Objective The Paleogene Shahejie Formation around the Bozhong Sag， Bohai Bay Basin， contains mixed-rock reservoirs with abundant oil and gas resources. The unique biomass cavity pores （lumens） in mixed-rock reservoirs are such that their initial porosity cannot be obtained by conventional formulas. No methods are known in China or elsewhere for recovering the initial porosity for mixed rocks， although accurate recovery is a key element in determining the evolution of the reservoir. Methods Experimental and numerical methods were used to determine the volume of the body cavity in modern snail samples. A physical simulation experiment was then conducted to simulate the cavity infill conditions in an actual depositional environment. Finally， a formula for calculating the initial porosity of mixed-rock reservoirs was derived based on commonly used formulas. Results Studies have shown that differences in the snail species have the greatest effect on the percentage of body cavity pore volume （i.e.， body cavity porosity）. Within the same species， the main reason for the difference in body cavity porosity is the size of the body cavity. For example， the mixed-rock sample from well QHD36-3-A at a depth of 3 765.03 m， with a high content of fragmented bioclasts， has an initial porosity of 51.68%. Conclusions A new calculation method for finding the initial porosity of mixed rocks is proposed based on previous formulas combined with physical simulation experiments. This is highly significant in the study of mixed-rock reservoir evolution.

Objective The southern Persian Gulf Fars region is strategically significant for Chinese overseas exploration due to its abundant Middle Permian to Lower Triassic oil and gas resources. However， currently available research lacks a comprehensive description of sequence stratigraphy and sedimentary evolution in this geological succession. The objective is to bridge these gaps. Methods This study focused on the middle to Late Permian Dalan Formation and the Lower Triassic Kangan Formation. Utilizing data from individual wells， cross-sections， core samples， thin sections， well logging， along with consideration of the regional geological context and taking existing knowledge into account， the study conducted sequence stratigraphic division of the target succession in the research area and conducted a detailed analysis of the characteristics and evolution of the depositional systems of each sequence. Results It was found that， in the study area， the Dalan Formation and Kangan Formation exhibit six sequence boundaries and five maximum flooding surfaces. On this basis， the stratum were divided into five third-order sequences， each comprising a transgressive systems tract and a highstand systems tract. Fischer plots based on gamma ray log curves for the Dalan Formation show significant transgressive and regressive processes during the SQ1 and SQ4 depositional periods. During the SQ3⁃SQ4 sequence development， limited accommodation space and a relatively low sea level were evident in the study area. The target succession represents a carbonate ramp depositional environment， further divided into inner-， middle- and outer ramp sub-environments. The inner ramp predominates， and was subdivided into six depositional microfacies： sabkha in the tidal zone， intertidal flat， lagoon， leeward shoal， mid-shoal， and seaward shoal. Each microfacies exhibits distinct lithologies such as anhydrite and anhydritic limestone in the sabkha and intertidal flat environments， limestone and anhydritic limestone in the lagoon environment， and grainstone and packstone in the shoal environments. The middle and outer ramp depositional environments were characterized by muddy limestone and marlstone with bioclasts. The sedimentation period in the study area was an arid and hot shallow-water carbonate depositional environment. During SQ1⁃SQ2 deposition， the rate of accommodation space growth was less than the sedimentation rate， leading to the development of a progradational depositional pattern. In the SQ3 deposition period， the rate of accommodation space growth exceeded the sedimentation rate， resulting in a retrogradational and aggradational depositional pattern. The SQ4 deposition period experienced a sea-level decrease， leading to a progradational depositional pattern. In the SQ5 deposition period， influenced by the expansion of the NeoTethys Ocean， tectonic activity along the basement fault caused subsidence in the eastern region， increasing accommodation space. The main depositional pattern was retrogradational. Conclusions Through the analysis of sequence stratigraphic characteristics and depositional systems， combined with the evolution of global sea level and the Neo-Tethys Ocean， it is concluded that the relative change between tectonically controlled accommodation space and sedimentation rate is the primary controlling factor for the regional sedimentary evolution.

Objective The Dengying Formation in the Penglai area of central Sichuan has achieved a major breakthrough in petroleum exploration. The Fourth member of the Dengying Formation has experienced multiple stages of oil and gas charging owing to its large burial depth， old age， and complex diagenetic evolution. However， the relationship between reservoir pore evolution and oil and gas charging remains unclear. Methods Based on drilling coring data， the petrological types， reservoir space characteristics， diagenetic types， diagenetic evolution sequence， pore evolution， and hydrocarbon charging of the Fourth member of the Dengying Formation were studied through thin section observation， cathodoluminescence， in situ microelement analysis， and fluid inclusion. Results The reservoir rock types of the Fourth member of the Dengying Formation in the Penglai area are mainly crystalline， granular， and microbial dolomite. The types of reservoir space can be divided into three types： cave， pore， and fracture. The main diagenetic types are syngene-parsyngenetic dissolution， epigenetic dissolution， buried dissolution， cementation and filling， tectonic rupture， silicification， and compaction. Diagenesis in different stages jointly controls the evolution of reservoir pores in the four members of the Dengying Formation， among which the constructive diagenesis is dissolution and rupture in different periods， and the destructive diagenesis is compaction and pressure-dissolution and cementation and filling. Conclusions The filling sequence of cement in the solution holes of the Fourth member of the reservoir can be divided into： the first generation blade-like dolomite → the second generation powdery dolomite → the first stage bitumen → the third generation fine crystalline dolomite → the fourth generation medium crystalline dolomite → the fifth generation coarse crystalline dolomite → the sixth generation giant crystalline saddle-shaped dolomite → the second stage bitumen → the seventh generation quartz， fluorite and other minerals. Based on the information， such as type， phase state， and homogenization temperature， of fluid inclusions captured by cemented fill of each stage the oil-gas charging process of the Fourth member of the Dengying Formation in the Penglai area was reconstructed， as follows： Paleo-oil reservoir charging in the Middle and Late Silurian period （the first phase of fossil oil reservoir） → Late Caledonian paleo-oil reservoir destruction → Middle Triassic paleo-oil reservoir charging （the second phase of fossil oil reservoir） → Late Jurassic paleo-gas cracking in paleo-oil reservoir → the adjustment and formation of paleo-gas reservoir from the Late Cretaceous to present， in which the late oil cracking gas → gaseous hydrocarbon charging is the main forming period of the Fourth member gas reservoir of the Dengying Formation.

Objective Carbonate-evaporite syngenetic systems are widely distributed in the Cambrian rocks of the Sichuan Basin. However， their development， depositional environments and processes and evolutionary modes have rarely been studied， and the research methods urgently need to be clarified. Methods The petrology and processes of the symbiotic system， the state of the evaporites， the depositional environment and the evolutionary pattern were investigated using drill core data， field sections， rock strata， C and O isotopes， Fe and Mn contents， and S isotopic composition. Neither the developmental characteristics of the symbiotic system and depositional environment nor its evolutionary pattern are well understood. Results （1） Five kinds of carbonate-evaporite symbiotic rock assemblages were found in the study area： interbedded carbonate rock and evaporite； evaporite sandwiched with carbonate rock； evaporite overlain by carbonate rock； carbonate rock overlain by evaporite rock； and carbonate rock sandwiched with evaporite rock. （2） The δ¹⁸O values ranged predominantly from -9.00‰ to -8.00‰， while δ¹³C values ranged between -1.00‰ and 3.00‰. Calculations of paleosalinity and paleotemperature using these isotope values gave the vast majority of Z>120 and δ¹³C>-2.00‰， with paleoseawater temperatures in the range 23.10 ℃-40.64 ℃. Fe was mainly concentrated in the range （0-2 000）×10^-5， and Mn from 10^-5 to 30×10^-5. These indicate a warm or hot paleoclimate and saline seawater environment during deposition of the Gaotai Formation， with a high degree of oxidation in the water body， and the rock-forming activity occurring in a system relatively open to precipitation of atmospheric water. （3） Deposition of marine carbonate rocks and evaporites took place in a symbiotic system against a background of an arid， hot climate and a calcium-rich， low-sulfate， highly saline calcitic sea. This period of time witnessed two types of carbonatite-evaporite symbiotic development： A falling-sea-level evaporite-dolomite deposition stage （“tidal sabkha mode”）， and a rising-sea-level dolomite-evaporite-greywacke deposition stage （“underwater condensed-deposition mode”）. Conclusions The carbonatite-evaporite symbiotic system has recorded information about the paleoenvironment， paleoclimate and paleohaline water chemistry during the deposition period， as well as the depositional process and evolutionary pattern of the symbiotic system. This study provides new ideas and understandings of the depositional environments and patterns of the carbonatite-evaporite symbiotic system in the evaporitic environment of the marine phase of the developing Cambrian Gaotai Formation.

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 In the western Sichuan Basin， the Middle Permian extensively features marine carbonate rocks， with dolomite being a focal point of geological investigation. However， the diverse and irregular distribution of dolomite types in the Middle Permian results in significant variations in dolomite characteristics across different regions. The rich variety of these dolomite types constitutes an excellent set of natural gas reservoirs in the Sichuan Basin. Methods To unravel the fluid dynamics of dolomites in the study area and reconstruct their diagenetic environments， this study extensively reviewed a substantial body of previous literature and references. Samples from 16 well cores and nine sections underwent a comprehensive analysis. Utilizing techniques such as microscopic thin section observation， cathodoluminescence， carbon-oxygen isotopes， strontium isotopes， and inductively coupled plasma mass spectrometry （ICP-MS） rare earth element （REE） analysis， the petrological and geochemical features were thoroughly investigated. Results The research findings can be summarized as follows： （1） Dolomite types： Dolomites in the region can be broadly categorized into homogeneous and zebra-like dolomite. The primary type of homogeneous dolomite is granular， whereas zebra-like dolomite includes homogeneous dolomite with dark bands， predominantly filled with hydrothermal saddle dolomite. （2） Isotopic analysis： Carbon isotopes： Samples from the study area exhibit positive anomalies in carbon isotopes. Oxygen isotopes： Oxygen isotope values show significant differences， with the filling material （saddle dolomite） exhibiting notably lower values than the homogeneous dolomite. Oxygen isotope values in samples from southwestern Sichuan are significantly lower than those from northwestern Sichuan. （3） Rare earth elements： REE analysis reveals a negative anomaly in δCe and a positive anomaly in δEu， indicating that the oxidation conditions of the products were influenced by later-stage hydrothermal alteration. （4） Strontium isotopes： Strontium isotopic values of homogeneous dolomite fall within the range of contemporaneous seawater. However， the filling material in southwestern Sichuan exhibits strontium isotopic values higher than the seawater range and significantly higher than that of homogeneous dolomite. Conclusions （1） Hydrothermal modification： The diagenetic fluids responsible for the formation of homogeneous dolomite in the western to northern Sichuan region are primarily derived from contemporaneous seawater. Subsequent hydrothermal activities lead to modifications， resulting in the formation of hydrothermal saddle dolomite. Notably， the intensity of hydrothermal activity is more pronounced in the southwestern region and relatively weaker in the northwestern part of western Sichuan. （2） Diagenetic environments： The diagenetic environments of dolomites in the study area encompass three types： marine diagenetic settings， shallow-to-intermediate burial diagenetic environments， and intermediate-to-deep burial diagenetic environments. The marine environment refers to an open-sea， grain shoal environment， predominantly developing fine to medium-crystalline dolomite. Inclusions exhibit a uniform temperature below 85 °C. Shallow-to-intermediate burial environments， with burial depths ranging from approximately 800-2 000 m， primarily foster homogeneous fine-crystalline and medium-to-coarse-crystalline dolomites. Inclusions exhibit a uniform temperature above 112 °C. Hydrothermal saddle dolomite mainly develops in intermediate-to-deep burial environments with burial depths exceeding 3 000 m， and inclusions exhibit a uniform temperature above 175 °C. This comprehensive research provides nuanced insights into the diverse dolomite types and their diagenetic histories， contributing significantly to the broader understanding of sedimentary processes and geological evolution in the western Sichuan Basin during the Middle Permian.

Objective The East Mariana Basin of the West Pacific Ocean， which is located east of the Mariana Trench， south of the Magellan Seamounts， and north of the Caroline Seamounts， is an ideal area for the study of Asian aeolian dust deposits， but the sediment research of the East Mariana Basin is still weak. To reveal the sediment geochemical characteristics and provide background data for further sediment provenance， seabed mineral resource evaluation and climate-environment evolution research， the element geochemistry of surface sediments in the East Mariana Basin was studied. Methods Based on 28 pelagic clay surface sediment （0-10 cm） samples collected in the eastern section of the East Mariana Basin using the box and gravity samplers， contents of major， trace， and rare earth elements of the sediments were analyzed using inductively coupled plasma optical emission and mass spectroscopy methods. Then， elements geochemical characteristics were analyzed， and their influencing factors and indicative significance were discussed. Results The results show that the contents of major elements in the pelagic clay sediments in the study area are roughly the same as those in the neighboring sea areas of the West Pacific Ocean. The distribution pattern of major elements （oxides） in sediments follows SiO₂> Al₂O₃ > Fe₂O₃> Na₂O > MgO > K₂O > CaO > MnO > TiO₂ > P₂O₅. SiO₂ has the highest content of all major elements， with an average of 49.14%， followed by Al₂O₃， with an average of 15.85%. The trace element with the highest content was Ba， with an average of 770×10^-6， followed by Cu， with an average of 289×10^-6. The average of total rare earth elements （∑REE） is 284×10^-6， which is light rare earth-rich type， with the highest Ce， Nd， and La contents. Principal component analysis of elements shows that the composition of chemical elements can be divided into four categories： The first type is closely related to rare earth elements， including most rare earth elements （except Ce）， P₂O₅， and TiO₂， the second type is related to Fe-Mn micronodules， including Fe₂O₃， MnO， Cr， Co， Ni， Cu， and Ba， the third type is related to terrigenous debris， including Al₂O₃， MgO， SiO₂， U， Hf， Th， and Ce， and the fourth type is related to biological sources， including Cd， CaO， and Mo. Conclusions The element combination indices （Si/Al， Fe/Al， La/Tb， Th/Sc， etc.） and projection diagrams （La-Th-Sc triangle diagram and La/Th-Hf bivariate diagram） further revealed that the sediments sources were dominated by terrigenous materials， particular terrestrial aeolian dust materials. Furthermore， the Chemical Index of Alteration （CIA） indicates that the parent rocks in the sediment source area are in low-medium chemical weathering conditions. The redox sensitive elemental （Cr， Ni， V， U， Th， etc.） combination reveals that the bottom sedimentary environment in the study area was oxidation-weak oxidation environment. This study has reference significance for understanding the influence of the Asian aeolian dust on the sediment provenance of the East Mariana Basin， revealing the sedimentary environment characteristics of the basin and the distribution of seabed mineral resources.

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 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 The sand and gravel in the Sanjie area of Juren town， Bin county， Heilongjiang province， was once considered as the lower limit of the Quaternary Luojiawopeng Formation in the Harbin area， but research on its stratigraphic properties and sedimentary environment has been relatively poor to date. This has greatly limited the in-depth understanding of the regional surface processes recorded in this stratum. Methods To discuss and compare the sedimentary environment and stratigraphic division， this study adopted a range of research methods. Sedimentology， mineralogy， elemental geochemistry and detrital zircon U-Pb chronology were used to investigate the chemical weathering characteristics， source rock properties， sedimentary environment and structural background of the source area in this section to determine the effects of chemical weathering， sedimentary cycles and material sources， and to explore the structural background and indicators of stratigraphic delineation and regional magmatic tectonic events. Results It was found that the sediment in the three sections is mainly composed of brownish-yellow sand and gravel mixed with muddy interlayers， with local oblique bedding. The weathering degree of the sand and gravel is low， the sorting is moderate， the roundness is good， and there is no obvious directional arrangement. The gravel rock is mainly granite （46.31%） and quartzite （28.19%）， with some syenite （0.2%）， tuff （0.01%） and schist （0.01%）. The heavy minerals are mainly spinel （65.18%） and epidote （11.87%）， with minor quantities of zircon （2.28%）， apatite （5.60%）， ilmenite （2.77%）， hematite （3.41%） and magnetite （5.15%）； white titanium （0.54%） and pyrrhotite （0.1%） account for less than 1%， and other heavy minerals account for 3.11%. Elemental geochemical analysis revealed that the fine-grained components in the sediments have experienced weak to moderate chemical weathering， and most have undergone initial weathering cycles. Gravel lithology and geochemical composition indicate that the parent rock of the sediments was mainly medium- to acidic magma. The geochemistry of the migration and enrichment of elements in the sediments， paleoclimate discrimination diagrams and sedimentary facies definition indicate that the regional environment of the sediments was a meandering river that transported the sediments over short distances in an arid oxidative environment. The distribution range of detrital zircon U-Pb ages is relatively narrow （134.2-220.3 Ma， peaking at about 168 Ma）. Comparison of the zircon ages of the surrounding potential source areas together with their geomorphological location suggests the detrital contribution of the Zhangguangcai Ridge and indicates the collision and assembly of the Jiamusi and Songnen Blocks， as well as the continuous subduction of the eastern oceanic plate. Significant differences were found between the three sections in terms of their sedimentological characteristics， genetic types and geomorphological features when compared with the standard strata of the Luojiawopeng Formation. It is speculated that formation of the three sections was roughly contemporaneous with the formation time of the Baitushan Formation in western Harbin. Conclusions This study is of great significance for the reconstruction of geological events such as Quaternary stratigraphic divisions and Upper Jurassic tectonic geomorphological-climate-water system evolution in the Harbin area.