Formation and Evolution of a Paleosol across the Lower Silurian-Lower Permian Boundary in Zunyi District,Northern Guizhou,China and Its Paleoenvironment and Paleoclimate Implications  

作　　者：XIONG Xiaohui XIAO Jiafei HU Ruizhong WANG Jian WANG Yi WANG Xinsong DENG Qi 

机构地区：[1]State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences [2]Chengdu Institute of Geology and Mineral Resources [3]Key Laboratory for Sedimentary Basin and Oil and Gas Resources,Ministry of Land Resources [4]Chinese Academy of Geological Sciences [5]Nanjing Institute of Geology and Palaeontology,Chinese Academy of Sciences

出　　处：《Acta Geologica Sinica(English Edition)》2015年第6期2012-2029,共18页地质学报（英文版）

基　　金：supported by 12th Five-Year Plan Project of State Key Laboratory Of Ore Deposit Geochemistry Chinese Academy of Sciences(SKLODGZY125-08);funds from State Key Laboratory of Palaeobiology and Stratigraphy Chinese Academy of Sciences;Chinese National Program on Key Basic Research and Development(2007CB411408)

摘　　要：This paper presents a set of bulk geochemical and mineralogical data from a paleoweathering profile located in Zunyi District, Northern Guizhou, China. It was formed at the top of the Hanjiadian Formation of the Lower Silurian. A truncated, argillic, gleyed, kryptic paleospodosol is recognized in the paleoweathering profile. Ratios of immobile elements（Ti/Zr, Ti/Al） and their binary（e.g., Nb vs. Zr/TiO_2 and Th/Sc vs. Zr/Sc）, triangular diagrams（La-Th-Sc, Th-ScZr/10, Zr-Cr-Ga） reflect that the Gaojiayan paleosol is the product of in-situ weathering of gray-green silty mudstone of the underlying Hanjiadian Formation. Mass balance calculations indicate K enrichment and Na enrichment in the upper and lower portions of paleosol, respectively. These findings both are the results of transgression, which brings substantial concentrations of such elements as K, Na, and Sr. In particular, K enrichment is achieved by the illitization of kaolinite. The biological processes of terrestrial vascular plants also enhance K concentration, especially at the top of the paleosol. Na enrichment is a consequence of albitization and/or adsorption by clay minerals through cation exchange. The mass distributions and relative mass changes of rare earth elements（REEs） in the studied profile display characteristics of vertical zonation. Three peaks in total REEs content are observed, indicating two paleoclimatic or paleoenvironmental changes. Mineralogical characteristics indicate that the paleoclimate changed first from warm and humid to cold and dry and later, to dry and lightly warmer. The corresponding soil environment varies from weakly acidic to strongly alkaline and later, to weakly acidic. Mass translocation characteristics of REEs and several transition metals suggest that the Gaojiayan paleosol may have undergone top erosion.This paper presents a set of bulk geochemical and mineralogical data from a paleoweathering profile located in Zunyi District, Northern Guizhou, China. It was formed at the top of the Hanjiadian Formation of the Lower Silurian. A truncated, argillic, gleyed, kryptic paleospodosol is recognized in the paleoweathering profile. Ratios of immobile elements（Ti/Zr, Ti/Al） and their binary（e.g., Nb vs. Zr/TiO_2 and Th/Sc vs. Zr/Sc）, triangular diagrams（La-Th-Sc, Th-ScZr/10, Zr-Cr-Ga） reflect that the Gaojiayan paleosol is the product of in-situ weathering of gray-green silty mudstone of the underlying Hanjiadian Formation. Mass balance calculations indicate K enrichment and Na enrichment in the upper and lower portions of paleosol, respectively. These findings both are the results of transgression, which brings substantial concentrations of such elements as K, Na, and Sr. In particular, K enrichment is achieved by the illitization of kaolinite. The biological processes of terrestrial vascular plants also enhance K concentration, especially at the top of the paleosol. Na enrichment is a consequence of albitization and/or adsorption by clay minerals through cation exchange. The mass distributions and relative mass changes of rare earth elements（REEs） in the studied profile display characteristics of vertical zonation. Three peaks in total REEs content are observed, indicating two paleoclimatic or paleoenvironmental changes. Mineralogical characteristics indicate that the paleoclimate changed first from warm and humid to cold and dry and later, to dry and lightly warmer. The corresponding soil environment varies from weakly acidic to strongly alkaline and later, to weakly acidic. Mass translocation characteristics of REEs and several transition metals suggest that the Gaojiayan paleosol may have undergone top erosion.

关 键 词：PALEOSOL PALEOCLIMATE PALEOENVIRONMENT Lower Silurian-Lower Permian NorthernGuizhou 

分 类 号：P534.4[天文地球—古生物学与地层学]