Journal of Asian Earth Sciences最新文献

The Potwar Basin (PTB) is a prominent geological feature located in northern part of Pakistan, and is considered as one of the active and productive regions for petroleum and gas exploration in Pakistan. In this study, eight crude oil specimens originating from three distinct fields within the PTB were comprehensively examined to decipher the environmental conditions, source of organic matter (OM) and oil-oil correlations using gas chromatography coupled with flame ionization detection (GC-FID) and gas chromatography-mass spectrometry (GC–MS). The molecular marker and hierarchical cluster analysis of PTB oils reveal two different crude oil families. Family-I showed relatively low values of Pr/Ph, C₁₉TT/C₂₃TT and C₂₅TT/C₂₄TeT, C₂₇-C₂₉ regular steranes, dibenzothiophene (DBT), fluorene (FL) and dibenzofuran (DBF), as well as C₂₆/C₂₈ TAS (20S) and C₂₇/C₂₈ TAS (20R). These results suggest that Family-I crude oils derived from marine environment of suboxic water bodies with higher contribution from green algae or planktonic microbes. However, Family II contains comparatively high values of the aforementioned molecular parameters, indicating that crude oils mainly originated from a lacustrine environment with a higher contribution of plant organisms under oxidizing conditions. Saturated hydrocarbon maturity parameters such as CPI and OEP, and C₃₁22S/(C₃₁22S + C₃₁22R) and C₃₂22S/(C₃₂22S + C₃₂22R) indicate PTB crude oils are thermally mature, while aromatic indices reveal that Family-II crude oils are high mature. The present research defines that PTB crude oils contributed from mixed organic matter sources of marine and lacustrine majorly from marine sedimentary environment with the bloom of algae and/or higher plants.

A new alkenone sea surface temperature (SST) record from the South China Sea (SCS) over the last 170 ka has been reported here. Our analysis of magnetic susceptibility and AMS ¹⁴C dating on the top portion of the core suggests that this record dates to the Marine Isotope Stage (MIS) 6. As indicated in Termination I and II, SST changes are correlated with clear glacial/interglacial cycles and likely dominated by atmospheric CO₂ and Western Pacific Warm Pool temperature changes. But the two Terminations were different in magnitude. In Termination I, the minimum and maximum SSTs are 24.5 °C and 27.5 °C, respectively, showing a smaller rise (3 °C) than in Termination II (24–28.3 °C). The n-alkane indices, such as average chain length (ACL) and carbon preference index (CPI), exhibited high/low values during glacial/interglacial periods, and possible more arid climate during MIS 6 than MIS 2. During Termination II, the maximum surface warming in the SCS is accompanied by a progressive lag of approximately 7000 years in relation to maximum summer insolation until Termination I, when they are nearly synchronous. According to the study, SSTs are continuously changing and are influenced by solar insolation, global ice volume changes, and ocean–atmosphere interactions across hemispheres.

Sediments in the muddy areas of marginal seas of East China can serve as natural archives of global climate and environmental changes. Studies of these sediments can offer valuable insights for paleoclimate changes. This study examined S04-2, a core located in the central of the inner-shelf muddy area of the East China Sea, to reveal the evolutionary history since 12 ka BP and investigate the relationship between the East Asian Winter Monsoon (EAWM) and East Asian Summer Monsoon (EASM). On a centennial timescale, the EASM was negatively correlated with EAWM and this relationship is mainly influenced by solar radiation, wherein increases or weakening of solar radiation led to a negative or positive correlation between the EASM and EAWM. Additionally, it was observed that the sustained negative correlation during the periods of 5.1–4.3 ka BP and 2.0–0.6 ka BP was modulated by the strong North Atlantic Oscillation (NAO), resulting in periods of heightened social sensitivity in ancient China during 2.0–0.6 ka BP.

The Tibetan Plateau hosts the majority of porphyry Cu deposits in China. There are two large metallogenic belts, the Gangdese and Bangong-Nujiang belts, in the Lhasa Terrane, Central Tibet. The Lhasa Terrane experienced multistage magmatic activity from the Mesozoic to Cenozoic, and the subaerial volcanic areas of the western part of the terrane are regarded as favorable targets of porphyry Cu deposits. In this paper, we describe the geology of our newly identified Early Cretaceous Suolong Cu-rich porphyry in the western Lhasa Terrane and present new U–Pb ages, trace element and Hf isotopic compositions of zircon and whole-rock elemental and Sr–Nd isotopic compositions. The Suolong porphyry contains zircon grains with ages ranging from 136 to 135 Ma, ε_Hf(t) values ranging from −1.5 ∼ +2.7 and logfO₂ values ranging from −16.27 ∼ −9.92. Geochemically, the porphyry rocks are peraluminous in nature, with whole-rock ε_Nd(t) values of −5.7 ∼ −5.4. We infer that the Suolong porphyry originated from a mixture of ∼53 % enriched lithospheric mantle and ∼47 % ancient lower crustal melt, triggered by the roll-back of the northward-subducting Neo-Tethyan Ocean. The conditions of high oxygen fugacity and water content and tectonic transition promoted the formation of the Suolong Cu-rich porphyry, but the condition of a thinned crust may have constrained the mineralization scale of the Cu deposits. This new identification of Early Cretaceous mineralization event provides important clues for identifying new potential exploration targets for porphyry Cu deposits in the western segment of the Lhasa Terrane.

The present study is aimed at understanding the sub-decadal to decadal scale variability of rainfall in southern India based on a sedimentary record (dated using AMS ¹⁴C, ²¹⁰Pb, ¹³⁷Cs methods) from Madagadakere lake (MK) situated in the foothills of the Western Ghats. A strong linkage between sediment magnetic signature and the instrumental rainfall record for the past 115 years demonstrates that the environmental magnetic proxies are useful and have greater applicability in the paleomonsoonal reconstructions. Fluctuations in the mineral magnetic, grain size, and geochemical parameters of the studied sediment profile revealed that pedogenic activity and terrigenous sediment flux to the lake varied cyclically during the Late Holocene period in response to varying intensities of rainfall. The region experienced higher or increasing trend of rainfall during periods 2100–1900, 1600–1250, 1050–925, 680–600, and 350–270 cal. years B.P., with low rainfall/decreasing trend during intervening periods. The spectral analysis of magnetic parameters revealed significant periodicities of 291, 164, 101, 54, 48, 44, 41, 39, 105, 48, and 41 years, which are very well documented in other paleoclimatic records, and whose origin is ascribed unequivocally to variation in Total Solar Irradiance (TSI). We propose that the periods of higher values for concentration-dependent magnetic parameters (higher rainfall) can be attributed to the timings of the increased TSI, positive mode of Indian Ocean Dipole (IOD), northward migration of Intertropical convergence zone (ITCZ) and weakened El-Niño southern oscillation (ENSO) activity in the region, establishing the teleconnection between different climatic systems.

During the Cenozoic, the eastern Sakarya Zone, northeastern Turkey, has witnessed voluminous Eocene and subsidiary Miocene magmatism. By contrast, except in one previous study, Oligocene magmatism has not been reported. Here, we present new data about an Oligocene dyke swarm from the Artvin district in the easternmost part of the Sakarya Zone. Our study improves our understanding of the Oligocene magmatic and geodynamic evolution of the central Tethyan orogenic belt.

The Oligocene dykes consist of two distinct rock types: quartz-bearing trachytic and adakitic trachyandesite/andesite, dated at 31.0 ± 0.2 Ma and 31.1 ± 0.2 Ma to 29.2 ± 0.3 Ma by U-Pb zircon geochronology, respectively. Geochemical analysis reveals enrichment in LREE and MREE for quartz-bearing trachytic dykes, whereas adakitic trachyandesite/andesite dykes show depletion in MREE and HREE. Radiogenic isotopic ratios (⁸⁷Sr/⁸⁶Sr_(i) and ¹⁴³Nd/¹⁴⁴Nd_(i)) and trace element data suggest that the source of Oligocene magmatism was linked to low degree (≈10–15 %) partial melting of a metasomatised lithospheric mantle previously enriched by slab-derived melts and fluids. During the magma ascent in the crust, parental magmas of the trachyandesite/andesite dykes have assimilated crustal rocks and undergone fractional crystallization dominated by amphibole. By contrast, quartz-bearing trachytic dykes have recorded plagioclase fractionation.

Local extension, in conjunction with continuous foundering of delaminated thickened lower crust beneath the eastern Sakarya Zone, which likely triggered asthenospheric mantle upwelling and resulted in sporadic Oligocene magmatism.

Our study highlights the distinct tectonic and magmatic setting of the rare Oligocene magmatism in the eastern Sakarya Zone compared to Oligocene magmatism in the Tauride-Anatolide and South Armenian blocks.

The Tianshan hosts numerous giant and world-class lode gold deposits, forming one of the world’s largest gold provinces. However, the sources of gold remain equivocal. Herein, we present a comprehensive Pb isotopic investigation of the Precambrian basement, Neoproterozoic mafic dykes, and the Lower Paleozoic sequences of the South Tianshan in NW China. These data were compared with existing Pb isotope datasets from major lode gold deposits and coeval granitoid and mantle-related rocks, to trace the sources of gold and constrain the relative contributions from potential reservoirs. Gold-bearing sulfides from major lode gold deposits have relatively uniform Pb isotopic ratios, which are significantly different from regional coeval granitoid and mantle-related rocks. Conversely, the Pb isotopic characteristics from gold-bearing sulfides are comparable to those from the Paleoproterozoic metasedimentary rocks, showing well-defined linear relations. Binary mixing modeling shows that the Paleoproterozoic metasedimentary rocks might have contributed 70% to 90% for the source of Pb and, by inference other metals. Integrating geochemical and isotopic features from major lode gold deposits in the region, we propose that it invokes fertilization of ancient Au archives during metamorphic volatilization in the deep crust during subduction of the South Tianshan Ocean. Following the final closure of the South Tianshan Ocean, the regional tectonic uplift and thermal effect during widespread granitoids emplacement associated with the amalgamation of the Tarim with Kazakhstan-Yili terranes, mobilizing the deep roots of the fertilized ancient Au reservoirs, leading to the formation of the gold deposit hosted in fault systems of the South Tianshan.

Accurately quantifying the carbon sink effect resulting from chemical weathering caused by anthropogenic H₂SO₄ is imperative to improve the assessment of the global carbon budget. Nevertheless, there is still a lack of precise understanding regarding the impact of anthropogenic H₂SO₄ on CO₂ consumption during chemical weathering. Here, spring water samples were collected monthly from three catchments with distinct bedrock lithologies affected by severe acid precipitation in Southwest China for analyses of hydrogeochemistry and δ¹³C_DIC to quantitatively estimate the effect of anthropogenic H₂SO₄ on the weathering carbon sink budget. The results show that carbonates contribute 97.4 %, 95.0 % and 88.8 % of the total cationic load using a straightforward method in the Beidiping carbonate catchment, as well as in the Shegengyan and Bianyan silicate catchments, respectively. The [Ca²⁺+Mg²⁺]/[HCO₃⁻] (0.98–1.19) and [Ca²⁺+Mg²⁺]/[HCO₃⁻+SO₄²⁻] (approximately 1) equivalent ratios, and δ¹³C_DIC values (−16.8 to −8.0 ‰) of the samples suggest that besides H₂CO₃, H₂SO₄ is involved in carbonate weathering. The stoichiometry of the chemical compositions of spring water indicates that the presence of H₂SO₄ enhances carbonate weathering rates by 14.8 %, 8.1 % and 7.5 % while decreasing the CO₂ consumption by 8.2 %, 4.3 % and 4.0 % in Beidiping, Shegengyan and Bianyan, respectively. Thus the reduced proportion of karst carbon sink in the carbonate catchment is approximately 2 times that in the silicate catchment, suggesting that carbonate weathering in the karst catchment is more sensitive to acid precipitation. The impact of acid precipitation on rock weathering in the silicate catchment is constrained by the soil buffering effect. Our study highlights the important role of anthropogenic H₂SO₄ in carbonate weathering, which should be critically evaluated in regional and global carbon cycles in future studies.

Both Pb-Zn and Au mineralization can simultaneously occur at the deposit, camp or regional scale, but their spatial-temporal and genetic relationships have received less attention so far. Here we present detailed field investigations and S-Pb-He-Ar isotope data for the Laoyachao deposit, South China, to interpret the intrinsic associations between Pb-Zn and Au mineralization. Both Pb-Zn and Au ores in the studied area are distributed independently but spatially associated with the same granodiorite. Field and microscopic observations, together with previous dating, show that the Au mineralization postdated the Pb-Zn mineralization. The relatively restricted range and lower δ³⁴S values for the Au ores (−0.72 to +0.94 ‰) and the Pb-Zn ores (−1.98 to +2.36 ‰) indicate that both metal mineralization types are attributed to a homogeneous magmatic sulfur source. Lead isotope compositions for the ores and the feldspars from the granodiorites define a well-defined linear array, with the Au ores displaying less radiogenic Pb. In addition, the Pb-Zn ores exhibit lower ³He/⁴He and ⁴⁰Ar/³⁶Ar ratios (0.01–0.26 Ra, 298–313) than the Au ores (0.16–2.93 Ra, 341–382). All evidence demonstrated that, besides the granodiorite end-member, an end-member with high-radiogenic Pb and lower ³He/⁴He values participated in the early Pb-Zn mineralization, in contrast, the other end-member with less radiogenic Pb and higher ³He/⁴He values was involved in the late Au mineralization. Considering that both Pb-Zn and Au mineralization in the studied deposit are spatially, temporally and genetically related to the same granodiorite, the Pb-Zn mineralization associated with granodiorite can provide an indicator for gold exploration.

The occurrence of shale oil is important for its mobility and holds great significance in determining the available shale oil resources. Here, shale samples from three representative wells with different shale oil production levels in the Jiyang Depression, eastern China, were collected to evaluate the mobility of shale oil from its occurrence. The samples were subjected to Rock-Eval pyrolysis, X-ray diffraction, soluble organic matter, and N₂ adsorption measurements. The results indicate that the shales in the high production well have higher contents of clay or felsic minerals, more apolar oil components, and smaller pore sizes than those in the low production well. In particular, the shale oil occurrence exhibits two stages involving pore surface adsorption followed by pore void filling, which are separated by a total organic carbon (TOC) content of 0.6 wt% OC (equivalent to 7.7 mg/gRock, the lower threshold of shale oil content for mobility). The corresponding threshold of pore diameter is 10 nm. By integrating the shale oil occurrence with the oil properties at the producing intervals, the following indices are proposed to evaluate the shale oil mobility and high production level: shale oil content greater than 0.6 wt% OC or 7.7 mg/gRock, oil saturation index greater than 100 mg/gTOC, apolarity index greater than 1, and pore diameter greater than 10 nm. Our work provides an index regime to evaluate the mobility and high production probability of shale oil, which will benefit the exploration and development of shale oil resources.