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HOU Zengqian，XU Bo，YANG Tiannan，ZHANG Haijiang，YU Nian，ZHAO Yi，MIAO Zhuang
2025,99(3):627-633, DOI: 10.1111/1755-6724.15313
Abstract:
A subducted continental slab is sometimes torn during collision, yet the exact impact of slab-tearing on the overlying lithosphere remains unclear. Here, we image the structure and architecture of the Asian lithosphere above the Indian slab in the eastern Tibetan Plateau using multiscale seismic tomography models and zircon Hf isotopic mapping, respectively. Our mantle Vp model shows that a large low-velocity anomaly extends laterally beneath the thinned Asian lithosphere above the tear zone roughly along the 26°N. The Vs images, magmatic records and Hf isotopic mapping indicate that this low-velocity anomaly recorded an asthenosphere flow eastward along the tear zone, which thermally eroded and refertilized the overlying Asian lithosphere, leading to the lithospheric melting, thinning and root delaminating. The vertical tear also generated a tectonic weak zone with associated Cenozoic potassic and carbonatitic magma suites. We argue that such a hot lithosphere discontinuity provided a reasonable mechanism for the abrupt change of crust thickness and the transformation of crust-mantle deformation from coupling to decoupling across the tear zone.
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CHEN Jun，MAO Fangyuan，WU Wenhao，MENG Jin
2025,99(3):634-645, DOI: 10.1111/1755-6724.15307
Abstract:
We report new material of the zalambdalestid, Zhangolestes jilinensis, from the Quantou Formation (lower Upper Cretaceous, Cenomanian to Turonian), Gongzhuling City, Jilin Province, NE China. Using micro-CT-scan, the material is shown to include dentocranial and postcranial elements recovered from the same matrix block containing the holotype specimen. The CT-images also show the labial and internal structures of the holotype fragment of the lower jaw of Z. jilinensis. Based on the preservation, relative size, and tooth wear, the new material and the holotype lower jaw likely belong to the same individual animal, whereas the hypodigm mandibular fragment assigned to Z. jilinensis in the original study is thought now to belong to a different individual, potentially representing a different species, which, if true, would increase the eutherian diversity in the Late Cretaceous Changchunsaurus Fauna. Furthermore, the new CT-images show that the incisor morphology is diverse within zalambdalestids and probably evolved independently from the enlarged incisors in placental mammals, such as Glires.
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ZHANG Yingjie，CEN Wenpan，QIN Yinglun，MA Chenglong，CHEN Jiyu，HUANG Wenfang，WANG Long
2025,99(3):646-666, DOI: 10.1111/1755-6724.15309
Abstract:
Silicalites are extensively developed in the Liujiang Formation (Fm.) of the Frasnian in the Dianqiangui Basin and are often associated with carbonaceous shales. This stratigraphic combination represents a special sequence stratigraphy formed in special deep-water environments, which not only gives the shales unusual spatio-temporal distribution features, but also induces the shales in the Liujiang Fm. to frequently be rich in organic matter (OM). This study summarises the special deep-water sedimentary succession of the Liujiang Fm., which is mainly distributed around synsedimentary faults, as well as establishing the sequence stratigraphic frameworks of the Liujiang Fm. in the west–east and southwest–northeast directions. Under the sequence stratigraphic frameworks, the spatio-temporal distribution features of the organic-rich shales of the Liujiang Fm. and the regional variations of the Liujiang Fm. were investigated. In addition, the rock components and OM occurrence states of the organic-rich shales were also observed and described in detail under the microscope. The results show that the organic-rich shales were formed temporally primarily during the third-order sea-level falling stage, developed spatially mainly on the east and west sides of the study area, as well as that the OM accumulation is closely related to tentaculitoids and seems to be influenced by a ‘biological pump’.
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Arkan O. SHARAZWRI，Bzhar A. DELIZY
2025,99(3):667-678, DOI: 10.1111/1755-6724.15314
Abstract:
The Govanda Formation was deposited during the Miocene in the intermontane areas between the Zagros suture and imbricate zones. The Govanda Formation was studied in the Sherwan Mazin area within Mergasor district, Erbil Governorate to identify the lithostratigraphy and microfacies analysis in order to determine the depositional environment of the formation. The formation in the studied section is 116 m thick and mainly consists of reddish-brown, hard, thick-bedded, chert-bearing conglomerate, pinkish shale and yellowish-grey, thick-bedded, detrital, fossiliferous limestone. The formation is unconformably underlain by the Upper Cretaceous Tanjero Formation and conformably overlain by the Merga Red Beds series. Four different lithostratigraphic units were identified, based on field observation and petrographic analysis, including a basal conglomerate unit (A), a shale unit (B), a well-bedded limestone unit (C) and a thick and massively-bedded limestone unit (D). The presence of a thick conglomerate bed at the base of the formation indicates a large unconformity that lasted nearly 40 million years. Based on detailed microfacies analysis of carbonate rocks, five main microfacies and 15 submicrofacies are recognized. The main microfacies types include mudstone, wackestone, packstone, grainstone and boundstone microfacies. Based on the microfacies types the depositional environment are defined as open lagoon, reef, fore-reef and back-reef environments of normal to saline, nutrient rich water.
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YIN Zhiqiang，LIU Longqiang，Lü Xiaochun，LI Nan，ZHU Lidong，LIU Qiang，HA Erjia
2025,99(3):679-692, DOI: 10.1111/1755-6724.15300
Abstract:
The tectonic setting of the Himalaya during the Early Paleozoic has been a subject of enduring debate within the scientific community. Newly discovered bimodal intrusive rocks from comprehensive field geological investigation in the central mountain range were subjected to petrology, zircon U-Pb geochronology, zircon Hf isotopes and whole-rock geochemistry analyses. The Palie bimodal intrusive rocks, comprising amphibolite and granitic gneiss, were formed at ~489 Ma. The amphibolite exhibits geochemical characteristics consistent with N-MORB, while the granitic gneiss is classified as high potassium calc-alkaline peraluminous S-type granite. Both igneous rocks exhibit negative zircon εHf(t) values and display ancient TDMC ages. In conjunction with regional geological survey findings, it can be inferred that the formation of the Palie bimodal intrusive rocks occurred within a post-collision extensional tectonic setting. The amphibolite genesis involved partial melting of an enriched lithospheric mantle with some crustal assimilation, whereas the origin of the granitic gneiss can be attributed to partial melting of pre-existing felsic crust. Our data indicate that during the Early Paleozoic, the Himalaya underwent a transition from a pan-African collisional setting to post-collisional extensional tectonics.
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DONG Peipei，LI Yingjie，WANG Shuai，ZHANG Xiawei，LIU Zhibin，WANG Jinfang，ZHAO Jinzhao，WANG Likao
2025,99(3):693-706, DOI: 10.1111/1755-6724.15306
Abstract:
High-Mg andesite/diorite (HMA) is useful for identifying subduction-related processes in orogenic belts, including the identification of ophiolites formed in suprasubduction zone (SSZ) environments. The E'rentaolegai high-Mg diorite from the Diyanmiao ophiolite in central Inner Mongolia, North China, has been investigated revealing low-K tholeiitic–calc-alkaline characteristics and have SiO2 contents of 53.44–54.92?wt%, MgO contents of 8.44–9.54?wt%, and Mg# of 54.35–57.60, with variable Fe2O3 (7.51–8.61?wt%), Al2O3 (11.95–15.09?wt%), and Na2O (3.42–3.94?wt%) contents, low K2O (0.34–0.97?wt%), TiO2 (0.35–0.67?wt%), and P2O5 (0.12–0.15?wt%) contents, and high Ni (43–193?ppm) and Cr (189–556?ppm) contents. Samples collected have low total rare earth element (REE) contents (30.58–77.80 ppm), with flat or slightly right-dipping REE patterns (LaN/YbN = 2.19–3.11) and a lack of pronounced Eu anomalies. The samples are also enriched in large-ion lithophile elements (LILEs, e.g., K, Rb, Ba, U, and Sr) and depleted in high field strength elements (e.g., Ta, Nb, Ti, and P). The E'rentaolegai high-Mg diorite has characteristics typical of HMA, and are similar to those of sanukites from the Setouchi Arc in SW Japan. They also display high positive εNd(t) values (+6.32 to +7.80), comparable to the values of their host rocks. Petrogenetic analyses suggest that the E'rentaolegai HMA was probably formed by the interaction of partial melts and aqueous fluids from subducted sediments with mantle peridotite. Zircon U-Pb dating reveals that the high-Mg diorite crystallized at 313.6?±?2.4 Ma, i.e., late Carboniferous. Combining our data with the temporal and spatial distribution of the Diyanmiao SSZ-type ophiolite, we propose that the eastern Paleo-Asian Ocean had not closed by the late Carboniferous, but intra-oceanic subduction was ongoing. A new model of the initiation of subduction in the eastern PAO during the late Paleozoic.
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JIA Xiaohui，WANG Xiaodi，QIU Xiaofei，YANG Wenqiang
2025,99(3):707-724, DOI: 10.1111/1755-6724.15296
Abstract:
This study presents whole-rock major, trace elements and Sr-Nd-Hf isotopic compositions, as well as zircon U-Pb geochronological data, for the peraluminous and aluminous granitoids in northern Guangdong Province, South China, in order to investigate their petrogenesis and tectonic implications. The Qingzhou granodiorites (458.5–455.4 Ma) are peraluminous (A/CNK = 1.05–1.96). They have relatively high initial 87Sr/86Sr ratios (ISr = 0.7087–0.7148), low εNd(t) values (?11.2 to ?10.1) and a variety of zircon εHf(t) values in the range ?13.4 to +4.81. By contrast, the Damaoshan granodiorites (458.1 Ma) are metaluminous (A/CNK = 0.79–0.94) in composition, with ISr values of 0.7083 to 0.7110, εNd(t) values of ?7.92 to ?5.28 and zircon εHf(t) values of ?8.69 to ?2.06. The Gaoshou quartz diorites (449 Ma) are metaluminous-peraluminous. Their ISr values vary from 0.7104 to 0.7111 with εNd(t) values from ?9.64 to ?8.63. Geochemical data and Sr-Nd-Hf isotope compositions indicate that the Qingzhou, Damaoshan and Gaoshou intrusions are primarily derived from the partial melting of metagreywackes, tonalitic rocks and amphibolite, respectively. The crustal materials in northern Guangdong, from top to bottom, consist of Paleozoic sequences, metasediments with a Vp of < 6.0 km/s, metaigneous rocks with a Vp of 6.3–6.7 km/s and amphibolite with a Vp of ~7.03 km/s.
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JIANG Yaohui，ZHAO Yajie，LIU Yunchao，HAN Boning
2025,99(3):725-742, DOI: .1111/1755-6724.15312
Abstract:
Granite origin is crucial to understanding the evolution of continental crust, yet many concerns about granite genesis remain yielding ongoing debates. A new integrated study of petrology, geochronology, mineral chemistry and whole-rock geochemistry of the Dupangling granitic complex in South China, indicate that the granites in the western complex were emplaced during the Caledonian (418 Ma); they have SiO2 contents of 68.1–70.4 wt%, and are calc-alkaline and strongly peraluminous with high maficity [(TFe2O3 + MgO) > 4.0 wt%] and exhibit 87Sr/86Sr(t) of 0.7234–0.7311 and εNd(t) of ?9.0 to ?6.7. The granites in the eastern complex, emplaced during the Indosinian (212 Ma), have high SiO2 contents (73.3–79.8 wt%) and exhibit affinities with A-type granites, such as enrichment in alkalis and rare earth elements (REEs), and depletion in Sr and Ba along with high TFeO/(TFeO + MgO), Ga/Al and Zr + Y + Ce + Nb; these granites exhibit 87Sr/86Sr(t) of 0.7221 and εNd(t) of ?9.2 to ?7.5. Geochemical characteristics suggest that the older Caledonian granites were derived through dehydration melting of Paleoproterozoic metasedimentary rocks plus additional (~20%–32%) input from mafic magma, whereas the Indosinian granites were generated through shallow dehydration melting of the Caledonian granitoids.
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REN Haidong，PAN Tong，WANG Tao，WANG Bingzhang，WANG Xiaoxia，ZHANG Jianjun，WANG Jianguo，ZHAO Wentao
2025,99(3):743-760, DOI: 10.1111/1755-6724.15294
Abstract:
In the western segment of the East Kunlun Orogen (WEKO), muscovite granite and garnet granite from the Hureguole intrusion exhibit zircon U-Pb ages of 435–442 Ma. Geochemically, these rocks contain high concentrations of SiO2, K2O and Al2O3, with low concentrations of TiO2 and MgO, indicating a peraluminous high-K calc-alkaline affinity. They are enriched in Rb, Th, U and LREE, depleted in Eu, Ba, Sr and Ti, being classified as S-type granites. Negative whole-rock εNd(t) values (?9.8 to ?9.1) and zircon εHf(t) values (?11.6 to ?8.2) for those granites indicate that they were derived from partial melting of pelitic rocks in the Paleoproterozoic Baishahe Formation of the Jinshuikou Group. Based on the collected zircon ages, Cambrian?Devonian magmatic activity in the WEKO was divided into three stages: early (446–520 Ma), middle (427–441 Ma) and late (372–424 Ma) stages. Statistically, whole-rock Nd and zircon Hf isotope data (εNd(t)/TDMNd, εHf(t)/TDMCHf) from Paleozoic igneous rocks in the WEKO reveal a magma source that was initially dominated by depleted mantle components in the northward subduction stage of the Proto-Tethyan Ocean plate (446–520 Ma), shifting to predominantly crustal sources during the closure period of the North Qimantagh back-arc basin (427–441 Ma), then to crust-mantle mixed sources in the post-collision stage (372–424 Ma).
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JI Changjun，CHEN Chong，ZOU Yuanbing，CHEN Yun，Zhou Lianfeng，ZHU Jiang
2025,99(3):761-773, DOI: 10.1111/1755-6724.15315
Abstract:
The Cretaceous andesites were discovered in the Biluocuo area, and provided key records to understand the late Mesozoic geodynamic evolution and crustal basement for the southern Qiangtang block in the central Tibet. In this study, we present a detailed study of zircon U-Pb dating, major and trace elemental composition, and Sr-Nd-Hf isotopes for the Biluocuo trachy-andesites. The trachy-andesites yielded zircon U-Pb ages at ca. 97 Ma, and exhibited SiO2 contents ranging from 55.92 to 69.04 wt%, low TiO2 contents (0.37 to 0.75 wt%) and low Mg# values (18.6 to 53.7), suggesting that they belong to high-K calc-alkaline series. They showed adakitic signatures, such as high Sr/Y ratios (almost 24 to 55) and low Y (<20 ppm), implying they were generated at great depths (>15 kbar). The samples have initial Sr isotopic ratios of 0.70963 to 0.70964, εNd(t) values of ?4.7 to ?4.6, and zircon εHf(t) values of ?1.2 to +1.3 with two-stage Hf model ages of 0.95 to 1.09 Ga. Elemental and Sr-Nd-Hf isotopic signatures suggest that the trachy-andesites were derived from the partial melting of the thickened lower crust with involvement of metasomatized mantle components. Combined with coeval high-Mg andesites, we proposed that underplating of mantle induced melting of the lower crust at ca. 97 Ma in the southern Qiangtang block, following by lithospheric delamination. Inherited/xenocrystic zircons from the trachy-andesites revealed magmatic activities at 2562 Ma, 1850–1804 Ma, 1768–1665 Ma, 1043–935 Ma, 851–736 Ma and 642–540 Ma. There is a Precambrian crustal basement in the southern Qiangtang block, which may have experienced the assembly and break-up of the Columbia, Rodinia, and Gondwana supercontinents.
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YE Xiqing，XU Zhitao，Guido VENTURA，SUN Liying，LI Zhongwei
2025,99(3):774-788, DOI: 10.1111/1755-6724.15301
Abstract:
Cenozoic trachytes are characteristic of some active volcanic fields in China. In particular, the origin and mechanisms of the evolution of trachytes from the Tianchi (Changbaishan) volcano (TV, China/North Korea) are poorly known. Here, we present new geochronological, geochemical and isotopic data on two trachytic suites outcropping on the northern and southern upper slopes of TV. Detailed zircon laser ablation-multicollector-inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS) U-Pb dating, Rb-Sr isochron dating of plagioclase and hornblende, 40Ar/39Ar chronology with mineral chemistry, whole-rock element and Sr-Nd-Pb isotope data are used to explore their origins and evolutionary mechanisms during the late Middle Pleistocene. Our data indicate that the trachytes mainly consist of sanidine, orthoclase and plagioclase, with minor albite, quartz and hornblende. They formed at 0.353–0.346 Ma (lava flow from the northern slope) and 0.383–0.311 Ma (lava flow from the southern slope), respectively. The TV trachytes are characterized by high K2O/Na2O and AR values, with low A/CNK and Mg# values. They are enriched in rare earth elements (REEs; except Eu), depleted in Sr and Ba, crystallizing at 742–858°C. The TV trachytes have high (87Sr/86Sr)i values (0.70776–0.71195), positive εNd(t) values (0.61–2.93) and radiogenic 206Pb/204Pb values (17.515–17.806). These values are similar to those of the Pleistocene and Holocene TV trachytes. Geochemical data indicate that they were formed by fractional crystallization from a basaltic melt and assimilated upper crust material.
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DUAN Xiaoxia，WANG Ziyi，CHEN Bin，ZHOU Lingli，WANG Zhiqiang，CHEN Yanjiao
2025,99(3):789-805, DOI: 10.1111/1755-6724.15311
Abstract:
Both fractional crystallization and fluid-melt-crystal interaction are involved in the formation of highly fractionated granites. This paper assessed those two processes using geochemistry of muscovite and tourmaline and bulk-rock chemistry of multi-phase Wangxianling granitoids, South China. Compositional variations suggest the coarse-grained muscovite granite is produced from fractional crystallization of the two-mica granite whereas the fine-grained muscovite granite represents a distinct magma pulse. Progressive fractionation of quartz, feldspar and biotite leads to elevated boron and aluminum content in melt which promoted muscovite and tourmaline to crystallize, which promotes two-mica granite evolving towards tourmaline-bearing muscovite granite. Fluid-melt-crystal interaction occurred at the magmatic-hydrothermal transitional stage and resulted in the textural and chemical zonings of tourmaline and muscovite in fine-grained muscovite granite. The rims of both tourmaline and muscovite are characterized by the enrichment of fluid mobile elements such as Li, Mn, Cs and Zn and heavier δ11B values of the tourmaline rims (?15.0‰ to ?13.6‰) compared to cores (?15.7‰ to ?14.3‰). Meanwhile, significant M-type REE tetrad effects (TE1,3 = 1.07?1.18) and low K/Rb ratios (48?52) also correspond to fluid-melt-crystal interaction. This study shows zoned muscovite and tourmaline can be excellent tracers of fractional crystallization and late-stage fluid-melt-crystal interaction in highly evolved magmatic systems.
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ZHAO Xiaoyan，YANG Zhusen，LIU Chang，DONG Yanrui，SHI Haiyan
2025,99(3):806-821, DOI: 10.1111/1755-6724.15310
Abstract:
Four Pb-Zn deposits, namely Bangpu (BP), Digei (DG), Nabuding (NB) and Cuoga (CG), are located within a 20 km distance of each other in the Gangdese porphyry copper belt (GPCB). The age and nature of the Pb-Zn mineralization, especially its relationship to magmatism, remain uncertain. In order to address this issue, mica from the four deposits was selected for in situ Rb-Sr dating, with sphalerite additionally being selected for in situ trace element analysis. Detailed geological research has revealed that the BP and NB deposits are primarily skarn-type Pb-Zn mineralization, while DG and CG are associated with magmatic hydrothermal breccia and are characterized by banded-type mineralization. The Rb-Sr isochron ages of syn-mineralization muscovite at the BP and CG deposits are 11 ± 6 Ma and 19.7 ± 0.7 Ma respectively. Fe, Cd, In, Mn and Sn occur as lattice substitutions in sphalerite from the four deposits. Cu exists as microinclusions in BP, but occurs isomorphically in the DG, NB and CG deposits. The formation temperatures of the four deposits, as calculated from sphalerite geothermometry, range from approximately 200°C to 300°C, indicating that they belong to medium temperature deposits. BP and NB are classified as skarn Pb-Zn deposits, while DG and CG are categorized as hydrothermal filled Pb-Zn deposits. These results suggest that, in addition to porphyry Cu mineralization, the GPCB also contains significant Miocene Pb-Zn mineralization.
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Geochemistry and Lithium Enrichment Modes of the No. 8 Coal, Late Carboniferous, Eastern Ordos Basin
2025,99(3):822-839, DOI: 10.1111/1755-6724.15304
Abstract:
Recent studies have highlighted the presence of lithium enrichment in coals within the Ordos Basin, which has garnered significant attention due to the potential economic value. However, most research has concentrated primarily on the coal seams of the Taiyuan and Shanxi formations, with limited reports on the Benxi Formation. To address this gap, our study focused on elucidating the geochemical characteristics and origins of the lithium enrichment in the No. 8 coal of the Benxi Formation through the use of optical microscopy and inductively coupled plasma mass spectrometry (ICP-MS). The results showed that the No. 8 coal was a bituminous coal, characterized by medium ash yield, low volatile matter, high total sulfur content and medium vitrinite proportion. The No. 8 coal was enriched in Li (average 91.7 ppm, CC = 6.55) and Zr (average 191 ppm, CC = 5.30), the unusual enrichment of Li being primarily located in the middle of the coal. The minerals in the coal were predominantly clay minerals, along with minor amounts of pyrite, quartz and calcite. The occurrence mode of Li in the No. 8 coal was associated with aluminosilicate minerals, presumably kaolinite. Based on geochemical characteristics, the sedimentary source of the No. 8 coal was intermediate-felsic volcanic rock from the Yinshan oldland. The enrichment of Li can be attributed to the supply of terrestrial debris from the Yinshan oldland and the depositional environment. Our analysis identifies three distinct stages of lithium enrichment, emphasizing the critical role played by the terrestrial debris, as well as the acidic to partially reducing conditions, in facilitating this process. In conclusion, our study sheds light on the mechanisms underlying lithium enrichment in the No. 8 coal of the Benxi Formation, highlighting the significance of geological factors in shaping the distribution and concentration of critical metals in coal.
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XIAO Fei，YANG Jianguo，YAO Yulai，LI Shichao，HUANG Yiming，GAO Xiaoyong
2025,99(3):840-861, DOI: 10.1111/1755-6724.15299
Abstract:
Organic-rich mudstones and shales, which hold significant potential for shale oil resources, characterize the first member of the Upper Cretaceous Qingshankou Formation (K2qn1) in the Sanzhao sag of the Songliao Basin, NE China. Focusing on 30 core samples obtained from the first shale oil parameter well, named SYY3 in the study area, we systematically analyzed the composition and stratigraphic distribution of the K2qn1 heteroatomic compounds using electrospray ionization Fourier transform–ion cyclotron resonance mass spectrometry (ESI FT-ICR MS), to assess their geological relevance to shale oil. The findings indicate that in the negative ion mode, the heteroatomic compounds predominantly consist of N1, N1O1–N1O8, O1–O8, O1S1–O6S1; contrastingly, in the positive ion mode, they are primarily composed of N1–N2, N1O1–N1O4, N2O1, O1–O4, O1S1–O2S1. Heteroatomic compound distributions vary significantly with depth in the negative ion mode, with minor variations in the positive ion mode. These distributions are categorized into three types based on the negative ion ratio ((N1 + N1Ox)/Ox): Type I (>1.5), Type II (0.8–1.5), and Type III (<0.8); types I and II generally exhibit a broader range of carbon numbers compared to Type III. The distribution of double bond equivalent (DBE) values across various sample types exhibits minimal variance, whereas that of carbon numbers shows substantial differences. Variations in heteroatomic compound compositions among the samples might have resulted from vertical sedimentary heterogeneity and differing biotic contributions. Type III samples show a decrease in total organic carbon (TOC) and free oil content (S1) compared to types I and II, but an increased oil saturation index (OSI), indicating a lower content of free oil but a higher proportion of movable oil. The reduced content of N-containing compounds implies lower paleolake productivity during deposition, leading to a reduction in TOC and S1. A lower TOC can enhance oil movability due to reduced oil adsorption, and the decreased presence of polar nitrogenous macromolecules with fewer high-C-number heteroatomic compounds further promote shale oil movability. Additionally, the negative ion ratios of N1/N1O1 and O2/O1 exhibit positive and negative correlations with the values of TOC, S1, and extractable organic matter (EOM), respectively, indicating that the salinity and redox conditions of the depositional water body are the primary controlling factors for both organic matter enrichment and shale oil accumulation?.
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TAN Jingqiang，HUA Shihao，MA Xinyao，MA Xiao，WANG Yaohua，ZHANG Baomin，TIAN Wei，WANG Bohao
2025,99(3):862-878, DOI: 10.1111/1755-6724.15308
Abstract:
The marine-continental transitional shale of the Upper Permian Longtan Formation is widely distributed in Hunan and shows significant exploration potential. Frequent changes in lithofacies have however notably influenced the shale gas enrichment. The strata of the Longtan Formation in the Shaoyang Depression, central Hunan, were taken as the study object for this project. Three lithofacies assemblages were identified: shale interbedded with sandstone layer (SAL), sandstone interbedded with shale layer (ASL) and laminated shale layer (LSL). The SAL shale shows significant variability in hydrocarbon generation potential, which leads to shale gas characterized by ‘hydrocarbon generation in high total organic carbon (TOC) shale, retention in low TOC shale and accumulation in sandstone’. The ASL shale, influenced by the redox conditions of the depositional environment, shows a lower concentration of organic matter. This results in an enrichment model of ‘hydrocarbon generation and accumulation in shale, with sealing by sandstone’. The laminar structure of LSL shale causes both quartz and clay minerals to control the reservoir. Shale gas is characterized by ‘hydrocarbon generation in mud laminae, retention and accumulation in silty laminae, with multiple intra-source migration paths’. In the marine-continental transitional shale gas system, the enrichment intervals of different types of shale gas reservoirs exhibit significant variability.
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XU Yang，LIU Chenglin，YANG Sibo，CAO Yangtong，WEN Longtao，LI Ruiqin
2025,99(3):879-895, DOI: 10.1111/1755-6724.15298
Abstract:
The phenomenon of ‘bamboo-like’ thin interlayers developed in rock salt is one of the most prominent features of Paleogene salt-bearing strata in eastern China, where centimeter-thick rock salts appear separately, forming rhythmic units. At present, detailed analyses of these rhythms of rock salt are still limited, which directly affects the achievement of comprehensive and in-depth understanding of the developmental laws pertaining to this kind of saline lake. Therefore, we selected the typical rhythmic ‘bamboo-like’ rock salts of the Shizhai Depression in Jiangsu Province as the research subject. Through careful observation of rock salts in hand samples and detailed petrographic and mineralogical analyses, we analyzed the hydrogen and oxygen isotopic compositions, homogenization temperatures and chemical compositions of individual fluid inclusions in halite crystals. Early-stage rhythmic deposition was a product of continental saline lake evolution in winter or spring, late-stage rhythmic deposition being the product of evolution in the summer. The seasonal evolution of the halite sequences was determined and two brine enrichment events were identified. In addition, the quiet saline lake environment with concentrated brine represented by rock salt was more likely to precipitate potassium. This study provides a new reference for the evolution of both Paleogene climate and saline lakes in eastern China.
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CAO Yong，SUN Zhiming，GAO Yang，LIU Jian，LI Bin，YANG Yuhan，YE Hao，XU Peng
2025,99(3):896-907, DOI: 10.1111/1755-6724.15297
Abstract:
Knowledge of the seismogenic environment of fault zones is critical for understanding the processes and mechanisms of large earthquakes. We conducted a rock magnetic study of the fault rocks and protoliths to investigate the seismogenic environment of earthquakes in the Motuo fault zone, in the eastern Himalayan syntaxis. The results indicate that magnetite is the principal magnetic carrier in the fault rocks and protolith, while the protolith has a higher content of paramagnetic minerals than the fault rocks. The fault rocks are characterized by a high magnetic susceptibility relative to the protolith in the Motuo fault zone. This is likely due to the thermal alteration of paramagnetic minerals to magnetite caused by coseismic frictional heating with concomitant hydrothermal fluid circulation. The high magnetic susceptibility of the fault rocks and neoformed magnetite indicate that large earthquakes with frictional heating temperatures >500°C have occurred in the Motuo fault zone in the past, and that the fault maintained an oxidizing environment with weak fluid action during these earthquakes. Our results reveal the seismogenic environment of the Motuo fault zone, and they are potentially important for the evaluation of the regional stability in the eastern Himalayan syntaxis.
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2025,99(3):908-908, DOI:
Abstract:
