This paper reports petrological and geochemical features and zircon U-Pb age of plagiogranite from the Hongliugou-Lapeiquan ophiolitic melange belt in the northern Altyn Tagh. The zircon U-Pb dating results yield a me...This paper reports petrological and geochemical features and zircon U-Pb age of plagiogranite from the Hongliugou-Lapeiquan ophiolitic melange belt in the northern Altyn Tagh. The zircon U-Pb dating results yield a mean ^238U/^206pb age of 512.1 ± 1.5 Ma, representing an emplacement time of the plagiogranites in the Middle Cambrian. The plagiogranites are interpreted to have derived from anatexis of hydrated amphibolites by ductile shearing during transports of the oceanic crust. Thus it is believed that the formation age of such type of plagiogranite was coeval to or slightly younger than the spreading of the Hongliugou-Lapeiquan limited oceanic basin. The new results from the plagiogranites suggest that an oceanic basin existed in the northern Altyn area during the Middle Cambrian.展开更多
Following the Ediacaran metazoan radiation,the "Cambrian Explosion" set up the major framework of todays' animal phyla as well as modern marine ecosystem.Here,we present a preliminary investigation on th...Following the Ediacaran metazoan radiation,the "Cambrian Explosion" set up the major framework of todays' animal phyla as well as modern marine ecosystem.Here,we present a preliminary investigation on the temporal and spatial(from shallow to deep waters) variations of the early Cambrian ocean chemistry in South China through analyzing a Fe-S-C systematic dataset integrated from literature.Our investigation indicates that the early Cambrian deep ocean in South China was still anoxic and Fe2+-enriched(i.e.,ferruginous) although its surface was oxic,and in between a metastable euxinic(anoxic and sulfidic) water zone may have dynamically developed in anoxic shelf waters with an increasing weathering sulfate supply.Furthermore,accompanying marine transgression and regression cycles in the early Cambrian,such a "sandwich" structure in ocean redox chemistry demonstrates five evolutional stages,which can be well correlated to the spatiotemporal patterns of fossil records in South China.The good correlation between metazoan fossil occurrences and water chemistry in South China suggests that early animals possibly possessed ability to inhabit anoxic but generally not euxinic environments as free H2S was fatal to most eukaryotes.This view can well explain why those small shell fauna and sponges disappeared from shelf to slope areas where sulfidic Ni-Mo-rich shales were widely deposited.Thus,we conclude that the spatiotemporal variations of ocean chemistry and its biological effects probably played a key role in the phased animal radiations and "extinctions" in the early Cambrian.展开更多
基金supported by the National Natural Science Foundationof China ( Grant Nos .40839910 , 40762001 and 40902003) the Foundation of the Mobile Projectof Science and Technology of Guizhou Province(Grant No . Gui Ji 2007-4004) +1 种基金the key project ofInternational cooperation of Guizhou Science andTechnology ( Gui . Co . G.[2008]700110]) the Major Basic Research Projects of MSTof China(2006CB806401)
文摘我国贵州东部乌溜-曾家崖凯里组剖面作为世界早-中寒武世界线层型侯选剖面,产出良好保存的大型无脊椎动物化石(尤其是三叶虫)。因此,更加详细研究该剖面海洋疑源类的生物地层非常重要,将提供围绕界线的生物和环境变化的细微记录。乌溜-曾家崖剖面凯里组的疑源类划分两个组合,它们是凯里组0-52m的Leiomarginata si mplex-Fi mbriaglomerella membranacea组合和52-140m的Cristallinium cambriense-Heliosphaeridiumnodosum-Globosphaeridiumcerinum组合。140-214m仅有很少疑源类标本,可能因为凯里组上部以白云岩为主,不适宜有机壁微体化石的保存。距凯里组底部往上约52m处疑源类组合出现重大变化,无疑为解释沉积环境提供重要资料。两疑源类组合间界线,位于52.3-52.7m,此稍低于被三叶虫Oryctocephalusindicus首现所指示的全球寒武系第5阶潜在层型剖面界线。
基金financially supported by the China Geological Survey (Grant No. 1212010911025)National Natural Science Foundation of China (Grant No. 41002020)
文摘This paper reports petrological and geochemical features and zircon U-Pb age of plagiogranite from the Hongliugou-Lapeiquan ophiolitic melange belt in the northern Altyn Tagh. The zircon U-Pb dating results yield a mean ^238U/^206pb age of 512.1 ± 1.5 Ma, representing an emplacement time of the plagiogranites in the Middle Cambrian. The plagiogranites are interpreted to have derived from anatexis of hydrated amphibolites by ductile shearing during transports of the oceanic crust. Thus it is believed that the formation age of such type of plagiogranite was coeval to or slightly younger than the spreading of the Hongliugou-Lapeiquan limited oceanic basin. The new results from the plagiogranites suggest that an oceanic basin existed in the northern Altyn area during the Middle Cambrian.
基金financially supported by National Basic Research Program of China(Grant Nos.2013CB955700&2011CB80880)National Natural Science Foundation of China(Grant No.41172030)Program for New Century Excellent Talents in University(Grant No.NCET-11-0724)
文摘Following the Ediacaran metazoan radiation,the "Cambrian Explosion" set up the major framework of todays' animal phyla as well as modern marine ecosystem.Here,we present a preliminary investigation on the temporal and spatial(from shallow to deep waters) variations of the early Cambrian ocean chemistry in South China through analyzing a Fe-S-C systematic dataset integrated from literature.Our investigation indicates that the early Cambrian deep ocean in South China was still anoxic and Fe2+-enriched(i.e.,ferruginous) although its surface was oxic,and in between a metastable euxinic(anoxic and sulfidic) water zone may have dynamically developed in anoxic shelf waters with an increasing weathering sulfate supply.Furthermore,accompanying marine transgression and regression cycles in the early Cambrian,such a "sandwich" structure in ocean redox chemistry demonstrates five evolutional stages,which can be well correlated to the spatiotemporal patterns of fossil records in South China.The good correlation between metazoan fossil occurrences and water chemistry in South China suggests that early animals possibly possessed ability to inhabit anoxic but generally not euxinic environments as free H2S was fatal to most eukaryotes.This view can well explain why those small shell fauna and sponges disappeared from shelf to slope areas where sulfidic Ni-Mo-rich shales were widely deposited.Thus,we conclude that the spatiotemporal variations of ocean chemistry and its biological effects probably played a key role in the phased animal radiations and "extinctions" in the early Cambrian.
