Objective The Late Ordovician to Early Silurian represents a critical transition in Earth's history， characterized by the Hirnantian glaciation and the end-Ordovician mass extinction event. However， significant uncertainties persist in the chronostratigraphic framework for this interval， limiting our understanding of the mechanisms driving biotic extinction and climatic evolution. This study aims to establish a high-resolution absolute astronomical time scale for the Late Ordovician-Early Silurian through the integration of cyclostratigraphy and isotopic geochronology， providing robust temporal constraints for major geological events. Methods Three sections （Shuanghe in Chang-ning， Sichuan； Anwen in Qijiang， Chongqing； and Wangjiawan in Yichang， Hubei） were selected as study sites. High-resolution elemental data （Si， Fe， Ca， Al， Rb/Sr， etc.） were analyzed using AnalySeries and Acycle software to identify Milankovitch cycle signals. Sedimentation rates were estimated using the COCO/eCOCO and TimeOpt methods to construct floating astronomical time scales. CA-ID-TIMS zircon U-Pb dating was conducted on volcanic ash beds to obtain absolute age anchors， enabling precise conversion from the depth domain to the time domain. Results （1） Stable sedimentary cycles corresponding to 405-kyr and ~100-kyr long and short eccentricity cycles were identified in the XRF elemental series. Floating astronomical time scales of 12.2 Myr， 10.3 Myr， and 2.75 Myr were established for the Shuanghe section， Anwen section， and Wangjiawan section， respectively. （2） Given the most complete geological record preserved in the Shuanghe section， the ages of the Ordovician/Silurian （O/S） boundary and the base of the Hirnantian stage， calibrated to 442.34 ± 0.22 Ma and 443.78 ± 0.22 Ma respectively through cyclostratigraphic analysis combined with U-Pb dating of volcanic ash beds （Shuanghe section： 438.47 ± 0.17 Ma）， can serve as a candidate for future international chronostratigraphic standards. （3） The duration of the Hirnantian stage is 1.44 Myr at the Shuanghe section， but only ~0.41 Myr at the Wangjiawan section， suggesting that a sedimentary hiatus may exist in the Wangjiawan section. （4） Paleoclimatic proxies and sea-level changes exhibited long-period fluctuations of 1.2 Myr and 2.4 Myr. Conclusions The high-precision astronomical time scale established in this study significantly improves the accuracy of the chronostratigraphic framework for the Late Ordovician-Early Silurian， revealing the rapid onset of the end-Ordovician mass extinction. Astronomical cycles played a significant role in driving climate-environmental evolution during this interval， providing key temporal constraints for understanding the triggering mechanisms of the end-Ordovician mass extinction.

Objective The Upper Paleozoic Yanghugou Formation-Taiyuan Formation in the northwestern margin of the Ordos Basin is a good prospect for oil and gas exploration. The strata are completely developed and continuous， with large thickness changes and various types of sedimentary facies. Defining the distribution characteristics of sand bodies and clarifying the law of sedimentary evolution directly affect the selection of preferred exploration zones for oil and gas. Methods This study takes the Yanghugou Formation to Taiyuan Formation in the northwestern margin of Ordos Basin as the target horizon. Based on previous studies， through typical field profile measurement， drilling core observation， paleocurrent direction analysis， logging data， and test data analysis， the sedimentary environment， facies type characteristics， evolution， and model of the study area were evaluated. ［Results and Conclusions］ There are 19 lithofacies types and three sedimentary systems in the study area， including four sedimentary facies types， and 13 sedimentary microfacies are further divided. The Yanghugou Formation-Taiyuan Formation in the study area is supplied by the two provenance systems of the Alxa ancient land in the northwest of the basin and the Yinshan ancient land in the northeast. The Dickinson triangle plot reveals that the tectonic background of the provenance area is dominated by the recycled orogenic belt. The characteristics of heavy mineral assemblages are clear. The northwestern margin of the basin has a clear affinity with the Alashan Group （Ar₃-Pt₁）， Archean Jining Group （Ar₃）， and the Wulashan Group （Ar_1-2）. The ZTR index shows that the unstable minerals gradually decrease from north to south； analysis of the paleocurrent direction also reflects the material sources from northwest to southeast and from northeast to southwest. Based on the above provenance analysis， paleo-sedimentary environment evolution and sedimentary facies type characteristics， it is clear that the main body of the Yanghugou Formation-Taiyuan Formation in the study area is the coexistence stage of sea and land. During the sedimentary deposition of the Yanghugou Formation， under the background of the revival of Helan aulacogen and the backlog of north-south tectonics， the sea water enters rapidly. The whole study area is controlled by the delta-clastic coastal sedimentary system. The northern source supply is sufficient， resulting in the development of tidal-controlled delta deposits in the north. Affected by tides and waves， tidal flat-barrier island-desalination of lagoons-shelf sedimentary microfacies are developed in the south. During the deposition of the Taiyuan Formation， the crust continued to sink and seawater invaded. During this period， the basin became the most widely distributed period of the sea area. The sedimentary environment was similar to that of the Yanghugou Formation. The overall performance was the coexistence of tidal-controlled delta， tidal flat， desalination of lagoons-barrier island sedimentary environment， and the erosion range in the northern region was relatively reduced， the source supply continued to increase， and the tidal-controlled delta range extended wider to the south.

Objective The western Hunan region hosts extensive Neoproterozoic marine sedimentary manganese deposits. Manganese （Mn） is a typical redox-sensitive metallic element whose enrichment in sediments is strongly correlated with the redox condition of the bottom water in the basin. A detailed study of the sedimentary redox conditions of such deposits helps to explain their metallogenic mechanisms and the constraints on their marine cycling during the mineralization period， and also provides theoretical support for the assessment of regional mineralization potential. Methods This study involved mineralogical， geochemical and inorganic carbon isotope analyses of 16 manganese ore samples of various grades from the Nanhua System Datangpo Formation in the Minle area， western Hunan. Results Mineralogical and carbon isotope analyses revealed that high-grade （MnO>20%） and medium-grade （10%<MnO<20%） manganese ores consist of predominantly subhedral granular microcrystalline rhodochrosite （grain size <5 μm） and are relatively enriched in light carbon isotope （δ¹³C=-10.4‰~-8.3‰； n=10）. Conversely， low-grade （MnO<10%） manganese ores contain larger- grained （>20 μm） subhedral platy rhodochrosite enriched in heavier carbon isotope （δ¹³C=-7.4‰~-5.3‰； n=6）. Pyrite morphology and element geochemical proxies （Mo， V， Ni concentrations and Ni/Co， V/Cr ratios） indicate that the high-grade manganese ores were deposited in oxic conditions， the medium-grade ore in suboxic conditions， and the low-grade ore in anoxic conditions. Additionally， high-grade ores exhibit geochemical characteristics indicating hydrothermal deposition （e.g.， high Eu^* values and high Fe/Ti ratios）. Conclusions These findings suggest that， in the Minle area of western Hunan， the rhodochrosite in the medium- to high-grade manganese ores was formed as a result of the reaction between Mn oxides with organic matter during diagenesis， whereas in the low-grade manganese ores the rhodochrosite was probably precipitated from Mn²⁺ and CO{}_{\mathrm{3}}^{\mathrm{2}-} in highly alkaline and anoxic conditions. Submarine gas-hydrothermal activity in the deep-water basin of northeastern Guizhou most likely supplied the Mn²⁺ ions for these manganese deposits； oxidation of bottom water in the basin was the key factor determining manganese enrichment and mineralization in the region.

Objective The Luojiawopeng Formation is a set of purplish red sand and gravel accumulation strata in the Lower Pleistocene Series in the southeastern margin of Songnen plain. The clay mineral analysis of this formation is conducive to understanding the paleoclimate characteristics in this region and defining its stratigraphic age. Methods Whole rock geochemistry， X-ray diffraction （XRD）， Scanning electron microscopy （SEM）， and High-resolution transmission electron microscopy （HRTEM） analysis of clay minerals in Luojiawopeng Formation were conducted to reveal their composition and transformation characteristics of clay minerals. Comparisons were performed on clay mineral composition between the red clays in the Chinese Loess Plateau and Luojiawopeng Formation. Results The clay mineral composition of Luojiawopeng Formation is dominated by kaolinite （content of 57%⁃73%）， followed by illite （ranging from 25% to 41%）， and the content of biotite /vermiculite mixed layer minerals is the least （average 1%）. Kaolinite shows pseudo hexagonal morphology， and its high degree of euhedral crystallinity indicates its authigenic origin， as does its high illite crystallinity （average 0.55） and illite chemical index （average 0.50）. These results， combined with the high clay to quartz ratio， indicate intense weathering characteristics. The transformation process of clay minerals is illite → kaolinite and biotite → biotite /vermiculite mixed layer minerals → kaolinite， which is consistent with the significant kaolinization trend of constant element 4Si-M⁺-R²⁺ ternary diagram. combined with the high chemical index of alteration（CIA） and hematite-to-goethite ratio of the formation， this process indicates that these minerals formed in a humid and hot environment with increasingly strong weathering. Conclusions Thus， the Luojiawopeng Formation was likely formed in a humid and hot climate， rather than through moraine accumulation as previously reported， and the stratigraphic chronology of the formation may be in the humid and hot period when the East Asian summer monsoon prevailed before the Early Pleistocene.

Objective The discharge rate regulates the sedimentary evolution and morphological scale of a braided river. In this study， the influence of discharge rate on the formation of braided channels， bars and internal sedimentary architecture is systematically analyzed for the first time. Methods Five groups of three-dimensional sedimentary numerical simulation experiments with different flow rates were carried out using Delft3D software to explore the evolution， morphological patterns and scale differences of braided channels and bars formed as a result of various flow rates. The models reproduce the internal architectural patterns of a range of bars developed in braided rivers with different flow rates and summarize the sedimentary characteristics and evolution of sandy braided rivers. Results （1） The rate of discharge is positively correlated with the sedimentary evolution of braided rivers. Low-discharge braided rivers exhibit limited evolution， in which bars mainly tend to migrate vertically and are less dissected by channels. By contrast， high-discharge braided rivers undergo intensive evolution， characterized by lateral migration and frequent dynamic equilibrium processes involving compound bars and dissection. （2） The discharge rate influences the plane pattern and channel depth of braided channels. As discharge increases， the braided channel becomes wider and deeper， resulting in a reduced overall number of channels but more highly developed chutes of the channel bars. Lower-discharge braided channels are shallower and primarily consist of numerous narrow， relatively fixed interwoven river networks. （3） Discharge further governs the co-evolution of channels and bars. Greater discharge enhances bar complexity， promoting the development of large complex compound bars and side bars with intricate internal stacking relationships and more frequent chutes. （4） Despite strong spatial heterogeneity in the internal architecture of channel bars in sandy braided rivers， consistent patterns emerge： all bars develop downstream accretions （DA） in the core， vertical accretions （VA） layered above， and lateral accretions （LA） deposited at the sides. A key distinction lies in the increased proportion of LA at higher discharge conditions. （5） Discharge correlates positively with accretion size but inversely with aspect ratio and flakiness ratio. Median aspect ratios of bars are 3.5 in low-discharge systems versus 4.5 in high-discharge systems. Conclusions The study proposes a positive correlation between discharge and the scale of channel bars and accretions in sandy braided rivers. This clarifies flow-controlled sedimentary characteristics and scale variations， providing a basis for analyzing complex subsurface reservoir architectures.

Objective The Wufeng Formation-Longmaxi Formation black rock series in eastern Sichuan and western Hubei is a focus for marine shale gas exploration in South China. These show great differences in sedimentary characteristics， which record major geological events during the Ordovician–Silurian transition. Further knowledge of these differences is of benefit to exploration for shale gas in western Hubei， and helps to understand global paleo-climate and sea-level changes during that time. Methods The sedimentary properties， main influencing factors and sedimentary processes of the black rock series in the Wufeng Formation and Longmaxi Formation were studied in detail by petrological， sedimentological and geochemical analysis. Results The sedimentary attributes of the Wufeng Formation are similar in both study areas， but in the Longmaxi Formation they differ significantly. In eastern Si-chuan， the large thickness of the Longmaxi black shale with completed graptolite zones and thick silty shale in the Rhuddanian-Aeronian transition is overlain by thick， organic-rich shale. Three long-term sedimentary cycles are recognized in the Longmaxi black rock series， but in western Hubei the Longmaxi black shale is very thin and only two long-term sedimentary cycles are identified. Neither silty shale nor Coronograptus cyphus and Demirastrites triangulatus graptolite zones are present in the Rhuddanian-Aeronian transition， but thin lime-bearing dolomitic mudstone covered by thin organic-rich shale are developed. Additionally， the Longmaxi black shale contains less quartz in eastern Sichuan than in western Hubei. Conclusions In this study， tectonic paleogeomorphology and paleoclimate changes are considered to be the main factors influencing the different evolutionary histories of the Wufeng Formation⁃Longmaxi Formation black rock series in the two study areas. During the Upper Ordovician， eastern Sichuan and western Hubei both subsided as a result of the Cathaysia Block⁃Yangtze Block collision. The paleogeomorphology and sedimentary environments in eastern Sichuan and western Hubei are not significantly different， but continuous tectonic compression beginning in the Early Silurian caused non-uniform subsidence. Continuing subsidence in eastern Sichuan and gradual uplift in western Hubei led to significantly different thicknesses of the Rhuddanian black shale in the two regions. Global sea-level fall during the Rhuddanian⁃Aeronian transition related to intensified glaciation further exacerbated the sedimentary differences in the two study areas， resulting in a sedimentary gap in western Hubei and abundant sandy deposits with low TOC in eastern Sichuan. Subsequent significant sea-level rise following global climatic warming promoted the development of black shale in both areas， although thicker in eastern Sichuan than in western Hubei. However， gradually intensifying tectonic compression and gradual sea-level fall， along with sufficient terrigenous sediment supply， sustained a sedimentary environment in both regions that led to the termination of development of the Longmaxi black shale in the two study areas.

Objective The Taiyuan Formation of Permian System in Ordos Basin has the characteristics of large thickness， wide distribution， and rich types of oil and gas resources， which indicates a substantial potential for exploration. At present， the study of this formation is mainly concentrated in the eastern part of the basin， while the exploration and study of Taiyuan Formation in the western part of the basin need to be further discussed due to the complex and variable tectonic pattern and sedimentary evolution. Methods The detrital material source， tectonic setting and paleogeographic evolution of Taiyuan Formation in western Ordos Basin are systematically studied by means of outcrop observation， drilling sample collection， detrital zircon U-Pb dating and paleo-flow analysis. Results The sediments in the northeastern part of the study area （Group A） are mainly from the Yinshan Orogenic Belt under the collision-compressional tectonic background， with strong provenances. The delta plain， delta front， tidal sand ridge and tidal sand bar are successively developed in the middle of the basin. The sediments in the northwest （Group B） are derived from the Alxa Block under the collisional compression and convergent orogenic tectonic background， and the delta plain， delta front and lagoon-tidal flat develop successively towards the middle of the basin. The sediments in the southern （Group D） area came from the North Qilian and North Qinling tectonic belts under the extension-subduction-collision tectonic environment of the Paleo-Tethyan Ocean. The central paleo-uplift of the Taiyuan Period was slow， the provenance-supply was weak， and the mainly developed barrier island-barrierisland-lagoon-tidal flat deposits. Conclusions The northern part of the study area is characterized by high uplift and strong provenance supply in the context of collision and convergence orogenic structures， and large tide-delta complex system， while the southern part is characterized by weak provenance supply in the context of tensile extension structures， and is dominated by tidal flat and lagoon. This study not only deepens the understanding of the sedimentary system and provenance supply mechanism in the western Ordos Basin， but also provides a new perspective and reference for the reconstruction of the tectono-sedimentary evolution process and paleogeographic pattern in the western Ordos Basin.

Objective To identify the next exploration direction， the main controlling factors and exploration potential of different types of shale oil enrichment in the Chang 7 member of the Ordos Basin are discussed. Methods In this study， the formation conditions and exploration potential of shale oil such as petrology， geochemical characteristics and reservoir capacity of the Chang 7 member shale were comprehensively studied using organic geochemistry， whole rock X-ray diffraction （XRD）， field emission scanning electron microscopy， and rock pyrolysis experiments. Results （1） The Chang 7₃ sub-member shale has high organic matter abundance， the best type， the highest maturity， and the greatest hydrocarbon generation potential. （2） The Chang 7 member shale is dominated by inorganic pores and fractures， with the largest proportion of micropores， and the shale reservoir capacity is stronger than that of mudstone. （3） The enrichment of shale oil in the Chang 7 member is controlled by five factors ： high-quality source rock， lithologic combination， fracture， mobility， and fracability. The distribution of high-quality source rocks controls the distribution range of shale oil， the lithology combination controls the hydrocarbon expulsion efficiency and the enrichment type of shale oil. The hydrocarbon expulsion efficiency of the source-reservoir interbedded type is the highest， which is conducive to the enrichment of sand bodies； the hydrocarbon expulsion efficiency of the thick source-thin reservoir type is the lowest， which is conducive to the in-situ retention and enrichment of shale oil. The two-sidedness of fractures controls the enrichment degree of shale oil. The development of fractures is conducive to the enrichment of sandstone interlayer shale oil， and the underdevelopment of fractures is conducive to the retention and enrichment of pure shale-type shale oil. The mobility and fracability of crude oil control the high yield of shale， and the mobility and brittleness index of shale crude oil are better than those of mudstone. Conclusions The Chang 7₃ sub-member in the Jiyuan area is a favorable exploration block for pure shale-type shale oil. The Zhengning and northern Shaanxi areas are favorable exploration blocks for sandstone-intercalated shale oil in the Chang 7₁ and Chang 7₂ sub-members. The Huachi area in Longdong is a favorable area for the exploration of both sandstone-intercalated and pure shale-type shale oil.

Objective The shale gas of the Cambrian Qiongzhusi Formation in the Sichuan Basin has good prospects for exploration and development， and a knowledge of its sedimentary environment is necessary to evaluate these resources. Methods The focus of this study was the Chengjiaba section shale series in the Qiongzhusi Formation. A detailed field geological survey and whole rock X-ray diffraction and geochemical analyses were carried out. The elements and ratio parameters in the study area were optimized to determine the sedimentary paleoenvironment of the organic-rich shale. Results （1） The First and Second members of the Qiongzhusi Formation are mainly gray-black or black mudstone and silty mudstone， with siliceous rock and siliceous shale facies. The horizontal bedding indicates a deep-water shelf paleoenvironment. （2） The shale TOC（Total Organic Carbon） is relatively high in the Qiongzhusi Formation， ranging from 0.22% to 4.34% （average 2.68%）. （3） The geochemistry of the elements indicates a warm and humid paleoclimate during the deposition of the black shale. The water body was anoxic and highly retained. Conclusions The formation of organic-rich shale in the Qiongzhusi Formation is controlled by multiple factors. Organic matter enrichment in the First member of the Qiongzhusi Formation conforms to the preservation mode， primarily controlled by redox conditions and sedimentation rate. In contrast， the organic matter enrichment in the Second member of the Qiongzhusi Formation follows the comprehensive model， synergistically controlled by paleoclimate， paleoproductivity， sedimentation rate， and redox conditions.

Objective The Second member of the Middle Permian Lucaogou Formation is the main exploration target for lacustrine carbonate shale oil in the Santanghu Basin， Xinjiang province， China. Clarifying its paleoenvironment and organic matter enrichment mechanism provides scientific evidence in support of shale oil exploration and development in the study area. Methods Tests for total organic carbon content， major and trace elements and carbon-oxygen isotopic composition of primary carbonate rocks were conducted on shale samples collected from the well Luye 1 in the Second member of the Lucaogou Formation in the in the Malang Sag， Santanghu Basin. These deciphered the paleoenvironment and associated organic matter enrichment mechanism of the shale sequence， hence helping to gain a better understanding of the effects of paleoproductivity， paleoclimate， paleosalinity and paleoredox conditions on the organic matter enrichment and the key elements. Results Shale oil sweet spots are present in the middle and upper parts of this shale sequence. The tests indicated a closed lacustrine setting. The lowest part of the middle sweet spot was deposited in an arid， saline and reduced deep-water environment with low paleoproductivity， whereas its upper section has high paleoproductivity and was deposited in a semi-arid， brackish and weakly reducing deep-water environment. The upper sweet spot was deposited in an arid， saline and weakly reduced semi-deep water setting with medium paleoproductivity. Conclusions The organic matter enrichment mechanisms vary between the different shale sections. The influencing elements were the redox conditions and paleoproductivity in the lowest part of the middle sweet spot， paleoclimatic conditions and paleoproductivity for the upper part of the middle sweet spot， and paleoproductivity in the upper sweet spot. This study will assist in shale oil exploration and development in the Second member of the Lucaogou Formation in the Santanghu Basin.