Acta Geologica Sinica ‐ English Edition最新文献

Mineral exploration under exotic overburden has been a great challenge in exploration geochemistry. Gas geochemical measurement is a potential method for mineral exploration due to the characteristics of strong penetrability and vertical migration. The previous rapid gas analyzer cannot determine low concentrations of soil gases because of inadequate sensitivity, therefore, it is necessary to develop a more sensitive analytical technique. In this paper, the pilot studies on CO₂ and SO₂ geochemical measurements were performed at the Zhuxi W-(Cu) deposit, Jiapigou gold ore-concentrated area, and Tukuzbay gold deposit. This study employed rapid gas analyzer based on Infrared Absorption Spectroscopy and Electrochemical Analysis, which can detect low concentrations of CO₂ and SO₂ and greatly improve the reliability of test data. The results show that CO₂ and SO₂ show clear anomalies over deeply concealed ore bodies and faults, demonstrating that CO₂ and SO₂ anomalies can reveal indicative information about concealed mineralization and faults. Moreover, CO₂ and SO₂ anomalies can identify mineralization information exceeding 1,000 m in depth, suggesting that this method has large detection depth. Therefore, CO₂ and SO₂ geochemical measurement method is a feasible tool to discern deeply concealed mineralization and faults, and can provide a new idea in prospecting for concealed ore deposits in covered areas.

The early evolutionary history of the Macrocerinae subfamily (Diptera: Keroplatidae) is poorly understood. However, new material from the Cretaceous, particularly in amber, provides a better understanding of this subject. We reassign the oldest known species of Macrocerinae, Hegalari minor Blagoderov & Arillo, 2002, from the amber of Álava (~105 Mya), to the genus Macrocera (M. minor comb. nov.). Furthermore, we reassess the systematic position of the problematic genus Burmacrocera Cockerell, 1917 from Cenomanian Burmese amber (~99 Mya), providing evidence that it should be classified within this subfamily. Most significantly, we describe five new species from Burmese amber, including a new genus, Electrocera Pełczyńska & Soszyńska, gen. nov., with two new species (E. prima Pełczyńska & Soszyńska, gen. et sp. nov. and E. payini Pełczyńska & Soszyńska, gen. et. sp. nov.) and three new Macrocera species (M. vonneguti Pełczyńska & Blagoderov, sp. nov., M. sevciki Pełczyńska & Krzemiński, sp. nov. and M. pawli Pełczyńska, sp. nov.).

The origins of peloidal micrites in reefal limestone are not yet well understood. Moscovian microbial reefs with abundant peloidal micrites from Guizhou, South China, provide an opportunity to study the peloids and their geological significance for this time interval. Three types of peloids are differentiated: microbial, lithic, and bioclastic peloids. Microbial peloids that are well-sorted and may form in situ by microbial activities. The poorly sorted lithic peloids are derived from erosion and redeposition of the micrite matrix caused by the bottom turbulence induced by periodic storms. Bioclastic peloids are completely micritized fragments of hard parts and shells. Microbial boring and encrustations promote the processes of micritization. Microbial peloids commonly develop in zones with low or normal energy levels, and contribute to the construction and stabilization of the framework. In contrast, the occurrence of lithic peloids reflects that the reefs are destroyed by bottom turbulence during growth. It is suggested that the microbial reefs were deposited under a dynamic balance between constructional versus destructive processes. By comparative analysis, the peloids as microbial in origin play a key role in the growth and stabilization of bioconstructions during Carboniferous, which should be paid more attention in the studies of Carboniferous buildups.

¹⁰Be surface exposure dating is one of the methods most used in the dating of glacial landforms due to its well-understood dating mechanism, readily accessible materials. However, numerous dating studies have shown that nuclide inheritance may overestimate the age as a result of the nuclide concentrations accumulating in glacial deposits prior to their eventual exposure. As the concentration is challenging to measure directly, it is typically assumed to be zero. This study investigated the potential nuclide inheritance in the Hailuogou Glacier by measuring ¹⁰Be concentrations in modern moraines. The results showed that (1) in the glacier foreland, the exposure ages of two sub-angular boulders aligned with the timing of glacier retreat suggested minimal or potentially negligible nuclide inheritance, whereas two amalgamated samples exhibited ¹⁰Be exposure ages of 820 ± 278 yr and 570 ± 168 yr, indicating that multiple cobbles may contain inherited nuclides; and (2) the exposure ages of the angular boulder samples from the modern glacier surface ranged from 366 ± 151 yr to 221 ± 85 yr, the coarse-grained (CG) sand samples ranged from 470 ± 129 yr to 178 ± 103 yr in age, and the ages of the amalgamated samples ranged from 1,114 ± 197 yr to 97 ± 37 yr, which may reflecting the upper limits of inherited ages.

Research on the distribution and development of black shales in the Lianggaoshan Formation has been deficient, which has hindered exploration for lacustrine shale oil in the Sichuan Basin. Our study characterized the well logging data, core samples, outcrops, and geochemistry of black shales in the Lianggaoshan Formation in the Sichuan Basin. Our analysis focused on the lake basin evolution and the migration characteristics, paleoenvironmental features, formation mechanisms, and developmental model of the black shales. The results indicated that black shales in the Lianggaoshan Formation exhibited significant lateral migration, with an overall thickening trend from east to west. Within the 1st Member of the formation, black shale occurred as a single thick layer in the eastern region that gradually thinned toward the central region. Multiple sets of shale developed within the 2nd and 3rd members, and these had lower thicknesses than the 1st Member and migrated toward central Sichuan. Paleoproductivity and terrigenous input were the main factors controlling the deposition of black shales. A semi-humid climate influenced the deposition of black shales, bringing abundant freshwater, terrigenous debris, and nutrients into the basin. Decomposition of organic matter consumed oxygen in sediment and bottom water, causing localized oxygen deficiency in the strata.

The subduction and closure history of the Paleo-Tethyan Ocean is of significant importance to the formation of the Alpine–Himalayan orogenic belt. However, in West Qinling, China, the evolution of the subducted Paleo-Tethyan oceanic slab in the mantle remains unclear. In this work, we determine high-resolution P-wave azimuthal anisotropic tomography of the crust and upper mantle beneath west Qinling by inverting newly collected local and teleseismic data. The local earthquakes are relocated by jointly using permanent and portable stations and weighted by their hypocentral errors during the inversion. Our model reveals a slab-like high P-wave velocity (V_p) anomaly below 300 km depth and significant depth variations of anisotropy in the upper mantle beneath the West Qinling orogen. By comparing with previous geophysical results and integrating with geological and geochemical findings, we interpret that this high-V_p anomaly is most likely the subducted Mianlue oceanic slab preserved in the upper mantle and the mantle transition zone since the early Mesozoic. Beneath the Songpan–Ganzi block and the Longzhong basin, low-V anomalies with weak azimuthal anisotropy suggest a vertical mantle upwelling at a depth of 120 to 200 km, providing positive buoyancy to the subducted oceanic slab and extends its stagnation duration in the upper mantle.

Detrital zircon and apatite U-Pb-Hf isotope and trace element analyses of the late Mesoproterozoic to early Neoproterozoic strata in southern Jilin provide detailed information on the sediment provenance and tectonic setting of the northeastern margin of the North China Craton (NCC). Here, we present U-Pb and Lu-Hf analyses of 712 detrital zircons, and U-Pb analyses of 347 detrital apatites from the Baifangzi, Diaoyutai and Qiaotou formations. The Baifangzi and Diaoyutai formations are dominated by Neoarchean (2.5–2.6 Ga) and Paleoproterozoic (1.8–1.9 Ga) zircons, indicating a predominant NCC provenance. The Qiaotou Formation is dominated by Mesoproterozoic (1.5–1.7 Ga and 1.1–1.3 Ga) zircons with mainly positive ε_Hf(t) values, which are similar to those from eastern Laurentia, implying a significant provenance transition. The detrital apatite age spectra of the Baifangzi and Diaoyutai Formations show major populations at 1.8–1.9 Ga and 1.1–1.3 Ga. Based on their trace element compositions, the Mesoproterozoic apatites were mainly sourced from metamorphic rocks, indicating regional metamorphism occurred in the NCC during 1.1–1.3 Ga. Combining these data with regional studies, we propose that the NCC was adjacent to eastern Laurentia during the assembly of the Rodinia supercontinent.

In the Fatira (Abu Zawal) mine area, located in the northern Eastern Desert of Egypt, fieldwork and mineralogical analysis, integrated with machine learning techniques applied to Landsat-8 OLI, ASTER, and Sentinel-2 multi-spectral imagery (MSI) data delineate gold-sulfide mineralization in altered rocks. Gold (Au) anomalies in hydrothermal breccias and quartz veins are associated with NE-oriented felsite dykes and silicified granitic rocks. Two main alteration types are identified: a pyrite-sericite-quartz and a sulfide-chlorite-carbonate assemblage, locally with dispersed free-milling Au specks. Dimensionality reduction techniques, including principal component analysis (PCA) and independent component analysis (ICA), enabled mapping of alteration types. Sentinel-2 PC125 composite images offered efficient lithological differentiation, while supervised classifications, i.e., the support vector machine (SVM) of Landsat-8 yielded an accuracy of 88.55% and a Kappa value of 0.86. ASTER mineral indices contributed to map hydrothermal alteration mineral phases, including sericite, muscovite, kaolinite, and iron oxides. Results indicate that post-magmatic epigenetic hydrothermal activity significantly contributed to the Au-sulfide mineralization in the Fatira area, distinguishing it from the more prevalent orogenic gold deposits in the region.

The Carboniferous, an important coal-forming period in geological history, was characterized by extensive vegetation and high oxygen levels. Evidence suggests frequent wildfires took place during this time, especially in peatlands. However, the control mechanisms for changes in wildfire activity in peatlands during this period remain unclear. In this study, evidence from the Gzhelian in the Ordos Basin, such as the inertinite/vitrinite (I/V) ratio, indicated varying wildfire frequencies. Climate indicators (CaO/MgO and CaO/MgO·Al₂O₃) revealed that high-frequency wildfires mainly occurred in warm and humid climates. Based on former age constraints, we deduced that orbital cycles (long eccentricity) controlled the climate influence on peatland wildfires during the Gzhelian. Higher eccentricity brought more sunshine and rainfall, creating warmer, wetter peatlands conducive to vegetation growth, which increased fuel loads and led to more wildfires. Global Gzhelian wildfire records show that wildfires occurred mainly in tropical regions with abundant vegetation, reinforcing the idea that fuel loads drove fire activity. While wildfires can release mercury (Hg), the frequent volcanic activity during this period likely contributed significantly to Hg enrichment.