Gondwana Research最新文献

{"title":"Neoproterozoic arc-magmatism of the Silet Terrane, Western Hoggar (Algeria), new constraints from zircon U-Pb-Hf isotope analyses and whole rock geochemistry","authors":"Narimene Berrahmane ,&nbsp;El-Hocine Fettous ,&nbsp;Abderrahmane Bendaoud ,&nbsp;Sid Ali Doukkari ,&nbsp;Basem Zoheir ,&nbsp;Armin Zeh","doi":"10.1016/j.gr.2024.10.003","DOIUrl":"10.1016/j.gr.2024.10.003","url":null,"abstract":"<div><div>This study presents results of zircon U-Pb-Hf isotope analyses and whole-rock geochemistry applied to magmatic rocks of the Silet terrane in the Western Hoggar, forming a part of the Neoproterozoic arc exposed along the boundary between the LATEA metacraton and the Paleoproterozoic In Ouzzal terrane. According to zircon U-Pb geochronology four distinct pulses of Neoproterozoic granitoids magmatism are recognized in the Silet terrane: Tonian (c. 870–840 Ma), Late Tonian (c. 770 Ma), Latest Tonian (c. 730 Ma) and Late Cryogenian (c. 675 Ma).</div><div>Geochemical and Hf isotope data indicate a progressive shift in geotectonic settings. The c. 870–840 Ma Tonian TTG pulses (Tonalite-Trondhjemite-Granodiorite) in the North Silet batholith, with superchondritic εHf values (+5.8 to + 7.2), suggest formation in a subduction zone. The subsequent c. 770 Ma Late Tonian magmatism, characterized by mafic compositions, reflects a back-arc tectonic setting, as evidenced by high Ti/V ratios, low V contents, and εHf values of + 6.12 to + 8.95. The c. 730 Ma Latest Tonian magmatism, with more evolved acidic pulses, indicates hybrid mantle–crustal involvement (εHf + 6.53 to + 8.08). The Late Cryogenian intrusions (c. 675 Ma), featuring the lowest εHf values (+1.84 to + 4.09) and inherited c. 870 Ma zircons, suggest formation from the melting of Tonian TTGs during continental collision.</div><div>Integrating U-Pb dating with geochemical data provides a comprehensive view of the Silet terrane’s tectonic evolution, supporting a continental arc origin. Disparities in magmatism ages between the northern (c. 870–675 Ma) and southern (c. 740–640 Ma) segments of the Silet arc correlate with the diachronous collision/subduction of a V-shaped “Silet Ocean”, forming an introverted oceanic system (oceans that have formed by rifted continental blocks that were subsequently re‑joined in approximately the same position) within the broader West Gondwana context. Structural analysis indicates that the regional structures of the Silet arc were shaped in a WNW-ESE collisional transpressive regime during the Pan-African orogeny, offering new insights into the Neoproterozoic Silet arc’s geodynamic evolution and its paleogeographical location in the West Gondwana orogeny.</div></div>","PeriodicalId":12761,"journal":{"name":"Gondwana Research","volume":"137 ","pages":"Pages 234-254"},"PeriodicalIF":7.2,"publicationDate":"2024-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142441199","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Crustal variations and tectonic implications across the South Yellow Sea based on active-source wide-angle seismic analyses","authors":"Lihua Liu ,&nbsp;Chuanchuan Lü ,&nbsp;Tianyao Hao ,&nbsp;Xunhua Zhang ,&nbsp;Kwanghee Kim ,&nbsp;Hanjoon Kim ,&nbsp;Yonggang Guo","doi":"10.1016/j.gr.2024.10.001","DOIUrl":"10.1016/j.gr.2024.10.001","url":null,"abstract":"<div><div>The South Yellow Sea and its environs are pivotal for unraveling the complexities of crustal dynamics and continental collision processes. A holistic assessment of deep structural variations from northern China to the Korean Peninsula is essential for a comprehensive and accurate determination of the tectonic affinity of the Korean Peninsula.Thus, we deployed a pioneering active-source seismic profile (Line2016) spanning the South Yellow Sea and the eastern onshore region of the Korean Peninsula, provides crucial insights into the collision dynamics between the Sino-Korean Block and the Yangtze Block. Our innovative approach, incorporating forward modeling, tomography, and finite-difference wavefield modeling, yielded a high-resolution crustal P-wave velocity model, addressing a significant knowledge gap in understanding the geological intricacies between northern China and the Korean Peninsula. The results confirmed and precisely located the West Marginal Fault of the Korean Peninsula, a significant crustal-scale tectonic structure, likely representing the eastern boundary between the Yangtze Block and the Sino-Korean Block. The study advocates for classifying the Korean Peninsula as part of the Sino-Korean Block, presenting evidence for the one-part affinity hypothesis. This collision resulted in the creation of two distinct suture zones—an orogenic belt in the northern part and a significant strike-slip fault zone in the eastern part of the South Yellow Sea. The study emphasizes the pivotal role of block morphology in regulating plate convergence, providing valuable insights for understanding similar phenomena in other collision zones.</div></div>","PeriodicalId":12761,"journal":{"name":"Gondwana Research","volume":"137 ","pages":"Pages 117-130"},"PeriodicalIF":7.2,"publicationDate":"2024-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142424206","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Carboniferous–Triassic subduction in the Qinling orogen","authors":"Thomas Bader ,&nbsp;Lothar Ratschbacher ,&nbsp;Leander Franz ,&nbsp;Rolf L. Romer ,&nbsp;Lifei Zhang ,&nbsp;Christian de Capitani ,&nbsp;Joseph Mullis ,&nbsp;Marion Tichomirowa ,&nbsp;Xiaowei Li","doi":"10.1016/j.gr.2024.09.015","DOIUrl":"10.1016/j.gr.2024.09.015","url":null,"abstract":"<div><div>The Qinling–Tongbai–Hong’an–Dabie–Sulu Orogen links two cratons, North China and South China, and records the reorganization and transfer of plates from Rodinia to Gondwana and Eurasia. The formation of North Qinling at the southern North China margin (524–378 Ma) by subduction–accretion processes and the collision between North and South China (270–190 Ma) are pivotal for this reorganization. We outline the geological processes that link both events by combining phase equilibria modeling, conventional thermobarometry, U–Pb (zircon, titanite, garnet–staurolite) and ⁴⁰Ar/³⁹Ar and Rb–Sr (amphibole, micas) geochronology. The North Qinling experienced transpressional reactivation of shear zones, local fluid percolation, and metamorphism up to the lowest amphibolite facies (≲ 550 °C) until 324 Ma; protracted uplift and erosion with slow cooling (1 °C/Myr) led to its peneplanation prior to 260 Ma. The southerly abutting Wuguan Complex underwent two consecutive metamorphic events: while the older was diverse (600–750 °C, 0.5–1.2 GPa), the younger had a regionally homogeneous peak (590 °C, 0.9 GPa) at <em>c.</em> 324 Ma. Subduction and early exhumation of the South China margin occurred at 299–250 Ma in East Qinling. During the exhumation, medium-grade blueschists (500 °C, 1.0–1.3 GPa) were imbricated with low-grade rocks (300 °C, 0.5–1.0 GPa). Subsequent extensional doming with percolation of a low-salinity, hydrous fluid and south-vergent thrusting brought these rocks to near-surface levels by 200 Ma. New and published data indicate that plate convergence governed geologic processes to the south of North China not only before 378 Ma but protractedly or episodically until 190 Ma. This prolonged history is inconsistent with the amalgamation of North China to Gondwana but substantiates paleogeographic reconstructions with North China as a Paleozoic island continent. Carboniferous–Triassic subduction in the Qinling ultimately led to the welding of North China and South China, completing their transfer from Rodinia to Eurasia.</div></div>","PeriodicalId":12761,"journal":{"name":"Gondwana Research","volume":"137 ","pages":"Pages 171-208"},"PeriodicalIF":7.2,"publicationDate":"2024-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142424297","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Classifying zircon: A machine-learning approach using zircon geochemistry","authors":"Jintao Kong ,&nbsp;Hongru Yu ,&nbsp;Junyi Sun ,&nbsp;Huan Zhang ,&nbsp;Miaomiao Zhang ,&nbsp;Zhi Xia","doi":"10.1016/j.gr.2024.09.010","DOIUrl":"10.1016/j.gr.2024.09.010","url":null,"abstract":"<div><div>This study presented a novel, rapid, and accurate method for determining zircon origin via a comprehensive analysis of a dataset containing 27,818 zircon trace element sets. This method integrated back propagation neural networks with the AdaBoost algorithm. The optimal classifier characterized as a linear combination of a two-layer neural network model, comprised 100 base classifiers and 400 hidden neurons. It was rigorously trained over 1000 iterations, which resulted in an unbiased error rate of 8.31%. To facilitate practical application, the classifier was integrated into a macro-enabled Excel spreadsheet.</div></div>","PeriodicalId":12761,"journal":{"name":"Gondwana Research","volume":"137 ","pages":"Pages 227-233"},"PeriodicalIF":7.2,"publicationDate":"2024-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142441100","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Crustal structures and anisotropy in southeastern China: Continental collision and intraplate earthquakes","authors":"H.B. Huang ,&nbsp;K.Y. Wan ,&nbsp;E.Y. He ,&nbsp;H. Jiang ,&nbsp;J. Guo ,&nbsp;X.L. Qiu","doi":"10.1016/j.gr.2024.09.011","DOIUrl":"10.1016/j.gr.2024.09.011","url":null,"abstract":"&lt;div&gt;&lt;div&gt;This study investigates the role of crustal structures and anisotropy in southeastern China regarding intraplate earthquakes within the context of concentrated and perturbed tectonic stresses. The region is characterized by a complex multiphase tectonic history,including the ongoing collision between the Philippine Plate and the South China Sea margin. Utilizing the teleseismic receiver function method, we offer a comprehensive depiction of the crustal structures and layered anisotropy in Guangdong and Fujian, two earthquake-prone areas. Our results reveal that the crustal anisotropy is stratified into two layers, with a slow axis perpendicular to the orogenic belt in the upper-middle crust, whereas the fast axis aligns perpendicularly at lower crust levels. The lateral heterogeneity and anisotropy of the crustal structure emphasize both the boundary delineation and differential movement between continental blocks. The observed increase in density and intensity of intraplate earthquakes across this boundary supports our conclusion regarding a connection between decoupled crustal deformation and seismicity. Specifically, the foliation of metamorphic rocks during the Mesozoic collision generated orogen-parallel fabrics in the upper-middle crust, while ductile shearing resulted in orogen-perpendicular fast directions at lower crust levels. In contrast, mismatch evolution between continental blocks reactivated by present collision provides stress conditions conducive to earthquake occurrence in southeastern China. Our findings provide valuable insights into mechanisms behind intraplate earthquakes as well as tectonic evolution within continental collision zones.&lt;/div&gt;&lt;div&gt;Plain Language Summary&lt;/div&gt;&lt;div&gt;The mechanism of intraplate earthquakes is a topic of great interest in the study of continental collision and regional tectonic evolution. The controlling factors behind these earthquakes are highly complex and uncertain. In this study, we aim to investigate the role of crustal structures and anisotropy in southeastern China within the context of intraplate seismic activity. This region, which is currently experiencing a collision between the Philippine Plate and the South China Sea Margin, has a multiphase tectonic history that includes remnants of paleo-Pacific subduction. By utilizing the receiver function method, we provide a detailed picture of crustal structures and layered anisotropy in Guangdong and Fujian, two earthquake-prone regions in southeastern China. Our findings reveal that anisotropy in the crust can be stratified into two layers: an upper-middle crust and a lower crust with a slow axis and a fast axis, both perpendicular to the orogeny, respectively. The lateral heterogeneity and anisotropy of the crustal structure highlight the boundary and differential movement between the continental blocks. The enhanced density and intensity of the intraplate earthquakes across this boundary provide evidence for a connection between ","PeriodicalId":12761,"journal":{"name":"Gondwana Research","volume":"137 ","pages":"Pages 1-12"},"PeriodicalIF":7.2,"publicationDate":"2024-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142424197","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"New Mesozoic APWP for Adria aided by data from the Transdanubian Range Unit – Tectonic interpretation in the Europe – Africa geodynamic system","authors":"Emő Márton ,&nbsp;János Haas ,&nbsp;Gábor Imre ,&nbsp;Máté Velki ,&nbsp;László Fodor","doi":"10.1016/j.gr.2024.09.006","DOIUrl":"10.1016/j.gr.2024.09.006","url":null,"abstract":"<div><div>Mesozoic paleomagnetic data from the Transdanubian Range Unit (TRU) of the Pannonian Basin has been revised and updated to enable its paleogeographic evolution within SE Europe to be evaluated. After a 30° declination correction, the TRU data are fully consistent with those for Adria which has an almost identical stratigraphic history. This enabled a revised Apparent Polar Wander Path (APWP) to be constructed for the combined data. Comparing this with the corresponding African and European APWP shows that Adria separated from Europe around 190 Ma, then moved independently southwards between 170–120 Ma (a 30° clockwise rotation changing to counter-clockwise around 155–145 Ma). After 155 Ma, there was a northward movement that brought Adria close to the stable European margin by 115 Ma. This latter may have been with or independently of Africa. After 100 Ma, Africa and Adria moved in coordination until the end of the Cretaceous. This sequence of events correlated well with geologically established tectonic events. These include the major extensional phases in the Alpine Tethys during the southward shift and large clockwise rotation (170–155/145 Ma). This was followed by ophiolite obduction in the Neotethys (West and East Vardar) around 155–145 Ma as a result of the dramatic reversal in the displacement of Adria. Finally, around 115 Ma, the TRU was emplaced over Austroalpine units as a thick nappe associated with the general uplift in the Adriatic realm.</div></div>","PeriodicalId":12761,"journal":{"name":"Gondwana Research","volume":"137 ","pages":"Pages 274-298"},"PeriodicalIF":7.2,"publicationDate":"2024-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142446828","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Chemical and isotopic investigation of the I-type Bega Batholith, southeastern Australia: Implications for batholith compositional zoning and crustal evolution in accretionary orogens","authors":"Jack E. Stirling ,&nbsp;Anthony I.S. Kemp ,&nbsp;Malcolm T. McCulloch ,&nbsp;Steven W. Denyszyn","doi":"10.1016/j.gr.2024.09.014","DOIUrl":"10.1016/j.gr.2024.09.014","url":null,"abstract":"<div><div>Cordilleran granitic batholiths represent significant episodes of crustal growth and differentiation, and commonly display lateral isotopic and chemical variations. Establishing the tectono-magmatic processes responsible for generating this compositional asymmetry is important for understanding crustal evolutionary processes throughout the Phanerozoic. The Bega Batholith, an example of a ‘Cordilleran style’ granite batholith, is the largest I-type Siluro-Devonian granite complex in the Lachlan Fold Belt (LFB) of southeastern Australia and comprises seven granite supersuites that display systematic lateral isotopic and chemical asymmetry. From west to east towards the present-day continental margin, an increase in the content of Na₂O, Sr, Al₂O₃, and P₂O₅, with concomitant decreases in CaO, Sc, Rb, and V are observed. In the same direction, whole-rock initial ⁸⁷Sr/⁸⁶Sr decreases from 0.7098 to 0.7039, ε_Nd values increase from −8.3 to +4.4, and δ¹⁸O decreases from 10.2 ‰ to 7.9 ‰. Depleted-mantle model ages also decrease from ca. 1800 Ma in the west to 600 Ma in the east. Here, we address whether these chemical and isotopic variations were generated by interaction between two distinct components (mantle-derived magmas and supracrustal sources) or were alternatively produced by partial melting of infracrustal source rocks formed sequentially by much earlier episodes of crustal underplating. Combined whole-rock Nd-Sr-O isotopic and geochemical analyses indicate that several I-type supersuites exhibit chemical and isotopic correlations consistent with two-component magma mixing. This new evidence challenges the long-held view that I-type granites derive exclusively from the melting of infracrustal sources, and that granite terranes represent wholesale crustal reworking rather than new crustal growth. Our results show that the compositional zoning within the Bega Batholith is multifaceted. Firstly, the presence of two discrete mantle sources endows chemically and isotopically distinct eastern and western segments in the batholith. Secondly, within these compositionally distinct regions the lateral compositional changes across supersuites derives from mixing between mantle-derived and supracrustal sources. Finally, progressive extension within a developing back-arc environment regulates the ratio of crust-mantle contributions and compositional architecture of each I-type supersuite.</div></div>","PeriodicalId":12761,"journal":{"name":"Gondwana Research","volume":"137 ","pages":"Pages 79-98"},"PeriodicalIF":7.2,"publicationDate":"2024-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142424202","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The mid-Cretaceous bauxites of SE France: Geochemistry, U-Pb zircon dating and their implications for the paleogeography at the junction between Alpine Tethys and Pyrenean Rift","authors":"Nicola Mondillo ,&nbsp;Cyril Chelle-Michou ,&nbsp;Francesco Putzolu ,&nbsp;Giuseppina Balassone ,&nbsp;Angela Mormone ,&nbsp;Licia Santoro ,&nbsp;Salvatore Cretella ,&nbsp;Gennaro Scognamiglio ,&nbsp;Marcella Tarallo ,&nbsp;Stefano Tavani","doi":"10.1016/j.gr.2024.09.012","DOIUrl":"10.1016/j.gr.2024.09.012","url":null,"abstract":"<div><div>Karst bauxites mark episodic exhumation of carbonate platforms, thus providing key information for basin analysis and paleoclimate processes at the regional to continental scale. Most karst bauxite deposits of SE France lie between Jurassic platform carbonates in the footwall and Upper Cretaceous marine to continental sediments in the hanging wall. These deposits delineate a stratigraphic gap coeval with the Durance extensional tectonics, which led to the separation of the Vocontian and South Provence Basins, and shaped the junction between the Alpine Tethys and the Pyrenean Rift.</div><div>Our new mineralogical and geochemical data show that SE France karst bauxites were affected by in-situ weathering and alteration in conjunction to sedimentary reworking. Statistical analysis of geochemical data indicates that bauxite deposits have a similar chemical footprint, likely pointing to a common and long-lasting bauxitization process. New U-Pb zircon data from the Provence deposits confirm that the source material for the SE France bauxites is to be primarily found in the Hercynian basement. The data suggest the presence of an additional exotic zircon source deriving either from Avalonia and/or Baltica. The comparison of the new U-Pb zircon data with those on coeval bauxites evidences a marked difference between the SE France and the Sardinian deposits. This difference indicates diversification in the detritus provenance of the two areas since the Lower Cretaceous, setting the bauxites of SE France and Sardinia in lateral continuity with the bauxites occurring on the two opposite margins of the Pyrenean Rift, and supporting the development of these deposits on the shoulders of the rift-related basin formed at the eastern termination of the Pyrenean Rift.</div></div>","PeriodicalId":12761,"journal":{"name":"Gondwana Research","volume":"137 ","pages":"Pages 145-170"},"PeriodicalIF":7.2,"publicationDate":"2024-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142424305","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Recognizing microbial manganese reduction in lacustrine carbonate and its linkage to terrestrial biogeochemical processes","authors":"Xubin Wang ,&nbsp;Lin Dong ,&nbsp;Yiwu Wang ,&nbsp;Zhijun Jin","doi":"10.1016/j.gr.2024.09.013","DOIUrl":"10.1016/j.gr.2024.09.013","url":null,"abstract":"<div><div>Carbonate authigenesis, the in situ precipitation of carbonate minerals within the sediment porewaters, is a key pathway for carbonate deposition and plays a crucial role in global biogeochemical cycles. Heterotrophic microorganisms are essential in regulating authigenic carbonate formation, primarily through the consumption of organic matter. Although bacterial manganese reduction is known to influence the formation of rhodochrosite and dolomite, its role in limestone deposition is unclear. Here, we present a systematic investigation of mixed calcareous siliciclastic rocks from a Paleogene freshwater lake to identify the formation of authigenic carbonate, decode the role of microbial Mn reduction, and understand the microbial response to ancient lacustrine environmental changes. The positive correlation between carbonate fraction in bulk samples (Carb%) and Mn content in carbonate minerals (Mn_carb) suggests that carbonate precipitation is stimulated by Mn²⁺ enrichment. The dissimilarity between Mn_carb and Fe_carb, along with the synergic variations of Mn_carb and diagenetic indicators, support an authigenic rather than a hydrogenetic origin for the carbonates. Using a one-dimensional diffusion–advection-reaction model, we quantify the impact of Mn reduction on promoting carbonate precipitation. Furthermore, correlations between P_carb and other values–positive with the chemical index alteration (CIA), negative with Mn_carb, and none with TOC–suggest that nitrogen availability, regulated by continental weathering, is likely the primary factor limiting both the primary productivity and the bacterial reduction intensity at the study site. Overall, this study uncovers the role of microbial Mn reduction in stimulating authigenic carbonate precipitation, and reveals the modulation mechanism of Mn-reducing microorganisms in an ancient lake. These findings shed new light on the authigenic limestone formation mechanisms and provide a new perspective on interpreting the authigenic impacts on carbonate chemistry.</div></div>","PeriodicalId":12761,"journal":{"name":"Gondwana Research","volume":"137 ","pages":"Pages 36-55"},"PeriodicalIF":7.2,"publicationDate":"2024-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142424200","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A new “silesaurid” from the oldest dinosauromorph-bearing beds of South America provides insights into the early evolution of bird-line archosaurs","authors":"Rodrigo Temp Müller","doi":"10.1016/j.gr.2024.09.007","DOIUrl":"10.1016/j.gr.2024.09.007","url":null,"abstract":"<div><div>Investigations regarding the early evolutionary history of bird-line archosaurs have undergone significant advancements in recent years. However, controversies remain, especially regarding the phylogenetic position of “silesaurids”. Whereas some hypotheses place these archosaurs as the sister-group to dinosaurs, others suggest that “silesaurids” are early ornithischian dinosaurs. Despite the phylogenetic disputes, “silesaurids” are a crucial group for comprehending the origins and early evolution of dinosaurs. In the present study, a new “silesaurid” from the Middle-Upper Triassic of Southern Brazil is described. <em>Gondwanax paraisensis</em> gen. et sp. nov. comes from the <em>Dinodontosaurus</em> Assemblage Zone of the Santa Maria Formation (Ladinian-Carnian boundary), representing one of the oldest “silesaurids” worldwide. Furthermore, <em>Gondwanax paraisensis</em> gen. et sp. nov is the oldest “silesaurid” with three sacral vertebrae, a feature usually observed in more derived forms. In addition, distinct from any other Triassic Pan-Aves, the new taxon bears an incipient fourth trochanter of the femur. This unique combination of features indicates a high diversity of locomotor strategies among early pan-avians. The co-occurrence of <em>Gondwanax paraisensis</em> gen. et sp. nov. and <em>Gamatavus antiquus</em> in the same Assemblage Zone represents the oldest evidence of sympatry among “silesaurids” in South America. Indeed, the unique combination of sacral and hindlimb features may suggest distinct behaviors for these species, potentially leading to niche differentiation within the same ecosystems.</div></div>","PeriodicalId":12761,"journal":{"name":"Gondwana Research","volume":"137 ","pages":"Pages 13-28"},"PeriodicalIF":7.2,"publicationDate":"2024-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142424198","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}