Search Results (161)

Accurately identifying organic-rich shale intervals remains a major challenge in lacustrine shale oil exploration, particularly in continental rift basins characterized by rapid environmental change and pronounced vertical heterogeneity. This study investigates the upper Jiufotang Formation in the Ludong Sag, Kailu Basin, NE China, using total organic carbon (TOC), vitrinite reflectance, multi-stage programmed rock pyrolysis, and major and trace element geochemistry to constrain the processes governing organic matter enrichment and hydrocarbon occurrence. The studied shales contain abundant organic matter, with TOC values ranging from 1.91% to 7.55% and averaging 4.22%. Type II₂ kerogen and vitrinite reflectance values of 0.60–0.94% indicate oil-prone organic matter at low-mature to mature stages within the oil generation window. Multi-stage pyrolysis shows that the hydrocarbon assemblage is dominated by bound oil and residual kerogen-derived fractions, whereas the low-temperature movable oil fraction is limited. TOC is more strongly associated with the high-temperature pyrolysis fractions than with the light free-oil fraction, indicating that organic matter abundance primarily controls residual hydrocarbon generation potential but does not directly determine present-day movable oil content. Multiple elemental proxies are collectively consistent with deposition in a hydrologically restricted, variably brackish–saline lacustrine system with water-mass differentiation. Redox-sensitive indicators, including V/(V + Ni) and Mo, suggest persistent weakly reducing to reducing bottom-water conditions. After correction for carbonate- and phosphate-associated Ca, CIA values fall within a narrow range of approximately 67–70, indicating moderate and relatively stable source area chemical weathering. Organic matter enrichment was governed by the coupled effects of organic matter supply, preservation under stratified oxygen-deficient waters, and sedimentary dilution. We therefore propose a two-stage process framework in which depositional productivity–preservation coupling first promoted organic matter accumulation, whereas subsequent thermal maturation, hydrocarbon expulsion, retention, and adsorption reshaped the present hydrocarbon occurrence state. The results demonstrate that high organic matter abundance and residual generation potential do not necessarily translate into high movable oil content and provide a well-scale geochemical basis for source rock evaluation and future multi-well assessment in continental rift lake systems. Full article

In the Mahanadi Basin (Site U1445), the mean δ¹³C_SOM (i.e., δ¹³C of sedimentary organic matter) value is consistently higher during the glacial periods (–18.8‰) than during the interglacial periods (–19.4‰), which implies either more deposition of terrestrial organic matter from C4 plants or increased marine primary production (MPP). We attempted to quantify the relative contributions of organic matter by C3 plant, C4 plant, and MPP, using the three end-member simple mixing model (IsoSource). This study reports that their partitions are distinctly different between the interglacial (29%, 28%, and 43%) and glacial (22%, 40%, and 38%) periods, despite the model’s limitations. The contribution of allochthonous terrestrial organic matter overwhelms the production of autochthonous marine organic matter in the Mahanadi Basin, particularly during the glacial periods, emphasizing that the freshwater discharge by the Indian monsoon precipitation is a key process of the organic carbon cycle. Our results also verify that C4 plants were more distributed in the Himalaya foreland during the glacial periods under the decreased atmospheric pCO₂ and humidity levels. Different contribution of terrestrial organic matter sources to the Mahanadi Basin depends on the orbital-scale Indian monsoon variability, highlighting the land–sea transfer of organic carbon. Full article

To clarify the composition and origin of the suspected solid bitumen, which is found in the fractures of the Jixian System in Tongcheng outcrops, the suspected solid bitumen samples, as well as dolomite samples, were collected from the Jixian System in Tongcheng and Qishan outcrops for various tests. The results show that the suspected solid bitumen samples are mainly composed of clay minerals. No solid bitumen was found in the pores and microcracks of the dolomite samples by microscope and Raman spectroscopy. The total organic carbon content of the solid bitumen ranges from 0.59% to 1.15%, revealing that the suspected solid bitumen is dark mudstone powder, rather than solid bitumen. The R_b values range from 2.59% to 2.77%, and the Ts/(Ts + Tm) values mostly approach 0.5, indicating that the organic matter in the suspected solid bitumen is in the mature to over-mature stage. The V/(V + Ni), Sr/Cu, and Sr/Ba values of the suspected solid bitumen indicate that it was deposited in a warm, humid, anoxic sedimentary environment. The slightly right-inclined rare earth element pattern of the suspected solid bitumen samples implies the sedimentation rate was slow or they were affected by weathering and leaching processes. Through a comparison of trace elements and hierarchical clustering analysis of rare earth elements, the suspected solid bitumen manifests the closest correlation with the mudstone source rocks of the Cambrian Zhangxia Formation. Early Devonian period, the Cambrian mudstone source rocks in the Tongcheng area were uplifted; then weathered, leached, and fragmented into powder; and then filled the fractures of the underlying Mesoproterozoic Jixian System. Of course, another geological scenario has not been ruled out: that some of the fractures in the Jixian System may be filled with solid bitumen, which may be the result of the destroyed paleo-oil reservoirs near the ancient uplift in the Tongcheng area. Full article

The Tajik Basin is located on the eastern edge of the Central Asian segment of the Tethyan tectonic domain. The basin underwent intense tectonic transformation during the Himalayan period, resulting in complex structural styles, unclear original sedimentary characteristics and oil and gas geological conditions, and a complex process of oil and gas accumulation, which restricts the further evaluation of the basin’s exploration potential. Studying the Tajik Basin in the macro background of the Tethys tectonic domain, the tectonic sedimentary evolution of the Tethys tectonic domain has a significant effect on the basin’s tectonic evolution, sedimentary characteristics, and oil and gas accumulation conditions. The Tajik Basin has gone through four stages of tectonic evolution: the Late Permian to Triassic was the stage of back arc foreland basin; the Jurassic period was the stage of back arc extensional faulting depression; the Cretaceous–Paleogene period was the stage of depression basins; and the Neogene is the stage of the regenerated foreland basins. Through field geological surveys and analysis of outcrop samples, it has been determined that the Tajik Basin has developed three sets of source rocks: the Middle and Lower Jurassic, Cretaceous, and Paleogene. Among them, the organic matter abundance of the Middle and Lower Jurassic is relatively high, most of them are in the mature stage, and they are primarily gas-generating source rocks. The Cretaceous and Paleogene source rocks are mainly oil generating and in a low-mature state. There are four sets of reservoirs developed in the Tajik Basin: Middle-Upper Jurassic carbonate rocks, Lower Cretaceous clastic rocks, Upper Cretaceous carbonate rocks and Paleogene carbonate rocks. Comprehensive research shows that the Tajik Basin mainly develops three types of oil and gas reservoirs: Jurassic carbonate gas reservoirs, distributed in the southwestern Gissar Uplift and Surhan Depression in the western part of the basin; Paleogene carbonate reservoirs, distributed in the southern Vakhsh Depression and the eastern Kuliabu Depression; and multi layer–multi lithology oil and gas reservoirs, distributed in the northern Dushanbe Depression. The primary controlling factor for the three types of oil and gas reservoirs is tectonic movement, which forms traps and simultaneously reshapes the reservoirs, ultimately leading to effective accumulation of oil and gas. The distribution of oil and gas in the Tajik Basin is characterized by “west gas and east oil, west more and east less, west pre-salt and east post-salt, and pre-salt gas and post-salt oil”. Affected by the regional tectonic movements of the Tethys rich oil and gas tectonic domain, the basin has high-quality hydrocarbon source rocks, reservoirs, and cap rock conditions. The pre-salt Jurassic has the potential to form large natural gas reservoirs, while the post-salt Cretaceous and Paleogene still have further potential for exploration. Full article

Following Yangtze River protection policies, many small dams have been removed. Using the Heishui River as an example, we compared food web structures among areas affected by dams (DAs), areas from which dams were removed (DRAs), and natural reference areas (NRAs) using stable isotopes and a Bayesian mixing model. NRAs had balanced basal carbon sources; DAs relied on periphytic algae (43.6%) and POM (23.5%); and DRAs were dominated by periphytic algae (50.8%), with terrestrial inputs lower in both DAs and DRAs. NRAs showed a compressed food chain (1.89–2.23). DAs exhibited an extended but inverted structure, with benthivorous fish (3.00) surpassing carnivores, perhaps reflecting the accumulation of sedimentary organic matter under the lentic conditions created by damming. DRAs expanded the vertical dimension, with carnivorous fish reaching the highest level (3.70). DAs had the fewest nodes (16) but the highest connectance (0.492). DRAs showed the most nodes (20), highest linkage density (4.00), lowest connectance (0.421), and lowest trophic redundancy, indicating functional differentiation. NRAs had an intermediate number of nodes (17) and the lowest linkage density (3.41). These findings indicate that small dam removal altered basal resource use, triggered food web reorganisation that increased the trophic position of carnivorous fish, and enhanced topological complexity, although terrestrial energy inputs in DRA remained below natural levels. Full article

The Carnian Pluvial Episode (CPE) was a major Late Triassic climatic event, but its recognition in the North China Block remains limited due to challenges in correlating continental strata with global marine records. This study integrates sedimentological, pyrolytic, and elemental geochemical data from the Yanchang Formation in the Ordos Basin to characterize the stratigraphic response to the CPE and evaluate its implications for hydrocarbon exploration. Results show high total organic carbon content and a negative δ¹³C excursion during the CPE, along with significant shifts in sedimentary microfacies. Palynological assemblages and recent geochronology identify the Chang 7₃ black shales as products of this event. Enrichments in Fe, P, Cu, and U indicate strong reducing conditions and high paleo-productivity. Elemental ratios (CIA, Sr/Cu, Fe/Mn) reveal a shift from arid to humid conditions between the Chang 8 and Chang 7 units. Redox (V/Cr, V/(V + Ni), U/Th) and productivity (TOC/P, P/P_UCC, Cu/Ti) proxies reflect enhanced reducing conditions and elevated productivity, consistent with the CPE. Correlation analyses link lithological transitions and organic matter characteristics to this event, highlighting the CPE as a key control on high-quality source rock development in the Ordos Basin. Full article

Deep coalbed methane (CBM) is a core exploration and development domain for increasing the reserves and production of unconventional natural gas in China. A systematic understanding has been established on the enrichment and accumulation mechanism of high-rank deep CBM in the southern section of the eastern margin of the Ordos Basin. However, the medium-rank deep CBM in the Mugua Area of the Shenfu Gas Field in the northern section of the eastern margin has essential differences from that in the southern section in terms of coal rank and hydrocarbon generation–occurrence mechanism, and its accumulation and enrichment regularity remain unclear. The core innovations of this study are as follows: aiming at the unclear accumulation regularity of medium-rank deep CBM in the northern section of the eastern margin of the Ordos Basin, we first reveal the spatiotemporal synergistic coupling reservoir-controlling mechanism of five factors (sedimentation–thermal evolution–temperature–pressure–preservation), determine the 1750 m critical transition zone of the deep CBM occurrence state, and establish two types of accumulation models adapted to the geological characteristics of medium-rank coal. Taking the No.8+9 coal seams of the Taiyuan Formation in the Mugua Area as the research object, based on the theoretical foundation of the dual properties of coal seams as the “source rock–reservoir”, this paper comprehensively adopted technical means such as core observation, drilling and logging data, and high-pressure isothermal adsorption experiments to carry out systematic multi-dimensional studies on sedimentary microfacies, coal reservoir characteristics, thermal evolution degree, and gas-bearing property; identified the main controlling factors of CBM accumulation; and constructed the accumulation model. The results show the following: ① The main burial depth of the coal seams is more than 1700 m, with a thickness ranging from 7.0 to 21.3 m and an average of 15.1 m, and the coal structure is dominated by the primary structure; maximum vitrinite reflectance (R_o,max) is generally distributed from 0.90% to 1.39% with an average of 1.08%, belonging to typical medium-rank coal; and the organic matter type is mainly Type III, with an average gas content of 10.01 m³/t, where the average proportion of desorbed gas in the total gas content is 83.91%, featuring superior source and reservoir conditions and a good foundation for CBM enrichment. ② The CBM accumulation in this area is jointly controlled by the coupling of four factors: sedimentation, thermal evolution degree, temperature–pressure effect, and preservation conditions. The tidal flat–lagoon facies control the development of high-quality coal seams; regional metamorphism dominates the hydrocarbon generation capacity and gas quality of coal seams; the temperature–pressure coupling forms a critical adsorption zone at 1750 m, defining the differentiation boundary of the occurrence state of deep CBM; and high-quality mudstone cap rocks, a stable structural environment, and closed hydrodynamic conditions constitute the three key guarantees for gas enrichment. ③ Two types of accumulation models are divided: “source–reservoir integration + multi-factor synergistic enrichment type” and “source–reservoir limited + insufficient accumulation condition type”. Among them, the four reservoir-controlling factors of the synergistic enrichment type are highly coupled, with excellent gas-bearing property and strong recoverability. This study systematically clarifies the enrichment and accumulation regularity of medium-rank deep CBM in the Mugua Area and improves the accumulation theory of medium-rank deep CBM in the northern section of the eastern margin of the Ordos Basin. Full article

The Chang 7₃ sub-member of the Yanchang Formation in Ordos Basin represents an important layer of uranium-rich source rocks. Exploring the genesis of phosphorus-bearing minerals and the mechanism of uranium enrichment are of great significance for deciphering basin evolution and uranium mineralization. The geochronology of phosphorus-bearing minerals and uranium enrichment mechanisms is investigated by using electron microscopy, laser ablation inductively coupled plasma mass spectrometry, U-Pb geochronology, and geochemical analysis. Results indicate the following: (1) The formation of phosphorus-bearing minerals can be divided into two independent stages. During the early sedimentary-diagenetic stage, influenced primarily by volcanic activity, volcanic ash tends to serve as the main source of both phosphorus and uranium. The coupling of high primary productivity and organic matter decomposition synergistically contributes to promoting apatite precipitation. During the Late Cretaceous hydrothermal diagenesis stage, the U-Pb isotopic systems of apatite were reset, yielding ages of 84 ± 2 Ma and 68 ± 1 Ma. This event also significantly modified the REE distribution patterns, resulting in flattened chondrite-normalized patterns and obvious LREE depletion. (2) Uranium enrichment in phosphorus-bearing minerals, which is closely associated with their formation, occurred through a two-stage process. During the sedimentary stage, U⁶⁺ was reduced to U⁴⁺ and incorporated into the mineral lattice via isomorphous substitution for Ca²⁺ or adsorbed onto mineral surfaces through complexation. Whereas the subsequent hydrothermal diagenesis stage led to further uranium enrichment as hydrothermal fluids introduced additional U⁶⁺, which was reduced to U⁴⁺ under anoxic conditions and incorporated into the apatite lattice via isomorphous substitution for Ca²⁺ or precipitated as discrete uranium minerals. Full article

Early Jurassic organic-rich shales deposited in fluvio-deltaic settings serve as important hydrocarbon source rocks, particularly in the highly petroliferous basins of the Middle East. The Lower to Middle Jurassic sedimentary succession of the frontier Kohat Basin, Pakistan, comprises thick sequences of shale, coaly, and carbonate rocks deposited along the northwestern margin of the Indian Plate, adjacent to the eastern Tethys Ocean, and records a crucial paleoenvironmental transition from fluvio-deltaic to shallow marine settings. Despite the economic significance of the Jurassic succession as a potential hydrocarbon source in the Kohat Basin and surrounding regions, their organic geochemical characteristics and role in the regional petroleum system remain poorly understood. This study presents an integrated organic geochemical and carbon isotopic evaluation of Jurassic source rocks using well cuttings and outcrop samples, focusing on organic matter (OM) input, depositional environment, hydrocarbon generation potential, thermal maturity, and oil–source rock correlation. Source rock characterization indicates that the Shinawari and Datta formations possess fair-to-excellent generative potential, whereas the Samana Suk Formation exhibits poor-to-marginal potential. Biomarker and isotopic evidence indicate that the Shinawari Formation is dominated by algal-derived OM, characterized by higher aquatic OM deposited under relatively reducing marine to marginal marine conditions. The relatively more depleted bulk and individual fraction δ¹³C values for the Shinwari Formation are also consistent with a stronger marine influence. In contrast, the Datta Formation shows mixed OM inputs with a greater terrestrial influence and suggests deposition in more oxic lacustrine to marginal marine settings. The thermal maturity-related parameters for both formations indicate early to peak oil window thermal maturity. The geochemical correlation of Jurassic source rock extracts with Kohat crude oils, based on published data, suggests that the Kohat oils differ significantly, exhibiting stronger terrestrial organic matter signatures, more oxic depositional conditions, and slightly higher maturity, thereby indicating no direct genetic linkage with the Jurassic source rocks. Overall, the Jurassic formations are unlikely to represent the primary source rocks for Kohat oils but may have contributed locally to a multi-source petroleum system. This underscores the need for integrated geochemical investigations combining biomarker and isotopic analyses, supported by broader source rock and crude oil datasets, to resolve uncertainties in oil–source correlations, source contributions, and hydrocarbon migration pathways, thereby better constraining the petroleum system framework. Full article

The development of effective source rocks is key to hydrocarbon accumulation. The Jinshan Rift Trough, located in the Ordos Basin, is generally considered to be a favorable zone for the formation of source rocks in the Mesoproterozoic Changcheng System. This study investigates mudstones of the Cuizhuang Formation (Changcheng System) from Well PT1 using petrological and geochemical methods to evaluate source rock potential and organic matter enrichment mechanisms. The results show that the original total organic carbon (TOC) and original S₁ + S₂ of the mudstone in the Cuizhuang Formation are 0.06–1.97% and 0.61–10.34 mg/g, respectively, and “good source rock” with a cumulative thickness of 6.7 m is developed in the lower part of the Cuizhuang Formation. The main hydrocarbon-forming organisms of the source rock are planktonic and benthic algae, among which planktonic algae account for a relatively high proportion. Equivalent vitrinite reflectance (R_o) exceeds 2%, indicating an over-mature stage. The TOC of the mudstone of the Cuizhuang Formation shows a weak relationship with the salinity and redox conditions of sedimentary water but has a significant correlation with the paleoproductivity and paleoclimate. Rather than anoxia or salinity, high productivity is the main controlling factor for the enrichment of organic matter in the Changcheng System. Under a warm–humid climate, increased surface runoff and terrestrial nutrient input promote the proliferation of bacteria and algae, leading to the formation and preservation of abundant sedimentary organic matter that forms “good source rocks”. This study provides a theoretical basis for the study of the petroleum system and oil and gas exploration in the Mesoproterozoic Changcheng System in the Ordos Basin. Full article

To elucidate the sources and spatial variations in organic matter in surface sediments from Lingdingyang of the Pearl River Estuary, 18 surface sediment samples were collected and analyzed for obtaining total organic carbon (TOC), total nitrogen (TN), atomic TOC/TN ratio (C/N_atom), stable carbon and nitrogen isotopes (δ¹³C, δ¹⁵N), and glycerol dialkyl glycerol tetraethers (GDGTs). A three-endmember framework was constructed using the BIT and δ¹³C to constrain the sources of the organic matter. The results showed a significant positive correlation between TOC and TN, with relatively higher values in Jiaoyi Bay and western Lingdingyang, lower values in eastern Lingdingyang, and intermediate values in Shenzhen Bay. The C/N_atom, δ¹³C, and δ¹⁵N results revealed that the sedimentary organic matter in the study area exhibits mixed-source characteristics, influenced by soil, C₃ plants, and marine autochthonous organic matter. Among the subregions, Jiaoyi Bay is more strongly influenced by terrestrial inputs, while Shenzhen Bay receives relatively higher contributions from marine autochthonous organic matter. The GDGTs results showed that Jiaoyi Bay is characterized by elevated abundances of both brGDGTs and isoGDGTs, whereas isoGDGTs were also relatively enriched in Shenzhen Bay. brGDGTs exhibited a significant negative correlation with δ¹³C, whereas BIT showed no significant correlation with either brGDGTs or δ¹³C, indicating that BIT cannot be simply regarded as a unique proxy for soil input, but rather reflects the combined effects of in situ production, changes in archaeal lipids, and sedimentary preservation. The three-endmember model further revealed significant spatial variations in the sources of organic matter in surface sediments from Lingdingyang. Overall, the combined use of multiple proxies is more effective than any single proxy in revealing the sources and spatial differentiation of sedimentary organic matter in this subtropical, complex estuarine environment. Full article

Understanding the development characteristics and controlling factors of organic-rich shales in carbonate platform settings is essential for predicting their distribution and assessing their natural gas exploration potential. However, the mechanisms governing the accumulation of such shales in these specific sedimentary environments remain poorly constrained, and the lack of integrated petrological and geochemical studies limits accurate evaluation of their resource potential. The key objective of this study is to investigate the development characteristics and formation mechanisms of organic-rich shales within intraplatform depressions. To address this objective, we conducted a comprehensive petrological and geochemical analysis of the Cambrian Shuijingtuo Formation organic-rich shale deposits deposited in a carbonate platform setting, particularly from Well EYY3 in Western Hubei, Central Yangtze region. The obtained results indicate that total organic carbon (TOC) contents in the Shuijingtuo Formation can reach up to 4.77%, with a thickness of approximately 9.5 m for shales containing over 2% TOC. Vertically, TOC content exhibits a rapid increase at the base, followed by a gradual decline toward the top, reflecting the evolution of depositional environments. The characteristics of organic-rich shale indicate a significant presence of carbonate minerals, which increase in concentration, alongside tuff lenticular bodies and lithological transition surfaces between tuff and shale. While the longitudinal variation of SiO₂ content in shale is subtle, there is a slight increase in land-sourced clasts and excess silica, and TOC has a significant positive correlation. At the base of the Shuijingtuo Formation, redox parameters, including U-EF and Mo-EF, display a rapid increase followed by a gradual decrease. Conversely, changes in Ni-EF, which indicate paleoproductivity, are less pronounced, and their correlation with TOC is relatively poor. These findings suggest that rapid sea-level rise associated with Cambrian transgressions was the main factor influencing organic matter enrichment in the carbonate platform depressions. This rise supplied nutrients and silica-rich organisms, altering the biological landscape and fostering anoxic conditions in the intraplatform depressions, promoting organic-rich shale formation. As sea levels declined, water circulation became restricted, leading to oxidation of shallow water bodies, decreased paleoproductivity, and shale deposits transitioned to tuff. Therefore, organic-rich shale can also be developed on carbonate platforms, with its formation primarily controlled by fluctuations in sea level. During highstand periods, intraplatform depressions may serve as favorable zones for shale gas exploration. Full article

Arsenic (As) is a ubiquitous and highly toxic metalloid with well-established carcinogenicity. Its accumulation and secondary release from lake sediments pose potential risks to lake ecosystem integrity and human health. Meanwhile, the ongoing intensification of lake eutrophication at the global scale has altered the sources, composition, and environmental behavior of internally derived dissolved organic matter (DOM). These changes have profoundly influenced As mobilization and transformation at the sediment-water interface (SWI). To advance understanding of the regulatory roles and underlying mechanisms of algal dissolved organic matter (ADOM) and submerged macrophyte dissolved organic matter (SMDOM) in As biogeochemical cycling under lake ecosystem regime shifts, extensive findings from the international literature were synthesized. The characteristic properties and environmental behaviors of ADOM and SMDOM were systematically compared, and their distinct regulatory pathways in lacustrine systems were further summarized. Results indicate that ADOM is typically characterized by low molecular weight, weak aromaticity, and high bioavailability. It can enhance As dissolution and mobilization from sediments through direct complexation, competition for adsorption sites, and stimulation of microbial metabolism and Fe(III) reduction. In contrast, SMDOM exhibits higher molecular weight, greater aromaticity, and a higher degree of humification. It tends to form stable complexes with mineral phases. Under the influence of radial oxygen loss (ROL) from submerged macrophyte roots during the growth phase, its capacity to promote mineral reduction is relatively limited. This process favors stable As retention in sediments. The regulatory effects of ADOM and SMDOM on As behavior are strongly modulated by environmental factors such as pH, redox potential (Eh), temperature, and light conditions, as well as by microbial communities. ADOM is more sensitive to reducing environments and photochemical processes. SMDOM, in contrast, exerts more persistent control under oxidizing conditions and at mineral-water interfaces. In addition, ADOM more readily drives microbial community shifts toward assemblages with enhanced capacities for Fe(III) reduction and As reduction or methylation. SMDOM is less likely to trigger strongly reducing processes. Based on these mechanisms, the outbreak and decay phases in algal-dominated lakes often correspond to critical periods of enhanced As mobilization and elevated ecological risk. In submerged macrophyte-dominated lakes, the decay phase may represent an important window for sedimentary As release. Finally, a conceptual framework describing the differential regulation of As biogeochemical cycling by ADOM and SMDOM is proposed. This framework provides a theoretical basis for As risk identification, the determination of critical risk periods, and the development of management strategies across lakes with different trophic states. Full article

Phosphatic bioclastic laminae distributed along bedding planes have been recently discovered within the Jurassic Lianggaoshan Formation shale in the eastern Sichuan Basin. However, their characteristics and potential as shale oil and gas reservoirs remain unclear. To reveal their microscopic pore structure characteristics and development model, this study focuses on samples of phosphatic bioclastic laminae obtained from drilling cores in the Fuxing area of eastern Sichuan. A multi-scale analytical approach was employed, integrating micro-X-ray fluorescence spectroscopy (μ-XRF), field emission scanning electron microscopy (FE-SEM), nitrogen adsorption, nuclear magnetic resonance (NMR), and geochemical analyses. The results indicate that the phosphatic bioclastic laminae are primarily composed of apatite and calcite and formed in a low-energy, anoxic, semi-deep to deep lacustrine environment. They exhibit an average total porosity of 4.84% and an average TOC of 1.99 mg/g. It is 14.7% and 17.8% higher than the clay laminae, and 255.9% and 109.57% higher than the calcareous bioclastic laminae. The pore system is dominated by mesopores and macropores, encompassing multiple pore types including dissolution pores, interparticle pores, interlayer pores, organic matter-hosted pores, and micro-fractures. Notably, a well-connected nanometer-scale pore network developed within fish bone fragments contributes substantially to the storage space. These intervals integrate high organic matter richness with superior reservoir properties, demonstrating typical “source-reservoir integration” characteristics. Their pore structure is synergistically regulated by sedimentary–diagenetic processes, with a core mechanism of primary biogenic pore foundation–late diagenetic dissolution enhancement–micro-fracture connectivity. This study systematically elucidates, for the first time, the reservoir formation mechanism of the phosphatic bioclast-rich laminae in the Lianggaoshan Formation. It confirms their potential as “geological-engineering” dual sweet spots for shale oil and gas exploration, providing a new basis for sweet spot prediction and exploration deployment targeting similar phosphatic bioclastic laminae in the Sichuan Basin and analogous regions. Full article

Continental rift lacustrine basins typically feature multiple sediment sources under the combined controls of volcanism, tectonics, water balance and sediment supply, resulting in complex stratigraphic successions. This complexity is particularly pronounced in fine-grained successions, which are of high interest for their potential to generate and accumulate hydrocarbons. Nevertheless, the mechanisms governing the sedimentary transition from volcaniclastic to siliciclastic-dominated fills within a rift cycle remain poorly constrained. The Lower Cretaceous Xiguayuan Formation in the Luanping Basin accumulated in a lacustrine setting influenced by explosive volcanism, providing an excellent archive of siliciclastic–volcaniclastic interaction. Based on field observations, core descriptions, and petrographic analysis, sixteen lithofacies have been grouped into seven facies associations, including subaqueous ignimbrite, volcanically sourced turbidites, subaqueous volcanic ridge, central-lake sedimentation, shallow-lacustrine margin deposits, low-density turbidites, and high-density turbidites. Their spatial relationships reveal two volcanic pulses and document the lake’s environmental evolution, with deep-water background sediments overlying volcaniclastics and a marked increase in siliciclastic input upsection, reflecting a transition from an underfilled, volcaniclastic-dominated underfilled lake to a siliciclastic-dominated lake. Notably, the fine-grained sediments associated with volcanism exhibit excellent hydrocarbon potential. Organic-rich claystones and carbonate laminae form a microscopic source–reservoir system, in which volcanic inputs appear to enhance organic matter preservation and promote the development of reservoir-quality layers. This study elucidates how volcanic activity modulates sedimentation and sediment supply in a deep-lacustrine rift, offering new insights into volcano-sedimentary interactions and related hydrocarbon systems in continental rift basins. Full article