Search Results (745)

Unauthorized fossil trafficking violates national legislation and deprives cultural and natural heritage. This study proposes a pilot method to fingerprint the origin of fossils by characterizing the carbon and oxygen stable isotope signatures of fossil-bearing limestones to provide a non-destructive quantitative tool against illegal fossil trade. This promising approach has been applied to the Crato Formation (NE Brazil), which is a renowned Lower Cretaceous fossiliferous lacustrine limestone. This study aims at establishing the range of isotopic oxygen (δ¹⁸O) and carbon (δ¹³C) values of the Crato Formation’s laminated calci-mudstone by compiling isotopic data from previous studies, conducting new analyses, and comparing with other fossiliferous lacustrine limestones from Brazil (Cretaceous Codó Formation) and the USA (Eocene Green River Formation). This preliminary evaluation determined a distinctive isotopic signature of the Crato Formation fossil-bearing “sete cortes” (“seven cuts”) ethnostratum, with VPDB δ¹⁸O and δ¹³C arithmetic means of −5.94‰ and +0.90‰, standard deviations 0.76‰ and 0.61‰, medians of −5.89‰ and +0.73‰, and interquartile ranges of 1.47‰ and 1.24‰, respectively. This pilot investigation establishes a methodological groundwork for the development of a global database integrating lithofacies and geochemical parameters of fossil-bearing limestones to expedite the identification and restitution of illegally extracted paleontological heritage. Full article

Hydrothermal fluids altered Mississippian (Osagian) carbonates in the Rebecca K. Bounds (RKB) core in western Kansas, U.S.A. Carbonate mineralization is similar to that associated with Mississippian valley type (MVT) mineralization. The RKB core displays fractures, vugs, channels, and breccias filled with saddle dolomite and blocky calcite cements. Homogenization temperature indicates that dolomite (65 to 126 °C, 18.4 to 23 wt. % NaCl) and calcite (67 to 101 °C, 13.2 to 22.4 wt. % NaCl) cements were precipitated by hot, saline fluids. These data are consistent with previous studies on the southern midcontinent. Carbon and oxygen isotope values for dolomite (δ¹³C 0.15 to 2.08‰, δ¹⁸O −6.44 to −4.66‰) and calcite (δ¹³C −1.01 to 1.79‰, δ¹⁸O −9.44 to −8.69‰) indicate multiple pulses of fluids likely sourced from basins to the south and west. Strontium isotopes data (0.7088812 to 0.7094432 in dolomite and 0.7089503 to 0.7111501 in calcite) indicate fluid interaction with granitic basement or basement-derived siliciclastics. These results are consistent with mixing of upwelling Ordovician-sourced fluids and Permian evaporitic brines, transported by advective and/or vertical migration. Although sulfide minerals were not observed in this study, earlier reports in western Kansas document sphalerite linked to hydrothermal brines in underlying strata. This study highlights the potential for MVT mineralization in the Mississippian of western Kansas. Full article

The rise in sea levels due to global warming and the excessive extraction of groundwater in coastal regions significantly encourages seawater intrusion, resulting in a cascade of ecological and environmental issues, including water quality degradation and soil salinization. The northern sector of Laizhou City, situated on the eastern coast of Laizhou Bay, exemplifies a typical location of seawater intrusion in China, where the rising salinity of groundwater has adversely affected local economic development and public health. This investigation involved the collection of 115 groundwater samples and 13 isotope samples from the northern region of Laizhou City. Statistical analysis, Piper’s trilinear diagrams, and various analytical techniques were employed to examine the chemical properties of the groundwater in the study area; characteristic ion ratios, Gibbs diagram, and hydrogen–oxygen isotope methods were utilized to analyze the sources of salinity and groundwater recharge; and a seawater intrusion groundwater quality index, which was applied to the present condition of seawater intrusion, was assessed utilizing the seawater intrusion groundwater quality index (GQI_SWI). The findings indicate that the chemical composition of groundwater in the research area is notably intricate. From freshwater to saline water, the groundwater chemistry transitions from Ca-HCO₃·Cl-type water to Ca·Na-SO₄·Cl-type water, and finally to Na-Cl-type water. Seawater intrusion in the research area is the primary cause of elevated groundwater salinity, alongside cation exchange and water–rock interactions that affect water chemistry. Seawater intrusion is predominantly focused in the northern region of the research area. The primary source of groundwater recharge is atmospheric precipitation. Full article

This study investigates geothermal waters in the Xinjiang region through hydrogeochemical methods, including cluster analysis, ionic ratios, and isotopic analysis. Cluster analysis categorized the geothermal water samples into three distinct groups (G1, G2, and G3). The predominant hydrochemical facies are SO₄-HCO₃-Na, SO₄-Cl-Na, and Cl-Na types, whose formation is controlled by multiple factors. Evidence from molar ratios of major ions suggests that geothermal waters in Group G1 are predominantly governed by water–rock interactions, whereas Groups G2 and G3 are mainly influenced by evaporative concentration. Hydrogen and oxygen isotopic signatures confirm that meteoric water serves as the primary recharge source for these geothermal waters. The spatial correlation between regional tectonic features and most geothermal discharge points demonstrates a consistent relationship between geothermal water occurrence and structural distribution in Xinjiang. Additionally, a conceptual circulation model is proposed wherein meteoric water undergoes deep circulation following local recharge, ascends along fault zones under tectonic pressure, and mixes with shallow groundwater. This research primarily elucidates the hydrogeochemical characteristics and recharge mechanisms of geothermal resources in Xinjiang, thereby providing a scientific basis for their future development and utilization. Full article

Skarn-type iron ore is economically significant, and numerous skarn ore deposits have been identified in the North China Craton. The newly discovered orbicular diorite in this region is distinguished from other analogous rocks due to the accumulation of large magnetite particles, which may shed new light on the genesis of this ore type. The magnetite in different parts of the orbicular structure exhibits distinct compositional differences. For example, magnetite at the edge has a small particle size (200 μm) and is associated with the minerals plagioclase and hornblende, indicating that it crystallized from normal diorite magma. By contrast, magnetite in the core has a relatively large particle size (>1000 μm), is associated with apatite and actinolite, and contains apatite inclusions as well as numerous pores. The size of magnetite in the mantle falls between that of the edge and the core. The syngenetic minerals of magnetite in the mantle include epidote and plagioclase. The magnetites in the cores of orbicules have a higher content of Ti, Al, Ni, Cr, Sc, Zn, Co, Ga, and Nb than those in the rim. The δ⁵⁶Fe value of the core magnetite (0.46‰–0.78‰) is much higher than that of the mantle and rim magnetite in orbicules. Moreover, the δ⁵⁶Fe value of magnetite increases as the V content of magnetite gradually decreases. This large iron isotope fractionation is likely driven by liquid immiscibility that forms iron-rich melts under high oxygen fugacity. The reaction between magma and carbonate xenoliths (Ca, Mg)CO₃ during magma migration generates abundant CO₂, which significantly increases the oxygen fugacity of the magmatic system. Under the action of CO₂ and other volatile components, liquid immiscibility occurs in the magma chamber, and Fe-rich oxide melts are formed by the melting of carbonate xenoliths. Iron oxides (Fe₃O₄/Fe₂O₃₎ will crystallize close to the liquidus due to high oxygen fugacity. These characteristics of magnetite in the Tanling orbicular diorite (Wuan, China) indicate that diorite magma reacts with carbonate xenoliths to form “Fe-rich melts”, and skarn iron deposits are probably formed by the reaction of intermediate-basic magma with carbonate rocks that generate such “Fe-rich melts”. A possible reaction is as follows: diorite magma + carbonate → (magnetite-actinolite-apatite) + garnet + epidote + feldspar + hornblende + CO₂↑. Full article

By employing thin section analysis, scanning electron microscopy (SEM), homogenization temperatures of fluid inclusions, and carbon–oxygen isotope analysis of carbonate cements, this study conducted a temporal-quantitative investigation into the porosity evolution of relatively high-quality reservoirs in the Second Member of the Xujiahe Formation (Xu-2 Member) in the Xinchang area of western Sichuan. The analysis focused on quantifying porosity loss due to compaction, cementation, and porosity enhancement from dissolution. Results indicate that compaction exerted the most significant impact on reservoir quality in the Xu-2 Member, causing over 70% of total porosity loss. Cementation processes, including carbonate cements, silica cements, and authigenic chlorite, further degraded reservoir properties. Authigenic chlorite precipitated earliest at burial depths of 600–800 m, while authigenic quartz and carbonate cements persistently affected the reservoir at depths of 2000–5000 m, reducing porosity by at least 10% (up to 21%). Dissolution processes initiated at approximately 3500 m burial depth, generating secondary porosity of ≥2%, with a maximum increase of 16%. Integrating these findings with the natural gas accumulation history, the coupling relationship between pore evolution and gas accumulation was elucidated. The study reveals that reservoir tightness in the Xu-2 Member developed at burial depths of 4050–5300 m, with large-scale gas accumulation predominantly occurring prior to reservoir densification. The findings provide critical guidance for identifying high-quality tight sandstone reservoirs and optimizing exploration targets in the Xu-2 Member of the Xinchang area, Western Sichuan Basin, thereby supporting efficient development of regional tight gas resources. Full article

Seawater intrusion into coastal river systems poses increasing challenges for freshwater availability and estuarine ecosystem integrity, especially under evolving climatic and anthropogenic pressures. This study presents a multidisciplinary investigation of marine intrusion dynamics within the Magra River estuary (Northwest Italy), integrating field monitoring, isotopic tracing (δ¹⁸O; δD), and multivariate statistical modeling. Over an 18-month period, 11 fixed stations were monitored across six seasonal campaigns, yielding a comprehensive dataset of water electrical conductivity (EC) and stable isotope measurements from fresh water to salty water. EC and oxygen isotopic ratios displayed strong spatial and temporal coherence (R² = 0.99), confirming their combined effectiveness in identifying intrusion patterns. The mass-balance model based on δ¹⁸O revealed that marine water fractions exceeded 50% in the lower estuary for up to eight months annually, reaching as far as 8.5 km inland during dry periods. Complementary δD measurements provided additional insight into water origin and fractionation processes, revealing a slight excess relative to the local meteoric water line (LMWL), indicative of evaporative enrichment during anomalously warm periods. Multivariate regression models (PLS, Ridge, LASSO, and Elastic Net) identified river discharge as the primary limiting factor of intrusion, while wind intensity emerged as a key promoting variable, particularly when aligned with the valley axis. Tidal effects were marginal under standard conditions, except during anomalous events such as tidal surges. The results demonstrate that marine intrusion is governed by complex and interacting environmental drivers. Combined isotopic and machine learning approaches can offer high-resolution insights for environmental monitoring, early-warning systems, and adaptive resource management under climate-change scenarios. Full article

This paper comprehensively reports experimental proof of parity violation in the ground and photoexcited states of three mirror-symmetric Si–Si bond polymers in homogeneous solutions of achiral molecules under non-stirring conditions by analyzing 370 chiroptical datasets relating to multiple second-order helix–helix transitions in the circular dichroism (CD) of poly(di-i-butylsilane) (iBS), poly(di-i-pentylsilane) (iPS), and poly(di-i-hexylsilane) (iHS) in achiral alkanols and p-dioxane-h₈/-d₈. Particularly large (–)-CD of g_abs = −3.1 × 10⁻² at 290 nm was found for iBS in i-pentanol at 25 °C. Notably, iPS in n-propanol at −5 °C generated (–)-CD with g_abs = −0.48 × 10⁻² at 300 nm, but (+)-circularly polarized luminescence (CPL) with g_lum = +0.84 × 10⁻² at 326 nm. In contrast, iHS in n-octanol at 0 °C showed only very weak (–)-CD of g_abs ~−0.03 × 10⁻² at 310 nm. The H/D isotopes of p-dioxane-h₈/-d₈ weakly affected the helix–helix transition characteristics of iBS. (–)-Sign vibrational CD signals assigned to the handed symmetric and asymmetric bending modes of the CH₃ and CH₂ groups of the solvents and other achiral molecules were observed. We assumed (i) three ¹H nuclear-spin-1/2 induced handed motions of CH₃ rotors at i-alkyl side chains and achiral alkanols, and (ii) helical main-chain Si atoms (δ⁺) coordinated by handed lone pairs at oxygen (δ⁻) in gauche-containing n- and i-alkanols induced by the CH₃ rotors. A possible origin of biomolecular handedness is proposed based on the first observation of far-UV CD and UV spectra of zwitterionic glycine bearing H₃N⁺ rotor in neutral H₂O. Full article

The Dulong Sn-polymetallic deposit in Yunnan Province of southwestern China serves as a unique case study for unraveling the evolution of skarn systems and tin mineralization. Four distinct garnet types (Grt I to Grt IV) were classified based on petrographic observations. Compositional analysis reveals a progression from Grt I to Grt III, marked by increasing andradite components, and elevated tin concentrations, peaking at 5039 ppm. These trends suggest crystallization from Sn-enriched magmatic-hydrothermal fluids. In contrast, Grt IV garnet exhibits dominant almandine components and minimal tin content (<2 ppm). Its association with surrounding rocks (schist) further implies its metamorphic origin, distinct from the magmatic origin of the other garnet types. Combined with previously published sulfur and lead isotopic data, as well as trace element compositions of garnet, our study suggests that Laojunshan granites supply substantial ore-forming elements such as S, Pb, W, Sn, In, and Ga. In contrast, elements such as Sc, Y, and Ge are inferred to be predominantly derived from, or buffered by, the surrounding rocks. The geochemical evolution of the garnets highlights the critical role of redox fluctuations and fluid chemistry in controlling tin mineralization. Under neutral-pH fluid conditions, early-stage garnets incorporated significant tin. As the oxygen fugacity of the ore-forming fluid declined, cassiterite precipitation was triggered, leading to tin mineralization. This study reveals the interplay between fluid redox dynamics, garnet compositional changes, and mineral paragenesis in skarn-type tin deposits. Full article

It is generally believed that the ancient oceans during the “boring billion” (1.85–0.8 Ga) lacked the capacity to form large-scale iron formations (IFs), though localized small-scale IFs deposition persisted. The Altyn region of China hosts abundant IFs, with the Dimunalike IFs being the largest and most representative, characterized by typical banded iron–silica layers. Detailed fieldwork identified a tuff layer conformably contacting the IFs at the roof rocks of IFs and a ferruginous mudstone layer at the floor rocks of IFs in drill core ZK4312. Geochemical and zircon U-Pb-Hf isotopic analyses were performed. The tuff has a typical tuff structure, mostly made of quartz, and contains a significant amount of natural sulfur. It also has high SiO₂ content (77.90%–80.49%) and sulfur content (0.78%–3.06%). The ferruginous mudstone has a volcanic clastic structure and is mainly composed of quartz and chlorite, with abundant coeval pyrite. It shows lower SiO₂ content (53.83%–60.32%) and higher TFe₂O₃ content (10.29%–16.24%). Both layers share similar rare earth element (REE) distribution patterns and trace element compositions, with light REE enrichment and negative Eu, Nb, and Ti anomalies, consistent with arc volcanic geochemistry. Zircon U-Pb ages indicate crystallization of the tuff at 1102 ± 13 Ma and maximum deposition of the mudstone at 1110 ± 41 Ma. These data suggest formation during different stages of the same volcanic–sedimentary process. The ε_Hf(t) values (3.60–12.35 for tuff, 2.92–8.19 for mudstone) resemble those of Algoma-type IF host rocks, implying derivation from re-melted new crust. The Dimunalike IFs likely formed in a submarine volcanic–sedimentary environment. In conclusion, although the Mesoproterozoic ocean was generally in a low-oxygen state, which was not conducive to large-scale IF deposition, localized submarine volcanic–hydrothermal activity could still lead to IF formation. Full article

The 1.1 Ga Mesoproterozoic Midcontinent rift hosts the Eagle, Eagle East, and Tamarack Ni-Cu-PGE deposits and Embayment Prospect. These deposits are hosted by ultramafic igneous rocks and have some of the highest Ni-Cu grades on Earth. We use new bulk-rock data and published datasets (bulk-rock, mineral chemistry, and isotopic analyses) to examine major, minor, and trace element trends of both Midcontinent rift-related alkaline and tholeiitic intrusions. In addition, we compare the geochemical data to local kimberlite-hosted lower-crustal xenoliths and local igneous (Archean) and sedimentary (Paleoproterozoic) country rocks. We found the peridotite magma compositions dominantly consist of primitive mantle compositions with varying abundances of subduction-related components, alkaline-transitional melts, and local country rock contaminates (e.g., Baraga and Animikie Basin sediments). The subduction-related components are interpreted to be derived from previous Archean and Paleoproterozoic subduction events and likely hosted within the sub-continental lithospheric mantle. Importantly, these subduction-related components are also interpreted to have acted as oxidizing agents within the melt, stabilizing sulfate (+2 FMQ (fayalite–magnetite–quartz) to FMQ) while inhibiting sulfide crystallization as the magma ascended through ~50 km of the Superior craton. This study largely corroborates the previous findings with respect to the contribution of local country rock contamination to the Eagle–Tamarack peridotite host rocks, which is estimated to be minimal (<5%). However, the incorporation of <5% reductive pelitic siltstone contamination results in strong shifts in the oxygen fugacity of the peridotite melt, from +2 FMQ to slightly below FMQ, as determined from spinel Fe³⁺/∑Fe ratios. This shift in oxygen fugacity resulted in the transition from total sulfate (+2 FMQ) to sulfate + sulfide (<+2 FMQ to FMQ) to total sulfide (<FMQ). This shift in oxygen fugacity is a key contributor to the formation of Ni-Cu-PGE-rich massive sulfides within the Eagle peridotite. This study presents an expanded geochemical interpretation for the exploration of Midcontinent rift-related Ni-Cu-PGE deposits to include peridotites with subduction-like signatures and contaminated via <5% reductive sedimentary country rocks. Full article

This study investigates geothermal clusters in the middle reaches of the Dawen River Basin, focusing on the developmental characteristics and genetic mechanisms of typical geothermal water exposures at key sites, including Daidaoan (Taishan), Qiaogou (Culai Town), and Anjiazhuang (Feicheng). Utilizing hydrogeochemical and environmental isotope analyses, we identify a dual groundwater recharge mechanism: (1) rapid infiltration via preferential flow through fissure media and (2) slow seepage with evaporative loss along gas-bearing zones. Ion sources are influenced by water–rock interactions and positive cation exchange. The hydrochemical types of surface water and geothermal water can be divided into five categories, with little difference within the same geothermal area. The thermal reservoir temperatures range from 53.54 to 101.49 °C, with the Anjiazhuang and Qiaogou geothermal areas displaying higher temperatures than the Daidaoan area. Isotope calculations indicate that the recharge elevation ranges from 2865.76 to 4126.69 m. The proportion of cold water mixed in the shallow part is relatively large. A comparative analysis of the genetic models of the three geothermal water groups shows that they share the common feature of being controlled by fault zones. However, they differ in that the Daidao’an geothermal area in Mount Tai is of the karst spring type with a relatively low geothermal water temperature, whereas the Qiaogou geothermal area in Culai Town and the Anjiazhuang geothermal area in Feicheng are of the gravel or sandy shale spring types with a relatively high geothermal water temperature. Full article

Deep carbonate reservoirs have garnered significant attention and demonstrated great potential for oil and gas exploration in recent years. The Majiagou Formation in the Ordos Basin has received much attention for its deep oil and gas deposits recently. However, the issue of fluid evolution within the great depth has been overlooked, and the relationship between fluid flow and the gas accumulation process remains unclear. This paper aims to explore the fluid evolution and its relationship with the gas accumulation, which poses a challenge for further petroleum exploration. To achieve this, petrological studies on dolomite samples were carried out and four types of secondary cements were identified: early gypsum-moldic pore-filling calcite, late gypsum-moldic pore-filling calcite, dissolution pore-filling calcite and fracture-filling calcite. Subsequently, an interdisciplinary approach that integrates petrography observation, microthermometry, laser Raman analysis of fluid inclusions, and carbon and oxygen isotope tests on these types of cements is employed to elucidate the fluid flow evolution. These investigations revealed that four different stages of inorganic fluid activity were coeval with two stages of organic fluid activity. The two stages of organic fluid flows were significantly important for petroleum accumulation. In the late Triassic to early Jurassic, there was small-scale liquid oil accumulation, which was associated with the second stage of fluids. In the early Cretaceous, there was large-scale gas accumulation, which was associated with the fourth stage of fluids. This research is crucial for understanding the fluid flow process and its relationship with hydrocarbon accumulation in deeply buried carbonate formations. Full article

The Xiaobaihegou fluorite deposit is located in the southwest of the Altyn-Tagh Orogen, NW China. However, the provenance, thermodynamic properties, and enrichment mechanisms of the ore-forming fluids in this deposit remain unclear. Fluorite mineralization primarily occurs in the vicinity of the contact zone between the granite and the wall rocks. The zircon U-Pb age of the alkali-feldspar granite in the Xiaobaihegou fluorite deposit is 482.3 ± 4.1 Ma. The ore-hosting lithologies are mainly calcareous rock series of the Altyn Group. The ore bodies are controlled by NE-trending faults and consist primarily of veined, brecciated, massive, and banded ores. The ore mineral assemblage is primarily composed of calcite and fluorite. The rare earth element (REE) patterns of fluorite and calcite in the Xiaobaihegou deposit exhibit right-dipping LREE enrichment with distinct negative Eu anomalies, which closely resemble those of the alkali-feldspar granite. This similarity suggests that the REE distribution patterns of fluorite and calcite were likely inherited from the pluton. The ore-forming process can be divided into an early stage and a late stage. The massive ores formed in the early stage contain mainly gas-rich two-phase fluid inclusions and CO₂-bearing three-phase inclusions, with homogenization temperatures ranging from 235 °C to 426 °C and salinities from 28.59% to 42.40% NaCl equivalent. In the late stage, brecciated and stockwork ores were formed. They host liquid-rich two-phase and gas-rich two-phase fluid inclusions, with homogenization temperatures ranging from 129 °C to 350 °C and salinities from 0.88% to 21.61% NaCl equivalent. The results of hydrogen and oxygen isotope studies indicate that the ore-forming fluids were derived from a mixture of magmatic–hydrothermal and meteoric water. Fluorite precipitation in the early stage was mainly due to the mixing of magmatic–hydrothermal solution and meteoric water, as well as a water–rock reaction. In the late stage, fluid mixing further occurred, resulting in a decrease in temperature and the formation of brecciated and stockwork ores. The ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios of fluorite from the deposit range from 0.71033 to 0.71272 and 0.511946 to 0.512073, respectively, indicating that the ore-forming material originates from the crust. Based on the ore-forming characteristics, it is proposed that Ca may be primarily leached from the strata formation, while F may predominantly originate from magmatic–hydrothermal solutions. The formation of fluorite deposits is closely related to the transition of the Central Altyn-Tagh Block and Qaidam Block from a compressional orogenic environment to an extensional tectonic environment. Full article

The Mid-Piacenzian Warm Interval (MPWI) is marked by warmer temperatures and higher atmospheric CO₂ levels than today, making it an analogue for late-21st-century-warming, whereas the early Pleistocene cooling is more like today. We compare seasonal growth temperatures derived from oxygen isotope ratios (δ¹⁸O) and clumped isotopes (∆₄₇) in Mercenaria. Modern shells were previously collected from coastal NC. The fossil shells are from the Duplin (MPWI) and Waccamaw Formations (early Pleistocene), NC. Oxygen isotope ratios range from −2.2‰ to 2.3‰ (modern), −0.9‰ to 2.4‰ (MPWI), and −0.9‰ to 2.9‰ (early Pleistocene). The values of Δ₄₇ range from 0.576‰ to 0.639‰ (modern), 0.566‰ to 0.621‰ (MPWI), and 0.581‰ to 0.615‰ (early Pleistocene). We show that Mercenaria do not require a species-specific ∆₄₇ calibration. Modern and MPWI ∆₄₇-derived summer/winter temperatures (SST_∆47) and seasonal amplitudes are indistinguishable from δ¹⁸O-derived temperatures. The early Pleistocene summer SST_∆47 is indistinguishable from δ¹⁸O-derived temperatures, but the winter SST_∆47 is warmer by 5 °C and may reflect within-shell time averaging. The modern summer/winter SST_∆47 are indistinguishable from the MPWI, but the MPWI has a lower seasonal amplitude by 5 °C. Compared to our calculated δ¹⁸O_sw values, modeled values for the MPWI are within error but are much lower, and they are not within error for the early Pleistocene. Full article