| 湘西中上寒武统界线层型侯选剖面沉积特征 |
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| 引用本文： | 傅启龙,周志澄.湘西中上寒武统界线层型侯选剖面沉积特征[J].地质科学,1999,34(2):204-212. |
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| 作者姓名： | 傅启龙 周志澄 |
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| 作者单位： | 中国科学院南京地质古生物研究所 南京 210008 |
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| 基金项目： | 中国科学院古生物与古人类学基础研究特别支持费资助项目,中国科学院现代地层古生物开放实验室资助项目 |
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| 摘 要： | 湘西中、上寒武统花桥组和车夫组主要由斜坡相和盆地边缘相的碳酸盐岩、泥质碳酸盐岩及钙质泥岩组成。重力流沉积十分发育,其中花垣排碧剖面以碎屑流砾屑灰岩和近源浊积岩为主;永顺王村剖面以浊流沉积为主;桃源瓦尔岗剖面则以远源浊积岩为主。成岩作用主要为海底埋藏胶结作用、新生变形作用和白云石化作用。排碧剖面大多数岩样酸不溶物重量含量在10%以下,王村和瓦尔岗剖面大多数岩样在10%以上。全岩δ18O值介于-11.2‰至-5.6‰(PDB)之间;δ13C值为-1.9‰至3.4‰(PDB).从Linguagnostus reconditus带开始,δ13C有较大的正漂移,漂移值达3‰(PDB)以上。沉积花桥组和车夫组时,湘西过渡区经历了4次海平面升降事件,台缘斜坡逐渐变陡,由缓坡型逐渐发展为镶边型和沟槽型。在湘西的诸多剖面中以王村剖面最适合于作为中、上寒武统界线层型候选剖面,界线选择在花桥组顶部。
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| 关 键 词： | 中上寒武统 界线层型 沉积特征 湘西 |
| 收稿时间： | 1998-04-07 |
| 修稿时间： | 1998-04-07; |
SEDIMENTOLOGY OF CANDIDATE SECTIONS FOR THE MIDDLE-UPPER CAMBRIAN BOUNDARY STRATOTYPE IN WESTERN HUNAN, CHINA |
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| Fu Qilong\,Zhou Zhicheng\,Peng Shanchi\,Li Yue.SEDIMENTOLOGY OF CANDIDATE SECTIONS FOR THE MIDDLE-UPPER CAMBRIAN BOUNDARY STRATOTYPE IN WESTERN HUNAN, CHINA[J].Chinese Journal of Geology,1999,34(2):204-212. |
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| Authors: | Fu Qilong\ Zhou Zhicheng\ Peng Shanchi\ Li Yue |
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| Institution: | Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing 210008 |
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| Abstract: | Huaqiao and Chefu formations of the Middle and Upper Cambrian in western Hunan are mostly composed of alternating beds of argillaceous and lime-riched carbonates (calcilutites to calcirudites) containing gravity flow deposits, which consist of shallow water limestone clasts and identifiable allochems derived from the adjacent Yangtze Platform. Debris flow sediments mainly occurring near Paibi village in Huayuan County represent upper continental slope deposits. The formations in Wangcun, Yongshun County, comprising turbidites and autochthonous sediments, are interpreted to have been deposited in the lower slope belt. While the units consisting of distal turbidites and hemipelagic sediments in Wa’ergang, Taoyuan County, suggest basin margin environments. Diagenetic processes mainly include burial cementation, neomorphisms and dolomization. The whole rock δ13C (PDB) values of the well preserved carbonates range between -1.9‰ and 3.4‰, and the δ18O (PDB) values range from -11.2‰ to -5.6‰. A large positive δ13 C excursion begins with the first occurrence of Linguagnostus reconditus. The excursion reaches values of more than 3‰. Most rock samples have less than 9wt% MgO. The lowest CaO content is 11.8%, and the highest is 53.4%. Generally, rocks from Paibi section contain <10wt% acetic-acid-insoluble residues; whe re as the acetic-acid-insoluble residues content of rocks from Wangcun and Wa’ergang sections is more than 10%. Four eustatic events of sea level are interpreted from the deposits of Huaqiao and Chefu formations by means of facies analysis and sequence stratigraphy. Three condensed sections containing pyrite and spongy bone needle indicate that deepest water deposition occurred near the beginning of the Ptychagnostus atavus and Lejopyge laevigata biochorons, and the midway within the P. punctuousus biochron. The forth occurred in Gushan Stage. Incipiently drowned platform and ramp evolved into accretionary platform and steepened ramp. Of all sections, richly fossi liferous, easily accessible, excellently exposed and continuous stratigraphic section in Wangcun is most competitive candidate section for the middle-upper cambrian boundary stratotype. |
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| Keywords: | Middle-Upper Cambrian Boundary stratotype Sedimentary characteristics W estern Hunan |
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