The Pearl River Mouth Basin,a typical Cenozoic continental margin rift basin,derives its major hydrocarbon resources from the lacustrine source rocks of the Wenchang Formation in the Eocene. Divided by the central uplift,faulted and detached depressions have developed respectively in the northern and southern parts of the basin. There are significant differences in hydrocarbon distribution,and the causes of these differences remain unclear. In this study,technical methods including structural evolution analysis,sedimentary system reconstruction,and source-fault-sandbody association analysis were employed. It reveals the basin’s structural evolution law of “faulting first then detaching,faulting in the north and detachment in the south” and the sedimentary evolution characteristics of “terrestrial environment in the early stage and marine environment in the late stage,deltas in the north and fan deposites(fan delta,sublacustrine fan or submarine fans)in the south”. The different tectonic sedimentary evolution processes of the two types of depressions formed source-fault-sandbody associations,resulting in different petroleum accumulation patterns and enrichment laws. Differential source-fault-sandbody associations and petroleum accumulation patterns were established separately. Characterized by high quality lacustrine source rocks,steep faults and sandbodies near sediment provenance,faulted depressions were apt to generate oil-rich accumulation pattern. But for detached depressions featured by high quality lacustrine source rocks,fault block tilting adjusted faults and sandbodies far away from sediment provenance,gas-rich accumulation pattern with locally oil-rich was predominating. The study points out that hydrocarbons in faulted sags are enriched in the steep slope zone,uplifts in the depression-center and inner gentle slope zone,while those in detachment depressions are enriched in the gentle slope zone. This provides constructive suggestions for petroleum exploration.

The continuous discovery of giant hydrocarbon reservoirs in continental rift basins has highlighted bioclastic dolomite reservoirs as a promising new exploration frontier. This study integrates petrography,geochemistry,and in-situ isotopic techniques to investigate the genesis and pore evolution of bioclastic dolomite reservoirs in the Member 2 of Shahejie Formation in eastern Shijiutuo uplift of Bohai Bay Basin. The results reveal the following: (1)Three sets of bioclastic dolomite reservoirs are developed,and four types of replacive dolomites are identified—micritic envelope dolomite(ME),micritic-fine crystalline matrix dolomite(MD),early fibrous dolomite cement(CD₁),and late mosaic dolomite cement(CD₂). (2)Two dolomitization mechanisms are proposed: reflux and burial dolomitization,elucidating the genesis of different dolomite types. ME,MD,and early CD₁ formed under hypersaline reflux conditions in hot,semi-saline,lacustrine shallow shoals. (3)In the high-temperature,closed diagenetic environment of the shallow burial stage,organic acids generated from kerogen thermal decomposition promoted the dissolution-reprecipitation of MD and CD₁ to form CD₂. Concurrently,pore fluids rich in Mg²⁺ released by compaction,together with retained connate water,facilitated CD₂ cementation,filling intergranular pores. (4)During the synsedimentary stage,meteoric freshwater leaching selectively dissolved aragonite and high-Mg calcite,forming early secondary pores such as moldic and intrabioclastic cavities. In the middle to late burial stage,abundant organic acid production and hydrocarbon charging led to non-selective dissolution and microfracture development. However,reservoir space remains dominated by primary intergranular pores and early secondary pores. By coupling in-situ isotopic temperature reconstruction with multi-stage dolomitization mechanisms,this study refines previous models focused solely on reflux and mixing-zone dolomitization and provides a theoretical framework and predictive approach for reservoir quality enhancement and efficient hydrocarbon development in bioclastic dolomite reservoirs.

Shallow-water delta front sand bodies are widely developed and represent important hydrocarbon reservoirs with high exploration potential in continental basins. However,frequent migration and avulsion of distributary channels result in vertically stacked thin interbeds and laterally interwoven distributions,leading to complex architectural patterns. Under sparse well coverage,this complexity makes reservoir prediction highly challenging and less accurate. This study takes the Member 1 of Jurassic Shaximiao Formation in the Tianfu Gas Field,Sichuan Basin,as a case example,and proposes an intelligent prediction method for thin sand bodies by integrating multi-frequency seismic attribute automated machine learning(AutoML)with waveform indication inversion(WII). Laterally,optimized frequency-decomposed seismic data were used to automatically select key attributes and integrate multi-model learning,building nonlinear mappings that improved the correlation between seismic attributes and well-derived sand thickness from 0.64 to 0.82. This enabled quantitative prediction of sand bodies under sparse well control. Vertically,WII introduced facies-controlled constraints and used uranium-free gamma ray as the inversion target,allowing stable identification of sand bodies thicker than 10 m and reliable responses from thin layers of about 4 m,and establishing seismic response templates of architectural element assemblages. Based on these results,four types of architectural elements were identified: distributary channel,residual mouth bar,levee,and interdistributary bay. Furthermore,six stacking patterns including vertical superimposition and lateral accretion were summarized. The results also reveal that,under different depositional cycles,isolated narrow channels and compound wide channels show distinct spatial distributions and vertical stacking characteristics. In three dimensions,a spatial differentiation pattern was clarified,evolving from near-source net-like distributary channels to distal tongue-shaped and lobe-shaped mouth bars. Finally,a depositional architectural model of the shallow-water delta was established. This study achieves fine-scale multi-level architectural characterization under sparse well conditions and provides new insights and methods for efficient exploration and development of complex shallow-water delta reservoirs.

Characterizing Lower Paleozoic carbonate thermal reservoirs is essential for evaluating the geothermal resource potential of the eastern margin of the South North China Basin. Integrating findings from prior studies with newly acquired drilling,core,outcrop,and geochemical analytical data,this study systematically characterizes Cambrian and Ordovician thermal reservoirs,delineates their spatial distribution patterns and associated geothermal field attributes,and identifies prospective exploration targets. Key findings are as follows: (1)Lower Paleozoic carbonate thermal reservoirs in the study area are predominantly hosted in the Zhangxia Formation and overlying strata. Reservoir types include oolitic shoal,dolomitic,and karst reservoirs. Late-stage tectonic activity has significantly influenced the oolitic shoal and dolomitic reservoirs,promoting secondary karstification;consequently,well-developed karst reservoirs—predominantly Class II and III fractured systems—are widespread across the region.(2)Karst reservoir distribution exhibits clear structural control,with dominant NW-and NE-trending orientations. In shallow-buried settings,the top of the Cambrian reservoir ranges from 500 to 2500 m depth,whereas the Ordovician reservoir top lies between 100 and 2000 m. Corresponding top-reservoir temperatures range from 30 to 90 ℃.(3)A quantitative evaluation framework for karst reservoir favorability was established,incorporating three key parameters: burial depth,caprock geothermal gradient,and degree of karst development. Application of this framework identifies the western Shangqiu area of the Taikang Uplift as the most prospective zone for karst-hosted geothermal resources—providing a robust scientific basis for prioritizing future geothermal exploration and development efforts in the basin.

Coal accumulation is a crucial component of the global carbon cycle,facilitating the large-scale and long-term burial of atmospheric CO₂ on land. It is one of the primary factors leading to a decrease in atmospheric CO₂ concentration,which in turn causes a drop in global temperatures and can trigger the onset of an ice age. At the end of the Carboniferous period,a basin-wide coal accumulation event(Coal #8+9)occurred in the North China Basin,after which the globe entered the Early Permian P1 ice age. This suggests a potential causal link between the widespread coal accumulation in the NCB and the onset of the P1 ice age. To investigate this relationship,this study focuses on Coal #8+9 in the Ordos Basin. Spectral analysis was performed on its natural gamma ray logging curves to reconstruct the accumulation duration of Coal #8+9. Based on coal thickness,carbon content,and apparent density data,the carbon burial rate of the peatland was reconstructed. Using this rate and the estimated area of the Late Carboniferous peatland in the NCB,the annual carbon burial amount in the basin during that time was calculated. Subsequently,based on existing atmospheric data,the annual reduction in atmospheric CO₂ concentration resulting from this carbon burial was estimated,ultimately revealing the relationship between coal accumulation in the Late Carboniferous NCB and the onset of the P1 ice age. The results indicate that Milankovitch cycles of obliquity(35.5 kyr)and precession(21.7 kyr)were identified in Coal #8+9 of the North China Basin. The depositional duration is estimated to be between 98.31 kyr and 277.66 kyr,with an average of 188.20 kyr. The carbon burial rate of the peatland ranged from 42.41 to 78.87 g/·a, with an average of 59.21 g/m²·a. According to estimates of total atmospheric mass and CO₂ concentration,removing approximately 2.13 GtC from the atmosphere is required to lower the atmospheric CO₂ concentration by 1 μL/L. The annual carbon burial amount in the Late Carboniferous NCB was calculated to be between 3.82×10⁷ t and 7.01×10⁷ t,averaging 5.33×10⁷ t. This corresponds to an annual reduction in atmospheric CO₂ concentration of 1.79×10^-2~3.33×10^-2 μL/L,with an average of 2.51×10^-2 μL/L. The atmospheric CO₂ concentration before the end-Carboniferous coal accumulation was approximately 400 μL/L,while it was about 200 μL/L before the onset of the P1 ice age. Based on the average annual carbon burial rate of the NCB,it would take only about 8000 years to reduce atmospheric CO₂ by 200 μL/L,reaching the level associated with the P1 ice age inception. However,the average depositional duration of Coal #8+9 is 188.20 kyr,far exceeding the time required to reach the ice age threshold. Therefore,the massive carbon burial in the NCB could have led to a rapid decrease in atmospheric CO₂ concentration just before the onset of the P1 glaciation. The decoupling of ρCO₂ from continental silicate weathering,coupled with the rapid expansion of tropical rainforests and their repeated reorganization,indicates that the extensive coal accumulation in the NCB during the latest Carboniferous was the primary cause of the atmospheric CO₂ decline preceding the P1 ice age.

Palaeogeographic units on the Earth’s surface exhibit a hierarchical structure,however,their connotations,research significance,reconstruction scales,and methodologies remain unclear,hindering the coordinated development of palaeogeography. Each palaeogeographic unit is a palaeogeographic unit with specific climatic,hydrological,and ecological characteristics. Based on the relative size and formation of landforms,palaeogeographic units are divided into three levels: large,medium,and small,correspondingly classifying palaeogeographic research scales into three levels. Large-scale palaeogeographic research investigates the spatiotemporal distribution and multi-sphere interactions of large-scale palaeogeographic units(oceans,continents,and large-scale geomorphic undulations within them)over millions to tens of millions of years. This research is conducted globally and across tectonic plates(or basins),aiming to predict habitable Earth and prospective areas for mineral resources. Medium-scale palaeogeographic research focuses on the characteristics,distribution,evolution,and associated surface processes of medium-scale palaeogeographic units(geomorphic units between large-scale geomorphic undulations and sub-environments)within a large geomorphic unit(such as a basin). It operates on timescales of hundreds of thousands of years and serves to predict habitable region and guide mineral resource exploration. Small-scale palaeogeographic research examines the characteristics,distribution,changes,and corresponding small-scale surface processes of sub-/micro-environments within a sedimentary system. This research covers timescales of tens to hundreds of thousands of years and aims to predict human habitable locality and to evaluate and develop mineral resources. Future palaeogeography should further develop multi-information quantitative interpretation methods for multi-scale palaeogeographic parameters,innovate intelligent reconstruction technologies of multi-scale palaeogeography,deepen the understanding of the formation mechanisms across different scales,establish models that explain how palaeogeography controls mineral resource distribution at various scales,and enhance collaborative research on multi-scale palaeogeography.

The transitional zone between land and sea is an area where rivers,waves and tides act together,and the interwoven hydrodynamic forces shape the sand body morphology and palaeogeographic pattern. This paper takes the Main-M1 member and LU sub-member of the oil and gas-rich Napo Formation in the Oriente Basin of Ecuador as an example. By using core,logging and mud logging data,the sequence framework is established. Provenance was constrained using heavy-mineral assemblages and detrital zircon U-Pb geochronology,while pre-depositional palaeogeomorphology was restored using residual-thickness and imprint methods. The study shows that the Napo Formation can be divided into one second-order sequence and five third-order sequences. The Main-M1 member and LU sub-member are both in the lowstand systems tract of their respective third-order sequences. The provenance mainly comes from the eastern and southeastern Amazon Craton,and the palaeogeomorphology is generally a single inclined slope with the east high and the west low. The LU sub-member is an intertidal delta system controlled by rivers and tides as a whole,with a delta plain in the east and a delta front in the west. The Main-M1 member has evolved into a mixed system of east tidal delta,west wave-controlled shallow marine shelf and coastal current interwoven transformation. The Napo Formation records the evolution process from the river-tide inter-control to the river-wave-tide ternary mixed system,indicating that under the constraints of tectonic subsidence and provenance conditions,the interwoven hydrodynamic forces are the key factors controlling the distribution of sand bodies and palaeogeographic patterns in the transitional zone between land and sea in the foreland basin. This has reference significance for the palaeogeographic restoration of similar transitional zones between land and sea in foreland basins.

The classification of microbialites constitutes a fundamental basis for investigating their origin and distribution. Owing to ambiguities in the definition of microbialites,these rocks are,in essence,predominantly bacterial in origin. Consequently,the term “bacterialite” is considered more precise than “microbialite” when referring to sedimentary rocks formed through bacterial activity. Bacterialites may be recognized as an independent category within the conventional classification of carbonate rocks,positioned alongside reef carbonates. Based on mineral composition,bacterialites can be divided into seven primary types: bacterial carbonates,siliceous,ferrous,phosphate,saline,bauxitic,and clastic bacterialites,each of which allows for further subdivision. Taking bacterial limestones as a representative example,they are classified according to macrostructural features into thrombolites,stromatolites,coatites,and leiolites. Thrombolites are subdivided into framework-bearing and non-framework types. Framework thrombolites can be further categorized into sparry,micritic-sparry,and micritic types,reflecting a progressive decrease in hydrodynamic energy and a corresponding increase in water depth from sparry to micritic forms. Stromatolites are classified based on lamination clarity into lamination-clear and lamination-obscure types;the former typically form in intertidal to supratidal(subaerial)environments,while the latter occur in subtidal(subaqueous)settings. Additionally,stromatolites are categorized morphologically into columnar,wavy,planar laminar,domal,conical,and wall-like forms,with each morphotype further differentiated by size. Coatites are similarly classified according to the distinctness of concentric lamination into lamination-clear and lamination-obscure types,which correspond to intertidal and subtidal depositional environments,respectively. They may also be subdivided based on size into oncolites and bacterial oolites. Leiolites are classified into microcrystalline and granular varieties. This classification system presents several innovative aspects: (1)mineral composition is introduced as the principal criterion for defining major bacterialite categories;(2)the nomenclature is revised by replacing “microbialite” with the more accurate term “bacterialite”;(3)the texture-based classification of framework thrombolites provides enhanced environmental interpretation;(4)stromatolites are classified both by lamination clarity—indicative of depositional conditions—and by morphology and size;(5)coatites are systematically categorized according to the degree of concentric lamination,which serves as an environmental indicator;and(6)a formal classification of leiolites is proposed,accompanied by clearly defined diagnostic criteria.

This study focuses on sandstone “concretions” in the Cretaceous Qingshuihe Formation at the Hongshanhu Section. It systematically investigates the lithological characteristics of concretion-bearing strata,as well as the external morphology,internal structure,material composition,formation environment and genesis of the concretions. The Cretaceous Qingshuihe Formation at the Hongshanhu Section mainly develops a set of shallow-water delta facies sandstones with large-scale cross-bedding. Spherical,hemispherical,ellipsoidal,and other shaped sandstone “concretions” are widely distributed in the bottom sandstones of distributary channels of different stages. Currently,there are three viewpoints on the genesis of these concretions: (1)spherical weathering genesis;(2)diagenetic genesis;(3)intraclast genesis. To clarify their genesis,this paper systematically studies the macro occurrence,microtexture,material composition of the concretions,and their genetic relationship with host sandstones through field geological section measurement and petrographic thin section observation. The results show that the concretions are not intraclasts,but products of “concretionary” diagenetic cementation of sandstones during the syngenetic-diagenetic stage,followed by differential weathering after uplift to the surface. Carbonized plant detritus is commonly developed in the center of the “concretions”,with ferruginous calcite and calcite cement zonations sequentially formed outward around the plant detritus. The bedding structure of the “concretions” is consistent with that of the host sandstones without later tectonic disturbance. Due to dense cementation,the sandstone “concretions” have significantly stronger weathering resistance than the surrounding uncemented or weakly cemented sandstones,presenting spherical,hemispherical,ellipsoidal,and other irregular shapes after epigenetic weathering. Combined with the analysis of regional sedimentary background and diagenetic environment,it is believed that the formation of such diagenetic “concretions” indicates strong hydrodynamic forces in distributary channels,abundant organic matter input during the shallow-water delta deposition of the Qingshuihe Formation,and weakly alkaline-neutral pore water medium during the early diagenetic stage,which provided favorable chemical conditions for cement precipitation. The research results not only clarify the controversy over the genesis of sandstone “concretions” in the Qingshuihe Formation,but also provide key geological evidence for the restoration of the Cretaceous shoreline shallow-water delta sedimentary environment and the study of diagenetic evolution in the Junggar Basin,and have reference value for the heterogeneity research of oil and gas reservoirs and oil and gas development.

Based on a systematic review of the evolution from macroscopic qualitative description to high-precision quantitative analysis of the Permian lithofacies palaeogeography in southern China,this study focuses on the rock evolution characteristics and formation mechanisms centered on the dolomite of the Qixia Formation-Maokou Formation and the siliceous rocks of the Gufeng Formation、Dalong Formation. The study emphasizes that the spatiotemporal distribution of lithofacies profoundly reflects the control of tectonics,especially the dynamic background driven by scissor-like collision and the distal effect of mantle plumes,which determine the spatiotemporal evolution of the sedimentary pattern and the characteristics of the platform-basin differentiation. In response to the current bottleneck problem in the delimitation of facies belts,this study proposes that the spatiotemporal constraints should be strengthened by relying on palaeobiogeographic similarity indicators,and combined with big data and artificial intelligence technologies,to promote the transformation from static map drawing to dynamic process prediction,aiming to provide more rigorous petrological evidence and evolution models for the evaluation of “sweet spots” in unconventional oil and gas exploration.