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The Sichuan basin has a great potential for hydrocarbon exploration. In recent years, Permian strata have been identified as one of the main target strata for natural gas exploration in the Sichuan basin. Not only the source rocks are abundant, but also there are good reservoirs due to the wide and complex continental oceanic interaction. However, there are still many shortcomings, especially the relationship between the tectonic evolution and the hydrocarbon accumulation model. Therefore, this research aims at understanding the characteristics of paleo-highs/lows of the Permian strata and their controlling effects on hydrocarbon migration/accumulation in the Sichuan basin. Firstly, the distribution patterns of paleo-highs/lows in the Permian strata at each critical tectonic period were constructed by integrating spatial erosion calculation. Then the temporal evolution of the Permian strata at each critical tectonic period will be revealed by restoring the upper strata sequentially. The results of this research improve the precision of paleo-highs/lows reconstruction and provide useful hints for the hydrocarbon exploration of the Sichuan basin: (i) Paleo-highs/lows directly determine the development location of the Permian key reservoirs; (ii) Tectonic evolution controls many factors and the process of hydrocarbon accumulation. [ABSTRACT FROM AUTHOR]

The Cambrian Longwangmiao gas reservoirs in the Moxi area of the Sichuan Basin have a complex associated gas accumulation history. Based on core and thin section examination, fluid inclusion analyses and 1-D burial-thermal modelling, the diagenetic evolution and hydrocarbon accumulation processes in the Longwangmiao Formation have been reconstructed. Various diagenetic events were identified, making up a complete pore fill sequence as follows: solid bitumen/dolomite→ nonfluorescent solid bitumen → dolomite → quartz/yellow fluorescent oily bitumen → residual hole. Analyses of oil inclusions and bitumen-bearing inclusions are key to the understanding of the hydrocarbon accumulation processes. The Th values of the aqueous inclusions that are contemporaneous with hydrocarbon inclusions range from 74.3 to 214.3°C. In conjunction with burial-thermal history modelling results, the results indicate that there were two stages of oil charge and three stages of natural gas accumulation in the Longwangmiao carbonate reservoirs. The two stages of oil charge occurred in the Late Silurian and Middle Triassic, respectively. Three gas accumulation events occurred in the Middle to Late Triassic, Middle Jurassic to Early Cretaceous, and Late Cretaceous, respectively. [ABSTRACT FROM AUTHOR]

According to drilling and seismic data, the Late Sinian-Early Cambrian intracratonic rift was found in the Deyang-Anyue area of the Upper Yangtze craton. This rift is controlled by a tensional fault and extends in the N-NW direction with a N-S length of 320 km and an E-W width of 50-300 km. After three stages of the rift evolution, i.e., the formation stage, development stage, and dying stage, a favorable near-source accumulation assemblage formed. The research results indicate that: (1) the sedimentation stage of the Late Sinian Dengying Formation is the rift formation stage, during which trough-basin facies sedimentation is developed in the rift, while platform marginal-facies mounds and shoals are developed on both sides, controlling the formation and distribution of high-quality reservoirs in the Dengying Formation; (2) the sedimentation stage of the Early Cambrian Meishucun-Qiongzhusi Formation is the rift development stage, during which deep-water continental-shelf facies argillaceous rocks accumulated in the rift with a thickness of 500-1000 m, indicating the sedimentation of high-quality source rocks; (3) the sedimentation stage of the Canglangpu Formation is the rift dying stage, terminating the evolution history of the intracratonic rift by gap filling. The intracratonic rift is a key factor for the formation of the Anyue giant gas field, where the high-quality source rocks provide abundant gases for the giant gas field. A regional lateral sealing occurred during the rapid rise of the western paleouplift in Central Sichuan during the Late Yanshan-Himalayan period, favorable for the preservation of the Gaoshiti- Moxi giant gas field on the eastern wing of the rift. The intracratonic rift and its role in giant gas accumulation provide a significant reference for deep oil and gas exploration in paleocratonic basins. [ABSTRACT FROM AUTHOR]

The Ediacaran gas exploration of the Sichuan Basin in the northwest Yangtze Block, South China, indicates that the paleogeography and lithofacies are of great significance for understanding sedimentary environments and further exploration. There are several contrarian views, however, regarding the Ediacaran paleogeographic configuration and lithofacies distribution in the north Yangtze Block. In this study, we systematically analyzed the Ediacaran stratigraphic, paleogeographic, and facies distributions by integrating outcrop observation, well correlation and seismic interpretation. The Ediacaran in the Micangshan-Hannan terrane is dominated by progressive onlap successions from west to east. We suggest that during the Ediacaran an overall paleogeographic configuration evolved from a shallow-water platform to deeper slope-basin and finally into an open ocean (i.e., the Proto-Tethys ocean) in the north Yangtze Block. The platform margin is roughly distributed along the north margin of the Micangshan-Hannan terrane and the present-day Chengkou fault. During the Doushantuo time, the paleogeographic configuration was characterized by a distally steepened ramp passing seaward into slope-basin facies. During the Dengying time, a rimmed carbonate platform developed on the Doushantuo Formation ramp. The platform margin facies predominantly contained microbially laminated dolomites and stromatolite reef complex. The slope-basin facies were dominated by thin-bedded and slump dolomites. The Ediacaran of the north Yangtze Block experienced a sedimentary evolution from a mixed carbonate-siliciclastic ramp of the Doushantuo Formation to a rimmed carbonate platform of the Dengying Formation, primarily controlled by tectonic subsidence differences and sea level changes. [ABSTRACT FROM AUTHOR]

Accurate definition of strike-slip fault systems is critically important for understanding the evolution of petroleum systems and the distribution of hydrocarbons in many basins. Our study characterizes the structure of cratonic strike-slip faults in the Sichuan Basin, China, and the role that they play in hydrocarbon systems. Using two- and three-dimensional seismic reflection surveys, well data and field mapping, we describe strike-slip faulting in the central Sichuan basin related to gypsum-salt layers in the Lower-Middle Triassic section. We identify six main strike-slip fault zones in the central Sichuan Basin based on the two different structural configurations between strike-slip faulting and its associated deformation, and the offset positions of carbonate platform margins in the Upper Ediacaran Dengying Formation. Moreover, through quantitative analysis of a representative growth structure between two strike-slip fault zones, combined with the analysis of regional structures, paleography, and diagenetic events, we define five stages in the evolution of strike-slip fault system. During these stages, characterized by transtentional deformation, the fault system controlled the paleogeography within the cratonic basin and defined vertical and lateral migration paths for diagenetic and hydrocarbon fluids. As such, strike-slip faults are a key factor controlling the formation and evolution of the multi-layer petroleum system in the central Sichuan Basin. The shallow continental tight oil and gas deposits accumulate in the structure traps within the Triassic-Jurassic section associated with the strike-slip faulting. The deeper, marine cracked gas migrated and accumulated along the strike-slip faults, forming a pattern of multi-layer accumulations with different hydrocarbon compositions. Our results show that strike-slip faults are important structural element that has influenced the sedimentary evolution and distribution of hydrocarbons in the central Sichuan Basin. This well documented case study provides insights into the structures and petroleum geology of other ancient cratonic basins with strike-slip faulting worldwide. [ABSTRACT FROM AUTHOR]

The Penglai area is an emerging giant gas field in the Sichuan Basin supporting the carbon neutrality goal. To accelerate the exploration, this study combines petrographic observations using optical and cold cathodoluminescence microscopy, fluid inclusion microthermometry, Raman spectroscopy, 1D basin modeling and fluid inclusion PVTX modeling techniques to reveal the paleo-fluid P-T evolution in the second member of the Dengying Formation (Ediacaran age). The results firstly showed a diagenetic sequence which includes three phases of dolomite (1–3), bitumen, quartz (core and overgrowth) and fluorite. Then, ten paleo-fluid episodes were identified based on microthermometric histograms of different mineral phases. Finally, by integrating the Raman results, the hydrostatic and lithostatic gradients calculated by the constructed 1D basin model, and the existing equation of states, the homogenization pressure of fluid inclusions from each fluid episode was determined. By assuming the system was saturated by CH 4 as suggested by Raman results, the homogenization pressure equals to the trapping pressure. The P-T trajectory indicates that the second member of the Dengying Formation experienced two sever pressure accumulation stages. One is between fluid episode #3 and #4 recorded by dolomite 3, due to oil generation, and the other is from fluid episode #5 in dolomite 3 to episode #7 in quartz overgrowth to episode #8 in fluorite due to oil cracking to gas. Also, two pressure releasing periods were recorded by fluid episode #5 in dolomite 3 and #9 and #10 in fluorite, caused by both basin uplifting and fluid pressure reaching the lithostatic pressure. This study provides insights into fluid pressure evolution in deeply buried carbonate reservoirs. The understandings can support further geoenergy utilization and reduce exploration risks. • Diagenetic evolution and fluid evolution of carbonate buried over 6000m. • Rigorous fluid inclusion data allows to quantify the evolution of P-T conditions in a deep carbonate reservoir with time. • Overpressure evolution results demonstrate that the area with pale-fluid over pressure favored the preservation of pore spaces in the deep carbonate reservoir. [ABSTRACT FROM AUTHOR]

• Isotopic compositions of gas in different areas of the basin differ considerably. • Natural gases of the Qixia and Maokou formations are high maturity oil-type gas. • Great differences exist in gas maturity among different regions of the basin. • Gas source of Qixia and Maokou Fms in different regions of the Sichuan basin varies. The Middle Permian Qixia and Maokou formations (Fms), are important targets for current gas exploration in the Sichuan Basin. In recent years, high-yield industrial gas flow has been obtained in different structural zones of the basin. Based on the molecular and isotopic compositions of natural gas and reservoir bitumen, biomarker composition, and geological conditions, the genetic types, maturity, and sources of natural gas reservoired in the Qixia and Maokou Fms in different structural zones in the basin were analyzed. The following conclusions can be drawn: (1) the molecular and isotopic compositions of natural gas reservoired in the Middle Permian Qixia and Maokou Fms from different areas in the Sichuan Basin differ considerably; (2) the Middle Permian natural gas is oil-type gas, which is mainly generated by oil cracking; (3) most of the natural gas reservoired in the Qixia and Maokou Fms in the Sichuan Basin has reached the over-mature stage. The maturity of the natural gas from the northwestern Sichuan Basin is the highest, followed by gas from eastern and southern Sichuan, and part of natural gas in Southern Sichuan is high-maturity; (4) except for the slight thermochemical sulfate reduction (TSR) secondary alteration in the central Sichuan Basin, an effect of TSR was not observed in other areas; and (5) natural gas is controlled by the regional hydrocarbon kitchen. Gas in the eastern and southern Sichuan areas mainly originates from the Lower Silurian Longmaxi Fm shale, with a small contribution from marl in the Maokou Fm. The gas of the first member of the Maokou Fm has self-generation and self-storage characteristics, with a small contribution of the Longmaxi Fm shale. The Middle Permian gas in northwestern Sichuan is a mixture of gas generated from source rocks of the Lower Cambrian Qiongzhusi and Maokou Fms, whereas that in central Sichuan mainly originates from source rocks of the Qiongzhusi Fm. The Middle Permian gas in southwestern Sichuan mainly originates from its own source rock, and the natural gas reservoired in Permian volcanic rocks in the Chengdu–Jianyang area was generated by the mudstone of the Qiongzhusi Fm. [ABSTRACT FROM AUTHOR]

Despite the ubiquity of hydrothermal fluid circulation in the crust, its timing is difficult to precisely determine using traditional thermometric dating due to strongly disturbed geothermal fields. We present a case study from the mid-Permian hydrocarbon-bearing dolostone reservoirs, situated proximally to strike-slip faults in the central Sichuan Basin (China), to highlight the utility of carbonate in-situ U-Pb geochronology in delineating the timing of hydrothermal fluid flow. Matrix and void-filling cement dolomite phases were identified in the porous Maokou Formation carbonates. Predominantly manifesting as saddle dolomites along fractures, these cements yielded statistically homogeneous U-Pb ages (242.5 ± 3.1 Ma, 238.9 ± 8.2 Ma, 244 ± 15 Ma, and 239.2 ± 6.5 Ma), slightly postdating the established stratigraphic timeline (ca. 273 to 259 Ma). The narrow temporal span suggests early emplacement following a short burial, compatible with the petrographic observation of burial stylolites crosscutting saddle dolomites. Integrating shallow emplacement depths inferred from a comparison between the dolomite U-Pb ages and a published burial history, with fluid-inclusion microthermometry, elucidates the hydrothermal system that was once present in this field. The pervasive occurrence of hydrofracturing, along with dolomite geochemical indicators represented by bell-shaped (REE + Y) PAAS patterns and elevated Y/Ho ratios, provide additional evidence for the hydrothermal fluid injection and resulting dolomitization. The dolomites' positive Eu anomalies and the parent fluids' 18O enrichment indicate a source from deeper basinal pore waters that have interacted significantly with ambient rocks. The overlying Triassic evaporites may have provided Mg-rich brines, mixing into the circulating hot fluids responsible for hydrothermal dolomitization. Our dolomite U-Pb ages coincide with the seismically estimated timing of transtensional strike-slip fault activation. This temporal correspondence, combined with spatial associations and lateral slickensides along fracture planes, suggests that the hydrothermal fluid movement is highly relevant to the active strike-slip faults. This observation reveals a previously unrecognized early-middle Triassic, structurally controlled hydrothermal activity in the region. We propose that this episode of hydrothermal circulation was driven by extensional tectonism in response to the spreading of the Proto-Tethys Ocean. This finding is not in line with the earlier research that considered late Permian Emeishan volcanism to have been the main trigger for hydrothermal fluid influx. The long-standing view regarding hydrothermal dolomitization in this region may need to be re-evaluated. • Dating hydrothermal circulation and associated dolomitization with carbonate U-Pb geochronology. • A previously unknown hydrothermal event in the Sichuan Basin. • Hydrothermal fluid circulation driven by strike-slip faulting. [ABSTRACT FROM AUTHOR]

Based on low-temperature thermochronological data (i.e., apatite fission-track (AFT) and (U–Th)/He (AHe)), structural evolution, burial and thermal history, this paper examines the relationship of multi-stage evolution between the upper Ordovician Wufeng and lower Silurian Longmaxi formations (i.e., the WL formation) and rapid exhumation at the Changning shale gas field in the southern Sichuan basin. AFT ages are generally young from southeast to northwest, decreasing from ca. 40 to 15 Ma while AHe single-grain ages range from ~35 to ~5 Ma. Inverse thermal histories show that a multi-stage cooling history with initial cooling began in the Late Cretaceous to early Cenozoic (middle Eocene), followed by accelerated rapid cooling in the late Cenozoic, with cooling rates of 2–4 °C/Myr across the Changning shale gas field. In particular, thermal models of samples in the western Changning area show a substantial increase in the cooling rates, i.e., from less than 1 °C/Myr to 3–5 °C/Myr in the Miocene. Integrated with inverse T-t models of low-temperature thermochronological data, the burial history indicates a four-stage thermal evolution of the WL Formation in the Changning shale-gas field: Early Mature from the middle Silurian to middle Permian, Middle Mature from the late Permian to Late Triassic, Late Mature from the Early Jurassic to Early Cretaceous, and Over mature since the middle Cretaceous, reaching a maximum burial depth of ~6000 m and maximum temperature of 190–200 °C at ca. 70–80 Ma. This evolution further suggests that a normal hydrostatic pressure index dominated the WL Formations in the Paleozoic. The gas generation and pressure index, however, have substantially increased since the Late Jurassic, particularly from the Early to middle Cretaceous, with a maximum pressure index of 2.1, which is indicative of the main shale gas accumulation and enrichment period in the WL Formation. Post-gas-generation structural deformation, uplift, and exhumation had a significant impact on shale gas enrichment, mainly through their influence on shale gas preservation. This suggests some relationships among the higher pressure coefficient of the WL Formation, the higher productivity and total gas content of the WL Formation, a weaker post-gas-generation structural deformation, and a weaker uplift, as indicated by the erosion and burial depth across the Changning shale gas field. Due to a significantly stronger cooling and uplift that occurred the in Late Cenozoic across the western Changning area, the pressure index decreased rapidly from ~2.0 to 1.0 with a normal pressure condition, indicating the destruction of the reservation condition in the WL Formation. • New low-temperature thermochronological data was from the SE Sichuan basin. • An accelerated cooling in the late Cenozoic was found. • Post-gas-generation deformation and exhumation controlled the shale gas enrichment. [ABSTRACT FROM AUTHOR]

In the Precambrian dolomites in the central Sichuan Basin, a substantial paleo-oil system previously existed, which has since evolved into a dry gas system that is currently in place. The genesis of this paleo-oil system remained poorly understood, leaving uncertainties regarding the timing of oil charging and associated source rocks. Integration of Re–Os geochronometry with basin modeling allows temporal-spatial constraints on the ancient petroleum system to be established. Two texturally distinct generations of reservoir bitumen were identified. Late-generation bitumen yielded a geologically meaningful Re–Os age of 189 ± 20 Ma (MSWD = 10.4, 2σ), distinct from the previously documented Re–Os ages such as the 414 ± 44 Ma reported by Shi et al. (2020). This new age, along with the ∼414 Ma, aligns within uncertainties with the two relative timings derived from our independent basin model (ca. 450–390 Ma and 260–180 Ma), revealing two temporally distinct oil generation-migration events. The date of ∼189 Ma also lends support to the previous oil charge timing inferred from fluid inclusions. We evaluated the imprecisions of these two Re–Os ages and considered them to result from a narrow spread in 187Re/188Os, and variations in initial Os isotopic compositions (Os i) due to the giant size of the petroleum system and a long duration of oil generation from source kitchen over a large geographical area in this play. Effects of asphaltene precipitation, due to uplift-induced decompression of the migrating oils, may also have contributed to the scatter. Separating the samples based on Os i produced a higher precision age (184.1 ± 5.7 Ma, Model 1) with an MSWD of 0.97. The first oil charge is relatively weak as shown by the basin model and observed bitumen volumes, and it had not been well preserved due to significant reservoir exhumation by Caledonian tectonism. Consequently, the younger oil charge is considered to be the principal precursor to the current dry gas accumulations. Os isotope histories for four potential source units were constructed using publicly available Re–Os data. Comparisons between bitumen and rock Os compositions tend to support the lower Cambrian Qiongzhusi Formation as the predominant source unit for the two major paleo-oil charges. However, contributions from the Duoshantuo, Dengying, and Maidiping source rocks can not be precluded. Overall, these new observations allow temporal-spatial constraints to be placed on the complex evolution, from paleo-oil generation to destruction and dry gas generation. • Two paleo oil charges sourced from the lower Cambrian Qiongzhusi shales. • Agreement between two bitumen Re–Os ages and modeled oil generation stages. • Assessing the precision limitations of hydrocarbon Re–Os ages. [ABSTRACT FROM AUTHOR]

Hydrothermal minerals and associated organic matter have been frequently found in the Ediacaran and lower Cambrian carbonate reservoirs, separated by internal shale source rocks, in the Central Sichuan Basin. This work provides a thorough comparison of petrography, geochemical signatures, fluid inclusions and ages between the hydrothermal minerals in the Ediacaran Dengying Formation (Fm) and the lower Cambrian Longwangmiao Formation. This comparison leads to a better understanding of the behaviour and migration history of hydrothermal fluids and petroleum. During the Ediacaran–Cambrian transition, the flux of silicon-rich hydrothermal fluid triggered by seafloor-related volcanic events, resulted in the exclusive occurrence of silicification in the Dengying Fm. During P 3 –T 3 , two different hydrothermal systems were found in the Dengying and Longwangmiao formations. The hydrothermal fluids in the Dengying reservoirs were dominated by a mixture of basement-derived Mississippi Valley Type [MVT] ore fluids and shale-derived oil-bearing brines, while those in the Longwangmiao Fm were mainly the oil-bearing brines. The upwards migration of the MVT ore fluids, characterized by very hot, saline, radioactive and Eu-rich conditions, was promoted by the activity of the Emeishan mantle plume 259.4–248 Ma and then blocked by the lower Cambrian shales and trapped only within the underlying Dengying reservoirs. The expulsion of the warm, less saline and moderately radioactive brines and oil was induced by thermal maturation of the organic-rich shales, which might have occurred over a longer duration (261–218.7 Ma). During 170.7–125.8 Ma (J 2 –K 2), the combined effects of the overmature source rocks and Yanshanian tectonic compression facilitated the migration of much hotter shale-derived brines, as well as gas hydrocarbons, across the Ediacaran to lower Cambrian carbonate reservoirs. This comparative study provides some insights into the behaviour of hydrothermal fluids and petroleum in carbonates with internal organic-rich shales. • Different stages of hydrothermal events are preserved in the Z 2 dn and Є 1 1 carbonates. • The Cambrian organic-rich shales played multiple roles in hydrothermal systems. • The petroleum-bearing fluids from shales acted as independent hydrothermal systems. • The ascending basement-derived MVT ore fluids were blocked by the shale top seals. • A genetic link exists between the shale-derived hot brines and petroleum systems. [ABSTRACT FROM AUTHOR]

In recent years, there have been significant discoveries of hydrocarbon resources with commercial value in the Dengying Formation of the central Sichuan Basin. However, the impact of tectonic evolution on hydrocarbon accumulation has not been appropriately documented. In this study, we employed multiple methods, including seismic interpretation, balanced cross-section restoration, deformation quantification, erosion calculation, and paleo-highs/lows reconstruction, to investigate the tectonic kinematics, erosion distribution, paleo-highs/lows evolution of the Sichuan Basin. The quantification of deformation reveals that the Sichuan Basin has experienced a complicated tectonic evolution, with two rounds of transition from tension to contraction since the Sinian. In the Late Ordovician, contraction caused by the Caledonian Orogeny resulted in a foreland basin being developed in the Sichuan Basin. Since the Late Triassic, the Sichuan Basin has experienced intense contraction, resulting in the development of its current structural pattern. By integrating the erosion distribution, the reconstructed paleo-highs/lows maps of Sinian strata indicate the development of inherited paleo-uplifts in the central and southwestern Sichuan Basin from the Early Cambrian to the present. The evolution of paleo-highs/lows plays a critical control on the hydrocarbon accumulation of the Weiyuan and Anyue gas fields, indicating there could be high potential for hydrocarbon exploration in areas with high slope gradients in the paleo-uplifts. • Balanced section restoration is employed to reveal the basin-scale kinematics. • The basin-scale structural deformation was quantitatively evaluated. • The paleo-highs/lows of the Sinian were reconstructed at key geological periods. • The distribution of paleo-highs/lows may present important hints for hydrocarbon exploration. [ABSTRACT FROM AUTHOR]

• Multi-stage dolomite cementation was related to tectonic events. • Dolomite U-Pb ages constrain on timings of two paleo-oil charge episodes. • Two episodes of hydrothermal events with different causes. Improved understanding of subsurface paleo-fluid circulation history can assist in reconstructing associated pore evolution of carbonate reservoirs. Multi-stage dolomite cements generated by basinal fluids over time were investigated using a combination of petrography, geochemistry, fluid-inclusion studies, LA-ICP-MS U-Pb geochronology, and seismic interpretation. This study aims to gain clues about diagenetic, hydrothermal and paleo-oil filling events within the Ediacaran Dengying Formation, Sichuan Basin, China. Four main phases of dolomite cementation were petrographically, geochemically and geochronologically distinguished that can be ascribed to major tectonic events throughout the basin evolution. The earliest dolomite generation occurs as fibrous dolomite crust (FDC) growing along the karst vug wall, interpreted as marine diagenetic cement formed in a submarine environment during the Late Ediacaran, most likely from the influx of seawaters following the uplift and subaerial exposure related to the Tongwang movement. In situ U-Pb ages obtained from the other three generations of cement dolomites are interpreted to coincide with the timing of repeated strike-slip fault movements as indicated by the seismic data, suggesting a direct link between cement emplacement and regional tectonic-thermal events. Sub-vertical extension dolomite veins (EDV), representing the second generation, are considered as being syntectonic, generated from slightly modified connate seawaters at a shallow to moderate burial depth in a transtensional stress regime during the Cambrian taphrogenesis. Two generations of saddle dolomite cements, SD1 and SD2, have recorded two major episodes of hot fluids circulating in the Dengying Formation. The SD1, filling in hydraulic fractures and vugs, formed during the third phase of cementation, as a result of a hydrothermal event associated with Caledonian exhumation. Deep-seated hot brines squeezed into the Dengying reservoirs along the sub-vertical strike-slip faults combined with some meteoric waters that percolated downward, are deemed responsible for precipitating SD1. The SD2 is the youngest cement present, which is interpreted to have formed during the ingress of deeper, hot, hypersaline brines arising from the late Permian hydrothermal activity likely triggered by the eruption of Emeishan flood basalts. Cross-cutting relationships between bitumen phases and different dolomite generations indirectly define the dates of two paleo-oil charging events. The first episode of paleo-oil charging occurred during the Late Ediacaran to Early Cambrian, likely sourced from underlying Ediacaran Doushantuo shales. Late oil emplacement occurred after the Late Permian, in agreement with the reported bitumen Re-Os age and the age inferred through fluid-inclusion analysis. Primary source rocks generating this phase of oil were considered as the Cambrian Qiongzhusi shales, because basin modeling-derived date of oil window matches with the second oil filling time. [ABSTRACT FROM AUTHOR]

The structural deformation of the eastern Sichuan Basin, South China, is characterized by a thin-skinned fold-and-thrust belt with exposed, approximately parallel narrow anticlines and wide synclines. A 196-km long regional cross section has been constructed parallel to the shortening direction to analyze structural styles and evolution of the fold-thrust belt. The stratigraphic succession is composed of competent layers separated by three main incompetent layers which act as detachments. The basal detachment, the Cambrian evaporites, played a dominant role in the deformation; the middle and top detachments accommodated the displacement during deformation. Structural styles are dominated by faulted detachment folds with the breakthroughs of the fore- and/or backlimbs. Balanced restoration shows that the shortening between basal and top detachments is about 26 km with the shortening ratio of 12.4–18.6%. Integrated analyses of kinematics and balanced restoration reveal the evolution succession of kink bands, detachment folds, and faulted detachment folds. Kink bands initiated and evolved into detachment folds above the basal detachment as the shortening took place; with progressive shortening the back- and/or forelimbs of these folds developed thrusts. • The deformation is characterized by a thin-skinned fold-and-thrust belt with the development of faulted detachment folds. • A 196-km long cross section has been constructed to investigate structural styles and evolution of the fold-thrust belt. • Multiple detachments are present including the Cambrian evaporites, the Silurian shales, and the Triassic evaporites. • The evolution succession could be kink bands, detachment folds, followed by breakthroughs of the fore- and backlimbs. • Restoration of the regional cross section yields 26 km of shortening, which corresponds to a shortening ratio of 12.4～18.6%. [ABSTRACT FROM AUTHOR]

• Three lamination types are distinguished in the Upper Ediacaran botryoidal dolostones in Western Yangtze Platform. • EPS and filaments are documented in botryoidal laminae which were previously believed to be abiogenic origin. • Different microbial mineralization types are recognized in different botryoidal laminae. Botryoidal dolostones are abundant in the Second Member of the Upper Ediacaran Dengying Formation in the Western Yangtze Platform. Although they have been extensively discussed as important host rocks for giant gas reservoirs, there is no consensus on the microbial impact on mineralization processes in the botryoidal laminations. Typical botryoidal laminations were studied under optical microscopes and scanning electron microscopes (SEMs) to investigate their origin. There are three macroscopic morphological types of botryoidal lamination: stromatoid lamination, cavity-lining lamination, and spherical-encrusting lamination. These three types of lamination are composed of fibrous and bladed crystals growing perpendicular to the botryoidal laminae, which have hitherto been implicitly considered to be from abiogenic chemical precipitation. There are many lines of new evidence that demonstrate microbial activities in the interbedded dark and bright laminae constituting the laminations. In the dark laminae, euhedral dolomite rhombs are observed sticking to linear and tubular filaments, or wrapped in sheets of extracellular polymeric substances (EPS) with dolomite crystal sizes of generally <5 μm. The bright laminae are dominated by coarser dolomites and connected by radial sheaths and trichomes with dolomite crystal sizes of primarily around 10 μm. Different species of bacteria, which are closely related to the macroscopic morphology of the laminations, are present in both the bright and dark laminae. The results are useful in understanding the origin and formation mechanisms of the Neoproterozoic botryoidal dolostones. The new findings may also shed new light on the occurrence and evolution of early life on Earth in the Precambrian Era. [ABSTRACT FROM AUTHOR]