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   

喀拉昆仑火烧云一带早侏罗世双峰式火山岩的发现及意义     

周能武  陈邦学  邓中飞  桑明帅  白权金 《现代地质》2019,33(5):990-1002

喀拉昆仑火烧云北火山岩发育在乔尔天山断裂附近,玄武岩体和安山岩体在时空上紧密伴生。主量元素测试结果显示,其中玄武岩和英安岩的SiO₂含量分别为48.84%~52.44%和62.22%~65.63%,具有明显的Daly间断面,属于典型的双峰式火山岩。玄武岩Al₂O₃含量较低, MgO、CaO、TiO₂含量较高,Sr、Ba、K等微量元素强烈亏损,高场强元素Ta、Nb、Ti、Zr无亏损。英安岩具有相对较高的Al₂O₃、Na₂O、K₂O含量,较低的MgO、CaO、TiO₂含量;微量元素具富集大离子亲石元素(Rb、Th、U、K)、亏损高场强元素(Ta、Nb、Ti),显示典型岛弧环境特征。岩石地球化学特征表明二者同属钙碱系列,形成于弧后盆地,属同源演化,英安岩为玄武岩结晶分异的产物。通过对英安岩进行LA-ICP-MS锆石U-Pb方法测年,获得流纹岩形成年龄为(195.5±1.1) Ma,属于早侏罗世。通过对该区域构造演化进行分析讨论,认为乔尔天山一带盆地整体可能处于弧后盆地的发育阶段,盆地形成过程中岩石圈地幔未被拉断,没有洋壳形成。  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 possible synglaciogenic Ediacaran hematitic banded iron salt formation (BISF) at Hormuz Island,southern Iran: Implications for a new style of exhalative hydrothermal iron-salt system     

《Ore Geology Reviews》2017

The Ediacaran BISF at Hormuz Island is a newly identified glaciogenic iron-salt deposit in the Tethyan margin of Gondwana. The BISF was formed by synchronous riftogenic A-type submarine felsic volcanism and evaporate deposition. The mineralization occurs in a proximal felsic tuff cone and jaspilitic distal zones and contains 1 million tonne of hematite-rich ore with an average grade of 58% Fe. The ore structure shows cyclicity of macrobandings, mesobandings and microbandings of anhydrite, halite, hematite and chert, which marks a new record in BIFs geohistory. The alteration minerals in the proximal and distal zones are actinolite, ripidolite, epidote, sericite, tourmaline, clinochlore, anhydrite and clay minerals. The occurrence of metamorphosed polygenetic bullet-shape dropstones in BISF attests that there was probably a continuous process of ice melting, episodic submarine volcanism and exhalative hydrothermal banded iron salt formation during the Late Ediacaran time. The non-metamorphosed Neoproterozoic stratigraphy, the presence of genus Collenia, U-Pb dating (558 ± 7 Ma) and the marked negative δ¹³C excursion in cap carbonates are representative of Late Ediacaran glaciation, which has been identified worldwide. The REE+Y display light REE enrichment, unusually strong Tb-Tm anomaly, a weak positive Y anomaly, but no distinguished Eu and Ce anomalies, reflecting the glaciogenic nature of the BISF. The contents of Zr, Hf, Nb, Ta, Th, La, Ce and Y in BISF, dropstones, halite and cap carbonates are similar to those of the Neoproterozoic glaciogenic BIFs. Also, the Ni/Fe, P/Fe ratios and Fe/Ti – Al/Al + Fe + Mn + Ca + Na + K diagram suggest an exhalative hydrothermal Ediacaran-type BISF. The absence of brecciated magnetite in the ore association and the low contents of copper (9–493 ppm) and gold (<5–8 ppb) are not in favor of the IOCG – Kiruna-type iron oxide ores. The co-paragenesis of hematite with several alteration minerals, in particular actinolite, tourmaline and anhydrite, indicates that the exhalative hydrothermal fluids were generated by the interaction of seawater with the felsic rocks and sediments at about 200–500 °C. The interaction of seawater with felsic magma and sediments led to the formation of Mg-rich alteration minerals, leaching Si, Fe, Mn and other elements and forming the potential ore fluids. It is highlighted that the A-type alkaline submarine felsic volcanism could be considered as an exploration target for BISF.  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