Major and Trace Elements Geochemistry and Geological Implications of Dolomite-Bearing Mudstones in Lower Part of Shahejie Formation in Tanggu Area,Eastern China
Li Le
Yao Guangqing
Liu Yonghe
Hou Xiuchuan
Wang Gang
Zhao Yao
Gao Yujie
Abstract：Fine mudstone can record and reflect geological aspects of source and sedimentary area.A set of lacustrine dolomite-bearing mudstones is developed in Lower Shahejie Formation of Tanggu area.To understand its tectonic setting,depositional setting,weathering and provenance,the geochemical characteristics of 25 rock samples were analyzed thoroughly.With dolo-mite-free modification,different indices and diagrams reveal identical geological information.Active continental margin setting (Andean-type)is revealed by the combination of high ∑REE(154.0×10-6 -219.3×10-6 ),moderate negative Eu anomaly (0.64-0.73)and tectonic setting discriminant diagram (K2 O/Na2 O-SiO2 ,SiO2/Al2 O3-K2 O/Na2 O,and discriminant function bivariate diagram).SiO2-(K2 O+Na2 O+Al2 O3 )bivariate discriminant diagram,equivalent B(200.17-313.21)and approxi-mate degree of pyritization (DOP apx )(0.02~0.38),authigenic U(0.14-1.22),U/Th(0.17-0.44)indicate arid,saline and oxic depositional condition respectively.Chemical index of alteration (CIA)(51.26 -65.74),plagioclase index of alteration (PIA)(51.65-78.06),modified index of composition variation (ICVm )(0.67-1.24)and A-CN-K diagram reflect mild to moderate weathering of source rock.Discriminant function diagram,K-Rb bivariate diagram,A-CN-K diagram,Al2 O3/TiO2 index(23.37-28.58),REE pattern similar to upper continental crust (UCC)and negative Eu anomaly deduce the felsic rocks as the major source for the dolomite-bearing mudstones.Under such geological constrain,it is concluded that the source mate-rials are mostly derived from Yanshan fold and thrust belt.
Keywords：Tanggu areaShahejie Formationdolomite-bearing mudstonegeochemistrydepositional settingsedimentology
Publication Date：2015-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：17( 1480-1496 )