Search Results (52)

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

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

The Mugan Syncline in northeastern Yunnan represents a significant relay area for shale gas exploration in China. However, due to the combined effects of tectonic superimposition and sedimentary heterogeneity, systematic investigations into the intervals hosting high-quality shales and the coupling relationships among microfacies, reservoir quality, and gas-bearing properties remain insufficient. The core objective of this study is to establish a high-resolution microfacies framework and to quantitatively elucidate the multi-parameter coupling mechanisms by which microfacies control organic matter enrichment, pore development, and gas storage capacity in this structurally complex, basin-margin setting. By integrating core observations, thin-section petrography, scanning electron microscopy (SEM), whole-rock X-ray diffraction (XRD), total organic carbon (TOC) analysis, trace-element geochemistry, and well-logging data, we establish a stratigraphic subdivision and cross-well correlation framework for the Wufeng (WF) Formation and the Long11 submember. Furthermore, a lithofacies (microfacies) identification scheme based on a “TOC + siliceous (quartz + feldspar)–carbonate–clay” ternary classification is applied. The results reveal the following: (1) Based on the locally developed erosional contact at the boundary between the Longmaxi (LMX) Formation and the underlying Guanyinqiao Formation, the WF Formation in the study area can be subdivided into two submembers, whereas the Long11 submember comprises four sublayers. The thicknesses of the Long11-1 through Long11-3 sublayers range from 21.42 to 25.47 m, exhibiting a subtle northward-thickening trend. In contrast, the Long11-4 sublayer displays a relatively uniform thickness and high stratigraphic continuity of shale deposition. (2) Based on TOC content and ternary mineral composition, the shales are classified into four lithofacies associations and sixteen lithofacies subtypes. The main favorable microfacies assemblages are identified as high-carbon siliceous/calcareous shale (C-1), high-carbon calcareous/siliceous mixed shale (M-1), carbon-rich argillaceous siliceous shale (S-3), and high-carbon siliceous/argillaceous mixed shale (M-2). (3) High-quality shales (TOC > 2%) are predominantly developed in the upper member of the WF Formation and in the Long11-1 through Long11-4 sublayers. Their lateral distribution is markedly controlled by variations in paleotopography and terrigenous sediment supply. (4) The microfacies exert a synergistic control on shale gas enrichment. Carbon-rich argillaceous siliceous and siliceous-rich microfacies generally correspond to higher TOC contents and better-developed organic-matter pores. Siliceous-rich and mixed microfacies exert a positive influence on pore preservation and rock brittleness. The gas-bearing properties are influenced not only by TOC content but also by pore structure, mineral composition, and tectonic preservation conditions. The findings of this study provide a scientific basis for the prediction of shale gas sweet spots and the optimization of target intervals in the Mugan Syncline and other structurally and sedimentologically complex regions of northeastern Yunnan. Full article

Organic-rich shales in China’s deep-water shelf environments possess significant shale gas resource potential. To investigate the reservoir development characteristics of deep-water shelf shale, 143 shale samples were collected from the low-maturity Xiamaling Formation in the Zhangjiakou area and the high to over-mature Wufeng–Longmaxi Formations in the southeastern margin of the Sichuan Basin. Basic analytical methods, including X-ray diffraction (XRD), total organic carbon (TOC) analysis, rock pyrolysis, and solid bitumen reflectance measurements, were employed alongside advanced reservoir characterization techniques such as field-emission scanning electron microscopy (FE-SEM), low-pressure CO₂/N₂ physisorption, mercury intrusion porosimetry (MIP), and focused ion beam scanning electron microscopy (FIB-SEM). This study focuses on the petrographical, geochemical, and microscopic pore structure characteristics of these marine shales. The results indicate that the mineral composition of deep-water shelf sedimentary shale is dominated by quartz, clay minerals, feldspar, calcite, dolomite, apatite, and pyrite, with quartz being the most abundant. The Xiamaling Formation shales, at low maturity, are relatively rich in siliceous components, while the high to over-mature Wufeng and Longmaxi Formation shales are richer in carbonate components. The kerogen type of organic matter in the Xiamaling Formation is primarily Types II₁ and II₂, whereas the Wufeng–Longmaxi shales are predominantly Types I and II₁. TOC content is highest in the Wufeng Formation, followed by the Longmaxi Formation, with the Xiamaling Formation exhibiting the lowest TOC levels. Pore development in the Wufeng and Longmaxi shales is significantly superior to that in the Xiamaling shales. Overall, the Wufeng and Longmaxi Formations demonstrate more favorable pore characteristics and hydrocarbon generation potential compared to the Xiamaling Formation. The Wufeng and Longmaxi Formations’ shales will be the key targets for shale gas exploration in the future. The findings of this study contribute to the understanding and development of theories of marine shale gas accumulation in China and hold both theoretical and practical significance for the efficient and rational exploitation of shale oil and gas resources. 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

Based on data from core observations, thin-section petrography, scanning electron microscopy, whole-rock X-ray diffraction, organic geochemical analysis, and element analysis, in this study, we characterized the mineralogical–petrological features and sedimentary environment of the Lower Cambrian Qiongzhusi Formation shale in Western Hubei Province, and we clarified their relationships with organic matter enrichment. The results are as follows: (1) Five dominant rock types were identified in the Qiongzhusi Formation, namely, siliceous shale, argillaceous–siliceous mixed shale, argillaceous–calcareous shale, calcareous–siliceous shale, and calcareous shale. Vertically, the lithofacies transition follows the sequence of siliceous shale facies → mixed shale facies → calcareous shale facies. Laterally, from the marine trough to the trough margin, the thicknesses of the siliceous shale, argillaceous–siliceous mixed shale, and calcareous–siliceous mixed shale gradually decrease, whereas the thickness of the argillaceous–calcareous mixed shale increases progressively. (2) From the early to late sedimentary periods of the Qiongzhusi Formation and from the marine trough to the trough margin, a consistent evolutionary trend can be observed: gradual shallowing of the water depth, intensified hydrodynamic conditions, increased dissolved oxygen content of the bottom water, weakened upwelling currents, reduced paleoproductivity in the surface water, enhanced water mass stagnation, increased terrigenous input, and a corresponding gradual decrease in the total organic carbon (TOC) content. (3) The formation of the late-stage organic-rich shale was comprehensively controlled by the terrigenous input, redox conditions, paleoproductivity, water mass stagnation, and upwelling activity. Among these factors, the redox conditions, water mass stagnation, and paleoproductivity were the primary drivers responsible for the difference in the TOC contents in the Western Hubei marine trough and its margin, while the terrigenous input played a secondary role. Full article

The Upper Permian marine shale of the inter-platform basin in the Nanpanjiang Basin are rich in organic matter, widely distributed, and relatively thick, indicating abundant resource potential for hydrocarbon exploration. To clarify the sedimentary condition and the variability of reservoir properties, the paleo-environment was reconstructed by using geochemical, mineralogical, rock-property, and pore-structure data. Building on a lithofacies classification, the development patterns of different shale lithofacies were revealed. Reservoir characteristics among lithofacies were compared using scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), and low-temperature Nuclear Magnetic Resonance Cryoporometry (NMRC) experiments. A fractal analysis was performed based on NMR and NMRC data to quantify pore-scale heterogeneity, calculate fractal dimensions (D₁, D₂, and D_c), and evaluate the complexity of pore systems across lithofacies. Correlation analysis and redundancy analysis were applied to further explore the controlling factors of reservoir heterogeneity. The results showed that organic-rich shale in the Permian Linghao Formation occurred mainly in the 1st Member, with average total organic carbon (TOC) content of 2.57%, and the lower part of the 3rd Member (average TOC content 2.88%). In the 1st Member, high-carbon shale was deposited under humid conditions with intense weathering, abundant fine-grained clastic input from basin margins, strongly reducing (anoxic) bottom waters, vigorous phosphorus recycling, and moderate to low primary productivity. Using TOC and mineral composition, seven shale lithofacies were identified in the Linghao Formation, and their development patterns were established based on depositional paleo-environment characteristics and evolution. In the 1st Member, organic-rich shale was dominated by mixed lithofacies with moderate to high TOC. The paleo-environment exerted a primary control on reservoir properties, gas content, pore structure, and heterogeneity. The high-carbon lithofacies had the most favorable rock properties—higher porosity, greater pore volume, and higher gas content—and contained a larger proportion of well-developed organic pores. Fractal analysis revealed that seepage pores exhibited greater structural complexity than adsorption-related pores, with the high-carbon lithofacies showing the highest overall fractal dimensions and thus the strongest heterogeneity. Across the formation, higher clay content and TOC were the primary drivers of increased pore-scale heterogeneity, whereas greater feldspar and quartz contents tended to diminish it. Carbonates exerted a minor effect. Heterogeneity in adsorption pores exerted the strongest influence on differences among lithofacies. These results highlighted the utility of fractal analysis in quantitatively linking shale mineralogy and organic content to multiscale heterogeneity in inter-platform basin settings. Full article

This study investigates the concentrations and geochemical behaviour of strategic elements—including Li, Co, Ni, Cu, Ga, Ge, rare earth elements (REEs), and yttrium (Y)—in bottom ash samples from the Afşin–Elbistan thermal power plant, Türkiye. Thirty bottom ash samples were analysed, revealing average ∑LREE and ∑HREE concentrations of 86.3 µg/g and 3.3 µg/g, respectively, resulting in an L/H ratio of 24.9, indicating pronounced enrichment in light REEs. The total ∑REE + Y concentration (111 µg/g) is comparable to the background value for coal but approximately 1.5 times lower than those reported for average Chinese coals and the upper continental crust (UCC). REE contents significantly exceed those of sedimentary (5.36 µg/g), mafic (16.77 µg/g), and felsic (3.60 µg/g) rocks. Elevated Li (30.5 µg/g) and Ni (114.4 µg/g) concentrations point to a mafic magmatic source, whereas Cu (28.7 µg/g) likely originates from basic volcanic rocks such as those of the Dağlıca Complex and the Kemaliye Formation. Chondrite-normalised REE patterns show Dy depletion relative to mafic rocks and Ho depletion compared to sedimentary rocks. Positive δEu anomalies (>1) support a mafic or UCC provenance, while slightly positive δCe values indicate hydrothermal leaching influences. The co-precipitation of Ce with Ca–Mg hydroxides and clay minerals in coal-bearing lacustrine sediments is suggested. Ga enrichment is attributed to aluminium-rich clay minerals and organic matter. Overall, these geochemical signatures reflect combined inputs from hydrothermal leaching and volcanic weathering within a coal-bearing lacustrine environment. Full article

With the progressive depletion of conventional oil and gas resources and the increasing demand for alternative energy, organic-rich sedimentary rock—oil shale—has attracted widespread attention as a key unconventional hydrocarbon resource. Pyrolysis is the essential process for converting the organic matter in oil shale into recoverable hydrocarbons, and a detailed understanding of its behavior is crucial for improving development efficiency. This review systematically summarizes the research progress on the pyrolysis characteristics of oil shale under laboratory conditions. It focuses on the applications of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) in identifying pyrolysis stages, extracting kinetic parameters, and analyzing thermal effects; the role of coupled spectroscopic techniques (e.g., TG-FTIR, TG-MS) in elucidating the evolution of gaseous products; and the effects of key parameters such as pyrolysis temperature, heating rate, particle size, and reaction atmosphere on product distribution and yield. Furthermore, the mechanisms and effects of three distinct heating strategies—conventional heating, microwave heating, and autothermic pyrolysis—are compared, and the influence of inherent minerals and external catalysts on reaction pathways is discussed. Despite significant advances, challenges remain in quantitatively describing reaction mechanisms, accurately predicting product yields, and generalizing kinetic models. Future research should integrate multiscale experiments, in situ characterization, and molecular simulations to construct pyrolysis mechanism models tailored to various oil shale types, thereby providing theoretical support for the development of efficient and environmentally friendly oil shale conversion technologies. Full article

Organic matter (OM)-hosted pores play a crucial role in unconventional shale reservoirs, with their development influenced by OM type and thermal maturity across terrestrial, transitional, and marine deposits. In this study, a comparative analysis of porosity and pore structures is presented using organic petrographical, petrophysical, and mineralogical methods on organic-rich samples from diverse depositional environments. A pore evolution model for these sediments in different settings is proposed. Results show that kerogen particles in terrestrial shales at low and moderate thermal maturity (Dameigou Formation and Qingshankou Formation) are mostly nonporous. Transitional shales (Longtan Formation) contain vitrinite and inertinite, with only some inertinite exhibiting visible primary pores. In marine shales at higher maturity (late oil window; Dalong Formation), the interparticle pore space is occupied by solid bitumen, and secondary porosity is present at higher maturity, approaching the thermal gas generation stage. In over-mature marine shales (Wujiaping and Daye Formations), secondary pores are densely distributed within pyrobitumen. A negative correlation between organic carbon content and pore volume is observed in low-maturity lacustrine and transitional shales due to poorly developed kerogen-bound pores and interparticle pore occlusion by solid bitumen. However, over-mature marine shales exhibit a strong positive correlation due to extensive secondary porosity in pyrobitumen. Thus, pore evolution within OM is controlled by kerogen type and maturity. In oil-prone marine and lacustrine shales, secondary porosity in solid bitumen and pyrobitumen increases with thermal maturity. In contrast, terrestrial kerogen rarely forms solid bitumen and mainly develops micropores rather than mesopores at high maturity. Full article

The lower Cambrian Yurtus Formation (Є₁y) in the Tarim Basin, characterized by its high organic matter content, serves as a critical source rock for oil and gas exploration in the platform basin. This study presents a high-resolution geochemical analysis of a geological section located near the Aksu Cement Plant in the northwest margin of the Tarim Basin. The focus is on elucidating the sedimentary environment, mechanisms of organic matter enrichment, and the depositional history of the Є₁y source rock. The Є₁y exhibits distinctive geochemical signatures, including elevated concentrations of Mo, Ba, and U, with an average rare earth element (REE) content of 155.75 μg/g. The formation shows significant light REE enrichment (LREE/HREE = 1.74–5.57), a moderate Ce negative anomaly (δCe = 0.4–0.71), and a notable Eu positive anomaly (δEu = 0.94–2.14), indicative of a unique depositional environment influenced by hydrothermal processes. Geochemical evidence suggests that the Є₁y siliceous shales were deposited in a highly reducing, anoxic, and sulfide-rich environment, promoting organic matter preservation and enhancing sedimentary productivity. The presence of hydrothermal trace elements, likely introduced by hydrothermal fluids from volcanic activity along fractures and faults, played a critical role in enriching the sedimentary system, preserving organic matter, and boosting paleoproductivity. The model of organic matter enrichment proposed in this study underscores the dynamic interplay between hydrothermal influences and high primary productivity. These findings provide important insights into the formation of high-quality source rocks and have significant implications for the exploration of deep and ultra-deep oil and gas reserves in the Tarim Basin. Full article

The ocean is a significant global reservoir of uranium (U) and thorium (Th). These elements can be incorporated into marine sediments through processes involving organic matter (OM), redox conditions, terrigenous inputs, and mineral interactions. Helium generated through the radioactive decay of U and Th within geological formations represents a critical potential resource. Marine black shales, which are rich in U and Th, are widespread in the Ediacaran Doushantuo Formation of the Upper Yangtze Platform, making them a key target for helium exploration. However, there is limited research on the mechanisms behind U and Th accumulation in these shales. This study focuses on shales from the Doushantuo Formation in Chongqing, China, aiming to explore the mechanisms of U and Th accumulation and assess the potential for helium generation, and argillaceous dolomites are included for comparative analysis. The results show that the average U and Th content in the black shales (17.58 and 9.78 ppm, respectively) is higher than that of argillaceous dolomites (3.52 and 2.75 ppm, respectively). Uranium mainly comes from authigenic precipitation and hydrothermal inputs, while thorium is primarily sourced from terrigenous and hydrothermal inputs. The semi-humid climate in the provenance area facilitated parent rock weathering, with atmospheric precipitation and river systems transporting U and Th to the ocean. However, excessive terrigenous input can dilute the U and Th content in the sediments. In the shales, uranium is primarily adsorbed and/or complexed by organic matter (OM), with the anoxic–euxinic sedimentary environment and high OM content (TOC = 0.06–34.58 wt.%, r = 0.95) promoting U accumulation. Thorium accumulation is largely controlled by adsorption onto clay minerals. The total amount of helium generated from the Doushantuo shales is estimated to be 7.20 × 10¹⁰ m³. Full article

In the early Cambrian period, a severe greenhouse effect subjected the Gondwanan continents to accelerated erosion, enriching oceanic waters with essential nutrients, including phosphate, silicon, calcium, magnesium, iron, and trace elements. The nutrient flux, sourced from the volcanic composition of west Gondwana, was recorded as sequences of nodular phosphoritic limestones intercalated with chlorite-rich silts, containing ferrous phyllosilicates such as chamosite and chlorite. The abundant and diverse fossil record within these deposits corroborates that the ion supply facilitated robust biogeochemical and nutrient cycling, promoting elevated biological productivity and biodiversity. This paper investigates the early Cambrian nutrient fluxes from the Gondwanan continental region, focusing on the formation of phosphoritic and ferrous facies and the diversity of the fossil record. We estimate and model the biogeochemical cycling within a unique early Cambrian ecosystem located in South Spain, characterized by calcimicrobial reefs interspersed with archaeocyathids that settled atop a tectonically elevated volcano-sedimentary platform. The configuration enclosed a shallow marine lagoon nourished by riverine contributions including ferric and phosphatic complexes. Geochemical analyses revealed varying concentrations of iron (0.14–3.23 wt%), phosphate (0.1–20.0 wt%), and silica (0.27–69.0 wt%) across different facies, with distinct patterns between reef core and lagoonal deposits. Using the Geochemist’s Workbench software and field observations, we estimated that continental andesite weathering rates were approximately 23 times higher than the rates predicted through modeling, delivering, at least, annual fluxes of 0.286 g·cm⁻²·yr⁻¹ for Fe and 0.0146 g·cm⁻²·yr⁻¹ for PO₄³⁻ into the lagoon. The abundant and diverse fossil assemblage, comprising over 20 distinct taxonomic groups dominated by mollusks and small shelly fossils, indicates that this nutrient influx facilitated robust biogeochemical cycling and elevated biological productivity. A carbon budget analysis revealed that while the system produced an estimated 1.49·10¹⁵ g of C over its million-year existence, only about 0.01% was preserved in the rock record. Sulfate-reducing and iron-reducing chemoheterotrophic bacteria played essential roles in organic carbon recycling, with sulfate reduction serving as the dominant degradation pathway, processing approximately 1.55·10¹¹ g of C compared to the 5.94·10⁸ g of C through iron reduction. A stoichiometric analysis based on Redfield ratios suggested significant deviations in the C:P ratios between the different facies and metabolic pathways, ranging from 0.12 to 161.83, reflecting the complex patterns of organic matter preservation and degradation. The formation of phosphorites and ferrous phyllosilicates was primarily controlled by suboxic conditions in the lagoon, where microbial iron reduction destabilized Fe(III)-bearing oxyhydroxide complexes, releasing scavenged phosphate. This analysis of nutrient cycling in the Las Ermitas reef–lagoon system demonstrates how intensified continental weathering and enhanced nutrient fluxes during the early Cambrian created favorable conditions for the development of complex marine ecosystems. The quantified nutrient concentrations, weathering rates, and metabolic patterns established here provide a baseline data for future research addressing the biogeochemical conditions that facilitated the Cambrian explosion and offering new insights into the co-evolution of Earth’s geochemical cycles and early animal communities. Full article

Strategic breakthroughs have been made in the exploration and evaluation of Gulong shale oil in the Songliao Basin. However, the Heiyupao Depression, located near the Gulong Depression, hosts a thick section of the Qingshankou Formation shale that has not been extensively studied. This paper presents novel insights into the lithofacies characteristics, depositional environment, and reservoir features of the Qingshankou Formation shale in the Heiyupao Depression, with a specific focus on the origin and maturation of organic-rich shale. Four core wells were drilled, and 152 core samples were analyzed through a variety of techniques, including rock type classification, mineral composition, TOC content, rare earth elements, rock pyrolysis, organic matter type determination, and CT scanning. Results indicate that the Qingshankou shale is dominated by felsic compositions and Type I kerogen, with organic maturity varying across the section. Based on lithology, sedimentary structures, mineralogy, and organic matter abundance, five distinct lithofacies are identified: high-organic mud-rich felsic shale, high-organic sand-rich felsic shale, medium-organic sand-rich felsic shale, medium-organic massive shale, and low-organic sand-rich felsic shale. Notably, the Type A lithofacies (high-organic mud-rich felsic shale) is identified as a primary source rock due to its intergranular and organic matter pores, albeit with low porosity and poor connectivity. In contrast, the Type E lithofacies (low-organic sand-rich felsic shale) have high porosity, well-developed micro- and nano-scale pores, and strong connectivity, marking them as the primary reservoirs. The characteristics of this region differ significantly from those of Gulong shale oil, requiring different extraction strategies. The mineral composition of such shale is predominantly felsic rather than mixed. The findings not only provide theoretical support for the exploration of complex lacustrine shale in the Songliao Basin but also offer valuable insights for the resource development of similar non-marine shale systems worldwide. Full article