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Current Issue   2026 Vol.  15 No.  1 Published: 2026-01-20 Research article Research article 100292 Shaolinopteris gen. nov., a new fern rhizome genus with solenostele from the Jurassic of Northeast China and its palaeogeographic and taxonomic implications Ning Tian, Zi—Hui Sheng, Fang—Yu Li, Ning Lu, Meng—Yu Chen, Wen—Tao Liu China possesses an abundant fossil record of Mesozoic ferns, predominantly preserved as leaf compressions or impressions. In contrast, permineralized fern fossils revealing anatomical details are comparatively rare. Recently, a novel permineralized flora was discovered from the Middle Jurassic Xinmin Formation in Horqin Right Wing Middle Banner, Northeast China, yielding diverse permineralized plant remains. Here, we report a new permineralized fern rhizome genus Shaolinopteris gen. nov. from this flora. The new genus is anatomically characterized by a solenostele with exarch protoxylem, a homogeneous pith, a two—layered rhizome cortex, and "Dennstaedtia—type" adventitious roots featuring diarch protoxylems. Notably, the rhizome inner cortex comprises aerenchymatous columns. Anatomical analysis of Shaolinopteris indicates probable phylogenetic affiliation with the extant fern family Dennstaedtiaceae. Furthermore, a comprehensive revision of the fossil diversity and palaeogeographical distribution of Mesozoic solenostelic fern rhizomes is presented. This new specimen constitutes the first documented occurrence of Mesozoic solenostelic ferns in continental East Asia, providing critical evidence for reconstructing the palaeophytogeography of these taxa. 2026 Vol. 15 (1): 100292- [Abstract] ( 5 ) [HTML 1KB] PDF (19875 KB)   ( 1 ) 100295 Palaeoweathering and palaeoclimate of the Lower Cretaceous upper Xiguayuan Formation in the Luanping Basin, North China: Implications for early Aptian global cooling Long Sun, Sheng—He Wu, Da—Li Yue, Si—Chong Jiang, Wei Du, Li—Jun Yang, Zhen—Hua Xu, Ke Zhang The Early Cretaceous greenhouse climate was interrupted by multiple intermittent cold snaps such as the Valanginian cold snap and late Aptian climate cooling events, but there is currently a lack of terrestrial palaeoweathering and palaeoclimate records for the early Aptian climate cooling event. The relationship between the regional climate of terrestrial lake basins and the global climate during the early Aptian is still unclear. The Luanping Basin, which is located in the northeastern North China Craton (NCC) and contains Lower Cretaceous sediments with a maximum thickness of ~3,200 m, is an ideal place for analysing the terrestrial weathering and climate. Sixteen mudstone samples were collected from the Lower Cretaceous upper Xiguayuan Formation in the Luanping Basin. The mineral compositions and major, trace and rare earth element contents of the mudstone samples were quantitatively determined via X—ray diffraction (XRD), X—ray fluorescence (XRF), and inductively coupled plasma—mass spectrometry (ICP—MS), respectively. Elemental geochemical analyses were carried out to determine palaeoweathering intensity, palaeoclimatic conditions, and their relationships with the global climate. The variation trends in multiple chemical weathering indices are reconstructed after the interference of nonweathering factors is eliminated, reflecting that the source area has experienced mainly weak to moderate weathering. After evaluating the influences of carbonate—sourced elements, we infer that the regional palaeoclimate is arid and cold on the basis of the Sr/Cu ratio, Rb/Sr ratio, C—value, land surface temperature (LST), and mean annual temperature (MAT). All chemical weathering indices and palaeoclimate proxies exhibit similar trends. Moreover, the cooling of palaeotemperatures could have been a response to the early Aptian global cold snap. The regional climate of the Luanping Basin is controlled mainly by global climate change, which provides terrestrial weathering and climate records for the early Aptian global cooling event. 2026 Vol. 15 (1): 100295- [Abstract] ( 5 ) [HTML 1KB] PDF (7140 KB)   ( 0 ) 100296 Sedimentary distribution of evaporites in Wusongge'er Formation in central Tarim Basin and reconstruction of prototype basin Qing Bian, Ji—Biao Zhang, Fan Feng, Yang Li, Chen—Jun Huang, Tie—Yi Wang, Kang—Kang Guo The Middle—Lower Cambrian Wusongge'er Formation in the Tarim Basin hosts extensive evaporite deposits, yet the formative processes of these evaporites under equatorial arid climates and their tectono—sedimentary implications remain poorly constrained. Previous studies, limited to low—resolution seismic data and outcrops in the northwestern margin, failed to resolve depositional variations in the central basin. This study aims to decipher the genetic mechanisms of evaporite precipitation and reconstruct the prototype basin’s tectono—sedimentary evolution by integrating high—quality 3D seismic data (2023), geophysical forward modeling, and palaeogeographic reconstructions. Integrated analyses revealed a distinct zoned “west halite—east gypsum/dolomite” pattern driven by paleosalinity gradients in a semi—closed lagoon system, alongside an elongated reef body in the middle ramp and thrombolite buildups in the inner ramp. Evaporite distribution was dominantly controlled by equatorial aridity (climate) and fault—induced differential subsidence (tectonics), with the latter creating thickness variations exceeding 300 m. This study establishes a genetic model of evaporite sedimentation under the Cambrian greenhouse conditions, providing analogues for coeval evaporite systems in Gondwana. The restored prototype basin configuration reveals salt—driven sediment partitioning processes, offering new insights into the tectono—sedimentary evolution of intracratonic basins. While seismic interpretations face limitations in deep zones with scarce drilling data, this framework guides future ultra—deep exploration targeting salt—tectonized traps below 8,000 m depth. 2026 Vol. 15 (1): 100296- [Abstract] ( 3 ) [HTML 1KB] PDF (21795 KB)   ( 0 ) 100297 Spatial slip rate partitioning along the Xianshuihe Fault Zone, eastern Tibetan Plateau Jun Ma, Zheng—Fang Li, Ben—Gang Zhou, Ming—Ming Wang, Mahdi Motagh The Xianshuihe Fault Zone (XSHF) frequently experiences strong earthquakes owing to its high slip rate; particularly, the Kangding segment within the XSHF is structurally complex. To conduct an accurate regional seismic hazard analysis of XSHF, it is necessary to understand the slip rates of the branch faults of the Kangding segment. In this study, we aimed to determine the slip rates of the Yalahe Fault (YLHF) and the northwestern segment of the Zheduotang Fault (ZDTF), which are both parts of the Kangding segment. We employed tectonic geomorphology, topographic data, terrestrial laser scanning, precise offset measurements using LaDiCaoz_v2 software, and 10Be cosmogenic nuclide dating techniques. Our analysis showed slip rates of 3.5±0.3 mm·yr—1 and 2.3±0.2 mm·yr—1 since 12.7 ka and 7.8 ka for the YLHF, implying a decreasing slip rate trend post the Holocene period. Furthermore, we obtained slip rates of 1.9±0.3 mm·yr—1 since 42.7 ka and 1.8±0.2 mm·yr—1 since 15.7 ka for the northwest segment of the ZDTF. Notably, these slip rates are significantly lower than those observed for the southeastern ZDTF. Furthermore, in the late Quaternary, the combined slip rate for the XSHF reached a maximum of 9.9—15.5 mm·yr—1. We also observed that the Anninghe Fault inherited 48.2% of slip rate from XSHF. These findings provide a comprehensive overview of slip rate partitioning among branch faults in the Kangding segment, offering novel insights into the seismic behavior of the XSHF and improving regional seismic hazard assessment. 2026 Vol. 15 (1): 100297- [Abstract] ( 3 ) [HTML 1KB] PDF (15193 KB)   ( 0 ) 100298 Effects of smectite—illitization and hydrocarbon generation on the pore structure: A case study from the continental shales in China Dan—Ting Luo, Jing Zhang, Jing—Lan Luo, Zi—Hui Feng, Chao Deng, Yu—Bin Bai, Hong—Mei Shao, Min Yan, Ze Tan Pore structure of shale significantly affects the occurrence and reserves of natural gas and oil. At present, the quantitative characterization of pore structure related to clay minerals in high—clay continental shale remains inadequate. The mechanism of clay mineral transformation and pore preservation of continental shale is still unclear. To address this gap, an organic—rich, high—clay shale from the first member of the Qingshankou Formation (K2qn1) in the Gulong Sag, Songliao Basin, China, was analyzed, based on the measurement of argon ion polishing—field emission scanning electron microscopy (FE—SEM), X—ray diffraction (XRD), total organic carbon (TOC), vitrinite reflectance (Ro), pore structure parameters, and fractal dimension obtained from the isothermal N2 adsorption experiment, integrated with well logging data. Quantitative characterization of the modification on shale pore structure by smectite illitization and hydrocarbon generation from organic matter was conducted. The primary factors influencing pore structure, and pore preservation mechanism were then elucidated. Research result shows that the mesopores (2—50 nm) formed during smectite illitization and micropores (< 2 nm) produced by hydrocarbon generation from the organic matters significantly contributed to the pore volume and specific pore surface area of the shale. The microcrystalline quartz, formed in the smectite illitization, caused the loss of some pores, but the rigid frame composed of the microcrystalline quartz, as well as the overpressure generated partly by hydrocarbon generation from organic matter and partly by smectite—to—illite transformation, preserved some pores. This work highlights that smectite illitization and hydrocarbon generation from organic matter are crucial mechanisms for pore formation and preservation in continental shale with a high content of clay minerals. 2026 Vol. 15 (1): 100298- [Abstract] ( 4 ) [HTML 1KB] PDF (13913 KB)   ( 0 ) 100299 Sedimentology, provenance, and paleoclimate of Jurassic—Cretaceous red beds: Example from the southern Front of the Central High Atlas and Northern Preafrican Trough, Morocco Said Adardor, Hicham Nasri, Hamid Haddoumi, Radouan El Bamiki, Rachid Chennouf, Hanane Miri Five stratigraphic sections from the Aghbalou N’Kerdouss—Tadighoust area were analyzed using integrated petrographic, granulometric, calcimetric, and mineralogical approaches applied to both bulk samples and clay fractions. The findings reveal a transitional depositional environment shaped by a dynamic interplay of continental and restricted marine influences, particularly within the Ifezouane Formation (Member 2), which reflects low—amplitude sea—level oscillations under confined paleoenvironmental conditions. Whole—rock mineralogy is dominated by quartz, K—feldspar, plagioclase, hematite, calcite, dolomite, siderite, and gypsum. The associated clay mineral assemblages comprise illite, kaolinite, smectite, and chlorite, with compositional variability across sections. Illite crystallinity and illite chemistry index data indicate a dual provenance, with sediment sources originating from both the Anti—Atlas and Sahara regions to the south, as well as the Jurassic uplands to the north. These interpretations are supported by petrographic evidence and mineralogical signatures. Furthermore, the mineralogical data suggest that arid to semi—arid climatic conditions and/or tectonic activity played a significant role during deposition. This study demonstrates how the integration of clay mineral signatures with petrography, grain—size distribution, and calcimetric data offers a reliable basis for reconstructing provenance, unraveling paleoenvironmental conditions, and refining palaeogeographic reconstructions of peri—Tethyan basins, while also providing a comparative framework applicable to analogous red bed systems worldwide. 2026 Vol. 15 (1): 100299- [Abstract] ( 2 ) [HTML 1KB] PDF (19948 KB)   ( 0 ) 100309 Organic lithofacies and its reservoir characteristics of lacustrine shales of the Dongyuemiao Member in the Jurassic Ziliujing Formation, eastern Sichuan Basin Ming—Yang Wei, Wang Chen, Xing—Zhi Wang, Zhi—Dong Bao, De—Ming Zeng, Jia—Hao Kang, Yang Li, Kai—Ming Liu, Fei Huo This study investigates the reservoir properties and main controlling factors of different organic lithofacies in the Jurassic Dongyuemiao Formation lacustrine shales, eastern Sichuan Basin. Based on lithofacies classification, the spatial characteristics and physical properties of the reservoirs, along with the primary controlling factors, were analyzed using core observation, scanning electron microscopy (SEM), low—temperature nitrogen adsorption, and other techniques. The results indicate that: 1) In the eastern Sichuan Basin, the Dongyuemiao Member is predominantly composed of clay minerals and quartz, which are the main mineral constituents of the lacustrine shales. Minor amounts of calcite, feldspar, dolomite, pyrite, and rhodochrosite are also present. Four main lithofacies were identified within the study area: argillaceous shale with high—medium TOC (Ⅰ2), mixed shale with low—medium TOC (Ⅱ1), argillaceous—silt mixed shale with medium—low TOC (Ⅱ2), and argillaceous siltstone with low TOC (Ⅲ2). 2) The shale microstructure is characterized by micropores, primarily comprising intergranular pores between clay minerals and organic—matter pores. Intragranular dissolution pores, notably within shell fragments, are locally developed. Microfractures are mainly observed as intra—layer shale fractures and fractures along the edges of shell fragments. 3) High organic matter abundance (>1%), high clay mineral content (>40%), and moderate carbonate mineral content (<10%) in the shale of the study area contribute to the development of pores. In contrast, high quartz and feldspar mineral content (>50%) and excessively high (>12%) or low (<8%) carbonate mineral content inhibit shale pore development. 4) A comprehensive analysis shows that the argillaceous—silt mixed shale with medium—low TOC (Ⅱ2) is the most favorable lithofacies for reservoir development, followed by argillaceous shale with high—medium TOC (Ⅰ2). The mixed shale with lower—medium TOC (Ⅱ1) is less favorable, and the argillaceous siltstone with low TOC (Ⅲ2) is the poorest. Considering the vertical distribution of lithofacies in the Dongyuemiao Member, it is concluded that the middle—upper part of the Dong 2 submember is the most prospective reservoir interval in the study area. 2026 Vol. 15 (1): 100309- [Abstract] ( 2 ) [HTML 1KB] PDF (16612 KB)   ( 0 ) 100310 First record of Araucaria with leafy shoots and reproductive organs from the Lower Cretaceous of NW China and its historical biogeography Ai—Jing Li, Bao—Xia Du, Jing Zhang, Jing Peng, Ming—Chen Zhang, Pei—Hong Jin, Shao—Hua Lin, Yi—Qiao Fu, Jing—Jing Cai The modern Gondwanan genus, Araucaria, exhibited a worldwide distribution during its early evolution in the late Mesozoic. However, the scarcity of fossil records restricted exploring its early radiation and evolution. A new species, Araucaria gansuensis sp. nov. was described based on well—preserved leafy shoots associated with female cones, deciduous pollen cones and bract—scale complexes from the Lower Cretaceous of Northwest China. Maximum parsimony analysis revealed that the phylogenetic position of A. gansuensis is within the basal clade of Sect. Eutacta. Moreover, palaeobiogeographic analysis suggested that Araucaria possibly originated in the low latitudes of the Pangea and formed differentiation centers in Laurasia (East Asia) and Gondwana (South America) in the Middle Jurassic. Furthermore, with the breakup of Pangea, Araucaria rapidly radiated globally, and exhibited a more extensive distribution in the Northern Hemisphere during the Cretaceous. The discovery of A. gansuensis as a significant representative has unveiled a pathway for the dispersion of Araucaria in East Asia and Europe. Subsequently, Araucaria, which had a more primitive lineage, started declining and facing extinction in the Northern Hemisphere in the Early Paleocene due to factors such as geographic isolation, climatic variations, and expansion and dominance of angiosperms. 2026 Vol. 15 (1): 100310- [Abstract] ( 2 ) [HTML 1KB] PDF (37607 KB)   ( 0 ) 100311 Grallatorid—eubrontid tridactyl track assemblages from Lower Jurassic, Sichuan Province, China: Insights into theropod diversity, locomotion and behavior Li—Da Xing, Shan Jiang, Qi—Yan Chen, Yong Ye, Guang—Zhao Peng, Anthony Romilio, Hendrik Klein, Yan—Yi Gong The Sichuan Basin in southwestern China is home to the most extensive theropod track record in the Lower Jurassic of China, comprising a range of minute— to medium—sized tracks that form the grallatorid—eubrontid (GE) plexus. The majority of these had previously been discovered in the Ma'anshan Member of the Ziliujing Formation. New material described herein is from the Wuli tracksite that suggests a flourishing paleoecological scene in a temporary waterfront habitat. Upon reviewing the GE plexus at different scales, we consider the locomotion style of these early theropod trackmakers, which likely included the 'grounded—running' gait of extant birds, as well as the possibility of a tail trace that may be related to intra— or interspecific interactions. 2026 Vol. 15 (1): 100311- [Abstract] ( 2 ) [HTML 1KB] PDF (18509 KB)   ( 0 ) 100312 Organic matter accumulation in limestone—marl alternations of the Middle Permian Maokou Formation, Sichuan Basin, China, and its response to the interglacial—glacial transition Feng—Bin Liu, Liang—Biao Lin, Bo—Lin Zhang, Yu Yu, Yong Dan, Si—Yu Liu The deposition of limestone—marl alternations (LMAs) with elevated organic matter (OM) content within the Middle Permian (Guadalupian) Maokou Formation of the Sichuan Basin, China, was influenced by the interglacial—glacial transition. However, the mechanisms of OM accumulation remain unclear. This study examines OM accumulation in the first member of the Maokou Formation (i.e., the Mao I Member) from the Hegou and Zaodu sections using multiple geochemical proxies, with a focus on its response to climatic shifts during the interglacial—glacial transition. OM accumulation was primarily influenced by this climatic transition through two interrelated processes: (1) by regulating the intensity of chemical weathering (Rb/Sr) in nearshore shallow—platform environments, which in turn controlled terrigenous nutrient input (Ti/Al); and (2) by enhancing upwelling in distal deeper waters (Cd/Mo), thereby stimulating primary productivity (OCAR, PAR, CuXS, and NiXS). These mechanisms overcame the typical constraints of an oxygenated carbonate platform setting (where Ce anomalies are mostly <1.3), exerting a stronger control on OM accumulation than redox conditions. As glacial conditions intensified, the dominant mode of OM accumulation in the Mao I Member shifted from a detrital—driven regime—characterized by high terrigenous input (Ti/Al) and clay—mediated preservation (Al2O3)—to a hybrid system jointly regulated by both detrital input and upwelling—related nutrient delivery (Cd/Mo). In this latter phase, enhanced upwelling compensated for the decline in terrigenous nutrients. OM accumulation persisted even under oxygenated bottom—water conditions. This finding contrasts with the anoxia—dependent models typical of high OM shales and underscores the predominance of productivity over preservation factors in this icehouse carbonate platform. The transition toward glacial conditions is evidenced by the decreasing Rb/Sr ratios, indicating weakened chemical weathering, and declining Ti/Al ratios, signifying reduced terrigenous input. Our findings elucidate how multi—factor interactions govern OM accumulation in mixed carbonate—clastic systems and provide valuable constraints for predicting the stratigraphic distribution and quality of potential hydrocarbon source rocks in such settings. 2026 Vol. 15 (1): 100312- [Abstract] ( 2 ) [HTML 1KB] PDF (14997 KB)   ( 0 ) 100313 The first fossil flower of Malpighiaceae from India sheds light on the historical biogeography of a mostly Neotropical family Ashif Ali, Rafael Felipe de Almeida, Mahasin Ali Khan, Raman Patel, Rajendra Singh Rana A fossil flower affinity to an extinct Malpighiaceae taxon, recovered from the early Eocene (~55—52 Ma) of Gurha Opencast Lignite Mine, Rajasthan, western India, helps to underscore the evolutionary significance of this angiosperm lineage in the Indian Cenozoic history. Based on several macromorphological traits, a new fossil genus and species of Malpighiaceae, named Eomalpighia indica Ali, R.F. de Almeida, and Khan sp. nov., is proposed. Additionally, a continental ancestral range reconstruction was performed using the generic molecular phylogeny of Malpighiaceae and the BioGeoBEARS package for historical biogeography to discuss the phylogenetic placement of this new fossil and its significance for Malpighiaceae biogeography. The fossil specimen is characterized by one anterior petal and four lateral petals, eglandular; one posterior sepal and four lateral sepals, clawed at the base, eglandular, elliptic; four stamens, free, anthers with two thecae; presence of gynoecium in the center with a trilobed apex. The newly described fossil flower is best placed as an ancestor of the tribe Acridocarpeae due to its unique morphology and fossil distribution. The ancestral range reconstruction evidenced that Malpighiaceae likely had two different dispersal waves from the Neotropics to the Paleotropics taking place at the beginning (55.0—45.0 Ma) and the end (52—50 Ma) of the Eocene Climate Optimum Maximum. The first wave dispersed through Antarctica, and the second wave through the Boreotropics. This study provided insights into the taxonomy, evolutionary history, morphological evolution, and paleoecological implications of Malpighiaceae lineages in India. 2026 Vol. 15 (1): 100313- [Abstract] ( 2 ) [HTML 1KB] PDF (9852 KB)   ( 0 ) 100314 Palaeogeography and its controls on organic carbon accumulation in the Wufeng—Longmaxi formations of Chongqing, southeastern Sichuan Basin, southwestern China Yan—Wen Shao, Feng—Hua Zhao, Feng—Xian Jin, Zhen—Sheng Shi, Qun Zhao, Shi—Long Kang, Long—Yi Shao The Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation are important target strata for shale gas exploration in the Sichuan Basin, China. In this paper, the sedimentary facies and palaeogeography of the two formations in Chongqing area have been analyzed, and total organic carbon (TOC) contents are correlated with the sedimentary facies to prospect the favorable areas for shale gas exploration. According to the lithological characteristics and sedimentary structures, five sedimentary facies are identified, i.e., siliceous deep—water shelf, muddy deep—water shelf, calcareous shallow—water shelf, muddy shallow—water shelf, and silty—muddy shallow—water shelf facies, respectively. The palaeogeography reconstruction is based on the lithological distribution in the study area. The lower part of Wufeng Formation was developed with the muddy deep—water shelf, siliceous deep—water shelf, and calcareous shallow—water shelf facies. The Guanyinqiao Member, representing the upper part of Wufeng Formation, was developed with the transition from siliceous deep—water shelf and muddy deep—water shelf facies to a domination of muddy shallow—water shelf and calcareous shallow—water shelf facies, which was deposited during the glacial—induced global regression. The Lower Member of Longmaxi Formation was characterized by the expansion of siliceous deep—water shelf facies and contraction of muddy shallow—water shelf and calcareous shallow—water shelf facies, signifying a rapid sea level rise associated with global warming. The Upper Member of Longmaxi Formation was developed with muddy shallow—water shelf facies, with the expansion of calcareous shallow—water shelf and silty—muddy shallow—water shelf facies. The shales with higher TOC content tend to be developed in the siliceous deep—water shelf and muddy deep—water shelf facies that were distributed in the Nanchuan, Shizhu, Yongchuan, and Wuxi areas. The results of lithofacies palaeogeography reconstruction have a certain significance to predict shale—gas target areas in Wufeng and Longmaxi formations of Chongqing. 2026 Vol. 15 (1): 100314- [Abstract] ( 4 ) [HTML 1KB] PDF (18168 KB)   ( 0 ) 100315 Middle Devonian stromatoporoid—dominated reefs at Maoying, South China: New insights into age, biotic turnover and palaeogeographical model Jia—Yuan Huang, Wen Guo, Yu—Cong Sun, Wen—Kun Qie Middle Devonian was the time for extensive reefs across South China, but their importance in understanding the development of reef communities was undervalued. This study described the lithostratigraphical and palaeontological features of the Middle Devonian reef deposits at Maoying Town, Guizhou Province, South China. Two different units are recognised based on five road—cut exposures. The lower unit is characterised by argillaceous limestone, yielding a variety of auto— to autoparabiostromes. The biostromes are dominated by morphologically diverse stromatoporoids, including Gerronostromaria, Salairella, Synthetostroma, and Stachyodes, with subordinate roles of tabulate corals, rugose corals, chaetetids, bryozoans, brachiopods, gastropods, bivalves, and tubeworms. The upper unit consists mainly of parabiostromes, characterised by abundant dendroid and bulbous stromatoporoids (Amphipora, Stachyodes, and Actinostroma), along with leperditicopid ostracods, parathuramminid foraminifers, and calcispheres. The environments of these two units are interpreted to be open marine and back—reef to lagoonal environments, respectively. Newly recognised icriodid and bipennatid conodonts from the lower unit and brachiopod Stringocephalus in the upper unit indicate a Givetian age of the entire succession, pushing back the age of the latter from Frasnian of the previous thought. Comparison with nearby two sections possibly reflects a palaeogeographical turnover from ramp to isolated platform. This study sheds light on understanding how reef communities changed in relation to environmental conditions in South China during the global Givetian reef expansion. 2026 Vol. 15 (1): 100315- [Abstract] ( 3 ) [HTML 1KB] PDF (32301 KB)   ( 0 ) 100316 Late Jurassic manganese microbial carbonates of West Siberian oil and gas basin: Diagnostic features, environmental sedimentation, secondary transformations Latypova Margarita, Gafurova Dina, Churkina Valeria, Kalmykov Anton, Kalmykov Georgy This study focuses on the investigation of Late Oxfordian—Early Tithonian manganese microbial carbonates (MC) found at the top of the Georgiev regional stage in the Western Siberian oil and gas basin. In some isolated areas, these MC are oil reservoirs. However, these rocks are still one of the least studied sediments in the carbonate interval at the boundary of the Bazhenov and Georgiev subregional stage. We have described their geochemical, lithological and mineralogical composition in detail. Based on the characteristics of MC, we assumed their formation settings. The elevated MnO content, associated with microbial processes, and the high concentration of biophilic elements, both suggest the active involvement of organic matter in the formation and development of microbial sediments. The isotopic composition of carbon in the microbial carbonates further supports a biogenic source of carbon dioxide playing an important role in the formation of these deposits. We have established that the Late Jurassic manganese MC were intensely secondary altered, partially recrystallized and calcified by catagenetic processes. Isometric pyrite crystal aggregates with kutnohorite fragments were formed at the contacts between kutnohorite and calcite zones. We suggest that the presence of caverns and high reservoir potential in the microbial carbonates from the Yem—Egovskaya field of the Krasnoleninsky arch may be attributed to intense secondary catagenetic alterations. 2026 Vol. 15 (1): 100316- [Abstract] ( 7 ) [HTML 1KB] PDF (37673 KB)   ( 0 ) 100317 Ecological stability of late Maastrichtian benthic foraminifera amidst Deccan volcanism Subham Patra, Kebenle Kesen, Gerta Keller, Thierry Adatte, Jahnavi Punekar The late Maastrichtian witnessed profound disruptions in biogeochemical cycles, leading to the fifth mass extinction at the Cretaceous—Paleogene (K/Pg) boundary. At Bidart section (France), the final ~60 kyr of the Maastrichtian coincide with mercury (Hg) peaks, low magnetic susceptibility, evidence of biological stress and taphonomic alteration in planktic foraminifera, indicative of an ocean acidification event. While this event primarily appears to be a surface—ocean phenomenon, previous studies also documented a minor rise in benthic foraminiferal test fragmentation beginning 0.5 m below the K/Pg boundary, with a pronounced spike at the boundary itself. A detailed investigation of benthic foraminifera in biozone CF1 at Bidart section (France) reveals a diverse and balanced assemblage preceding the K/Pg boundary, with minimal taphonomic alterations. At the K/Pg boundary, infaunal populations diminished, diversity declined sharply, test fragmentation intensified, yet paradoxically, the absolute abundance of genera rose markedly. Preferential preservation is evident in the dominance of robust taxa (Cibicidoides spp., Coryphostoma spp.), while a high fragmentation index reflects strong taphonomic dissolution and time—averaging. A plausible explanation for this could be CO?—rich waters mixing into the ocean interior over 100—1,000 years, driving dissolution during the ~10,000—year deposition of the K/Pg boundary red clay. The stark contrast between the planktic and benthic census and morphometric data at Bidart section clearly constrains any Deccan—related calcification stress to the surface mixed layer. Lastly, the integrated planktic and benthic considerations re—emphasize a need to carefully separate taphonomic signals from true ecological stress. 2026 Vol. 15 (1): 100317- [Abstract] ( 2 ) [HTML 1KB] PDF (7336 KB)   ( 0 )

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