Middle Permian organic carbon isotope stratigraphy and the origin of the Kamura Event     

《Gondwana Research》2020

Large carbon cycle perturbations associated with the Middle Permian (Capitanian) mass extinction have been widely reported, but their causes and timing are still in dispute. Low resolution carbon isotope records prior to this event also limit the construction of a Middle Permian chemostratigraphic framework and global or local stratigraphic correlation, and hence limit our understanding of carbon cycle and environmental changes. To investigate these issues, we analyzed the ¹³C_org values from the Middle Permian chert-mudstone sequence (Gufeng Formation) in the Lower Yangtze deep-water basin (South China) and compared them with published records to build a chemostratigraphic scheme and discuss the underlying environmental events. The records show increased δ¹³C_org values from late Kungurian to early Guadalupian, followed by a decrease to the late Wordian/early Capitanian. The early-mid Capitanian was characterized by elevated δ¹³C_org values suggesting the presence of the “Kamura Event”: an interval of heavy positive values seen in the δ¹³C_carb record. We propose that these heavy Capitanian δ¹³C values may be a response to a marked decline in chemical weathering rates on Pangea and associated reduction in carbonate burial, which we show using a biogeochemical model. The subsequent negative δ¹³C excursion seen in some carbonate records, especially in shallower-water sections (and in a muted expression in organic carbon) coincide with the Capitanian mass extinction may be caused by the input of isotopically-light carbon sourced from the terrestrial decomposition of organic matter.  相似文献   

ENVIRONMENTAL RESPONSE OF THE PERMIAN VOLCANISM IN LUCAOGOU FORMATION IN JIMSAR SAG,JUNGGAR BASIN,NORTHWEST CHINA          下载免费PDF全文

QU Chang-sheng  QIU Long-wei  YANG Yong-qiang  YU Kuan-hong  TANG Li-li  WAN Min 《地震地质》2019,41(3):789-802

The lithological features, the types of organic matter and its occurrence and carbon and oxygen isotopic value were clarified by combining core observation, thin slice authentication, X ray diffraction analysis, kerogen type identification and carbon and oxygen isotope analysis. The characteristic of strata, the distribution of volcanoes of Junggar Basin were also taken into consideration. A comprehensive analysis was conducted to evaluate environmental response of volcanism in Lucaogou formation in Jimsar sag. The results show that rocks is a mixed sedimentation of effusive rock and carbonate rocks, volcanic materials is widely developed in Lucaogou formation and origins from the edge of sag or distant source volcano activity. Organic matter is predominantly unstructural algae and asphaltene. The carbon isotopic value of carbonates ranges between 6.8‰ and 9.7‰ with an average of 8.3‰, featured in high positive excursions, while oxygen isotopic value varies from -11.9‰ to -4.3‰ with an average of -6.2‰. During the period of volcanic activity, the volcanic material released high amounts of nutrient to the lake basin, which is beneficial to the algae and other organic organisms. In the poor oxygen and calm water environments, the organic matter is distributed in the laminar algal and the carbon isotope value is high positive drift. During the intermittent period of volcanic activity, the lake level decreased and the lake bottom water changed to the oxygen-enriched environments. The organic matter is locally enriched or dispersed in local layers, and the carbon isotope values decreased slightly. The frequent volcanic activity promoted the organism boom, which lead carbon isotope value to have high positive characteristics and change trends.  相似文献   

Lakes of the Jom-Bolok Volcanoes Valley in the East Sayan Mts., Baikal region     

Shchetnikov  Alexander  Bezrukova  Elena V. 《地理学报(英文版)》2019,29(11):1823-1840

Journal of Geographical Sciences - This article describes the lake basins of the Jom-Bolok volcanic region in the East Sayan (the largest manifestation of the Holocene eruptions in Central Asia)....  相似文献   

黔西南泥堡金矿床容矿火山岩系中“粉砂岩”夹层的岩石类型归属研究          下载免费PDF全文

祁连素 《贵州地质》2021,38(1):22-28, 64

原先认为泥堡金矿床容矿火山岩系中间的"粉砂岩夹层",研究发现其具有与火山碎屑岩的成分与结构构造特征,包括熔蚀石英晶屑和长石板状晶假象,局部还出现大量生物化石碎片,应归属为蚀变凝灰岩。火山岩系的原"粉砂岩夹层"并不存在,只是短暂的火山喷发间隙,整个容矿火山岩系形成从偏基性火山碎屑岩到中基性火山角砾岩的晚二叠世火山喷发旋回。火山岩旋回的早期到晚期,金矿成矿作用强度逐渐增强,印证金成矿作用与火山岩的密切成因联系。  相似文献   

大同盆地形成机制的构造研究   总被引：1，自引：0，他引：1  

岑敏  董树文  施炜  周涛发  陈龙  陈兴强 《地质论评》2015,61(6):1235-1247

大同盆地为位于华北地块中部的新生代断陷盆地,自中新世晚期以来经历了持续的强烈伸展作用。基于边界断裂滑动的运动学及动力学分析,结合对本区新生界沉积地层与玄武岩资料的总结归纳以及对区域动力学背景的讨论,本文提出了大同盆地的形成机制:自10~8 Ma以来,鄂尔多斯地块东北缘形成NW向伸展的构造应力场,其中σ1垂直,σ2、σ3水平,σ2的方位角为60°,σ3方位角为150°,此构造应力场控制边界断裂的运动,形成NE向大同断陷盆地。盆地的形成对应岩石圈减薄深部过程,可能受到了印度——欧亚板块碰撞、太平洋——欧亚板块碰撞板缘动力作用的影响。本文将岩石圈浅部构造应力场与深部地幔活动结合起来综合分析大同盆地的形成机制,并提出了一些新的认识:控制大同盆地形成的正断型构造应力场不同于华北区域性走滑型构造应力场;首次测得了与地幔活动相关的大同火山群大峪口玄武岩K-Ar年龄为0.68±0.13Ma;大同盆地具有板内狭窄型裂谷的构造特征。本文为建立鄂尔多斯地块东缘山西地堑系的运动学和动力学模型提供新的依据。  相似文献   

板内橄榄玄粗岩(shoshonite)地幔流体交代作用及成因的元素地球化学证据:以赣南会昌橄榄玄粗岩为例   总被引：2，自引：0，他引：2  

章邦桐  吴俊奇  凌洪飞  陈培荣 《地球化学》2011,(5):443-453

根据稀土元素和微量元素ICP-MS分析结果,通过对流体作用敏感的元素对比值(U/Th、Pb/Ce、Ba/La、Cs/Rb和Ce/Y等)的研究对比,为赣南会昌橄榄玄粗岩的形成有地幔流体交代作用参与提供了重要的地球化学证据.应用主元素氧化物(K2O、Na2O、FeOT、CaO、MgO和TiO2)与SiO2的变异分析,判明会...  相似文献   

内蒙古贺斯格乌拉牧场白音高老组火山岩U-Pb年龄及地球化学特征     

胡振华 《地质与勘探》2020,56(2):359-371

白音高老组火山岩在大兴安岭地区广泛分布,本文对大兴安岭中南部贺斯格乌拉牧场白音高老组酸性火山岩进行了锆石U-Pb年代学、岩石地球化学和Sr-Nd同位素分析,探讨其岩石成因及构造背景。位于大兴安岭中南段东乌旗地区的白音高老组火山岩,主要岩性为流纹岩、流纹质凝灰岩等,LA-ICP-MS锆石U-Pb年龄分别为129. 8±0. 8 Ma、128. 2±2. 8 Ma,属早白垩世早期;从岩石地球化学特征上看,其主量元素SiO_2含量68. 76%～76. 18%、Al_2O_3含量11. 84%～13. 38%,属高钾钙碱性岩石;稀土总量较高,(La/Yb)N 6,(La/Sm)_N 3,显示为轻稀土富集型,δEu显示负铕异常(0. 4～0. 6),微量元素以富集大离子亲石元素K、Rb、Ba,贫高场强元素Nb、P、Ti为特征; Sr-Nd同位素组成上具有低I_(Sr)、高ε_(Nd)(t)和低t_(DM)的特征(I_(Sr)=0. 7039～0. 7045,ε_(Nd)(t)=2. 65～4. 39)。火山岩浆来源于下地壳基性物质的部分熔融,综合研究并结合前人资料认为,白音高老组流纹岩形成于滨太平洋板块俯冲后伸展及蒙古-鄂霍次克洋闭合后的综合效应下。  相似文献   

The influence of tectonic subsidence on volcaniclastic sedimentation: The Cretaceous upper Daeri Member,Wido Island,Korea          下载免费PDF全文

Yong Sik Gihm  Min‐Cheol Kim  Moon Son  In Gul Hwang 《Island Arc》2017,26(3)

The Daeri Member, a Cretaceous volcanic–sedimentary succession, can be divided into lower, middle, and upper parts based on vertical changes in its lithologic characters. The lower Daeri Member is composed of siliciclastic deposits formed in a semi‐arid floodplain environment, which is overlain by the middle Daeri Member consisting mainly of andesite lava flow. After the emplacement of the andesite, activities of intrabasinal normal faults created accommodation on hanging wall blocks together with the development of intrabasinal topographic relief. The upper Daeri Member occurs only in hanging wall blocks and is composed of rhyolitic volcaniclastic sediments formed during an explosive volcanic eruption. Following the eruption, owing to semi‐arid climatic conditions and the destruction of vegetation, the eruptive materials were easily remobilized and deposited by episodic sediment gravity flows, resulting in deposition of the resedimented volcaniclastic deposits with sheet‐like geometry. Away from the intrabasinal normal faults, the resedimented volcaniclastic deposits show a decrease in grain size together with changes in inferred depositional processes from debris flows to hyperconcentrated flows and supercritical sheetfloods. This suggests that the resedimented volcaniclastic deposits were stacked on alluvial fan environments induced by intrabasinal topographic relief associated with normal fault activities. In addition, episodic movement of the faults gave rise to periodic fluctuation of the accommodation and an increase in gradient of the alluvial fan surface, resulting in the development of coarsening‐upward trends in the resedimented volcaniclastic deposits. The development of the alluvial fan and the coarsening‐upward trends indicate that dynamic tectonic subsidence and concomitant changes in the intrabasinal physiographic relief influenced the depositional processes and sizes of the transported volcaniclastic sediments of the upper Daeri Member. Thus, it is necessary to carefully observe tectonic signatures in volcaniclastic successions, particularly the syneruptive lithofacies, in order to reconstruct the tectonic and volcanic histories of receiving basins.  相似文献   

Shallow‐water microbialite‐volcaniclastic facies association in the Cambro‐Ordovician Mt Windsor Subprovince,Australia     

M. G. Doyle  J. McPhie 《Australian Journal of Earth Sciences》2013,60(6):815-831

The Trooper Creek Formation is a mineralised submarine volcano‐sedimentary sequence in the Cambro‐Ordovician Seventy Mile Range Group, Queensland. Most of the Trooper Creek Formation accumulated in a below‐storm‐wave‐base setting. However, microbialites and fossiliferous quartz‐hematite ± magnetite lenses provide evidence for local shoaling to above fairweather wave‐base (typically 5–15 m). The microbialites comprise biogenic (oncolites, stromatolites) and volcanogenic (pumice, shards, crystal fragments) components. Microstructural elements of the bioherms and biostromes include upwardly branching stromatolites, which suggest that photosynthetic microorganisms were important in constructing the microbialites. Because the microbialites are restricted to a thin stratigraphic interval in the Trooper Creek area, shallow‐water environments are interpreted to have been spatially and temporarily restricted. The circumstances that led to local shoaling are recorded by the enclosing volcanic and sedimentary lithofacies. The microbialites are hosted by felsic syneruptive pumiceous turbidites and water‐settled fall deposits generated by explosive eruptions. The microbialite host rocks overlie a thick association (≤?300 m) of andesitic lithofacies that includes four main facies: coherent andesite and associated autoclastic breccia and peperite; graded andesitic scoria breccia (scoriaceous sediment gravity‐flow deposits); fluidal clast‐rich andesitic breccia (water‐settled fall and sediment gravity‐flow deposits); and cross‐stratified andesitic sandstone and breccia (traction‐current deposits). The latter three facies consist of poorly vesicular blocky fragments, scoriaceous clasts (10–90%), and up to 10% fluidally shaped clasts. The fluidal clasts are interpreted as volcanic bombs. Clast shapes and textures in the andesitic volcaniclastic facies association imply that fragmentation occurred through a combination of fire fountaining and Strombolian activity, and a large proportion of the pyroclasts disintegrated due to quenching and impacts. Rapid syneruptive, near‐vent aggradation of bombs, scoria, and quench‐fragmented clasts probably led to temporary shoaling, so that subsequent felsic volcaniclastic facies and microbialites were deposited in shallow water. When subsidence outpaced aggradation, the depositional setting at Trooper Creek returned to being relatively deep marine.  相似文献   

Structure and Quaternary tectonic history of the Woodlark triple junction region,Solomon Islands     

Keith A. W. Crook  Brian Taylor 《Marine Geophysical Researches》1994,16(1):65-89

The Woodlark triple junction region, a topographically and structurally complex triangular area of Quaternary age, lies east of Simbo Ridge and southwest of the New Georgia island group, Solomon Islands, at the junction of the Pacific, Australian and Solomon Sea plates. SeaMARC II side-scan imagery and bathymetry in conjunction with seismic reflection profiles, 3.5 kHz records, and petrologic, magnetic and gravity data show that the active Woodlark spreading centre does not extend into this region.South of the triple junction region, the Woodlark spreading centre reoriented at about 2 Ma into a series of short ESE-trending segments. These segments continued to spread until about 0.5 Ma, when the lithosphere on their northern sides was transferred from the Solomon Sea plate to the Australian plate. Simultaneously the Simbo transform propagated northwards along the western side of the transferred lithosphere, forming a trench-trench-transform triple junction located NNW of Simbo island and a new leaky plate boundary segment that built Simbo Ridge.As the Pacific plate approached, the area east of northern Simbo Ridge was tilted northwards, sheared by dominantly right-lateral faults, elevated, and intruded by arc-related magmas to form Ghizo Ridge. Calc-alkalic magmas sourced beneath the Pacific plate built three large strato-volcanic edifices on the subducting Australian plate: Simbo at the northern end of Simbo Ridge, and Kana Keoki and Coleman seamounts on an extensional fracture adjoining the SE end of Ghizo Ridge.A sediment drape, supplied in part from Simbo and Kana Keoki volcanoes, mantles the east-facing slopes of northern Simbo and Ghizo Ridges and passes distally into sediment ponded in the trench adjoining the Pacific plate. As a consequence of plate convergence, parts of the sediment drape and pond are presently being deformed, and faults are dismembering Kana Keoki and Coleman seamounts.The Woodlark system differs from other modern or Tertiary ridge subduction systems, which show wide variation in character and behaviour. Existing models describing the consequences of ridge subduction are likely to be predictive in only a general way, and deduced rules for the behaviour of oceanic lithosphere in ridge subduction systems may not be generally applicable.  相似文献