Jianghan Basin Research Articles

Cenozoic surface Earth system evolution and dynamic paleogeomorphic reconstruction from the Tibet Plateau to the Western Pacific linked by the Yangtze River

The formation of the modern east-flowing Yangtze River is marked by the incision of the Three Gorges (TG) between the Sichuan and Jianghan basins. However, it is still controversial on the timing of the TG incision, due to diverse tectonic, sedimentological and geochemical records. These records, together with other geological data, i.e. curves of paleo-climate and sea level fluctuation, are critical parameters in the software Badlands , a tool to simulate large-scale and long-term geomorphic evolution. Using Badlands , we modeled the geomorphology and drainage evolutionary process of the Yangtze River since the Late Cretaceous (80 Ma). It revealed that the drainage system in the Sichuan Basin was gradually reversed from southward flowing to northward flowing during the Late Eocene and the Oligocene, due to the periodic uplift of the eastern Tibet Plateau and the southwestern Yangtze Block. Coevally, the Jianghan Basin experienced a base level drop, controlled by the collapse of a paleo-coastal mountain range and the subsequent continental rifting along the Southeast China continental margin. The tectono-geomorphic interplay eventually led to the incision of the TG at the Late Oligocene (about 24Ma), when the drainage system of the Upper Yangtze River was captured by the Middle-Lower Yangtze River.

An optimization framework with dimensionality reduction using Markov Chain Monte Carlo and genetic algorithms for groundwater potential assessment

Limited samples and high-dimensional feature spaces often hinder the accuracy of machine learning (ML) models in regional groundwater potential assessment (GPA). This study proposes a novel framework, the GPA with Dimensionality Optimization (GPADO), that optimizes feature dimension reduction to enhance prediction performance. Taking the Jianghan Basin as an example, data on nine continuous variables and five categorical variables influencing the region's GPA were gathered, expanding the feature set to 37 through One-hot encoding for categorical variables. Three scenarios were devised to assess prediction outcomes following various dimensionality reduction approaches. Comparative analysis revealed that a hybrid dimension reduction method, incorporating both continuous and categorical variables, yielded the highest validation set accuracy. Consequently, genetic algorithm and Markov Chain Monte Carlo methods were employed to determine the optimal solution and uncertainties associated with four unknown parameters: the chosen dimension reduction method for continuous and categorical variables, and the number of dimensions retained. Results indicated that utilizing singular value decomposition to reduce categorical variables to three dimensions, coupled with principal component analysis reducing continuous variables to three dimensions, produced the highest model validation accuracy of 0.834 within the GPADO framework. This optimal configuration facilitated automated ML training, resulting in a final validation set accuracy of 0.851 and a test set accuracy of 0.836. The resulting model provided a more precise spatial distribution of groundwater potential and demonstrated the GPADO framework's effectiveness in improving GPA accuracy, particularly in data-scarce regions. The GPADO framework offers a valuable approach for enhancing GPA studies.

Mechanisms of terrestrial organic matter accumulation across the Paleocene-Eocene thermal maximum in the Jianghan Basin, Central China

Marine settings provide major carbon sinks for organic carbon, and act as a key reservoir that can sequester excess carbon during times of high CO2 and global warming. Organic carbon burial in lake sediments also plays an important, but perhaps less appreciated, role in the global carbon cycle. However, the fate of organic carbon burial during times of increasing CO2 and rapid global warming in lacustrine settings is still unclear. This study investigates organic carbon accumulation and its mechanism during the globally significant Paleocene-Eocene Thermal Maximum (PETM, ∼56 Ma) hyperthermal event in the Jianghan Basin, China, based on organic and element geochemistry data. The PETM is identified in our studied rocks based on their broad age constraints and the presence of a 4.3‰ negative excursion in organic carbon isotope. Our study shows that organic carbon accumulation during the PETM in the Jianghan Basin might be mainly controlled by preservation conditions and sediment accumulation rates (SAR), which responded to changing hydrology/climate. A hot and humid climate during the PETM could lead to an increase in terrestrial input and SAR, which might dilute the overall organic matter concentration. Also, enhanced rainfall could contribute to the ventilation of the lake water and expedite the oxidation of organic matter, thus, contributing to relatively low organic matter concentration in the Jianghan Basin. In contrast, an arid and relatively low oxygen environment during the post-PETM interval of our studied section created conditions conducive to the retention of organic matter, resulting in high organic matter content. An examination of other terrestrial PETM records reveals that the poor preservation condition of the organic matter and higher SAR might also have been the primary factors for the low organic matter concentrations in PETM terrestrial sections at other subtropical and mid-latitude locations. Compared to marine settings, terrestrial settings may exhibit lower efficiency in sequestering excess CO2 from the atmosphere through organic carbon burial during the PETM.

Numerical simulation of CO2 storage by basalts in Xingouzui formation, Jianghan Basin, China

Sedimentary basins often develop large amounts of basalts, but there are few studies. The diagenetic history of basalts in sedimentary basins is different from that of continental flood basalts and deep-sea basalts. A large amount of basalt is developed in the Jianghan Basin. Minerals undergo varying degrees of alteration, such as the alteration of olivine into serpentine. Numerical simulations were used to study the interaction between basalt-CO2-formation water in the Xingouzui Formation. The effects of basalt alteration and CO2 injection mode (supercritical CO2, saturated CO2 water, co-injection of CO2 and water) on CO2 storage were investigated. The results show that the reactivity between unaltered basalt and CO2 is strong, and the maximum CO2 mineral trapping reaches 22–49 kg/m3 after CO2 injection for one month. However, the reactivity between the altered basalt and CO2 is obviously decreased. Compared with the unaltered basalt, the maximum CO2 mineral trapping for the altered basalt decreased by at least 15.4 % after CO2 injection for one year. For severely altered basalt with high serpentine content, the maximum CO2 mineral trapping even drops by more than 90 %. CO2 mineral trapping will be overestimated when the feedback of reservoir porosity and permeability changes on flow is not considered. The co-injection of CO2 and water can make full use of the advantages that water injection can promote CO2 dissolution and the resulting acidic environment is beneficial to mineral dissolution. This method could be an option after careful assessment of CO2 leakage risks and technical feasibility.

Differences and Causal Mechanisms in the Lithospheric Thermal Structures in the Cratons in East China: Implications for Their Geothermal Resource Potential

The thermal structure of the lithosphere is key to understanding its thickness, properties, evolution, and geothermal resources. Cratons are known for their low heat flow and deep lithospheric roots. However, present-day cratons in East China have geothermal characteristics that are highly complex, with variable heat flow values, diverging from the typical thermal state of cratons. In this study, we conducted a detailed analysis of the geothermal geological background of the cratons in East China, summarizing the thermal state and tectono-thermal processes of different tectonic units, calculating the temperature at various depths, and discussing differences in temperature and thermal reservoirs at different depths. The observed lithospheric thermal thickness within the North Jiangsu Basin and the Bohai Bay Basin is notably reduced in comparison to that of the Jianghan Basin and the Southern North China Basin. The phenomenon of craton destruction during the Late Mesozoic emerges as a pivotal determinant, enhancing the geothermal resource prospects of both the Bohai Bay Basin and the North Jiangsu Basin. Our findings contribute significantly to the augmentation of theoretical frameworks concerning the origins of heat sources in global cratons. Furthermore, they offer invaluable insights for the methodical exploration, evaluation, advancement, and exploitation of geothermal resources.

New insights on the retention and migration of shale oil within the hypersaline Qianjiang Formation in the Jianghan Basin, China

New insights on the retention and migration of shale oil within the hypersaline Qianjiang Formation in the Jianghan Basin, China

The Geochemical Characteristics and Environmental Implications of the Paleocene–Eocene in the Jiangling Depression, Southwestern Jianghan Basin

Various isotopic and palynological indicators have shown interspersed periods of aridity and humidity for the late Paleocene to early Eocene in central China, so the paleoclimate conditions remain unclear. This research investigates the environmental characteristics of a saline lake in the Jiangling depression, southwestern Jianghan Basin, from the Paleocene to the Eocene, using bulk-rock geochemistry in a 1280 m sediment core. The ratios of FeO/MnO, Al2O3/MgO, and C-value indicate a semi-humid to semi-arid climate in the early–middle Paleocene. There was a rapid shift to a humid climate during the late Paleocene to early Eocene, following a short time of intense dryness. The Eocene climate was arid, but experienced intermittent humidity. The variation trend of the CIA, CIW and PIA was similar to that of FeO/MnO, Al2O3/MgO, and the C-value, so chemical weathering of the surrounding rocks was controlled by climate change. The lake redox conditions in the Jiangling depression from the Paleocene to the Eocene were reconstructed using the ratios of U/Th, Ni/Co, and V/Cr. During humidity and alternations of aridity and humidity, the lake water received external water input, resulting in weak stratification, so the sediments were in oxidizing conditions. During aridity, lakes become endorheic, leading to sediments forming in reduced conditions. The salinity of the lake in the Jiangling depression from the Paleocene to the Eocene was determined through analysis of sedimentary sequences and the trend of the Sr/Ba ratio. In the early–middle Paleocene, lake salinity varied greatly. From the late Paleocene to the early Eocene, lake salinity decreased. In the Eocene, lake salinity increased and halite precipitated, but lake salinity finally decreased due to a humid climate. During the late Paleocene–early Eocene, the occurrence of multiple humid climates in the Jiangling depression were not merely regional effects. The most significant humidity was caused by a global hyperthermal (PETM), which caused a huge increase in precipitation in the whole of East Asia and even in low latitudes around the world.

Genesis of salt deposits in the Jiangling Sag, Jianghan Basin, China: Constraints from H, O, and C isotopes and fluid inclusions of evaporites

Due to Yanshan movement and Himalayan movement, a series of faulted basins were formed in the late Cretaceous and Paleogene, including Shashi Formation of Paleocene in Jiangling sag of Jianghan Basin, when a set of salt lake was deposited. Analysis of lacustrine carbonate rocks in Shashi Formation of Paleocene shows that the δ13CPDB values of carbonate rocks range from −4.8 ‰ to −1.0 ‰, with an average value of −3.3 ‰. The δ18OPDB values ranged from −5.4 ‰ to −0.6 ‰, with an average value of −3.2 ‰. The positive correlation between δ13CPDB and δ18OPDB of the Shashi Formation carbonate rocks indicates that they developed in a relatively closed brackish lake system with obvious evaporation. The homogenization temperature of the upper Shashi Formation in Jiangling sag ranges from 15.3 °C to 51.8 °C, mainly concentrated in 25–30 °C. The δ18O isotope of halite inclusions ranges from −0.8‰ to 9.4‰, with an average of 4.9‰. The δD isotope of halite inclusions ranges from −91.3‰ to −65.0‰ with an average of −79.3‰, which are all lower than the Global Meteoric Water Line. The intense evaporation environment is consistent with the overall drought paleoclimate at that time. The quantitative LA-ICP-MS was used to analyze the composition of the primary inclusion of halite, and it was concluded that the original brine composition was Na-K-Mg-Cl-SO4 system with relative low concentration of Ca2+, high concentration of Mg and SO42- ions and K ions. The high content of Li, B, Br and Rb is related to the intense volcanic activity, deep fluid source and hot spring recharge in Jiangling Depression at that time. Based on carbonate carbon and oxygen isotopes, fluid inclusions temperature and composition, it is concluded that during the Shashi Formation period of Paleocene in Jiangling Sag, the lake basin was well sealed, with high salinity and high temperature, and belonged to a salt lake sedimentary environment, which was favorable for the deposit of salt deposits.

Late Mesozoic Exhumation of the Huangling Massif: Constraints on the Evolution of the Middle Yangtze River

AbstractPlate subduction leads to complex exhumation processes on continents. The Huangling Massif lies at the northern margin of the South China Block. Whether the Huangling Massif was exhumed as a watershed of the middle reaches of the Paleo‐Yangtze River during the Mesozoic remains under debate. We examined the exhumation history of the Huangling Massif based on six granite bedrock samples, using apatite fission track (AFT) and apatite and zircon (U‐Th)/He (AHe and ZHe) thermochronology. These samples yielded ages of 157–132 Ma (ZHe), 119–106 Ma (AFT), and 114–72 Ma (AHe), respectively. Thermal modeling revealed that three phases of rapid cooling occurred during the Late Jurassic–Early Cretaceous, late Early Cretaceous, and Late Cretaceous. These exhumation processes led to the high topographic relief responsible for the emergence of the Huangling Massif. The integrated of our new data with published sedimentological records suggests that the Huangling Massif might have been the watershed of the middle reaches of the Paleo‐Yangtze River since the Cretaceous. At that time, the rivers flowed westward into the Sichuan Basin and eastward into the Jianghan Basin. The subduction of the Pacific Plate beneath the Asian continent in the Mesozoic deeply influenced the geomorphic evolution of the South China Block.

Eocene monsoon climate expansion in East Asia: Evidence from orbital‐cycle driven terrestrial successions in the Jianghan Basin, Central China

ABSTRACTEast Asia experienced complex climatic changes during the Eocene. Due to the lack of a high‐precision time framework covering the Eocene, the characteristics of sedimentary and climate evolution in this period remain unclear. The Jianghan Basin (Central China) developed an Eocene continental succession, which is composed of lower red beds and upper salt‐lake deposits exhibiting clear sedimentary rhythms, making these strata an ideal target for astronomical cycle analysis. Based on the established floating astronomical timescale, the lower red beds in the basin formed during the early–middle Eocene and were dominated by eccentricity cycles. The upper salt‐lake deposits formed during the middle–late Eocene and recorded obliquity cycles. The change in facies indicates that the climate transitioned from continuously arid to less arid with periodic relative wetness, which was forced by orbital cycles. Significant obliquity signals recorded by salt rhythmites responded to Eocene global temperature changes and Tibetan region uplift, which can be important markers of a monsoon‐like climate. Comparing the sedimentary and climatic characteristics of other Eocene lake basins in East Asia, the extension of the Eocene East Asian monsoon may have initiated during ca 43.6 to 40.0 Ma. This study provides a new perspective for understanding the early evolution of the East Asian monsoon.

Stepwise astronomical tuning of obliquity-driven evaporite cycles in an Eocene salt lake (Jianghan Basin, Hubei Province, China): Implications for middle Eocene East Asian monsoon-like climate evolution

The rhythmic evaporation cycle is an ideal recorder of astronomical cycle signals, but studies on cyclostratigraphy have yet to be directly conducted on halite-rich strata. The Qianjiang Depression of the Jianghan Basin is a representative Eocene East Asian halite-rich basin, and the salt rhythmites that developed therein are important recorders of climate evolution in East Asia. This study selected five wells for basin-scale cyclostratigraphy analysis, taking the Lower Qian 4 member of the Qianjiang Formation as the research object. This study found that the basinal salt lake facies were dominated by obliquity cycles, whereas the shallow-water deposits mainly recorded short eccentricity cycles. The study also found that s3−s6 obliquity cycles could be detected throughout the salt lake sedimentary record. Therefore, a stepwise astronomical tuning scheme was adopted. First, the target intervals in different sedimentary areas were preliminarily tuned to s3−s6 obliquity cycles, and stratigraphic correlation was performed. Then, the tuned data were further adjusted using obliquity cycles to reveal the impact of obliquity on the development of salt rhythmites and establish a floating astronomical time scale (ATS). Sedimentary noise models and pollen analysis further demonstrated that obliquity amplitude modulation cycles drove periodic changes in hydrology and climate. Based on the spatiotemporal distribution of salt rhythmite−rich strata in Paleogene East Asia, this study proposes that the development of rhythmic evaporites can reveal the existence of a monsoon-like climate. Astronomical influence was an important driving force for developing the middle Eocene East Asian monsoon.

Carbon Isotopic Behavior During Hydrocarbon Expulsion in Semiclosed Hydrous Pyrolysis of Type I and Type II Saline Lacustrine Source Rocks in the Jianghan Basin, Central China

Abstract Organic carbon isotopic analysis is a significant approach for oil-source correlation, yet organic carbon isotopic behavior during oil expulsion from saline lacustrine source rocks is not well constrained, and this hinders its wide application for fingerprinting oils generated by saline lacustrine source rock. To resolve this puzzle, semiclosed hydrous pyrolysis was conducted on typical saline lacustrine source rocks from the Qianjiang Formation (type I kerogen) and Xingouzui Formation (type II kerogen) sampled in the Jianghan Basin, China, under high-temperature high-pressure conditions (T = 275℃–400℃; P = 65–125 MPa). Experimental results show that there is minor carbon isotopic fractionation (<3‰) between pyrolyzed and nonpyrolyzed retained oil fractions during the main oil generation/expulsion stage of both type I and II source rocks. Carbon isotopic fractionations between expelled and retained oil fractions are also minor (<2‰) during this stage. The δ13C values of retained and expelled oil fractions generated by the type I saline lacustrine source rock correlate positively with the degree of oil expulsion, whereas the influence of oil expulsion on the δ13C values of oil fractions generated by the type II source rock was not consistent. In addition, carbon isotopic analysis also unravels the mixing of oil-associated gases with different maturity levels and/or generated via different processes. Outcomes of this study demonstrate that oil expulsion from type I and II saline lacustrine source rocks cannot be able to result in large-degree carbon isotopic fractionation, indicating that carbon isotopic analysis is a feasible approach for conducting oil-source correlation works in saline lacustrine petroleum systems.

Resolving Cenozoic climate pattern debate in East Asia: Insights from orbital-scale oscillations

Paleoclimate reconstruction and aeolian deposits in China indicate a major environmental reorganization – the formation of a nonzonal monsoon-dominated climate pattern – in East Asia in the late Oligocene and the early Miocene. In contrast, a zonal planetary-wind-dominated climate pattern has prevailed during the Paleocene and Eocene. However, this classical paradigm describing the climate transition has been questioned by recent studies. Here, our study emphasizes the importance of considering orbital-scale climate oscillations to better understand and reassess the paradigm. By examining the halite and mudstone sequence in the Jianghan Basin and conducting numerical experiments using the Norwegian Earth System model, we propose the concept of a “green Yangtze” phenomenon, which utilizes orbital-scale climate oscillations to reconcile the wet and dry environmental indicators in Eastern China during the Paleogene. It is essential to differentiate the Paleogene climate, characterized by intense orbital-scale wet and arid oscillations, from the Neogene monsoon-dominated climate. The classic paradigm remains valuable in understanding the long-term mean environment, albeit without capturing the orbital-scale details. Future research should focus on uncovering orbital-scale variations to enhance our understanding of climate evolution and dynamics in East Asia during the Cenozoic.

Origin of lithium in oilfield brines in continental petroliferous basin: Insights from Li and Sr isotopes in the Jianghan Basin, central China

Oilfield brines are a significant alternative lithium resource to meet the global demand in the next decades. However, their metallogenic characteristics and mechanism remain unclear. To constrain the source and enrichment process, this study presents chemical and multi-isotope data for oilfield brines from the Middle Eocene to Lower Oligocene Qianjiang Formation of the Jianghan Basin, central China. These formation water samples collected from 159 oil wells have salinities of 47–355 g/L and lithium contents of 5.36–150.00 mg/L. The good linear relationship between δD and δ18O values indicates that the salinities are achieved by dilution of the primary brine by meteoric water. Waters from the lower of the Qianjiang Formation have higher δD and δ18O values and 87Sr/86Sr ratios than those from the upper, in conjunction with the low correlation between the δD and δ18O value and the salinity and between the Sr content and the 87Sr/86Sr ratio, indicating the impact of associated water-rock interactions. Moreover, contributions from diagenetic processes of dolomitization, dissolution of evaporites and albitization are also indicated by the high Cl/Br mass and Na/Cl molar ratios and the Ca excess and Na deficit. Chemical geothermometers give reservoir temperature values of 118 °C and 138 °C on average for the oilfield brines from the upper and lower formation, respectively. The binary linear relationships between Li contents and TDS values and Br contents imply specific enrichment processes in addition to evapo-concentration. Variations in δ7Li values (+10.6‰–+21.3%) and 87Sr/86Sr ratios (0.709479–0.711516) were used to trace the process of Li enrichment in oilfield brines. The lower δ7Li values with more enriched Li in comparison to Na indicate a significant lithium input from clastic host rocks, which is also confirmed by the fact that more radiogenic waters have relatively lower δ7Li values. Overall, these results suggest that Li enrichment in the Qianjiang oilfield brines was generated by the interaction of Li-bearing minerals in the clastic host rocks with water formed by original evaporitic brines diluted by meteoric water. This work represents a significant role of lithium and strontium isotopic systematics in elucidating the Li origins of deep-seated oilfield brines in continental petroliferous basins.

Vegetation, hydrology, and quantitative monsoon precipitation since the Last Glacial Maximum in Central China

The Yangtze River Basin is a crucial region in the monsoon region of China, and reconstructing its hydrological and precipitation evolution is important for developing a more robust understanding of the evolution of the East Asian Summer Monsoon. A pollen record from a strata profile (JZ2010) in the Jianghan Basin of Central China reveals variations in paleovegetation and paleoenvironmental and paleoclimatic conditions covering the last 24 cal kyr BP at ~90 years resolution. We perform a quantitative precipitation reconstruction (based on a weighted averaged partial least squares method). Results of the study show that the vegetation in the region experienced a succession from coniferous and broad-leaved mixed forest to evergreen and deciduous mixed forest and then to secondary coniferous forest. Over the past 24 kyr, the climate was relatively dry during the deglacial period, particularly during HS1 and the Younger Dryas cold event, interrupted by a warm and humid Bølling-Allerød. Precipitation in the early Holocene was at its maximum, peaking between 10.0 and 7.0 cal kyr BP followed by drier conditions between 6.5 and 4.5 cal kyr BP. Subsequent wetter conditions lasted until 3.8 cal kyr BP, after which precipitation gradually declined. Overall, the quantitative precipitation reconstruction is consistent with other proxy-based precipitation reconstructions in the Yangtze River region. However, the temporal pattern of variations in precipitation is distinct from that of the northern China monsoon region, where the precipitation peak occurred during the mid-Holocene. The study suggests that, prior to the Holocene, climate change was controlled by insolation dynamics and high latitude teleconnections, while during the Holocene it was primarily influenced by low latitude teleconnections, including the El Niño-Southern Oscillation, which controlled the dipolar rainfall pattern in the monsoon region of China. The high resolution record of changing climate in the East Asian monsoon region over a period spanning the LGM and Holocene provides a useful benchmark for modelling future precipitation change in southern and northern China against the background of global warming.

A novel method for quantitative evaluation of oil content and mobility in shale oil reservoirs by NMR logging: a case study of the inter-salt shale oil in the Jianghan Basin

The evaluation of oil content and mobility in shale oil reservoirs is the key to the optimization of the "sweet spot" of shale reservoirs and the evaluation of available resources. In order to address the challenge of quantitative evaluation of oil content and mobility in shale oil reservoirs, a combined multi-temperature pyrolysis and NMR experimental platform and experimental procedure are innovatively designed and implemented in this paper. The experiments reveal the NMR T2 distribution characteristics of hydrocarbon components in different reserve states. Accordingly, the NMR T2 cutoff values of different hydrocarbon components are determined, and the quantitative evaluation method based on NMR logging for total oil content and movable hydrocarbon content is established. The method has been applied to the inter-salt shale oil BYY2 well in Jianghan Oilfield, and the results show that the total porosity of the shale reservoir in the Qian 4 sub-Member is similar, but the total hydrocarbon content (0.04 g/kg∼16.0 g/kg) and the movable oil content (0.02 g/kg∼4.9 g/kg) are significantly different. Compared with the preferred scheme of reservoir based on porosity, accurate quantitative evaluation results of oil content and mobility based on logging provide a more straightforward indication of the resource potential of the reservoir that is available for exploitation. The experimental scheme of multi-temperature pyrolysis-NMR and the quantitative evaluation method for oil content and motility based on NMR logging will provide an important basis for resource evaluation, optimal formation selection and efficient development of shale oil reservoirs.

Origin and evolution of deep lithium-rich brines in the southwest Jianghan Basin, central China: Evidence from hydrochemistry and stable isotopes

Lithium-rich brines from the upper Cretaceous and lower Eocene in the Jiangling depression, southwest Jianghan Basin were collected. In order to study the origin, evolution of the brines and the enrichment mechanism of lithium, the hydrochemical compositions and stable isotopes of the brines were tested and analyzed. The highest concentrations of potassium and lithium in the brine were 3.21 g/L and 97.85 mg/L, respectively. The brines of upper Cretaceous are mainly weakly acidic, while the lower Eocene brines are acid to alkalescent, and they are all Cl-Na type water. Compared with the ion trajectories of seawater evaporation, the brines showed enrichment of Cl, Ca, and Sr and depletion of Mg, which may be due to the dissolution of halite and water–rock interaction. The δD and δ18O compositions of the brines in both aquifers are similar, with δD values ranging from −51.4 to –33.0 ‰ and δ18O values ranging from −3.8 to 3.7 ‰. The data of δD and of δ18O indicate that the two aquifer brines originated from meteoric waters and experienced intense evaporation. The 87Sr/86Sr values (0.710144 to 0.712448) in the Upper Cretaceous brines are similar to the Paleocene sandstones, and the 87Sr/86Sr values (0.709982 to 0.710806) in the Lower Eocene brines are similar to the Paleocene anhydrite and glauberite. And the average content of lithium element in the upper Cretaceous brine is 54.38 mg/L, and the δ7Li values ranges from 10.2 to 14.1 ‰; the average content of lithium in lower Eocene brine is 23.81 mg/L, and the δ7Li values ranges from 17.7 to 21.9 ‰. The characteristics of 87Sr/86Sr and δ7Li indicate that the water–rock interaction between brine and silicate rock and the dissolution of halite lead to the enrichment of lithium in the brine of the two aquifers.

Late Oligocene–Early Miocene incision of the Three Gorges and the initial establishment of an east-flowing Yangtze River

The evolutionary history of the Yangtze River plays a key role for understanding the Cenozoic landscape evolution of East Asia. The Three Gorges currently separate the Sichuan Basin from the Jianghan Basin to the east, and their formation is considered to establish an initial connection between the Upper and Middle reaches of the modern Yangtze River. However, despite their importance in the Yangtze River evolution, the age of the initial incision of the Three Gorges remains an ongoing debate. In this study, we use apatite-fission track and (UTh)/He data to model the thermal history of the crust during the gorge formation. Based on the modeled time–temperature paths of samples on vertical profiles and the 3D thermos-kinematic modeling of the gorge region, we suggest that the gorges were initially carved during the Late Oligocene–Early Miocene. This event connected the drainages to the west and east of the gorge regions, leading to the formation of the modern east-flowing Yangtze River. This is also consistent with the sediment provenance of the Yangtze Gravels in the Lower Yangtze reported in previous studies. The gorge formation could be a response to the base level drop in the Jianghan and Subei Basins, which led to an upstream propagation of high erosion rates in the Three Gorges areas.

Sedimentary provenance constraints on the Cretaceous to Cenozoic palaeogeography of the western margin of the Jianghan Basin, South China

Provenance analysis of sedimentary basins is a direct way to understand the uplift of orogenic belts, basin deposition, and evolution of large rivers. A series of Mesozoic and Cenozoic strata from the western Jianghan Basin provides key sedimentary archives for investigating the growth of the surrounding orogenic belts and the evolution of the Yangtze drainage. However, the provenance of these sediments remains unclear. In this study, we report U–Pb data for 1098 detrital zircons from the western Jianghan Basin. We combine these data with published zircon U–Pb ages of potential source areas, paleocurrent data, and paleomagnetic age constraints to reconstruct provenance areas and establish related mountain-building processes. All Cretaceous and Early Cenozoic samples show five major age peaks at 131–210, 432–461, 720–986, 1836–1908, and 2470–2552 Ma. We infer that these sediments are primarily derived from recycled sediments associated with the uplift of the western Jiangnan Orogen. The tectonic uplift of the Jiangnan orogenic belt in the Cretaceous and Early Cenozoic was mainly controlled by the subduction of the Pacific and Indian plates underneath Eurasia. The detritus in the current upper reaches of the Yangtze River did not enter the Jianghan Basin before the Late Eocene (34 Ma). Early Pleistocene strata (1.2–0.7 Ma) show a distinct Cenozoic zircon U–Pb (41 Ma) peak age, which is mainly derived from the detrital sediments of the upper reaches of the Yangtze River. The combination of these data with published provenance tracing results for boreholes in the Jianghan Basin and Yangtze River Delta indicates that the Yangtze River was completely connected between 34 and 1.2 Ma. Such a long time interval may correspond to the tectonic uplift of the Tibetan Plateau and environmental changes during the Late Cenozoic.

Freshwater ecosystem collapse and mass mortalities at the Paleocene-Eocene thermal maximum

The Paleocene-Eocene thermal maximum (PETM), an abrupt global warming event linked to massive injections of carbon into the ocean-atmosphere system, was associated with large-scale deep-sea benthic extinction and major changes in planktonic ecosystems. However, due to the paucity of well-preserved fossils and high-resolution paleoenvironmental records, the PETM impacts on terrestrial ecosystems remain unclear. Here, we present geochemical and biological records of a lacustrine PETM section with exquisite fossils preserved from the Jianghan Basin, eastern China. Our data reveal the temporal relationship between carbon cycle perturbation, environmental changes, and biotic responses. Paleotemperatures derived from carbonate clumped isotope indicate a rapid increase by ~11 °C, synchronous with a negative carbon isotope excursion in organic matter and carbonates. Mass mortalities of terrestrial and aquatic animals were coincident with rapid warming during the PETM. Taphonomic features of animals, along with geochemical and sedimentological evidence, suggest that hyperthermal-induced toxigenic cyanobacterial blooms appear to be the most probable cause of the mass mortalities. Our findings expose a direct link between extreme warmth and increased probability of catastrophic ecological events in terrestrial ecosystems.