Objective The C-6 oilfield is one of the main oilfields in the billion ton Caofeidian oilfield group of the Bohai Sea. Its main development layer is the Guantao Formation III oil formation （N₁gIII）， which is a set of sand rich braided river sediments. The connectivity of the internal reservoir is not yet clear， restricting the improvement of oilfield development efficiency. Methods The intelligent fusion technology of seismic attributes based on a deep feedforward neural network （DFNN） was used to finely characterize the spatial distribution of the fourth level configuration units in the braided river reservoir of the oilfield under the calibration of limited logging information. Results Based on log interpretation， N₁gIII of the C-6 oilfield mainly contains two types of level-4 architectural units： channel bar and braided channel； braided bar is the best reservoir with high sandstone thickness and excellent physical properties. Based on seismic attribute extraction and correlation analysis with lithological and physical parameters， reflection intensity， relative impedance， sweet point， original amplitude， and envelop were chosen as intelligent fusion seismic attributes with the DFNN algorithm with porosity. The three-dimensional （3D） attribute of DFNN fusion， representative of lithology and petrophysical property， largely improves the detecting ability of the braided river sandstone unit and its boundary. A NE-SW braided flow zone was developed in N₁gIII of the C-6 oilfield and could be internally sub-divided into 15 rhombic level-4 architectural units. Distributary channels， another level-4 architectural unit， surrounded the braided bar in a narrow strip. The level-4 architectural interface between the two units acted as seepage barriers for fluid migration. The braided bars cut and overlapped one another vertically， forming a “big bar and small channel” plan reservoir architectural pattern. Conclusions The fine characterization of reservoir architecture based on the intelligent fusion of seismic attributes deepens our understanding of the connectivity of braided river reservoirs controlled by sparse well networks， providing direct geological basis for the adjustment of the C-6 oilfield development plans， and has certain significance for the fine characterization of reservoir architecture in oil fields with the same sedimentary type under offshore sparse well network conditions..

Objective This study aimed to define the high-quality reservoir development model of the Xu3 member in the source rock stratum， that is， the tight sandstone gas exploration in the Xu3 member of the Xujiahe Formation， Western Sichuan Depression， and provide theoretical guidance. Methods The core， thin section， scanning electron microscope， fluid inclusion， situ stable carbon and oxygen isotopes， porosity， and permeability data were integrated. Based on the basic characteristics of Xu3 member tight sandstone reservoirs in the Western Sichuan Depression and the types of diagenesis， the heterogeneity of the reservoirs and the development model of high-quality reservoirs were analyzed systematically. Results The results show that lithic quartz sandstone and lithic sandstone were the main rock type of the Xu3 member， and the reservoir space was primarily composed of intragranular dissolution pores and fractures， with porosity less than 7% and permeability less than 1×10^-3μm². Therefore， the sandstone reservoirs could be divided into intragranular dissolution pore and fracture- intragranular dissolution pore types. The diagenesis of the Xu3 member sandstones included compaction， cementation， and dissolution and experienced early humic acid， middle organic acid， and late hydrothermal fluids during the evolution process. In addition， two types of vertical sedimentary cycles， sandstone with sandstone and sandstone with mudstone， were identified in the Xu3 member. Conclusions The results indicated that the tight sandstone was altered by the early humic acid and middle organic acid continuously via the intergranular pore throat and fracture and in favour of reservoir formation. However， the late hydrothermal fluid acted solely in the late large scale fracture and had an insignificant effect on reservoir quality. In addition， the high-quality reservoir of the sandstone with the sandstone vertical sedimentary cycle mainly developed in the lower part of the cycle which characterized by relatively coarse-grain， but the high-quality reservoir of the sandstone with mudstone vertical sedimentary cycle mainly developed in the lower part of the cycle with relatively coarse-grain； the upper part of the cycle is adjacent to the mudstone.

Objective Reconstruction of atmospheric carbon dioxide concentrations （pCO₂） during the Cenomanian-Turonian （C-T） has been previously limited to stage-scale temporal resolutions， which have greatly constrained its effectiveness in unveiling the extreme greenhouse climate of the C-T period and perturbations in the global carbon cycle. Methods To enhance our understanding of pCO₂ fluctuations and the paleoclimatic response during the C-T "greenhouse climate，" this study reconstructed high-resolution atmospheric pCO₂ and mean annual precipitation （MAP） during the C-T period by analyzing the stable carbon and oxygen isotopes of paleosol carbonates from the Upper Cretaceous Nanxin Formation in the Qamdo Basin， southeastern Xizang. Results Our results reveal a gradual decline in pCO₂ during the Early Cenomanian period， followed by an increase in the Middle and Late Cenomanian stages. Moreover， we observed significant fluctuations in pCO₂ during the Early and Middle Turonian stage. These findings align with the variations in pCO₂ throughout the C-T period that have been estimated using the stomata ratio method of plant fossils and the geochemical models. In addition to the long-term pCO₂ fluctuations， the paleosols of the Nanxin Formation also documented two crucial carbon cycle perturbations during the Cenomanian period： Oceanic Anoxia Event 2 （OAE2） and Mid-Cenomanian Event （MCE）. The atmospheric pCO₂ rose by 309 μmol/mol and followed by a rapid decline of 520 μmol/mol across the initiation of MCE， accompanied by a positive shift of 1.25‰ in organic carbon isotopes （¹³C_org）. During OAE2， there were two distinct CO₂ pulses， with the maximum pCO₂ concentration coeval with the lowest ¹³C_org. The pCO₂ increased up to approximately 1 300 μmol/mol at the OAE2 boundary， followed by a reduction of approximately 17% owing to substantial organic carbon burial during OAE2. The increased concentration of CO₂ throughout the Mid-Late Cenomanian intensified the greenhouse effect and elevated atmospheric humidity， resulting in significant negative shifts in ¹³C_org that were decoupled with inorganic carbon isotopes. Our conclusion further suggests that there would be an increase of 511 mm/yr in MAP as the atmospheric pCO₂ elevated from 500 μmol/mol to 1 000 μmol/mol during the C-T period. Conclusions We assumed that the elevated atmospheric pCO₂ and climatic sensitivity during the mid-Cretaceous considerably intensified the hydrological cycle， contributing to an extreme greenhouse climate period.

Objective The genetic mechanism and sedimentary filling process of the Dongying Formation sublacustrine fan are unclear in the slope zone of the southeastern part of Bozhong Depression， which restricts the fine study of sublacustrine fan and deployment of well location in the study area， Methods From the perspective of source-sink system and three-dimensional seismic data， we semi-quantitatively analyzed the denude capacity and transportation path of the Bonan low uplift provenance. In addition， we clarified the characteristic sedimentary response and source coupling mechanism of a large-scale sublacustrine fan. We established the sedimentary filling process of a sublacustrine fan and summarized the development mode of a sublacustrine fan. Results （1） the Dong 2 subsequence is in the stage of lake-basin fracture-sink transition， which can be divided into two third-order sequences， in which the sublacustrine fan is developed in the highstand systems tract period of the lower Dong 2 subsequence； （2） during the period of lower Dong 2， the flux of denudation of the eastern section of the Bonan low uplift is larger than that of a sublacustrine fan. The detrital material provided by near provenances in the western part of the Bonan low uplift is unloaded under the depositional break of the slope along seven ancient gullies and five restricted ancient gullies. The coupling of near source supply， transport channel， and sedimentary slope break formed a large contiguous lacustrine fan deposit； and （3） the sedimentary filling process of asublacustrine fan is controlled by the location of restricted paleogeomorphology and the amount of space. Among them the early restricted paleogeomorphic formation can create large accommodating space， the sublacustrine fan sand body is preferentially unloaded. It formed the three major fan deposits， A， B and C. Owing to the spatial restriction of the two sides， the strong hydrodynamic conditions and seismic phases exhibit a chaotic down-cut channel superimposed on the lateral migration， and the formed fans are more sand-rich. With the entry of gravity flow with continuous replenishment in the later stage， the accommodating space gradually decreases， while the gravity flow along the replenishment channel overflows to the center of the open lake basin， forming two fans， D and E. Owing to the energy gradually weakening， the seismic phases have the characteristics of laminar strong-amplitude reflections， with the characteristics of the watercourse being inconspicuous， and the sand-richness is moderate. Late-stage source supply and energy is weak， and localized erosion and modification of seismic relative to early fan bodies exhibits weak amplitude reflections dominated by muddy watercourses. The large lake bottom fan has a spatiotemporal distribution and evolution pattern of early restrictive filling， middle overflow adjustment and late erosion and modification， which constitutes a developmental feature of lateral contiguous and vertical multi-phase superposition. Conclusions The three sectors， A， B， and C， below the first terrace are sand-rich and shallowly buried， with good conditions for oil and gas transportation and aggregation and excellent reservoir-cover combinations. The sweet spot area of sector C sector is large and has been an important target for the exploration of rocky reservoirs in the Bohai Sea in recent years.

Objective The 1st member of Jurassic Badaowan Formation （J₁b₁） in the slope area of Mahu Sag is a set of sandy （gravel） rock deposits of coal-bearing rock series close to the Jurassic / Triassic （J/T） unconformity. The shale rich conglomerate belt near the bottom of the J/T unconformity has clear oil and gas thickened， and light oil and gas are concentrated in the thin sandstone belt above the coal seam. There is still no research on the origin of oil and gas thickening zone in the relatively deep buried area， the percolation mechanism of atmospheric fresh water to overlying strata on the unconformity surface， and the origin of light oil and gas enrichment above coal seam of coal-bearing rock series. Methods Based on the properties of crude oil and carbon isotope analysis of natural gas， combined with the data of burial history， thermal history， pore evolution history， and laser Raman spectrum analysis of hydrocarbon salt water inclusions， the genetic types of J₁b₁ natural gas and the origin and distribution of hydrocarbon thickening zone and light oil and gas zone are discussed. Results （1） The J₁b₁ coal-bearing rock series can be divided into oil and gas thickening zone and light oil and gas zone based on the characteristics of oil and gas density viscosity. The former is mainly distributed in the upper wall of the fault zone， the fault zone， and the bottom of the slope zone adjacent to the J/T unconformity. The latter is distributed in the thin sandstone zone above the coal seam in the slope zone， and the coal-derived gas content is high. （2） The origin of the shale rich conglomerate oil and gas thickening zone at the bottom of the slope zone adjacent to the J/T unconformity is closely related to the atmospheric freshwater compacting-centrifugal flow oxidation degradation. The “Yanshan normal fault - J/T unconformity - shale rich conglomerate assemblage” and the associated capillary imbibition of wetting water phase led to the formation of atmospheric freshwater compaction-centrifugal flow oil-gas thickening zone closely related to the unconformity in the slope area of relatively deep burial. （3） The thin sandstone reservoir above the coal seam has the characteristics of “self-generated and self-stored （deinspiratory charging in the J₁b₁ coal seam）” and “bottom-generated and upper-stored （hydrocarbon supply from P₁ f source rock）” and has the advantage of light oil and gas enrichment. The coal seam desorption diffused upward through the positive fracture into the thin sandstone at the top， and the methane carbon isotope value was relatively light， which was different from the retained adsorbed gas in the coal seam （δ¹³C₁=-48.2‰ in the former and δ¹³C₁=-43.6‰ in the latter）. The geological stratification effect caused by long distance migration of P₁f source rock oil and gas further promotes the accumulation of light oil and gas in thin sandstone above the coal seam. Conclusions The upper thin sandstone belt of J₁b₁ is the first choice for exploration of light oil and gas enrichment belt. The quantitative lithological logging identification map of coal-bearing rock series with the combined restraint of CNL-IMP was established， and the effective reservoir distribution area of the upper thin sandstone of J₁b₁ with a thickness≥10m was identified in the Yanbei1 three-dimensional （3D） seismic zone.

Objective The reticulated laterite in southern China is a good geological carrier for Quaternary environmental changes， but there is still a weakness in microscopic research on sandstone reticulation. Methods Through micro-area analysis techniques， geostatistical and factor analysis， and other methods， we conducted elemental geochemical analysis on the white vein micro-area of the sandstone and reticular red clay in the Langxi profile. Results （1）The content of iron group elements such as Fe₂O₃ （1.14%-13.29%） and Mn （87×10^-6-3 230×10^-6） in sandstone layers increased from the center of the white veins to the periphery. However， the spatial distribution of other major elements and stable elements such as Ti （1 294×10^-6-2 454×10^-6） and Zr （171 ×10^-6-197×10^-6） showed the opposite trend. The results of the reticulated red soil layer are consistent. （2） Ti/Zr （sandstone layer： 7.23-12.89； reticulated red soil layer： 12.82-21.84） and Ti/Al₂O₃ （sandstone layer： 0.013-0.018； reticulated red soil layer： 0.044-0.062） were divided into two groups through cluster analysis and scatter plots. The results show that they have different provenances. （3） The leaching intensity of elements such as Al₂O₃ （17.3%）， Fe₂O₃ （73.91%）， and MnO （76.68%） in the sandstone white vein micro-area and Al₂O₃ （15.78%） ， Fe₂O₃ （70.39%）， and MnO （74.84%） in the reticulated red soil layer white vein micro-area decreased from the center of the white veins to the periphery. （4） The common factors in the white vein micro-area of the sandstone layer and the reticulated red soil layer are that they reflect the leaching migration of iron and iron group elements in the white vein， as well as the relative enrichment process of constant elements such as Al₂O₃， SiO₂，_{and K2O and stable elements such as Ti and Zr. Conclusions During reticulation， the leaching of iron group elements dominates， but other elements also have a certain degree of migration. Additionally， it exhibits spatial characteristics of strong leaching at the center of the network pattern and weak leaching at the periphery. Affected by local environmental differences， the development of reticulation is a spatial process that expands from the center of the reticulation to the periphery. The material composition inside the reticulate pattern is non spatially homogeneous. The sandstone and reticulated red soil layers have different material foundations， and the larger reticulation in the sandstone layer indicates that it experienced a relatively humid and hot climate during its development.}

Objective By analyzing the influence of the periodic change of earth orbit on the periodic change of climate， this study examined the climate change characteristics of the Xiayoushashan Formation in Qaidam Basin and established its high-resolution astronomical scale based on Milankovitch theory to identify and divide high-frequency sequences. Methods First， the Laskar algorithm was used to calculate the variation period of the orbital parameters of Earth during the summer solstice at 35°N from 14.5-23.8 Ma， and the Miocene cycle theory and ratio in this sedimentary period were determined. Then， taking wells Xianzhong 39， Xianzhong 8-9 and Xianzhong 8-12 in the Nanbaxian oil and gas field as examples， the natural gamma data were analyzed by their frequency spectrum and continuous wavelet transform. Finally， based on the orbital period， the average sedimentation rate of the Xiayoushashan Formation was calculated， and the "floating" astronomical scale of well Xianzhong 39 was established. Results Through the analysis of frequency spectrum and continuous wavelet transform， the Neogene Xiayoushashan Formation was shown to be mainly controlled by eccentricity periods of 400 and 95 ka. The average sedimentation rate of the Xiayoushashan Formation was 0.094 41 m/ka， and the sedimentation duration was 7.2 Ma. Based on the 400 ka long and 95 ka short eccentric period curves as benchmark curves， 18 fourth-order quasi-sequence groups and 72 fifth-order quasi-sequence groups were identified. Conclusions The results show that the climate change recorded in the Xiayoushashan Formation is controlled and driven by cycles. Identification and division based on Milankovitch theory can reduce the influence of subjective factors， improve the accuracy of division results， and more accurately describe the climate change characteristics in sediments. These research results are helpful for deeply understanding the evolution law of the Warth's climate and providing important reference for oil and gas exploration and resource evaluation.

Objective The QT Basin is located in the eastern segment of the Tethyan tectonic domain， the world’s most important oil-gas accumulation zone. Due to the low degree of exploration in the basin， there has been great controversy over its hydrocarbon resource potential. Restoring the basin erosion amount and burial process during key tectonic periods is crucial for deepening the understanding of the hydrocarbon generation potential of major source rocks and the overall oil-gas resource potential in the QT Basin. Methods Using the tectono-sedimentary filling extrapolation method， we analyzed the major tectonic activity episodes of the QT Basin and restored the erosion amount during key tectonic periods. Meanwhile， the burial processes of three sets of source rocks from the Upper Triassic to Jurassic were analyzed by the TSM basin simulation and resource evaluation system. Results （1） Since the Late Triassic， the QT Basin has experienced four phases of erosion events： Late Triassic-Early Jurassic （210-180 Ma）， Early Cretaceous （120-110 Ma）， Paleocene-Early Eocene （60-45 Ma）， and since the Early Miocene （25 Ma - present）. （2） During 210-180 Ma， the main part of the basin was uplifted， with intense erosion in the central uplift belt and the northern QT Depression； during 120-110 Ma， the strongest erosion occurred in the central uplift belt， its both sides and the eastern part of the basin， while the erosion in the mid-western part of the northern QT Depression was relatively weak； during 60-45 Ma， the average uplift and erosion of the basin was about 0.75 km； since ~25 Ma， the basin has shown an overall uplift characteristic. （3） Affected by sedimentary thickness， differential erosion during multi-stage tectonic uplift and other factors， the two maximum burial depths of the Upper Triassic-Jurassic source rocks in the QT Basin occurred after the deposition of the Xueshan Formation， and after the deposition of the Paleogene Kangtuo Formation and Neogene Suonahu Formation， respectively. The two major hydrocarbon generation periods correspond to the maximum burial depths and the subsequent tectonic uplift. （4） There are significant differences in the hydrocarbon generation evolution of the two sets of source rocks： the source rocks of the Xiaochaka Formation （T₃x） generated hydrocarbons relatively early with a long hydrocarbon generation and evolution cycle； the source rocks of the Buqu Formation （J₂b） and Xiali Formation （J₂x） generated hydrocarbons relatively late. In particular， the J₂x source rocks once experienced a hydrocarbon generation stagnation during the geological history， entered the secondary hydrocarbon generation evolution stage after the Paleogene deposition， and still have continuous hydrocarbon generation potential at present. Conclusions The Upper Triassic-Jurassic source rocks in the QT Basin have experienced different uplift and erosion histories， and there are obvious differences in their hydrocarbon generation and evolution processes. Horizontally， the mid-western part of the northern QT Depression， where the strata are best preserved， has great resource potential and should be the favorable exploration area for the next step.

Objective The Qigebrak Formation developed abundant microbial carbonates， which are the favorable target for deep to ultra-deep oil and gas exploration. However， the existing stratigraphic division scheme of the Qigebrak Formation remains controversial， hindering the analysis of reservoir depositional evolution and distribution prediction. Further in-depth research and clarification are urgently needed. Methods This study focused on the Shiairik section in the northwest Aksu area of the Tarim Basin to define the depositional environment and sea-level change， and conduct a sequence stratigraphic division of the Qigebrak Formation based on the analysis of high-precision depositional facies and the Fischer plot. Results Ten main facies are recognized from the Qigebrak Formation and grouped into a carbonate ramp platform. Two subfacies； i.e.， inner and middle ramp， are developed under this setting. The inner ramp consists of the tidal flat， lagoon， tidal channel， and grain shoals. Eight subtypes of peritidal cycles， two subtypes of shallow subtidal cycles and two subtypes of middle-ramp cycles are identified. Based on the stacking patterns reflected in the Fischer diagrams， analysis of orders of depositional facies and proportion of subtidal facies， the Qigebrak is divided into four third-order T-R sequences （SQ1-SQ4）. Among these sequences， SQ1 only records the regressive system tract in the Qigebrak Formation， whereas SQ4 only preserves the transgressive system tract. Conclusions This study suggests that （1） it is reasonable to divide the Qigebrak Formation into four sequences； （2） the top of the Qigebrak Formation could have experienced the million-year-scale exposure and erosion， which would favor the formation of scaled reservoirs.

Objective The redox states of the Early Ediacaran ocean have long been a research hotspot， particularly its material composition and distribution. The formation process of sedimentary barite nodules in the lower part of the Doushantuo Formation was studied to explore the redox variation of the Ediacaran ocean immediately after the Snowball Earth event using sedimentology and petrology. Additionally， a detailed analysis of the formation process of barite nodules in the lower part of the Doushantuo Formation in the northern part of the Yangtze Block， specifically at the Jinguadun profile， was conducted to infer its depositional environment. Methods Analysis on sedimentary environments of barite nodules from calcareous mudstone of the lower Doushantuo Formation in Jinguadun section were developed via sedimentologic and petromineralogical methods. Results Based on field observations， the surrounding rock layers were found to exhibit a distribution pattern around the nodules. Examining the contact relationships between the nodules and their internal bedding， in accordance with the summary by Sellés-Martínez in 1996， indicates that the barite nodules in this profile formed during the early burial stage. The barite， quartz， and pyrite are the three top authigenic sedimentary minerals in the nodules. The mineral distribution is stratified in the barite nodules. Specially， the inner layer contains dense pyrite aggregates dominated by euhedral-to-subhedral pyrite grains and quartz minerals that grow interwoven together. From the core to the outer edge， radial aggregates were developed in barite and quartz. This study preliminarily demonstrates that the formation of authigenic sedimentary minerals occurring in different parts of the barite nodules precipitate in different redox zones. First， in the sulfate reduction zone within the sediment， an area enriched in organic matter forms a loose outer shell primarily composed of pyrite aggregates. Subsequently， as burial depth increases towards the sulfate-methane transition zone， barite begins to deposit around the pyrite outer shell， causing the high-content pyrite aggregates to gradually become denser. The isolating effect of the pyrite aggregates results in a relatively closed internal space， impacting the deposition of stable barium ions and sulfate radicals by barite. In a slightly acidic environment， the process of pyrite generation promotes the stable deposition of quartz， leading to an internal mineral composition predominantly consisting of quartz. Simultaneously， the external environment evolves into a radial mixture of interwoven barite and quartz. This process highlights the interaction between pyrite and barite under different geological conditions and their influence on the deposition of barium ions and sulfate radicals. The Ba²⁺ sources in the barite likely originate from the methanogenic zone， where dissolution of labile and biogenic barite associated with organic matter occurs. The upward spreading Ba²⁺ ions react with downward diffusing seawater sulfate radicals and deposit barium sulfate in the upper front of sulfate-methane transition zone. Conclusions In summary， the barite nodules form in the early diagenetic soft sediments， exhibiting a phased development. In the initial stages， they are primarily composed of pyrite and quartz； in the later stages， barite and quartz deposition becomes dominant. With the increase in sulfate concentration， it is suggested that in the Early Ediacaran oceans， the sulfate reduction interface may have descended into the sediments near the water-rock interface. As a result， methane in the sulfate-methane transition zone underwent oxidation， thereby reducing their emissions into the atmosphere.