Pub Date : 2023-02-17DOI: 10.1017/S0016756823000018
N. Salehi, A. Torkian, T. Furman, P. L. le Roux
Abstract The Pliocene–Quaternary volcanic rocks which outcrop between Qorveh and Bijar are part of post-collisional within-plate volcanic activity in northern Iran. These mafic alkaline rocks form part of the northern arm of the Sanandaj–Sirjan (Hamedan–Tabriz) zone. Thermobarometry on equilibrium clinopyroxene – whole-rock pairs yields pressures and temperatures of 4–6 (±1.8) kbar and 1182–1213 (±27) °C, respectively; olivine – whole-rock (melt) equilibrium thermometry yields crystallization temperatures of 1212–1264 (±27) °C. Field relationships, including the presence of pyroxenitic xenoliths, and geochemical evidence (e.g. high FeO/MnO, and low CaO compared to lavas derived from peridotite sources) suggest a pyroxenitic mantle source for the studied rocks. Variation of trace elements and isotopic ratios (i.e. Ce/Pb, Ba/La, 87Sr/86Sr) indicate that this pyroxenite mantle source was generated by interaction between melted sediments of the subducted Neo-Tethys slab with ambient peridotitic lithospheric mantle. The resulting metasomatized lithosphere is denser and has a lower viscosity than the peridotitic mantle, and tectonic disturbance can cause it to fall into the depths of the mantle. The descending volatile-rich material starts to melt with increasing temperature. Modelling of rare earth element (REE) abundances suggests that <1 % partial melting of the descending pyroxenite could create the Plio-Quaternary alkali basaltic magma of the Qorveh–Bijar. The geochemical evidence for lithospheric foundering, and hence drip magmatism, in the Qorveh–Bijar volcanic belt is supported by seismographic studies indicating thinned lithosphere beneath the study area.
{"title":"Petrogenesis and geochemical characteristics of Plio-Quaternary alkali basalts from the Qorveh–Bijar volcanic belt, Kurdistan Province, NW Iran","authors":"N. Salehi, A. Torkian, T. Furman, P. L. le Roux","doi":"10.1017/S0016756823000018","DOIUrl":"https://doi.org/10.1017/S0016756823000018","url":null,"abstract":"Abstract The Pliocene–Quaternary volcanic rocks which outcrop between Qorveh and Bijar are part of post-collisional within-plate volcanic activity in northern Iran. These mafic alkaline rocks form part of the northern arm of the Sanandaj–Sirjan (Hamedan–Tabriz) zone. Thermobarometry on equilibrium clinopyroxene – whole-rock pairs yields pressures and temperatures of 4–6 (±1.8) kbar and 1182–1213 (±27) °C, respectively; olivine – whole-rock (melt) equilibrium thermometry yields crystallization temperatures of 1212–1264 (±27) °C. Field relationships, including the presence of pyroxenitic xenoliths, and geochemical evidence (e.g. high FeO/MnO, and low CaO compared to lavas derived from peridotite sources) suggest a pyroxenitic mantle source for the studied rocks. Variation of trace elements and isotopic ratios (i.e. Ce/Pb, Ba/La, 87Sr/86Sr) indicate that this pyroxenite mantle source was generated by interaction between melted sediments of the subducted Neo-Tethys slab with ambient peridotitic lithospheric mantle. The resulting metasomatized lithosphere is denser and has a lower viscosity than the peridotitic mantle, and tectonic disturbance can cause it to fall into the depths of the mantle. The descending volatile-rich material starts to melt with increasing temperature. Modelling of rare earth element (REE) abundances suggests that <1 % partial melting of the descending pyroxenite could create the Plio-Quaternary alkali basaltic magma of the Qorveh–Bijar. The geochemical evidence for lithospheric foundering, and hence drip magmatism, in the Qorveh–Bijar volcanic belt is supported by seismographic studies indicating thinned lithosphere beneath the study area.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":"160 1","pages":"888 - 904"},"PeriodicalIF":2.3,"publicationDate":"2023-02-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43366465","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}
Pub Date : 2023-02-15DOI: 10.1017/S0016756822001315
A. Chatterjee, N. C. Chalapathi Rao, R. Pandey, Ashutosh Pandey
Abstract Subduction-related kimberlite-borne eclogite xenoliths of the Precambrian age may provide significant information about the evolution and recycling of a subducting crust as exhumed/orogenic eclogites of the pre-Mesoproterozoic time-frame are globally rare. In this paper, we report a kimberlite-borne eclogite xenolith from the diamondiferous Kalyandurg kimberlite cluster of the Eastern Dharwar Craton, India, which contains a plethora of ultra-high-pressure minerals such as coesite, majoritic garnet, and supersilicic K-rich omphacite. The presence of these ultra-high-pressure minerals is confirmed by in situ X-ray diffractometry, laser Raman spectra and electron probe microanalysis. The presence of coesite undisputedly pinpoints a subduction origin for the eclogite at ∼2.8 GPa pressure, which corresponds to ∼100 km depth. The geothermobarometric estimations involving garnet–omphacite–kyanite–coesite reveal that such an eclogitic assemblage equilibrated at ∼5–8 GPa (∼175–280 km) pressure during ultra-deep subduction. The textural relationship between omphacite, coarse-grained garnet and majoritic garnet coupled with the laser Raman spectra and geobarometric estimations obtained from the majoritic garnet demonstrate that the majoritic garnet formed at ∼8–19 GPa (∼280–660 km) owing to disassociation of omphacite and coarse-grained garnet to majoritic garnet during increment of pressure up to the mantle transition zone. Thus, the mineralogical and geothermobarometric data suggest that the studied eclogite possibly travelled down to the mantle transition zone before it was rapidly carried up by a pre-Mesoproterozoic mantle plume, and subsequently entrained as a xenolith by the Mesoproterozoic (∼1.1 Ga) kimberlite.
{"title":"Mantle transition zone-derived eclogite xenolith entrained in a diamondiferous Mesoproterozoic (∼1.1 Ga) kimberlite from the Eastern Dharwar Craton, India: evidence from a coesite, K-omphacite, and majoritic garnet assemblage","authors":"A. Chatterjee, N. C. Chalapathi Rao, R. Pandey, Ashutosh Pandey","doi":"10.1017/S0016756822001315","DOIUrl":"https://doi.org/10.1017/S0016756822001315","url":null,"abstract":"Abstract Subduction-related kimberlite-borne eclogite xenoliths of the Precambrian age may provide significant information about the evolution and recycling of a subducting crust as exhumed/orogenic eclogites of the pre-Mesoproterozoic time-frame are globally rare. In this paper, we report a kimberlite-borne eclogite xenolith from the diamondiferous Kalyandurg kimberlite cluster of the Eastern Dharwar Craton, India, which contains a plethora of ultra-high-pressure minerals such as coesite, majoritic garnet, and supersilicic K-rich omphacite. The presence of these ultra-high-pressure minerals is confirmed by in situ X-ray diffractometry, laser Raman spectra and electron probe microanalysis. The presence of coesite undisputedly pinpoints a subduction origin for the eclogite at ∼2.8 GPa pressure, which corresponds to ∼100 km depth. The geothermobarometric estimations involving garnet–omphacite–kyanite–coesite reveal that such an eclogitic assemblage equilibrated at ∼5–8 GPa (∼175–280 km) pressure during ultra-deep subduction. The textural relationship between omphacite, coarse-grained garnet and majoritic garnet coupled with the laser Raman spectra and geobarometric estimations obtained from the majoritic garnet demonstrate that the majoritic garnet formed at ∼8–19 GPa (∼280–660 km) owing to disassociation of omphacite and coarse-grained garnet to majoritic garnet during increment of pressure up to the mantle transition zone. Thus, the mineralogical and geothermobarometric data suggest that the studied eclogite possibly travelled down to the mantle transition zone before it was rapidly carried up by a pre-Mesoproterozoic mantle plume, and subsequently entrained as a xenolith by the Mesoproterozoic (∼1.1 Ga) kimberlite.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":"160 1","pages":"874 - 887"},"PeriodicalIF":2.3,"publicationDate":"2023-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43109172","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}
Pub Date : 2023-02-15DOI: 10.1017/S001675682300002X
Jin-bo Hou, N. Hughes, M. Hopkins
Abstract Efficient extraction of oxygen from ambient waters played a critical role in the development of early arthropods. Maximizing gill surface area enhanced oxygen uptake ability but, with gills necessarily exposed to the external environment, also presented the issue of gill contamination. Here we document setae inserted on the dorsal surface of walking legs of the benthic-dwelling middle Cambrian Olenoides serratus and on the gill shaft of the Late Ordovician Triarthrus eatoni. Based on their physical positions relative to gill filaments, we interpret these setae to have been used to groom the gills, removing particles trapped among the filaments. The coordination between setae and gill filaments is comparable to that seen among modern crustaceans, which use a diverse set of setae-bearing appendages to penetrate between gill filaments when grooming. Grooming is known relatively early in trilobite evolutionary history and would have enhanced gill efficiency by maximizing the surface area for oxygen uptake.
{"title":"Gill grooming in middle Cambrian and Late Ordovician trilobites","authors":"Jin-bo Hou, N. Hughes, M. Hopkins","doi":"10.1017/S001675682300002X","DOIUrl":"https://doi.org/10.1017/S001675682300002X","url":null,"abstract":"Abstract Efficient extraction of oxygen from ambient waters played a critical role in the development of early arthropods. Maximizing gill surface area enhanced oxygen uptake ability but, with gills necessarily exposed to the external environment, also presented the issue of gill contamination. Here we document setae inserted on the dorsal surface of walking legs of the benthic-dwelling middle Cambrian Olenoides serratus and on the gill shaft of the Late Ordovician Triarthrus eatoni. Based on their physical positions relative to gill filaments, we interpret these setae to have been used to groom the gills, removing particles trapped among the filaments. The coordination between setae and gill filaments is comparable to that seen among modern crustaceans, which use a diverse set of setae-bearing appendages to penetrate between gill filaments when grooming. Grooming is known relatively early in trilobite evolutionary history and would have enhanced gill efficiency by maximizing the surface area for oxygen uptake.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":"160 1","pages":"905 - 910"},"PeriodicalIF":2.3,"publicationDate":"2023-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41471227","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}
Pub Date : 2023-02-14DOI: 10.1017/S0016756822001297
M. Rakociński, Daria Książak, Agnieszka Pisarzowska, M. Zatoń, M. Aretz
Abstract The mid-Tournaisian black radiolarian cherts of the Lydiennes Formation are exposed in deep-shelf successions of the Puech de la Suque and Col des Tribes sections of the Mont Peyroux Nappe area in the Montagne Noire, southern France. This interval represents the mid-Tournaisian anoxic event that is also termed the Lower Alum Shale Event. This event is associated with a global marine transgression that was characterized by increased productivity and drastic facies changes from pelagic carbonate sedimentation to the widespread deposition of black organic-rich siliceous shales and radiolarites in many parts of the world. In the present study, high-resolution inorganic geochemistry and framboidal pyrite analyses were employed to decipher changes in depositional conditions during the mid-Tournaisian anoxic event in the Montagne Noire. The results show that the total organic carbon contents of sediments associated with the Lower Alum Shale Event vary from 0.09 to 1.9 wt %. These low to moderate total organic carbon contents, high U/Th, low Corg/P and intermediate V/Cr ratios, enrichment in redox-sensitive trace elements, such as U, Mo and V, as well as varying sizes of pyrite framboids, indicate periodic dysoxic to anoxic bottom-water conditions during deposition of the studied sediments. Anomalous Hg spikes (>500 ppb) are also reported in the mid-Tournaisian deep-water marine succession of the Montagne Noire in the present study, which confirm a possible influence of increased regional volcanic activity during this environmental turnover.
摘要Lydiennes组的Tournaisian中期黑色放射虫燧石暴露在法国南部Noire Monta Peyroux Nappe地区Puech de la Suque和Col des Tribes地区的深陆架序列中。该层段代表图尔奈期中期缺氧事件，也称为下明矾页岩事件。这一事件与全球海侵有关，其特征是生产力的提高和从远洋碳酸盐沉积到世界许多地区广泛沉积的富含有机物的黑色硅质页岩和放射虫的剧烈相变化。在本研究中，采用了高分辨率无机地球化学和锤状黄铁矿分析来解读黑蒙塔涅图尔奈期中期缺氧事件期间沉积条件的变化。结果表明，与下明矾页岩事件有关的沉积物的总有机碳含量在0.09-1.9wt%之间。这些低至中等的总有机碳含量、高U/Th、低Corg/P和中等V/Cr比率、氧化还原敏感微量元素（如U、Mo和V）的富集，以及不同大小的黄铁矿碎屑，表明在所研究沉积物的沉积过程中，底层水条件周期性地缺氧。在本研究中，在蒙塔涅-诺伊尔的图尔奈期中期深水海洋序列中也报告了异常汞峰值（>500 ppb），这证实了在这种环境转换过程中区域火山活动增加的可能影响。
{"title":"Weak and intermittent anoxia during the mid-Tournaisian (Mississippian) anoxic event in the Montagne Noire, France","authors":"M. Rakociński, Daria Książak, Agnieszka Pisarzowska, M. Zatoń, M. Aretz","doi":"10.1017/S0016756822001297","DOIUrl":"https://doi.org/10.1017/S0016756822001297","url":null,"abstract":"Abstract The mid-Tournaisian black radiolarian cherts of the Lydiennes Formation are exposed in deep-shelf successions of the Puech de la Suque and Col des Tribes sections of the Mont Peyroux Nappe area in the Montagne Noire, southern France. This interval represents the mid-Tournaisian anoxic event that is also termed the Lower Alum Shale Event. This event is associated with a global marine transgression that was characterized by increased productivity and drastic facies changes from pelagic carbonate sedimentation to the widespread deposition of black organic-rich siliceous shales and radiolarites in many parts of the world. In the present study, high-resolution inorganic geochemistry and framboidal pyrite analyses were employed to decipher changes in depositional conditions during the mid-Tournaisian anoxic event in the Montagne Noire. The results show that the total organic carbon contents of sediments associated with the Lower Alum Shale Event vary from 0.09 to 1.9 wt %. These low to moderate total organic carbon contents, high U/Th, low Corg/P and intermediate V/Cr ratios, enrichment in redox-sensitive trace elements, such as U, Mo and V, as well as varying sizes of pyrite framboids, indicate periodic dysoxic to anoxic bottom-water conditions during deposition of the studied sediments. Anomalous Hg spikes (>500 ppb) are also reported in the mid-Tournaisian deep-water marine succession of the Montagne Noire in the present study, which confirm a possible influence of increased regional volcanic activity during this environmental turnover.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":"160 1","pages":"831 - 854"},"PeriodicalIF":2.3,"publicationDate":"2023-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41705398","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}
Pub Date : 2023-02-10DOI: 10.1017/S0016756822001273
Mahboob Alam, Tripti Muguli, G. P. Gurumurthy, M. Arif, Y. Sohrin, A. Singh, T. Radhakrishna, D. Pandey, Komal Verma
Abstract Palaeo-monsoon and palaeoclimate conditions over Southeast Asia are a matter of debate despite notable studies on the continental and oceanic sedimentary record. The present study investigates the environmental magnetic and geochemical records preserved in the deep marine sediments of the northeastern (NE) Arabian Sea to elucidate the erosion history of the western Himalayas and its link with the prevailing hydroclimatic conditions since the late Miocene. For this, the sediment core retrieved during International Ocean Discovery Program (IODP) Expedition 355 at Site U1457 in the NE Arabian Sea has been explored. The results reveal that the hydroclimatic conditions were predominantly arid during the late Miocene, except for humid intervals from 6.1 Ma to 5.6 Ma. Humid climate conditions in the Indus River Basin returned during the mid-Pliocene and continued to the Pleistocene with an intense chemical weathering regime from 1.9 Ma to 1.2 Ma. The dominant sediment source to the NE Arabian Sea at Site U1457 during the late Miocene and the Pliocene was the Indus River, while during the Pleistocene, mixed sediments brought by the Indus River and the Peninsular Indian rivers were observed. The sediment contribution from a chemically less altered mafic source (the Deccan basalts) increased between 1.2 Ma and 0.2 Ma, possibly linked to a weak Indian Summer Monsoon. The summer monsoon wind strength and associated shift in the Inter-Tropical Convergence Zone (ITCZ) influenced the dominant sediment provenance at Site U1457 of the Laxmi Basin.
{"title":"Hydroclimatic conditions and sediment provenance in the northeastern Arabian Sea since the late Miocene: insights from geochemical and environmental magnetic records at IODP Site U1457 of the Laxmi Basin","authors":"Mahboob Alam, Tripti Muguli, G. P. Gurumurthy, M. Arif, Y. Sohrin, A. Singh, T. Radhakrishna, D. Pandey, Komal Verma","doi":"10.1017/S0016756822001273","DOIUrl":"https://doi.org/10.1017/S0016756822001273","url":null,"abstract":"Abstract Palaeo-monsoon and palaeoclimate conditions over Southeast Asia are a matter of debate despite notable studies on the continental and oceanic sedimentary record. The present study investigates the environmental magnetic and geochemical records preserved in the deep marine sediments of the northeastern (NE) Arabian Sea to elucidate the erosion history of the western Himalayas and its link with the prevailing hydroclimatic conditions since the late Miocene. For this, the sediment core retrieved during International Ocean Discovery Program (IODP) Expedition 355 at Site U1457 in the NE Arabian Sea has been explored. The results reveal that the hydroclimatic conditions were predominantly arid during the late Miocene, except for humid intervals from 6.1 Ma to 5.6 Ma. Humid climate conditions in the Indus River Basin returned during the mid-Pliocene and continued to the Pleistocene with an intense chemical weathering regime from 1.9 Ma to 1.2 Ma. The dominant sediment source to the NE Arabian Sea at Site U1457 during the late Miocene and the Pliocene was the Indus River, while during the Pleistocene, mixed sediments brought by the Indus River and the Peninsular Indian rivers were observed. The sediment contribution from a chemically less altered mafic source (the Deccan basalts) increased between 1.2 Ma and 0.2 Ma, possibly linked to a weak Indian Summer Monsoon. The summer monsoon wind strength and associated shift in the Inter-Tropical Convergence Zone (ITCZ) influenced the dominant sediment provenance at Site U1457 of the Laxmi Basin.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":"160 1","pages":"813 - 829"},"PeriodicalIF":2.3,"publicationDate":"2023-02-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46078224","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}
Pub Date : 2023-02-08DOI: 10.1017/S0016756822001261
R. Bicknell, J. D. Holmes, D. García‐Bellido, J. Paterson
Abstract Malformed trilobite specimens present important insight into understanding how this extinct arthropod group recovered from developmental or moulting malfunctions, pathologies, and injuries. Previously documented examples of malformed trilobite specimens are often considered in isolation, with few studies reporting on multiple malformations in the same species. Here we report malformed specimens of the ellipsocephaloid trilobite Estaingia bilobata from the Emu Bay Shale Konservat-Lagerstätte (Cambrian Series 2, Stage 4) on Kangaroo Island, South Australia. Ten malformed specimens exhibiting injuries, pathologies, and a range of teratologies are documented. Furthermore, five examples of mangled exoskeletons are presented, indicative of predation on E. bilobata. Considering the position of malformed and normal specimens of E. bilobata in bivariate space, we demonstrate that the majority of malformed specimens cluster among the larger individuals. Such specimens may exemplify larger forms successfully escaping predation attempts, but could equally represent individuals exhibiting old injuries that were made during earlier (smaller) growth stages that have healed through subsequent moulting events. The available evidence from the Emu Bay Shale suggests that this small, extremely abundant trilobite likely played an important role in the structure of the local ecosystem, occupying a low trophic level and being preyed upon by multiple durophagous arthropods. Furthermore, the scarcity of malformed E. bilobata specimens demonstrates how rarely injuries, developmental malfunctions, and pathological infestations occurred within the species.
{"title":"Malformed individuals of the trilobite Estaingia bilobata from the Cambrian Emu Bay Shale and their palaeobiological implications","authors":"R. Bicknell, J. D. Holmes, D. García‐Bellido, J. Paterson","doi":"10.1017/S0016756822001261","DOIUrl":"https://doi.org/10.1017/S0016756822001261","url":null,"abstract":"Abstract Malformed trilobite specimens present important insight into understanding how this extinct arthropod group recovered from developmental or moulting malfunctions, pathologies, and injuries. Previously documented examples of malformed trilobite specimens are often considered in isolation, with few studies reporting on multiple malformations in the same species. Here we report malformed specimens of the ellipsocephaloid trilobite Estaingia bilobata from the Emu Bay Shale Konservat-Lagerstätte (Cambrian Series 2, Stage 4) on Kangaroo Island, South Australia. Ten malformed specimens exhibiting injuries, pathologies, and a range of teratologies are documented. Furthermore, five examples of mangled exoskeletons are presented, indicative of predation on E. bilobata. Considering the position of malformed and normal specimens of E. bilobata in bivariate space, we demonstrate that the majority of malformed specimens cluster among the larger individuals. Such specimens may exemplify larger forms successfully escaping predation attempts, but could equally represent individuals exhibiting old injuries that were made during earlier (smaller) growth stages that have healed through subsequent moulting events. The available evidence from the Emu Bay Shale suggests that this small, extremely abundant trilobite likely played an important role in the structure of the local ecosystem, occupying a low trophic level and being preyed upon by multiple durophagous arthropods. Furthermore, the scarcity of malformed E. bilobata specimens demonstrates how rarely injuries, developmental malfunctions, and pathological infestations occurred within the species.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":"160 1","pages":"803 - 812"},"PeriodicalIF":2.3,"publicationDate":"2023-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46127235","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}
Pub Date : 2023-02-06DOI: 10.1017/S0016756822001236
Zaitian Zhang, Yadong Sun
Abstract Subdivisions of Ladinian–Carnian boundary beds and the lower Carnian strata in South China are challenging owing to a paucity of west Tethyan ammonoids. We investigated a conodont fauna in a continuous section at Yize in eastern Yunnan Province to provide a biostratigraphic solution. Five genera and 24 conodont species are recognized, and five conodont zones are established. The zones are, in ascending order, the Paragondolella inclinata Zone, the Quadralella polygnathiformis Zone, the Quadralella praelindae Zone, the Quadralella auriformis Zone and the Quadralella robusta Zone. The Ladinian–Carnian boundary is provisionally defined by the first occurrences of Quadralella polygnathiformis and Quadralella intermedia in the cherty limestone member of the Zhuganpo Formation. Regional correlations via conodont biostratigraphy indicate that the Zhuganpo Formation is probably diachronous, with a maximal range spanning the upper Ladinian to the lower Carnian. Amongst all common late Ladinian – early Carnian conodont genera, Paragondolella, Quadralella and Mazzaella are probably cosmopolitan. Budurovignathus was restricted to a few basins and probably preferred offshore or deep-water environments.
{"title":"The Ladinian–Carnian conodont fauna at Yize, Yunnan, southwestern China, with implications for conodont palaeoecology and palaeogeography","authors":"Zaitian Zhang, Yadong Sun","doi":"10.1017/S0016756822001236","DOIUrl":"https://doi.org/10.1017/S0016756822001236","url":null,"abstract":"Abstract Subdivisions of Ladinian–Carnian boundary beds and the lower Carnian strata in South China are challenging owing to a paucity of west Tethyan ammonoids. We investigated a conodont fauna in a continuous section at Yize in eastern Yunnan Province to provide a biostratigraphic solution. Five genera and 24 conodont species are recognized, and five conodont zones are established. The zones are, in ascending order, the Paragondolella inclinata Zone, the Quadralella polygnathiformis Zone, the Quadralella praelindae Zone, the Quadralella auriformis Zone and the Quadralella robusta Zone. The Ladinian–Carnian boundary is provisionally defined by the first occurrences of Quadralella polygnathiformis and Quadralella intermedia in the cherty limestone member of the Zhuganpo Formation. Regional correlations via conodont biostratigraphy indicate that the Zhuganpo Formation is probably diachronous, with a maximal range spanning the upper Ladinian to the lower Carnian. Amongst all common late Ladinian – early Carnian conodont genera, Paragondolella, Quadralella and Mazzaella are probably cosmopolitan. Budurovignathus was restricted to a few basins and probably preferred offshore or deep-water environments.","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":"160 1","pages":"776 - 793"},"PeriodicalIF":2.3,"publicationDate":"2023-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45621185","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}
Pub Date : 2023-02-01DOI: 10.1017/S0016756823000171
Meng-long Duan, Chao-Ming Xie, Bin Wang, Yuhang Song, Wen-qing Li, Y. Hao
{"title":"Late Permian to early Triassic gabbro in North Lhasa, Tibet: evidence for plume - subduction-zone interaction of the Palaeo-Tethys ocean – RETRACTION","authors":"Meng-long Duan, Chao-Ming Xie, Bin Wang, Yuhang Song, Wen-qing Li, Y. Hao","doi":"10.1017/S0016756823000171","DOIUrl":"https://doi.org/10.1017/S0016756823000171","url":null,"abstract":"","PeriodicalId":12612,"journal":{"name":"Geological Magazine","volume":"160 1","pages":"409 - 409"},"PeriodicalIF":2.3,"publicationDate":"2023-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45946629","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：