Late Paleocene Paleoclimate recorded in halite deposits in Subei basin ,East China

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Santosh Santosh, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3913270/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 11 You are reading this latest preprint version Abstract Salt deposits correspond to relatively extreme climate events. However, due to insufficient independent temperature proxies, there is a lack of paleotemperature records obtained from salt laminae deposition .The Paleocene evaporite sequence deposited in the Hongze Depression of Subei Basin provides an important terrestrial sediment record during this period. In this study we carry out a detailed fluid inclusion study on halite crystals in these rocks and present total of 488 homogenizaton data from eight samples. The results show temperatures ranging from 17.7°C to 52.3°C, and the mean T h value of 34.1°C is in good agreement with the previous studies of climatic proxies. Our study shows that fluid inclusions can be used as a robust tool to construct the ancient earth surface temperature. Earth and environmental sciences/Climate sciences/Palaeoclimate Earth and environmental sciences/Solid earth sciences/Geochemistry Earth and environmental sciences/Solid earth sciences/Geology Earth and environmental sciences/Solid earth sciences/Sedimentology halite fluid inclusions homogenization temperature paleoenvironment Late Paleocene Subei basin Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1 Introduction The Paleocene-Early Eocene warm climate period (65 − 50 Ma). The Paleocene climate was relatively warm, with global deep-sea temperatures about 8°C higher than today [ 1 ] , oxygen isotopes was lower [ 2 ] , and atmospheric carbon dioxide concentration similar to today's atmospheric carbon dioxide concentration (390 ppm) [ 2 ] . However, with the passage of time, the global deep sea temperature continued to increase and δ 18 O further decreased. Around 55 Ma, the atmospheric CO 2 concentration began to rise sharply. The ancient air temperature rose sharply in a short period of time. The deep sea temperature exceeded 10°C. Carbon isotopes and Oxygen isotopes are negatively biased, but this process lasts for a short time, less than 0.01 Ma [2、3] , and is the Paleocene-Eocene Thermal Maximum (PETM) event [2、4、5、6、7、8] . After the PETM event, the paleotemperature continued to increase and entered the climate optimal period of the Early Eocene. During this period, the δ18O and δ13C values were negatively biased, the temperature reached the highest point since the Cenozoic [2、9、10、11] , and the deep-sea temperature was about 12°C higher than today [1、12] . The plane height has also reached the highest level since the Cenozoic Era, 50–100 m or even higher than today [6、13] Evaporites are mainly formed in dry and hot climate environments and are a good analytical indicator of paleoclimate [ 14 ] . Evaporites were formed on the earth, indicating that they can directly record the temperature, chemical composition of ancient water bodies, and biological conditions at that time [ 15 ] ). The fluid inclusions formed during the crystallization process of halite seal the paleoenvironmental information at that time [ 16 ] . In recent years, with the intensification of the earth's greenhouse effect and the continuous occurrence of abnormal climate, the evolution of the ancient environment has become one of the focuses of research. The uniform temperature of the original fluid inclusion of halite can reflect the ancient water temperature when the halite crystallized [17、18] . This method has been widely used at home and abroad [20、21、22、17] [21]Meng (2011) studied the inclusions of synthetic halite in the laboratory and concluded that the primary fluid inclusions in halite exist in funnel crystals formed at the air-water interface and herringbone crystals formed at the bottom of the water. Both can be used To reflect the temperature of the ancient environment, and only the maximum uniform temperature is closest to the temperature when the brine crystallized. ] Zhao [22 and others [ 23 ] ) conducted comparative experiments on the uniform temperature of a single liquid inclusion in halite rock under different freezing conditions and different high temperature conditions and showed that: without experiencing high temperature (110°C) and low temperature (-20°C) freezing Under interference conditions, the homogenization temperature of a single liquid inclusion in halite obtained at a slow heating rate (usually less than 1°C/min) can represent the ancient water temperature when the halite was formed. In this study of the salt-bearing system of the 4th member of the Funing Formation in the Hongze Sag of the Subei Basin, the author found that halite rocks contain a large number of primary fluid inclusions, which provides important materials for studying ancient water temperatures. This article carries out homogeneous temperature analysis on these primary halite inclusions to reveal the paleowater temperature characteristics of the Hongze Sag in the Subei Basin and explore its paleoclimate significance, which is an important reference for studying climate changes in the early Paleogene. 2 Study area 2.1 Geological Setting The Subei Basin is the onshore part of the North Subei-Yellow Sea Basin in eastern China. It is located northeast of the Yangtze Platform, bordering the Binhai Uplift and the Sulu Orogenic Belt to the north, the South Jiangsu Uplift and the Zhangbaling Uplift to the south, and the Tanlu Fault Zone to the west. It reaches the Yellow Sea in the east and covers an area of approximately 4.2✕104 km2. There are abundant structural units in the area, which are generally represented by a series of asymmetric fault depressions with "south fault and north superposition", and a basic structural pattern of secondary basins of "two depressions and one uplift" running east-west, which can be divided from north to south into: Yanfu Depression-Jianhu Uplift-Dongtai Depression (Fig. 1). Bounded by the Jianhu uplift in the middle of the basin, the area to the north to the Binhai uplift is called the Yanfu Depression, and to the south to the South Jiangsu uplift area is called the Dongtai Depression. The Hongze Sag is located in the northwest of the Subei Basin, adjacent to the Lusu Uplift to the north, the Dengma Fault to the south, the Jianhu Uplift and the Zhangbaling Uplift, the Nihuzhuang Fault to the east to the Huai'an Uplift, and the West to the Huai'an Uplift. Bounded by the Zhenglu Fault Zone, it runs northeast and is a Mesozoic and Cenozoic skip-shaped fault depression that is thicker in the south than in the north and thicker in the north than in the north. The sag began to receive sedimentation from the Cretaceous, and reached its peak in the Paleogene and Neogene, with a cumulative sedimentary thickness of up to 5,800 meters. Drilling in the area revealed that the Upper Cretaceous Pukou Formation, Chishan Formation, Paleogene Taizhou Formation, Funing Formation, Dainan Formation, Sanduo Formation, Neogene Yancheng Formation and Quaternary Dongtai Formation. The sag is a compound sag with alternating depressions and uplifts. From the southwest to the northeast, it is the Jinli sub-sag, the Guanzhen sub-sag, and the Zhaoji sub-sag. The rock salt deposits occur in the fourth section of the Funing Formation in the Zhaoji sub-sag. The secondary sag and Guanzhen secondary sag are dominated by gypsum-containing mudstone, and no salt rock deposits have been found. Figure 1 Simplified geology of the study area and location of core SB18 Figure 1 is about here The Upper Cretaceous-Cenozoic strata of Hongze sag show the following stratigraphy from the bottom to the top(figure2 ): the Upper Cretaceous Pukou Formation, Chishan Formation and Taizhou Formation; the Palaeogene Funing Formation, Dainan Formation, and Sanduo Formation; and the Neogene Yancheng Formation and the Quaternary Dongtai Formation [24、25、26] . Compared with other depressions in the Subei basin, a section of the Neogene Yancheng Formation is missing. At present, all the stratigraphic sections of the Hongze sag have been revealed. The Funing formation can be divided into four members (E 1 f 1 -E 1 f 4 ) from bottom to top [ 27 ] . The first member (E 1 f 1 ) consists of a set of fluvial-deltaic deposits and the E 1 f 2 is recognized as a set of lacustrine deposits, of which the lithology is dominantly dark gray–black mudstones/shales interbedded with marls, limestone and dolomite. The E 1 f 3 is composed of deltaic deposits, and the lithology of E 1 f 4 is saline mineral layers [ 27 ] . The E 1 f 4 saline formation mainly developed halite-rich rock, sulfate rock and a small amount of carbonate rock. The halite and sulfate mineral layers are relatively thick Figure 2 Generalized stratigraphic sequences, sedimentation facies of the Subei basin ( Age data are base on [28、29] Major reflectors and tectonic events are marked.Courtesy of the Jiangsu oilfield Company (Sinopec) Figure 2 is about here 2.2 Lithology and Stratigraphy of Core SB18 The lithology of Core SB18(Fig. 3) consist of distinct evaporitic-evaporitic–siliciclastic cycles which represent the lower Members of Funing formation which are widely distributed throughout the Subei basin. These members are mainly composed of evaporites separated by carbonate and sulfate. According to the color of halite recrystallization, orange and gray varieties are recognized. The orange halite is mostly medium- and fine-grained halite, while the gray halite is mostly fine-grained halite with a small amount of anhydrite. Figure 3 is about here Figure 3 Lithology of core sb18 and Samples Pictures 3 Method Most of the primary inclusions in the studied samples are single-phase aqueous liquid inclusions at room temperature, though some are two phase inclusions containing gases or solids. Before undertaking the ‘cooling nucleation’ process, we recorded their photographs in order to distinguish inclusions with gas bubbles at room temperature from inclusions in which vapor bubbles were artificially nucleated after cooling. Other studies that observed gas bubbles at room temperature prior to cooling have interpreted the bubbles to be trapped atmospheric air, and noted that they produce homogenization temperatures that are unrealistically high [14、19、21、30] . During the preparation process of fluid inclusion sheets, in order to avoid changes in the original temperature information of the halite inclusions caused by the cutting and grinding and polishing processes, the processing of the inclusion test samples was based on the methods of [17、18] . First use a knife to cut the halite particles along the cleavage plane to obtain a thickness .Halite cleavage pieces of 5 to 1 mm. The cleavage slices were observed and photographed under a microscope, focusing on recording the occurrence and shape of fluid inclusions formed by primary and early diagenetic recrystallization, and focusing on photographing single liquid inclusions(Fig. 4). Then seal it with a plastic zip lock bag, put it into a well-sealed plastic box, put in desiccant for protection, and freeze it in the refrigerator for about 1 week (the temperature in the refrigerator has been stabilized at -18°C after multiple measurements), and wait until single The homogenization temperature is measured after bubbles appear in the liquid inclusions when they are frozen and nucleated. The test of uniform temperature was completed using the Linkam THMSG600 hot and cold stage, using a heating rate of 0. 5°C/min, which was reduced to 0. 1 to 0. 2°C/min when the bubbles gradually became smaller and closer to uniformity. ) Regarding how to determine whether the bubbles in the inclusions have really disappeared, that is, they have reached uniformity, or whether the bubbles have become smaller in size and are difficult to observe under the microscope due to problems with the accuracy of the microscope, causing the illusion of uniformity, it can be verified by the following method: Lower the temperature again 10 ~ 15℃, if the bubbles still exist, the volume of the bubbles will grow again until they are visible in the field of view, and the bubbles will not reappear even if the fluid inclusion reaches a completely uniform temperature and is cooled again by 10 ~ 15℃ [ 19 ] . ​ Figure 4 Primary fluid inclusions in the Lower member of Funing formation Figure 4 is about here 4 Results Nucleated vapor bubbles after cooling were observed in less than15% of primary single phase liquid fluid inclusions of the halite samples(Fig. 5). The recorded Th (temperature of homogenization) data are summarized in Table 1.In total, 488 homogenization temperature data were obtained from nucleated vapor bubbles in the first round, with a maximum Th of 52.3°C and a minimum Th of 17.7°C. About 70% of the Th data are in the range from 30–50°C. The Th ranges of the six stratigraphic intervals are 17.7–41.1°C(1754.87 m),21.549.2°C (1756.82 m), 21.2–51.2°C (1758.61 m), 25.7–51.2°C(1759.58 m), 26.7–48.7°C (1760.52 m) ,28.1–50.1°C(1763.57m༉,25.1–45.3༈1768.21m༉and 28.4–50.1°C (1770.31 m), respectively. All samples yielded similar maximum homogenization temperatures or temperature ranges for cumulate crystals and chevron crystals(Fig. 6༉. More than 96% of fluid inclusion assembles (FIA) have ranges of homogenization temperatures that fall within 15°C and more than 90% of fluid inclusion assembles have ranges that fall into an even smaller interval of less than 20°C (more than 90%). Details of this data are shown in Fig. 6 and listed in Table 1. Figure 5 Changes of primary fluid inclusion during the “cooling nucleation process” Figure 5 is about here Table 1 is about here Table 1 Homogenization temperatures of halite fluid inclusions of the Funing Formation Figure 6. Histogram of homogenization temperature plotted against number of fluid inclusions. Figure 6 is about here 5 Discussion 5.1 Rationality and stability of Th data Due to the deliquescence and solubility of halite, it is easily damaged or recrystallized during its burial and preservation, which will affect the rationality and stability of Th data, especially for ancient halite samples [ 18 ] . The Th data do not need to be pressure corrected because halite was deposited in a shallower depositional environment and the temperature trapped by fluid inclusions at low pressure is approximately equal to Th, thus providing a direct temperature record of halite deposition. From the same inclusion Primary fluid inclusions in the growth zone are captured at the same time [ 18 ] . However, multiple primary fluid inclusion bands in well-developed halite crystals may not form at the same time, such as in the morning and evening of the same day. Therefore, Th data from different inclusion bands are acquired at different temperatures [ 18 ] . We use two methods to verify whether native fluid inclusions undergo changes or disruptions in thermal reequilibration, including thermal reequilibration analysis of Th data and the relationship between fluid inclusion size and Th. On the one hand, in a given FIA The consistency of Th data can be used as an indicator to evaluate thermal reequilibration [ 18 ] noted that approximately 90% of Th data in a single FIA fluctuated within a range of less than 15°C, indicating primary fluid inclusions Has not undergone changes or disruptions in thermal rebalancing. On the other hand, the relationship between fluid inclusion size and Th can also act as another criterion for determining possible alteration from thermal reequilibration. Large inclusions are more extensible than smaller inclusions, and fluid inclusions that were subjected to extension have higher Th than actual capture temperature [31、32、33] . In other words, if inclusions have undergone extension, then large inclusions are more likely to yield higher Th than small ones. Our results show no relationship between fluid inclusions size and corresponding Th (Fig. 7). The Th data, therefore, show no alteration or damage by thermal reequilibration, which further supports that the data are reliable for paleotemperature interpretations. We thus conclude that Th data presented here from halite of the Funing Formation are likely to accurately reflect Late paleocene seawater temperatures. Figure 7 Histogram of homogenization temperatures plotted against size of inclusions. Figure 7 is about here 5.2 Record of paleotemperature by halite fluid inclusions Primary fluid inclusions in halite are usually contained in cumulate and chevron crystals. Cumulate crystals often precipitate at the airewater interface or within the upper water column and later sink to the bottom under the effect of gravity [17、19、23] , Chevron crystals are vertically oriented bottom-growth crystals which precipitate in shallow water [33、34] . Therefore, the homogenization temperatures of fluid inclusions from both cumulate crystals and chevron crystals record brine surface temperatures during halite deposition or approximate surface air temperatures in the case of shallow environments [17、20、34、35、36、23] Although all homogenization temperature data represent surface brine or shallow water temperatures, it cannot be expected that the complete temperature variation of surface brines will be captured based on homogenization temperatures of halite fluid inclusions no matter how many homogenization temperature data were analyzed and how large a sample is. This insufficient reconstruction of the full temperature range results from the fact that salts and contained fluid inclusions do not form at constant rates over the full daily and seasonal temperature variation range. Salt formation is usually higher during daytime, especially the afternoon, and during summer [17、19、18] In addition, the formation of salt reflects not only temperatures but also factors such as humidity and wind velocity [19、33] . More importantly, only a limited number of the millions of fluid inclusions in an individual sample can artificially nucleate vapor bubbles, and thus, can be used for Th measurements. These observations imply that the ranges of homogenization temperatures may best represent the average temperature conditions during halite deposition [ 19 ] . 5.3 Comparison with modern evaporative environments Robert [ 19 ] reported the homogenization temperatures from modern halite precipitated in April to May and August at Badwater Basin, Death Valley, California. These Th fall in two ranges (25–39 ◦C and 45–49 ◦C) that are very close to the temperature of brine recorded in April to May (20–38 ◦C) and August (43–50 ◦C). As discussed above, our results are more likely to reflect seasonal temperature variations and have similar Th distribution pattern to those by Roberts and Spencer (1995). The lack of Th data from the lowest brine temperature (20 ◦C) to the lowest Th (25 ◦C) was interpreted due to the absence of halite formation at a low temperature and low diurnal evaporative conditions [ 19 ] . Thus, the low temperature ranges in this study is more likely to characterize a low temperature and strong evaporation environment. Lowenstein [ 17 ] pointed out that only the maximum Th in “laboratory grown halite” matches the temperature of brine from which the halite was precipitated, denoting lower Th data of a certain range would be unreliable. [ 37 ] Liu reported both extremely higher and lower Th than the temperature of brines from both laboratory and natural halite, but the deviations were considered to be due to the sample pretreatment process of using a saw for polishing. Nonetheless, the extremely low Th compared to the brine temperature was not observed in halite samples with proper pretreatments from modern natural settings [ 19 ] . Although some discrepancies exist in the measured water temperature values from where the halite was precipitated, but they are still close to the air temperature [17、18、19、38] . Therefore, the paleotemperature annual fluctuations during the deposition of halite at 1754.87–1770.31 m of E 1 f 4 (56 Ma) in well sb18 in the Subei Basin can be considered from17.7-52.3◦C (Table 1). In colder months, air temperature has varied from 17.7 to 32.1 ◦C, whereas it has been from 26.8 to 52.3 ◦C in warmer months. Some of the Th recorded values between 21.75 and 40.37 ◦C (Fig. 6) reveal a sharp temperature transition from cold to warmer seasons in a year, or possibly no halite precipitation in spring and autumn(Table 2). Table 2 is about here Table 2 Th values range in cumulate and chevron crystals 5.4 Local and regional climate conditions during the Late Paleocene Duringthe Late Paleocene, The characteristics of the plant pollen in assemblage (Ulmipollenites minor ; Ulmipollenites; Subtriporopollenites; Quercoidites;Rhoipites; Retitricolpites ) in Subei basin indicate that the plants during the deposition period of the Funing Formation were high-temperature tolerant plants, and the climate at that time was arid-hot [39、40、41] . The analysis of paleomagnetic data during the Funing Formation period of Subei Basin shows that the average paleolatitude is between 10.5 and 23.9°N, which suggests a location in the low-middle latitude region. Our study of the homogenization temperature of fluid inclusions on halite also shows that the paleotemperature was high during Late Paleocene. 6. Conclusions The fluid inclusion composition analysis and the appearance of cumulate and chevron halite crystals in the same beds indicate the massive halite that is deposited in the Funing Formation of the Subei Basin were not originated from seawater intrusions but were formed in a shallow, certainly centimeter scale water depth, lake environment. We obtained quantitative Late Paleocene paleotemperature records by measuring the Th data of primary fluid inclusions in halite crystals. The average paleotemperature is 34.11°C, with the highest value being 52.3°C°C and the lowest at 17.7°C. This shows that the temperature of the ancient salt lake water was relatively high at that time. It can also be seen from the correspondence between paleowater temperature and paleo air temperature that the climate of the Hongze Sag in the Northern Subei Basin corresponds to the high temperature characteristics during the Paleocene. Declarations Author Contribution Ting Ding do the writing and the idea. Bin pan drawed the figure , Hua Zhang and M. Santosh modify the paper , Chenglin Liu give the idea. Yang zhen did the field work. Acknowledgements This study was supported Major State Basic Research Development Program of China(NO.2023YFC2906603) and The Major Science and Technology Projects of Xinjiang (41972092), and The Third Xinjiang Scientific Expedition Program (2022xjkk1303). References Beerling, D.J., Royer, D.L., 2011. Convergent Cenozoic CO2 history. Nature Geofenced. 4(7): 418–420. Zachos J. C., Pagani M., Sloan L., 2001. Trends, rhythms, and aberrations in global climate 65 Ma to present. Science, 292(5517), 686–693. Luo, L., 2017. Calcium-carbonate nodules and carbon-oxygen isotopes in the strata of Lanzhou and Liupan Mountain basins and the concentration of atmospheric CO2 in the Early Cretaceous and Oligocene. Lanzhou University, Lanzhou, China (in Chinese with English abstract). 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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-3913270","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":273621085,"identity":"6156bbab-b3ce-4f4f-a1e1-34c0faef7ca0","order_by":0,"name":"Ting Ding","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+UlEQVRIiWNgGAWjYDCCwyDCgIGBn7354GOwCDNzA2EtB4BaJHuOJRuDNTMzEtByAIoNbuSoSYO1MBDQwnec9/DrDwV37Gb2nGGrLqj4E83fDtTyo2IbTi2Sh/nSLA4YPEvuZ+89dnvGGYPcGYcZGxh7ztzGqcXgMI+ZwQGDw8mSPefSbvO2GeQ2ALUwM7YRoQXoF7NikJb5RGgxfgDUYgfSwgzSsoGQFkmgLQxnDA4ngAJZmueMce5GoJaD+PzCd/6M8YeKP4ftQVH5madCLnfe+cMHH/yowK0FCNgkgERiA7LQAXzqgYD5A5CwJ6BoFIyCUTAKRjIAABAQYZbkKzSMAAAAAElFTkSuQmCC","orcid":"","institution":"East China university of technology, Nanchang Jiangxi","correspondingAuthor":true,"prefix":"","firstName":"Ting","middleName":"","lastName":"Ding","suffix":""},{"id":273621086,"identity":"66b029df-fb79-4ff8-97d4-841da1ea0366","order_by":1,"name":"Bing Pan","email":"","orcid":"","institution":"East China university of technology, Nanchang Jiangxi","correspondingAuthor":false,"prefix":"","firstName":"Bing","middleName":"","lastName":"Pan","suffix":""},{"id":273621087,"identity":"a0011f15-0562-46e5-9be6-6837b1086277","order_by":2,"name":"Hua zhang","email":"","orcid":"","institution":"Chinese Academy of Geological Sciences","correspondingAuthor":false,"prefix":"","firstName":"Hua","middleName":"","lastName":"zhang","suffix":""},{"id":273621088,"identity":"a71b2705-d5ed-4b22-97af-747abccfe60e","order_by":3,"name":"Chenglin Liu","email":"","orcid":"","institution":"China University of Geosciences","correspondingAuthor":false,"prefix":"","firstName":"Chenglin","middleName":"","lastName":"Liu","suffix":""},{"id":273621089,"identity":"86e83e63-dddb-4266-90ea-823c9c5243f1","order_by":4,"name":"M. Santosh Santosh","email":"","orcid":"","institution":"The University of Adelaide.Adelaide","correspondingAuthor":false,"prefix":"","firstName":"M.","middleName":"Santosh","lastName":"Santosh","suffix":""},{"id":273621090,"identity":"0e322c6e-fa93-4ce5-9f79-557bb07b442c","order_by":5,"name":"zhen Yang","email":"","orcid":"","institution":"China University of Geosciences","correspondingAuthor":false,"prefix":"","firstName":"zhen","middleName":"","lastName":"Yang","suffix":""}],"badges":[],"createdAt":"2024-01-31 09:14:09","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3913270/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3913270/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":51452315,"identity":"77eee729-1a0b-4f81-9740-d1e279e3d3b7","added_by":"auto","created_at":"2024-02-21 21:49:30","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":991731,"visible":true,"origin":"","legend":"\u003cp\u003eSimplified geology of the study area and location of core SB18\u003c/p\u003e","description":"","filename":"fig1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3913270/v1/8df514e217b96ff4d5ef2bdd.jpg"},{"id":51452316,"identity":"3549386f-5af4-4602-ad75-1d5b952995c8","added_by":"auto","created_at":"2024-02-21 21:49:30","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":943025,"visible":true,"origin":"","legend":"\u003cp\u003eGeneralized stratigraphic sequences, sedimentation facies of the Subei basin\u003c/p\u003e\n\u003cp\u003e( Age data are base on\u003csup\u003e[28]、[29] \u003c/sup\u003eMajor reflectors and tectonic events are marked.Courtesy of the Jiangsu oilfield Company (Sinopec)\u003c/p\u003e","description":"","filename":"fig2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3913270/v1/b89eced8b3c4dccf3287418b.jpg"},{"id":51452320,"identity":"e8642e22-d137-40ce-9fa2-60e7b46d1011","added_by":"auto","created_at":"2024-02-21 21:49:30","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":3236628,"visible":true,"origin":"","legend":"\u003cp\u003eLithology of core sb18 and Samples Pictures\u003c/p\u003e","description":"","filename":"fig3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3913270/v1/35ef7ac1e08f08fa9c421890.jpg"},{"id":51452319,"identity":"3876464d-d658-46fd-a722-a9640c113adb","added_by":"auto","created_at":"2024-02-21 21:49:30","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1038883,"visible":true,"origin":"","legend":"\u003cp\u003ePrimary fluid inclusions in the Lower member of Funing formation\u003c/p\u003e","description":"","filename":"fig4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3913270/v1/fabe0b4e4e690f6ef58b3e75.jpg"},{"id":51452374,"identity":"91088089-b7ca-4e2c-899b-91da31e03519","added_by":"auto","created_at":"2024-02-21 21:57:30","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1080361,"visible":true,"origin":"","legend":"\u003cp\u003eChanges of primary fluid inclusion during the “cooling nucleation process”\u003c/p\u003e","description":"","filename":"fig5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3913270/v1/c54b6b9bf31be07850dfad52.jpg"},{"id":51452322,"identity":"0924813e-a9d0-45cd-92cb-be62155340fc","added_by":"auto","created_at":"2024-02-21 21:49:30","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1116829,"visible":true,"origin":"","legend":"\u003cp\u003eHistogram of homogenization temperature plotted against number of fluid inclusions.\u003c/p\u003e","description":"","filename":"fig6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3913270/v1/f961fa9797b0d2a05634f943.jpg"},{"id":51452323,"identity":"f4107a42-5f76-458a-ac6a-289220d95df4","added_by":"auto","created_at":"2024-02-21 21:49:31","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":941840,"visible":true,"origin":"","legend":"\u003cp\u003eHistogram of homogenization temperatures plotted against size of inclusions.\u003c/p\u003e","description":"","filename":"fig7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3913270/v1/480390ab5ed05cf534b58d4f.jpg"},{"id":51452479,"identity":"ce029b2a-fb70-40ce-be2b-6d916204bf8f","added_by":"auto","created_at":"2024-02-21 22:05:30","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":999283,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3913270/v1/b3d59e77-b309-4ff2-a85d-8311ec7c3853.pdf"},{"id":51452314,"identity":"26cbf38d-5060-4317-9e8b-7f2c27e93f9f","added_by":"auto","created_at":"2024-02-21 21:49:30","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":21109,"visible":true,"origin":"","legend":"","description":"","filename":"table1.docx","url":"https://assets-eu.researchsquare.com/files/rs-3913270/v1/cd66464ece3a66ff1be4b320.docx"},{"id":51452317,"identity":"b3763065-f2f0-425c-8578-41ceb4f48486","added_by":"auto","created_at":"2024-02-21 21:49:30","extension":"xlsx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":10008,"visible":true,"origin":"","legend":"","description":"","filename":"table2.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-3913270/v1/145baa15a4378a89c0788596.xlsx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Late Paleocene Paleoclimate recorded in halite deposits in Subei basin ,East China","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eThe Paleocene-Early Eocene warm climate period (65\u0026thinsp;\u0026minus;\u0026thinsp;50 Ma). The Paleocene climate was relatively warm, with global deep-sea temperatures about 8\u0026deg;C higher than today\u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]\u003c/sup\u003e, oxygen isotopes was lower\u003csup\u003e[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e, and atmospheric carbon dioxide concentration similar to today's atmospheric carbon dioxide concentration (390 ppm)\u003csup\u003e[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e. However, with the passage of time, the global deep sea temperature continued to increase and δ\u003csup\u003e18\u003c/sup\u003eO further decreased. Around 55 Ma, the atmospheric CO\u003csub\u003e2\u003c/sub\u003e concentration began to rise sharply. The ancient air temperature rose sharply in a short period of time. The deep sea temperature exceeded 10\u0026deg;C. Carbon isotopes and Oxygen isotopes are negatively biased, but this process lasts for a short time, less than 0.01 Ma \u003csup\u003e[2、3]\u003c/sup\u003e, and is the Paleocene-Eocene Thermal Maximum (PETM) event\u003csup\u003e[2、4、5、6、7、8]\u003c/sup\u003e. After the PETM event, the paleotemperature continued to increase and entered the climate optimal period of the Early Eocene. During this period, the δ18O and δ13C values were negatively biased, the temperature reached the highest point since the Cenozoic\u003csup\u003e[2、9、10、11]\u003c/sup\u003e, and the deep-sea temperature was about 12\u0026deg;C higher than today\u003csup\u003e[1、12]\u003c/sup\u003e. The plane height has also reached the highest level since the Cenozoic Era, 50\u0026ndash;100 m or even higher than today\u003csup\u003e[6、13]\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eEvaporites are mainly formed in dry and hot climate environments and are a good analytical indicator of paleoclimate \u003csup\u003e[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e. Evaporites were formed on the earth, indicating that they can directly record the temperature, chemical composition of ancient water bodies, and biological conditions at that time \u003csup\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/sup\u003e). The fluid inclusions formed during the crystallization process of halite seal the paleoenvironmental information at that time\u003csup\u003e[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e. In recent years, with the intensification of the earth's greenhouse effect and the continuous occurrence of abnormal climate, the evolution of the ancient environment has become one of the focuses of research. The uniform temperature of the original fluid inclusion of halite can reflect the ancient water temperature when the halite crystallized \u003csup\u003e[17、18]\u003c/sup\u003e. This method has been widely used at home and abroad \u003csup\u003e[20、21、22、17]\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e[21]Meng (2011) studied the inclusions of synthetic halite in the laboratory and concluded that the primary fluid inclusions in halite exist in funnel crystals formed at the air-water interface and herringbone crystals formed at the bottom of the water. Both can be used To reflect the temperature of the ancient environment, and only the maximum uniform temperature is closest to the temperature when the brine crystallized.\u003csup\u003e]\u003c/sup\u003e Zhao\u003csup\u003e[22\u003c/sup\u003e and others\u003csup\u003e[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e) conducted comparative experiments on the uniform temperature of a single liquid inclusion in halite rock under different freezing conditions and different high temperature conditions and showed that: without experiencing high temperature (110\u0026deg;C) and low temperature (-20\u0026deg;C) freezing Under interference conditions, the homogenization temperature of a single liquid inclusion in halite obtained at a slow heating rate (usually less than 1\u0026deg;C/min) can represent the ancient water temperature when the halite was formed.\u003c/p\u003e \u003cp\u003eIn this study of the salt-bearing system of the 4th member of the Funing Formation in the Hongze Sag of the Subei Basin, the author found that halite rocks contain a large number of primary fluid inclusions, which provides important materials for studying ancient water temperatures. This article carries out homogeneous temperature analysis on these primary halite inclusions to reveal the paleowater temperature characteristics of the Hongze Sag in the Subei Basin and explore its paleoclimate significance, which is an important reference for studying climate changes in the early Paleogene.\u003c/p\u003e"},{"header":"2 Study area","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Geological Setting\u003c/h2\u003e \u003cp\u003eThe Subei Basin is the onshore part of the North Subei-Yellow Sea Basin in eastern China. It is located northeast of the Yangtze Platform, bordering the Binhai Uplift and the Sulu Orogenic Belt to the north, the South Jiangsu Uplift and the Zhangbaling Uplift to the south, and the Tanlu Fault Zone to the west. It reaches the Yellow Sea in the east and covers an area of approximately 4.2✕104 km2. There are abundant structural units in the area, which are generally represented by a series of asymmetric fault depressions with \"south fault and north superposition\", and a basic structural pattern of secondary basins of \"two depressions and one uplift\" running east-west, which can be divided from north to south into: Yanfu Depression-Jianhu Uplift-Dongtai Depression (Fig.\u0026nbsp;1). Bounded by the Jianhu uplift in the middle of the basin, the area to the north to the Binhai uplift is called the Yanfu Depression, and to the south to the South Jiangsu uplift area is called the Dongtai Depression.\u003c/p\u003e \u003cp\u003eThe Hongze Sag is located in the northwest of the Subei Basin, adjacent to the Lusu Uplift to the north, the Dengma Fault to the south, the Jianhu Uplift and the Zhangbaling Uplift, the Nihuzhuang Fault to the east to the Huai'an Uplift, and the West to the Huai'an Uplift. Bounded by the Zhenglu Fault Zone, it runs northeast and is a Mesozoic and Cenozoic skip-shaped fault depression that is thicker in the south than in the north and thicker in the north than in the north. The sag began to receive sedimentation from the Cretaceous, and reached its peak in the Paleogene and Neogene, with a cumulative sedimentary thickness of up to 5,800 meters. Drilling in the area revealed that the Upper Cretaceous Pukou Formation, Chishan Formation, Paleogene Taizhou Formation, Funing Formation, Dainan Formation, Sanduo Formation, Neogene Yancheng Formation and Quaternary Dongtai Formation. The sag is a compound sag with alternating depressions and uplifts. From the southwest to the northeast, it is the Jinli sub-sag, the Guanzhen sub-sag, and the Zhaoji sub-sag. The rock salt deposits occur in the fourth section of the Funing Formation in the Zhaoji sub-sag. The secondary sag and Guanzhen secondary sag are dominated by gypsum-containing mudstone, and no salt rock deposits have been found.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;1 Simplified geology of the study area and location of core SB18\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;1 is about here\u003c/p\u003e \u003cp\u003eThe Upper Cretaceous-Cenozoic strata of Hongze sag show the following stratigraphy from the bottom to the top(figure2 ): the Upper Cretaceous Pukou Formation, Chishan Formation and Taizhou Formation; the Palaeogene Funing Formation, Dainan Formation, and Sanduo Formation; and the Neogene Yancheng Formation and the Quaternary Dongtai Formation \u003csup\u003e[24、25、26]\u003c/sup\u003e. Compared with other depressions in the Subei basin, a section of the Neogene Yancheng Formation is missing. At present, all the stratigraphic sections of the Hongze sag have been revealed.\u003c/p\u003e \u003cp\u003eThe Funing formation can be divided into four members (E\u003csub\u003e1\u003c/sub\u003ef\u003csub\u003e1\u003c/sub\u003e-E\u003csub\u003e1\u003c/sub\u003ef\u003csub\u003e4\u003c/sub\u003e) from bottom to top \u003csup\u003e[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]\u003c/sup\u003e. The first member (E\u003csub\u003e1\u003c/sub\u003ef\u003csub\u003e1\u003c/sub\u003e) consists of a set of fluvial-deltaic deposits and the E\u003csub\u003e1\u003c/sub\u003ef\u003csub\u003e2\u003c/sub\u003e is recognized as a set of lacustrine deposits, of which the lithology is dominantly dark gray\u0026ndash;black mudstones/shales interbedded with marls, limestone and dolomite. The E\u003csub\u003e1\u003c/sub\u003ef\u003csub\u003e3\u003c/sub\u003e is composed of deltaic deposits, and the lithology of E\u003csub\u003e1\u003c/sub\u003ef\u003csub\u003e4\u003c/sub\u003e is saline mineral layers\u003csup\u003e[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]\u003c/sup\u003e. The E\u003csub\u003e1\u003c/sub\u003ef\u003csub\u003e4\u003c/sub\u003e saline formation mainly developed halite-rich rock, sulfate rock and a small amount of carbonate rock. The halite and sulfate mineral layers are relatively thick\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;2 Generalized stratigraphic sequences, sedimentation facies of the Subei basin\u003c/p\u003e \u003cp\u003e( Age data are base on\u003csup\u003e[28、29]\u003c/sup\u003e Major reflectors and tectonic events are marked.Courtesy of the Jiangsu oilfield Company (Sinopec)\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;2 is about here\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Lithology and Stratigraphy of Core SB18\u003c/h2\u003e \u003cp\u003eThe lithology of Core SB18(Fig.\u0026nbsp;3) consist of distinct evaporitic-evaporitic\u0026ndash;siliciclastic cycles which represent the lower Members of Funing formation which are widely distributed throughout the Subei basin. These members are mainly composed of evaporites separated by carbonate and sulfate. According to the color of halite recrystallization, orange and gray varieties are recognized. The orange halite is mostly medium- and fine-grained halite, while the gray halite is mostly fine-grained halite with a small amount of anhydrite.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;3 is about here\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;3 Lithology of core sb18 and Samples Pictures\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Method","content":"\u003cp\u003eMost of the primary inclusions in the studied samples are single-phase aqueous liquid inclusions at room temperature, though some are two phase inclusions containing gases or solids. Before undertaking the \u0026lsquo;cooling nucleation\u0026rsquo; process, we recorded their photographs in order to distinguish inclusions with gas bubbles at room temperature from inclusions in which vapor bubbles were artificially nucleated after cooling. Other studies that observed gas bubbles at room temperature prior to cooling have interpreted the bubbles to be trapped atmospheric air, and noted that they produce homogenization temperatures that are unrealistically high \u003csup\u003e[14、19、21、30]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eDuring the preparation process of fluid inclusion sheets, in order to avoid changes in the original temperature information of the halite inclusions caused by the cutting and grinding and polishing processes, the processing of the inclusion test samples was based on the methods of \u003csup\u003e[17、18]\u003c/sup\u003e. First use a knife to cut the halite particles along the cleavage plane to obtain a thickness .Halite cleavage pieces of 5 to 1 mm. The cleavage slices were observed and photographed under a microscope, focusing on recording the occurrence and shape of fluid inclusions formed by primary and early diagenetic recrystallization, and focusing on photographing single liquid inclusions(Fig.\u0026nbsp;4). Then seal it with a plastic zip lock bag, put it into a well-sealed plastic box, put in desiccant for protection, and freeze it in the refrigerator for about 1 week (the temperature in the refrigerator has been stabilized at -18\u0026deg;C after multiple measurements), and wait until single The homogenization temperature is measured after bubbles appear in the liquid inclusions when they are frozen and nucleated. The test of uniform temperature was completed using the Linkam THMSG600 hot and cold stage, using a heating rate of 0. 5\u0026deg;C/min, which was reduced to 0. 1 to 0. 2\u0026deg;C/min when the bubbles gradually became smaller and closer to uniformity. )\u003c/p\u003e \u003cp\u003eRegarding how to determine whether the bubbles in the inclusions have really disappeared, that is, they have reached uniformity, or whether the bubbles have become smaller in size and are difficult to observe under the microscope due to problems with the accuracy of the microscope, causing the illusion of uniformity, it can be verified by the following method: Lower the temperature again 10\u0026thinsp;~\u0026thinsp;15℃, if the bubbles still exist, the volume of the bubbles will grow again until they are visible in the field of view, and the bubbles will not reappear even if the fluid inclusion reaches a completely uniform temperature and is cooled again by 10\u0026thinsp;~\u0026thinsp;15℃ \u003csup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e​\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;4 Primary fluid inclusions in the Lower member of Funing formation\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;4 is about here\u003c/p\u003e"},{"header":"4 Results","content":"\u003cp\u003eNucleated vapor bubbles after cooling were observed in less than15% of primary single phase liquid fluid inclusions of the halite samples(Fig.\u0026nbsp;5). The recorded Th (temperature of homogenization) data are summarized in Table\u0026nbsp;1.In total, 488 homogenization temperature data were obtained from nucleated vapor bubbles in the first round, with a maximum Th of 52.3\u0026deg;C and a minimum Th of 17.7\u0026deg;C. About 70% of the Th data are in the range from 30\u0026ndash;50\u0026deg;C. The Th ranges of the six stratigraphic intervals are 17.7\u0026ndash;41.1\u0026deg;C(1754.87 m),21.549.2\u0026deg;C (1756.82 m), 21.2\u0026ndash;51.2\u0026deg;C (1758.61 m), 25.7\u0026ndash;51.2\u0026deg;C(1759.58 m), 26.7\u0026ndash;48.7\u0026deg;C (1760.52 m) ,28.1\u0026ndash;50.1\u0026deg;C(1763.57m༉,25.1\u0026ndash;45.3༈1768.21m༉and 28.4\u0026ndash;50.1\u0026deg;C (1770.31 m), respectively. All samples yielded similar maximum homogenization temperatures or temperature ranges for cumulate crystals and chevron crystals(Fig.\u0026nbsp;6༉. More than 96% of fluid inclusion assembles (FIA) have ranges of homogenization temperatures that fall within 15\u0026deg;C and more than 90% of fluid inclusion assembles have ranges that fall into an even smaller interval of less than 20\u0026deg;C (more than 90%). Details of this data are shown in Fig.\u0026nbsp;6 and listed in Table\u0026nbsp;1.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;5 Changes of primary fluid inclusion during the \u0026ldquo;cooling nucleation process\u0026rdquo;\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;5 is about here\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;1 is about here\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;1 Homogenization temperatures of halite fluid inclusions of the Funing Formation\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;6. Histogram of homogenization temperature plotted against number of fluid inclusions.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;6 is about here\u003c/p\u003e"},{"header":"5 Discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e5.1 Rationality and stability of Th data\u003c/h2\u003e \u003cp\u003eDue to the deliquescence and solubility of halite, it is easily damaged or recrystallized during its burial and preservation, which will affect the rationality and stability of Th data, especially for ancient halite samples \u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e. The Th data do not need to be pressure corrected because halite was deposited in a shallower depositional environment and the temperature trapped by fluid inclusions at low pressure is approximately equal to Th, thus providing a direct temperature record of halite deposition. From the same inclusion Primary fluid inclusions in the growth zone are captured at the same time \u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e. However, multiple primary fluid inclusion bands in well-developed halite crystals may not form at the same time, such as in the morning and evening of the same day. Therefore, Th data from different inclusion bands are acquired at different temperatures \u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eWe use two methods to verify whether native fluid inclusions undergo changes or disruptions in thermal reequilibration, including thermal reequilibration analysis of Th data and the relationship between fluid inclusion size and Th. On the one hand, in a given FIA The consistency of Th data can be used as an indicator to evaluate thermal reequilibration \u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e noted that approximately 90% of Th data in a single FIA fluctuated within a range of less than 15\u0026deg;C, indicating primary fluid inclusions Has not undergone changes or disruptions in thermal rebalancing.\u003c/p\u003e \u003cp\u003eOn the other hand, the relationship between fluid inclusion size and Th can also act as another criterion for determining possible alteration from thermal reequilibration. Large inclusions are more extensible than smaller inclusions, and fluid inclusions that were subjected to extension have higher Th than actual capture temperature \u003csup\u003e[31、32、33]\u003c/sup\u003e. In other words, if inclusions have undergone extension, then large inclusions are more likely to yield higher Th than small ones. Our results show no relationship between fluid inclusions size and corresponding Th (Fig.\u0026nbsp;7). The Th data, therefore, show no alteration or damage by thermal reequilibration, which further supports that the data are reliable for paleotemperature interpretations. We thus conclude that Th data presented here from halite of the Funing Formation are likely to accurately reflect Late paleocene seawater temperatures.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;7 Histogram of homogenization temperatures plotted against size of inclusions.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;7 is about here\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e5.2 Record of paleotemperature by halite fluid inclusions\u003c/h2\u003e \u003cp\u003ePrimary fluid inclusions in halite are usually contained in cumulate and chevron crystals. Cumulate crystals often precipitate at the airewater interface or within the upper water column and later sink to the bottom under the effect of gravity\u003csup\u003e[17、19、23]\u003c/sup\u003e, Chevron crystals are vertically oriented bottom-growth crystals which precipitate in shallow water \u003csup\u003e[33、34]\u003c/sup\u003e. Therefore, the homogenization temperatures of fluid inclusions from both cumulate crystals and chevron crystals record brine surface temperatures during halite deposition or approximate surface air temperatures in the case of shallow environments \u003csup\u003e[17、20、34、35、36、23]\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eAlthough all homogenization temperature data represent surface brine or shallow water temperatures, it cannot be expected that the complete temperature variation of surface brines will be captured based on homogenization temperatures of halite fluid inclusions no matter how many homogenization temperature data were analyzed and how large a sample is. This insufficient reconstruction of the full temperature range results from the fact that salts and contained fluid inclusions do not form at constant rates over the full daily and seasonal temperature variation range. Salt formation is usually higher during daytime, especially the afternoon, and during summer \u003csup\u003e[17、19、18]\u003c/sup\u003e In addition, the formation of salt reflects not only temperatures but also factors such as humidity and wind velocity \u003csup\u003e[19、33]\u003c/sup\u003e. More importantly, only a limited number of the millions of fluid inclusions in an individual sample can artificially nucleate vapor bubbles, and thus, can be used for Th measurements. These observations imply that the ranges of homogenization temperatures may best represent the average temperature conditions during halite deposition \u003csup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e5.3 Comparison with modern evaporative environments\u003c/h2\u003e \u003cp\u003eRobert\u003csup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e reported the homogenization temperatures from modern halite precipitated in April to May and August at Badwater Basin, Death Valley, California. These Th fall in two ranges (25\u0026ndash;39 ◦C and 45\u0026ndash;49 ◦C) that are very close to the temperature of brine recorded in April to May (20\u0026ndash;38 ◦C) and August (43\u0026ndash;50 ◦C). As discussed above, our results are more likely to reflect seasonal temperature variations and have similar Th distribution pattern to those by Roberts and Spencer (1995).\u003c/p\u003e \u003cp\u003eThe lack of Th data from the lowest brine temperature (20 ◦C) to the lowest Th (25 ◦C) was interpreted due to the absence of halite formation at a low temperature and low diurnal evaporative conditions\u003csup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e. Thus, the low temperature ranges in this study is more likely to characterize a low temperature and strong evaporation environment. Lowenstein\u003csup\u003e[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e pointed out that only the maximum Th in \u0026ldquo;laboratory grown halite\u0026rdquo; matches the temperature of brine from which the halite was precipitated, denoting lower Th data of a certain range would be unreliable. \u003csup\u003e[\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]\u003c/sup\u003eLiu reported both extremely higher and lower Th than the temperature of brines from both laboratory and natural halite, but the deviations were considered to be due to the sample pretreatment process of using a saw for polishing. Nonetheless, the extremely low Th compared to the brine temperature was not observed in halite samples with proper pretreatments from modern natural settings\u003csup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e. Although some discrepancies exist in the measured water temperature values from where the halite was precipitated, but they are still close to the air temperature\u003csup\u003e[17、18、19、38]\u003c/sup\u003e. Therefore, the paleotemperature annual fluctuations during the deposition of halite at 1754.87\u0026ndash;1770.31 m of E\u003csub\u003e1\u003c/sub\u003ef\u003csub\u003e4\u003c/sub\u003e (56 Ma) in well sb18 in the Subei Basin can be considered from17.7-52.3◦C (Table\u0026nbsp;1). In colder months, air temperature has varied from 17.7 to 32.1 ◦C, whereas it has been from 26.8 to 52.3 ◦C in warmer months. Some of the Th recorded values between 21.75 and 40.37 ◦C (Fig.\u0026nbsp;6) reveal a sharp temperature transition from cold to warmer seasons in a year, or possibly no halite precipitation in spring and autumn(Table\u0026nbsp;2).\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;2 is about here\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;2 Th values range in cumulate and chevron crystals\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e5.4 Local and regional climate conditions during the Late Paleocene\u003c/h2\u003e \u003cp\u003eDuringthe Late Paleocene, The characteristics of the plant pollen in assemblage\u003cem\u003e(Ulmipollenites minor\u003c/em\u003e;\u003cem\u003eUlmipollenites; Subtriporopollenites; Quercoidites;Rhoipites; Retitricolpites\u003c/em\u003e ) in Subei basin indicate that the plants during the deposition period of the Funing Formation were high-temperature tolerant plants, and the climate at that time was arid-hot \u003csup\u003e[39、40、41]\u003c/sup\u003e. The analysis of paleomagnetic data during the Funing Formation period of Subei Basin shows that the average paleolatitude is between 10.5 and 23.9\u0026deg;N, which suggests a location in the low-middle latitude region. Our study of the homogenization temperature of fluid inclusions on halite also shows that the paleotemperature was high during Late Paleocene.\u003c/p\u003e \u003c/div\u003e"},{"header":"6. Conclusions","content":"\u003cp\u003eThe fluid inclusion composition analysis and the appearance of cumulate and chevron halite crystals in the same beds indicate the massive halite that is deposited in the Funing Formation of the Subei Basin were not originated from seawater intrusions but were formed in a shallow, certainly centimeter scale water depth, lake environment.\u003c/p\u003e \u003cp\u003eWe obtained quantitative Late Paleocene paleotemperature records by measuring the Th data of primary fluid inclusions in halite crystals. The average paleotemperature is 34.11\u0026deg;C, with the highest value being 52.3\u0026deg;C\u0026deg;C and the lowest at 17.7\u0026deg;C. This shows that the temperature of the ancient salt lake water was relatively high at that time. It can also be seen from the correspondence between paleowater temperature and paleo air temperature that the climate of the Hongze Sag in the Northern Subei Basin corresponds to the high temperature characteristics during the Paleocene.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eTing Ding do the writing and the idea. Bin pan drawed the figure , Hua Zhang and M. Santosh modify the paper , Chenglin Liu give the idea. Yang zhen did the field work.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThis study was supported Major State Basic Research Development Program of China(NO.2023YFC2906603) and The Major Science and Technology Projects of Xinjiang (41972092), and The Third Xinjiang Scientific Expedition Program (2022xjkk1303).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBeerling, D.J., Royer, D.L., 2011. Convergent Cenozoic CO2 history. Nature Geofenced. 4(7): 418\u0026ndash;420.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZachos J. C., Pagani M., Sloan L., 2001. Trends, rhythms, and aberrations in global climate 65 Ma to present. Science, 292(5517), 686\u0026ndash;693.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLuo, L., 2017. 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The research on the homogenous temperatures of inclusions in halite from the isothermal evaporation of brine and natural halite from lop nor playa, xinjiang, china.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRigaudier, T., Christophe L\u0026eacute;cuyer, V\u0026eacute;ronique Gardien, Suc, J. P., \u0026amp; Martineau, F., 2011. The record of temperature, wind velocity and air humidity in the delta d and delta(18)o of water inclusions in synthetic and messinian halites. Geochimica Et Cosmochimica Acta, 75(16), 4637\u0026ndash;4652.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSong, Z.S., Z, Y.H., L, J.L., et al., 1981. Cretaceous-tertiary palynous assemblage in Jiangsu area. Geological Publishing House. 1\u0026ndash;268 (in Chinese with English abstract).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang, Q.S., 1989. The age and contact relationship of the first member of the Taizhou Formation and Funing Formation in northern Jiangsu Basin. Nanjing University Press. 1\u0026ndash;32 (in Chinese with English abstract).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhu, Y.H., Yan, S.M., Yang, X.Q., 2004. The upper cretaceous to Paleogene micropalaenotological stratigraphy and palaeoenvironment of the well D1 in the Gaoyou depression,North Jiangsu Basin. Acta Micropalaenotologica Sinica. 21(3),267\u0026ndash;272(in Chinese with English abstract).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTable 1 and 2 are available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"halite, fluid inclusions, homogenization temperature, paleoenvironment, Late Paleocene, Subei basin","lastPublishedDoi":"10.21203/rs.3.rs-3913270/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3913270/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSalt deposits correspond to relatively extreme climate events. However, due to insufficient independent temperature proxies, there is a lack of paleotemperature records obtained from salt laminae deposition .The Paleocene evaporite sequence deposited in the Hongze Depression of Subei Basin provides an important terrestrial sediment record during this period. In this study we carry out a detailed fluid inclusion study on halite crystals in these rocks and present total of 488 homogenizaton data from eight samples. The results show temperatures ranging from 17.7\u0026deg;C to 52.3\u0026deg;C, and the mean T\u003csub\u003eh\u003c/sub\u003e value of 34.1\u0026deg;C is in good agreement with the previous studies of climatic proxies. Our study shows that fluid inclusions can be used as a robust tool to construct the ancient earth surface temperature.\u003c/p\u003e","manuscriptTitle":"Late Paleocene Paleoclimate recorded in halite deposits in Subei basin ,East China","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-02-21 21:49:25","doi":"10.21203/rs.3.rs-3913270/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-05-03T07:14:12+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-04-25T19:11:28+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"5394ad8d-d960-455b-8add-e74161c8cfc8","date":"2024-04-24T21:36:03+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-03-15T10:26:43+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"8fd29423-2f17-41dc-b8b6-5cee4dbe5a30","date":"2024-02-26T00:28:44+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"644a6ef1-22e6-4172-b69d-88350371d5a3","date":"2024-02-22T12:27:22+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-02-22T08:49:17+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-02-22T08:47:27+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2024-02-19T04:48:26+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-02-19T04:40:04+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2024-01-31T09:05:48+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"824c3bf4-6911-4c41-9260-ffb991549cf8","owner":[],"postedDate":"February 21st, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":28832426,"name":"Earth and environmental sciences/Climate sciences/Palaeoclimate"},{"id":28832427,"name":"Earth and environmental sciences/Solid earth sciences/Geochemistry"},{"id":28832428,"name":"Earth and environmental sciences/Solid earth sciences/Geology"},{"id":28832429,"name":"Earth and environmental sciences/Solid earth sciences/Sedimentology"}],"tags":[],"updatedAt":"2024-07-02T10:14:23+00:00","versionOfRecord":[],"versionCreatedAt":"2024-02-21 21:49:25","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3913270","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3913270","identity":"rs-3913270","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}