Constraints on the onset age of the Sturtian glaciation from the Southeast Yangtze Block,South China     

《International Geology Review》2012,54(15):1876-1886

ABSTRACT

The Neoproterozoic glaciations represent a milestone in the Earth evolution due to their influence on atmosphere, biosphere and hydrosphere. Evidence for the Sturtian glaciation, the early stage of Cryogenian, has been recorded worldwide, but the precise timing and synchroneity of its counterpart, the Chang’an glaciation, in South China have been controversial. As such, new zircon U–Pb ages from the pre-Sturtian Gongdong Formation and the overlying the Chang’an Formation in southeastern Yangtze Block were reported. The youngest U–Pb zircon age from a tuff sample of the topmost Gongdong Formation was 716.8 ± 6.8 Ma, and that from a sandstone sample of the lower Chang’an Formation was 725.9 ± 4.4 Ma. The zircon weighted mean age of 716.8 ± 6.8 Ma was interpreted as the maximum depositional age of the termination of the Danzhou Group. This age, along with the ages reported from the bottom of the Danzhou Group, constrains deposition of the Danzhou Group to between ca. 820 Ma and ca. 715 Ma. The age of 716.8 ± 6.8 Ma from the top of the Gongdong Formation is consistent with the SIMS U-Pb age of 715.9 ± 2.8 Ma from the Sibao section, as well as ages from the Banxi Group, Liantuo Group, and Kaijianqiao Formation in the Yangtze Block, which further constrain the onset time of the Sturtian glaciation in South China at ca. 715 Ma. It is also, with uncertainties, consistent with ages from pre-Sturtian strata in Laurentia and Oman, which indicates a global synchroneity and extent for the Sturtian glaciation.  相似文献   

A simple method to classify diamicts by scanning electron microscope from surface microtextures     

Mats O. Molén 《Sedimentology》2014,61(7):2020-2041

Interpretation of quartz sand grain surface microtextures with scanning electron microscopy has been riddled with inconsistencies, invalid assumptions and much subjectivity. Therefore, a novel classification for analysing grain surface microtextures is presented based on the origin of complete grain surfaces. This novel method has solved most of the earlier problems of interpretation of surface microtextures, and it is easy to use and to quickly find evident genetic interpretations of diamicts. The data are plotted graphically in ‘2‐History Diagrams’ or ‘3‐History Diagrams’ for quick visual inspection and statistical evaluation. Source rocks and Quaternary glacial deposits from Scandinavia and Southern Ontario, representing different ice‐substrate dynamics, are analysed to define surface microtextures from typical glacigenic grains, bedrock and fluvially transported grains. Typical glacially crushed grains display large‐scale fractures and abrasion. Shield bedrock grains display large or small‐scale fractures and solution/precipitation microtextures. Fluvially transported grains exhibit abrasion and solution/precipitation microtextures.  相似文献   

Global perturbation of the marine Ca isotopic composition in the aftermath of the Marinoan global glaciation     

J.C. Silva-Tamayo  T.F. Nägler  A.N. Sial  A. Nogueira  K. Kyser  C. Riccomini  N.P. James  G.M. Narbonne  I.M. Villa 《Precambrian Research》2010

Ca isotopic compositions of Marinoan post-glacial carbonate successions in Brazil and NW Canada were measured. Both basal dolostones display δ^44/40Ca values between 1 and 0.7‰, overlying limestones show a negative Ca isotope excursion to values around 0.1‰, and δ^44/40Ca values rapidly increase up-section to near 2.0‰. In the Brazilian successions, those high δ^44/40Ca values rapidly decrease and stabilize to values between 0.6 and 0.9‰. These Ca isotope secular variation trends are unlike those of Sturtian post-glacial carbonate successions, but similar to those of Marinoan post-glacial carbonate successions in Namibia, suggesting that the perturbation of the marine Ca cycle was global. This recommends Ca isotope stratigraphy as a tool to correlate Neoproterozoic post-glacial carbonate successions worldwide.  相似文献   

再论山脊壶穴的冰川融水成因——兼与施雅风院士商榷     

吕洪波  任晓辉  许民  欧阳江城 《地质论评》2010,56(5):693-702

针对施雅风院士新提出的壶穴之"负球状风化"说,笔者特撰文与施老商榷。笔者认为:壶穴的形成并不受花岗岩中节理的控制,也与风化作用无关,不能用"负球状风化"来解释。壶穴是高速旋转水流侵蚀的结果,在中国东部花岗岩山脊上发现的壶穴是第四纪冰川融水侵蚀的标志。近年来观察到的格陵兰冰上湖泊的突然排泄为壶穴的冰川融水成因说提供了重要的证据。壶穴成因争论的本质是中国东部是否曾经发育过第四纪冰川,建议第四纪学界关注中国东部第四纪冰川的其他地貌标志。韩同林研究员的"冰臼论"促进了中国东部第四纪冰川地貌的再研究,应当给予积极评价。  相似文献   

南海深水区末次冰期和冰后期沉积物堆积速率的特征   总被引：3，自引：0，他引：3  

黄维  汪品先 《海洋学报》2007,29(5):69-73

通过统计南海100 m以下深水区的136个沉积柱状样的分析数据,对南海末次冰期以来的堆积速率进行了统计.计算出MIS(marine isotope stage)1期的年均沉积量为152.3 Mt/a,2期的为215.2 Mt/a,主要为陆源物质的贡献.无论在末次冰期还是在冰后期,堆积速率均在南海西南部最高,其次是在东北部,在其他地区较低.由于侧向搬运和顺坡搬运频繁,虽然整体上末次冰期的堆积速率高于冰后期的,但在沉积物高速堆积地区附近有相反的变化趋势.  相似文献   

倒数第二次冰期晚期东亚季风气候演变的石笋δ18O记录     

任晓辉  陈仕涛  明艳芳  汪永进 《海洋地质与第四纪地质》2007,27(1):47-52

基于南京洞穴2支石笋的11个230Th年龄、658个氧碳同位素分析数据,建立了倒数第二次冰期晚期(155-128 kaBP)东亚季风高分辨率的气候演化序列。在岁差尺度上,石笋δ18O记录与65°N夏季太阳辐射量曲线变化基本一致,说明北纬夏季太阳辐射对该地区气候演变起宏观调控作用。石笋δ18O变化曲线千年尺度上显示了8个明显的峰谷变化,δ18O值平均变幅约为1.5‰,平均频率在2 ka左右,十分类似于末次冰期东亚季风Dans-gaard-Oeschger旋回,说明东亚季风气候在末次冰期的千年级不稳定波动也可能存在于更久远的冰期过程中,冰期气候的不稳定性很可能是第四纪冰盖、大尺度海洋/大气环流共同作用的结果。  相似文献