Search Results (318)

The Offshore Indus Basin is located on the western margin of the Indian Plate, adjacent to the onshore Lower Indus Basin in Pakistan and the Kutch Basin along India’s western coast. Deepwater and deep formations in this basin are characterized by low exploration intensity and poor early data quality, which hinder the verification of hydrocarbon potential. Based on newly acquired high-resolution seismic data and onshore–offshore correlation, this study analyzes basin evolution and systematically evaluates petroleum geological conditions and exploration potential of deepwater and deep formations. The results show that the basin has experienced three evolutionary stages: Mesozoic rifting, Cenozoic post-rift thermal subsidence, and passive continental margin development, which collectively control the petroleum geological conditions of deepwater and deep strata. Mesozoic strata (Jurassic and Cretaceous) are widely developed beneath the Deccan volcanic rocks, with a stable distribution. Three sets of potential source rocks are identified: Cretaceous (Type II/III organic matter, high maturity, high quality), Paleo–Eocene (Type III, moderate maturity, high quality), and Lower Miocene (Type II₂/III, low maturity, poor–moderate quality). Three sets of high-quality reservoirs are developed: Cretaceous deltaic–shallow marine sandstones, Paleocene reef limestones, and Miocene deltaic and subaqueous fan sandstones. Three hydrocarbon accumulation models are established. Favorable structural belts are mainly distributed in the NW, NE, and SE parts of the basin, dominated by structural and lithological traps. Thin Deccan volcanic rocks in deepwater areas exert a positive effect on the preservation of deep Mesozoic strata and petroleum system development. This study clarifies the key petroleum geological conditions and accumulation rules of deepwater and deep formations, providing a robust basis for hydrocarbon exploration potential evaluation in the Offshore Indus Basin. Full article

Thailand preserves one of the most extensive records of Mesozoic vertebrate tracks in Tropical Asia, yet these ichnological data have never been comprehensively synthesized. This review compiles and reassesses all known Triassic to Cretaceous vertebrate tracksites in Thailand to clarify their stratigraphic distribution, taxonomic diversity, and palaeobiogeographical significance. Published records, new field observations, and updated stratigraphic correlations are integrated to evaluate trackmaker attributions and temporal patterns. The Thai record documents diverse assemblages including chirotheriids, early theropods, sauropodomorphs, ornithopods, sauropods, and crocodilians. Late Triassic–Early Jurassic assemblages capture a major faunal transition, revealing the co-occurrence of non-dinosaurian archosaurs and some of the earliest dinosaurs in the region, whereas Lower Cretaceous sites are dominated by theropods, sauropods and diverse ornithopods. Comparison with other Asian ichnofaunas indicates faunal continuity across eastern Asia and supports early dinosaur dispersal into equatorial low latitudes. This synthesis also evaluates site conservation, highlighting the vulnerability of several Triassic localities and a positive trend of community-led discoveries since 2009, underscoring the need for proactive management and standardized digital documentation. Overall, the Thai ichnological succession represents the most complete Mesozoic track record presently known from Tropical Asia and provides key insights into vertebrate evolution, palaeoecology, and regional biogeography. Full article

Recently, a substantial quantity of oil and gas has been discovered in the pre-salt Lower Cretaceous microbialite successions of Brazil’s Santos Basin, thereby prompting a global surge in research related to microbialites. It has been demonstrated that microbial shoal reservoirs yield the highest hydrocarbon production, with optimal reservoir properties, as evidenced by experience in the field of oilfield production. However, as research progresses, it has become increasingly evident that significant heterogeneity exists in both the lithology and physical properties within microbial shoal bodies. In order to address the identified knowledge gap, the present study employs systematic petrological and petrophysical datasets. These include 30-m continuous core samples, thin-section analyses, routine petrophysical tests and mercury injection capillary pressure (MICP) measurements. The aim is to characterize the internal microfacies architecture and reservoir heterogeneity of microbial shoals. It is imperative to ascertain the principal factors that govern the heterogeneity observed in these reservoirs. This critical step is essential for a comprehensive understanding of the subject matter. The results of the study demonstrate that: the Barra Velha Formation microbial shoals in the Santos Basin can be subdivided into three microfacies, which are delineated from base to top. The foundation of the shoal is the shoal base. The rock composition is dominated by the presence of spherulites, with intracrystalline pores functioning as the primary reservoir spaces. The compositional rocks of the shoal flank are poorly sorted microbial debris, with intergranular and intragranular pores formed by penecontemporaneous dissolution. The sedimentary succession of the shoal core is characterized by well-sorted microbial debris rocks displaying multiple shallowing-upward sequences, with reverse-graded textures. The primary storage space is constituted by fabric-selective pores from penecontemporaneous dissolution, though these are subject to local disruption by destructive silicification. Meanwhile, the microbial shoals demonstrate wide porosity (8.8–26.4%, mean 16.8%) and permeability (0.13–839 mD, mean 169 mD) ranges, thus classifying them as medium-porosity, high-permeability reservoirs. The superimposition of microfacies and diagenetic processes gives rise to considerable reservoir heterogeneity. It is evident that the shoal core microfacies exhibits robust energy and substantial grain size, characteristics that facilitate its exposure above lake level during periods of high-frequency lake-level oscillation. This exposure is further compounded by the influence of atmospheric water dissolution, which remodels the microfacies during the quasi-contemporaneous period. The reservoir quality is optimal, exhibiting the highest proportion of large pores. The reservoir properties of the shoal flank are closely followed by medium and large pores, and those of the shoal base are the worst, with micro and medium pores. Full article

Sandstone of the Lower Cretaceous Luohe Formation is the main water inrush source in the Binchang Mining Area in the southwestern Ordos Basin. Its sedimentary environment and provenance features are critical for local coal development and safe mining. The Luohe Formation at Xiaozhuang Coal Mine comprises three vertical members: the lower member dominated by coarse- to medium-grained sandstones, the middle member mainly composed of fine-grained sandstones, and the upper member characterized by interbedded fine- to medium-grained sandstones and sandy conglomerates. This subdivision newly identifies a complete hydrodynamic evolutionary cycle of depositional environments from high-energy to low-energy and back to high-energy conditions. Integrated petrographic observations and analyses of major and rare earth elements first confirm that the tectonic affinity of the Luohe Formation progressively shifted from a passive continental margin to an active continental margin, accompanied by a corresponding transition in sediment provenance from the North China Craton to a magmatic arc source region. Trace element compositions precisely indicate that the Luohe Formation was deposited in a fluvial freshwater environment under hot, arid, and oxidizing conditions, thus providing new constraints on the paleoenvironmental evolution of the region. Full article

This study investigates the heterogeneity of pore structures in lacustrine shale gas reservoirs, with a specific focus on shales from the Lower Cretaceous Shahezi Formation in the Lishu Fault Sag of the Songliao Basin. By integrating multi-scale characterization techniques—including high-pressure mercury intrusion, N₂/CO₂ adsorption, and nuclear magnetic resonance (NMR)—we examined the pore networks across five identified lithofacies: organic-rich clayey shale, organic-rich mixed shale, organic-rich siliceous shale, organic clayey shale, and organic mixed shale. The results indicate that mesopores (2–50 nm) constitute the dominant fraction of pore volume (31.7%–56.6%), followed by micropores (<2 nm) and macropores (>10 μm). Notable lithofacies-dependent variations were observed: organic-rich clayey shale exhibits abundant organic pores, clay interlayer pores, and intragranular dissolution pores with favorable connectivity; organic-rich siliceous shale is mainly dominated by inorganic pores with limited organic porosity; mixed shales are characterized by clay mineral contraction fractures and intergranular pores. The key controlling factors are mineral composition and organic matter abundance: clay content shows a positive correlation with pore volume and surface area in organic-rich clayey shale, but a negative correlation in organic mixed shale. Brittle minerals (quartz and feldspar) generally reduce porosity through compaction. Total organic carbon (TOC) displays a weak positive correlation with mesopore volume, while thermal maturity (Ro = 1.2%–1.73%) exerts influences that vary by lithofacies. In contrast to marine shales—which are dominated by high-maturity (Ro > 2.0%) organic pores and quartz-supported frameworks—terrestrial shales primarily rely on inorganic pores derived from clay minerals (e.g., illite). This study clarifies the relationships among lithofacies, pore structure, and controlling factors, thereby providing a basis for evaluating the gas potential of terrestrial shales. Full article

The Late Jurassic–Early Cretaceous Oloy complex was formed in the setting of convergence between the Chukotka microcontinent and the Kolyma–Omolon margin. Its evolution reflects the closure of the South Anyui Ocean, with controversial timing estimates. This study emphasizes the integration of lithological data with magmatic and metallogenic information to reconstruct geodynamic processes. The article presents the results of detailed petrographic and geochemical studies, Sm-Nd isotope analyses, and U-Pb dating of detrital zircons from Kimmeridgian–Lower Hauterivian volcaniclastic and epiclastic sandstones. Petrographic studies and U-Pb dating of detrital zircons identified the main sources at different stages and the amount of synchronous pyroclastic material. Isotope-geochemical investigations suggest a young undifferentiated arc provenance for Kimmeridgian deposits, whereas Tithonian–Valanginian sediments accumulated due to the erosion of more differentiated igneous rocks and input of clastic material from the continent. New data on changes in sedimentation environments and provenance enabled the tracing of the evolution of the Oloy arc. In the Kimmeridgian, the Oloy island arc existed on a heterogeneous basement, with south-dipping subduction towards the Kolyma–Omolon margin. During the Late Tithonian, the arc accreted and magmatic activity continued in the active margin setting. Collision initiated in the latter half of the Berriasian, reaching its active phase in the Valanginian time. Full article

Tamusu, the only identified super-large sandstone-hosted uranium deposit in the Bayingobi Basin, provides an important natural laboratory for evaluating ore-controlling factors and genetic models of sandstone-type uranium mineralization. Based on core descriptions from more than 200 boreholes, log facies analysis and geochemical environmental proxies, this study constrains the sedimentary–mineralization architecture and key controlling factors of the deposit. Uranium orebodies are mainly hosted in the upper member of the Lower Cretaceous Bayingobi Formation (Sq2) within a gravity flow-dominated fan-delta–lacustrine system. Braided distributary channel sands on the fan-delta plain and subaqueous distributary channel sands on the delta front constitute the principal uranium reservoirs, controlling both the migration pathways and storage space for U-bearing fluids. Mineralization is jointly governed by fan-delta architecture, interlayer oxidation zonation and reducing agents. The interlayer oxidation zone displays a north-thick–south-thin geometry, and uranium orebodies are concentrated at redox transition positions, with grades of 0.01–0.33 wt%. The metallogenic evolution can be summarized in three stages: syndepositional uranium pre-enrichment, interlayer oxidation mineralization, and a late hydrothermal/diagenetic overprint that mainly modified reservoir properties, favored ore preservation, and did not contribute to the primary uranium budget. Accordingly, a genetic model of “fan-delta architecture + interlayer oxidation control + late overprint and preservation” is proposed to guide exploration in the Bayingobi Basin and analogous sandstone-type uranium systems. Full article

Rare earth elements (REEs) play a critical role in provenance tracing and the environmental reconstruction of the Earth. However, systematic investigations into the geochemical behavior and fractionation mechanisms of REEs during halite crystallization in brine–salt systems remain limited. This study reports new trace element and REE data for Late Cretaceous halites from the Thakhek Basin, Laos. Ratios of Sr/Ba, Sr/Cu, and V/Cr indicate a marine origin for the halites, which formed under hot climatic and oscillating oxidizing–anoxic redox conditions. Both primary and secondary halites display uniform Post-Archean Australian Shale (PAAS)-normalized REE distribution patterns, characterized by relative enrichment in medium rare earth elements (MREE) and depletion in light (LREE) and heavy rare earth elements (HREE). Similar REE patterns are also observed in halites from other modern and ancient, continental and marine salt basins worldwide. These observations suggest that the influences of parent brine composition and external provenance supplies on REE fractionation are negligible, given the consistent source, salinity, and redox conditions recorded in these halites. Accordingly, REE fractionation in halite was largely controlled by crystallographic effects, with aqueous MREE preferentially incorporated into halite crystals during deposition. In addition, the relatively lower Zr/Hf ratios in secondary halites compared to primary halites further validate the utility of the Zr/Hf ratio for distinguishing authigenic halite from salt modified by diagenesis, weathering, dissolution, or recrystallization. While our results establish a fundamental REE distribution pattern for halite, further research is needed to better constrain the underlying fractionation mechanisms of REEs in evaporite minerals within brine–salt systems. Full article

Phosphorus is crucial for reconstructing long-term feedback mechanisms between climate, the environment and ecology, as well as for assessing global biogeochemical changes. This study documents two thin yet laterally continuous phosphorite beds from the lower Nenjiang Formation (Late Cretaceous) of the Songliao Basin in NE China and evaluates their mineralogical characteristics and paleoenvironmental significance. The phosphorite beds occur in sharp contact with adjacent black shale and contain well-preserved Ostracoda and conchostracan fossils, providing biological constraints on the depositional conditions. Bulk rock compositions indicate elevated P₂O₅ contents, ranging from approximately 20 to 30 wt%. Mineralogical analyses reveal that the dominant phosphate mineral is carbonate-fluorapatite (CFA), accompanied by minor quartz, hydromica, goethite and pyrrhotite. Integrated fossil, sedimentological, and geochemical evidence suggests that CFA precipitated in a deep, stratified, eutrophic lacustrine environment. Enhanced productivity, biological enrichment and microbial decomposition of organic matter likely promoted phosphorus enrichment in bottom waters, facilitating CFA precipitation at or near the sediment-water interface during deposition and early diagenesis. Variations in physicochemical conditions, including pH and Ca²⁺ concentrations, may have further influenced mineral precipitation and subsequent diagenetic processes. These findings contribute to our understanding of phosphorus precipitation mechanisms in lacustrine basins and provide new constraints on the Late Cretaceous paleoenvironment of the Songliao Basin. 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

The Dakhla Formation in the Western Desert of Egypt comprises a thick Cretaceous–Paleocene, ranging from light gray to dark gray, that represents an underexplored geological resource relevant to sustainable energy and environmental conditions. The present study integrates mineralogical and geochemical data based on samples collected from outcrop at Mut-Manflout and subsurface core samples from Abu Tartur (62–150 m depth) to evaluate depositional environments, paleoclimate, chemical weathering, and organic carbon accumulation. Major and trace element geochemistry, clay mineralogy, total organic carbon (TOC), Rock-Eval pyrolysis, and calorific values are used to assess hydrocarbon potential while minimizing exploration uncertainty. Mineralogical analyses indicate that smectite and kaolinite dominate the Mut-Manflout shales; in contrast, significant relationships among primary oxides and trace elements indicate a source from detrital materials, and elevated Chemical Alteration Index (CIA) values are indicative of intense chemical weathering under humid paleoclimatic conditions. The geochemical results show that Abu Tartur shale core samples contain higher TOC values (0.73–2.08 wt%) and oil-prone kerogen (types I–II to II–III), while Mut-Manflout outcrop samples exhibit lower TOC contents (0.23–1.15 wt%) and gas-prone kerogen (types III–IV). Both successions are thermally immature, with a strong relationship between TOC and S₁ values indicating the presence of indigenous hydrocarbons. By comparing surface and subsurface shales, the present study highlights the importance of site-specific characterization in reducing environmental and economic risks associated with unconventional resource exploration. The results support sustainable resource planning by improving understanding of organic carbon storage, paleoclimate controls, and the responsible evaluation of black shale systems in arid regions such as the Western Desert of Egypt. Full article

Interconnected fractures induced by coal mining, known as water-conducting fracture zones (WCFZs), form a fractured zone where water from overlying aquifers flows into the goaf. Substantial findings have been established on the development height of WCFZs; however, these analyses have been based on intact structures or rock masses. Research on how primary fissures or other water-conducting structures influence the development of WCFZs remains limited. The mining seam of the Gaojiapu Coal Mine in the Ordos Basin, China, is overlaid by a gigantic and highly confined Cretaceous aquifer. Additionally, the primary fissures of the overlying strata are highly developed. Geophysical inversion of the primary fissures and vertical and horizontal drilling were undertaken in order to systematically investigate the characteristics of WCFZ development in the overlying strata. The results show that a dense network of primary fissures is connected with the middle and lower Cretaceous aquifer developed in Mining Zone 1. These fissures are prone to connecting with mining-induced fractures to form the highly developed WCFZs observed and verified in this study. A grouting engineering approach was adopted at the Gaojiapu Coal Mine to block the primary fissures in advance, as this can effectively control the abnormal development of the WCFZs and decrease the discharge of mine water, ultimately protecting the water resources of the Cretaceous aquifer. Our research clarifies the significant role of primary fissures in the development of water-conducting fracture zones, and provides important theoretical guidance for the accurate prediction and prevention of mine roof water hazards in areas with similar mining conditions. Full article

Jurassic–Cretaceous marine–continental carbonate–evaporitic sequences in the Neuquén Basin of Argentina host numerous stratabound Ba–Sr deposits. Mineralization (Sr–barite, Ba–celestine, and minor Pb–Zn–Cu–Fe sulphides) occurs as bedding parallel lenses and crosscutting veins. The stratiform mineralization is formed by replacements of carbonate and gypsum beds and often exhibits typical zebra textures. Dissolution processes associated with Neogene regional uplift produced karstic cavities where a new generation of barite was deposited. Regionally, W to E distribution of carbonates/evaporites and that of Ba–Sr deposits is coincidental. Lower Cretaceous Sr–Ba deposits are spatially related to large N-S reverse faulting, frequently limited to the eastern limb of the folded structures. Average δ¹⁸O and δ³⁴S of stratiform and crosscutting vetiform mineralization do not differ significantly, suggesting a common source of sulphate and cations. Deposits spatially linked to areas with magmatic activity and those that are not have similar isotopic values, compatible with bacterial and/or thermochemical reduction of contemporaneous seawater sulphate, although sulphides only occur in deposits with evidence of nearby magmatic activity. Thermal convection of basinal brines leached metals from the Mesozoic sedimentary pile; Ba and Sr were extracted from siliciclastic and carbonate rocks, and sulphur from evaporite layers. Fluids related to Tertiary magmatism helped producing an epithermal mineral association composed of barite, quartz, adularia, and minor sulphides/sulphosalts hosted by veins. Arroyo Nuevo mine (Ba) is different, as it seems to be the product of hydrothermal SedEx deposition onto the anoxic seafloor. Full article

This study investigates a karst bauxite deposit from NE Spain with a dual objective incorporating the novel aspect of directly linking genetic processes to industrial ceramic performance. First, the bauxite is mineralogically and texturally characterized using X-ray diffraction and field emission scanning electron microscopy. Second, the mineralogical and textural transformations of the bauxite during firing at 1000, 1200 and 1300 °C are analyzed, together with their effects on the physical properties of the fired products. The Lower Cretaceous bauxite is autochthonous, shows a pisolithic structure, and formed in situ under tropical monsoon conditions through intense chemical weathering involving dissolution–crystallization processes. For ceramic testing, the bauxite was mixed with illitic–kaolinitic clays in a 90/10 proportion. During firing, kaolinite and illite destabilize and transform into mullite, initially by solid-state reactions at 1000 °C and subsequently by crystallization from a vitreous phase at higher temperatures, producing larger crystals and composition closer to the empirical mullite formula. The formation of vitreous phase and mullite leads to reduced porosity and increased density and linear shrinkage, particularly between 1000 and 1200 °C. Specimens fired at 1300 °C show higher mechanical strength, related to higher mullite content and a larger size of its crystals. The results demonstrate the potential interest of these bauxites for ceramic manufacturing. Full article

The northern segment of the Great Xing’an Range, northeastern China, hosts a previously unrecognized near-E–W-trending rhyolite belt in the Tulihe area. We conducted systematic geochronological and geochemical investigations to constrain its formation age, petrogenesis, and regional tectonic significance. Field investigation, petrographic observation, and zircon laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) U–Pb dating indicate that the rhyolite belt was formed during the Early Cretaceous, with emplacement ages directly determined from three samples ranging from 143.8 to 131.5 Ma. Geochemically, the rhyolites yielded high SiO₂ contents (74.44–75.88 wt.%), high total alkalis (K₂O + Na₂O = 8.50–8.99 wt.%), and low MgO contents (0.16–0.55 wt.%). They displayed strong enrichment in light rare earth elements and depletion in high field strength elements, weakly negative Eu anomalies, A/CNK ratios near unity, and relatively high Nb/Ta ratios. Trace element signatures and incompatible element abundances (Zr + Nb + Ce + Y = 193.2–338.3 × 10⁻⁶) are mostly consistent with highly fractionated I-type volcanic rocks, rather than S-type or M-type affinities. The geochemical data suggest that the rhyolites were mainly generated by partial melting of a medium- to high-K basaltic lower crust, with minor crustal assimilation and limited mantle input. Tectonically, Early Cretaceous magmatism in the northern Great Xing’an Range was governed by flat-slab subduction and subsequent rollback of the Paleo-Pacific (Izanagi) plate, while the local E–W-trending rhyolite belt was controlled by pre-existing faults, reflecting localized post-orogenic extension consistent with regional NE-trending volcanic belts. The northwest-to-southeast younging trend records asthenospheric upwelling and enhanced crust–mantle interaction induced by slab rollback. These results highlight the petrogenetic and tectonic evolution of medium- to high-K magmatism along the NE Asian continental margin and improve our understanding of Mesozoic volcanism in the Great Xing’an Range. Full article