Abstract The early Late Cretaceous hothouse was featured by intense storms and a prevailing monsoon climate, yet direct evidence for regional extreme precipitation events is rare. Here, we reconstruct local weathering and hydrological processes using magnesium and strontium isotopes (δ26Mg and 87Sr/86Sr) from lacustrine dolostones in the Upper Cretaceous Qingshankou Formation, Songliao Basin, Northeast China. The δ26Mg and 87Sr/86Sr records exhibit coherent bimodal variations. Surficial Mg cycling reveals two hydroclimatic regimes: during 91.9 ∼ 91.2 Ma, high precipitation intensified weathering, especially a 500‐kyr pluvial interval with rainfall exceeding 2,000 mm/yr (millimeters per year), which triggered lake flooding and organic carbon burial; during 91.2 ∼ 90.7 Ma, declined weathering and precipitation indicated monsoon retreat. The Hadley circulation shrinkage, orbital‐paced aquifer‐eustasy, and coastal mountains induced by Okhotomorsk‐East Asia collision, were triple amplifiers in elevating the Songliao Basin into a unique mid‐latitude humidity hotspot with carbon burial, while contemporaneous inland and low‐latitude areas experienced aridification or exhumation.

Geothermal field characteristics fundamentally control hydrocarbon generation, phase evolution, and preservation, and are particularly critical in deep to ultra-deep hydrocarbon exploration. The Tazhong Uplift is a key area for deep to ultra-deep hydrocarbon exploration in the Tarim Basin; however, its deep thermal regime and controlling factors remain inadequately characterized. This study aims to accurately characterize the geothermal field and crustal thermal structure of the Tazhong Uplift to provide thermal constraints for ultra-deep exploration. We systematically compiled system steady-state temperature data from 24 wells, bottom-hole temperature (BHT) data from 51 wells, and rock thermal property measurements. Using the one-dimensional steady-state heat conduction equation, present-day geothermal gradients at 0-5000 m depths and terrestrial heat flow were calculated, and formation temperatures were predicted at deep horizons (6000-10,000 m). Results show geothermal gradients at 0-5000 m of 18.5-26.7 degrees C/km (average 23.06 degrees C/km) and heat flow of 39.3-59.8 mW/m(2) (average 48.1 mW/m(2)), both significantly higher than basin averages. The distribution of the geothermal field is jointly controlled by basement structure and rock thermophysical properties. Basement highs typically exhibit elevated geothermal gradients and high heat flow. The dual-layer structure of "upper clastic rocks (low thermal conductivity, high heat production) + lower carbonate rocks (high thermal conductivity, low heat production)" results in a vertical differentiation characterized by a "high-upper, low-lower" geothermal gradient. Notably, the thick Upper Ordovician mudstone acts as a regional "thermal blanket", significantly reducing geothermal parameters in the northern slope area. Crustal thermal structure analysis indicates a "cold mantle" signature of cratonic basins, with a thermal lithosphere thickness of similar to 134-145 km and a Moho temperature of similar to 581 degrees C. These findings reveal that despite the ultra-deep burial (>8000 m), the "cold" thermal background and the thermal regulation of the overlying diverse lithologies maintain formation temperatures within a range favorable for liquid hydrocarbon preservation, significantly expanding the depth limit for oil exploration in the Tarim Basin.

Organic matter degradation is a vital component of the carbon cycle, which has been extensively studied in modern marine and lacustrine systems. However, the degradation process in their deep-time counterpart is poorly understood due to the lack of suitable proxies. We propose using biomarker concentrations for tracing biodegradation and carbon cycle that happened in the deep-time lacustrine systems, based on two hypotheses: 1) Hopanes will be enriched against total organic carbon (TOC) if the original organic matter has undergone significant reworking, as hopanoids are more recalcitrant than many organic compounds and are derived from heterotrophic bacteria during degradation; 2) The biomarker concentrations relative to sedimentary rock should positively correlate with TOC if the original organic matter undergoes limited biodegradation, while strong reworking will decouple biomarker concentrations and TOC. To test our hypotheses, we focus on the Songliao Basin in Northeast Asia, where the Cretaceous Qingshankou Formation records lacustrine expansion and contraction offering an exceptional natural laboratory to investigate the relationship among redox conditions, biodegradation, and biomarker concentrations. Our study shows that in more oxidized conditions (low TOC and MoEF), hopane concentrations relative to TOC (hopane/TOC) can be two orders of magnitude higher than those in more reducing conditions (high TOC and MoEF) indicating that hopane concentration reflects the intensity of redox-controlled biodegradation. We also analyze the relationships between biomarker concentrations (biomarker/rock) and TOC from the perspective of the microbial communities living in the ancient lacustrine system. The biomarkers, such as sterane, pristane, phytane, and gammacerane, generated by microbes living above the oxycline or in the transitional zone show no correlation with TOC, whereas the aryl isoprenoids generated beneath the oxycline correlate well with TOC. The distinct correlation patterns suggest that organic matter produced beneath the oxycline undergoes limited biodegradation and predominates the sedimentary organic matter, whereas organic matter generated from surface water is strongly reworked and could be the secondary contributor to sedimentary organic matter. We deduced that biodegradation is stronger in lacustrine than in marine environments after further compiling previously reported hopane concentrations of black shales and modern sediments. Our study highlights the application of biomarker concentrations for evaluating biodegradation and understanding carbon transfer from the photic zone to sediments in geological records.

The preservation of organic matter (OM) into sediments plays a critical role in regulating the global carbon cycle. Although bottom water anoxia enhances OM preservation by limiting aerobic degradation, anoxic conditions also permit anaerobic degradation, the impact of which on the preservation efficiency of OM remains unclear. Herein, total organic carbon content (TOC), Rock-Eval Hydrogen Index (HI), redox-sensitive elements, Fe and S speciation were explored to evaluate the influence of redox conditions on OM preservation efficiency in the Triassic Chang 7 Member, Ordos Basin. This interval is characterized by high TOC but exhibits HI lower than those of most lacustrine shales deposited under anoxic conditions. Moreover, high Fe and S content indicates that intensive anaerobic degradation could occur during the preservation process. The elevated enrichment factor of molybdenum (Mo-EF) and uranium (U-EF), a high proportion of highly reactive Fe (Fe-HR/Fe-T > 0.38), a moderate pyrite Fe to highly reactive Fe ratio (Fe-py/Fe-HR < 0.7) and low organic sulfur content (atomic S-org:C-org < 0.03) indicate that the Chang 7-3 submember was deposited under ferruginous conditions. In contrast, the varied Mo-EF and U-EF, Fe-HR/Fe-T and Fe-py/Fe-HR ratio indicate that Chang 7-2 and Chang 7-1 submembers were deposited under oxic-ferruginous conditions. Chang 7-3 shows the highest TOC and HI, suggesting enhanced OM preservation efficiency as the redox conditions shifting towards anoxic. However, within Chang 7-3, HI decreases with increasing concentrations of reduced Fe, S, indicating that anaerobic degradation lowered the preservation efficiency of OM. By comparing with previous studied euxinic shales, we find that the fate of sulfides produced by microbial sulfate reduction determines how anaerobic degradation affects OM preservation. The positive correlation between HI and atomic S-org:C-org ratio in euxinic shales suggests that free sulfides promote the preservation of OM through OM sulfurization. Nevertheless, the low atomic S-org:C-org ratio in Chang 7-3 indicates that most sulfides were sequestered by reduced iron to form pyrite, weak OM sulfurization did not enhance the preservation of OM. OM sulfurization under euxinic conditions makes euxinic conditions the most suitable for OM preservation, while anaerobic degradation can still reduce the preservation efficiency of OM when OM sulfurization is limited.

The ultra-deep (deeper than 8 000 m) petroleum in the platform-basin zones of the Tarim Basin has been found mainly in the Lower Paleozoic reservoirs located to the east of the strike-slip fault F5 in the north depression. However, the source and exploration potential of the ultra-deep petroleum in the Cambrian on the west of F5 are still unclear. Through the analysis of lithofacies and biomarkers, it is revealed that there are at least three kinds of isochronous source rocks (SRs) in the Cambrian Newfoundland Series in Tarim Basin, which were deposited in three sedimentary environments, i.e. sulfide slope, deep-water shelf and restricted bay. In 2024, Well XT-1 in the western part of northern Tarim Basin has yielded a high production of condensate from the Cambrian. In the produced oil, entire aryl-isoprenoid alkane biomarkers were detected, but triaromatic dinosterane was absent. This finding is well consistent with the geochemical characteristics of the Newfoundland sulfidized slope SRs represented by those in wells LT-1 and QT-1, suggesting that the Newfoundland SRs are the main source of the Cambrian petroleum discovered in Well XT-1. Cambrian crude oil of Well XT-1 also presents the predominance of C29 steranes and is rich in long-chain tricyclic terpanes (up to C39), which can be the indicators for effectively distinguishing lithofacies such as siliceous mudstone and carbonate rock. Combined with the analysis of hydrocarbon accumulation in respect of conduction systems including thrust fault and strike-slip fault, it is found that the area to the west of F5 is possible to receive effective supply of hydrocarbons from the Cambrian Newfoundland SRs in Manxi hydrocarbon-generation center. This finding suggests that the area to the west of F5 will be a new target of exploration in the Cambrian ultra-deep structural-lithologic reservoirs in the Tarim Basin, in addition to the Cambrian ultra-deep platform-margin facies-controlled reservoirs in the eastern part of the basin.

The classic model of the carbon cycle suggests that the extensive burial of 12C-enriched organic carbon leads to a positive carbon isotope (δ13C) excursion (CIE), while massive oxidation of organic carbon results in a negative CIE. However, global events such as the BAsal Cambrian Carbon isotope Excursion (BACE) and the Steptoean Positive Carbon Isotope Excursion (SPICE) are global negative and positive δ13C excursions, respectively, and they also exhibit significant organic carbon burial anomalies, displaying decoupling between carbon isotope anomalies and organic carbon burial. Based on the analyses of the Cambrian carbon cycle and paleoceanographic evolution records from well Tadong2 in the Tarim Basin, we propose a novel model of the carbon cycle in the Cambrian ocean that incorporates oceanic dissolved organic carbon (DOC). Our findings are as follows. (1) The Cambrian ocean maintained substantial DOC reservoirs, which were regulated by ocean currents and paleo-redox conditions and exerted significant influence on the oceanic carbon cycle. (2) The oxidation of the oceanic DOC reservoirs during the early Cambrian led to the BACE and the Asian Phenomenon of the Cambrian petroleum systems, while the expansion of the oceanic DOC reservoirs during the SPICE resulted in a global positive δ13C excursion and the absence of significant organic carbon burial. (3) The deep-basin sedimentary environment in the eastern depression of the Tarim Basin may have fostered the development of organic-rich black shales during the Furongian Series, corresponding to organic carbon burial during the SPICE and representing potential prospects for ultra-deep oil and gas exploration. Future research should focus on the formation mechanism, reserve scale, and influencing factors of the oceanic DOC reservoirs, as well as their resource and environmental effects. It is expected that new breakthroughs will be made in the fields of Earth system science and oil and gas exploration.

The Tabei uplift in the Tarim Basin is one of the deepest and most important petroleum-producing areas in China, with more than 3 billion t (21 billion bbl) of oil equivalent discovered in the Paleozoic carbonate reservoirs. Further petroleum exploration and development in the Tabei and neighboring areas will greatly bene fit from an in-depth understanding of the hydrocarbon charge and accumulation history of these deeply buried carbonate reservoirs. The molecular correlation of reservoir oils indicates that oils from major accumulations in the area share similar geochemical characteristics and were presumably derived from the same source rocks deposited in a marine environment. The Shunbei reservoir oil has the highest thermal maturity, followed by the Yuecan reservoir oil, whereas the Tahe reservoir oil has the lowest thermal maturity. Six generations of calcite cementation spanning over 130 m.y. have been delineated in calcite veins, with U-Pb ages ranging from ca. 446 Ma to ca. 316 Ma. The second and fifth generations of calcite cementation were accompanied by oil charge events, as indicated by the occurrence of bitumen and primary oil inclusions. Fluid inclusion analysis coupled with basin modeling results reveal that the Tabei area experienced two major oil charges, with the first charge occurring during the late Caledonian Orogeny, at 426 to 415 Ma, and the second charge during the middle-late Hercynian Orogeny, at 339 to 278 Ma. The Shunbei and Yuecan reservoirs contain well-preserved oils accumulated during the two charge events, whereas the Tahe reservoir oil has been partially biodegraded.

Taking the Paleozoic of the Sichuan and Tarim basins in China as example, the controlling effects of the Earth system evolution and multi-spherical interactions on the formation and enrichment of marine ultra-deep petroleum in China have been elaborated. By discussing the development of “source-reservoir-seal” controlled by the breakup and assembly of supercontinents and regional tectonic movements, and the mechanisms of petroleum generation and accumulation controlled by temperature-pressure system and fault conduit system, Both the South China and Tarim blocks passed through the intertropical convergence zone (ITCZ) of the low-latitude Hadley Cell twice during their drifts, and formed hydrocarbon source rocks with high quality. It is proposed that deep tectonic activities and surface climate evolution jointly controlled the types and stratigraphic positions of ultra-deep hydrocarbon source rocks, reservoirs, and seals in the Sichuan and Tarim basins, forming multiple petroleum systems in the Ediacaran–Cambrian, Cambrian–Ordovician, Cambrian–Permian and Permian–Triassic strata. The matching degree of source-reservoir-seal, the type of organic matter in source rocks, the deep thermal regime of basin, and the burial-uplift process across tectonic periods collectively control the entire process from the generation to the accumulation of oil and gas. Three types of oil and gas enrichment models are formed, including near-source accumulation in platform marginal zones, distant-source accumulation in high-energy beaches through faults, and three-dimensional accumulation in strike-slip fault zones, which ultimately result in the multi-layered natural gas enrichment in ultra-deep layers of the Sichuan Basin and co-enrichment of oil and gas in the ultra-deep layers of the Tarim Basin.

The Lower Cambrian petroleum system in the Tarim Basin has undergone multiple periods of tectonic movements, leading to successive hydrocarbon expulsion events and adjustments. The complex process of hydrocarbon accumulation occurred under deep burial conditions, persisting at depths of nearly 6,000 m over an extended period. This has resulted in the current occurrence of various phases including light oil, condensate, and gas in the deep-ultradeep strata of the Tarim Basin. The intricacies of formation of hydrocarbon accumulations and phase evolution have posed challenges to understanding the accumulation mechanisms and enrichment patterns of the Cambrian in the Tarim Basin, consequently lowering the success rate of oil and gas exploration. Such characteristics of multi-stage accumulation and adjustment are prevalent in deep hydrocarbon systems. Therefore, based on data from Well ZH1 in the Tazhong Uplift, combined with basin simulation, Compositional kinetics model, and PVT performance simulation, this study investigates the hydrocarbon generation and phase evolution processes in the deep hydrocarbon systems of the Tazhong Uplift. The results indicate that Well ZH1 entered the hydrocarbon generation peak during the Late Ordovician, followed by secondary cracking as the predominant hydrocarbon evolution process. Hydrocarbon fluids within the Lower Cambrian reservoir transitioned into the condensate phase towards the end of the Cambrian, with increasing depth resulting in higher gas-oil ratios and a decreasing trend in viscosity and density.

The Yurtus Formation is generally believed as one of the most potential hydrocarbon source rocks under the Cambrian gypsum-salt bed in the Tarim Basin of China. This formation exhibits unique geochemical characteristics during the Ediacaran-Cambrian transition period. In this study, we investigated the lower and upper black shales from the Yurtus Formation for the high-resolution geochemical analysis in order to further characterize the prevailing redox conditions and sedimentary mechanisms involved in the organic matter accumulation process. During the deposition of the lower black shale with high TOC in Unit2, the high concentrations of phosphorite and barite, and the REE geochemistry manifested a mixture of hydrothermal fluid and seawater. Through in-situ laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS), we explored the element distribution of the drill-core-preserved phosphate nodule, indicating that the phosphogenesis may be related to the involvement of bacteria activities under intermittently oxic bottom waters or consistently free oxygen conditions. Biomarker evidence by the identification of green sulfur bacteria demonstrated the occurrence of photic zone euxinia (PZE), and the trace metal patterns revealed intermittently bottom water oxygenation and stratified ocean which was consistent with the scenario of phosphate nodule formation. In contrast, the upper black shale with relatively low TOC was characterized by a detrital input, with significantly decreasing redox-sensitive trace mental enrichment (UEF, MoEF, VEF) and positive excursion of carbon isotopes, as well as a positive relationship between ∑REE and Al. The present study provides more explicit insights into not only the sedimentary mechanism of the black shale, but also the evolution of the Earth system at the key interval of the early Cambrian.

Cyanobacteria have evolved since the early history of the Earth and played a critical role in Earth’s carbon cycle. However, the contribution of cyanobacteria to organic carbon burial has rarely been underscored due to their lack of lipids membrane, which are refractory materials ready for preservation in sediments. To clarify the role of cyanobacteria in organic carbon burial, we focus on kerogen, which is the precursor of petroleum and also one of the most important organic carbon pools. We first review the physiological and environmental characteristics of modern cyanobacteria, which sets the theoretical foundations for kerogen formation. Cyanobacteria cell wall contains refractory algaenan, biomacromolecules rich in long-chain aliphatic structures, which are ready to be preserved in sediments and generate hydrocarbons during pyrolysis. Cyanobacteria can also form dense blooms in special environments, such as high temperatures with limited nitrogen supply. We then compile the cyanobacteria-dominant kerogen to reveal its temporal distribution in geological history. The cyanobacteria-dominant kerogen is identified mainly by three criteria including high total organic carbon, high hopane/sterane ratio, and high 2-MeHop index. The results show that the biological parent material of Proterozoic kerogen is dominated by cyanobacteria when eukaryotic algae did not experience massive blooms. In Phanerozoic, cyanobacteria-dominant kerogen is formed in episodic ocean anoxic conditions, where strong denitrification reduced nitrogen supply and hindered the growth of eukaryotic algae. Rock-Eval results show that cyanobacteria-dominant kerogen could have higher hydrogen content than cyanobacteria algaenan. In addition, we compare two Proterozoic cyanobacteria-dominant black shales deposited in anoxic and partially oxic environments and find that the kerogen formed in the anoxic environment has much higher hydrocarbon potential than that formed in the oxic environment. The difference in hydrocarbon potential, together with kerogen compositions, indicates that decomposable molecules with higher hydrocarbon potential could also form kerogen besides refractory algaenan. Based on this holistic review, we propose a model for cyanobacteria flourishing and organic matter preservation and highlight the critical role cyanobacteria played in organic carbon burial in Earth's history.

Nitrogen is an essential nutrient for all life on Earth. It is, and likely has been, a critical limiting nutrient controlling primary production rates in the oceans. The marine N budget is regulated by the balance between nitrogen loss as N2 (and N2O) in low-oxygen settings in the oceans including marine sediments and coastal oxygenminimum zones and nitrogen inputs, mainly from nitrogen fixation. How this balance has changed through Earth history, particularly considering changing degrees of ocean oxygenation, is a frontier research area. Here, we explore ancient ocean nitrogen dynamics as revealed through stable nitrogen isotopes in the ca. 1400 million year old (Ma) Xiamaling Formation of North China. We compare these dynamics to other Mesoproterozoic-aged settings and to modern environments. Through these comparisons, we see that Mesoproterozoic (1600 to 1000 Ma) oceans experienced both nitrogen replete- and nitrogen-deplete conditions with isotope systematics very similar to modern analogues. We provide models explaining the ancient ocean nitrogen dynamics, and we conclude that Mesoproterozoic oceans generally maintained extensive regions of nitrate-replete conditions. These nitrate-deplete conditions could have corresponded with extensive areas of deoxygenated seawater or vast nitrate-replete marine environments similar to modern oxygen-minimum zone environments. We also evaluate, generally, what nitrogen isotope systematics can and cannot tell us about nitrogen limitation in ancient oceans.

The ultra-deep Cambrian System in the Tarim Basin is an important field for petroleum exploration, while fine division of the Cambrian strata remains controversial. In recent years, carbon isotope stratigraphy of the Cambrian System has been established and widely used. Here, we report an integrated profile of carbonate and organic carbon isotopic values(δ 13 C carb and δ 13 C org ) from cuttings of the Tadong2 Well in the eastern Tarim Basin. Three carbon isotope anomalies of BACE, ROECE and SPICE were recognized on the δ 13 C carb profile. Three apogees and a nadir on the δ 13 C org profile and the onset of ROECE on the δ 13 C carb profile were suggested as boundaries of the present four series of the Cambrian System. Suggested boundaries are easily identifiable on the gamma logging profile and is consistent with the previous division scheme, based on biostratigraphic evidence in outcrop sections. Abnormal carbon cycle perturbations and organic carbon burials during the BACE and SPICE events might be related to the reduction and expansion of a huge dissolved organic carbon reservoir in the deep ocean of the ancient Tarim Basin.

Almost 8 x 108 tons marine condensate reserveshave been estimated to be present in the Paleozoic to Cenozoic reservoirs of the Tarim Basin. Thethermal maturity of condensate gases are estimated to be greater than 2.2%REo (vitrinite reflectance equivalent),which are higher than the calculated maturity of thecondensates <1.9%REo. Therefore, the formation of gas-condensates might include a mixture of later cracked gases with earlieroil ac-cumulations. The mixture model indicates that the relative content of oil-cracking gases varies from 42% to 98% in condensate gases, and the mixing extent of kerogen and oil cracking gas with various maturities could also lead to the carbon isotope reversal of methane and ethane. The positive correlation between the gas-oil ratio (GOR) of gas condensates and the maturity of cracking gas shows that the cracking gas is much more enriched in the eastern Tabei uplift of the northern Tarim Basin thanthe Tazhong uplift ofcentral Tarim Basin. The relative abundance of the triaromatic dinosteranes in the condensates coincides with the feature of hydrocarbons derived from Cambrian source rocks Furthermore, based on the multi-stagethermal maturity of the Cambrian source rocks, the formation mechanism of secondary gas condensates has been demonstrated and reconstructed. Recent exploration discoveries in the ultra-deep Cambrian of the Tabei and Tazhong uplifts, involving ZS-1 and LT-1wells, confirmed the cracking gases were derived from the post-high mature Manjar Depression and that liquid hydrocarbons could be maintained in the ultra-deep of Tabei uplift. The findings are helpful toestimate the exploration potential of the deeper cracking gases in the high-temperature and high-pressurereservoirs of the Tarim Basin.

To understand the effect of thermochemical sulphate reduction (TSR) on the stable carbon isotopes of light hydrocarbons (LHs) associated with natural gas, 15 gases with varying H 2 S content from Ordovician reservoir of the Tazhong gas field (TZ-I) in Tarim Basin and Triassic Leikoupo reservoir of the Zhongba gas field (ZB) in Sichuan Basin were collected. Based on the data from molecular components and stable carbon isotope ratios of the C 1 -C 4 alongside the individual LHs (C 6 -C 7 ) in these gases, the origin of natural gas and the effect of TSR on the stable carbon isotope ratio of individual LHs were studied. The δ 13 C in ethane (<−28‰), LHs (<−26‰) and the composition distribution characteristic of C 6 -C 7 indicated that the gases were oil-associated gases. Moreover, the gas sourness index, defined as H 2 S/(H 2 S+∑C n ) demonstrated that the gases from the TZ-I and ZB gas fields were in the early liquid-hydrocarbon-involved and heavy-hydrocarbon-gas-dominated TSR stages, respectively. The comparison of stable carbon isotope ratios of the LHs between the two gas fields revealed that TSR exhibited a complex effect on the carbon isotope values of LHs, but only little effect on 2-methylpentane (2-MP) and 3-methylpentane (3-MP). The δ 13 C values of benzene (BEN) and toluene (TOL) were -28.3‰ and -29.4‰ in the TZ-I and -27.7‰ and -28.1‰ in the ZB gas field. The stable carbon isotope ratios of BEN and TOL in ZB gas field exhibited more enriched 13 C than those in TZ-I gas field, likely driven by TSR. Meanwhile, cycloalkanes, such as methyl cyclopentane (MCP), cyclohexane (CH), and methylcyclohexane (MCH), enriched 13 C with TSR process and displayed a greater trend than aromatic compounds, about 2‰. Therefore, the influence of TSR on the carbon isotopes of individual LHs should be considered while using the stable carbon isotope ratio of cycloalkanes, BEN, and TOL to identify the genetic type and source of marine natural gas, especially at the cross plot (δ 13 C = −24‰) of coal-derived gas and oil-associated gas.

Mesoproterozoic marine organic-rich rocks are widely distributed in the North China Craton,include the Gaoyuzhuang（GYZ）,the Hongshuizhuang（HSZ）,and the Xiamaling（XML） formations.According to the T max value and isomerisation ratio of C 31 homohopanes,the XML,HSZ,and GYZ samples were in low mature,mature and high mature stage,respectively.Biomarker distribution in extractable organic matter（EOM） of three Mesoproterozoic organic-rock samples in different maturity were analysed to reveal the organic precursor and preservation pathway of in the Mesoproterozoic Combined with gold-tube pyrolysates of three Mesoproterozoic samples,it could further illuminate the chemical composition of Mesoproterozoic kerogen,given excluding.The results indicated that the three formations were all deposited under reducing condition and their organic precursors mainly were some aquatic organisms.High content of rearranged hopanes was detected in EOM of XML and HSZ samples,whereas they were relatively low in the high mature GYZ sample.Contrast to that in EOM,the relative concentration of rearranged hopanes sharply decreased in the gold-tube pyrolysates of the XML kerogen,then slightly increased but was still significantly lower than the EOM of XML sample,which indicated that catalysis of clay minerals in the early diagenesis only changed the chemical composition of the unstable functional groups of the kerogen during the preservation.Due to the thriving heterotrophic microbes and low sink rate of particulate organic matter during the Mesoproterozoic,primary producers suffered extensive degradation during sinking process,only some resistant biopolymers lacking of lipid compounds survived from heterotrophic degradation,while heterotrophic microbes contained more proportion of organic precursors.Abundant pristane（Pr） and phytane（Ph）were only released in high mature stage because of the protection of the macromolecular structure of resistant biopolymers which prevented biomarkers from being altered by the thermal stress.The absence of 13 α（n-alkyl）-tricyclic terpanes in the high matured hydrocarbon products also indicated the different precursors between different parts of Mesoproterozoic kerogen.The evolution of the biomarker composition and content of Mesoproterozoic kerogen showed some special characteristics differing from those of Phanerozoic kerogen.The total concentrations of hopanes displayed with an order of low mature stage＞ high mature stage＞ mature stage.Relative content of rearranged hopanes in the hydrocarbon generated in high mature stage was significantly lower than that in the low maturity stage.The ratios of Pr/n-C 17 and Ph/n-C 18 increased with thermal maturity,and the ratio of nC 21- /nC 22+ decreased in the high maturity stage,thus displaying another order of mature stage＞ high maturity stage＞ low maturity stage.The unique preservation pathway of Mesoproterozoic organisms was attributed to the special evolution characteristics of biomarker distributions,which should be considered in the Mesoproterozoic marine environment and biological studies.

The Tarim Basin is the only petroliferous basin enriched with marine oil and gas in China. It is presently also the deepest basin for petroleum exploration and development in the world. There are two main sets of marine Source Rocks (SRs) in the Tarim Basin, namely the high over‐mature Cambrian–Lower Ordovician (∊ –O1) and the moderately mature Middle–Upper Ordovician (O2–3). The characteristic biomarkers of SRs and oils indicate that the main origin of the marine petroleum is a mixed source of ∊ –O1 and O2–3 SRs. With increasing burial, the hydrocarbon contribution of the ∊ –O1 SRs gradually increases. Accompanied by the superposition of multi‐stage hydrocarbon‐generation of the SRs and various secondary alteration processes, the emergence and abnormal enrichment of terpenoids, thiophene and trimethylaryl isoprenoid in deep reservoirs indicate a complex genesis of various deep oils and gases. Through the analysis of the biofacies and sedimentary environments of the ∊ –O1 and O2–3 SRs, it is shown that the lower Paleozoic high‐quality SRs in the Tarim Basin were mainly deposited in a passive continental margin and the gentle slope of the platform, deep‐water shelf and slope facies, which has exhibited a good response to the local tectonic‐sedimentary environment. The slope of the paleo‐uplift is the mutual area for the development of carbonate reservoirs and the deposition of marine SRs, which would be favorable for the accumulation of petroleum. Due to the characteristics of low ground temperature, the latest rapid and deep burial does not cause massive oil‐cracking in the paleo‐uplift and slope area. Therefore, it is speculated that the marine reservoirs in the slope of the Tabei Uplift are likely to be a favorable area for deep petroleum exploration, while the oil‐cracking gas would be a potential reserve around the west margin of the Manjiaer Depression. Hydrocarbons were generated from various unit SRs, mainly migrating along the lateral unconformities or reservoirs and the vertical faults. They eventually brought up three major types of exploration fields: middle and lower Cambrian salt‐related assemblages, dolomite inner reservoirs and Middle and Lower Ordovician oil‐bearing karst, which would become the most favorable target of marine ultra‐deep exploration in the Tarim Basin.

塔里木盆地海相油气储量规模大,目前发现的下寒武统烃源岩TOC高,但厚度薄,能否支撑目前储量规模仍不确定,同时前寒武系烃源岩的发育情况及其对海相油气的成藏贡献不清.为了更全面地评价塔里木盆地海相油气资源的潜力,利用碳同位素地层曲线、沉积充填和地震反射特征,建立了塔里木盆地南华系—寒武系与全球的地层对比格架,识别出南华系特瑞艾肯组、震旦系育肯沟组和水泉组等潜在烃源岩,明确了寒武系烃源岩发育的层段、厚度和有机质丰度.创新建立了烃源岩TOC归一化评价技术,更加精确地反映地层中有机碳的含量.通过烃源岩生烃评价,计算出寒武系烃源岩的油气资源量约为7500×108t油当量,是对塔里木盆地海相油气资源贡献最大的烃源岩.