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 Upward shallowing sequences are widely developed in shallow-water carbonate environments， and the identification of upward shallowing sequences in deep-water carbonate rocks has a unique advantage in analyzing the evolutionary process of shallow-water carbonate sedimentary environments. Analyzing the high-precision upward shallowing sequences of the late Cambrian Xixiangchi Formation in the Upper Yangtze region can provide important references for understanding the late Cambrian global environmental changes. Methods Detailed field sedimentological dissection and indoor microfacies analysis were conducted on the upper Cambrian Xixiangchi Formation in Chengkou town along the northern margin of the Upper Yangtze. Carbonate rock decimeter- and meter-scale upward shallowing sequences were identified， and their compositional characteristics and vertical superposition relationships were analyzed to explore the sedimentary environment and its evolution in the late Cambrian of the Upper Yangtze region. Results Based on detailed field observations and thin section identification， and referring to the Flügel sedimentary microfacies classification scheme， 14 microfacies types were identified in the Xixiangchi Formation at the Chengkou section， including subtidal sedimentary microfacies MF0-MF10； intertidal sedimentary microfacies MF11-MF12； and supratidal sedimentary microfacies MF13. These microfacies include： MF0 argillaceous shale， MF1 micrite， MF2 bright crystal gravel limestone， MF3 bright crystal sand limestone， MF4 muddy siltstone， MF5 dolomitic microcrystalline limestone， MF6 gravel dolomite， MF7 bright crystal sand dolomite， MF8 sandy gravel dolomite， MF9 sandy dolarenite， MF10 sandy dolomite， MF11 laminated dolomite， MF12 bamboo leaf-like gravel dolomite， and MF13 grain dolomite with dissolution pores. Based on microfacies interpretation and vertical stacking relationships， C1-1 to C1-6 decimeter-scale upward shallowing subtidal， C2-1 to C2-6 decimeter-scale upward shallowing subtidal to intertidal， and C3-1 to C3-2 decimeter-scale upward shallowing intertidal to supratidal sedimentary sequences were identified. These decimeter-scale upward shallowing cycles constitute three secondary transgressive-regressive sedimentary cycles， which from bottom to top， constitute the rapid transgression-slow regression upward shallowing sedimentary cycle of the Xixiangchi Formation. Secondary cycle I was developed by subtidal sedimentary microfacies， secondary cycle II was developed by subtidal to intertidal sedimentary microfacies， and secondary cycle III was developed by intertidal to supratidal sedimentary microfacies. From bottom to top， the thickness of subtidal sedimentary microfacies in the lower part of each secondary cycle decreases successively， whereas the thickness and exposure degree of intertidal to supratidal sedimentary microfacies in the upper part of each secondary cycle gradually increase. Conclusions Based on the identification of upward shallowing sedimentary sequences and the analysis of their compositional characteristics and vertical stacking relationships， the Xixiangchi Formation in the late Cambrian was significantly influenced by high-frequency sea level changes， strongly controlled by tides， waves， and storms. It experienced early rapid transgression and late slow regression， and underwent multiple secondary transgressive-regressive cycles， forming a limited carbonate platform sedimentation model characterized by mixed tidal flat subfacies， micritic lagoon subfacies， and intraplatform grain shoal subfacies. Furthermore， the development of paleo-weathering crust at the top indicates significant regression and erosion events in the late Cambrian in this region. By comparing with chronostratigraphic and evolutionary characteristics of platforms in the Yangtze Platform， North China Platform， Tarim Platform， United States， and Australia， it further confirms the global sea level fall events in the late Cambrian.

Objective Mixed sediments were widely developed in the lower First member of the Shahejie Formation in the Lixian slope and their influence on the development of hydrocarbon reservoirs is of great significance. The aim of this study was to clarify their properties to determine the target area for exploration and development in the next step. Methods The types， distribution regularity， control factors， sedimentary model and mechanism of high-quality reservoir formation in mixed sediments were analyzed from cores， thin sections， seismic well logging and laboratory analysis data. Results Two types of mixed sedimentation occur in the study area： mixed sedimentary rock and mixed sedimentary strata. Three major categories of mixed sedimentary rock （mixed sandstones， mixed mudstones and mixed carbonate rocks） are further divided into six types. The mixed sedimentary strata are divided into 16 types in four lithofacies assemblages： terrigenous rock-carbonate rock， terrigenous rock-mixosedimentite， carbonate rock-mixosedimentite， and mixosedimentite. The lower First member of Shahejie Formation in the Lixian slope has typical mixed features， which occur in eight microfacies types： underwater distributary channel microfacies， mouth bar sheet microfacies， underwater diversion bay microfacies， mud flat microfacies， sandy beach bar microfacies， carbonate beach bar microfacies， inner beach microfacies and semi-deep lake mud microfacies. The mixed sediments display rapid phase transformation laterally， and multiple rock types are frequently superimposed vertically. The mixed sediments are distributed differently at different intervals， two mixed depositional models are evident， one developed during lowstand periods， and one during highstand periods influenced by climatic and water environments， tectonic background， paleogeomorphology， sediment supply and lake level changes. The mixed sediments play a significant role in reservoir control； the sandy beach bars and carbonate beach bars that were developed in high-energy facies zones contain the most favorable mixed sedimentary microfacies. A closed saline water environment is the foundation of reservoir formation， controlling the formation and distribution of high-quality reservoirs； sedimentary cycles control the degree of development and distribution. Conclusions The paleogeomorphology highland in the southwestern region contains favorable areas for mixed beach bar development and exploration.

Significance Climate plays an important role in controlling marine organic carbon enrichment， but relevant studies have primarily focused on the mechanism of organic carbon enrichment under high insolation and a warm humid climate， summarized the relationship between organic-rich basin sedimentation and astronomical cycle， and have rarely involved the development mechanism of marine source rocks during deglaciation. Several sets of marine source rocks were deposited during the deglaciation of Proterozoic and Paleozoic in China. Studying and summarizing the mechanism of climate on organic carbon enrichment in basins during deglaciation is helpful for establishing a coupling relationship model between different climatic conditions and organic matter abundance from the perspective of Earth system. Progress Research has found that the main source rocks of Mesozoic and Cenozoic corresponding to large oil and gas fields in China were developed in the greenhouse climate period of middle and high latitudes， whereas the main source rocks of Proterozoic and Paleozoic were mainly developed in deglaciation of middle and low latitudes. Abundant dating data indicate that the source rocks of the deglaciation period were distributed in the Neoproterozoic， Ediacaran-Cambrian transition， Ordovician-Silurian transition， and Permian. The source rock of the second member of the Doushantuo Formation in the Neoproterozoic was formed after the Nantuo glaciation. The Yurtus Formation and Qiongzhusi Formation of the early Cambrian were formed in the cold stage of the early Cambrian， after the North China Luoquan and Ediacaran glaciations. The Longmaxi Formation of the Early Silurian was formed after the Hernant glaciation. The Chihsian Formation of the Middle Permian was formed after the Late Paleozoic global ice age. Through the study of the paleoenvironment， paleoclimate， and productivity of source rocks in each periods， it is found that the unique climatic conditions in the deglaciation period played an important role in the organic carbon enrichment of marine source rocks. High temperatures and humidity in the middle and low latitudes， and high insolation corresponding to high obliquity during the deglaciation favor biological growth， reproduction， and organic carbon enrichment. Glacial meltwater input during deglaciation can cause transgression and import nutrients to the ocean. The chemical index of alteration （CIA） values， which rise sharply and fluctuate significantly between 50 and 90 in each period， reflect the warming and unstable climate characteristics during the deglaciation， corresponding to enhanced chemical and freeze-thaw weathering， leading to increased terrestrial nutrient input and productivity enhancement. During the initial stages of ice melting， strong equator-polar temperature differences and sea surface wind lead to intense upwelling， increasing surface water primary productivity， whereas surface biological blooms and oxygen consumption create a reducing environment conducive to organic matter preservation. Volcanism is more intense during interglacial deglaciation， the input of nutrients from volcanic eruptions increases the productivity of the marine surface， and the input of reducing substances improves the preservation conditions of organic matter. Conclusions and Prospects Under the control of Milankovitch cycles， high insolation， warming， and fluctuating climate lead to enhanced rock weathering， extensive marine transgression， intense upwelling， and frequent volcanism， collectively resulting in increased water productivity and anoxic reduction during deglaciation， thereby promoting organic carbon enrichment and source rock formation. This relationship model between climate and source rock formation during deglaciation reflects the control of the ocean-land-atmosphere earth system on organic carbon enrichment under the control of climate cycles. In the future， combining climate simulations and quantitative calculations， certain predictions can be made regarding the distribution of large shale oil and gas fields.

Objective To discuss the high-frequency sequence division and its control on reservoirs in carbonate strata. Methods This study used the Th/U curve in natural gamma ray spectrum logging as the indicator curve. combined with the Fischer diagram and lithological assemblage sequence， high frequency sequence of Ma{}_{\mathrm{5}}^{\mathrm{1}\mathrm{⁃}\mathrm{5}}_{sub-member of Majiagou Formation was divided quantitatively in the Tao 7 block of the Ordos Basin. Results The research shows that the Th/U value in natural gamma-ray spectroscopy logging can be used as an indirect alternative index of astronomical orbit in carbonate strata. The high-frequency sequence can be effectively divided by quantitative and qualitative analysis methods such as spectrum analysis combined with the Fischer diagram and lithologic lithofacies analysis. The Ma{}_{\mathrm{5}}^{\mathrm{1}\mathrm{⁃}\mathrm{5}} sub-member in the Tao 7 block can be divided into one third-order sequence， six fourth-order sequences， and twenty fifth-order sequences. It is estimated that the average deposition rate of the Ma{}_{\mathrm{5}}^{\mathrm{1}\mathrm{⁃}\mathrm{5}} sub-member is 5.03 cm/kyr， and the deposition time is approximately 2.43 Ma. The gypsum pseudocrystal dolomite， which developed in the upper part of the intertidal zone and in the top of the high-frequency sedimentary cycle with upward shallowing， is the dominant facies belt for reservoir development. Near the high-frequency sequence boundary of the fourth-order sequence is the favorable interval for reservoir development. The early karst caused by frequent changes of sea level was the main driving force for the formation of model pores in the Ma{}_{\mathrm{5}}^{\mathrm{1}\mathrm{⁃}\mathrm{4}} sub-member and laid the foundation for the krast in later supergene stage. Conclusions Quantitative identification and division of high-frequency sequence is important for reservoir prediction in carbonate strata.}