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101.
102.
On the evolution and histology of some Cambrian protoconodonts,paraconodonts and primitive euconodonts 总被引:4,自引:0,他引:4
DONG Xiping Department of Geology Peking University Beijing China Laboratory of Palaeobiology & Stratigraphy Nanjing Institute of Ge-ology Palaeontology Chinese Academy of Sciences Nanjing China 《中国科学D辑(英文版)》2004,47(7):577-584
Although the history of Cambrian conodont study goes back to a century ago, it was not until 1959 that the systematic study of Cambrian conodonts was initi-ated[1]. During the last 44 years Cambrian conodonts have been well documented from all continents but Africa. However, the morphological evolution of para- conodonts and protoconodonts have been subjected to less study than the primitive euconodonts in the inter-val across the Cambrian-Ordovician boundary. Miller (1984) proposed a Weste… 相似文献
103.
Release of heavy metals during weathering of the Lower Cambrian Black Shales in western Hunan,China 总被引:8,自引:0,他引:8
Bo?PengEmail author Zhaoliang?Song Xiangling?Tu Meilian?Xiao Fucheng?Wu Huanzhe?Lv 《Environmental Geology》2004,45(8):1137-1147
Weathering of heavy metal enriched black shales may be one of the most important sources of environmental contamination in areas where black shales are distributed. Heavy metal release during weathering of the Lower Cambrian Black Shales (LCBS) in western Hunan, China, was investigated using traditional geochemical methods and the ICP-MS analytical technique. Concentrations of 16 heavy metals, 8 trace elements and P were measured for samples from selected weathering profiles at the Taiping vanadium ore mine (TP), the Matian phosphorous ore mine (MT), and Taojiang stone-coal mine (TJ). The results show that the bedrock at these three profiles is enriched with Sc, V, Cr, Co, Ni, Cu, Zn, Pb, Th, U, Mo, Cd, Sb, Tl, and P. Based on mass-balance calculation, the percentages of heavy metals released (in % loss) relative to immobile element Nb were estimated. The results show significant rates of release during weathering of: V, Cr, Co, Ni, Cu, Zn, U, Mo, Cd, Sn, Sb, and Tl for the TP profile; Sc, Cr, Mn, Co, Ni, Cu, Zn, Pb, Th, Cd, and Sn for the MT profile; and Sc, Mn, Co, Ni, Zn, Th, Cd, Sn, and Tl for the TJ profile. Among these heavy metals, Co, Ni, Zn, Cd, and Sn show very similar features of release from each of the three weathering profiles. The heavy metals released during weathering may affect the environment (especially topsoil and surface waters) and are possibly related to an observed high incidence of endemic diseases in the area. 相似文献
104.
M.?D.?Rodríguez-AlonsoEmail author M.?Peinado M.?López-Plaza P.?Franco A.?Carnicero J.?C.?Gonzalo 《International Journal of Earth Sciences》2004,93(5):897-920
Petrographic, geochemical and field studies in low grade metamorphic areas (Ciudad Rodrigo-Hurdes-Sierra de Gata domain, CRHSG, central-western Spain) show that Neoproterozoic-Lowermost Cambrian series in the Central Iberian Zone (CIZ) record two kinds of provenance sources including: (1) detrital material derived from recycled orogens and (2) a Cadomian coeval juvenile contribution that governs their isotopic signature. Evidence of magmatism contemporaneous with Neoproterozoic-Cambrian sedimentation is provided by the presence of coherent, massive volcanic rocks (metabasalts, metaandesites, and metarhyolites), volcaniclastic shales, sandstones, conglomerates and breccias. The appearance of volcanogenic lithic fragments and crystals mixed in different proportions with siliciclastic constituents and also present within calcareous components in the sedimentary succession, reinforces this evidence. Although most of the selected volcanic and volcaniclastic samples appear to show tholeiitic affinity, some of them display calc-alkaline affinity. Different trace element ratios, such as Sm/Nd, Nb/Yb and Ta/Yb, suggest a magmatic evolution in the same tectonic setting. The geochemical results reported here support the existence of an active geodynamic setting as a direct contributor to the synsedimentary and magmatic content of the Neoproterozoic–Lowermost Cambrian successions in the CIZ. In particular, the relatively high Nd (T) values and the high range of f Sm/Nd ratios are consistent with an active margin during the Neoproterozoic–Early Cambrian. The existence of tectonic activity is also confirmed by the presence of synsedimentary deformation and volcanic rocks. All of these traits favour a geodynamic model in which the Iberian Cadomian segment represented in the CIZ would have been part of an active northern margin of Gondwana, with an associated magmatic arc and related basins during Neoproterozoic–Lower Cambrian times. A proposed link between the Ossa Morena and the Central Iberian Zones might account for late Cadomian pull-apart basins developed on both sides of the magmatic arc, sharing the same scenario and involving similar magmatic activity during the Neoproterozoic–Cambrian transition.
相似文献
M. D. Rodríguez-AlonsoEmail: Phone: +34-923-294498Fax: +34-923-294514 |
105.
华北地台中寒武统张夏组上部高频层序研究 总被引:8,自引:1,他引:7
根据华北地台东部寒武系露头层序地层研究,将张夏组划分为两个正层序,其中上部正层序(530-525MaB.P.,三叶虫带Amphoton-Taitzuia带至Damesela带)由4个亚层序和17-23个小层序组成,其中正层序和亚层序具有高分辨率区域地层对比意义。每一级层序均表现为向上变浅和变粗进积型序列,底部常以间断-加深面或洪泛面为界。该时期的海平面变化具有高频振荡特点,构成一个三级复合海平面变化旋回。由不同级别层序所反映的海平面变化旋回可以分别与天文周期的奥特周期(2—5Ma)、米兰科维奇长周期(0.1—0.4Ma)和米兰科维奇短周期(0.02—0.04Ma)相对比。据层序地层和相序及相模式的研究,识别出6种类型的小层序,陆棚盆地至上缓坡显示出由A—F类型的规律性变化。 相似文献
106.
河南省华北型寒武纪—早奥陶世地层可分为7个组、21个生物带、10个阶。各组均为向北东、北西向的穿时体。向北东向穿时较高,反映向北东向的海侵较慢。自晚寒武世起,南西方向开始抬升,海水向北东方向运移。向北东方向抬升比北西方向慢,结束沉积晚。 相似文献
107.
中朝地台南部下、中寒武统 (风台组—张夏组 )可划分 9个三级层序。除底部的 DS-A层序外 ,其余 8个层序均可与中朝地台大部分地区进行对比。下部的 3个层序 (DS- A~ DS-2 )属 型层序 ,其余为 型层序。研究表明 ,本区的沉积层序除受早古生代全球海平面变化控制之外 ,秦岭板块的俯冲对中朝地台南部层序地层的发育也具有一定的影响 相似文献
108.
Biological and Molecular Geochemical Evidence for Dinoflagellate Ancestors in the Upper Sinian-Cambrian 总被引:5,自引:0,他引:5
J.Mike MOLDOWAN 《《地质学报》英文版》2000,74(4):740-747
Dinoflagellates are single celled organisms that reflect the ecological conditions in modern oceans and lakes. Their earliest undisputed fossil record suggests that dinoflagellates originated from the Middle Triassic (c. 240 Ma ago). However, the presence of molecular biomarkers (dinosterane, 4α-methyl-24-ethylcholestane and tria-romatic dinosteroids) in rock extracts and coccoid dinoflagellate fossils from the upper Sinian to Cambrian of the Tarim basin confirms the hypothesis that dinoflagellates have an ancient origin, and predate the oldest undisputed dinoflagellate fossils at least by 300 Ma, as early as the late Sinian-Cambrian. 相似文献
109.
Organic carbon isotopes of the Sinian and Early Cambrian black shales on Yangtze Platform, China 总被引:5,自引:0,他引:5
Organic matter of the Sinian and early Cambrian black shales on the Yangtze Platform belongs to the light carhon group of
isotopes with the δ13C values from - 27% to - 35 %, which are lower than those of the contempomneously deposited carbonates and phosphorites. A carbon isotope-stratified
paleooceanographic model caused by upwelling is proposed, which can be used not only to interpret the characteristies of organic
carbon isotopic compositions of the black shales, but also to interpret the paleogeographic difference in the organic carbon
isotope compositions of various types of sedimentary rocks.
Project supported by the National Natural Science Foundation of China (Grant No. 49472114) and the Open Laboratory of Organic
Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences. 相似文献
110.