The mixed Oligocene–Miocene succession of the Asmari formation constitutes an important clastic-carbonate petroleum reservoir in southeastern Iraq, where a detailed understanding of depositional settings and reservoir evolution is essential for optimizing exploration and development strategies. This study aims to improve reservoir characterization by establishing a refined lithofacies classification through the integration of core data, well logs, petrographic analyses, and seismic information. A multidisciplinary approach was applied to interpret the vertical and lateral facies architecture of the formation, and Sequential Indicator Simulation (SIS) was employed to construct a three dimensional lithofacies model capable of capturing both vertical stacking patterns and lateral facies variability within the reservoir. The results indicate that depositional environments and subsequent diagenetic processes play a fundamental role in controlling reservoir heterogeneity. Depositional settings were interpreted through the integration of lithofacies characteristics, textural attributes, and seismic impedance patterns, allowing the identification of deltaic, mixed shallow marine, and restricted lagoonal environments. These environments reflect the interaction between a delta influenced siliciclastic system and a carbonate platform, governed by repeated relative sea level fluctuations that influenced the distribution of mixed sediment types. Reservoir quality varies spatially from poor to good and is significantly affected by diagenetic alterations, particularly the development of authigenic clays and cementation, which reduce porosity and permeability. Member A is characterized by low porosity and low to moderate permeability, whereas Member B exhibits moderate porosity and moderate to high permeability, indicating more favorable reservoir conditions. Overall, the application of integrated lithofacies modeling and advanced geological analysis provides a more reliable representation of reservoir architecture and heterogeneity. The results enhance the understanding of the Asmari formation as a complex carbonate clastic reservoir and support improved reservoir evaluation, modeling, and heterogeneous oilfield development.

Large strike-slip fault zones commonly develop through-going architectures through progressive linkage of fault segments. However, quantitatively characterizing the through-going evolution of strike-slip fault zones remains challenging. Based on the pure strike-slip tectonic setting of the Tarim Basin, twelve sandbox analogue experiments were conducted to quantify the through-going process and evaluate its controlling factors, including displacement pattern, cover thickness, and displacement velocity. The results indicate that simple-shear strike-slip fault zones evolve through a progressive sequence from the en échelon stage to soft-linkage, hard-linkage, and ultimately a through-going stage. Each evolutionary stage corresponds to distinct threshold values of relative displacement (D/L). En échelon faults initiate at the base of the model during the embryonic stage and propagate upward to the surface during the soft-linkage stage when D/L ranges from 1.37% to 2.38%. Subsequently, Y-shear faults link individual fault segments during the hard-linkage stage at D/L values of 2.59%–4.81%, followed by the formation of a fully through-going fault zone at D/L values of 6.14%–7.76%. Generally, displacement threshold values increase with greater cover thickness during upward fault propagation. Threshold values also increase from bilateral codirectional displacement to unilateral displacement, and further to bilateral antidirectional displacement patterns, whereas higher displacement velocities tend to reduce the threshold values. The experimentally derived quantitative evolution is consistent with the fault segmentation and linkage mechanisms observed in strike-slip faults of the central Tarim intracratonic basin. These results demonstrate that the through-going process of pure strike-slip fault zones can quantitatively constrained by displacement, while strata thickness, displacement patterns, and displacement velocity exert significant control on the corresponding threshold values.

Determining the timing of hidden faults that terminate beneath the subsurface remains a significant challenge. For this contribution, seismic fault interpretation, fracture diagenesis analysis, and U-Pb dating of fracture cements are integrated to constrain the activity of hidden thrust faults in the southeastern Sichuan Basin. The results show that the EW- and NW-trending hidden thrust faults developed in the Permian, while the NE-trending faults have inherited later fault activity till the Cenozoic. The hidden thrust fault propagates upward from the top of the Upper Permian to the Lower Triassic strata. Fault inversion within the Permian is firstly identified by the thickness variation between the two fault walls. Core-based fracture diagenesis analysis indicates that multiple fractures and associated dissolution porosity developed within the tight matrix reservoir. In situ U-Pb dating of fracture cements yields ages of 247.4 ± 2 Ma and 234.8 ± 9.1 Ma, indicating that the hidden fault activity predates the Early Triassic. The absence of strata, evidence of structural uplift, and fault inversion collectively suggest that the first faulting in the eastern Sichuan Basin occurred at the end of the Middle Permian. The findings highlight that fracture–cave reservoir along the hidden thrust fault zone has been controlled by the coupling of the fracturing and karstification at the end of the Middle Permian, and is the key target for high gas production.

At the end of Early Cambrian time, the Sichuan basin（South China） was located in a wide carbonate platform, with hundreds of meters of carbonate deposited. The Longwangmiao Formation carbonate in Sichuan basin is partially to completely dolomitized, displaying a mottled texture in the northern area of the exposure. The mottled dolomitic limestone developed parallel to bedding, with shape irregular boundaries with limestone that has not been dolomitized. The mottled dolomite is composed of powder crystalline and finely crystalline dolomite, while the matrix limestone is composed of micritic calcite. the isotopic composition of mottled dolomite(δ 13 C = +0.29‰PDB, δ 18 O =-1.15‰PDB) is similar to that of micrite calcite(δ 13 C =-0.49‰PDB, δ 18 O =-1.45‰PDB). Both isotopic values and trace element data indicate that the dolomitized fluid is originated from sea water. Some beds contain gypsum pseudomorphs and mud cracks, indicating a shallow and evaporative environment with local high salinity during deposition. Dolomitization likely took place early, in part as a result of sea water salinity concentration. Trace fossils thalassinoides horizontalis, thalassinoides callianassa and planolites developed in the Longwangmiao Formation, and the sharp edges of mottled dolomite are similar to these trace fossils. The beds are intensely bioturbated. In the burrow network, the sediments and burrow fill were coarse and loose with little clay, and it is interpreted here as being easier to be dolomitized than the surrounding sediments.Partial dolomitization is thus interpreted to have occurred in the burrow system, and the degree of dolomitization was related to the degree of bioturbation, which is controlled by the trace-making creatures.

The Lower Ordovician Tongzi Formation containing abundant shoal sediments is the most promising stratum for the petroleum exploration in the Sichuan Basin. However, the current studies mainly focus on the central part of the Basin, the systematic analysis of the southeastern part with well-developed shoal facies is lacking. This paper aims to clarify the characteristics and genesis of the Tongzi Formation reservoir in Southeastern Sichuan Basin, following an analysis of sedimentary facies within the sequence stratigraphic framework. The research shows that the main types of reservoir rocks are oolitic, intraclastic and bioclastic dolostones. And the reservoir spaces consist mainly of intergranular (dissolved) pores, intercrystalline (dissolved) pores, intragranular dissolved pores and fractures. Among them, intergranular pores account for the highest proportion, which is followed by intragranular dissolved pores. In addition, most throats are necking and flaky which mainly connect intergranular and intercrystalline pores, respectively. The diagenetic sequence shows that penecontemporaneous karst well improved the porosity of the reservoir in the early-stage although the cementation and compaction reduced parts of pores. The reservoir formation is associated with the tectonic-depositional settings, diageneses and terrigenous contamination. Paleohighlands and submerged uplifts, forming in the early Ordovician amalgamation between Yangtze and Cathaysia blocks, accumulated shoal sediments as the material basis for the reservoir formation. Penecontemporaneous karst forming intragranular dissolved pores and the dolomitization aiding grainstones to resist the pressure solution are the key to increasing porosity and preserving pores. The absence of terrigenous contamination prevented intergranular pores from being strongly cemented, which resulted in the reservoir difference between the central and southeastern Sichuan Basin. The study can be used as a reference for the further exploration of Ordovician petroleum in the Sichuan Basin and other regions owning similar geological settings.

Based on the research results of stratigraphic sedimentary facies, plane maps of sedimentary facies for four periods of the Neogene terrestrial foreland basin in Southwest Tarim were compiled. Research results conclude that the Neogene Miocene developed alluvial fan facies, fan delta facies, and lacustrine facies successively from the piedmont belt to the Maigaiti Slope. During the sedimentation of the Miocene Anju’an Formation, the lake range expanded to its maximum. According to the new division scheme for five-order sequences in prototype sedimentary basin, the stratigraphic sequence of a terrestrial foreland basin was divided and compared, and a sequence development and evolution model was established. Research results show that: (1) the Neogene–Quaternary is a typical type I sedimentary sequence with huge thickness; (2) the Neogene is a period of tectonic compression and flexural subsidence sedimentation in the foreland basin; with the maximum lake flooding surface at the top of the Miocene Anju’an Formation as the boundary, the lower part is a second-order super-sequence of the lacustrine transgression system tracts (TST), the upper part is a second-order super-sequence of the highstand system tracts (HST), and the Quaternary is a second-order super-sequence of the lowstand system tracts (LST) in forced lacustrine regression caused by the Late Himalayan tectonic movement; (3) the classic sequence stratigraphy made an error in establishing the theoretical model of marine type I sequences, as it placed the LST in the wrong position. The corrected type I sequences are in the order of TST, HST, and LST. (4) Finally, two examples were applied to demonstrate the development position of the LST, indicating that whether it is a marine or terrestrial prototype sedimentary basin, the LST was developed during the late stage of tectonic compression and uplift in a basin, and is the sedimentary sequence at the top of the prototype sedimentary basin.

Although the Ordovician petroleum exploration in the Sichuan Basin has been developed slowly for a long time, deepening the research of reservoir characteristics and genesis is still a robust way to accelerate it. This paper characterizes the Ordovician reservoirs in the central part of Sichuan Basin and analyzes their genesis based on cores, thin sections, well logs and drilling data. The results show the reservoirs concentrated in the Lower Ordovician Tongzi Formation, which consist mainly of sandy oolitic dolostones, bioclastic dolostones, fine crystalline dolostones, sandy dolomitized conglomerates, sandy dolostones and dolomite sandstone. The porosity types include interparticle pore, intraparticle pore, moldic pore, fracture and vug. Throats are mostly necked and flaky. The Tongzi Formation reservoirs mainly experienced three types of diageneses, including compaction, cementation and dissolution. The reservoir development was controlled by multiple factors of deposition, diagenesis and tectonics; the shoal facies is the basis, the penecontemporaneous dissolution and dolomitization are the main driving force, and the burial dissolution is the aid. The study can provide reference for deepening the Ordovician petroleum exploration and development in the Sichuan Basin.

Recognition of the existence of an Andean-type continental margin in southern Tibet prior to its collision with India has provided crucial constraints on the formation of the Tibetan Plateau and South Asian climate evolution. Here, we focused on well-dated Late Cretaceous successions in the Linzhou Basin and determined the elevation changes from sea level to high mountains in the Gangdese magmatic arc in southern Tibet. Our results show that the Linzhou Basin was still submerged in the Tethyan Sea at around 92 Ma when it accumulated Cenomanian (ca. 105−92 Ma) shallow-marine orbitolinid-bearing limestones (Takena Formation); these limestones are unconformably overlain by Campanian (83−78 Ma) fluvial-lacustrine deposits (Shexing Formation) after an ∼9 m.y. depositional hiatus. A prominent unconformity between the tightly folded Shexing Formation and gently tilted overlying Paleocene−Eocene Linzizong successions represents the formation of the regional Lhasaplano ca. 70 Ma, which may have been linked to the rise of an Andean-type Gangdese mountain range along the southern margin of the Lhasa terrane. Using carbonate oxygen isotope and clumped isotope thermometry data from the Shexing Formation paleosols, we quantitatively documented the rise of the Andean-type Gangdese Mountains with a peneplain surface at an elevation of 2.7 +0.5/−0.9 km above sea level prior to onset of the India-Asia collision ca. 65−63 Ma. This scenario of surface gain may have been an isostatic compensation response to the crust thickening to over 50 km during the Late Cretaceous. Subsequently, the surface isostatically rose to its near-present elevation of ∼4.6 km due to the removal of overthickened mantle lithosphere and revival of intense Gangdese magmatism by 56 Ma.

Acid gases such as H2S, CO2, SO2 carried in natural gas will form acid liquid with water during transportation, which is prone to serious corrosion problems such as perforation and leakage. Corrosion inhibitors are often used as one of the main anti-corrosion processes. With regard to the serious internal corrosion of the gas gathering pipeline in a well in Moxi, based on the actual operational conditions, this paper establishes a CFD model to study the distribution of corrosion inhibitors. The simulation results show that: ① the larger the pipeline angle and the faster the injection velocity, the better the distribution of the inhibitor particles in the pipe. Although the injection rate will affect the inhibitor concentration in the pipe, the regularity remains unchanged; ② when the injection velocity increases, the inhibitor becomes better distributed and can protect the longer range of the pipeline; ③ the corrosion inhibitor at the top of the pipe will settle and attach to the wall due to the gravity, and the fluid would rise to the middle and upper part of the pipeline due to the influence of secondary flow after passing through the elbow, causing the inhibitor concentration to increase rapidly.

The transmission medium of natural gas gathering and transportation pipelines usually contains cor-rosive gases, which will cause serious corrosion on the inner wall of the pipelines when they coexist with water. Therefore, it is necessary to add corrosion inhibitor to form a protective film to protect the pipeline. The distribution of corrosion inhibitors in a gathering and transportation pipeline in Moxi gas field was studied by combining experiment and simulation. The Pearson function was used to calculate the experimental and simulation results, and the correlation was more than 80%, indicating a high degree of agreement. The simulation results show that: ① The larger the pipe angle, filling speed and gas flow rate, the smaller the particle size, the better the distribution of corrosion inhibitor particles in the pipe. The filling amount will affect the concentration, but the distribution trend is unchanged; ② A method to determine the filling mode based on the loss was proposed, and for this pipeline, the loss of corrosion inhibitor was determined to be 5.31 x 10-3 kg/s, and the filling amount was recommended to be adjusted to 20 L/h, which has certain guiding significance for the actual filling strategy of pipeline corrosion inhibitor.& COPY; 2023 The Authors. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

Table S1. Names of sections and boreholes in the Figure 1. This table comprise names of sections and boreholes which are used in the study and presented by numbers in the Figure 1. Table S2. Point-counting data of samples for the model sandstone petrology in the Xinjigu section. We obtain the modal framework grain compositons of 42 samples of medium- to coarse-grained sandstones from the Xinjigu section by point-counting standard thin sections according to the Gazzi-Dickinson method (Ingersoll et al., 1984). Table S2 documents the point-counting data of these sandstone samples. Table S3. Detrital zircon U-Pb dating from the measured Xinjigu section in the southwestern margin of the Sichuan Basin, western Yangtze region. We collected four sandstone samples from the lower Ordovician Hungshihyen Formation (XJG-102.4 and XJG-175) and upper Ordovician Taching Formation (XJG-806 and XJG-836) for zircon U-Pb dating. U-Pb geochronology of zircon was conducted by LA-ICPMS at the laboratory of carbonate sedimentary and diagenetic geochemistry, Southwest Petroleum University. Table S3 documents the data of detrital zircon U-Pb dating from these Xinjigu samples.

Amalgamation of the Yangtze and Cathaysia blocks in the context of Gondwana assembly in the early Paleozoic has been addressed for decades, but the far -field effects on the Yangtze Block during the amalgamation remain unclear. In this study, we outline the sequence stratigraphic framework of the Ordovician succession in the central-upper Yangtze Block and analyze provenance records in sandstone compositions, distributions, and detritus zircon U-Pb dating. The Ordovician succession in the central-upper Yangtze Block is subdivided into six third-order sequences, which were deposited mainly in a carbonate platform with restricted sediments in Tremadocian to early Floian stages, mixed terrigenous-carbonate deposits in mid-to late Floian stages, and open circulation sediments in Dapingian to middle Katian stages. These sequences show the central-upper Yangtze Block experienced syn-tectonic deformation with northeast-trending long-wavelength uplift and depression alternatively and the depocenter shifting from the east during Tremadocian to mid-Floian stages to the southwest in late Floian to early Hirnantian stages. Provenance data indicate that detritus in the Ordovician succession was mainly from the northern India and Kangdian paleohighland to the southwest of South China Block. Incorporating the depositional and deformation variations, we propose a retroarc foreland basin that was developed on the South China Block in response to final suturing between the South China Block and East Gondwana at Sanya suture zone. The South China Block was thus involved in the global tectonics of the Gondwana supercontinental cycle during the Ordovician.

A great breakthrough was achieved on the Middle Devonian's oil-gas exploration in the Longmenshan area in northwestern Sichuan. However, only the Guanwushan Formation was researched in detail. The underlying formation - Jinbaoshi Formation as a set of the potential well reservoir and its reservoir characteristics have not been discussed. Based on the section's fine description, thin section analysis, and core borehole logging, combined with petrophysical analysis, the reservoir characteristics, controlling factors, and evolution process of the Jinbaoshi Formation reservoir in the Longmenshan area are deeply studied in this paper. The results showed that the Jinbaoshi Formation has developed a set of sand-shale interbedding deposit of terrigenous clastic and carbonate rocks. The reservoir lithology is mainly quartz sandstone and calcareous quartz sandstone. The quartz sandstone reservoir has good physical properties, but the calcareous quartz sandstone has the characteristics of strong heterogeneity, low porosity, and permeability. Residual intergranular pores are mainly developed in the reservoir space. And the development of intercrystalline pores and intergranular dissolved pores can also be seen, but the development frequency is low, and the scale is small. Among them, the Devonian Jinbaoshi Formation quartz sandstone's average porosity is about 8%, and the highest is 18.43%. The main diagenesis types of the Jinbaoshi Formation are compaction, recrystalization, and dissolution. Compaction is the main reason for the destruction of original pores, and dissolution is the main driving force for later porosity and permeability improvement. Rock fragments, calcareous silty clasts, and bioclastic grains are the main dissolution objects. The formation of intergranular dissolved pores significantly improves the physical properties of the reservoir. Therefore, the reservoir development of the Jinbaoshi Formation is mainly controlled both by favourable sedimentary facies and diagenesis. Quartz sandstone and calcareous sandstone of the Jinbaoshi Formation were controlled by early sedimentary facies in the syngenetic rock stage and developed more early intergranular pores; in the early diagenesis stage, compaction-pressure solution and cementation resulted in residual intergranular pores. In the middle-late diagenesis stage, the calcareous cement is dissolved, and more pores were formed.

Spatial and temporal variations of PAHs deposition flux and sources may significantly facilitate risk evaluations of super magacity in China. A study on polycyclic aromatic hydrocarbons of wet deposition and dry deposition in Shanghai was conducted from January to December, 2019. 17 sites were investigated located in four representative functional areas, covering iron and steel industry (BS), petrochemical industry (JS), central city (CC) and agricultural area (CM). The results showed that atmospheric PAHs level in shanghai was the lowest in autumn and the highest in winter. As industrial area, BS and JS demonstrated higher PAHs deposition fluxes than those in CC and CM sites. Triangle map indicated that the PAHs distribution in winter and spring samples were more homogeneous, suggesting possible common origins, whereas that of summer and autumn seemed to be more dispersed. Isomar ratio and positive matrix factorization model were employed to identify the potential sources of PAHs in specific functional areas. BS was dominated by a high percentage (46%) of coal combustion. In JS site, the petroleum volatilization source percentage was 47.6%. The highest biomass burning (55.3%) contributions were in CM. Vehicle emission (49.3%) was identified as the predominant source of PAHs in CC. This study highlighted that local emission sources have a greater influence on PAHs deposition to specific functional regions in Shanghai.

华南上扬子地区下奥陶统湄潭组是一套厚度较大的泥页岩沉积,黑色页岩十分发育,但对其沉积环境的认识争议较大.文中以贵州遵义板桥剖面为例,通过对黑色页岩及其共生岩石的沉积特征及地球化学特征的综合研究,着重分析湄潭组黑色页岩沉积期的相对水深、沉积水动力条件以及古海水物理化学性质等沉积环境条件.结果表明:(1)板桥剖面湄潭组黑色页岩以颜色暗黑和水平纹理发育良好为显著特征,不产出宏体生物化石,主要以与生屑灰岩或钙质粉砂岩不等厚频繁互层的共生形式产出,说明湄潭组黑色页岩应该不是深水环境的沉积产物,而是在混积台地内低能的浅水泥质潟湖环境中沉积的;(2)与黑色页岩互层的生屑灰岩层段多发育下细上粗的逆粒序结构,顶部可见铁质氧化物,钙质粉砂岩则多发育浪成交错层理和生物钻孔,均呈现出浅水沉积特征;(3)黑色页岩的V/(V+Ni)、Th/U、V/Cr以及Ni/Co的平均值分别为0.71、5.52、1.07和2.04,均指示次氧化—氧化环境;Sr/Ba值介于0.11～2.20之间,平均值为0.55,指示淡水—半咸水环境;(4)生屑灰岩的部分层段可见明显的侵蚀面,镜下可见岩溶发育,同时其REE配分形态趋于水平,ΣREE值较高、Y/Ho值较低,具暴露岩溶特征;(5)黑色页岩TOC值介于0.09％～1.05％之间,平均值为0.39％,恢复的原始TOC含量介于0.28％～3.16％之间,平均值为1.25;RO平均值为2.095,有机质类型主要为腐泥型.综合上述分析结果,认为遵义板桥剖面湄潭组黑色页岩为一套形成于浅水、次氧化-氧化环境的有效烃源岩,高的古生产力是有机质富集的主要原因.研究结果为判识川南地区湄潭组黑色岩系沉积环境和生烃潜力提供有力的证据,也为浅水成因黑色页岩沉积环境条件判识研究提供了一个新的实例.

通过野外露头与钻井剖面的室内外分析,确认在四川盆地西北部(川西北)下二叠统栖霞组中发育有微生物丘,它们主要由凝块灰(云)岩、叠层灰(云)岩和微生物粘结颗粒灰(云)岩等组成.这些微生物碳酸盐岩发育较为典型的凝块、叠层、窗格、粘结等组构.微生物丘大小不一,实测高度一般为几十厘米至几米,宽度通常变化于几米至几十米之间,具有底平顶凸的典型丘形外貌,以发育向上变浅的沉积序列为特征,一般由丘基、丘核、丘盖3 个微相组成,也可与颗粒滩共同构成微生物丘滩复合体.基于区域古地理背景和微生物丘特征的剖析,认为川西北地区栖霞期沉积环境总体受限,推测为半局限—局限台地环境,水深较浅,能量普遍不高;海平面频繁的相对升降变化和微生物丘的侧向迁移叠置,导致发育于缓坡背景下的碳酸盐岩台地极易受限,引起早期沉积物发生与丘滩发育密切相关的准同生期白云石化作用.因此,微生物丘滩复合体是栖霞组白云岩储集层发育的物质基础,台缘坡折带、台内缓坡折带和高地是栖霞组白云岩储集层发育的有利区带,这对寻找规模性层位不稳定的带状白云岩储集层具有重要的指导作用,并将大大拓展栖霞组白云岩储集层的勘探领域.

Fibrous marine cements are widely distributed in the terminal Ediacaran Dengying Formation of South China and are an important record for reconstructing paleoseawater chemistry. However, the morphological characteristics and filling sequence of these cements, and their formation mechanism and paleoceanographic significance, are poorly understood. Our investigation of five outcrop sections in the northern upper Yangtze region allows four types of fibrous dolomite cement to be identified: fascicular fast dolomite (FFD), radial fast dolomite (RFD), radial slow dolomite (RSD), and fascicular slow dolomite (FSD), where "fast" and "slow" refer to the optical character of cement crystals. FFD cements possess original aragonitic mineralogy, whereas RFD cements had high-Mg calcitic precursors that subsequently underwent mimetic dolomitization via syntaxial replacement. RSDs and FSDs are primary marine precipitates, whereas fibrous dolomite cements with length-fast optical characteristics (FFDs and RFDs) are of secondary origin. These fibrous cements are widely distributed laterally in the Dengying Formation, although the RSDs and FSDs occur only in the second member of this formation. Therefore, the seawater chemistry of the terminal Ediacaran period in the upper Yangtze area was dominated by an aragonite sea, with a regional short-lived "dolomite sea" during the late depositional stage of the second member of the Dengying Formation, from which dolomite may have directly precipitated.

Widespread development of microbialites harbors a series of clues about microbial activity, environmental condition, and aquatic chemistry. The Ediacaran-Cambrian transition draws extensive attention on the co-evolution of complex life and Earth's environment but the associated microorganism development has been largely ignored. In this study, we present a high-resolution database with respect to the spatial and temporal distributions of microbialites in China through the terminal Ediacaran to the early Cambrian Period and describe morphological and petrological characteristics of stromatolites and thrombolites in detail to shed light on the evolutionary process of microbial carbonates. Microbialite development experienced two thriving intervals during the Ediacaran-Cambrian transition: latest Ediacaran to early Fortunian, and Cambrian Age 3 to middle Age 4. The columnar and domical stromatolites show no marked morphological changes in the Ediacaran-Cambrian transition, but stratiform stromatolites exhibit a notable decline in Cambrian time, likely caused by increasing bioturbation in the Cambrian shelf environments. Meanwhile, thrombolites evolved to form large and complicated structures in the early Cambrian featured by meter-level mound morphology and columnar-branching microbial forms (fan-like/dendritic structures), likely indicating an improved environmental adaptation (e.g., photosynthesis efficiency and hydrodynamic conditions). Another remarkable change in microbialites is the emergence of large numbers of calcified microbial microfossils preserved within the laminated/clotted mesostructures in Cambrian facies, compared with the Ediacaran forms that lack such unique structural features. For the main control over the Cambrian microbial calcification event, this study stresses again the essential role of seawater chemistry (Mg/Ca molar ratios and Ca2+ concentrations) in the formation and preservation of calcified microorganisms based on previous insights and elaborate characteristics of their occurrence and microstructures in China. The transition of the Neoproterozoic "aragonite-dolomite sea" to the Cambrian "calcite sea" (likely widely distributed in Age 3) may have promoted to the generation of an original calcite mineralogy in microbial fossils, which has a stronger ability to resist diagenetic dissolution and substitution (e.g., phosphatization and silicification) than that of the aragonite precursor.

通过塔里木盆地西北部阿克苏—柯坪—乌什地区露头剖面的宏微观工作发现,寒武系纽芬兰统玉尔吐斯组存在3期稳定发育的古暴露面,并具有(1)铁质结壳层、(2)近地表喀斯特(塑形)角砾、(3)溶沟、溶缝及囊状溶洞、(4)岩溶系统内的角砾、陆源碎屑充填物、(5)暴露面之上的地层超覆等暴露标志.综合分析认为研究区玉尔吐斯组并非连续沉积,内部存在多个沉积间断,并与肖尔布拉克组为区域性不整合接触.同时,在与灰岩和白云岩早成岩期岩溶特征对比分析的基础上,指出先期渗滤条件较差的混积岩(硅质碎屑-碳酸盐混合沉积)早成岩期岩溶以充填程度较高的溶沟、溶缝和小型溶洞发育为特征,且水平潜流岩溶带发育不成熟;以此区别于灰岩和云岩型早成岩期岩溶发育的相控溶蚀孔洞、岩溶花斑和近原地角砾化等典型特征.研究结果表明开放条件下的早成岩期暴露岩溶特征及储集层优化与否更多受岩石组构特征控制,由此推断在相对封闭的埋藏条件下,先期致密化的岩石难以经历岩溶改造形成相控的孔洞型储集层.这一认识不仅对深埋条件下储集层的形成和保持具有重要的借鉴意义,也为早成岩期岩溶地质理论的丰富和发展提供了新的材料.