The Qaidam Basin is endowed with abundant Tertiary hydrocarbon resources and possesses major exploration potential. Lacking an overall understanding on sequence stratigraphy and sedimentary facies of the basin is not favorable for making new progress in hydrocarbon exploration. In this study, using outcrop, core, well logging and seismic data, the Tertiary strata of the Qaidam Basin was divided into 7 second-order sequences, 12 third-order sequences and 24 system tracts. In addition, 7 sedimentary facies types were identified, i.e., diluvial fan, braided river, flood plain, fan delta, braided river delta, lacustrine deposit and turbidite fan. Six single sedimentary factors were selected for analysis, and with third-order sequences as the unit, the distribution and evolution of sedimentary systems were defined. For the controlling factors of lithofacies paleogeography, “snow mountains controlling lakes” and “fault steps control basins” were proposed. It is believed that under a compressional tectonic setting, lake level fluctuation is closely related to elevations of peripheral mountains, and lake water is sourced principally from mountain snowmelt. A higher structural uplifting amplitude will result in a larger area of mountain snow, a greater water supply and a larger lake area. Boundary faults of the basin retreated towards the mountains in a step way, resulting in an expanded basin. However, the faults advancing towards the center of the basin aroused basin shrinkage. From a sedimentary view, the distribution characteristics of Tertiary source rocks and reservoirs of the Qaidam Basin were analyzed; it is proposed that the periphery of the hydrocarbon generation center of the Shizigou–Mangya sag is the present-day optimum exploration zone, and the periphery of the hydrocarbon generation center of the Yiliping depression center is a potential favorable exploration zone.

Sedimentary structures induced by water seepage are described from modern beach bars within the Zhoushan Archipelago in China, including two unique types, herein referred to as: 1) seepage tubes; 2) seepage beads. Their formation is related to water seepage in sandy sediments, where the seepage tubes are formed by the downward seepage of pore water in sandy sediment, while the seepage beads are formed by the vertical superposition of multiple beaded horizontal seepage layers. The results show that unique terrain and rapid water ingress and retreat related to tides control the formation of these sedimentary structures. The seepage-induced sedimentary structures can be divided into vertical vadose belts that develop seepage tubes, horizontal undercurrent belts with seepage beads, and water-table variation belts with both seepage tubes and seepage beads appearing alternately. These sedimentary structures are hitherto undescribed and contribute to an improved understanding of similar sedimentary structures in the geological record.

Various studies have indicated that microbes were involved in the precipitation of dolostones in the Proterozoic.The identification of ancient microbial dolostones remains challenging due to the rare preservation of microbe fossils.In this study,we found ancient microbial dolostones in Paleoproterozoic Chuanlinggou Formation in Beijing,North China,employing thin-section observations,trace and rare earth elements as well as carbon and oxygen isotope analyses to reveal the origin.The paleoenvironment has also been reconstructed.The results indicate that dolostones found in the Chuanlinggou Formation are formed through primary dolomite precipitation induced by cyanobacterial activity.These dolomitized geobodies exhibit various morphologies of mounded,banded and bedded,and all dolostones are microcrystalline tex-tures.The geochemical characteristics of these dolostones show a relatively low δ18O value(average=-7.34‰),Fe(Ⅱ)enrichment,Ce anomaly and comparable patterns of REY.The specific geo-morphology(mounded,banded and bedded)and mottled structures of the dolostones indicate that they are formed through in-situ dolomite precipitation induced by cyanobacterial activity.The high Fe(Ⅱ)content suggests a reducing environment,whereas the Ce anomaly indicates anoxic conditions within the water body.The REY patterns provide evidence for the microbial origin of the dolostones.These dolostones were formed in clastic off-shore shelf environments.The seawater was warm,normal in salinity,and the sea floor was slightly agitated to quiet and reducing.The geomorphology of the dolomitized geobodies changes from mounded to banded and bedded in correlation with depth increase and hydrodynamic energy decrease.This study may provide another type of environments for microbial dolostones and the geochemical characteristics of these dolostones may serve as a valuable reference for identifying similar ancient microbial dolostones.

Tight shell interlayers are widely distributed in global marine and lacustrine organic-rich shale successions, serving as key targets for reservoir prediction. However, the limited understanding of these interlayers presents challenges in characterising reservoirs and optimising hydrocarbon recovery in shell-rich shale formations. This study investigates the Lower Jurassic Dongyuemiao Member in the Sichuan Basin, Southwest China, using petrological, geochemical, and pore structure characterization techniques to differentiate shale from shell interlayers, and investigate the mechanisms underlying the tight properties of shell-rich interlayers. Results suggest that two shale lithofacies (e.g., laminated argillaceous shale and massive mixed mudstone) and two shell interlayer lithofacies (e.g., bedded-to-laminated shelly-bearing argillaceous mudstone and massive shell limestone) were identified. Porosity, permeability, and total organic carbon content of shale lithofacies are significantly higher than those of interlayer lithofacies. Special attention was therefore given to the analysis of sedimentary processes and diagenesis occurring in the two interlayer lithofacies. Shell interlayers were deposited by sediment gravity flows triggered by storm events. The two shell interlayers were considered the products of low-density turbidity currents and cohesive debris flows. Among the two shell interlayers, massive shell limestones exhibited the worst reservoir quality due to their fine mud-grade matrix compositions and non-lamellar textures. Differential compaction had a significant impact on the heterogeneous distribution of cements in interlayer lithofacies. Additionally, massive shell limestones experienced three distinct stages of cementation, including eogenetic calcareous cement and pyrite, and mesodiagenetic microquartz, which filled intergranular pores in the massive shell limestones and reduced reservoir quality. By contrast, the bedded-to-laminated shelly-bearing argillaceous mudstone also underwent three stages of cementation, comprising eogenetic pyrite, mesodiagenetic microquartz and ferroan calcite cement. However, close contact with black shales facilitated the development of dissolved pores within the lithofacies. Finally, based on sedimentary and diagenetic processes, tight models were established for different shell interlayers, making them applicable to other shell-rich shale successions for shale gas and oil exploration and production worldwide.

(1) This paper selects the modern delta formed by the Ganjiang tributary in Poyang Lake. By performing high density statistical analysis of distribution channel parameters in the area using satellite images and geographic information processing software (LucaSpaceViewer 4.5.2, ArcGIS Pro 3.0.2, Global Mapper v23.1), including length, width, bifurcation angle, bifurcation frequency, and channel sinuosity, the distribution characteristics of delta distribution channels are derived and quantitatively characterized. (2) Classification and evaluation of these characteristics are carried out using factor and cluster analysis, ultimately identifying controlling factors affecting the morphology and distribution of the distribution channels. By statistically analyzing the geometric and bifurcation data of the channels, factor and cluster analysis for data reduction and classification, the channel is finally divided into three categories: Type I channels have relatively high channel length, width, sinuosity, bending amplitude, and a lower bifurcation (or confluence) growth rate; Type II channels are characterized by low channel length, moderate channel width, low sinuosity, low bending amplitude, and a high bifurcation (or confluence) growth rate; Type III channels are defined by moderate channel length, low width, high sinuosity, high bending amplitude, and low bifurcation (or confluence) frequency. (3) After excluding the influence of other factors, it was found that the main controlling factor for the morphology of the Ganjiang Delta channel is flow velocity, which is influenced by changes in the terrain slope. Flow velocity directly affects channel sinuosity, bending amplitude, and bifurcation (or confluence) frequency, and indirectly affects channel length and width.

As an important type of microbial carbonate, the study of bioherm sedimentary models is of great significance to the exploration and development of carbonate rock. Bioherms from the Lower Zhangxia Formation of the Middle Cambrian Miaolingian were discovered in the Xiaweidian section of Western Hills, Beijing. The stratigraphic sequence from bottom to top consists of micritic oolitic limestones, flat-pebble conglomerates, laminated limestones (bioherm), shales, sparry oolitic limestones, and mud-ribboned limestones. This study uses a range of techniques to analyze the geochemistry of these rocks, including scanning electron microscopy (SEM), X-ray diffraction (XRD), carbon and oxygen isotope analysis, and major and trace element analysis. To ensure the accuracy of the results, factor analysis was used to screen the data and identify the elements that best represent the characteristics of the samples, obtaining the most reliable factors for analyzing the deposition environment and determining the deposition model. Through factor analysis, carbon and oxygen isotopes, Fe, Ti, Ni, and V were selected to reconstruct the paleoenvironment and deposition model. The results suggest that the Zhangxia Formation bioherm formed in the shallow-water environment of the open platform facies at the edge of the carbonate platform, which provides ideal conditions for the growth of microorganisms and the development of extensive bioherms during this time period. Subsequently, as water depth decreased and hydrodynamic and oxidative conditions intensified, the environment became unsuitable for microbial growth, leading to the cessation of bioherm development. This study confirms the effectiveness of numerical analysis methods in reconstructing bioherm deposition model and expands the application of these methods in carbonate studies.

The Lower Cambrian Changping Formation in the Western Hills of Beijing hosts tidal flat and lagoonal carbonates comprising dolomites, limestones, and dolomitic limestones, reflecting the processes of dolomite cementation and dolomitization within a sedimentary framework. Based on petrographic textures, two types of dolomites were identified: microcrystalline dolomite and fine-mesocrystalline dolomite. Integrating petrological and geochemical data unveils two diagenetic stages. The initial dolomite formation, attributed to hypersaline fluids, occurred in a supratidal-sabkha setting during the early Cambrian. The dolomitization at the top of the Changping Formation, driven by evaporatively concentrated brines from the overlying Mantou Formation, altered peritidal carbonates. This study evaluates the original sedimentary environment and dolomitization within a sequence stratigraphic context, revealing a correlation between dolomitization episodes and the stratigraphic framework in the study area. Factors influencing this framework profoundly impact depositional environments and material composition, leading to micromorphological differences in dolomites. Sabkha dolomite formation, associated with evaporative pumping, predominates near the base of transgressive systems tracts. Seepage reflux dolomite, often linked with evaporative pumping dolomite, constitutes a vertical cycle in the sequence framework. The sequence from bottom to top is sabkha microcrystalline dolomite, limestone and dolomitic limestone, seepage reflux saccharoidal dolostone, and sabkha dolomite.

In sedimentary basins, deep-seated overpressure conditions are frequently encountered. However, the precise origins of these overpressure conditions and the assessment of their formation times have long presented challenges. Previous studies have primarily relied on qualitative approaches to investigate overpressure origins, leading to substantial uncertainties in their findings. Based on theories such as the effective stress law, disequilibrium compaction, equilibrium depth, and nested fluid trapping containers in this paper, a new quantitative methodology is introduced for identifying the disequilibrium-compaction-induced origins of overpressure conditions. Additionally, the formation times of overpressure can be also estimated by nested fluid trapping container theory. This methodology is successfully applied to the northwestern Bozhong subbasin in the Bohai Bay Basin, China. The results indicate that the overpressure within the Dongying Formation of the northwestern Bozhong subbasin is primarily attributed to the disequilibrium compaction of mudstone, because the disequilibrium compaction of mudstone accounts for over 90% of the pressure in sandstone. Furthermore, the overpressure system in this area is not singular but comprises multiple nested relative fluid trapping containers. The application of nested fluid trapping container theory allows for an estimation of the overpressure's formation time, although further validation of these estimates is required. It should be noted that the method proposed in this paper is particularly suited for sedimentary basins with relatively weak tectonic activity.

鲕粒不仅是古环境的重要指示标志,由其构成的鲕粒石灰岩通常也是重要的油气储集层.但自鲕粒被发现一个多世纪以来,关于其无机成因还是有机成因就一直存在争议.分别系统归纳了典型鲕粒的物理化学成因及微生物成因、鲕粒的圈层结构类型及成因,结合前人研究成果建立了新的鲕粒成因模式,解释了常见鲕粒的形成过程.对鲕粒研究综述和实例分析认为,鲕粒新圈层的形成是微生物介导的,鲕粒圈层形态是受沉积水体能量控制的,光合微生物及硫酸盐还原细菌等建设性微生物群落均促进了鲕粒圈层的沉淀;鲕粒的圈层结构主要为径向生长的放射状、随机分布的杂乱状和切线状,在地质历史时期观察到的其他鲕粒结构均是受活跃的破坏性钻孔生物及不同程度成岩作用改造的结果;鲕粒最原始的结构是径向生长的放射状,是在低能静水环境中由非晶质钙碳酸盐(ACC)矿化形成的,随机分布结构及切线状结构是被水动力剪切改造形成的结构,鲕粒中明显的暗色同心薄层是鲕粒生长过程中间歇性出现的微生物群落建设性或破坏性定殖后生物矿化的产物,受水动力影响这三种结构既可以单独发育,也可以组合出现,构成了鲕粒形态的多样性;核心供给速率大小、沉积水体碳酸钙饱和度高低、沉积水体能量强弱及建设性微生物群落活跃程度共同控制了鲕粒粒径大小.

As one of the most important forcing factors, relative sea‐level changes exert a major influence on the building of shelf‐margin clinothems. However, it is still not well understood how these changes control the growth of shelf edges and the condition of sediments transporting into deep water, especially over the individual‐clinothem scale of several 100 ky. On the late‐Quaternary Pearl River margin, there are two distinct shelf‐margin clinothems: SQ3 and SQ4. They have different shelf‐edge trajectories (slight rising vs. steep rising) and different styles of deep‐water deposition (fan lobes consisting mainly of MTDs vs. fan lobes consisting mainly of turbidites). This work takes those SQ3 and SQ4 as study objects and runs a total of 136 experiments from the Dionisos stratigraphic forward model to investigate how relative sea‐level changes control the trajectories of shelf edges and the volumes of MTDs in deep water over the individual‐clinothem scale. Our quantitative results suggest that under the geological background of high sediment supply on the late‐Quaternary Pearl River margin, the duration of highstand systems tracts (HST) relative to lowstand systems tracts (LST) or forced regressive systems tracts (FST) has a significant influence on the building of individual shelf‐margin clinothems. If the relative duration of HST is either very short or very long, slight‐rising shelf‐edge trajectories and large‐volume MTDs would be formed, whereas if the relative duration of HST is comparable with LST or FST, steep‐rising shelf‐edge trajectories and limited MTDs would be formed. Through the constrains of the model set to the real geological condition of the SQ3 and SQ4 clinothems, it is found that SQ3 was caused by the quite long relative duration of HST, which made highstand deltaic systems advance over the pre‐existing shelf‐slope break, leading to significant accretion and instability of the shelf edge and thus, giving rise to the formation of slight‐rising shelf‐edge trajectories and fan lobes with high MTDs contents. SQ4, however, formed as a result of the comparable durations of HST, LST, and FST, which made highstand deltaic systems advance to but not beyond the previous shelf‐slope break allowing the subsequent FST to be directly perched on the clinoform slope. Such building processes did not drive pronounced accretion and instability of the shelf edge and thus, caused the formation of steep‐rising shelf‐edge trajectories and fan lobes with low MTDs contents.

Reservoirs in nonmarine and marine fine-grained rocks differ in both material composition and sedimentary environment, and the factors influencing reservoir quality are also different. In this study of the Lower Jurassic in the Sichuan Basin, the methods used were whole rock analysis of X-ray diffraction（XRD）, He permeability, elemental geochemistry, organic geochemical analysis, scanning electron microscopy（SEM）, analysis of nonmarine finegrained rock composition, reservoir space types and microstructure. The factors controlling the reservoir quality of nonmarine fine-grained rocks are discussed. It is shown that the main minerals of the Lower Jurassic fine-grained rocks in the Sichuan Basin are clay minerals, quartz and carbonate minerals. The contents of clay minerals and quartz are high in the whole section, but the carbonate mineral content is locally enriched. The nonmarine fine-grained rocks mainly consist of five rock types: shale, shell mudstone, silty mudstone, siltstone and shell limestone. The shale and shell mudstone have high organic matter content and good shale gas reservoir physical properties. The reservoir space of the terrestrial fine-grained rock reservoir mainly consists of clay mineral interlamellar pores and microfractures, but fewer organic pores. The reservoir quality is mainly affected by sedimentary environment and diagenesis, and has little relation to its composition. Semi-deep lake conditions control the distribution of organic-rich fine-grained rocks; a reducing depositional environment of low salinity, humidity and sufficient provenance is conducive to the development of pore space in fine-grained rocks and provides the basic material for the formation of reservoirs. The interlaminar pores in clay minerals are preserved by overburden pressure and provide storage space for shale gas enrichment.

苏北盆地溱潼凹陷阜三段地层是一套浅水缓坡三角洲沉积,水体动荡水位变化频繁,岩性主要为泥页岩、泥质粉砂岩及细砂岩,分选差,非均质性强,常规单一物性参数难以准确表征储层性质.为明确苏北盆地溱潼凹陷阜三段储层物性及孔隙结构参数之间关系并总结储层分类依据,在明确地层主要孔隙类型的基础上,利用分形理论对地层物性参数及样品高压压汞实验数据加以分析,最终获得了砂体物性、孔隙结构与分形维数之间的相互关系.优选孔渗参数、孔隙结构系数、孔喉半径及孔喉分选系数5项参数作为主要参考因素,以此建立了以分形维数为基础的储层分类评价标准,并采用因子分析法对其适用性加以验证,将溱潼凹陷阜三段储层划分为3类:Ⅰ类中砂岩储层(D:2.31～2.42,-D=2.36);Ⅱ类细—粉砂储层(D:2.53～2.86,-D=2.75);Ⅲ类泥质储层(D:2.94～2.99,-D=2.97).该研究为研究区储层结构定量化表征及储层类型判别提供了一种新的参考依据.

The geological characteristics and enrichment laws of the shale oil in the third submember of the seventh member of Triassic Yanchang Formation (Chang 73) in the Ordos Basin were analyzed by using the information of core observations, experiments and logging, and then the exploration potential and orientation of the Chang 73 shale oil were discussed. The research findings are obtained in three aspects. First, two types of shale oil, i.e. migratory-retained and retained, are recognized in Chang 73. The former is slightly better than the latter in quality. The migratory-retained shale oil reservoir is featured with the frequent interbedding and overlapping of silty–sandy laminae caused by sandy debris flow and low-density turbidity current and semi-deep–deep lacustrine organic-rich shale laminae. The retained shale oil reservoir is composed of black shale with frequent occurrence of bedding and micro-laminae. Second, high-quality source rocks provide a large quantity of hydrocarbon-rich high-quality fluids with high potential energy. The source-reservoir pressure difference provides power for oil accumulation in thin interbeds of organic-poor sandstones with good seepage conditions and in felsic lamina, tuffaceous lamina and bedding fractures in shales. Hydrocarbon generation-induced fractures, bedding fractures and microfractures provide high-speed pathways for oil micro-migration. Frequent sandstone interlayers and felsic laminae provide a good space for large-scale hydrocarbon accumulation, and also effectively improve the hydrocarbon movability. Third, sand-rich areas around the depression are the main targets for exploring migratory-retained shale oil. Mature deep depression areas are the main targets for exploring retained oil with medium to high maturity. Theoretical research and field application of in-situ conversion in low-mature deep depression areas are the main technical orientations for exploring retained shale oil with low to medium maturity.

Palaeogeomorphology and palaeo-environment conditions are the main environmental factors affecting the sedimentation. Due to the frequent water change, complex terrain and high difficulty in seismic identification and tracking, the reconstruction research of palaeogeomorphology and palaeo-environment in the 3rd member of Funing Formation in Qintong Sag of Subei Basin is still insufficient, which affects the overall exploration evaluation of the study area. In order to clarify the palaeogeomorphology and palaeo-environmental conditions of the 3rd member of Funing Formation in Qintong Sag during the deposition period, the formation core, logging data and rock material data are comprehensively analyzed. The semi-quantitative reconstruction of the palaeogeomorphology of the 3rd member of Funing Formation is carried out by combining the palaeo-geologic map, impression method and residual thickness method, and the pyrolysis experiment data, TOC and trace element content data of 33 rock samples from two wells are selected to carry out the palaeo-environment reconstruction analysis. Accordingly, paleogeomorphology reconstruction in map form and the curves of palaeo-environment changes of the 3rd member of Funing Formation in Qintong Sag are drawn, which prove that the study area is a half-graben, lower in the South and higher in the North with the convergence across the east-west direction, the climate is warm and humid during the sedimentary period, the water body activity is frequent and recurrent, the water salinity is low, the multiple source is supplied intermittent, the material source input continues to increase, and the deposition rate is fast. Therefore, the corresponding relationship between stratigraphic physical parameters and paleogeomorphology, geochemical parameters and paleoenvironment in the study area are clarified, which provide reference for the further exploration and development.

为了满足进一步勘探开发的需求,以测井、地震、岩心等资料为基础,结合普通薄片、X射线衍射(X-ray diffraction,XRD)等手段,详细研究了哈法亚油田Nahr Umr组碎屑岩的岩石学和沉积学特征,明确了其为海陆过渡带潮控三角洲环境的沉积产物.Nahr Umr组碎屑岩以细砂岩、粉砂岩夹泥岩及页岩为主,砂岩的结构和成分成熟度高,表明沉积期研究区气候炎热、湿润,地形平缓,具备潮控三角洲发育的有利条件;碎屑岩内部发育过渡性层理(脉状、波状及透镜状)、羽状交错层理、泥披层等与潮汐作用相关的典型沉积构造,并可划分为 3 种主要的岩石组合:泥岩-砂岩(脉状、波状和透镜状层理泥岩-砂岩亚类)、砂岩(交错层理正粒序、反粒序砂岩亚类)、泥(页)岩(粉砂质泥岩和水平层理页岩);根据岩石类型组合特征及沉积序列,Nahr Umr组碎屑岩整体为 1 个"海侵—海退—海侵"的沉积序列,可识别出潮控三角洲平原、前缘和前三角洲(或陆棚)3 种亚相类型;根据平面相分布,其存在东、西 2 个物源,且以西部物源为主,三角洲整体沿NEE向呈"漏斗状"向海方向展开.

The Permian-Triassic transitional interval exposed well at Kangjiaping section, northwestern Hunan, South China, contains microbialites, oolitic and oncolitic limestones intercalated with vermiculate micritic limestones in the Lower Triassic overlying the uppermost Permian bioclastic limestones, which provides an excellent opportunity to study the environmental changes after the end-Permian mass extinction (EPME) and the origins and environmental significance of these various anomalous sediments. In this paper, we describe in detail the petrographic and geochemical characteristics of these anomalous sediments, together with the reconstruction of the marine environment after the EPME. The continental margin weathering was significantly enhanced after the EPME, indicated by the higher concentrations of terrigenous minerals, Th, Sc, Sr, and rare earth elements in the Lower Triassic carbonates than in the uppermost Permian bioclastic limestones. Indicators such as V/(V + Ni) and Ni/Co ratios suggest that the oxygen content of shallow seawater significantly decreased after the EPME. While, most samples from the Kangjiaping section preserve a negative cerium anomaly, indicating the shallow seawater was still oxygenated both before and after the EPME. In addition, the abnormally rapid carbonate precipitation rate indicates a supersaturation state with respect to calcium carbonate in the shallow seawater after the EPME, but the depth and salinity of seawater and climate indicated by different microfacies are still different. Under the setting of a rapid transgression after the EPME, the microbialites first deposited on the platform with the exclusion of grazers at the beginning of the Early Triassic, followed by the oncolites formed when the climate turned humid with a relative sea-level rise. The oolites were primarily deposited in an arid climate with a relative sea-level fall, and the salinity and hydrodynamics of seawater controlled the ooids’ grain sizes. In contrast, the (vermiculate) micritic limestones were mainly formed in a humid climate with a relative sea-level rising and more terrigenous inputs. Therefore, the periodic relative sea-level fluctuation and arid-humid climate alternations play a vital role in the evolution and repeat stacking of various microfacies in the Kangjiaping section.

The middle Permian strata in western Sichuan basin are mainly carbonate platform face deposites. The Dongwu Movement at the end of the Middle Permian resulted in the uplift of the Maokou Formation, which was eroded by atmospheric fresh water leaching and developed the epigenetic karst palaeogeomorphology, producing a large number of dissolution pores and providing good conditions for the storage of oil and gas. In response to the poor understanding of the development pattern and controlling factors of the Middle Permian epigenetic karst in western Sichuan, this paper summarizes in detail the typical characteristics of karst in Qixia and Maokou forma-tions based on field outcrops, cores, logs and geochemistry. Through the statistical analysis of karst characteristics, this paper systematically summarizes the development pattern of karst re-servoir in vertical and plane. The palaeogeomorphology of the top of Maokou formation and Qixia Formation is described by residual thickness method, which is divided into three geomorphic units: karst depression, karst slope and karst highland. Based on the superposition of drilling and outcrop karst, it is concluded that karst depression is the most conducive to the development of epigenetic karst reservoirs. Although the karst depression can collect water, it does not accumu-late water. The convergence of surface water is conducive to the development of karst reservoirs by downward and lateral erosion of strata. After discussion and analysis, it is obtained that the epigenetic karst reservoirs of Middle Permian in western Sichuan basin are mainly controlled by palaeogeomorphology, sedimentary interruption, lithology and sedimentation. This study can provide geological theory and basis for the exploration and development of Middle Permian epigenetic karst reservoirs in western Sichuan Basin.

Recently, a number of breakthroughs in oil and gas exploration have been made in the Permian Qixia Formation in the Sichuan Basin, such as the discovery of large oil and gas reservoirs in Shuangyushi area in the northwest Sichuan Basin. However, during the actual exploration and development process, different well test production of Qixia Formation reservoirs varied greatly, and some wells experienced failures, indicating that the reservoir has strong heterogeneity and the sedimentary facies as a key control factor for high-quality reservoir needs to be further stu-died. To address this issue, this study systematically sorted out the different types of rock features and sedimentary faces of the Qixia Formation through detailed field outcrops and extensive thin section identification analysis. In this study, the carbonates of the Qixia Formation in the western Sichuan area can be classified into four rock types according to their rock morphology: laminated limestone, porphyritic limestone, sugary dolomites, and reef limestone. According to the structur-al classification scheme, the carbonate rocks of Qixia Formation in western Sichuan can be divided into limestone and dolomite, of which the limestone can be subdivided into lime mudstone group, grain limestone group, reefstone group and calcareous limestone, and the dolomite can be subdivided into micrite dolomite, fine crystalline dolomite, medium coarse crystalline dolomite and dolomite cement. The Qixia Formation in western Sichuan is mainly composed of a set of weakly bound platform facies, including three subfacies of shoal, reef and platform sag. The beach facies of Qixia Formation is dominated by thin to medium limudy-sparry grain beaches and limudy grain beaches, which are developed both at the platform margin and within the platform. High-energy beaches are rare, with medium to low-energy beaches predominating, and the beaches are not contiguous and have strong heterogeneity. The platform sag is the most important sedimentary facies type of Qixia Formation, among which open platform sag is the most widely distributed, and lithology is dominated by bioclastic lime mudstone. The relatively restricted water bodies and elevated Mg/Ca ratios due to the separation of the beaches provide conditions for medium salinity reflux seepage dolomitization, which promotes dolomitization of limestone in restricted platform sag and surrounding beaches to form high quality reservoirs.

关于白云岩成因,前人提出了多种机理,但许多机理并没有过硬的证据,难以令人信服.近些年的研究表明,白云石借助微生物的作用在常温下可以沉淀出来,形成微生物白云岩.模拟实验证明了这种机理的正确性.微生物白云岩的发现表明,自然界中可以存在原生白云岩,因此具有重要科学意义.实验表明,多种微生物可形成白云岩.文章主要描述了其中4类已在自然界中发现且资料较丰富的微生物白云岩的形成机理:厌氧硫酸盐还原菌形成白云岩的机理、甲烷氧化菌形成白云岩的机理、厌氧甲烷生成菌形成白云岩的机理、喜氧喜盐菌形成白云岩的机理.详细阐述了每种机理的基本原理和关键数据等,以便读者不用查阅原文就能掌握其核心内容和资料,并激发读者的思考;尤其总结出了各类微生物白云岩的识别标志,同时指出了微生物白云岩形成机理仍存在的一些问题.

为了分析含气陆相页岩中石英矿物的成因、分布及其影响因素,以四川盆地自流井组含气页岩层段为主要研究对象,利用X射线衍射分析、普通薄片、扫描电镜、阴极发光、电子探针及元素地球化学分析测试手段,识别出陆源石英和成岩过程中形成的石英.陆源石英在阴极光下表现为棕色光,粒径较大.成岩过程中形成的石英在阴极发光下不发光,晶形较好,粒径较小.根据成岩作用的不同,将成岩过程中形成的石英细分为黏土矿物转化过程中形成的石英和硅质交代介壳边缘形成的石英.分析不同成因的石英分布特征发现,东岳庙段内石英矿物主要为陆源输入和黏土转化成因;马鞍山段内的石英主要为陆源石英;大安寨段内的石英则为硅质交代自生和陆源输入成因.在此基础上,总结了陆相页岩中不同成因石英的影响因素,包括沉积环境和地层压力.在沉积环境方面,随陆源物质输入的增加,陆源石英增加.同时,适合的湖水盐度,有利于介壳生物的生存,为硅质交代介壳形成石英提供物质基础.此外,地层的异常高压会抑制黏土转化,减少硅质析出,阻碍自生石英的沉淀.