Characteristics of Trace Element and REE Geochemistry of the Cretaceous Mudrocks and Shales from Southern Tibet and Its Analysis of Redox Condition
详细信息
- 责任者：Xiong Guoqing (Chengdu Institute of Geology and Mineral Resources ; Chengdu 610082 ; China) ; Jiang Xinsheng
- 刊名：Advances in Earth Science
- 出版年：2010
- 卷期：25(7)
- 关键词：泥岩 ; mudstone ; 页岩 ; shale ; 西藏 ; Tibet
- 页码：p.730-745
- 图表：illus., 5 tables, 105 refs.
- 分类号：0803
- issnNo：ISSN1001-8166
- isbnNo：CN62-1091/P
摘要
///To understand the redox conditions of bottom water column of the Cretaceous mudrocks and shales during their deposition from two main marine basins in southern Tibet,the tests and analysises of trace elements and REEs from the samples were done by the ICP-MS method. The results reveal that the trace elemens in study area have changed both spatially and temporally,and the changes are related to redox-sensive extent of those elements to the water-column. The variable trends of all Al-normalized elements are almost different and their vertical variations have reflected redox condition of bottom water column of sediments and biological production,related to multiple facters:sea-level osccilation,the flux of terrigenous debris,remobilization of diagensis and post-deposition oxygen. The ratios of V/（ V + Ni） 、U/Th、V/Cr、Ni/Co、Re/Mo、Uau and δU indicate that condition of bottom water column in southern Tibet basins is generally moderate-stratified oxic condition during the early cretaceous and middle and late cretaceous,but those elements have suddenly changed between the Cenomanian-Turonian boundary during the early cretaceous in Gamba-Tingri basin,and revealed anoxic condition. Chondritic-normalized REEs both exhibit LREE enriched,right-tilted,LREE/HREE between 7.42 and 14.80, LaN /YbN range from 7.93 to 18.54, δEu negative abnormal, δCe unclearly abnormal,showing oxic condition. The analysis of trace elements and their REEs combined with field observation of outcrop can be direct foundation for divided and contrasted strata,and determine the condition of bottom water column more accurately and effectively during the deposition.
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