Geological Magazine最新文献

{"title":"U-Pb zircon dates from North American and British Avalonia bracket the Lower–Middle Cambrian boundary interval, with evaluation of the Miaolingian Series as a global unit","authors":"Ed Landing, Mark D. Schmitz, Stephen R. Westrop, Gerd Geyer","doi":"10.1017/s0016756823000729","DOIUrl":"https://doi.org/10.1017/s0016756823000729","url":null,"abstract":"High-precision U-Pb zircon ages on SE Newfoundland tuffs now bracket the Avalonian Lower–Middle Cambrian boundary. Upper Lower Cambrian Brigus Formation tuffs yield depositional ages of 507.91 ± 0.07 Ma (<jats:italic>Callavia broeggeri</jats:italic> Zone) and 507.67 ± 0.08 Ma and 507.21 ± 0.13 Ma (<jats:italic>Morocconus-Condylopyge eli</jats:italic> Assemblage interval). Lower Middle Cambrian Chamberlain’s Brook Formation tuffs have depositional ages of 506.34 ± 0.21 Ma (<jats:italic>Kiskinella cristata</jats:italic> Zone) and 506.25 ± 0.07 Ma (<jats:italic>Eccaparadoxides bennetti</jats:italic> Zone). The composite unconformity separating the Brigus and Chamberlain’s Brook formations is constrained between these ages. An Avalonian Lower–Middle Cambrian boundary between 507.2 ± 0.1 and 506.3 ± 0.2 Ma is consistent with maximum depositional age constraints from southwest Laurentia, which indicate an age for the base of the Miaolingian Series, as locally interpreted, of ≤ 506.6 ± 0.3 Ma. The Miaolingian Series’ base is interpreted as correlative within ≤ 0.3 ± 0.3 Ma between Cambrian palaeocontinents, although its exact synchrony is questionable due to taxonomic problems with a possible <jats:italic>Oryctocephalus indicus</jats:italic>-plexus, invariable dysoxic lithofacies control of <jats:italic>O. indicus</jats:italic> and diachronous occurrence of <jats:italic>O. indicus</jats:italic> in temporally distinct δ <jats:sup>13</jats:sup>C chemozones in South China and SW Laurentia. The lowest occurrence of <jats:italic>O. indicus</jats:italic> assemblages is linked to onlap (epeirogenic or eustatic) of dysoxic facies. A united Avalonia is shown by late Early Cambrian volcanics in SW New Brunswick; Cape Breton Island; SE Newfoundland; and the Wrekin area, England. The new U-Pb ages revise Avalonian geological evolution as they show rapid epeirogenic changes through depositional sequences 4a–6.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":null,"pages":null},"PeriodicalIF":2.3,"publicationDate":"2023-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138530988","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"How old is the Ordovician–Silurian boundary at Dob’s Linn, Scotland? Integrating LA-ICP-MS and CA-ID-TIMS U-Pb zircon dates","authors":"Hector K. Garza, Elizabeth J. Catlos, Kevin R. Chamberlain, Stephanie E. Suarez, Michael E. Brookfield, Daniel F. Stockli, Richard A. Batchelor","doi":"10.1017/s0016756823000717","DOIUrl":"https://doi.org/10.1017/s0016756823000717","url":null,"abstract":"Sedimentary rocks exposed at Dob’s Linn, Scotland, have significantly influenced our understanding of how life evolved over the Ordovician to Early Silurian. The current interpreted chronostratigraphic boundary between the Ordovician and Silurian periods is a Global Boundary Stratotype Section and Point (GSSP), calibrated to 443.8 ± 1.5 Ma (Hirnatian–Rhuddanian age), based on biostratigraphic markers, radioisotopic dates and statistical modelling. However, challenges arise due to tectonic disturbances, complex correlation issues and the lack of systematic dating in Ordovician–Silurian stratigraphic sections. Here, hundreds of zircon grains from three metabentonite ash horizons were dated using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). A subset of the grains were re-analyzed using Chemical Abrasion Isotope Dilution Thermal Ionization Mass Spectrometry (CA-ID-TIMS). We present a high-precision CA-ID-TIMS <jats:sup>238</jats:sup>U-<jats:sup>206</jats:sup>Pb weighted mean date of 440.44 ± 0.55/0.56/0.72 Ma (±analytical/with tracer/with U-decay constant) for the <jats:italic>Coronagraptus cyphus</jats:italic> biozone. However, the study reports younger, and in certain cases, older LA-ICP-MS zircon dates within the <jats:italic>Coronagraptus cyphus</jats:italic>, <jats:italic>Akidograptus ascensus</jats:italic> and <jats:italic>Dicellograptus anceps</jats:italic> zones, suspected as being influenced by Pb loss and LA-ICP-MS matrix mismatch. The study reports concerns about the suitability of Dob’s Linn as a GSSP section and examines various LA-ICP-MS maximum depositional age (MDA) approaches, suggesting the use of the TuffZirc date and the youngest mode weighted mean (YMWM) as suitable MDA calculations consistent with CA-ID-TIMS results.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":null,"pages":null},"PeriodicalIF":2.3,"publicationDate":"2023-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138530990","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Genesis of the Jinying gold deposit, southern Jilin Province, NE China: Constraints from geochronology and isotope geochemistry","authors":"Yong Zhang, Yushi Wu, Huali Li, Jilong Han, Quanheng Song","doi":"10.1017/s0016756823000705","DOIUrl":"https://doi.org/10.1017/s0016756823000705","url":null,"abstract":"The Jinying gold deposit is located in southern Jilin Province in northeast China and is representative of the large Early Cretaceous gold deposits in this area. To better understand ore genesis of this deposit, a multi-isotope integrated analysis of U–Pb–Rb–Sr–He–Ar–S has been carried out. Laser ablation inductively coupled plasma–mass spectrometry (LA–ICP–MS) dating of zircons from the granodiorite porphyry and dioritic porphyrite in the study area yields ages of 172.1 ± 1.2 Ma and 122.5 ± 0.8 Ma, suggesting that corresponding intrusion occurred in the Middle Jurassic and the Early Cretaceous. Rb–Sr dating of the pyrite yields an isochron age of 120 ± 3 Ma, suggesting that gold mineralization occurred in the Early Cretaceous. The fluid inclusions in pyrite yield <jats:sup>3</jats:sup>He/<jats:sup>4</jats:sup>He ratios clustered within a small range from 0.08 to 0.13 Ra, <jats:sup>40</jats:sup>Ar/<jats:sup>36</jats:sup>Ar ratios between 331.6 and 351.3, and mantle He in the range of 1.0–1.6%, indicating that the ore-forming fluids originated from a mixed crustal and mantle source. The in situ S isotopic values of pyrite vary between + 0.1 ‰ and + 2.8 ‰, suggesting that the ore-related sulphur came from the deep magmatic source. Combined with the geological history of the study area, it can be concluded that the gold mineralization was possibly related to the extensional setting associated with the rollback of the Palaeo-Pacific Plate.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":null,"pages":null},"PeriodicalIF":2.3,"publicationDate":"2023-11-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138530989","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Subducted oceanic slab break-off in a post-collisional setting: Constraints from petrogenesis of Late Carboniferous dykes in central West Junggar, Xinjiang, NW China","authors":"Rui Gao, Jinke Li, Andrew C. Kerr, Tao Wu, Long Xiao, Guocan Wang, Xinxing He","doi":"10.1017/s0016756823000663","DOIUrl":"https://doi.org/10.1017/s0016756823000663","url":null,"abstract":"Numerous Late Carboniferous – Early Permian dykes are found in West Junggar and represent an important part of the Central Asian Orogenic Belt. In this contribution, we use these dykes to assess the tectonic regime and stress state in the Late Carboniferous – Early Permian. The West Junggar dykes are mainly diorite/dioritic porphyrite with minor diabase and were formed in 324–310 Ma. They have been divided into two groups based on their orientation, petrology and geochronology. Group 1 dykes mostly comprise WNW-striking dioritic porphyrite and NE-striking diorite with minor diabase and resemble the Karamay-Baogutu sanukitoid. They were probably formed from depleted mantle at a relatively high temperature and pressure with the addition of 1–2% sediment/sedimental partial melt and 0–5% trapped oceanic crust-derived melts. Group 2 dykes are ENE-striking and are similar to sanukite in the Setouchi Volcanic Belt. These dykes were also derived from depleted mantle at a shallow depth but high temperature with the addition of 2–3.5% sediment/sedimental partial melt. Magma banding and injection folds in dykes and host granitoids indicate magma flow. Paleostress analysis reveals that both groups of dykes were formed in a tensile stress field. Their emplacement is favoured by presence of pre-existing joints or fractures in the host granitoids and strata. We conclude that large-scale asthenosphere mantle upwelling induced by trapped oceanic slab-off can explain the magmatism and significant continental crustal growth of West Junggar during Late Carboniferous to Early Permian.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":null,"pages":null},"PeriodicalIF":2.3,"publicationDate":"2023-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138543122","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The prevalence of invertebrate bioerosion on Mesozoic marine reptile bone from the Jurassic and Cretaceous of the United Kingdom: new data and implications for taphonomy and environment","authors":"Sarah Jamison-Todd, Paul Upchurch, Philip D. Mannion","doi":"10.1017/s0016756823000651","DOIUrl":"https://doi.org/10.1017/s0016756823000651","url":null,"abstract":"Abstract Invertebrate bioerosion on fossil bone can contribute to reconstructions of benthic taxonomic assemblages and inform us about oxygenation levels, water depth and exposure time on the seafloor prior to burial. However, these traces are not commonly described in the fossil record. To date, there have been only 13 published studies describing a total of 15 instances of invertebrate bioerosion on marine reptile fossil bones from the Mesozoic globally. We surveyed the collections of several UK museums with substantial occurrences of Mesozoic marine reptiles for evidence of invertebrate bioerosion. Here, we document 153 specimens exhibiting 171 newly recorded instances of invertebrate bioerosion on Jurassic and Cretaceous marine reptile bones. Several major bioeroding taxonomic groups are identified. Within the geological strata of the United Kingdom, there is a higher prevalence of bioerosion in the Cretaceous relative to the Jurassic, despite greater sampling of specimens from the Jurassic. Although biotic turnover and food web restructuring might have played a role, potentially pertaining to heightened productivity during the later stages of the Mesozoic Marine Revolution, we consider it more likely that this temporal change corresponds to differences in depositional environment and taphonomic history between the sampled rock units. In particular, the Cretaceous deposits are characterized by heightened oxygenation levels relative to their Jurassic counterparts, as well as reworking, which would have allowed two phases of bioerosion. A spatiotemporally broader dataset on invertebrate bioerosion on vertebrate bone will be important in further testing this and other hypotheses.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135872367","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Multiple sediment source infill in a low-accommodation basin: implications for the late Paleozoic sediment routing system in the southeastern Ordos Basin","authors":"Chao Fu, Xinghe Yu, Shunli Li","doi":"10.1017/s0016756823000572","DOIUrl":"https://doi.org/10.1017/s0016756823000572","url":null,"abstract":"Abstract Late Paleozoic strata in the southeastern Ordos Basin comprise targeted reservoirs for tight gas exploration. As a typical intracratonic basin, the Ordos Basin is characterized by low-accommodation space and a complex sediment infilling process, which attracts much attention. During the early Permian, the southeast area was fed by sediments from multiple sediment sources, which makes it difficult to identify the pinch-out of the sand bodies and reconstruct the sediment routing system. In this study, we reconstruct the paleo-topography of the late Paleozoic setting using high-resolution 2D and 3D seismic data. Thus, we identify two types of topography: the eastern block is presented as a semiclosed depression, and the western block is observed as a flat platform. Based on detrital zircon U–Pb data and heavy mineral assemblages, we reconstruct the provenance area and show that early Permian sediments originate from the northern margin of the Ordos Basin and from the northern Qinling orogenic belt in the south. By integrating the trace element contents, carbon and oxygen isotope data and sedimentary structure from core samples, we can observe the paleoenvironment and the corresponding facies associations in these blocks. The eastern block was infilled by a prograding delta; the western block was infilled by a tide-dominated delta or a wavy-dominated delta. By using stratigraphic forward modelling, we find that most sediments in the semiclosed setting are progradational and intensely interacted. In contrast, the sediments in the western block present an open setting, infilled and gently interacted. The fine-grained deposits were not easily preserved due to tidal or wave reworking processes in the shallow-water marine setting, and they were transported into deep-water areas. Furthermore, to explore the dominant factors in a pattern of fluvial–deltaic sand bodies formed in the low-accommodation basin, we rebuild the sediment routing system parameters and plot them on a bubble chart. According to the fitness between the depositional volume and the above parameters, we determine the key factors in the routing systems that formed. The results show that the sediment supply has a high relevance to the depositional volume in a semiclosed setting, such as the eastern block, while the terrain height may drive sedimentation in an open marine setting, such as the western block. We demonstrate that two different infill patterns and different sand-body stacking patterns with multiple sediment sources in a low-accommodation basin may serve as a model for similar settings.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135870332","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Phosphorous concentration in iron-rich rocks of the Chilpi Group, Bastar Craton, India: implications on late Palaeoproterozoic seawater palaeo-productivity","authors":"Prasanta Kumar Mishra, Sarada Prasad Mohanty, Debadutta Mohanty, Mrinal Kanti Mukherjee","doi":"10.1017/s001675682300064x","DOIUrl":"https://doi.org/10.1017/s001675682300064x","url":null,"abstract":"Abstract The concentration of the bio-limiting nutrient element, phosphorus (P), in seawater is important for primary marine productivity and the evolution of life on geological time scales. The molar percentage of P/Fe in banded iron formations (BIF) and iron oxide-rich chemical sediments is a good proxy for the first-order approximation of seawater P concentration. Bio-available concentration of phosphorus in Precambrian, especially during the late Palaeoproterozoic Era (2.0–1.8 Ga), is poorly constrained. We evaluated the P/Fe ratios of iron-rich rocks from the late Palaeoproterozoic Chilpi Group, Bastar Craton, Central India. The bulk rock molar percentage of P/Fe ratios of the Chilpi rocks vary between 0.11 and 1.17 (average 0.51 ± 0.3), and the average of EPMA spot analysis P/Fe molar ratio is 0.32 ± 0.4; both have values similar to Archaean BIFs of the world. The observed low molar ratio is not an artefact of contamination from terrestrial sources, diagenetic alterations or high-temperature hydrothermal inputs; it indicates the deposition from phosphorus-lean seawater. The modelled P/Fe molar ratio in the Chilpi Group suggests that the concentration of phosphorus in the shallow marine environment was less than 0.12 μM. The low level of phosphorus concentration in seawater during the late Palaeoproterozoic Era is interpreted to be a consequence of the low primary production during a period of low atmospheric oxygen content, which might have impeded the evolution of eukaryotes.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136261542","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 Ediacaran biota from the oldest Nama Group, Namibia (Tsaus Mountains), and re-definition of the Nama Assemblage","authors":"Rachel Wood, Fred. T. Bowyer, Ruaridh Alexander, Mariana Yilales, Collen-Issia Uahengo, Kavevaza Kaputuaza, Junias Ndeunyema, Andrew Curtis","doi":"10.1017/s0016756823000638","DOIUrl":"https://doi.org/10.1017/s0016756823000638","url":null,"abstract":"Abstract The Nama Group, Namibia (≥550.5 to <538 million years ago, Ma), preserves one of the most diverse metazoan fossil records of the terminal Ediacaran Period. We report numerous features that may be biological in origin from the shallow marine, siliciclastic, lowermost Mara Member (older than ca. 550.5 Ma) from the Tsaus Mountains. These include forms that potentially represent body fossils, Beltanelliformis and an indeterminate juvenile uniterminal rangeomorph or arboreomorph frond, plug trace fossils, Bergaueria , as well as sedimentary surface textures, which are possibly microbially induced. These are the oldest documented macrofossils in the Nama Group. They represent taxa that persist from the Avalon or White Sea assemblages prior to the later appearance of new biota, including calcified metazoans, calcified and soft-bodied tubular taxa including all cloudinids, as well as more complex trace fossils. Using a new age model that allows more accurate stratigraphic placement of major Ediacaran macrofossil morphogroups and taxa, we propose a re-definition of the Nama Assemblage following the practice for Phanerozoic evolutionary faunas to include only new morphogroups of soft-bodied tubular, calcified taxa and complex trace fossils, defined by first appearance of Cloudina , which postdates deposition of the Kanies and lower Mara members and first appears ca. 550 Ma and persists until at least 539 Ma. Finally, the Tsaus Mountain environment is pristine, unspoilt by geologists and naturalists. Following World Heritage Convention, we suggest a pledge of non-destructive excavation that all future scientists should be able to make in publications of work that involve research in this area.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135412317","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"First confident evidence of moulting in eodiscid trilobites from the Cambrian Stage 3 of South China","authors":"Yifan Wang, Jorge Esteve, Xinglian Yang, Rongxing Yu, Dezhi Wang","doi":"10.1017/s0016756823000584","DOIUrl":"https://doi.org/10.1017/s0016756823000584","url":null,"abstract":"Abstract Trilobite moulting behaviour has been extensively investigated. However, exuviae in eodiscid trilobites are poorly known. Here, we report two eodiscid trilobite specimens, Tsunyidiscus niutitangensis and Tsunyidiscus sp., showing Somersault configuration from the Niutitang Formation and Mingxinsi Formation of South China, respectively (Cambrian Series 2, Stage 3). The arrangements of the exoskeletons indicate that the two specimens are the slightly disturbed and undisturbed exuviae. The impression of the lower cephalic unit (LCU) displays the rostral plate in Tsunyidiscus niutitangensis . The exuviae showing the LCU inverted anteriorly under the trunk. The opening of the facial and rostral sutures would have allowed the emergence of the post-ecdysial trilobite with the partial enrolment of exoskeleton. Moreover, our discovery indicates a Somersault configuration which employed the facial and rostral sutures to create an anterior exuvial gape that also exists in eodiscid trilobites besides redlichiid trilobites, corynexochid trilobites and ptychopariid trilobites during the Cambrian.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135731752","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"High primary productivity in an Ediacaran shallow marine basin influenced by strong seasonal to perennial upwelling","authors":"A.H. Ansari, S.K. Pandey, Shamim Ahmad, Mukund Sharma, Pawan Govil, Amritpal Singh Chaddha, Anupam Sharma","doi":"10.1017/s0016756823000614","DOIUrl":"https://doi.org/10.1017/s0016756823000614","url":null,"abstract":"Abstract A significant area of late Neoproterozoic–early Cambrian seafloor hosted a ferruginous to euxinic condition as a result of expanded primary productivity-driven pumping of organic matter into subsurface water column and weak water column mixing in the concomitant sea. However, the cause and extent of increased marine primary productivity during this time interval remain unknown. To estimate the primary productivity in a late Neoproterozoic sea, this study investigated the Sirbu Shale, Vindhyan Supergroup, for trace elements, organic carbon isotopes and total organic carbon (TOC). Among the trace elements, cadmium (Cd), known for extremely low concentration in crustal rocks but higher abundance in biogenic organic matter, was the key parameter in the palaeoproductivity estimation. The Cd enrichment in the Sirbu Shale samples is comparable to that in modern marine sediments of the oxygen minimum zones in Chilean margins, Arabian Sea and Gulf of California characterized by high primary productivity and seasonal upwelling. In terms of Cd enrichment, the lower section of the Sirbu Shale was deposited under suboxic conditions, while the upper section was deposited under a relatively less reducing condition. Cd/Mo ratios &gt; 0.36 in the shale sample indicate that the palaeoproductivity was strongly influenced by the nutrient supply through sea-shelf upwelling. Using non-detrital enrichment of Cd in Sirbu Shale samples, we calculated that the TOC exported to the floor of Sirbu Shale palaeodepositional setting through primary productivity ranged from 0.71 to 10.16%.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135729933","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}