Search Results (135)

The earliest Cambrian (ca., 538.8–524.8 Ma) was an important period in geological history witnessing significant environmental change, during which organic-rich facies were developed in the Yangtze Platform, South China. However, the contemporaneous paleogeographic and stratigraphic framework within which the environmental change and organic matter accumulation took place remains poorly understood. We investigate this based on facies, sequence stratigraphic, and geochemical analyses of the lowermost Cambrian Maidiping and Zhujiaqing formations in the northwestern Yangtze Block. The results show that the terminal Ediacaran rimmed platform changed into a foredeep carbonate ramp and backbulge basin after the onset of the earliest Cambrian transgression. Across the Ediacaran–Cambrian boundary, the shallow-marine redox condition rapidly transitioned from relative euxinia to an oxygen-rich state. During the late transgression to highstand normal regression, the foredeep carbonate ramp expanded to the cratonic interior, and nutrients brought by intensified continental weathering and upwelling promoted significant phytoplankton proliferation, an increase in oxygen level and primary productivity, and then organic matter enrichment. During the forced regression, the carbonate ramp gradually changed into a rimmed platform. The weakening continental weathering and expanding anoxic area during the forced to lowstand normal regression led to the significant organic carbon burial in the foredeep basin. Full article

In the absence of appropriate tools and a knowledge base for exploring high-grade metamorphic terrains, felsic gneiss complexes at granulite facies have long been considered barren and have remained undermapped and understudied. This was the case of the Bondy gneiss complex in the southwestern Grenville Province of Canada which consists of 1.39–1.35 Ga volcanic and plutonic rocks metamorphosed under granulite facies conditions at 1.19 Ga. Iron oxide–apatite and Cu-Ag-Au mineral occurrences occur among gneisses rich in biotite, cordierite, garnet, K-feldspar, orthopyroxene and/or sillimanite-rich gneisses, plagioclase-cordierite-orthopyroxene white gneisses, magnetite-garnet-rich gneisses, garnetites, hyperaluminous sillimanite-pyrite-quartz gneisses, phlogopite-sillimanite gneisses, and tourmalinites. Petrological and geochemical studies indicate that the precursors of these gneisses are altered volcanic and volcaniclastic rocks with attributes of pre-metamorphic Na, Ca-Fe, K-Fe, K, chloritic, argillic, phyllic, advanced argillic and skarn alteration. The nature of these hydrothermal rocks and the ore deposit model that best represents them are further investigated herein through lithogeochemistry. The lithofacies mineralized in Cu (±Au, Ag, Zn) are distinguished by the presence of garnet, magnetite and zircon, and exhibit pronounced enrichment in Fe, Mg, HREE and Zr relative to the least-altered rocks. In discrimination diagrams, the metamorphosed mineral system is demonstrated to exhibit the diagnostic attributes of, and is interpreted as, a metasomatic iron and alkali-calcic (MIAC) mineral system with iron oxide–apatite (IOA) and iron oxide copper–gold (IOCG) mineralization that evolves toward an epithermal cap. This contribution demonstrates that alteration facies diagnostic of MIAC systems and their IOCG and IOA mineralization remain diagnostic even after high-grade metamorphism. Exploration strategies can thus use the lithogeochemical footprint and the distribution and types of alteration facies observed as pathfinders for the facies-specific deposit types of MIAC systems. Full article

Red sandstones of the Cambrian age are globally distributed and represent an important sedimentation phase during this critical time interval. Their sedimentology and geochemistry can provide key information about the sedimentation style, paleoclimatic conditions, and weathering trends during the Cambrian. In the Salt Range of Pakistan, the Khewra Sandstone constitutes the Lower Cambrian strata and consists of red–maroon sandstones with minor siltstone and shale in the basal part. Cross-bedding, graded bedding, ripple marks, parallel laminations, load casts, ball and pillows, desiccation cracks, and bioturbation are the common sedimentary features of the formation. The sandstones are fine to medium to coarse-grained with subangular to subrounded morphology and display an overall coarsening upward trend. Petrographic analysis indicates that the sandstones are sub-arkose and sub-lithic arenites, and dolomite and calcite are common cementing materials. X-ray Diffraction (XRD) analysis indicates that the main minerals in the formation are quartz, feldspars, kaolinite, illite, mica, hematite, dolomite, and calcite. Geochemical analysis indicates that SiO₂ is the major component at a range of 53.3 to 88% (averaging 70.4%), Al₂O₃ ranges from 3.1 to 19.2% (averaging 9.2%), CaO ranges from 0.4 to 25.3% (averaging 7.4%), K₂O ranges from 1.2 to 7.4% (averaging 4.8%), MgO ranges from 0.2 to 7.4% (averaging 3.5%), and Na₂O ranges from 0.1 to 0.9% (averaging 0.4%), respectively. The results of the combined proxies indicate that the sedimentation occurred in fluvial–deltaic settings under overall arid to semi-arid paleoclimatic conditions with poor to moderate chemical weathering. The Khewra Sandstone represents the red Cambrian sandstones on the NW Indian Plate margin of Gondwana and can be correlated with contemporaneous red sandstones in the USA, Europe, Africa, Iran, and Turkey (Türkiye). Full article

Understanding mineral–fluid interactions in shale under supercritical CO₂ (scCO₂) conditions is relevant for assessing long-term geochemical containment. This study characterizes mineralogical transformations and elemental redistribution in five Caney Shale samples serving as proxies for reservoir (R1, R2, R3) and caprock (D1, D2) facies, subjected to 30-day static exposure to pure scCO₂ at 60 °C and 17.23 MPa (2500 psi), with no brine or impurities introduced. SEM-EDS analyses were conducted before and after exposure, with mineral phases classified into silicates, carbonates, sulfides, and organic matter. Initial compositions were dominated by quartz (38–47 wt.%), illite (16–23 wt.%), carbonates (12–18 wt.%), and organic matter (8–11 wt.%). Post-exposure, carbonate loss ranged from 15 to 40% in reservoir samples and up to 20% in caprock samples. Illite and K-feldspar showed depletion of Fe²⁺, Mg²⁺, and K⁺ at grain edges and cleavages, while pyrite underwent oxidation with Fe redistribution. Organic matter exhibited scCO₂-induced surface alteration and apparent sorption effects, most pronounced in R2 and R3. Elemental mapping revealed Ca²⁺, Mg²⁺, Fe²⁺, and Si⁴⁺ mobilization near reactive interfaces, though no secondary mineral precipitates formed. Reservoir samples developed localized porosity, whereas caprock samples retained more structural clay integrity. The results advance understanding of mineral reactivity and elemental fluxes in shale-based CO₂ sequestration. Full article

The lower sub-member of Member 2, Dongying Formation (Paleogene) in the HHK Depression hosts an extensively developed thin-bedded beach-bar system characterized by favorable source rock conditions and reservoir properties, indicating significant hydrocarbon exploration potential. Integrating drilling cores, wireline log interpretations, three-dimensional seismic data, geochemical analyses, and palynological data, this study investigates the sedimentary characteristics, sandbody distribution patterns, controlling factors, and genetic model of this lacustrine beach-bar system. Results reveal the following: (1) widespread thin-bedded beach-bar sandbodies dominated by fine-grained sandstones and siltstones, exhibiting wave ripples and low-angle cross-bedding; (2) two vertical stacking patterns, Type A, thick mudstone intervals intercalated with laterally continuous thin sandstone layers, and Type B, composite sandstones comprising thick sandstone units overlain by thin sandstone beds, both demonstrating significant lateral continuity; (3) three identified microfacies: bar-core, beach-core, and beach-margin facies; (4) key controls on sandbody development: paleoenvironmental evolution establishing the depositional framework, secondary fluctuations modulating depositional processes, strike-slip extensional tectonics governing structural zonation, paleobathymetry variations and paleotopography controlling distribution loci, and provenance clastic influx regulating scale and enrichment (confirmed by detrital zircon U-Pb dating documenting a dual provenance system). Collectively, these findings establish a sedimentary model for a thin-bedded beach-bar system under the strike-slip extensional tectonic framework. Full article

The Upper Carboniferous strata in the eastern Qaidam Basin, comprising several hundred meters of thick, mixed clastic–carbonate successions that have been little reported or explained, provide an excellent geological record of paleoenvironmental and paleo-sea level changes during the Late Carboniferous icehouse period. This tropical carbonate–clastic system offers critical constraints for correlating equatorial sea level responses with high-latitude glacial cycles during the Late Paleozoic Ice Age. Based on detailed outcrop observations and interpretations, five facies assemblages, including fluvial channel, tide-dominated estuary, wave-dominated shoreface, tide-influenced delta, and carbonate-dominated marine, have been identified and organized into cyclical stacking patterns. Correspondingly, four third-order sequences were recognized, each composed of lowstand, transgressive, and highstand system tracts (LST, TST, and HST). LST is generally dominated by fluvial channels as a result of river juvenation when the sea level falls. The TST is characterized by tide-dominated estuaries, followed by retrogradational, carbonated-dominated marine deposits formed during a period of sea level rise. The HST is dominated by aggradational marine deposits, wave-dominated shoreface environments, or tide-influenced deltas, caused by subsequent sea level falls and increased debris supply. The sequence stratigraphic evolution and geochemical records, based on carbon and oxygen isotopes and trace elements, suggest that during the Late Carboniferous period, the eastern Qaidam Basin experienced at least four significant sea level fluctuation events, and an overall long-term sea level rise. These were primarily driven by the Gondwana glacio-eustasy and regionally ascribed to the Paleo-Tethys Ocean expansion induced by the late Hercynian movement. Assessing the history of glacio-eustasy-driven sea level changes in the eastern Qaidam Basin is useful for predicting the distribution and evolution of mixed cyclic succession in and around the Tibetan Plateau. Full article

The Wangfu Fault Depression (WFD) is located in the southeastern uplift zone of the Songliao Basin and is an important geological site for studying tectonic evolution and volcanic stratigraphy. This study explores the complexity of the structure of the depression and the volcanic stratigraphy. The sedimentary sequence is divided into rift period and post-rift deposition, and the volcanic rocks are mainly concentrated in the Huoshiling Formation. Rhyolite deposits mark the bottom of the Yingcheng Formation. The volcanostratigraphic sequences are described by a detailed analysis of the seismic profiles, cutting samples, core data, geochemical, and well logging data, revealing the interaction between tectonic dynamics and volcanic activity. The volcanic facies are divided into vent breccia, pyroclastic, lava flow, and volcaniclastic sedimentary types, highlighting the diversity of depositional environments. In addition, the study identified key volcanic stratigraphic boundaries, such as eruptive and tectonic unconformities, which illustrate the alternation of intermittent volcanic activity with periods of inactivity and erosion. The study highlights the important role of faults in controlling the distribution and tectonic characteristics of volcanic rocks, and clearly distinguishes the western sag, middle slope, and eastern uplift zones. The chronostratigraphic framework supported by published U-Pb zircon dating elucidates the time course of volcanic and sedimentary processes, with volcanic activity peaking in the Early Cretaceous. Overall, the Wangfu Fault Depression is a dynamic geological entity formed by complex tectonic-volcanic interactions, providing valuable insights into the larger context of basin evolution and stratigraphic complexity. Full article

The Tankou area is a vital production capacity replacement area in the Jianghan oilfield. The recovery of the amount of erosion in Qianjiang Formation and Jinghezhen Formation is significant for studying this area’s tectonic evolution and geothermal history. The target layer, characterised by well-developed plastic materials, intense tectonic deformation, and insufficient well data, fails to meet the applicability criteria of the conventional denudation estimation methods. This study proposes a novel approach based on the structural strain characteristics. The method estimates the stratigraphic denudation by analysing residual formation features and fault characteristics. First, a stress analysis is performed using the fault characteristics, and the change law for the thickness of the target layer is summarised based on the characteristics of the residual strata to recover the amount of erosion in the profile. Second, a grid of the stratigraphic lines in the profiles of the main line and the tie line is used to complete the recovery of the amount of erosion in the plane through interpolation, and the results of the profile recovery are corrected again. Finally, the evolution results of the geological equilibrium method and the stress–strain analysis are compared to analyse the reasonableness of their differences and verify the accuracy of the erosion recovery results. The area of erosion in each layer increases from bottom to top. The amount of denudation in each layer gradually increases from the denudation area near the southern slope to the surrounding area. It converges to 0 at the boundary of the denudation area. The maximum amount of erosion is distributed in the erosion area close to the side of the residual layer with a low dip angle. The specific denudation results are as follows: Qian1 Member + Jinghezhen Formation has a denudation area of 6.3 km² with a maximum denudation thickness of 551 m; Qian2 Member has a denudation area of 2.6 km² with a maximum denudation thickness of 164 m; Qian3 Member has a denudation area of 2.3 km² with a maximum denudation thickness of 215 m; Upper Qian4 Submember has a denudation area of 1.54 km² with a maximum denudation thickness of 191 m; and Lower Qian4 Submember has a denudation area of 1.2 km² with a maximum denudation thickness of 286 m. This method overcomes the conventional denudation restoration approaches’ reliance on well logging and geochemical parameters. Using only seismic interpretation results, it achieves relatively accurate denudation restoration in the study area, thereby providing reliable data for timely analyses of the tectonic evolution, sedimentary facies, and hydrocarbon distribution patterns. In particular, the fault displacement characteristics can be employed to promptly examine how reasonable the results on the amount of denudation between faults are during the denudation restoration process. Full article

Serpentinite is a common lithology in Greece with significant geotectonic and petrogenetic implications, yet its archaeometric study remains limited. This also applies to the Ras serpentinite outcrop on Tinos Island—an enigmatic ancient quarry with no prior documentation of its exploitation. This study aims to provide a holistic provenance analysis and full material characterization to establish a unique fingerprint for future comparative research. A multidisciplinary methodology was applied, including petrography, XRD, FTIR, BET, LA-ICP-MS, electron microprobe analyses, and lichenometry—the latter used to estimate the quarry’s period of activity. The Ras serpentinite consists of a dark-green, brecciated lizardite matrix cut by a pale-green chrysotile network, and notably hosts the first recorded occurrence of minnesotaite in Greece. Relict antigorite within the matrix indicates high-pressure, high-temperature metamorphism preceding a greenschist facies overprint. Geochemical data classify the Ras occurrence as a subduction-related serpentinite derived from a depleted ultrabasic protolith. The aforementioned traits distinguish it from other Greek examples. Lichenometric analysis suggests the quarry was active in the 13th century A.D., with evidence of deliberate extraction techniques. These findings offer valuable insights into archaeometric studies and the provenance of serpentinites in the Aegean. Full article

The lower and middle Carboniferous shale sequences are one of the important potential hydrocarbon source rocks in the piedmont of the southwestern Tarim Basin, China (PSTB). Rock samples were collected from the lower and middle Carboniferous formations on the Kushanhe, Altash, and Aitegou outcrops in the PSTB with the intention of mapping the hydrocarbon molecules within these shale sources and disclosing the relevant geochemical implications. The ratios of Pr/Ph < 1.0 and DBT/P < 0.4 and the enrichment of C₂₃ tricyclic terpanoid indicate that the Carboniferous shale sources were deposited in a reducing and sulfate-poor marine setting with the contribution of terrestrial freshwater. Marine aquatic algae act as the major contributor, resulting in the formation of Type II₁ kerogen. The Carboniferous shale sequences contain abundant diamondoids with 2–4 cages with the predominance of methyldiamantanes, dimethyldiamantanes, and methyltriamantanes. Quantitative extended diamondoid analysis indicates the occurrence of carbonate-rich and carbonate-poor organic facies in the PSTB. Compared to the carbonate-poor facies, the carbonate-rich facies is relatively depleted in C₂₇ diasteranes and rich in gammacerane, C₂₇ regular steranes, and alkylated triamantanes. This indicates that it was deposited in the more salty and stratified water column but with less input of land higher plants. The clay catalysis effects are assumed to be responsible for the discrepancy in steranes and diamondoids. The Carboniferous shale sequences also contain abundant polycyclic aromatic hydrocarbons with 2–5 rings with the predominance of C_0–1-phenanthrenes, chrysenes, and benzofluoranthenes. Thermal maturity parameters associated with polycyclic aromatic hydrocarbons and diamondoids suggest that the Carboniferous shale sources have arrived at the late mature to highly mature stage. This study provides the detailed molecular fingerprints of the lower and middle Carboniferous shale source sequences and explores the underlying geochemical implications. This should be helpful for oil–oil and oil–source correlations and hence petroleum exploration activity in the PSTB. Full article

Cenozoic alkali-rich porphyries are widely distributed in the junction zone between the Sanjiang Orogenic belt and the Yangtze Plate. They are of great significance for understanding the regional geodynamics, tectonic evolution, and metallogenesis. However, the origin of these porphyries remains controversial. In this study, new petrological, geochemical, and geochronological data are presented for Cenozoic syenite porphyry from the Beiya porphyry Au-polymetallic deposit in western Yunnan. Zircon U-Pb dating results show that the Beiya syenite porphyries formed around 36.3–35.0 Ma, coinciding with the magmatic peak in the Jinshajiang-Red River (JSJ-RR) alkali-rich porphyry belt. Geochemical analyses indicate that the Beiya porphyries have potassic characteristics and an arc-like geochemical affinity, with C-type adakite affinity, suggesting a post-collisional setting. The JSJ-RR fault zone is unlikely to be the primary mechanism responsible for the formation of this alkali-rich porphyry magmatism. Instead, the development of the Beiya alkali-rich porphyries is likely associated with the convective removal of the lower part of the overthickened lithospheric mantle and asthenospheric upwelling during the Eocene–Oligocene. Their magmas probably originated from the partial melting of Paleo–Mesoproterozoic garnet amphibolite facies rocks in the thickened lower continental crust, with the addition of shoshonitic mafic magmas produced by the partial melting of metasomatized lithospheric mantle triggered by asthenospheric upwelling. This study provides additional reliable evidence to further constrain the origin of Cenozoic alkali-rich porphyries in the JSJ-RR belt. Full article

The interglacial period of the Cryogenian glaciation is a pivotal interval in geological history, marked by two “Snowball Earth” events and the emergence of early animals. Currently, there is considerable debate regarding the paleo-oceanic environment and the dominant factors controlling organic matter enrichment. Here, based on inorganic geochemical data and mineral composition from the Datangpo Formation in Xiangtan (South China), combined with previous research, we have analyzed the paleo-climate, redox condition, seawater restriction, and primary productivity across different sedimentary facies during this critical interval. The results exhibit that the Datangpo Formation can be divided into three members (Da1–Da3) based on lithology. Paleoclimatic proxies suggest the environment was relatively cold during the deposition of the Da-1 Member, while it was relatively warm and humid during the deposition of the Da 2–3 members. Compared to shallow water areas, deep-water areas experienced a more rapid transition in paleotemperature following the Sturtian glaciation event. Combining Mo-U elements, Ce_N/Ce*_N, and C_org/P ratios, the environment was characterized by an oxic environment during the early deposition period of the Datangpo Formation, then gradually transitioned to suboxic, and finally anoxic conditions. Furthermore, the decompression of terrestrial magma chambers led to intense volcanic/hydrothermal activity during the deglaciation period. Hydrothermal activity was most intense during the Da-1 depositional period, followed by Da-2, and gradually declined during Da-3 depositional period. Hydrothermal activity not only provided essential materials for the formation of Mn carbonate ores but also significantly enhanced the primary productivity by introducing large amounts of nutrients in the paleo-ocean. The primary productivity indicators (Ni/Al, Cu/Al) exhibited an obvious coupling with Ce_N/Ce*_N and C_org/P ratios in the Datangpo Formation, indicating that oxygen-rich environments were favorable for biological proliferation, thereby providing abundant organic matter. Anoxic conditions further facilitated the preservation of organic matter, which may be the primary factor driving organic matter enrichment in the Datangpo Formation. Full article

The Mun River watershed, a vital water resource in Northeastern Thailand and a major tributary of the Mekong River, faces significant water quality challenges driven by climate change and human activities. This study examines seasonal biogeochemical variations in the watershed, with a focus on how climate fluctuations affect water quality and geochemical processes. Water samples were collected from 19 surface sites during the dry and wet seasons of 2024 and analyzed for major dissolved ions. Using the geochemical mass balance method, we quantified rates of mineral weathering and biomass degradation. Our findings reveal a notable shift in hydrochemical facies from Na-Cl dominance in the dry season to Ca-HCO₃ dominance in the wet season, indicating reduced salinity and changes in geochemical conditions. Wet season mineral weathering rates averaged 300–700 µmol m⁻² d⁻¹, approximately 10–20 times higher than those in the dry season. The highest weathering and biomass degradation rates, ranging from 900 to 1200 µmol m⁻² d⁻¹, were observed in the northern subwatersheds, likely due to intensified agricultural practices and underlying geological conditions. These results highlight the urgent need for adaptive watershed management strategies to address the growing impact of climate change on regional water quality. Full article

This study focuses on the Fourque massif, one of the thirty Variscan plutons outcropping along the Axial zone of the Pyrenees. It hosts a significant tungsten deposit that was actively mined until 1986. However, since the closure of the mine, no detailed geochemical or geochronological studies have been conducted until recent investigations in 2019, leaving a significant gap in our understanding of this intrusion. This lack of research, along with the ongoing debate and uncertainties regarding the timing and magmatic processes of Variscan plutonism in the Pyrenees, underscores the importance of further investigations. To address these gaps, we present new zircon U–Pb geochronology, whole-rock and zircon geochemistry (X-ray fluorescence and LA-ICP-MS), and Ti-in-zircon thermometry. Our study compares nine new whole-rock geochemistry samples with the limited previous dataset from 1987, refining the petrogenetic interpretation of the intrusion. These efforts are framed within the ongoing debate surrounding the different Variscan intrusions in the Pyrenees, including the discussions on their emplacement age, magmatic context, type, and origin. Geochronological data indicate an age ranging from 304.6 ± 2.3 to 308.4 ± 2.6 Ma, with crystallization temperatures ranging from 700 to 800 °C. The granodiorite is characterized by differentiated petrogenetic facies, related to successive batches of magma rising from a deeper source. The granodiorite exhibits high ASI ratios (>1.3), classifying it as strongly peraluminous. While I-type granites are typically metaluminous to weakly peraluminous, such elevated ASI values suggest a significant influence of crustal assimilation during magmatic evolution. The geochemical signature of the intrusion is enriched in large ion lithophile elements (LILE) and light rare earth elements (LREEs) while showing depletion in heavy rare earth elements (HREEs), consistent with a high-K calc-alkaline, magnesian, syn-orogenic setting. Whole-rock and zircon trace element data suggest that the magma source involved partial melting of the continental crust, with evidence of interaction with a subduction-modified mantle component. By applying methods previously unapplied to this pluton, this study provides new data on its geochemistry and geochronology, revealing significant differences from previous interpretations. These findings offer deeper insights into the emplacement and evolution of the Fourque granodiorite, refining its role within the broader context of Variscan orogenesis in the Pyrenean Axial Zone and similar plutonic systems worldwide. Full article

Understanding the characteristics of groundwater chemistry is essential for water resource development and utilization. However, few studies have focused on the chemical evolution processes of shallow groundwater in typical areas of the Huaibei Plain. We analyzed 28 water samples from the study area using hydrogeochemical mapping, multivariate statistical analysis, and other approaches. The study found that the hydrogeochemical facies of groundwater are mainly HCO₃-Ca·Mg (64.3%), mixed SO₄·Cl-Ca·Mg, and SO₄·Cl-Na. The hydrochemical composition is primarily controlled by natural water–rock interactions, including carbonate weathering and cation exchange processes. Correlation analysis and principal component analysis (PCA) revealed that mineral dissolution was the predominant source of Na⁺, Mg²⁺, Cl⁻, and SO₄²⁻ in shallow groundwater, significantly contributing to total dissolved solids (TDS) accumulation. Hierarchical cluster analysis (HCA) identified three characteristic zones: (1) agricultural/urban-influenced areas, (2) high-F⁻/low-hardness zones, and (3) nitrate-contaminated regions. These findings provide critical insights for assessing the geochemical status of groundwater in the Huaibei Plain and formulating targeted resource management strategies. Full article