bathonian stage marks the second major drought event in northern China during the Jurassic period and had a profound impact on the development of modern terrestrial ecosystems. This study reconstructs the paleoclimate and paleoecosystem of the Middle Jurassic Santanghu Basin by analyzing palynological assemblages and clay minerals from the Xishanyao and Toutunhe formations. Two distinct palynological assemblages were identified: the Cyathidites-Deltoidospora-Osmundacidites-Cycadopites (CDOC) assemblage (Aalenian–Bajocian) and the Cyathidites-Classopollis-Quadraeculina (CCQ) assemblage (Bathonian). In terms of vegetation types, during the Aalenian–Bajocian stage, the Santanghu Basin was dominated by ground cover vegetation primarily consisting of ferns, with a midstory composed mainly of cycads/ginkgophytes, and a sparse canopy dominated by conifers. By the Bathonian stage, this shifted to a vegetation structure dominated by coniferous canopy vegetation, a subordinate midstory of cycads/ginkgophytes, and a severely degraded ground cover dominated by ferns. Sporomorph EcoGroup (SEG) analysis indicates that the CDOC assemblage is characterized by high Lowland SEG wetter/drier and warmer/cooler ratios, reflecting a warm and humid climate. In contrast, the CCQ assemblage also shows high Lowland SEG wetter/drier and warmer/cooler ratios but indicates a warm and arid climate. Clay mineral data reveal that the kaolinite content in the CCQ assemblage is significantly lower than in the CDOC assemblage. Evidence from both palynology and clay minerals suggests that the Santanghu Basin experienced a transition from a humid to a semi-arid climate near the Bajocian–Bathonian boundary in the Middle Jurassic. palynological assemblage Sporomorph EcoGroup Model kaolinite paleoclimate northern China Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 0 Introduction The Jurassic period is recognized as a classic greenhouse climate phase in Earth’s geological history, with atmospheric CO 2 concentrations and sea surface temperatures significantly higher than those of the present day (Berner 1994; Berner and Kothavala 2001; Lenton et al. 2018). However, the Jurassic climate was not uniformly stable; it experienced several pronounced fluctuations (Pearce et al. 2008; Dera et al. 2011; Korte et al. 2015; Nordt et al. 2022). Extensive marine oxygen isotope studies reveal substantial variability in seawater surface temperatures across different regions and time periods (Dera et al. 2009 2012; Alberti et al. 2020). By integrating global data, Dera et al. (2011) constructed a Jurassic global paleoseawater temperature curve, indicating frequent fluctuations. After a high-temperature phase in the Early Jurassic, global seawater temperatures reached a low during the Pliensbachian, surged to a peak in the Toarcian, and then declined through the early Middle Jurassic, continuing until the Bathonian. Temperatures rose again in the Callovian and peaked during the Late Jurassic Tithonian. Due to the uneven global distribution of water resources, trends in aridity and humidity varied regionally, requiring localized studies. Zhong et al. (2003) reconstructed the Jurassic paleoclimate of northern China using palynological, paleobotanical, and mineralogical data, identifying two long-term aridification events: one during the Early Jurassic Toarcian and another from the Middle Jurassic Bathonian to the end of the Late Jurassic. The Early Jurassic Toarcian aridification event is believed to be a consequence of the Toarcian Oceanic Anoxic Event (T-OAE), characterized by a significant negative carbon isotope excursion, termination of coal formation, plant decline, and increased temperatures leading to arid conditions (Deng et al. 2012). This event has been documented in multiple basins across northern China (Zhang et al. 1998; Wang et al. 2005; Deng et al. 2012; Yang et al. 2024a). In contrast, the aridification event from the Middle Jurassic Bathonian to the end of the Late Jurassic has received comparatively less attention, and its impact on terrestrial ecosystems remains poorly understood. This study employs palynological and clay mineral evidence from the Middle Jurassic Xishanyao and Toutunhe formations in the Santanghu Basin to elucidate the effects of this climatic transition on vegetation patterns and ecosystem dynamics in the region. 1 Geological settings The Santanghu Basin is located at the junction of the Altay Fold Belt and the Northern Tianshan Fold Belt in northeastern Xinjiang. It is a narrow, irregular intermontane basin, bordered by the Junggar Basin to the west and the Turpan-Hami Basin to the south. The basin extends approximately 500 km east to west and 40–70 km north to south, covering a total area of 23,000 km². Following multiple tectonic events, including the Hercynian, Indosinian, Yanshanian, and Himalayan movements (Liu et al. 2024), the basin evolved into three secondary structural units: the northern uplift belt, the central depression belt, and the southern thrust belt (Zhang et al. 2023). During the Early and Middle Jurassic, the basin experienced a relatively stable phase, with the regional stress field characterized by weak NW-oriented compressive forces and minimal tectonic activity. This stability facilitated the deposition of the Lower Jurassic Badaowan and Sangonghe formations, as well as the Middle Jurassic Xishanyao and Toutunhe formations. In the Late Jurassic, influenced by the Yanshanian Orogeny, the regional stress field exhibited stronger NW-oriented compression, causing slight uplifts in local areas and leading to the deposition of the Upper Jurassic Qigu and Kalazha formations (Zhang et al. 1993; Liu 2010). Well TYY1 is located 12 km northwest of Santanghu Town in Barkol County, Hami Prefecture, Xinjiang, within the southern thrust belt (Fig. 1). The stratigraphic sequence encountered in this well, from bottom to top, includes the Lower Jurassic Sangonghe Formation, and the Middle Jurassic Xishanyao and Toutunhe formations. The Xishanyao Formation, occurring between 611.5 m and 377.1 m depth, consists primarily of gray-black mudstone, gray-white sandstone, and interbedded coal seams, representing deposits from braided river delta and lacustrine systems. The Toutunhe Formation, from 377.1 m to the surface, comprises brownish siltstone, mudstone, and gray-green conglomerate and sandstone, indicative of a fluvial depositional environment. 2 Materials and methods In this study, thirteen palynological samples were collected from the upper part of the Xishanyao Formation (sample nos. A7, S18, S17, S16, S15, S14 and S13) and the lower part of the Toutunhe Formation (sample nos. A1, A2, A3, A4, A5, and A6). Each 50 g sample was crushed into fragments smaller than 1.0 mm in diameter and subjected to the following chemical treatments: hydrochloric acid (HCl, 10%) for 12 hours, hydrofluoric acid (HF, 40%) for 2 days, and hydrochloric acid (HCl, 36%) for an additional 12 hours. A heavy liquid mixture of zinc chloride (ZnCl) and potassium iodide (KI) with a density of 2.2 g/cm³ was used to extract the palynomorphs. Spore-pollen analysis was conducted at the Research Center of Paleontlogy and Stratigraphy, Jilin University. The prepared samples, slides, and stubs, all numbered accordingly, are stored at the Cores and Samples Centre of Natural Resources in Langfang, China. Each sample contained over 200 sporopollen grains for statistical analysis. The relative abundances of sporopollen fossils were calculated using Tilia software (version 3.0.3). assemblages were identified using the CONISS clustering method within Tilia in ascending stratigraphic order. Further details of the samples are provided in the Supplementary Material. The Sporomorph EcoGroup (SEG) model, established by Abbink et al. (2004), is founded on the principle that sporopollen assemblages reflect the plant communities from which they originated. This model posits that during various geological periods, specialized paleoecological communities existed, wherein plants within these communities shared similar ecological characteristics. The spores and pollen produced by these plants coexisted within the same ancient communities, and the dispersed assemblages of these terrestrial plants are categorized as SEGs. The SEG model facilitates detailed paleoecological interpretations of quantitative sporopollen data (Abbink et al. 2004; Li et al. 2016). Abbink et al. (2004) classified non-marine Jurassic-Cretaceous sporopollen floras into six SEG types: upland SEG, lowland SEG, river SEG, pioneer SEG, coastal SEG, and tidally influenced SEG. Each SEG type represents distinct ecological settings and associated plant communities (Abbink et al. 2004; Li et al. 2016; Li et al. 2018). For the interval between 480.0 m and 215.0 m in Well TYY1, 21 samples were analyzed for clay mineralogy using X-ray diffraction (XRD). Initially, 2-3 grams of rock powder (finer than 200 mesh) were used to prepare non-oriented mounts by placing the powder in the recess of a glass slide. Additionally, 20-30 grams of powder were treated with dilute hydrochloric acid (HCl) to remove carbonates. Once the solution became weakly acidic, deionized water was added, and the mixture was allowed to settle. The supernatant was carefully decanted, and this process was repeated with fresh deionized water until an optimal mineral suspension was achieved. The turbid liquid was then drawn off, and the clay minerals were thoroughly mixed and uniformly spread to create oriented mounts. After initial testing, the oriented mounts were saturated with ethylene glycol for over 8 hours to produce ethylene glycol-saturated mounts. They were subsequently heated at 490°C for 2 hours to create high-temperature heated mounts, both of which were analyzed. All clay mineral analyses were performed at the State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences (Wuhan), using a PANalytical X’Pert Pro X-ray diffractometer. The experimental procedures followed those outlined by Xu et al. (2007). 3 Results 3.1 Characteristics of Palynological Assemblages Based on CONISS analysis using Tilia software on 26 dominant and representative spore-pollen genera, the thirteen palynological samples were divided into two spore-pollen assemblages (Fig. 2). Cyathidites-Deltoidospora-Osmundacidites-Cycadopites (CDOC) assemblage: This assemblage includes samples from the Xishanyao Formation (A7, S18, S17, S16, S15, S14, S13). Pteridophyte spores dominate over gymnosperm pollen, ranging from 45.5% to 84.8% with an average of 62.0%. Gymnosperm pollen ranges from 15.2% to 53.7%, averaging 37.7%. Bryophyte spores are sporadically present, with an average of only 0.1%. Among the peridophyte, the dominant taxa are Cyathidites and Deltoidospora (Dicksoniaceae) and Osmundacidites (Osmundaceae), with Cyathidites minor Couper, 1953 being notably more abundant than other species. Concavisporites is also well-represented. In the gymnosperms, colpate pollen such as Cycadopites and Chasmatosporites is predominant. The content of bisaccate pollen is relatively low, ranging from 1.9% to 16.7% (average 10.2%) and shows a decreasing trend upward. Among the bisaccate taxa, Quadraeculina is the most common, while other genera are rare. Araucariaceae pollen ( Araucariacites and Callialasporites ) is present but with an average content of less than 2.0%. Bryophyte spores, including Alsophilidites , Annulispora , and Sphagnumsporites , are observed sporadically. These characteristics are consistent with the CDOC assemblage established by Yang et al. (2024b), and therefore, these seven samples are assigned to the CDOC palynological assemblage. Cyathidites-Classopollis-Quadraeculina (CCQ) assemblage: This assemblage includes samples from the lower part of the Toutunhe Formation (A1, A2, A3, A4, A5, A6). A total of 147 species of 40 genera and of spores and pollen were identified, including 30 undetermined species. Gymnosperm pollen dominates, ranging from 68.7% to 76.3% with an average of 72.2% (94 species of 23 genera). Pteridophyte spores are less abundant, ranging from 23.2% to 30.8% with an average of 27.3% (52 species of 16 genera). Bryophyte spores are scarce, comprising only 1 species, with an average content of less than 0.2%. In the pteridophyte spores, Cyathidites (Dicksoniaceae) and Osmundacidites (Osmundaceae) are dominant, with average contents of 9.0% and 6.7%, respectively. Cyathidites minor is the most abundant, ranging from 3.4% to 8.4% (average 4.9%). Deltoidospora has an average content of less than 3.0%. Other pteridophyte spores, such as Lycopodiumsporites , Neoraistrickia , Auritulinasporites , Alsophilidites , Laevigatosporites , Calamospora , Klukisporites , Converrucosisporites , Cyclogranisporites , Dictyophyllidites , Concavisporites , and Undulatisporites , each have contents below 2.0%. Bryophytes include Sphagnumsporites , Annulispora , and Alsophilidites (Fig. 3). In the gymnosperm, Classopollis (monosulcate pollen) is highly abundant, ranging from 11.4% to 21.5% (average 17.1%), represented by species such as Classopollis annulatus (Verbitzkaja) Li, 1974, Classopollis qiyangensis Shang, 1981, and Classopollis classoides Pflug,1953 emend. Pocock et Jansonius, 1961. Cycadopites (monocolpate pollen) is the second most abundant, ranging from 7.2% to 19.1% (average 10.6%), with species including Cycadopites adjectus (De Jersey) De Jersey, 1964, Cycadopites altilis Zhang, 1984, Cycadopites clavatus Lei, 1986, Cycadopites formosus Singh, 1964, Cycadopites fragilis Singh,1964, Cycadopites granulatus (De Jersey) De Jersey, 1964, Cycadopites pyriformis (Nisson) Zhang, 1984, Cycadopites reticulate (Nisson) Arjang, 1975, Cycadopites striatus Ouyang et Norris, 1988, Cycadopites subgranulosu s (Couper) Bharadwaj et Singh, 1964, and Cycadopites typicus (Mal.) Pocock, 1970. Bisaccate pollen content is higher in this assemblage compared to the Xishanyao Formation, ranging from 28.1% to 34.4% (average 30.7%). Dominant bisaccate genera include Quadraeculina , Pinuspollenites , Piceaepollenites , Piceites , Erlianpollis , Podocarpidites , Alisporites , Cedripites , Protopinus , Pseudopicea , and Protoconiferus , with Quadraeculina being the most common (6.9%–8.8%, average 8.0%). Non-saccate gymnosperm pollen includes Psophosphaera , Araucariacites , Inaperturopollenites , and Granasporites , each with an average content of less than 3.0%. Saccizonate genera such as Callialasporites and Cerebropollenites are also present, each with an average content below 2.0%. Notable species include Callialasporites segmentatus (Balme) Sukh Dev, 1961, Callialasporites dampieri (Balme) Sukh Dev, 1961, Cerebropollenites carlylensis Pocock, 1970, and Cerebropollenites macroverrucosus (Thierg.) Pocock, 1970 (Fig. 4). 3.2 Characteristics of Clay Minerals In the TYY1 well, the upper part of the Xishanyao Formation (480.0 m - 377.1 m) and the lower part of the Toutunhe Formation (377.1 m - 215.0 m) are primarily composed of clay minerals, including illite, kaolinite, chlorite, smectite, and illite/smectite mixed layers. Notably, the high content of illite and kaolinite is characteristic of this section, with both minerals present in comparable amounts, generally exhibiting an inverse relationship in their abundance. Thus, the clay minerals can be classified as an illite-kaolinite assemblage. During the CDOC assemblage period (480.0 m - 377.1 m), the average content of kaolinite was 38.9%, remaining relatively stable, while the average content of illite was 35.1%. In contrast, during the CCQ assemblage period (377.1 m - 215.0 m), the average content of kaolinite decreased to 22.3%, whereas the average content of illite increased to 43.7%. The contents of chlorite, smectite, and illite/smectite mixed layers were relatively low and showed no distinct distribution pattern. Specifically, the average content of chlorite was 15.4%, smectite averaged 7.3%, and illite/smectite mixed layers averaged 6.7%. 4 Discussion 4.1 Geological Time Previous studies indicate that the CDOC assemblage of the Xishanyao Formation in the TYY1 well dates back to the Aalenian-Bajocian stage (Yang et al. 2024a). The majority of the spores in the CCQ assemblage of the Toutunhe Formation are derived from the Xishanyao Formation, with the continued abundance of Cyathidites minor and Cycadopites indicating the palynological characteristics of the Middle Jurassic (Wang et al. 1998; He et al. 2024). A notable difference is that, compared to the CDOC assemblage, the CCQ assemblage shows a significant increase in the abundance of bisaccate pollen, reflecting an evolutionary trend consistent with the early to late Jurassic evolutionary patterns observed in other regions of northwestern China (Wang et al. 1998; Huang 2002; Huang and Li 2007; Sun et al. 2017). Additionally, the CCQ assemblage features the new appearance of Klukisporites pseudoreticulatus Couper, 1958 and Callialasporites dampieri (Balme) Sukh Dev , 1961. Klukisporites pseudoreticulatus Couper, 1958 was first reported from the Lower Cretaceous in the UK (Couper 1958) and has since been commonly found in the Middle Jurassic of the former Soviet Union, Canada, France, and Germany (Ilyina 1986; Pocock 1970; Srivastava 1987). This species is also widely distributed in some Mesozoic strata across various regions of China (Huang 1995; Wang et al. 1998; Huang and Li 2007). Callialasporites dampieri (Balme) Sukh Dev , 1961 is prevalent in the Middle to Late Jurassic and is characteristic of the Bathonian to Callovian stages in Germany, France, and other parts of Europe (Srivastava 1987). It is also one of the zonal fossils from the Middle Jurassic Bathonian to Callovian in Australia (Filatoff 1975). The genus Classopollis shows a distinct distribution pattern in the Jurassic of northwestern China, Siberia, and Central Asia, with two peak periods. The first peak occurs during the Early Jurassic Toarcian stage, while the second peak begins in the Middle Jurassic Bathonian stage and continues until the Late Jurassic (Vakhrameev 1991; Wang et al. 1998). Compared to the first peak, the second peak has a broader impact in Northwest China. For instance, in the upper part of the Shimen Gou Formation of the Jurassic in the Qaidam Basin, the content of Classopollis sharply increases, with an average of 19.8% (Xie 2023). In the Jurassic Toutunhe Formation at the Honggou section of the Manas River in Xinjiang, Classopollis content reaches 11.7% (Huang and Li 2007). In the Kuqa Basin of Tarim, Classopollis content can reach 27.6% in the Qiaokemak Formation (Huang and Li 2007), while in the Shanjianfang Formation of the Turpan-Hami Basin, it reaches 31.5% (Wang et al. 1997). In the current study, the Classopollis content in the CCQ assemblage of the Toutunhe Formation shows a marked increase, with an average content of 17.1%, aligning with the palynological characteristics of Classopollis during the Bathonian stage. This suggests that the geological age of the CCQ assemblage is later than the Bajocian stage. Furthermore, the last occurrence of Quadraeculina anellaeformis is in the Bathonian stage (Santos et al. 2018), which also constrains the geological age of this assemblage to be earlier than the Callovian stage. Based on the evidence presented, the age of the CCQ palynological assemblage can be constrained to the Middle Jurassic Bathonian stage. 4.2 Reconstruction of Paleovegetation The parent plants of spore and pollen fossils can be used to reconstruct paleovegetation, as well as to infer paleoclimate and paleoenvironmental conditions (Li et al. 2016; Yang et al. 2024a 2024b). The plant groups in the CDOC and CCQ assemblages primarily include conifers, ferns, cycads/ginkgophytes, lycopsids, bryophytes, and horsetails (Fig. 5). The characteristics of each assemblage are as follows: CDOC assemblage: In this assemblage, ferns dominate, comprising 37.5% to 81.0% of the total, with an average of 56.8%. This group is predominantly represented by the families Cyatheaceae ( Cyathidites and Deltoidospora ) and Osmundaceae ( Osmundacidites ), along with a small number of taxa from the Dipteridaceae/Matoniaceae families, such as Dictyophyllidites and Concavisporites . Cycads/ginkgophytes occupy a secondary position in this assemblage, with an average content of only 19.8%, represented by genera such as Cycadopites , Chasmatosporites , and Monosulcites . Conifers are present in even lower abundance than cycads/ginkgophytes, averaging just 15.4%. This group primarily consists of Pinaceae, with notable genera including Piceites , Erlianpollis , and Pinuspollenites , along with some representatives from the seed fern genera Alisporites . Lycopsids are relatively rare, averaging only 5.3%, represented by genera such as Lycopodiumsporites , Neoraistrickia , Punctatisporites , and Aratrisporites . Bryophytes and horsetails are present in minimal amounts, with a total content of about 1.0%. CCQ assemblage: The main distinction of this assemblage from the CDOC assemblage is that conifers have replaced ferns as the dominant group, averaging 56.6%. This group includes similar contributions from Pinaceae, Araucariaceae, Cheirolepidiaceae, and Podocarpaceae. Additionally, there are minor occurrences of Taxodiaceae and seed ferns. Ferns have become a secondary component in this assemblage, averaging only 23.8%, primarily represented by Cyatheaceae and Osmundaceae. The content of cycads/ginkgophytes is slightly lower than in the CDOC assemblage, averaging just 14.8%, with genera such as Cycadopites , Chasmatosporites , and Monosulcites present. The abundance of lycopsids has significantly decreased in this assemblage, with an average of only 2.7%. Bryophytes and horsetails remain minimal, with a total content of approximately 1.0%. The evolution of the vegetation groups in the CDOC and CCQ assemblages indicates that the plant ecosystem of the Santanghu Basin transitioned from a dominant ground cover of ferns during the Early to Middle Jurassic (Aalenian-Bajocian) to a canopy dominated by conifers in the late Middle Jurassic (Bathonian). During this transition, cycads/ginkgophytes shifted to a subordinate role, while the ground cover of ferns experienced severe degradation (Fig. 6). 4.3 Evolution of the Paleoclimate 4.3.1 Sporomorph EcoGroup Model By analyzing the palynological samples from the upper part of the Xishanyao Formation and the lower part of the Toutunhe Formation in the TYY1 well of the Santanghu Basin, we conducted a percentage composition analysis of the SEG. This analysis revealed the relative abundance variations of different SEGs within the Jurassic palynological flora of the basin, as well as the curves representing the content of wet-type molecules, dry-type molecules, wetter/drier ratios, and warmer/cooler ratios of the lowland SEG. A total of five SEGs were identified in the spore assemblages of the Xishanyao and Toutunhe formations: Lowland SEG, Upland SEG, River SEG, Pioneer SEG, and Coastal SEG. Among these, the Lowland SEG and Upland SEG are dominant, with comparable abundances that exhibit an inverse relationship. The River SEG is relatively scarce, while the Pioneer SEG and Coastal SEG are present in minimal amounts (Fig. 7). The characteristics of each assemblage are as follows: CDOC assemblage: The Lowland SEG molecules dominate this assemblage, with a content ranging from 66.2% to 95.7% and an average of approximately 81.7%. There is a declining trend near the boundary with the CCQ assemblage. The Upland SEG molecules are present in lower quantities, ranging from 1.9% to 17.5%, with an average of about 11.0%. This group reaches its minimum value in the upper part of the assemblage and shows an increasing trend near the boundary with the CCQ assemblage. The wetter/drier ratio of Lowland SEG molecules is relatively high, ranging from 1.1 to 6.2, with a declining trend near the boundary with the CCQ assemblage. The warmer/cooler ratio of Lowland SEG molecules is also relatively high, ranging from 5.25 to 26.59. These findings indicate that the CDOC assemblage generally reflects a hot and humid climate environment; however, over time, it gradually transitions towards a more arid climate. CCQ assemblage: In this assemblage, the Lowland SEG molecules continue to dominate, but their content has significantly decreased compared to the CDOC assemblage, ranging from 58.2% to 64.5%, with an average value of 61.2%. Conversely, the Upland SEG molecules have increased substantially, with a content range of 30.0% to 35.9% and an average of 32.6%, demonstrating stability. The wetter/drier ratio of Lowland SEG molecules has sharply decreased, ranging from 0.52 to 0.97. Given that the content of wet-type molecules in the Lowland SEG can reach 25%, it can be classified as a semi-arid environment. The warmer/cooler ratio of Lowland SEG molecules remains relatively high, ranging from 8.70 to 21.43, with fluctuations that show overall consistency with the CDOC assemblage. From this evidence, it can be concluded that the Santanghu Basin experienced a transition from a humid climate to a semi-arid climate from the Early to Late Middle Jurassic (Aalenian-Bajocian to Bathonian), with relatively stable temperatures, consistently indicating a hot climate. 4.3.2 Clay Mineral Evidence The composition, abundance, and assemblage characteristics of detrital clay minerals are important indicators for reconstructing paleoclimate and paleoenvironment. Illite is generally believed to primarily exist in weakly alkaline environments and cold, dry climatic conditions. It forms from the weathering of potassium feldspar under strong physical weathering and weak leaching processes. Therefore, a high content of illite indicates arid climatic conditions (Singer 1984; Chamley 1989; Xu et al. 2017). In contrast, under warm and humid climatic conditions, leaching is more intense, leading to the loss of alkali and alkaline earth metals from the parent rock, which facilitates the formation of kaolinite (Chamley 1989; Velde 1995; Murru et al. 2003). From the perspective of mineral assemblages, clay combinations indicative of humid climates typically feature the presence of kaolinite. Common combinations include kaolinite + illite/smectite + illite, kaolinite + illite, and kaolinite + illite + chlorite (Dong and Song, 2009). Clay combinations dominated by illite generally represent arid to semi-arid environments (Yang et al. 2024a). The mineral assemblage analysis indicates that both the upper part of the Xishanyao Formation and the lower part of the Toutunhe Formation belong to the kaolinite-illite assemblage, suggesting that the climate during the Aalenian-Bathonian period in the study area was generally relatively humid. Notably, the content of kaolinite in the upper part of the Xishanyao Formation is significantly higher than that in the lower part of the Toutunhe Formation, indicating that the climate during the Early Jurassic (Aalenian-Bajocian) in the study area was markedly more humid than in the Late Middle Jurassic (Bathonian). 4.4 Comparison Both palynological evidence and clay mineral evidence indicate that the Santanghu Basin experienced a transition from a humid climate to a semi-arid climate during the Early to Late Middle Jurassic (Aalenian-Bajocian to Bathonian). This climatic shift is not only observed in the Santanghu Basin but is also reflected in other regions of northern China. For instance, in the Ordos Basin, the palynological assemblage of the Yan'an Formation from the Aalenian-Bajocian stage shows a high abundance of humid and warm vegetation from the families Cyatheaceae and Osmundaceae. However, in the Bathonian stage, the palynological assemblage of the extended formation shows a significant decrease in humid and warm vegetation, alongside the emergence of a considerable amount of drought-resistant vegetation, represented by the Classopollis of the Cheirolepidiaceae family (Xu et al. 2023). In the Junggar Basin, at the Honggou section of the Manas River, the palynological assemblage from the Aalenian-Bajocian stage of the Xishanyao Formation reveals that the Cyatheaceae content exceeds 25.0%, with the maximum value for Osmundaceae reaching 18.4%, while Classopollis from the Cheirolepidiaceae family appears sporadically. In contrast, the palynological assemblage from the Bathonian stage of the Toutunhe Formation shows a significant decrease in the contents of Cyatheaceae and Osmundaceae, while the abundance of Classopollis sharply increases, reaching up to 11.7% (Huang and Li 2007). In the Turpan-Hami Basin, the palynological assemblage of the Xishanyao Formation shows that the content of Cyatheaceae exceeds 20.0%, with a maximum value for Osmundaceae of 15.6%, while Classopollis content is only between 1.4% and 3.2%. In the Bathonian stage, the palynological assemblage from the Sanjianfang Formation shows a decrease in Cyatheaceae content to 11.7%–19.3% and Osmundaceae content below 1.5%, while Classopollis flourishes, with a maximum content of 31.5% (Wang et al. 1998). In the northern Tarim Basin, the content of Classopollis in the Aalenian-Bajocian stage of the Kizilnur Formation is only 0.8%, while in the Bathonian stage of the Qiaokemak Formation, the content of Classopollis reaches as high as 27.9% (Liu 1998). This evidence illustrates that major basins in northern China underwent a transition from a humid climate to an arid (or semi-arid) climate from the Early to Late Middle Jurassic. It is generally believed that this arid event may be related to global warming during the same period (Wang et al. 2005; Deng et al. 2017). As a result of this event, the coal accumulation processes in most basins in northern China sharply weakened (Zhong et al. 2003; Jiao et al. 2019; Huang et al. 2023). The transition from “black” rock facies to “variegated” rock facies in northern China also indicates dramatic changes in terrestrial climate and environment during this period (Zhong et al. 2003; Zhang et al. 2007; Sun et al. 2017; Huang et al. 2023). 5 Conclusions Through the identification and analysis of fossils from 13 spore samples of the Xishanyao Formation and the Toutunhe Formation in the Santanghu Basin, we determined the geological age of the strata. By examining the characteristics of the spore assemblages, we reconstructed the ecosystem, and utilized the SEG model in conjunction with clay minerals to restore the paleoenvironment and reconstruct the paleoclimate. The following conclusions were drawn: The palynological assemblage of the lower Toutunhe Formation is classified as the Cyathidites - Classopollis - Quadraeculina (CCQ) assemblage, dating to the Late Middle Jurassic (Bathonian). Evidence from the spore vegetation indicates that during the Aalenian-Bajocian period, the ecosystem of the Santanghu Basin was characterized by a ground cover predominantly composed of ferns, with cycads/ginkgophytes representing a secondary mid-layer vegetation, and conifers being relatively scarce in the canopy. By the Bathonian, the ecosystem transitioned to one dominated by coniferous canopy vegetation, with cycads/ginkgophytes occupying a subordinate role and a significant degradation of fern-dominated ground cover. Analyses from the SEG model and clay minerals both indicate that the Santanghu Basin experienced a transition from a humid climate to a semi-arid climate during the early to late Middle Jurassic. Declarations Acknowledgments We thank Prof. Hu Jun from China University of Geosciences (Wuhan) for the help in clay mineral analysis. Funding This research was supported by the Collection and Digitization of Physical Geological Data Project (grant number DD20230138). Conflict of interest The authors declare that they have no confict of interest. Data availability The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request. The material (slides) is stored in the department laboratory (Cores and Samples Center of Natural Resources, China Geological Survey). A uthors contribution Bing Yang and Di Zhang designed the study. Bing Yang and Xinzhi Zhang identified the sporopollen. Di Zhang and Siyuan Sun carried out the clay minerals analysis. Weitong Li collected and prepared cores. Bing Yang wrote the paper, and all authors contributed to editing the paper. References Abbink, O. A., Van Konijnenburg-Van Cittert, J. H. A., & Visscher, H. (2004). A sporomorph ecogroup model for the Northwest European Jurassic—Lower Cretaceousi: Concepts and framework. Netherlands Journal of Geosciences , 83 , 17–31. Alberti, M., Leshno, Y., Fürsich, F. T., Edelman-Furstenberg, Y., Andersen, N., & Garbe-Schönberg, D. (2020). Stress in the tropics? Impact of a latitudinal seawater δ 18 O gradient on Middle Jurassic temperature reconstructions at low latitudes. Geology, 48 , 1210–1215. Berner, R. A. (1994). GEOCARB II: A revised model of atmospheric CO 2 over phanerozoic time. American Journal of Science, 294 , 56–91. Berner, R. A., & Kothavala, Z. (2001). GEOCARB III: a revised model of atmospheric CO 2 over Phanerozoic time. American Journal of Science, 301 , 182–204. Chamley, H. (1989). Clay formation through weathering. In Clay sedimentology (pp. 21–50). Springer-Verlag. Couper, R. A. (1958). British Mesozoic microspores and pollen grains. A systematic and stratigraphic study . Palaeontographica Abteilung B, 103, 75–179. Deng, S. H., Lu, Y. Z., Fan, R., Fang, L. H., Li, X., & Liu, L. (2012). Early Jurassic Toarcian ocean hypoxia event and its response in terrestrial ecosystem. Earth Science, 37 (S2): 23–38 (in Chinese with English abstract). Deng, S. H., Lu, Y. Z., Zhao, Y., Fan, R., Yang, X. J., Li, X., & Sun, B. N. (2017). The Jurassic palaeoclimate regionalization and evolution of China. Earth Science Frontiers, 24 (1), 107–142. (in Chinese with English abstract) Dera, G., Brigaud, B., Monna, F., Laffont., R., Puceat, E., Deconinck, J. F., Pellenard, P., Joachimski, M. M., & Durlet, C. (2011). Climatic ups and downs in a disturbed Jurassic world. Geology, 39 , 215–218. Dera, G., Pucéat, E., Pellenard, P., Neige, P., Delsate, D., Joachimski, M. M., Reisberg, L., & Martinez, M. (2009). Water mass exchange and variations in seawater temperature in the NW Tethys during the Early Jurassic: Evidence from neodymium and oxygen isotopes of fish teeth and belemnites. Earth and Planetary Science Letters, 286 , 198–207. Dong, H., & Song, Y. G. (2009). Clay mineralogy and its application to paleoenvironmental reconstruction. Marine Geology & Quaternary Geology, 29(6), 119–130 (in Chinese with English abstract). Filatoff, J. (1975). Jurassic palynology of the Perth Basin, Western Australia. Palaeontographica, B, 154 , 1–113. Fu, J. H. (1998). Geological events and their significance in the subdivision and correlation of continental Jurassic in northwest China. Acta Sedimentolocica Sinica, 16 (3), 147–152 (in Chinese with English abstract). He, F. Q., Zhang, S., Jiang, Z. C., Yang, B., Yuan, Q., Gong, X. J., Guo, C. Q., & Cao, J. (2023). Discovery of sporopollen assemblages of Yan’an formation in Yanchi, Ordos Basin, and its paleoclimate significances. Acta Geologica Sinica , 98 (1), 200–213 (in Chinese with English abstract). Huang, L., Zhang, X. J., Li, G. Z., Ji, X. K., Han, X., Wang, Z. Y., Liu, Z. Q., Hou, Z. M., & Ai, Z.H. (2023). Sporopollen assemblage from the Middle Jurassic of the northeastern Ordos Basin, Inner Mongolia, and their paleoclimatic implications. Acta Geologica Sinica , 97 , 1390–1406 (in Chinese with English abstract). Huang, P. (1995). Early-middle Jurassic sporopollen assemblages from Dananhu coalfield of Thuha basin, Xinjiang and their stratigraphical significance. Acta Micropalaeontologica Sinica, 34 , 171–197 (in Chinese with English abstract). Huang, P. (2002). Middle Jurassic sporopollen assemblages from Tangqiang-3 well of Santanghu basin, Xinjiang. Acta Micropalaeontologica Sinica, 19 , 178–192 (in Chinese with English abstract). Huang, P., Li, J. G. (2007). Sporopollen assemblages from the Xishanyao and Toutunhe formation at the Honggou Section of the Manasi River, Xinjiang and their stratigraphical significance. Acta Micropalaeontologica Sinica, 24 , 170–193 (in Chinese with English abstract). Ilyina, V. I. (1986). Subdivision and correlation of the marine and non-marine Jurassic sediments in Siberia based on palynological evidence. Review of Palaeobotany and Palynology, 48 , 357–364. Jiao, Y. Q., Wu, L. Q., Rong H., & Zhang, F. (2021). Coal accumulation regularity of Zhiluo formation and its indication to paleoclimate and uranium metallogenic environment Ordos Basin. Journal of China Coal Society, 46 (7), 2331–2345 (in Chinese with English abstract). Korte, C., Hesselbo, S. P., Ullmann, C. V., Dietl, G., Ruhl, M., Schweigert, G., & Thibault, N. (2015). Jurassic climate mode governed by ocean gateway. Nature Communications, 6 , 1–7. Lenton, T. M., Daines, S. J., & Mills, B. J. W. 2018. COPSE reloaded: An improved model of biogeochemical cycling over Phanerozoic time. Earth-Science Reviews, 178 , 1–28. Li, L. Q., Wang, Y. D., Liu, Z. S., Zhou, N., & Wang, Y. (2016). Late Triassic palaeoclimate and palaeoecosystem variations inferred by palynological record in the northeastern Sichuan Basin, China. Palaontologische Zeitschrift, 90 , 327–348. Li, L. Q., Wang, Y. D., Vajda, V., & Liu, Z. S. (2018). Late Triassic ecosystem variations inferred by palynological records from Hechuan, southern Sichuan Basin, China. Geological Magazine, 155 , 1793–1810. Liu, J. T., Xie, D. H., Liu, Y., Chen, J. G., Jia, G. Q., & Wang, B. (2024). Petroleum exploration history and understandings in Santanghu Basin. Petroleum Geology and Engineering, 38 (4), 1–10 (in Chinese with English abstract). Liu, Y. (2010). The tectomic evolution in the Santanghu Basin and its relationship to oil and gas (pp.1-64). Thesis. China University of Geosciences (Beijing). Liu, Z. S. (1998). Jurassic palynological assemblages from the northern margin in the Tarim Basin of Xinjiang, NW China. Acta Micropalaeontologica Sinica , 15 (2), 144–165 (in Chinese with English abstract). Murru, M., Ferrara, C., Da Pelo, S., & Ibba, A. (2003). The Palaeocene–Middle Eocene deposits of Sardinia (Italy) and their palaeoclimatic significance. Comptes Rendus Geoscience, 335 (2), 227–238. Nordt, L., Breecker, D., & White, J. (2022). Jurassic greenhouse ice-sheet fluctuations sensitive to atmospheric CO 2 dynamics. Nature Geoscience, 15 , 54–59. Pearce, C. R., Cohen, A. S., & Coe, A. L. (2008). Molybdenum isotope evidence for global ocean anoxia coupled with perturbations to the carbon cycle during the Early Jurassic. Geology, 36 , 231–234. Pocock, S. A. J. (1970). Palynology of the Jurassic sediments of Western Canada. Part I. Palaeontographica Abteilung B, 130 (1–6), 12–136. Santos, A.A., Wang, X., Qiang, F.Q., & Diez, J.B. (2018). First palynological data from the Jurassic South Xiangshan Formation (Nanjing area, China). Geobios, 51 , 559–570. Singer, A. (1984). The paleoclimatic interpretation of clay minerals in sediments—A review. Earth-Science Reviews, 21 , 251–293. Song, Z. C., Shang, Y. K., Liu, Z. S., Huang, P., Wang, X., Qian, L. J., Du, B., & Zhang, D. H. (2000). Fossil spores and pollen of China (volume II): The Mesozoic spores and pollen . Science Press (in Chinese). Srivastava, S. K. (1987). Jurassic spore-pollen assemblages from Normandy (France) and Germany. Geobios, 20 , 5–79. Sun, L. X., Zhang, Y., Zhang, T. F., Cheng, Y. H., Li, Y. F., Ma, H. L., Yang, C., Guo, J. C., Lu, C., & Zhou, X.G. (2017). Jurassic sporopollen of Yan’an formation and Zhiluo formation in the northeastern Ordos basin, Inner Mongolia, and its paleoclimatic significance. Earth Science Frontiers , 24 , 32–51 (in Chinese with English abstract). Vakhrameev, V. A. (1991). Jurassic and Cretaceous Floras and Climates of the Earth . Cambridge: Cambridge University Press. Velde, B., 1995. Origin and Mineralogy of Clays (pp. 207-210). Paris: Springer Verlag Berlin and Heidelberg, 207–210. Wang, Y. D., Jiang, D. X., Yang, H. Q., & Sun, F. (1997). Middle Jurassic palynoflora and its palaeoenvironmental implication in Turpan depression, Xinjiang. Acta Sedimentolocica Sinica, 15 , 133–140 (in Chinese with English abstract). Wang, Y. D., Jiang, D. X., Yang, H. Q., & Sun, F. (1998). Middle Jurassic spore-pollen assemblages from Turpan-Shanshan area, Xinjiang. Acta Botanica Sinica , 40 , 969–976 (in Chinese with English abstract). Wang, Y. D., Mosbrugger, V., & Zhang, H. (2005). Early to Middle Jurassic vegetation and climatic events in the Qaidam Basin, northwest China. Palaeogeography, Palaeoclimatology, Palaeoecology, 224 (1–3), 200–216. Xie, W. Q. (2023). Late Middle Jurassic paleoclimate and paleoenvironmental evolution and organic matter accumulation mechanism , Qaidam Basin (pp. 1–152) , Thesis. Central South University (Changsha). Xu, G. Z., Deconinck, J. F., Feng, Q. L., Baudin, F., Pellenard, P., Shen, J., & Bruneau, L. (2017). Clay mineralogical characteristics at the Permian–Triassic Shangsi section and their paleoenvironmental and/or paleoclimatic significance. Palaeogeography, Palaeoclimatology, Palaeoecology, 474 , 152–163. Xu, Z. L., Cheng, Y. H., Ao, C., Zhang, T. F., & Wang, S. Y. (2023). Middle Jurassic palaeoclimate changes within the central Ordos Basin based on palynological records. Palaeobiodiversity and Palaeoenvironments, 103 , 21–42. Yang, B., Xu, G. Z., Hui, G. J., Wei, Y., Zhang, X. Z., Yi, J. J., Sun, S. Y., & Zhang, X. Z. (2024a). Sedimentary Expressions of the Early Jurassic Jenkyns Event in an Inland Lacustrine System in the Yin'gen–Ejinaqi Basin, North China. Acta Geologica Sinica (English Edition), 98 (5): 1359–1375 Yang, B., Zhang, X., Li, W., Sun, S., & Yi, J. (2024b). Palynological Record of the Aalenian–Bajocian Cooling Event from the Santanghu Basin, Northwest China. Diversity, 16 , 369. Zhang, H. Q., Wang, T. D., Yan, C. F., & Yuan, J. Y. (2007). The subdivision and correlation of the Jurassic system of the Minhe Basin. Journal of Stratigraphy, 31 (1), 62–67 (in Chinese with English abstract).. Zhang, K. (1993). The characteristic of plate tectonic evolution and the evaluation of hydrocarbon prospect of Santanghu basin, Xinjiang. Xinjiang Petroleum Geology, 14 , 1–13 (in Chinese with English abstract). Zhang, L. W., Yan, D. T., Yang, S. G., Li, B. Q., Fu, H. J., Wang, G., Yang, X. R., Zhang, W. L., & Zhang, J. F. (2023). Evolution of the Middle Jurassic paleoclimate: Sedimentary evidence from coal-bearing strata in the Santanghu Basin, NW China. Journal Asian Earth Science, 242 , 105495. Zhong, X. C., Zhao, C. B., Yang, S. Z., & Shen, H. (2003). Jurassic System in the North of China Volume Ⅱ Palaeoenvironment and Oil-Gas Source (pp. 1–243) . Beijing: Petroleum Industry Press (in Chinese with English summary). Supplementary Files Supplementaryappendix1.xlsx Supplementaryappendix2.xlsx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5779811","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":409050776,"identity":"ac1ab62b-4977-44d3-8ff2-ace3f7511028","order_by":0,"name":"Bing Yang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA9UlEQVRIiWNgGAWjYJACZgYDBgY29vaDDz4Y2MgRr4Wf50yy4YyCNGMitQCB5IwEM2meD4cTCSo3OH728OuCgjt2G24kJEjbGDAnMLAfProBr5YzeWnWMwyeJW848/CAcY4BWx4DT1raDbxaDuSYGfMYHE42OJ6QkJxjwFPMIMFjhl/L+TdQLQcSDA5bGEgkNhDUciPH+DFQi51kR4JhM4OBAWEtkjfemDHPMDicAApkxh6DBGM2Qn7hO59j/Lngz2F7YFQe//Hjz385fvbDx/BqUTjAwCYBpBMbYCJs+JSDgHwDA/MHIG1PSOEoGAWjYBSMYAAAgtdQiPTEFCYAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0002-8088-2247","institution":"Cores and Samples Center of Natural Resources","correspondingAuthor":true,"prefix":"","firstName":"Bing","middleName":"","lastName":"Yang","suffix":""},{"id":409050777,"identity":"a1fb54e2-7380-41d1-8daa-e58145e877d4","order_by":1,"name":"Di Zhang","email":"","orcid":"https://orcid.org/0009-0005-3305-7956","institution":"Shenyang institute of Geology and Mineral Resources, China Geological Survey","correspondingAuthor":false,"prefix":"","firstName":"Di","middleName":"","lastName":"Zhang","suffix":""},{"id":409050778,"identity":"e1605e53-904d-4835-863d-cf06f8b99fe2","order_by":2,"name":"Xinzhi Zhang","email":"","orcid":"","institution":"Cores and Samples Center of Natural Resources","correspondingAuthor":false,"prefix":"","firstName":"Xinzhi","middleName":"","lastName":"Zhang","suffix":""},{"id":409050779,"identity":"9da18309-d5c3-4805-a9c5-1914019de843","order_by":3,"name":"Siyuan Sun","email":"","orcid":"","institution":"Cores and Samples Center of Natural Resources","correspondingAuthor":false,"prefix":"","firstName":"Siyuan","middleName":"","lastName":"Sun","suffix":""},{"id":409050780,"identity":"2557bae8-4e3f-4ff7-b8ee-4f2c78c65c80","order_by":4,"name":"Weitong Li","email":"","orcid":"","institution":"Cores and Samples Center of Natural Resources","correspondingAuthor":false,"prefix":"","firstName":"Weitong","middleName":"","lastName":"Li","suffix":""}],"badges":[],"createdAt":"2025-01-07 09:22:13","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5779811/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5779811/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":75290079,"identity":"a6ebf49a-2d22-41a6-9590-d58930c78da5","added_by":"auto","created_at":"2025-02-03 05:32:34","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1294296,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea \u003c/strong\u003eGlobal paleogeographic map of Middle Jurassic. \u003cstrong\u003eb\u003c/strong\u003eGeologic map of the Santanghu Basin (modified from the Yang et al., 2024b)\u003c/p\u003e","description":"","filename":"Fig.1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5779811/v1/3c58502ca7f2c84a70aa78db.jpg"},{"id":75290083,"identity":"ee62a14c-dd33-4a47-a9e5-5f88408f4d44","added_by":"auto","created_at":"2025-02-03 05:32:40","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1770150,"visible":true,"origin":"","legend":"\u003cp\u003eVertical distribution of major representatives of spores and pollen through the Xishanyao and Toutunhe formations in the Well TYY1, Santanghu Basin. F. = Formation.\u003c/p\u003e","description":"","filename":"Fig.2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5779811/v1/32bf9e301aaad0b197093b12.jpg"},{"id":75290084,"identity":"f028a52e-d96b-4d31-a625-34888939f6e8","added_by":"auto","created_at":"2025-02-03 05:32:43","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":2401257,"visible":true,"origin":"","legend":"\u003cp\u003eRepresentatives of spores in the Xishanyao and Toutunhe formations of the Santanghu Basin: (\u003cstrong\u003ea,b\u003c/strong\u003e) \u003cem\u003eCyathidites minor \u003c/em\u003eCouper, 1953; (\u003cstrong\u003ec,d\u003c/strong\u003e) \u003cem\u003eCyathidites trilobayus \u003c/em\u003eSan. et Jain, 1964; (\u003cstrong\u003ee\u003c/strong\u003e) \u003cem\u003eCyathidites punctatus \u003c/em\u003eDelcourt, Dettmann et Hughes, 1963; (\u003cstrong\u003ef\u003c/strong\u003e) \u003cem\u003eDeltoidospora hallii \u003c/em\u003eMiner, 1935; (\u003cstrong\u003eg,h\u003c/strong\u003e) \u003cem\u003eDeltoidospora torosus\u003c/em\u003e Zhang, 1984; (\u003cstrong\u003eI\u003c/strong\u003e) \u003cem\u003eDictyophyllidites mortoni \u003c/em\u003e(De Jersey) Playford et Dettmann, 1965; (\u003cstrong\u003ej,k\u003c/strong\u003e) \u003cem\u003eDictyophyllidites harrisii \u003c/em\u003eCouper, 1958; (\u003cstrong\u003el,m\u003c/strong\u003e) \u003cem\u003eConcavisporites toralis \u003c/em\u003e(Leschik, 1955) Nilsson, 1958; (\u003cstrong\u003en\u003c/strong\u003e)\u003cem\u003e Converrucosisporites venitus \u003c/em\u003eBatten, 1973; (\u003cstrong\u003eo\u003c/strong\u003e) \u003cem\u003eUndulatisporites concavus \u003c/em\u003eKedves, 1961; (\u003cstrong\u003ep\u003c/strong\u003e)\u003cem\u003e Punctatisporites weiyuanensis \u003c/em\u003eZhang, 1984; (\u003cstrong\u003eq\u003c/strong\u003e) \u003cem\u003eOsmundacidites elegans \u003c/em\u003e(Verb.) Xu et Zhang, 1980; (\u003cstrong\u003er\u003c/strong\u003e) \u003cem\u003eOsmundacidites wellmanii \u003c/em\u003eCouper, 1953; (\u003cstrong\u003es\u003c/strong\u003e) \u003cem\u003eOsmundacidites parvus \u003c/em\u003eDe Jersey, 1962; (\u003cstrong\u003et\u003c/strong\u003e) \u003cem\u003eKlukisporites\u003c/em\u003e sp.; (\u003cstrong\u003eu\u003c/strong\u003e) \u003cem\u003eLycopodiumsporites subrotundum\u003c/em\u003e (Kara-Mursa) Pocock, 1970; (\u003cstrong\u003ev\u003c/strong\u003e) \u003cem\u003eNeoraistrickia gristhorpensis \u003c/em\u003e(Couper) Tralau, 1968; \u003cstrong\u003e(w)\u003c/strong\u003e \u003cem\u003eNeoraistrickia clavula \u003c/em\u003eXu et Zhang, 1980;\u003cstrong\u003e (x)\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003e \u003c/strong\u003e\u003c/em\u003e\u003cem\u003ePunctatosporites ovatus \u003c/em\u003eZhang, 1978; \u003cstrong\u003e(y)\u003c/strong\u003e \u003cem\u003eCyclogranisporites leopoldi\u003c/em\u003e (Kremp) Potonié et Kremp, 1955. (The scale bar represents 20 µm)\u003c/p\u003e","description":"","filename":"Fig.3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5779811/v1/9e2430e76cf0746b185b982a.jpg"},{"id":75290073,"identity":"c6dbb3ca-20c1-45b5-966d-4bfb3b35b23e","added_by":"auto","created_at":"2025-02-03 05:32:08","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":2466283,"visible":true,"origin":"","legend":"\u003cp\u003eRepresentatives of pollen in the Xishanyao and Toutunhe formations of the Santanghu Basin: (\u003cstrong\u003ea\u003c/strong\u003e) \u003cem\u003eCycadopites subgranulosus \u003c/em\u003e(Couper) Bharadwaj et Singh, 1964; (\u003cstrong\u003eb,c\u003c/strong\u003e) \u003cem\u003eCycadopites granulatus \u003c/em\u003e(De Jersey) De Jersey, 1964; (\u003cstrong\u003ed\u003c/strong\u003e) \u003cem\u003eMonosulcites minimus \u003c/em\u003eCookson, 1947; (\u003cstrong\u003ee\u003c/strong\u003e) \u003cem\u003eChasmatosporites triangularis \u003c/em\u003eLi, Duan et Du, 1982; (\u003cstrong\u003ef\u003c/strong\u003e) \u003cem\u003eCerebropollenites carlylensis\u003c/em\u003e Pocock, 1970; (\u003cstrong\u003eg\u003c/strong\u003e) \u003cem\u003eCallialasporites dampieri\u003c/em\u003e (Balme) Sukh Dev, 1961; (\u003cstrong\u003eh\u003c/strong\u003e) \u003cem\u003eErlianpollis minisculus \u003c/em\u003eZhao, 1987; (\u003cstrong\u003ei\u003c/strong\u003e) \u003cem\u003eConcentrisporites hallei \u003c/em\u003e(Nilsson) Wall, 1965; (\u003cstrong\u003ej\u003c/strong\u003e)\u003cem\u003e Inaperturopollenites dubius\u003c/em\u003e (Potonié et Venitz) Thomson et Pflug, 1953; (\u003cstrong\u003ek\u003c/strong\u003e) \u003cem\u003eClassopollis qiyangensis \u003c/em\u003eShang, 1981; (\u003cstrong\u003el,k\u003c/strong\u003e)\u003cem\u003e Classopollis annulatus\u003c/em\u003e(Verbitzkaja) Li, 1974; (\u003cstrong\u003en\u003c/strong\u003e) \u003cem\u003eAlisporites parvus \u003c/em\u003eDe Jersey, 1962; (\u003cstrong\u003eo\u003c/strong\u003e) \u003cem\u003eAlisporites rotundus \u003c/em\u003eRouse, 1959; (\u003cstrong\u003ep\u003c/strong\u003e) \u003cem\u003ePodocarpidites multisimus \u003c/em\u003e(Bolkh.) Pocock, 1970; (\u003cstrong\u003eq\u003c/strong\u003e) \u003cem\u003ePodocarpidites transversus\u003c/em\u003e Qu et Wang, 1986; (\u003cstrong\u003er\u003c/strong\u003e) \u003cem\u003eQuadraeculina anellaeformis \u003c/em\u003eMaljavkina, 1949; (\u003cstrong\u003es\u003c/strong\u003e) \u003cem\u003eQuadraeculina limbate \u003c/em\u003eMaljavkina, 1949; (\u003cstrong\u003et\u003c/strong\u003e) \u003cem\u003ePiceaepollenites singularae \u003c/em\u003e(Bolkh.) Zhang, 1986; (\u003cstrong\u003eu\u003c/strong\u003e) \u003cem\u003ePiceites expositus \u003c/em\u003eBolkhovitina, 1956; (\u003cstrong\u003ev\u003c/strong\u003e) \u003cem\u003ePseudopicea variabiliformis \u003c/em\u003e(Mal.) Bolkhovitina, 1956; (\u003cstrong\u003ew\u003c/strong\u003e) \u003cem\u003ePiceites flavidus \u003c/em\u003eBolkhovitina, 1956; (\u003cstrong\u003ex\u003c/strong\u003e) \u003cem\u003ePinuspollenites insignis \u003c/em\u003e(Naumova) Pu et Wu, 1982; (\u003cstrong\u003ey\u003c/strong\u003e) \u003cem\u003ePinuspollenites divulgatus \u003c/em\u003e(Bolkh.) Qu, 1980. (The scale bar represents 20 µm).\u003c/p\u003e","description":"","filename":"Fig.4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5779811/v1/5aaab029839a6ae15edd392d.jpg"},{"id":75290085,"identity":"27b10e39-e51e-457f-bdbc-8208b04be9c0","added_by":"auto","created_at":"2025-02-03 05:33:00","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1068236,"visible":true,"origin":"","legend":"\u003cp\u003eVariations of major vegetation groups of the Xishanyao and Toutunhe formations in the Santanghu Basin, China\u003c/p\u003e","description":"","filename":"Fig.5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5779811/v1/44ece2ecb2979ce515c2c52e.jpg"},{"id":75290075,"identity":"e19d92a0-c36a-48a9-bf96-b94d4643f5ae","added_by":"auto","created_at":"2025-02-03 05:32:20","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1641079,"visible":true,"origin":"","legend":"\u003cp\u003eThe sketch map of paleoenvironmental and paleovegetation evolution in the Middle Jurassic Santanghu Basin.\u003c/p\u003e","description":"","filename":"Fig.6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5779811/v1/344a0233933bf1a8f7f1dbac.jpg"},{"id":75290074,"identity":"06aad302-d4e8-4457-8fea-39fe2b0ad528","added_by":"auto","created_at":"2025-02-03 05:32:18","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":987239,"visible":true,"origin":"","legend":"\u003cp\u003eRelative abundances of the SEGs of the Xishanyao and Toutunhe formations in the Santanghu Basin, China\u003c/p\u003e","description":"","filename":"Fig.7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5779811/v1/3b3aaa02cee6a888d5d8843d.jpg"},{"id":75290072,"identity":"c7d13d6e-1c7f-45b5-bae7-d49d157d92e9","added_by":"auto","created_at":"2025-02-03 05:31:51","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":1029805,"visible":true,"origin":"","legend":"\u003cp\u003eSEG curves and clay mineral composition of the Xishanyao and Toutunhe formations in the Santanghu Basin, China\u003c/p\u003e","description":"","filename":"Fig.8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5779811/v1/3049e636395942724f9ea0aa.jpg"},{"id":79194655,"identity":"803ea51b-e80f-4d33-a04f-7fdc5a3fd43e","added_by":"auto","created_at":"2025-03-25 13:25:29","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":23779676,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5779811/v1/6a7a1e76-ba0f-4c82-876e-ef46f10b69c6.pdf"},{"id":75290077,"identity":"4f9d04ea-b1b7-483c-ae7d-f5bd706827f7","added_by":"auto","created_at":"2025-02-03 05:32:24","extension":"xlsx","order_by":12,"title":"","display":"","copyAsset":false,"role":"supplement","size":30800,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementaryappendix1.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-5779811/v1/87020cd2faad1c2850e990b6.xlsx"},{"id":75290076,"identity":"6397cd2a-030b-42e5-a113-d35856a27562","added_by":"auto","created_at":"2025-02-03 05:32:24","extension":"xlsx","order_by":13,"title":"","display":"","copyAsset":false,"role":"supplement","size":11788,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementaryappendix2.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-5779811/v1/20e63e458d6f40d045b1ddd0.xlsx"}],"financialInterests":"","formattedTitle":"Paleoclimate Transition Recorded by Palynological and Clay Mineral Evidence in the Santanghu Basin during the Middle Jurassic","fulltext":[{"header":"0 Introduction ","content":"\u003cp\u003eThe Jurassic period is recognized as a classic greenhouse climate phase in Earth\u0026rsquo;s geological history, with atmospheric CO\u003csub\u003e2\u003c/sub\u003e concentrations and sea surface temperatures significantly higher than those of the present day (Berner 1994; Berner and Kothavala 2001; Lenton et al. 2018). However, the Jurassic climate was not uniformly stable; it experienced several pronounced fluctuations (Pearce et al. 2008; Dera et al. 2011; Korte et al. 2015; Nordt et al. 2022). Extensive marine oxygen isotope studies reveal substantial variability in seawater surface temperatures across different regions and time periods (Dera et al. 2009 2012; Alberti et al. 2020). By integrating global data, Dera et al. (2011) constructed a Jurassic global paleoseawater temperature curve, indicating frequent fluctuations. After a high-temperature phase in the Early Jurassic, global seawater temperatures reached a low during the Pliensbachian, surged to a peak in the Toarcian, and then declined through the early Middle Jurassic, continuing until the Bathonian. Temperatures rose again in the Callovian and peaked during the Late Jurassic Tithonian.\u003c/p\u003e\n\u003cp\u003eDue to the uneven global distribution of water resources, trends in aridity and humidity varied regionally, requiring localized studies. Zhong et al. (2003) reconstructed the Jurassic paleoclimate of northern China using palynological, paleobotanical, and mineralogical data, identifying two long-term aridification events: one during the Early Jurassic Toarcian and another from the Middle Jurassic Bathonian to the end of the Late Jurassic. The Early Jurassic Toarcian aridification event is believed to be a consequence of the Toarcian Oceanic Anoxic Event (T-OAE), characterized by a significant negative carbon isotope excursion, termination of coal formation, plant decline, and increased temperatures leading to arid conditions (Deng et al. 2012). This event has been documented in multiple basins across northern China (Zhang et al. 1998; Wang et al. 2005; Deng et al. 2012; Yang et al. 2024a).\u003c/p\u003e\n\u003cp\u003eIn contrast, the aridification event from the Middle Jurassic Bathonian to the end of the Late Jurassic has received comparatively less attention, and its impact on terrestrial ecosystems remains poorly understood. This study employs palynological and clay mineral evidence from the Middle Jurassic Xishanyao and Toutunhe formations in the Santanghu Basin to elucidate the effects of this climatic transition on vegetation patterns and ecosystem dynamics in the region.\u003c/p\u003e"},{"header":"1 Geological settings","content":"\u003cp\u003eThe Santanghu Basin is located at the junction of the Altay Fold Belt and the Northern Tianshan Fold Belt in northeastern Xinjiang. It is a narrow, irregular intermontane basin, bordered by the Junggar Basin to the west and the Turpan-Hami Basin to the south. The basin extends approximately 500 km east to west and 40\u0026ndash;70 km north to south, covering a total area of 23,000 km\u0026sup2;. Following multiple tectonic events, including the Hercynian, Indosinian, Yanshanian, and Himalayan movements (Liu et al. 2024), the basin evolved into three secondary structural units: the northern uplift belt, the central depression belt, and the southern thrust belt (Zhang et al. 2023).\u003c/p\u003e\n\u003cp\u003eDuring the Early and Middle Jurassic, the basin experienced a relatively stable phase, with the regional stress field characterized by weak NW-oriented compressive forces and minimal tectonic activity. This stability facilitated the deposition of the Lower Jurassic Badaowan and Sangonghe formations, as well as the Middle Jurassic Xishanyao and Toutunhe formations. In the Late Jurassic, influenced by the Yanshanian Orogeny, the regional stress field exhibited stronger NW-oriented compression, causing slight uplifts in local areas and leading to the deposition of the Upper Jurassic Qigu and Kalazha formations (Zhang et al. 1993; Liu 2010).\u003c/p\u003e\n\u003cp\u003eWell TYY1 is located 12 km northwest of Santanghu Town in Barkol County, Hami Prefecture, Xinjiang, within the southern thrust belt (Fig. 1). The stratigraphic sequence encountered in this well, from bottom to top, includes the Lower Jurassic Sangonghe Formation, and the Middle Jurassic Xishanyao and Toutunhe formations. The Xishanyao Formation, occurring between 611.5 m and 377.1 m depth, consists primarily of gray-black mudstone, gray-white sandstone, and interbedded coal seams, representing deposits from braided river delta and lacustrine systems. The Toutunhe Formation, from 377.1 m to the surface, comprises brownish siltstone, mudstone, and gray-green conglomerate and sandstone, indicative of a fluvial depositional environment.\u003c/p\u003e"},{"header":"2 Materials and methods","content":"\u003cp\u003eIn this study, thirteen palynological samples were collected from the upper part of the Xishanyao Formation (sample nos. A7, S18, S17, S16, S15, S14 and S13) and the lower part of the Toutunhe Formation (sample nos. A1, A2, A3, A4, A5, and A6). Each 50 g sample was crushed into fragments smaller than 1.0 mm in diameter and subjected to the following chemical treatments: hydrochloric acid (HCl, 10%) for 12 hours, hydrofluoric acid (HF, 40%) for 2 days, and hydrochloric acid (HCl, 36%) for an additional 12 hours. A heavy liquid mixture of zinc chloride (ZnCl) and potassium iodide (KI) with a density of 2.2 g/cm\u0026sup3; was used to extract the palynomorphs.\u003c/p\u003e\n\u003cp\u003eSpore-pollen analysis was conducted at the Research Center of Paleontlogy and Stratigraphy, Jilin University. The prepared samples, slides, and stubs, all numbered accordingly, are stored at the Cores and Samples Centre of Natural Resources in Langfang, China. Each sample contained over 200 sporopollen grains for statistical analysis. The relative abundances of sporopollen fossils were calculated using Tilia software (version 3.0.3). assemblages were identified using the CONISS clustering method within Tilia in ascending stratigraphic order. Further details of the samples are provided in the Supplementary Material.\u003c/p\u003e\n\u003cp\u003eThe Sporomorph EcoGroup (SEG) model, established by Abbink et al. (2004), is founded on the principle that sporopollen assemblages reflect the plant communities from which they originated. This model posits that during various geological periods, specialized paleoecological communities existed, wherein plants within these communities shared similar ecological characteristics. The spores and pollen produced by these plants coexisted within the same ancient communities, and the dispersed assemblages of these terrestrial plants are categorized as SEGs. The SEG model facilitates detailed paleoecological interpretations of quantitative sporopollen data (Abbink et al. 2004; Li et al. 2016).\u003c/p\u003e\n\u003cp\u003eAbbink et al. (2004) classified non-marine Jurassic-Cretaceous sporopollen floras into six SEG types: upland SEG, lowland SEG, river SEG, pioneer SEG, coastal SEG, and tidally influenced SEG. Each SEG type represents distinct ecological settings and associated plant communities (Abbink et al. 2004; Li et al. 2016; Li et al. 2018).\u003c/p\u003e\n\u003cp\u003eFor the interval between 480.0 m and 215.0 m in Well TYY1, 21 samples were analyzed for clay mineralogy using X-ray diffraction (XRD). Initially, 2-3 grams of rock powder (finer than 200 mesh) were used to prepare non-oriented mounts by placing the powder in the recess of a glass slide. Additionally, 20-30 grams of powder were treated with dilute hydrochloric acid (HCl) to remove carbonates. Once the solution became weakly acidic, deionized water was added, and the mixture was allowed to settle. The supernatant was carefully decanted, and this process was repeated with fresh deionized water until an optimal mineral suspension was achieved.\u003c/p\u003e\n\u003cp\u003eThe turbid liquid was then drawn off, and the clay minerals were thoroughly mixed and uniformly spread to create oriented mounts. After initial testing, the oriented mounts were saturated with ethylene glycol for over 8 hours to produce ethylene glycol-saturated mounts. They were subsequently heated at 490\u0026deg;C for 2 hours to create high-temperature heated mounts, both of which were analyzed.\u003c/p\u003e\n\u003cp\u003eAll clay mineral analyses were performed at the State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences (Wuhan), using a PANalytical X\u0026rsquo;Pert Pro X-ray diffractometer. The experimental procedures followed those outlined by Xu et al. (2007).\u003c/p\u003e"},{"header":"3 Results","content":"\u003cp\u003e3.1 Characteristics of Palynological Assemblages\u003c/p\u003e\n\u003cp\u003eBased on CONISS analysis using Tilia software on 26 dominant and representative spore-pollen genera, the thirteen palynological samples were divided into two spore-pollen assemblages (Fig. 2).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eCyathidites-Deltoidospora-Osmundacidites-Cycadopites\u0026nbsp;\u003c/em\u003e(CDOC) assemblage: This assemblage includes samples from the Xishanyao Formation (A7, S18, S17, S16, S15, S14, S13). Pteridophyte spores dominate over gymnosperm pollen, ranging from 45.5% to 84.8% with an average of 62.0%. Gymnosperm pollen ranges from 15.2% to 53.7%, averaging 37.7%. Bryophyte spores are sporadically present, with an average of only 0.1%.\u003c/p\u003e\n\u003cp\u003eAmong the peridophyte, the dominant taxa are \u003cem\u003eCyathidites\u003c/em\u003e and \u003cem\u003eDeltoidospora\u0026nbsp;\u003c/em\u003e(Dicksoniaceae) and \u003cem\u003eOsmundacidites\u003c/em\u003e (Osmundaceae), with \u003cem\u003eCyathidites minor\u003c/em\u003e Couper, 1953\u003cem\u003e\u0026nbsp;\u003c/em\u003ebeing notably more abundant than other species. \u003cem\u003eConcavisporites\u0026nbsp;\u003c/em\u003eis also well-represented. In the gymnosperms, colpate pollen such as \u003cem\u003eCycadopites\u003c/em\u003e and \u003cem\u003eChasmatosporites\u003c/em\u003e is predominant. The content of bisaccate pollen is relatively low, ranging from 1.9% to 16.7% (average 10.2%) and shows a decreasing trend upward. Among the bisaccate taxa, \u003cem\u003eQuadraeculina\u003c/em\u003e is the most common, while other genera are rare. Araucariaceae pollen (\u003cem\u003eAraucariacites\u003c/em\u003e and \u003cem\u003eCallialasporites\u003c/em\u003e) is present but with an average content of less than 2.0%. Bryophyte spores, including \u003cem\u003eAlsophilidites\u003c/em\u003e, \u003cem\u003eAnnulispora\u003c/em\u003e, and \u003cem\u003eSphagnumsporites\u003c/em\u003e, are observed sporadically. These characteristics are consistent with the CDOC assemblage established by Yang et al. (2024b), and therefore, these seven samples are assigned to the CDOC palynological assemblage.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eCyathidites-Classopollis-Quadraeculina\u0026nbsp;\u003c/em\u003e(CCQ) assemblage: This assemblage includes samples from the lower part of the Toutunhe Formation (A1, A2, A3, A4, A5, A6). A total of 147 species of 40 genera and of spores and pollen were identified, including 30 undetermined species. Gymnosperm pollen dominates, ranging from 68.7% to 76.3% with an average of 72.2% (94 species of 23 genera). Pteridophyte spores are less abundant, ranging from 23.2% to 30.8% with an average of 27.3% (52 species of 16 genera). Bryophyte spores are scarce, comprising only 1 species, with an average content of less than 0.2%.\u003c/p\u003e\n\u003cp\u003eIn the pteridophyte spores, \u003cem\u003eCyathidites\u003c/em\u003e (Dicksoniaceae) and \u003cem\u003eOsmundacidites\u0026nbsp;\u003c/em\u003e(Osmundaceae) are dominant, with average contents of 9.0% and 6.7%, respectively. \u003cem\u003eCyathidites minor\u003c/em\u003e is the most abundant, ranging from 3.4% to 8.4% (average 4.9%). \u003cem\u003eDeltoidospora\u003c/em\u003e has an average content of less than 3.0%. Other pteridophyte spores, such as \u003cem\u003eLycopodiumsporites\u003c/em\u003e, \u003cem\u003eNeoraistrickia\u003c/em\u003e, \u003cem\u003eAuritulinasporites\u003c/em\u003e, \u003cem\u003eAlsophilidites\u003c/em\u003e, \u003cem\u003eLaevigatosporites\u003c/em\u003e, \u003cem\u003eCalamospora\u003c/em\u003e, \u003cem\u003eKlukisporites\u003c/em\u003e, \u003cem\u003eConverrucosisporites\u003c/em\u003e, \u003cem\u003eCyclogranisporites\u003c/em\u003e, \u003cem\u003eDictyophyllidites\u003c/em\u003e, \u003cem\u003eConcavisporites\u003c/em\u003e, and \u003cem\u003eUndulatisporites\u003c/em\u003e, each have contents below 2.0%. Bryophytes include \u003cem\u003eSphagnumsporites\u003c/em\u003e, \u003cem\u003eAnnulispora\u003c/em\u003e, and \u003cem\u003eAlsophilidites\u0026nbsp;\u003c/em\u003e(Fig. 3).\u003c/p\u003e\n\u003cp\u003eIn the gymnosperm, \u003cem\u003eClassopollis\u0026nbsp;\u003c/em\u003e(monosulcate pollen) is highly abundant, ranging from 11.4% to 21.5% (average 17.1%), represented by species such as \u003cem\u003eClassopollis annulatus\u003c/em\u003e (Verbitzkaja) Li, 1974, \u003cem\u003eClassopollis qiyangensis\u0026nbsp;\u003c/em\u003eShang, 1981, and \u003cem\u003eClassopollis classoides\u003c/em\u003e Pflug,1953 emend. Pocock et Jansonius, 1961. \u003cem\u003eCycadopites\u0026nbsp;\u003c/em\u003e(monocolpate pollen) is the second most abundant, ranging from 7.2% to 19.1% (average 10.6%), with species including \u003cem\u003eCycadopites adjectus\u0026nbsp;\u003c/em\u003e(De Jersey) De Jersey, 1964, \u003cem\u003eCycadopites altilis\u003c/em\u003e Zhang, 1984, \u003cem\u003eCycadopites clavatus\u003c/em\u003e Lei, 1986, \u003cem\u003eCycadopites formosus\u003c/em\u003e Singh, 1964, \u003cem\u003eCycadopites fragilis\u003c/em\u003e Singh,1964, \u003cem\u003eCycadopites granulatus\u003c/em\u003e (De Jersey) De Jersey, 1964, \u003cem\u003eCycadopites pyriformis\u0026nbsp;\u003c/em\u003e(Nisson) Zhang, 1984, \u003cem\u003eCycadopites reticulate\u0026nbsp;\u003c/em\u003e(Nisson) Arjang, 1975, \u003cem\u003eCycadopites striatus\u0026nbsp;\u003c/em\u003eOuyang et Norris, 1988,\u003cem\u003e\u0026nbsp;Cycadopites subgranulosu\u003c/em\u003es (Couper) Bharadwaj et Singh, 1964, and \u003cem\u003eCycadopites typicus\u0026nbsp;\u003c/em\u003e(Mal.) Pocock, 1970.\u003c/p\u003e\n\u003cp\u003eBisaccate pollen content is higher in this assemblage compared to the Xishanyao Formation, ranging from 28.1% to 34.4% (average 30.7%). Dominant bisaccate genera include \u003cem\u003eQuadraeculina\u003c/em\u003e, \u003cem\u003ePinuspollenites\u003c/em\u003e, \u003cem\u003ePiceaepollenites\u003c/em\u003e, \u003cem\u003ePiceites\u003c/em\u003e, \u003cem\u003eErlianpollis\u003c/em\u003e, \u003cem\u003ePodocarpidites\u003c/em\u003e, \u003cem\u003eAlisporites\u003c/em\u003e, \u003cem\u003eCedripites\u003c/em\u003e, \u003cem\u003eProtopinus\u003c/em\u003e, \u003cem\u003ePseudopicea\u003c/em\u003e, and \u003cem\u003eProtoconiferus\u003c/em\u003e, with \u003cem\u003eQuadraeculina\u003c/em\u003e being the most common (6.9%\u0026ndash;8.8%, average 8.0%). Non-saccate gymnosperm pollen includes \u003cem\u003ePsophosphaera\u003c/em\u003e, \u003cem\u003eAraucariacites\u003c/em\u003e, \u003cem\u003eInaperturopollenites\u003c/em\u003e, and \u003cem\u003eGranasporites\u003c/em\u003e, each with an average content of less than 3.0%. Saccizonate genera such as \u003cem\u003eCallialasporites\u003c/em\u003e and \u003cem\u003eCerebropollenites\u003c/em\u003e are also present, each with an average content below 2.0%. Notable species include \u003cem\u003eCallialasporites segmentatus\u0026nbsp;\u003c/em\u003e(Balme) Sukh Dev, 1961,\u003cem\u003e\u0026nbsp;Callialasporites dampieri\u0026nbsp;\u003c/em\u003e(Balme) Sukh Dev, 1961, \u003cem\u003eCerebropollenites carlylensis\u0026nbsp;\u003c/em\u003ePocock, 1970, and \u003cem\u003eCerebropollenites macroverrucosus\u003c/em\u003e (Thierg.) Pocock, 1970 (Fig. 4).\u003c/p\u003e\n\u003cp\u003e3.2 Characteristics of Clay Minerals\u003c/p\u003e\n\u003cp\u003eIn the TYY1 well, the upper part of the Xishanyao Formation (480.0 m - 377.1 m) and the lower part of the Toutunhe Formation (377.1 m - 215.0 m) are primarily composed of clay minerals, including illite, kaolinite, chlorite, smectite, and illite/smectite mixed layers. Notably, the high content of illite and kaolinite is characteristic of this section, with both minerals present in comparable amounts, generally exhibiting an inverse relationship in their abundance. Thus, the clay minerals can be classified as an illite-kaolinite assemblage.\u003c/p\u003e\n\u003cp\u003eDuring the CDOC assemblage period (480.0 m - 377.1 m), the average content of kaolinite was 38.9%, remaining relatively stable, while the average content of illite was 35.1%. In contrast, during the CCQ assemblage period (377.1 m - 215.0 m), the average content of kaolinite decreased to 22.3%, whereas the average content of illite increased to 43.7%. The contents of chlorite, smectite, and illite/smectite mixed layers were relatively low and showed no distinct distribution pattern. Specifically, the average content of chlorite was 15.4%, smectite averaged 7.3%, and illite/smectite mixed layers averaged 6.7%.\u003c/p\u003e"},{"header":"4 Discussion","content":"\u003cp\u003e4.1 Geological Time\u003c/p\u003e\n\u003cp\u003ePrevious studies indicate that the CDOC assemblage of the Xishanyao Formation in the TYY1 well dates back to the Aalenian-Bajocian stage (Yang et al. 2024a). The majority of the spores in the CCQ assemblage of the Toutunhe Formation are derived from the Xishanyao Formation, with the continued abundance of \u003cem\u003eCyathidites minor\u0026nbsp;\u003c/em\u003eand \u003cem\u003eCycadopites\u003c/em\u003e indicating the palynological characteristics of the Middle Jurassic (Wang et al. 1998; He et al. 2024). A notable difference is that, compared to the CDOC assemblage, the CCQ assemblage shows a significant increase in the abundance of bisaccate pollen, reflecting an evolutionary trend consistent with the early to late Jurassic evolutionary patterns observed in other regions of northwestern China (Wang et al. 1998; Huang 2002; Huang and Li 2007; Sun et al. 2017).\u003c/p\u003e\n\u003cp\u003eAdditionally, the CCQ assemblage features the new appearance of \u003cem\u003eKlukisporites pseudoreticulatus\u0026nbsp;\u003c/em\u003eCouper, 1958\u003cem\u003e\u0026nbsp;\u003c/em\u003eand \u003cem\u003eCallialasporites dampieri\u0026nbsp;\u003c/em\u003e(Balme) Sukh Dev\u003cem\u003e,\u0026nbsp;\u003c/em\u003e1961. \u003cem\u003eKlukisporites pseudoreticulatus\u003c/em\u003e Couper, 1958 was first reported from the Lower Cretaceous in the UK (Couper 1958) and has since been commonly found in the Middle Jurassic of the former Soviet Union, Canada, France, and Germany (Ilyina 1986; Pocock 1970; Srivastava 1987). This species is also widely distributed in some Mesozoic strata across various regions of China (Huang 1995; Wang et al. 1998; Huang and Li 2007). \u003cem\u003eCallialasporites dampieri\u003c/em\u003e (Balme) Sukh Dev\u003cem\u003e,\u0026nbsp;\u003c/em\u003e1961\u0026nbsp;is prevalent in the Middle to Late Jurassic and is characteristic of the Bathonian to Callovian stages in Germany, France, and other parts of Europe (Srivastava 1987). It is also one of the zonal fossils from the Middle Jurassic Bathonian to Callovian in Australia (Filatoff 1975).\u003c/p\u003e\n\u003cp\u003eThe genus \u003cem\u003eClassopollis\u003c/em\u003e shows a distinct distribution pattern in the Jurassic of northwestern China, Siberia, and Central Asia, with two peak periods. The first peak occurs during the Early Jurassic Toarcian stage, while the second peak begins in the Middle Jurassic Bathonian stage and continues until the Late Jurassic (Vakhrameev 1991; Wang et al. 1998). Compared to the first peak, the second peak has a broader impact in Northwest China. For instance, in the upper part of the Shimen Gou Formation of the Jurassic in the Qaidam Basin, the content of\u003cem\u003e\u0026nbsp;Classopollis\u003c/em\u003e sharply increases, with an average of 19.8% (Xie 2023). In the Jurassic Toutunhe Formation at the Honggou section of the Manas River in Xinjiang, \u003cem\u003eClassopollis\u003c/em\u003e content reaches 11.7% (Huang and Li 2007). In the Kuqa Basin of Tarim, \u003cem\u003eClassopollis\u0026nbsp;\u003c/em\u003econtent can reach 27.6% in the Qiaokemak Formation (Huang and Li 2007), while in the Shanjianfang Formation of the Turpan-Hami Basin, it reaches 31.5% (Wang et al. 1997).\u003c/p\u003e\n\u003cp\u003eIn the current study, the \u003cem\u003eClassopollis\u003c/em\u003e content in the CCQ assemblage of the Toutunhe Formation shows a marked increase, with an average content of 17.1%, aligning with the palynological characteristics of \u003cem\u003eClassopollis\u003c/em\u003e during the Bathonian stage. This suggests that the geological age of the CCQ assemblage is later than the Bajocian stage. Furthermore, the last occurrence of \u003cem\u003eQuadraeculina anellaeformis\u003c/em\u003e is in the Bathonian stage (Santos et al. 2018), which also constrains the geological age of this assemblage to be earlier than the Callovian stage. Based on the evidence presented, the age of the CCQ palynological assemblage can be constrained to the Middle Jurassic Bathonian stage.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e4.2 Reconstruction of Paleovegetation\u003c/p\u003e\n\u003cp\u003eThe parent plants of spore and pollen fossils can be used to reconstruct paleovegetation, as well as to infer paleoclimate and paleoenvironmental conditions (Li et al. 2016; Yang et al. 2024a 2024b). The plant groups in the CDOC and CCQ assemblages primarily include conifers, ferns, cycads/ginkgophytes, lycopsids, bryophytes, and horsetails (Fig. 5). The characteristics of each assemblage are as follows:\u003c/p\u003e\n\u003cp\u003eCDOC assemblage: In this assemblage, ferns dominate, comprising 37.5% to 81.0% of the total, with an average of 56.8%. This group is predominantly represented by the families Cyatheaceae (\u003cem\u003eCyathidites\u003c/em\u003e and \u003cem\u003eDeltoidospora\u003c/em\u003e) and Osmundaceae (\u003cem\u003eOsmundacidites\u003c/em\u003e), along with a small number of taxa from the Dipteridaceae/Matoniaceae families, such as \u003cem\u003eDictyophyllidites\u003c/em\u003e and \u003cem\u003eConcavisporites\u003c/em\u003e. Cycads/ginkgophytes occupy a secondary position in this assemblage, with an average content of only 19.8%, represented by genera such as \u003cem\u003eCycadopites\u003c/em\u003e, \u003cem\u003eChasmatosporites\u003c/em\u003e, and \u003cem\u003eMonosulcites\u003c/em\u003e. Conifers are present in even lower abundance than cycads/ginkgophytes, averaging just 15.4%. This group primarily consists of Pinaceae, with notable genera including \u003cem\u003ePiceites\u003c/em\u003e, \u003cem\u003eErlianpollis\u003c/em\u003e, and \u003cem\u003ePinuspollenites\u003c/em\u003e, along with some representatives from the seed fern genera \u003cem\u003eAlisporites\u003c/em\u003e. Lycopsids are relatively rare, averaging only 5.3%, represented by genera such as \u003cem\u003eLycopodiumsporites\u003c/em\u003e,\u003cem\u003e\u0026nbsp;Neoraistrickia\u003c/em\u003e, \u003cem\u003ePunctatisporites\u003c/em\u003e, and \u003cem\u003eAratrisporites\u003c/em\u003e. Bryophytes and horsetails are present in minimal amounts, with a total content of about 1.0%.\u003c/p\u003e\n\u003cp\u003eCCQ assemblage: The main distinction of this assemblage from the CDOC assemblage is that conifers have replaced ferns as the dominant group, averaging 56.6%. This group includes similar contributions from Pinaceae, Araucariaceae, Cheirolepidiaceae, and Podocarpaceae. Additionally, there are minor occurrences of Taxodiaceae and seed ferns. Ferns have become a secondary component in this assemblage, averaging only 23.8%, primarily represented by Cyatheaceae and Osmundaceae. The content of cycads/ginkgophytes is slightly lower than in the CDOC assemblage, averaging just 14.8%, with genera such as \u003cem\u003eCycadopites\u003c/em\u003e, \u003cem\u003eChasmatosporites\u003c/em\u003e, and \u003cem\u003eMonosulcites\u003c/em\u003e present. The abundance of lycopsids has significantly decreased in this assemblage, with an average of only 2.7%. Bryophytes and horsetails remain minimal, with a total content of approximately 1.0%.\u003c/p\u003e\n\u003cp\u003eThe evolution of the vegetation groups in the CDOC and CCQ assemblages indicates that the plant ecosystem of the Santanghu Basin transitioned from a dominant ground cover of ferns during the Early to Middle Jurassic (Aalenian-Bajocian) to a canopy dominated by conifers in the late Middle Jurassic (Bathonian). During this transition, cycads/ginkgophytes shifted to a subordinate role, while the ground cover of ferns experienced severe degradation (Fig. 6).\u003c/p\u003e\n\u003cp\u003e4.3 Evolution of the Paleoclimate\u003c/p\u003e\n\u003cp\u003e4.3.1 Sporomorph EcoGroup Model\u003c/p\u003e\n\u003cp\u003eBy analyzing the palynological samples from the upper part of the Xishanyao Formation and the lower part of the Toutunhe Formation in the TYY1 well of the Santanghu Basin, we conducted a percentage composition analysis of the SEG. This analysis revealed the relative abundance variations of different SEGs within the Jurassic palynological flora of the basin, as well as the curves representing the content of wet-type molecules, dry-type molecules, wetter/drier ratios, and warmer/cooler ratios of the lowland SEG. A total of five SEGs were identified in the spore assemblages of the Xishanyao and Toutunhe formations: Lowland SEG, Upland SEG, River SEG, Pioneer SEG, and Coastal SEG. Among these, the Lowland SEG and Upland SEG are dominant, with comparable abundances that exhibit an inverse relationship. The River SEG is relatively scarce, while the Pioneer SEG and Coastal SEG are present in minimal amounts (Fig. 7). The characteristics of each assemblage are as follows:\u003c/p\u003e\n\u003cp\u003eCDOC assemblage: The Lowland SEG molecules dominate this assemblage, with a content ranging from 66.2% to 95.7% and an average of approximately 81.7%. There is a declining trend near the boundary with the CCQ assemblage. The Upland SEG molecules are present in lower quantities, ranging from 1.9% to 17.5%, with an average of about 11.0%. This group reaches its minimum value in the upper part of the assemblage and shows an increasing trend near the boundary with the CCQ assemblage. The wetter/drier ratio of Lowland SEG molecules is relatively high, ranging from 1.1 to 6.2, with a declining trend near the boundary with the CCQ assemblage. The warmer/cooler ratio of Lowland SEG molecules is also relatively high, ranging from 5.25 to 26.59. These findings indicate that the CDOC assemblage generally reflects a hot and humid climate environment; however, over time, it gradually transitions towards a more arid climate.\u003c/p\u003e\n\u003cp\u003eCCQ assemblage: In this assemblage, the Lowland SEG molecules continue to dominate, but their content has significantly decreased compared to the CDOC assemblage, ranging from 58.2% to 64.5%, with an average value of 61.2%. Conversely, the Upland SEG molecules have increased substantially, with a content range of 30.0% to 35.9% and an average of 32.6%, demonstrating stability. The wetter/drier ratio of Lowland SEG molecules has sharply decreased, ranging from 0.52 to 0.97. Given that the content of wet-type molecules in the Lowland SEG can reach 25%, it can be classified as a semi-arid environment. The warmer/cooler ratio of Lowland SEG molecules remains relatively high, ranging from 8.70 to 21.43, with fluctuations that show overall consistency with the CDOC assemblage.\u003c/p\u003e\n\u003cp\u003eFrom this evidence, it can be concluded that the Santanghu Basin experienced a transition from a humid climate to a semi-arid climate from the Early to Late Middle Jurassic (Aalenian-Bajocian to Bathonian), with relatively stable temperatures, consistently indicating a hot climate.\u003c/p\u003e\n\u003cp\u003e4.3.2 Clay Mineral Evidence\u003c/p\u003e\n\u003cp\u003eThe composition, abundance, and assemblage characteristics of detrital clay minerals are important indicators for reconstructing paleoclimate and paleoenvironment. Illite is generally believed to primarily exist in weakly alkaline environments and cold, dry climatic conditions. It forms from the weathering of potassium feldspar under strong physical weathering and weak leaching processes. Therefore, a high content of illite indicates arid climatic conditions (Singer 1984; Chamley 1989; Xu et al. 2017). In contrast, under warm and humid climatic conditions, leaching is more intense, leading to the loss of alkali and alkaline earth metals from the parent rock, which facilitates the formation of kaolinite (Chamley 1989; Velde 1995; Murru et al. 2003). From the perspective of mineral assemblages, clay combinations indicative of humid climates typically feature the presence of kaolinite. Common combinations include kaolinite + illite/smectite + illite, kaolinite + illite, and kaolinite + illite + chlorite (Dong and Song, 2009). Clay combinations dominated by illite generally represent arid to semi-arid environments (Yang et al. 2024a).\u003c/p\u003e\n\u003cp\u003eThe mineral assemblage analysis indicates that both the upper part of the Xishanyao Formation and the lower part of the Toutunhe Formation belong to the kaolinite-illite assemblage, suggesting that the climate during the Aalenian-Bathonian period in the study area was generally relatively humid. Notably, the content of kaolinite in the upper part of the Xishanyao Formation is significantly higher than that in the lower part of the Toutunhe Formation, indicating that the climate during the Early Jurassic (Aalenian-Bajocian) in the study area was markedly more humid than in the Late Middle Jurassic (Bathonian).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e4.4 Comparison\u003c/p\u003e\n\u003cp\u003eBoth palynological evidence and clay mineral evidence indicate that the Santanghu Basin experienced a transition from a humid climate to a semi-arid climate during the Early to Late Middle Jurassic (Aalenian-Bajocian to Bathonian). This climatic shift is not only observed in the Santanghu Basin but is also reflected in other regions of northern China. For instance, in the Ordos Basin, the palynological assemblage of the Yan\u0026apos;an Formation from the Aalenian-Bajocian stage shows a high abundance of humid and warm vegetation from the families Cyatheaceae and Osmundaceae. However, in the Bathonian stage, the palynological assemblage of the extended formation shows a significant decrease in humid and warm vegetation, alongside the emergence of a considerable amount of drought-resistant vegetation, represented by the \u003cem\u003eClassopollis\u003c/em\u003e of the Cheirolepidiaceae family (Xu et al. 2023).\u003c/p\u003e\n\u003cp\u003eIn the Junggar Basin, at the Honggou section of the Manas River, the palynological assemblage from the Aalenian-Bajocian stage of the Xishanyao Formation reveals that the Cyatheaceae content exceeds 25.0%, with the maximum value for Osmundaceae reaching 18.4%, while \u003cem\u003eClassopollis\u003c/em\u003e from the Cheirolepidiaceae family appears sporadically. In contrast, the palynological assemblage from the Bathonian stage of the Toutunhe Formation shows a significant decrease in the contents of Cyatheaceae and Osmundaceae, while the abundance of \u003cem\u003eClassopollis\u003c/em\u003e sharply increases, reaching up to 11.7% (Huang and Li 2007).\u003c/p\u003e\n\u003cp\u003eIn the Turpan-Hami Basin, the palynological assemblage of the Xishanyao Formation shows that the content of Cyatheaceae exceeds 20.0%, with a maximum value for Osmundaceae of 15.6%, while \u003cem\u003eClassopollis\u003c/em\u003e content is only between 1.4% and 3.2%. In the Bathonian stage, the palynological assemblage from the Sanjianfang Formation shows a decrease in Cyatheaceae content to 11.7%\u0026ndash;19.3% and Osmundaceae content below 1.5%, while \u003cem\u003eClassopollis\u003c/em\u003e flourishes, with a maximum content of 31.5% (Wang et al. 1998).\u003c/p\u003e\n\u003cp\u003eIn the northern Tarim Basin, the content of \u003cem\u003eClassopollis\u0026nbsp;\u003c/em\u003ein the Aalenian-Bajocian stage of the Kizilnur Formation is only 0.8%, while in the Bathonian stage of the Qiaokemak Formation, the content of \u003cem\u003eClassopollis\u003c/em\u003e reaches as high as 27.9% (Liu 1998). This evidence illustrates that major basins in northern China underwent a transition from a humid climate to an arid (or semi-arid) climate from the Early to Late Middle Jurassic. It is generally believed that this arid event may be related to global warming during the same period (Wang et al. 2005; Deng et al. 2017). As a result of this event, the coal accumulation processes in most basins in northern China sharply weakened (Zhong et al. 2003; Jiao et al. 2019; Huang et al. 2023). The transition from \u0026ldquo;black\u0026rdquo; rock facies to \u0026ldquo;variegated\u0026rdquo; rock facies in northern China also indicates dramatic changes in terrestrial climate and environment during this period (Zhong et al. 2003; Zhang et al. 2007; Sun et al. 2017; Huang et al. 2023).\u003c/p\u003e"},{"header":"5 Conclusions","content":"\u003cp\u003eThrough the identification and analysis of fossils from 13 spore samples of the Xishanyao Formation and the Toutunhe Formation in the Santanghu Basin, we determined the geological age of the strata. By examining the characteristics of the spore assemblages, we reconstructed the ecosystem, and utilized the SEG model in conjunction with clay minerals to restore the paleoenvironment and reconstruct the paleoclimate. The following conclusions were drawn:\u003c/p\u003e\n\u003col\u003e\n \u003cli\u003eThe palynological assemblage of the lower Toutunhe Formation is classified as the\u003cem\u003e\u0026nbsp;Cyathidites\u003c/em\u003e-\u003cem\u003eClassopollis\u003c/em\u003e-\u003cem\u003eQuadraeculina\u003c/em\u003e (CCQ) assemblage, dating to the Late Middle Jurassic (Bathonian).\u003c/li\u003e\n \u003cli\u003eEvidence from the spore vegetation indicates that during the Aalenian-Bajocian period, the ecosystem of the Santanghu Basin was characterized by a ground cover predominantly composed of ferns, with cycads/ginkgophytes representing a secondary mid-layer vegetation, and conifers being relatively scarce in the canopy. By the Bathonian, the ecosystem transitioned to one dominated by coniferous canopy vegetation, with cycads/ginkgophytes occupying a subordinate role and a significant degradation of fern-dominated ground cover.\u003c/li\u003e\n \u003cli\u003eAnalyses from the SEG model and clay minerals both indicate that the Santanghu Basin experienced a transition from a humid climate to a semi-arid climate during the early to late Middle Jurassic.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003eWe thank Prof. Hu Jun from China University of Geosciences (Wuhan) for the help in clay mineral analysis.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e This research was supported by\u0026nbsp;the Collection and Digitization of Physical Geological Data Project (grant number\u0026nbsp;DD20230138).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003eThe authors declare that they have no confict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request. The material (slides) is stored in the department laboratory (Cores and Samples Center of Natural Resources, China Geological Survey).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eA\u003c/strong\u003e\u003cstrong\u003euthors contribution\u003c/strong\u003e Bing Yang and Di Zhang designed the study. Bing Yang and Xinzhi Zhang identified the sporopollen. Di Zhang and Siyuan Sun carried out the clay minerals analysis. Weitong Li collected and prepared cores. Bing Yang wrote the paper, and all authors contributed to editing the paper.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAbbink, O. A., Van Konijnenburg-Van Cittert, J. H. A., \u0026amp; Visscher, H. (2004). A sporomorph ecogroup model for the Northwest European Jurassic\u0026mdash;Lower Cretaceousi: Concepts and framework. \u003cem\u003eNetherlands Journal of Geosciences\u003c/em\u003e\u003cem\u003e, 83\u003c/em\u003e, 17\u0026ndash;31.\u003c/li\u003e\n\u003cli\u003eAlberti, M., Leshno, Y., F\u0026uuml;rsich, F. T., Edelman-Furstenberg, Y., Andersen, N., \u0026amp; Garbe-Sch\u0026ouml;nberg, D. (2020). Stress in the tropics? Impact of a latitudinal seawater \u0026delta;\u003csup\u003e18\u003c/sup\u003eO gradient on Middle Jurassic temperature reconstructions at low latitudes. \u003cem\u003eGeology, 48\u003c/em\u003e, 1210\u0026ndash;1215.\u003c/li\u003e\n\u003cli\u003eBerner, R. A. (1994). GEOCARB II: A revised model of atmospheric CO\u003csub\u003e2\u003c/sub\u003e over phanerozoic time. \u003cem\u003eAmerican Journal of Science,\u003c/em\u003e \u003cem\u003e294\u003c/em\u003e, 56\u0026ndash;91.\u003c/li\u003e\n\u003cli\u003eBerner, R. A., \u0026amp; Kothavala, Z. (2001). GEOCARB III: a revised model of atmospheric CO\u003csub\u003e2\u003c/sub\u003e over Phanerozoic time. \u003cem\u003eAmerican Journal of Science, 301\u003c/em\u003e, 182\u0026ndash;204.\u003c/li\u003e\n\u003cli\u003eChamley, H. (1989). Clay formation through weathering. In \u003cem\u003eClay sedimentology\u003c/em\u003e (pp. 21\u0026ndash;50). Springer-Verlag.\u003c/li\u003e\n\u003cli\u003eCouper, R. A. (1958). British Mesozoic microspores and pollen grains. \u003cem\u003eA systematic and stratigraphic study\u003c/em\u003e. Palaeontographica Abteilung B, 103, 75\u0026ndash;179.\u003c/li\u003e\n\u003cli\u003eDeng, S. H., Lu, Y. Z., Fan, R., Fang, L. H., Li, X., \u0026amp; Liu, L. (2012). Early Jurassic Toarcian ocean hypoxia event and its response in terrestrial ecosystem.\u003cem\u003e Earth Science, 37\u003c/em\u003e(S2): 23\u0026ndash;38 (in Chinese with English abstract).\u003c/li\u003e\n\u003cli\u003eDeng, S. H., Lu, Y. Z., Zhao, Y., Fan, R., Yang, X. J., Li, X., \u0026amp; Sun, B. N. (2017). The Jurassic palaeoclimate regionalization and evolution of China. \u003cem\u003eEarth Science Frontiers, 24\u003c/em\u003e(1), 107\u0026ndash;142. (in Chinese with English abstract)\u003c/li\u003e\n\u003cli\u003eDera, G., Brigaud, B., Monna, F., Laffont., R., Puceat, E., Deconinck, J. F., Pellenard, P., Joachimski, M. M., \u0026amp; Durlet, C. (2011). Climatic ups and downs in a disturbed Jurassic world. \u003cem\u003eGeology, 39\u003c/em\u003e, 215\u0026ndash;218.\u003c/li\u003e\n\u003cli\u003eDera, G., Puc\u0026eacute;at, E., Pellenard, P., Neige, P., Delsate, D., Joachimski, M. M., Reisberg, L., \u0026amp; Martinez, M. (2009). Water mass exchange and variations in seawater temperature in the NW Tethys during the Early Jurassic: Evidence from neodymium and oxygen isotopes of fish teeth and belemnites. \u003cem\u003eEarth and Planetary Science Letters, 286\u003c/em\u003e, 198\u0026ndash;207.\u003c/li\u003e\n\u003cli\u003eDong, H., \u0026amp; Song, Y. G. (2009). Clay mineralogy and its application to paleoenvironmental reconstruction. Marine Geology \u0026amp; Quaternary Geology, 29(6), 119\u0026ndash;130 (in Chinese with English abstract).\u003c/li\u003e\n\u003cli\u003eFilatoff, J. (1975). Jurassic palynology of the Perth Basin, Western Australia. \u003cem\u003ePalaeontographica, B, 154\u003c/em\u003e, 1\u0026ndash;113.\u003c/li\u003e\n\u003cli\u003eFu, J. H. (1998). Geological events and their significance in the subdivision and correlation of continental Jurassic in northwest China.\u003cem\u003e Acta Sedimentolocica Sinica, 16\u003c/em\u003e(3), 147\u0026ndash;152 (in Chinese with English abstract).\u003c/li\u003e\n\u003cli\u003eHe, F. Q., Zhang, S., Jiang, Z. C., Yang, B., Yuan, Q., Gong, X. J., Guo, C. Q., \u0026amp; Cao, J. (2023). Discovery of sporopollen assemblages of Yan\u0026rsquo;an formation in Yanchi, Ordos Basin, and its paleoclimate significances. \u003cem\u003eActa Geologica Sinica\u003c/em\u003e, \u003cem\u003e98\u003c/em\u003e(1), 200\u0026ndash;213 (in Chinese with English abstract).\u003c/li\u003e\n\u003cli\u003eHuang, L., Zhang, X. J., Li, G. Z., Ji, X. K., Han, X., Wang, Z. Y., Liu, Z. Q., Hou, Z. M., \u0026amp; Ai, Z.H. (2023). Sporopollen assemblage from the Middle Jurassic of the northeastern Ordos Basin, Inner Mongolia, and their paleoclimatic implications. \u003cem\u003eActa Geologica Sinica\u003c/em\u003e\u003cem\u003e,\u003c/em\u003e \u003cem\u003e97\u003c/em\u003e, 1390\u0026ndash;1406 (in Chinese with English abstract).\u003c/li\u003e\n\u003cli\u003eHuang, P. (1995). Early-middle Jurassic sporopollen assemblages from Dananhu coalfield of Thuha basin, Xinjiang and their stratigraphical significance. \u003cem\u003eActa Micropalaeontologica Sinica,\u003c/em\u003e \u003cem\u003e34\u003c/em\u003e, 171\u0026ndash;197 (in Chinese with English abstract).\u003c/li\u003e\n\u003cli\u003eHuang, P. (2002). Middle Jurassic sporopollen assemblages from Tangqiang-3 well of Santanghu basin, Xinjiang. \u003cem\u003eActa Micropalaeontologica Sinica,\u003c/em\u003e \u003cem\u003e19\u003c/em\u003e, 178\u0026ndash;192 (in Chinese with English abstract).\u003c/li\u003e\n\u003cli\u003eHuang, P., Li, J. G. (2007). Sporopollen assemblages from the Xishanyao and Toutunhe formation at the Honggou Section of the Manasi River, Xinjiang and their stratigraphical significance. \u003cem\u003eActa Micropalaeontologica Sinica, 24\u003c/em\u003e, 170\u0026ndash;193 (in Chinese with English abstract).\u003c/li\u003e\n\u003cli\u003eIlyina, V. I. (1986). Subdivision and correlation of the marine and non-marine Jurassic sediments in Siberia based on palynological evidence.\u003cem\u003e Review of Palaeobotany and Palynology, 48\u003c/em\u003e, 357\u0026ndash;364.\u003c/li\u003e\n\u003cli\u003eJiao, Y. Q., Wu, L. Q., Rong H., \u0026amp; Zhang, F. (2021). Coal accumulation regularity of Zhiluo formation and its indication to paleoclimate and uranium metallogenic environment Ordos Basin. \u003cem\u003eJournal of China Coal Society, 46\u003c/em\u003e(7), 2331\u0026ndash;2345 (in Chinese with English abstract).\u003c/li\u003e\n\u003cli\u003eKorte, C., Hesselbo, S. P., Ullmann, C. V., Dietl, G., Ruhl, M., Schweigert, G., \u0026amp; Thibault, N. (2015). Jurassic climate mode governed by ocean gateway.\u003cem\u003e Nature Communications, 6\u003c/em\u003e, 1\u0026ndash;7.\u003c/li\u003e\n\u003cli\u003eLenton, T. M., Daines, S. J., \u0026amp; Mills, B. J. W. 2018. COPSE reloaded: An improved model of biogeochemical cycling over Phanerozoic time. \u003cem\u003eEarth-Science Reviews, 178\u003c/em\u003e, 1\u0026ndash;28.\u003c/li\u003e\n\u003cli\u003eLi, L. Q., Wang, Y. D., Liu, Z. S., Zhou, N., \u0026amp; Wang, Y. (2016). Late Triassic palaeoclimate and palaeoecosystem variations inferred by palynological record in the northeastern Sichuan Basin, China. \u003cem\u003ePalaontologische Zeitschrift,\u003c/em\u003e \u003cem\u003e90\u003c/em\u003e, 327\u0026ndash;348.\u003c/li\u003e\n\u003cli\u003eLi, L. Q., Wang, Y. D., Vajda, V., \u0026amp; Liu, Z. S. (2018). Late Triassic ecosystem variations inferred by palynological records from Hechuan, southern Sichuan Basin, China. \u003cem\u003eGeological Magazine,\u003c/em\u003e \u003cem\u003e155\u003c/em\u003e, 1793\u0026ndash;1810.\u003c/li\u003e\n\u003cli\u003eLiu, J. T., Xie, D. H., Liu, Y., Chen, J. G., Jia, G. Q., \u0026amp; Wang, B. (2024). Petroleum exploration history and understandings in Santanghu Basin.\u003cem\u003e Petroleum Geology and Engineering, 38\u003c/em\u003e(4), 1\u0026ndash;10 (in Chinese with English abstract).\u003c/li\u003e\n\u003cli\u003eLiu, Y. (2010). \u003cem\u003eThe tectomic evolution in the Santanghu Basin and its relationship to oil and gas \u003c/em\u003e(pp.1-64). Thesis. China University of Geosciences (Beijing).\u003c/li\u003e\n\u003cli\u003eLiu, Z. S. (1998). Jurassic palynological assemblages from the northern margin in the Tarim Basin of Xinjiang, NW China. \u003cem\u003eActa Micropalaeontologica Sinica\u003c/em\u003e\u003cem\u003e, 15\u003c/em\u003e(2), 144\u0026ndash;165 (in Chinese with English abstract).\u003c/li\u003e\n\u003cli\u003eMurru, M., Ferrara, C., Da Pelo, S., \u0026amp; Ibba, A. (2003). The Palaeocene\u0026ndash;Middle Eocene deposits of Sardinia (Italy) and their palaeoclimatic significance. \u003cem\u003eComptes Rendus Geoscience, 335\u003c/em\u003e(2), 227\u0026ndash;238.\u003c/li\u003e\n\u003cli\u003eNordt, L., Breecker, D., \u0026amp; White, J. (2022). Jurassic greenhouse ice-sheet fluctuations sensitive to atmospheric CO\u003csub\u003e2\u003c/sub\u003e dynamics. \u003cem\u003eNature Geoscience, 15\u003c/em\u003e, 54\u0026ndash;59.\u003c/li\u003e\n\u003cli\u003ePearce, C. R., Cohen, A. S., \u0026amp; Coe, A. L. (2008). Molybdenum isotope evidence for global ocean anoxia coupled with perturbations to the carbon cycle during the Early Jurassic.\u003cem\u003e Geology, 36\u003c/em\u003e, 231\u0026ndash;234.\u003c/li\u003e\n\u003cli\u003ePocock, S. A. J. (1970). Palynology of the Jurassic sediments of Western Canada. Part I. \u003cem\u003ePalaeontographica Abteilung B, 130\u003c/em\u003e(1\u0026ndash;6), 12\u0026ndash;136.\u003c/li\u003e\n\u003cli\u003eSantos, A.A., Wang, X., Qiang, F.Q., \u0026amp; Diez, J.B. (2018). First palynological data from the Jurassic South Xiangshan Formation (Nanjing area, China). \u003cem\u003eGeobios, 51\u003c/em\u003e, 559\u0026ndash;570. \u003c/li\u003e\n\u003cli\u003eSinger, A. (1984). The paleoclimatic interpretation of clay minerals in sediments\u0026mdash;A review. \u003cem\u003eEarth-Science Reviews, 21\u003c/em\u003e, 251\u0026ndash;293.\u003c/li\u003e\n\u003cli\u003eSong, Z. C., Shang, Y. K., Liu, Z. S., Huang, P., Wang, X., Qian, L. J., Du, B., \u0026amp; Zhang, D. H. (2000).\u003cem\u003e Fossil spores and pollen of China (volume II): The Mesozoic spores and pollen\u003c/em\u003e. Science Press (in Chinese).\u003c/li\u003e\n\u003cli\u003eSrivastava, S. K. (1987). Jurassic spore-pollen assemblages from Normandy (France) and Germany. \u003cem\u003eGeobios, 20\u003c/em\u003e, 5\u0026ndash;79.\u003c/li\u003e\n\u003cli\u003eSun, L. X., Zhang, Y., Zhang, T. F., Cheng, Y. H., Li, Y. F., Ma, H. L., Yang, C., Guo, J. C., Lu, C., \u0026amp; Zhou, X.G. (2017). Jurassic sporopollen of Yan\u0026rsquo;an formation and Zhiluo formation in the northeastern Ordos basin, Inner Mongolia, and its paleoclimatic significance. \u003cem\u003eEarth Science Frontiers\u003c/em\u003e\u003cem\u003e, 24\u003c/em\u003e, 32\u0026ndash;51 (in Chinese with English abstract).\u003c/li\u003e\n\u003cli\u003eVakhrameev, V. A. (1991). \u003cem\u003eJurassic and Cretaceous Floras and Climates of the Earth\u003c/em\u003e. Cambridge: Cambridge University Press. \u003c/li\u003e\n\u003cli\u003eVelde, B., 1995. \u003cem\u003eOrigin and Mineralogy of Clays\u003c/em\u003e (pp. 207-210). Paris: Springer Verlag Berlin and Heidelberg, 207\u0026ndash;210.\u003c/li\u003e\n\u003cli\u003eWang, Y. D., Jiang, D. X., Yang, H. Q., \u0026amp; Sun, F. (1997). Middle Jurassic palynoflora and its palaeoenvironmental implication in Turpan depression, Xinjiang. \u003cem\u003eActa Sedimentolocica Sinica,\u003c/em\u003e \u003cem\u003e15\u003c/em\u003e, 133\u0026ndash;140 (in Chinese with English abstract).\u003c/li\u003e\n\u003cli\u003eWang, Y. D., Jiang, D. X., Yang, H. Q., \u0026amp; Sun, F. (1998). Middle Jurassic spore-pollen assemblages from Turpan-Shanshan area, Xinjiang. \u003cem\u003eActa Botanica Sinica\u003c/em\u003e, \u003cem\u003e40\u003c/em\u003e, 969\u0026ndash;976 (in Chinese with English abstract).\u003c/li\u003e\n\u003cli\u003eWang, Y. D., Mosbrugger, V., \u0026amp; Zhang, H. (2005). Early to Middle Jurassic vegetation and climatic events in the Qaidam Basin, northwest China. \u003cem\u003ePalaeogeography, Palaeoclimatology, Palaeoecology, 224\u003c/em\u003e(1\u0026ndash;3), 200\u0026ndash;216.\u003c/li\u003e\n\u003cli\u003eXie, W. Q. (2023). \u003cem\u003eLate Middle Jurassic paleoclimate and paleoenvironmental evolution and organic matter accumulation mechanism\u003c/em\u003e,\u003cem\u003e Qaidam Basin \u003c/em\u003e(pp. 1\u0026ndash;152)\u003cem\u003e,\u003c/em\u003e Thesis. Central South University (Changsha).\u003c/li\u003e\n\u003cli\u003eXu, G. Z., Deconinck, J. F., Feng, Q. L., Baudin, F., Pellenard, P., Shen, J., \u0026amp; Bruneau, L. (2017). Clay mineralogical characteristics at the Permian\u0026ndash;Triassic Shangsi section and their paleoenvironmental and/or paleoclimatic significance.\u003cem\u003e Palaeogeography, Palaeoclimatology, Palaeoecology, 474\u003c/em\u003e, 152\u0026ndash;163.\u003c/li\u003e\n\u003cli\u003eXu, Z. L., Cheng, Y. H., Ao, C., Zhang, T. F., \u0026amp; Wang, S. Y. (2023). Middle Jurassic palaeoclimate changes within the central Ordos Basin based on palynological records.\u003cem\u003e Palaeobiodiversity and Palaeoenvironments, 103\u003c/em\u003e, 21\u0026ndash;42.\u003c/li\u003e\n\u003cli\u003eYang, B., Xu, G. Z., Hui, G. J., Wei, Y., Zhang, X. Z., Yi, J. J., Sun, S. Y., \u0026amp; Zhang, X. Z. (2024a). Sedimentary Expressions of the Early Jurassic Jenkyns Event in an Inland Lacustrine System in the Yin\u0026apos;gen\u0026ndash;Ejinaqi Basin, North China. \u003cem\u003eActa Geologica Sinica\u003c/em\u003e\u003cem\u003e (English Edition), 98\u003c/em\u003e(5): 1359\u0026ndash;1375\u003c/li\u003e\n\u003cli\u003eYang, B., Zhang, X., Li, W., Sun, S., \u0026amp; Yi, J. (2024b). Palynological Record of the Aalenian\u0026ndash;Bajocian Cooling Event from the Santanghu Basin, Northwest China. \u003cem\u003eDiversity, 16\u003c/em\u003e, 369.\u003c/li\u003e\n\u003cli\u003eZhang, H. Q., Wang, T. D., Yan, C. F., \u0026amp; Yuan, J. Y. (2007). The subdivision and correlation of the Jurassic system of the Minhe Basin. \u003cem\u003eJournal of Stratigraphy, 31\u003c/em\u003e(1), 62\u0026ndash;67 (in Chinese with English abstract)..\u003c/li\u003e\n\u003cli\u003eZhang, K. (1993). The characteristic of plate tectonic evolution and the evaluation of hydrocarbon prospect of Santanghu basin, Xinjiang. \u003cem\u003eXinjiang Petroleum Geology, 14\u003c/em\u003e, 1\u0026ndash;13 (in Chinese with English abstract).\u003c/li\u003e\n\u003cli\u003eZhang, L. W., Yan, D. T., Yang, S. G., Li, B. Q., Fu, H. J., Wang, G., Yang, X. R., Zhang, W. L., \u0026amp; Zhang, J. F. (2023). Evolution of the Middle Jurassic paleoclimate: Sedimentary evidence from coal-bearing strata in the Santanghu Basin, NW China. \u003cem\u003eJournal Asian Earth Science,\u003c/em\u003e\u003cem\u003e242\u003c/em\u003e, 105495.\u003c/li\u003e\n\u003cli\u003eZhong, X. C., Zhao, C. B., Yang, S. Z., \u0026amp; Shen, H. (2003).\u003cem\u003e Jurassic System in the North of China Volume \u003c/em\u003e\u003cem\u003eⅡ\u003c/em\u003e\u003cem\u003e Palaeoenvironment and Oil-Gas Source \u003c/em\u003e(pp. 1\u0026ndash;243)\u003cem\u003e. \u003c/em\u003eBeijing: Petroleum Industry Press (in Chinese with English summary).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"palynological assemblage, Sporomorph EcoGroup Model, kaolinite, paleoclimate, northern China","lastPublishedDoi":"10.21203/rs.3.rs-5779811/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5779811/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe arid event that began in the Middle Jurassic Bathonian stage marks the second major drought event in northern China during the Jurassic period and had a profound impact on the development of modern terrestrial ecosystems. This study reconstructs the paleoclimate and paleoecosystem of the Middle Jurassic Santanghu Basin by analyzing palynological assemblages and clay minerals from the Xishanyao and Toutunhe formations. Two distinct palynological assemblages were identified: the \u003cem\u003eCyathidites-Deltoidospora-Osmundacidites-Cycadopites\u003c/em\u003e(CDOC) assemblage (Aalenian–Bajocian) and the \u003cem\u003eCyathidites-Classopollis-Quadraeculina\u003c/em\u003e(CCQ) assemblage (Bathonian). In terms of vegetation types, during the Aalenian–Bajocian stage, the Santanghu Basin was dominated by ground cover vegetation primarily consisting of ferns, with a midstory composed mainly of cycads/ginkgophytes, and a sparse canopy dominated by conifers. By the Bathonian stage, this shifted to a vegetation structure dominated by coniferous canopy vegetation, a subordinate midstory of cycads/ginkgophytes, and a severely degraded ground cover dominated by ferns. Sporomorph EcoGroup (SEG) analysis indicates that the CDOC assemblage is characterized by high Lowland SEG wetter/drier and warmer/cooler ratios, reflecting a warm and humid climate. In contrast, the CCQ assemblage also shows high Lowland SEG wetter/drier and warmer/cooler ratios but indicates a warm and arid climate. Clay mineral data reveal that the kaolinite content in the CCQ assemblage is significantly lower than in the CDOC assemblage. Evidence from both palynology and clay minerals suggests that the Santanghu Basin experienced a transition from a humid to a semi-arid climate near the Bajocian–Bathonian boundary in the Middle Jurassic.\u003c/p\u003e","manuscriptTitle":"Paleoclimate Transition Recorded by Palynological and Clay Mineral Evidence in the Santanghu Basin during the Middle Jurassic","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-02-03 05:15:40","doi":"10.21203/rs.3.rs-5779811/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"602ccd06-b9ce-4343-8c66-1bf2c7eb22f0","owner":[],"postedDate":"February 3rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-03-25T13:17:10+00:00","versionOfRecord":[],"versionCreatedAt":"2025-02-03 05:15:40","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5779811","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5779811","identity":"rs-5779811","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}