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Cambrian shales in China and elsewhere contain abundant oil and gas resources. However, due to its deep burial and limited outcrop, there has been relatively little research conducted on it. The Cambrian shale of the Tadong low uplift in the Tarim Basin of western China, specifically the Xidashan–Xishanbulake Formation (Fm.) and overlying Moheershan Fm. provide a case study through the use of organic petrology, mineralogy, organic and elemental geochemistry, with the aim of analyzing and exploring the hydrocarbon generation potential (PG) and organic matter (OM) enrichment mechanisms within these shale formations. The results indicate that: (1) the Cambrian shale of the Tadong low uplift exhibits relatively dispersed OM that consists of vitrinite‐like macerals and solid bitumen. These formations have a higher content of quartz and are primarily composed of silica‐based lithology; (2) shale samples from the Xidashan–Xishanbulake and Moheershan formations demonstrate high total organic carbon (TOC) and low pyrolytic hydrocarbon content (S2) content. The OM is predominantly type I and type II kerogens, indicating a high level of maturation in the wet gas period. These shales have undergone extensive hydrocarbon generation, showing characteristics of relatively poor PG; (3) the sedimentary environments of the Xidashan–Xishanbulake and Moheershan formations in the Tadong low uplift are similar. They were deposited in warm and humid climatic conditions, in oxygen‐deficient environments, with stable terrigenous inputs, high paleoproductivity, high paleosalinity, weak water‐holding capacity, and no significant hydrothermal activity; and (4) the relationship between TOC and the paleoproductivity parameter (P/Ti) is most significant in the Lower Cambrian Xidashan–Xishanbulake Fm., whereas correlation with other indicators is not evident. This suggests a productivity‐driven OM enrichment model, where input of land‐derived material was relatively small during the Middle Cambrian, and the ancient water exhibited lower salinity. A comprehensive pattern was formed under the combined control of paleoproductivity and preservation conditions. This study provides valuable guidance for oil and gas exploration in the Tarim Basin. [ABSTRACT FROM AUTHOR]

Mangrove wetlands are among the four most productive tropical and subtropical ecosystems. They are also a core component of the coastal blue carbon ecosystem, which is of great ecological significance to human beings, plants, animals, and the global carbon balance. There has been a global decrease in the distribution of mangrove forests, and their ecological function has gradually degenerated since the Holocene. Sediment from coastal mangrove wetlands can provide records of climate change and human activities, and multiple proxies including palynology, leaf fossil, biomarkers, DNA, phytolith and stable isotopes, can be used to reconstruct the evolutionary stages of paleo-mangroves and to identify the effect of natural processes and human activities on the distribution and evolution of mangroves. This information can provide theoretical support for mangrove protection and for improving carbon sequestration capacity. This paper summarizes and compares the multiple proxies for mangrove reconstruction, reviews progress in the study of natural succession of global mangroves since the Holocene, expands on the influence mechanisms of human activities on mangrove growth and development and uses past information to lay a foundation for a model to predict future mangrove development. [ABSTRACT FROM AUTHOR]

This investigation focuses on the prevalent continental oil shale within the Triassic Chang 7, a member of the Yanchang Formation in the Ordos Basin and the Permian Lucaogou Formation in the Junggar Basin of western China, and delves into the impacts of hydrocarbon generation and the derived organic acids on the physical attributes of oil shale reservoirs. Water-soluble organic acids (WSOAs) were extracted via Soxhlet extraction and analyzed by a 940 ion chromatograph (Metrohm AG), supplemented with core observations, thin-section analyses, pyrolysis, and trace element assays, as well as the qualitative observation of pore structures via FIB-SEM scanning electron microscopy. The study discloses substantial disparities in the types and abundances of organic acids within the oil shale strata of the two regions, with mono-acids being conspicuously more prevalent than dicarboxylic acids. The spatial distribution of organic acids within the oil shale strata in the two regions is non-uniform, and their generation is inextricably correlated with the type of organic matter, thermal maturity, and depth at which they are buried. During diverse stages of diagenesis, the hydrocarbons and organic acids produced from the pyrolysis of organic matter not only exert an impact on the properties of pore fluids but also interact with diagenetic processes such as compaction, dissolution, and metasomatism to enhance the reservoir quality of oil shale. The synergy between chemical interactions and physical alterations collectively governs the migration and distribution patterns of organic acids as well as the characteristics of oil shale reservoirs. Furthermore, the sources of organic acids within the oil shale series in the two regions demonstrate pronounced dissimilarities, which are intimately associated with the peculiarities of their sedimentary milieu. The oil shale of the Yanchang Formation was formed in a warm and humid freshwater lacustrine basin environment, while the oil shale of the Lucaogou Formation was deposited in a brackish to saline lacustrine setting under an arid to semi-arid climatic regime. These variances not only illuminate the intricacy and multiplicity of the sedimentary attributes of oil shale but also accentuate the impact of the sedimentary environment on the genesis and distribution of organic acids, especially the transformation and optimization of reservoir dissolution by organic acids generated during hydrocarbon generation—a factor of paramount significance for the precise identification and effective development of the "sweet spot" area of shale oil. These areas, characterized by an abundance of organic matter, their maturity, and superior reservoir properties, are the foci of the efficient exploration and development of continental shale oil. [ABSTRACT FROM AUTHOR]

The Permian Qipan Formation (P1-2q) is the aim horizon for hydrocarbon source rocks in the piedmont area of southwestern Tarim Basin. In the present study, the depositional environment and geochemical characteristics of muddy hydrocarbon source rocks of P1-2q were systematically evaluated using total organic carbon (TOC), Rock-Eval pyrolysis, vitrinite reflectance (Ro), reflected light microscopy, main and trace element, and biomarker parameters of 167 outcrop samples and 176 core samples. The TOC of P1-2q is primarily concentrated within the range of 0.36% to 2.77%, with an average of 1.58%. This suggests that the overall evaluation of the hydrocarbon source rock is fair to good. The source rocks of P1-2q predominately contain Type III and Type II2 kerogen. The overall Tmax values of P1-2q hydrocarbon source rocks are notably elevated, with the majority exceeding 490 °C or falling between 455 °C and 490 °C. The Ro value is between 0.90% and 2.00%, indicating that the maturity has reached a high, over-mature evolutionary stage. The trace element and biomarker parameters indicate that hydrocarbon source rocks of P1-2q are predominantly slightly oxygen-rich, with a minor anoxic component. The asymmetric 'V' arrangement of the C27-C29 regular steranes indicates that the hydrocarbon parent material is predominantly derived from algae or aquatic organisms, with varying degrees of mixing with organic matter of terrestrial origin. The study of source rock geochemistry of the P1-2q makes the exploration target of the southwest depression of the Tarim Basin more accurate in the complex tectonic geological environment. [ABSTRACT FROM AUTHOR]

The enrichment of organic matter in high-quality marine shale is generally controlled by factors such as the redox conditions of sedimentary environments, productivity levels, terrigenous input, and ancient productivity. However, the controlling effect of the sedimentary environment on organic matter enrichment in intracratonic sag is still unclear. This study takes samples from the Qiongzhusi formation shale in southern Sichuan Basin as the research object, focusing on trace elements as well as rare earth elements in different stratigraphic intervals. The provenance of the Qiongzhusi formation shale is mainly terrigenous, with sediment sources mainly consisting of sedimentary rocks and granites. The primary sedimentary environment transitions from a continental margin setting, influenced by rift-related tectonic activity and sediment influx from adjacent landmasses, to an open oceanic environment characterized by mid-ocean ridge processes and oceanic plate subduction zones. During sedimentation, saline water was present, with predominant sedimentary environments ranging from shallow water to deep water continental shelves. The shale in the study area is characterized by a higher content of silicates and a lower content of carbonate minerals. Its siliceous sources are mainly influenced by biogenic and terrigenous debris, indicating higher ancient primary productivity and representing a favorable target for shale gas exploration. [ABSTRACT FROM AUTHOR]

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The age and dolomitization processes in the Paleo-oil reservoir zone, which is composed of massive dolostones found in the Qiangtang Basin (SW China), are still debated. In this research, the Long'eni-Geluguanna Area was selected. Macroscopic information, thin sections, and geochemical methods were used to investigate the dolomitization characteristics and the processes that controlled dolomitization. Five types of replacive dolomites and two types of dolomite cement were observed. Some of the dolomites displayed ghosts of primary sedimentary structures. Saddle dolomites were prevalent, occurring in the interparticle and moldic pores of the limestone which should have been filled at an early diagenetic stage. Ten microfacies types were identified. The foraminifera assemblage provides evidence that the studied interval is of Early Jurassic age. The δ13C values are similar to the contemporaneous seawater signature. The REE+Y patterns of limestones and dolostones exhibit similarities to that of seawater. The mean Na and Sr values are comparable to those of other near-normal seawater dolomites. The δ18O values of all lithologies are markedly depleted. The dolomitization started penecontemporaneously, with deposition. A general sand shoal setting with patch reefs developed. The dolomitizing fluids, near-normal seawater, was probably formed by slight evaporation on top of the shoal. Saddle dolomites in the interparticle and moldic pores might indicate hydrothermal activity, which also caused the recrystallization of some pre-existing dolomites. The recrystallization might have slightly increased the crystal size, demolished the ghost structures, formed saddle dolomites, and altered the REE+Y patterns. The recrystallization extent diminished with increasing distance from the fluids-providing fracture. Furthermore, the existence of protected areas within the sand shoal settings could enhance the vertical and horizontal heterogeneity of dolostone reservoirs. [ABSTRACT FROM AUTHOR]

The mud deposit areas on continental shelf have developed in a relatively steady sedimentary condition with high sedimentation rates, thus rendering them ideal regions for exploring high-resolution paleo-sedimentary environment records. Since the sedimentary environment of the continental shelf is subject to the compound influence of multiple factors, the reconstruction of water salinity and temperature and comprehensive analysis of their response to global climate change remains challenging. Therefore, the present study characterized water salinity and temperature of the North Yellow Sea (NYS) using proxies, such as ratios of halogen elements of sediments and stable isotopic compositions of benthic foraminifera, and found the halogen elements of Cl in sediments was good proxy for water salinity. The evolutions of water salinity and temperature of the NYS for the past 3000 years were reconstructed, while the evolution stages and drivers of the sedimentary environment were explored. From approximately 3000 cal yr BP, the sea bottom salinity and temperature of the NYS were found to follow the same evolution trends predominantly consisting of the three stages: relatively low seawater salinity and temperature during 3000−2000 cal yr BP; relatively high seawater salinity and temperature during 2000−460 cal yr BP; and rapid changes of seawater salinity and temperature since 460 cal yr BP. The changes in seawater salinity and temperature of the NYS were largely driven by the East Asian winter monsoon (EAWM) as well as the influence of the Kuroshio Current. As the EAWM fluctuated, changes occurred in the flux of low temperature, low salinity coastal current water into the Yellow Sea, with concomitant changes in bottom temperature and salinity. Strengthening of the Kuroshio Current promoted the development of the Yellow Sea Warm Current, while the influx of warm, salty water into the Yellow Sea influenced the respective sea region. The abrupt global climate changes such as the "Little Ice Age" and the Medieval Warm Period first affected the East Asian monsoon, followed by the respective sea region. [ABSTRACT FROM AUTHOR]

Copyright of Petroleum Geology & Experiment is the property of Petroleum Geology & Experiment Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Petroleum Geology & Experiment is the property of Petroleum Geology & Experiment Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Acta Scientiarum Naturalium Universitatis Pekinensis is the property of Editorial Office of Acta Scientiarum Naturalium Universitatis Pekinensis and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The sedimentary environment of the Upper Triassic in the southeastern Sichuan Basin is obviously controlled by Luzhou paleo-uplift (LPU). However, the influence of paleo-uplift on the sedimentary patterns of the initial stages of this period in the southeastern Sichuan Basin has not yet been clear, which has plagued oil and gas exploration and development. This study shows that there is a marine sedimentary sequence, which is considered to be the first member of Xujiahe Formation (T3X¹ ) in the southeastern Sichuan Basin. The development of LPU resulted in the sedimentary differences between the eastern and western Sichuan Basin recording T3X¹ and controlled the regional sedimentary pattern. The western part is dominated by marine sediments, but the eastern paleo-uplift area is dominated by continental sedimentation in the early stage of T3X¹, and it begins to transform into a marine sedimentary environment consistent with the whole basin in the late stage of the period recorded by the Xujiahe Formation. The evidences are as follows: (1) time series: based on the cyclostratigraphy analysis of Xindianzi section and Well D2, in the southeastern Sichuan Basin, the period of sedimentation of the Xujiahe Formation is about 5.9 Ma, which is basically consistent with the Qilixia section, eastern Sichuan basin, where the Xujiahe Formation is widely considered to be relatively complete; (2) distribution and evolution of palaeobiology: based on analysis of abundance evolution of major spore-pollen, many land plant fossils are preserved in the lower part of T3X¹, indicates the sedimentary environment of continental facies. In the upper part of T3X¹, the fossil of terrestrial plants decreased, while the fossil of marine and tidal environment appeared, this means that it was affected by the sea water in the late stages of T3X¹ ; (3) geochemistry: calculate the salinity of water from element indicates that the uplift area is continental sedimentary environment in the early stage of T3X¹, while the central and western areas of the basin are marine sedimentary environment. Until the late stage of T3X¹, the southeast of the basin gradually turns into marine sedimentary environment, consisting with the whole basin; (4) types of kerogen: type III kerogen representing continental facies was developed in the early stage of T3X¹ in the uplift area, and type II kerogen, representing marine facies, was developed in the late stage; while type II kerogen was developed in the central and western regions of the basin as a whole in T3X¹ . This study is of great significance for understanding of both stratigraphic division and sedimentary evolution providing theoretical support for the exploration and development of oil and gas. [ABSTRACT FROM AUTHOR]

Copyright of Acta Geoscientica Sinica is the property of Acta Geoscientica Sinica Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The carbonate rock of the Qiulitage Formation is a significant stratum for oil and gas exploration in the Tarim Basin. To elucidate its environmental characteristics, we conducted tests and analyses of trace elements, carbon, and oxygen isotopes of the carbonate rocks of the Qiulitage Formation in the Kekeqigankake section of the Keping area. The results reveal that δ13C values range between −1.7‰ and 4.3‰, with an average value of 1.645‰. δ18O values fluctuate from −11.4‰ to −6‰, with an average value of −8.2475‰. Z values (paleosalinity) vary from 120.33 to 131.67, significantly exceeding 120 with an average value of 126.52, indicating a marine sedimentary environment. Paleotemperature values (T) range from 12.75 to 29.09 °C, with an average value of 21.36 °C, suggesting warm climate conditions. The Sr/Ba (3.42~24.39) and Sr/Cu (57.5~560) ratios are elevated, while Th/U (<1.32) and V/Cr (0.989~1.70) ratios are reduced, suggesting that the Qiulitage Formation was deposited in an oxygen-rich, warm marine sedimentary environment with relatively high salinity. [ABSTRACT FROM AUTHOR]

As one of the important minerals in marine shale reservoirs, the development characteristics of pyrite can provide guidance for the exploration of deep shale gas resources and the study of high-quality reservoir development mechanisms. In this study, samples of the Wufeng and Longmaxi Formation in the southeast Chongqing area were selected, and the development characteristics of framboidal pyrite were revealed through a combination of qualitative and quantitative method. High-quality reservoirs of the upper Wufeng Formation and the bottom of the Longmaxi Formation are developed with smaller sizes, weaker variation and a narrower size distribution of pyrite framboids compared with other units of the strata, suggesting relatively stable euxinic conditions during deposition. The development characteristics of framboidal pyrite and some of the key reservoir evaluation parameters such as organic matter content and brittle mineral content, etc., are controlled by similar factors. Therefore, pyrite morphological evidence can be used as a potential indicator of high-quality shale reservoirs. [ABSTRACT FROM AUTHOR]

The Cambrian life explosion is closely related to the redox environment of plaeoocean, and the Lower Cambrian phosphorite in the Upper Yangtze Block has recorded a relatively complete information of the Early Cambrian. The Yangchang phosphate deposit in western margin of the Yangtze Block is a super-large phosphate deposit occurring in the Meishucun Formation of the Lower Cambrian, which can reconstruct the paleomarine environment of this period. In this paper, ICP-MS and other techniques were used to analyze the elemental geochemical composition characteristics of the phosphorite and its surrounding rocks and explore the geological environment of the Yangchang phosphate deposit. The results show that the CIA value of phosphorite is 46.40~65.60, with an average of 57.43, indicating that the weathering degree is low, the total amount of rare earth element (∑REE) in phosphorites in this deposit is relatively low (140.0x10-6 ??? 237.4x10-6, but yttrium is relatively rich (87.0x10-6 ~ 183.2x10-6). The North American standardized rare earth distribution pattern is relatively flat, the LREE/HREE is of 4.22 ~ 7.50, shows that the diffrernce of light and heavy rare earth elements is not obvious, with obvious Ce negative anomaly (0.22 ~ 0.42), Eu anomaly is not obvious with δEu of 0.90 ~ 1.21, and U/ Th ratio of 2.55 ~ 27.68, which reflect that the phosphorite was affected by a certain influx of hydrothermal fluid during the sedimentary of phosphorites. Combined with the analysis of δCe, V/Cr, Y/Ho, Sr/Cu and other elements, it is indicate that from the bottom of Dengying Formation in the Sinian Period, to the phosphate-bearing layer Cambrian Meishucun Formation, to the upper cover Niutitang Formation, the ancient ocean redox environment changes from the relative reduction environment at the bottom to the oxidation environment upward until the top becomes the relative reduction environment. The paleoclimatic environment is cold and dry-warm and moist alternatively appear. The salinity of ancient seawater is the evolution process of salt water to semi-salt water to salt water to fresh water. The above analysis shows that the phosphorite deposit in a relatively oxidized saline water and arid climatic environment, and the climatic environment is relatively arid during sedimentation, and may be affected by the influx of hydrothermal fluid. [ABSTRACT FROM AUTHOR]

Brine groundwater in Quaternary salt lakes is widely exploited to extract potassium, lithium, and boron; the complex hydrogeological parameters of brine aquifers could cause significant difficulties in brine resource assessment and exploitation. However, the origin and porosity of brine aquifers remain unclear. This study presents an approach that utilizes geochemical indicator analysis with paleogeographic reconstruction to better assess porosity in salt lake aquifers. We identified 15 representative boreholes in Mahai Salt Lake, and the lithology, porosity, and chloride contents of their respective sediments, the pore porosity of each borehole in the study area ranges from 38.17 to 0.51%, the average chloride content of each borehole ranges from 26.63 to 38.74%, found that the vertical porosity fluctuations of halite deposits were significantly larger than those of detrital deposits, the sediments in the boreholes consisted predominantly of halite-containing debris or fine-debris-containing halite, reflecting the paleoenvironmental signatures of the salt lake. According to lithology and sedimentary environment, four brine aquifers were classified and the chloride and porosity distribution characteristics in the I–IV brine aquifers were further illustrated. Based on information of paleolake evolution in Qaidam Basin, we established a conceptual model to identify the impact factors for the porosity distribution pattern in the I–IV brine aquifers. [ABSTRACT FROM AUTHOR]

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As the cornerstone for evaluating the storage capacity of shale reservoirs and assessing the viability of shale gas exploitation, shale pores play a very important role in shale reservoirs. Based on drilling well and test data, deep learning, and artificial intelligence for image analysis, the types, characteristics, structures, and vertical heterogeneity of shale pores were studied. Additionally, we conducted a comprehensive investigation into the sedimentary environment characteristics and their influence on the heterogeneity of shale reservoir pores in the Longmaxi Formation using associated geochemical analyses. The results revealed that the sedimentary environment underwent significant changes in the Longmaxi Formation, characterized by a sea level fall, accelerated sedimentation rates, weakened reducing conditions, decreased palaeoproductivity, and increased terrigenous influx, which led to a decrease in the frequency of organic matter (OM) pores, paralleled by a gradual increase in inorganic pores. In the S1l11−1, S1l11−2, S1l11−3 sections of the Long11 sub-member, OM pores constitute the primary pore type. Conversely, in the S1l11−4 section and the Long12 sub-member, inorganic pores prevail as the primary pore type. Furthermore, the strongly anoxic sections are also pay zones that are not only enriched in OM but also concentrated with OM pores. The S1l11−1 and S1l11−2 sections are characterized by anoxic conditions, with total organic carbon (TOC) content exceeding 4% and abundant biogenic silica. Notably, an increased terrigenous influx adversely impacts the development and preservation of pores in the Long11 sub-member while exerting a dual effect in the Long12 sub-member. The increased terrigenous influx dilutes the OM and decreases the probability of intergranular pores and intragranular pores filled by OM. Moreover, more brittle mineral particles were deposited, which promotes the development and preservation of intergranular and intragranular pores.

Objective The coastal sedimentary environment is fundamental to the comprehending the evolution and movement of groundwater. To investigate the impact of the distribution and mobility of brackish groundwater along the southern coast of Laizhou Bay, Methods this study collected samples from two archetypal Quaternary boreholes (LZ01 and LZ02), extracted pore water using the mechanical squeezing technique, and measured the grain size composition of the sediments and the Cl- content of the pore water. Results Both boreholes are dominated by fine-grained sediments with an average particle size of 5.5ϕ. Based on the sediment lithology and grain size parameters, it was found that the LZ01 and LZ02 boreholes contained 10 and 9 alternating sedimentary facies, respectively, revealing three sets of marine stratigraphic units since the late Pleistocene. The porewater was found to be predominantly composed of brine (saline) water, with the Cl- profile displaying three peaks corresponding to the three sets of marine stratigraphic units. These results demonstrate the presence of residual ancient marine brine water in the sediment and its permeation into neighboring sediments. In this study, it was observed that the hydraulic index of sedimentary water exhibited a clear zonal pattern, with the vertical change rate of Cl- serving as a crucial indicator. Notably, under moderate hydraulic conditions, Cl- displayed a robust diffusion and migration capability in pore water, as confirmed by detailed particle size analysis. The dominant particle size range for pore water migration was 45.61-111.47 μm. Conclusion The paleo-marine transgression events in the study area controlled the distribution of brine, while low permeability and lithological combinations played a significant role in the preservation of ancient brine. The results of this study provide a theoretical basis for research on the origin of brine, groundwater salinization, and migration in the Laizhou Bay coastal plain.

Shale oil and gas are important strategic resources in China's energy sector, existing in shale formations with self-generation and self-storage characteristics. In 2012, a significant breakthrough was achieved in Fuling, China, with the discovery of marine shale gas, which led to the formulation of the "two-factor enrichment" theory. This theory proposes that the development of high-quality mud shale in deep-water continental shelves is fundamental for hydrocarbon generation and controlled storage, while favorable preservation conditions are key to reservoir formation and controlled production. Recent efficient exploration and development practices in shale oil and gas have indicated that China's continental shale oil also exhibits "two-factor enrichment" characteristics. By analyzing the characteristics of typical shale oil and gas reservoirs in China, this study incorporates shale oil and gas into a unified system of hydrocarbon formation, storage, and accumulation, further deepening the theoretical connotation of the "two-factor enrichment" theory and forming a new understanding of the uniformity in shale oil and gas enrichment. Future research trends are also explored. Results show that: (1) Sedimentary environments dominated by semi-deep to deep-water continental shelves and semi-deep to deep lakes are the basis for hydrocarbon generation and controlled storage, controlling both the abundance and type of organic matter in shales as well as the distribution of high-quality reservoirs and favorable lithofacies combinations. (2) Stable tectonic conditions, effective top and bottom seals, and self-sealing properties of shale, in conjunction with overpressure, provide good preservation conditions that are crucial for reservoir formation and controlled production, providing key guarantees for the enrichment and high production of shale oil and gas. (3) The formation and enrichment of shale oil and gas are part of a unified dynamic evolutionary system, with thermal evolution as the main driver, following the sequential formation of shale oil, condensate oil, and shale gas. (4) Future study should focus on strengthening the integrated evaluation of conventional and non-conventional resources, deepening the understanding of distribution coefficients for conventional and non-conventional oil and gas, and considering the distribution patterns of oil and gas from a holistic perspective. The research results have important scientific and practical significance for deepening the theory of shale oil and gas enrichment and guiding their exploration and development.

The Upper Cretaceous Qingshankou Formation in the Songliao Basin contains thick, widespread, and organic matter-rich shale layers, offering abundant shale oil resources. Studying the sedimentary environment during shale formation and exploring the oil-bearing characteristics of shale oil enrichment intervals provide a theoretical basis for the prediction of the intervals and sweet spots. Based on previous research, the study compared organic carbon content, pyrolysis data, types of organic macerals, and major and trace elements of samples from two typical wells of different sags, well GY8HC in the Gulong Sag and well ZY1 in the Sanzhao Sag, in the central depression zone of the Songliao Basin. The analysis delved into the differences in oil-bearing characteristics and sedimentary environment of the Qingshankou Formation shales in two different sags, further analyzing the factors influencing these differences. The oil-bearing indicators of shales from the two wells in the Qingshankou Formation of the Songliao Basin showed that the total organic carbon (TOC) content in well ZY1 was significantly higher than that in well GY8HC. However, the free hydrocarbon content (S1) and oil saturation index (OSI) in well ZY1 were lower than those in well GY8HC. The geochemical environment during shale formation controlled organic matter enrichment. Comparing major and trace elements in samples from both wells, it was found that the climate in well ZY1 was more humid during its sedimentary period, the water body had stronger reducing conditions, and its paleoproductivity and paleo-water depth were significantly higher than those in well GY8HC. These conditions were favorable for the preservation of organic matter, thereby forming a higher organic matter abundance in the shale of well ZY1. In addition, it was found that the organic matter type in well GY8HC is mainly Type Ⅰ, sapropelic kerogen, at a mature to highly mature stage, whereas well ZY1 contains mainly Type Ⅱ1 kerogen, with less Type Ⅰ, at a low to mature stage. Therefore, the shale in well GY8HC possesses better oil generation potential.

Bioturbation is one of the important processes that affect the structure and function of sedimentary environments. The particle mixing and element migration processes caused by bioturbation can interfere with the circulation of matter and the explanation of sedimentary records. Therefore, the quantitative characterization of bioturbation structures in the sedimentary sequence is of great significance in the field of sedimentology. Estuaries, where fresh and saltwater mix, exhibit high ecological heterogeneity and biodiversity, making them ideal places to explore bioturbation. This paper targets the subaqueous Yellow River Delta to quantitatively characterize bioturbation structures and their spatial distribution patterns using computed tomography (CT) scanning and three-dimensional reconstruction technology. By combining sediment characteristics and sedimentary environment analysis, the main factors affecting bioturbation structures are elucidated. The results show that bioturbation structures in the subaqueous Yellow River Delta can be divided into four types based on their morphology: uniaxial type, biaxial type, triaxial type, and multiaxial type. Skolithos, Palaeophycus in the uniaxial type, and Thalassinoides in the multiaxial type are the most developed structures. Different types of bioturbation may be constructed by trace-making organisms belonging to the same category or functional group. The intensity of bioturbation in this area ranges from 0 to 4%, with a decreasing trend from nearshore to offshore. There is a downward decreasing trend in the intensity of bioturbation overall in the sedimentary cores, with three vertical distribution patterns: exponential decay pattern, fluctuating decay pattern, and impulsive pattern. The impulsive pattern of bioturbation in a core may indicate the abrupt change in sedimentary environment induced by the Yellow River channel shift in 1996. These results suggest that factors affecting the development of bioturbation include grain size, porosity, consolidation, organic matter content of sediments, and sedimentation rate that is mainly influenced by local hydrodynamic conditions. The environment with clayey silt (average grain size 10 µm) and moderate sedimentation rate (around 0.5 cm yr−1) is the most suitable area for the development of bioturbation in the Yellow River subaqueous delta. [ABSTRACT FROM AUTHOR]

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Objective The good oil test results of Taiye 1 and Xingye L1 wells in the Jurassic Lianggaoshan Formation shale indicate the breakthrough of shale oil/gas exploration in the Jurassic continental shale in the Fuxing area of the eastern Sichuan Basin. To further clarify the oil/gas exploration potential and the organic matter enrichment mechanism of the Jurassic Lianggaoshan Formation shale, utilizing logging and core data of two typical wells Xingye X and Xingye Y, the whole-rock X-ray diffraction, organic carbon, major and trace elements were analyzed. Methods The Liang-2 lower submember was deposited in the environment of warm-wet (moderate weathering conditions) and freshwater, and there was no obvious difference in palaeoclimates of different unit formations. The La-Co data suggests a semi-deep to deep lake environment with a palaeowater depth ranging from 10.9 to 56.1 m; the anoxic reducing environment persisted on the lake floor despite the lake level fluctuation, but the palaeoproductivity was vertically increased. The shale interval is rich in sandy laminae, but the deposition rate of the shale layer is lower than that of the sandstone layer. Results According to the correlation analysis between sedimentary environment parameters and organic carbon content (TOC), the organic matter enrichment in the Liang-2 lower submember shale was mainly controlled by factors of palaeowater depth, palaeoredox environment, deposition rate, and palaeoproductivity, and slightly affected by the palaeosalinity and palaeoclimate conditions. The variation in the deposition environment resulted in the vertical heterogeneity of shale. Conclusion The shale facies of Unit 6, formed in the good conditions for the organic matter enrichment referring to an anoxic environment in deep water, with a low deposition rate, a high palaeoproductivity, and the slight influence of terrigenous sources, was a favorable target layer for exploration.

Abstract The Lower Jurassic Ziliujing Formation in China’s Sichuan Basin is a significant shale target for exploration; however, the strong heterogeneity of the properties of organic matter (OM) in shale makes it challenging to identify the target area for exploration, and the mechanism of OM enrichment is still unclear. Furthermore, the mechanisms of the response of the Da’anzhai member to the Toarcian Oceanic Anoxic Event (T-OAE) are controversial. Previous studies have focused on sedimentary facies analysis based on mineralogy and elemental abundances and have provided minimal information about organic geochemistry, which adds to the challenge of deeply understanding the influence of the T-OAE on the molecular geochemical characteristics of the Da’anzhai member. In this study, the Da’anzhai member of the Lower Jurassic Ziliujing Formation in the Langzhong area, Sichuan Basin, is studied via X-ray diffraction, total organic carbon, gas chromatography–mass spectrometry, organic carbon isotope, organic petrographical and pyrolysis analyses. To accurately identify the trend of the paleosedimentary environmental proxies, the Mann‒Kendall test is utilized to identify the trend of the data. Our results show that the Da’anzhai shale was deposited in a dysoxic transitional environment to an intermittent reducing environment with freshwater to brackish conditions. The response to the T-OAE can be identified in the middle and upper parts of the middle submember and the bottom of the upper submember of the Da’anzhai member. The T-OAE influenced the redox conditions, salinity, and OM origins during deposition in the middle of the Da’anzhai member, which resulted in the enrichment of OM. The abnormally high C30 diahopane/C30 hopane (C30D/C30H) ratio can be considered a potential proxy for locating the section of strata that responded to the T-OAE in the Da’anzhai member. In the study area, the mechanism of the response of the Da’anzhai shale to the T-OAE manifested as an improvement in hydrological cycling rather than a marine incursion. Our study provides new information that deepens the understanding of the mechanisms of the response of lacustrine shales to oceanic anoxic events from the perspective of molecular organic geochemistry.

The sedimentary environment and organic matter (OM) accumulation are vital indicators for shale gas exploration. However, research on deep shale gas systems is relatively limited; moreover, the exploration of deep shale gas in the southeastern Sichuan Basin has entered a period of stagnation. In this study, systematic geochemical analysis of Wufeng (WF) and the first member of the Longmaxi (Long-1) deep shale samples from the recently drilled DY7 well in the Dingshan area of the Sichuan Basin is carried out, and the longitudinal variations in major and trace elements are revealed. The differences in the WF, lower section of the Long-1 (Long-11) and upper section ofthe Long-1 (Long-12) shales are studied in terms of redox conditions, paleoproductivity, terrigenous detrital input, sedimentation rate and paleoclimate, and the different main controlling factors of OM accumulation for these three layers are discussed. The WF shale has a higher TOC content (mean: 5.73%), the Long-11 shale has a high TOC content (mean: 2.89%), while the Long-12 shale has a low TOC content (mean: 1.44%). For the WF shale, due to complex geological events and large fluctuations in element contents, its TOC content is poorly correlated with these indices, redox and paleoproductivity proxies have a positive association with the Long-11 shale's TOC content, but negatively correlated with terrigenous input and sedimentation rate indices. The formation of these two sets of organic-rich shales (TOC > 2%) is jointly controlled by good preservation conditions. In contrast, the TOC content of the WF shale is higher than that of the Long-11 shale as the result that terrigenous input and sedimentation rate of the Long-11 shale represent the dilution and destruction of OM, which is different from the former. During the Long-12 depositional period, the water column experienced weak reducing conditions and low productivity, and its high terrigenous debris input further diluted the OM, leading to a low TOC content. [ABSTRACT FROM AUTHOR]

17β-Estradiol (E2) is a novel micro-pollutant that is widely distributed in aquatic sediments and has a universal toxicological effect on aquatic organisms. However, its ecological impact on aquatic microorganisms is not yet clear. In this study, we designed a simulation system for oligotrophic water deposition in the laboratory, analyzed the impact of different concentrations of E2 pollution on the carbon metabolism activity (carbon gas emission rate) of water microorganisms. Based on high-throughput sequencing results, we revealed the impact of E2 pollution on the community structure succession and metabolic function of bacteria, archaea, and methanogens in the simulated system, explored the impact mechanism of E2 pollution on microbial carbon metabolism in water bodies. Our results suggested that E2 significantly impacts the bacterial and archaeal community rather than the methanogen community, thereby indirectly inhibiting methane production. The achievements will bridge the theoretical gap between estrogen metabolism and carbon metabolism in sedimentary environments and contribute to enriching the ecological toxicology theory of steroid estrogen. [ABSTRACT FROM AUTHOR]

Structured marine clay is commonly encountered in offshore engineering projects and engineers are concerned about its impact on the engineering properties of marine clay as well as its correlation with index properties. Current research has emphasized the role of soil structure in these aspects of marine clay. In this study, we investigated the influence of depositional environment and oxidation-induced evolution of clay microstructure on the formation of clay structure in structured clay from Zhanjiang area, a coastal city located in South China. The distinct soil structure observed in marine-terrigenous clay deposited under different environments exhibited sensitivity ranging from 1.6 to 8.9 at varying moisture content levels. The wide range of sensitivity observed in structured marine-terrigenous clay was attributed to free iron oxide derived from siderite present in an acidic environment. Compared to other regions, Zhanjiang marine clay demonstrated favorable mechanical properties but poor physical properties due to its unique clay structure characteristics. Based on these findings, we proposed a modified approach for correlating index properties with engineering properties that yielded good predictions. [ABSTRACT FROM AUTHOR]

The end of the Neoproterozoic global ice age has promoted the evolution of the Earth's surface system and initiated the 'Great Explosion of Life'. Glaciation deposits provide valuable insights into the extreme climate conditions. In the southern margin of the North China Craton (NCC), an Ediacaran glacial deposit named 'Luoquan Formation' has been recently described in Luonan County, Shaanxi Province. It has significant characteristics of dark grey and black glacial deposits. Through extensive research in sedimentology, geochemistry and geochronology, the glacial sedimentary evolution sequence of the Luoquan Formation has been established. This research also help to define the age of the formation and reveal its provenance and sedimentary environment. The study reveals that four lithofacies associations were identified in the Luoquan Formation: diamictites, carbonates, dropstone‐bearing rock and black shale. The Luoquan Formation has experienced three cycles of glacial advance–retreat. Sedimentological evidence suggests that the sedimentary environments of the Luoquan Formation evolved from subglacial (diamictite) to intertidal, then to intertidal lagoon, or from subglacial deposits to shoreface (inner shelf, subtidal), then to deep water basin and fine‐grained turbidite and ice‐rafting. The age of the Luoquan Formation is estimated to be 562–550 Ma constrained by indirect chronological and paleontological data, maybe representing an Upper Ediacaran glaciation that occurred later than the Gaskiers glaciation. The overall age profile of detrital zircons from the Luoquan Formation can be divided into six groups, ranging from 1.1 to 1.6, 1.85 to 1.95, ~2.1, ~2.3, ~2.5 and 2.65 to 2.9 Ga. These age groups are consistent with the Archean to Meso‐Neoproterozoic magmatic–tectonic events in the southern margin of NCC, indicating they are ascribed to an origination directly from the southern margin of NCC. The Luoquan Formation exhibits the characteristics of isochronous and different sedimentary facies, with the glacial front moving from north to south. The discovery of Luoquan Formation in Lianshuigou section not only reflects the important significance of the restoration and reconstruction of the Ediacaran ice age, paleoenvironment and palaeogeography of the NCC but also provides significant evidence to support the further subdivision and correlation within the Ediacaran glacial deposits globally. [ABSTRACT FROM AUTHOR]

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Copyright of Special Oil & Gas Reservoirs is the property of Special Oil & Gas Reservoirs Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Introduction: Sedimentary evolution and river channel changes of large river delta (e.g. Huang River, Changjiang River) in response to environmental changes have been one of the key issues in global change research. Methods: This study reconstructed sedimentary environment changes in the modern Yellow River Delta (YRD), based on grain size and elemental chemical analysis of two short cores (YDC and YDG) from the southern region of the Qing 8 course delta of the modern YRD. Results: The results indicated that the cores YDC and YDG sediment were dominated by silt (58.47% and 67.6%, respectively) with varied grain-size variations and poor sediment sorting. The cores YDC and YDG sediments are both predominantly composed of the major element SiO2, and have an average content of 55.53% and 58.45%, respectively. The R-mode factor analysis showed the content of chemical substances of core sediments was controlled by three factors: grain size, sedimentary provenance, and marine sedimentary dynamics. Discussion: Before the diversion of the Yellow River to the Qing 8 course in 1996, the two cores sediment were mainly sources from the Yellow River, and both cores were in the delta-front sedimentary environment under weak hydrodynamic conditions. After the Yellow River was diverted to the Qing 8 course, the cores YDC and YDG experienced significant erosion under the nearshore strong waves and tides. And then the sedimentary environment of the YRD changed from siltation to erosion. The results of the study would be helps to further our understanding of the changes in sediment grain size and geochemical element characteristics in the Yellow River estuary, and reveal the evolution of its sedimentary environment. [ABSTRACT FROM AUTHOR]

The Jimsar Sag is an important shale oil exploration target area in the Junggar Basin, northwestern China. The Permian Lucaogou Formation, with a thickness of 200–300 m, is the primary exploration target. High-frequency variation in lithology is a typical feature of the Lucaogou Formation, reflecting the fluctuation of the depositional environment and organic matter enrichment. The evolution of the depositional environment and accumulation mechanism of organic matter still need to be elucidated for the Lucaogou Formation. High-resolution sampling of the entire Lucaogou Formation was applied to a 248 m long core from Well JX in the Jimsar Sag to examine the depositional environment and organic matter enrichment. The findings unveiled that the Lucaogou Formation was deposited under a hot and arid climate, within the confines of a closed saline paleo-lake, where sediments endured an extended period of anoxic conditions, displayed periodic oscillations in paleo-temperature and paleo-salinity values over time, alongside a continuous rise in paleo-water depth. The predominant source lithology of the Lucaogou Formation is felsic igneous rock. Small-scale transgression and hydrothermal sedimentation occurred during the deposition of the Lucaogou Formation. The prevailing hot climate and enduring reducing environment fostered ideal circumstances for the enrichment of organic matter in the Lucaogou Formation. Due to different sedimentary environments and enrichment mechanisms, organic matter is enriched in two modes in the Lucaogou Formation. [ABSTRACT FROM AUTHOR]

Copyright of Geology & Exploration is the property of Geology & Exploration Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Erlian Basin is a Mesozoic–Cenozoic rift basin with a large thick Pliocene sandstones deposit, which has important oil, gas, and uranium resources exploration potential. The paleo-sedimentary environment plays an important role in controlling the development of mineral resource. However, provenance and depositional environment of the Pliocene sandstones remain enigmatic. To address it, this study reports the whole rock geochemical compositions of sandstones from the Youqi and Siziwangqi regions to reflect the paleo-sedimentary environment. The Youqi sandstones are classified as litharenite-arkose, whereas the Siziwangqi sandstones exhibit a graywacke affinity. Furthermore, both the Youqi and Siziwangqi sandstones exhibit low CIA, PIA, ICV, and Th/U values, suggesting that their source rocks were of great maturation and experienced low to moderate chemical weathering processes. The Ni/Co, U/Th, and Ce/Ce* values in these sandstones range from 0.4 to 5.9, 0.20 to 0.37, and 0.80 to 1.09, respectively, indicating that these sandstones were formed in an oxygen-rich depositional environment. Additionally, interelement ratios such as Sr/Cu, SiO2/Al2O3, and Rb/Sr suggest a hot and arid paleoclimate during the deposition of these sandstones. Tectonic discrimination diagrams reveal a continental arc environment for the studied sandstones, Combining regional structural background, implying that the Erlian Basin was influenced by both Himalayan and the Pacific-Ocean-surrounding tectonism during the Pliocene period. [ABSTRACT FROM AUTHOR]

Lamination is the predominant and widely developed sedimentary structure in mudstones. Similar to organic pores in shale gas reservoirs, the inorganic pores in the laminae of shale oil reservoirs are equivalently important high-quality reservoir spaces and flow channels. The laminae characteristics are strongly heterogeneous, being controlled by both deposition and diagenesis. However, the origin of this diversity is poorly understood. A detailed examination of cores, thin sections, and scanning electron microscopy analyses were conducted on the lacustrine mudstone of the Qingshankou Formation in the Songliao Basin to study the influence of deposition and diagenesis on laminae characteristics and their relationship to reservoir quality. Three types of laminae are mainly developed, namely thick siliceous laminae, thin siliceous laminae, and thin siliceous and argillaceous mixed laminae. Deposition controls the type and distribution of laminae. The thin siliceous and argillaceous mixed laminae are controlled by climate-driven seasonal flux variations. The thick siliceous laminae and thin siliceous laminae are controlled by bottom current or gravity-driven transport processes due to increased terrestrial input. The thin siliceous laminae have the optimum reservoir properties, followed by the thin siliceous and argillaceous mixed laminae, while the thick siliceous laminae have the worst properties. Diagenesis controls the pore evolution of the laminae. Different laminae have different paths of diagenesis. The thin siliceous laminae are mainly cemented by chlorite, preserving some primary porosity. The clay mineral content of the thin siliceous and argillaceous mixed laminae is high, and the primary pores are mainly destroyed by the strong deformation of the clay minerals during compaction. The thick siliceous laminae are intensely cemented by calcite, losing most of the porosity. The present study enhances the understanding of reservoir characteristics in laminae and provides a reference for shale oil exploration. [ABSTRACT FROM AUTHOR]

The marine–continental transitional shale of the Upper Permian Longtan Formation in northern Guizhou is an important source rock in the upper Yangtze region of China, and it holds significant potential for the exploration of shale gas. To investigate the correlation between sedimentary conditions and the accumulation of organic matters in marine–continental transitional shale, this paper performed an extensive analysis using organic geochemical testing, organic petrology examination, a cross-section polisher–scanning electron microscope (CP-SEM), and geochemical analysis. The Jinsha and Dafang drilling cores were selected as the research subjects. The results showed that the TOC of the Longtan Formation in the study area was relatively high, and the TOC content of the tidal flat–lagoon environment (average of 8.37%) was significantly higher than that of the delta samples (average of 2.77%). The high content of Al2O3 (average of 17.41% in DC-1, average of 16.53% in JC-1) indicated strong terrigenous detrital input. The proxies indicated that the Longtan Formation shale in northern Guizhou was deposited in a climate that was both warm and humid, with oxic–dysoxic sedimentary water characterized by high biological productivity and a rapid sedimentation rate. The organic-rich shales during the marine and continental transitional phases were affected by various factors, including the paleo-climate, water redox properties, paleo-productivity, sedimentation rate, and other variables, which directly or indirectly impacted the availability, burial, and preservation of organic matter. [ABSTRACT FROM AUTHOR]

There are abundant bauxite and ceramic-making claystone resources with advantageous and developmental potential in the central area of Guizhou Province. Through the research into the route survey, section measurement and mineral identification on Jiujialu Formation in Datang age of GuiZhou Province, in combination with the analysis of paleoenvironment by finger trace element, the findings firstly illustrate that: the microscope observation on this strata of rocks shows vadose pisolith structure of the aluminous clay rocks, isocrystalline structure of the siliceous rocks and micrite-cluster structure of the ferraginous rocks, suggesting a characteristic of continental sedimentary environment in the study area, meanwhile, the rock type and lithology combination characteristics roughly reflect that the whole area is terrigenous clastic deposition under the settings of the reducing environment and low energy hydrodynamic. Secondly, the Th/U ratio indicates that the clay rocks of Jiujialu Formation in the Datang age are basically formed in a weak oxidation environment, and with the rising ratio during the deposition process, the oxidation gradually strengthened at the same time. Lastly, the values of facies element B, Sr and Ba, and the ratios of B/Ga and Sr/Ba indicate that the clay rocks in the Datang age of Jiujialu Formation underwent several transgressions stages and regressions stages in the Early Carboniferous, and eventually turned into a continental environment. It is inferred that Jiujialu Formation in the Datang age of Early Carboniferous in Jinsha area was located in the epicontinental sea zone. As constrained by the shape and position of the palaeokarst and the direction of seawater influx, Jiujialu Formation in Jinsha area appears complex sedimentary characteristics in different areas. [ABSTRACT FROM AUTHOR]

The comprehension of sediment grain size parameters and the corresponding sedimentary environment holds paramount importance in elucidating the engineering geological attributes of the subaqueous seabed. This study delineated the sedimentary environment zoning in the northern sea area of Qingdao through cluster analysis of grain size parameters derived from 123 surface sediment samples. The study analyzed the correlation between sediment geotechnical indices and grain size parameters across diverse sedimentary environments. A correlation equation was established for samples exhibiting a strong correlation. The study found four distinct sedimentary environments in the study area: coastal, transitional, shallow sea, and residual. Within the same sedimentary environment, the average grain size and sorting coefficient exhibit significant correlations with geotechnical indices such as water content, density, shear strength, plastic limit, liquid limit, and plastic index. However, notable disparities in the correlation between grain size parameters and geotechnical indices emerge across different sedimentary environments. [ABSTRACT FROM AUTHOR]

As a hydrocarbon-rich depression within the Bohai Bay Basin, the Huanghekou Depression is a focal region for exploring hydrocarbons in the eastern China Sea. Previous studies have insufficiently examined the correlation between the enrichment of organic matter and the environments in which it is deposited. Herein, the hydrocarbon potential, palaeoclimate, sedimentary environment, organic matter sources, and organic matter enrichment of the source rocks of the Shahejie Formation in the Huanghekou Depression were investigated using organic and inorganic geochemical indicators. The organic matter type of the source rock in Huanghekou Depression's Shahejie Formation was predominantly Type II, with a minor presence of Type III. Furthermore, the source rock had a poor-to-good comprehensive evaluation grade in E3s1–2, whereas E2s3 and E2s4 had medium-to-good comprehensive evaluations in their source rocks. In terms of maturity, E3s1 was in an intermediate position between the immature and mature stages and E3s2 and E2s3 were between the low-maturity and mature stages, whereas E2s4 transitioned into full maturity. Biomarkers and sensitive element indicators indicated that the organic matter in E3s1–2 was primarily derived from lower aquatic organisms and algae. This palaeoclimate was characterised by aridity, a water body containing saline and semi-saline water, and a strongly reducing environment resulting from water body stratification, leading to oxygen deficiency. The organic matter in E2s3 was primarily derived from aquatic organisms and algal inputs; these deposits were formed in a reduced environment characterised by relatively low salinity, ranging between semi-saline and freshwater conditions. The organic matter enrichment model of the Shahejie Formation was established based on sedimentary environment, palaeoclimatic, and organic matter source analyses, utilising E3s1–2 as preservation models and E2s3 as the productivity model. This study provides a basis for in-depth exploration and advancement of oil and gas reserves. [ABSTRACT FROM AUTHOR]

The studied section is located in the 113Km east of Birjand (25Km Asadiyeh City) and east of Pating Village. The mentioned sequence, aged Late Cretaceous, is totally 246m in thickness and mostly consists of thick and medium bedded limestones along rock units. The lower boundary has been limited by basal red conglomerate and the upper boundary has been covered by red-colored sandstone unit. In This research, based on both field and laboratory studies, the main components of carbonate rocks include both skeletal and non-skeletal grains and totally 7 carbonate microfacies have been determined which have been deposited within 3 facies belts including tidal flat, Semi-restricted lagoon and shoal. According to the obtained evidences from the microfacies analysis, the suggested depositional model for the Pating section is a homoclinal ramps type carbonate platform. All of the microfacies are mainly deposited in the inner part of the ramp slope. The obtained geochemical data from carbonate samples analysis indicate a calcitic original mineralogy and dominance of a closed diagenetic system for the studied sequence. Also, according to the geochemical data, a temperate climatic condition could be considered for the formation environment of this sequence which is confirmed by the Late Cretaceous Palaeogeographic global map. The studied limestone samples have been widely affected by different diagenetic processes that the most important of which are micritization, cementation, mechanical and chemical compaction, formation of various types of porosity, dissolution, neomorphism, replacement, fracturing and vein-filling cements that have been formed in a variety of marine, meteoric, shallow burial and uplift diagenetic environments. [ABSTRACT FROM AUTHOR]

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[Objective] The Jurassic was a period of typical fluctuating greenhouse climate that resulted in the deposition of sediments in terrestrial basins. In China, a number of large terrestrial basins were formed during the Jurassic, and the discrepancies in sedimentation records have been preserved in several basins. This study focused on the Middle-Upper Jurassic terrestrial redbeds in the northeastern Sichuan Basin to determine changes in the sedimentary environment and paleoclimate. [Methods] Based on the observation of outcrops, analyses of microscopic clastic composition and C-O isotopes, and to estimate the atmospheric CO2 concentration in this area. [Results] Medium-to-fine clastic rocks are the predominant lithologies, and five sandstones are further classified by composition and lithological content. Three sedimentary environmental units are recognized: meandering river, lake, and paleosol, which represents a simpler system than in the western Sichuan Basin. The upwards facies sequence is pedogenic, beginning with low sand/mud ratio meandering mudrocks in the Middle Jurassic Shaximiao Formation, lacustrine mudrocks with siltstones in the lower Suining Formation of the lower Upper Jurassic, and upward-coarsening and thickening high sand/mud ratio meandering sandstones in the upper Suining and Penglaizhen Formations of the Middle-Upper Jurassic. Two and a half cycles of semi-arid and arid climate were distinguished in the Middle-Upper Jurassic sequence by F/Q and F/L indices, corresponding to the lower Shaximiao Formation, the upper Shaximiao Formation + lower Suining Formation, and the upper Suining Formation + Penglaizhen Formation, respectively. From the pCO2, it is postulated that the Middle Jurassic was relatively cool, becoming warmer in the early Late Jurassic and hot in the middle-to-late Late Jurassic, roughly consistent with the framework of global marine climates. [Conclusion] The climate was (semi-) arid overall in northeastern Sichuan, similar to that in other regions of the Sichuan Basin. It will be necessary to further verify that an intermittent semi-wet climate occurred in western Sichuan and that a hot climate prevailed in northeastern Sichuan. [ABSTRACT FROM AUTHOR]