Chemical Sequence Stratigraphy of the Wufeng Formation-lower Member of Longmaxi Formation in Shuanghe Outcrop, upper Yangtze

Based on the theories and methods of comprehensive geochemistry and high resolution sequence stratigraphy, the data of Shuanghe outcrop and sample test are used to optimize the indicator system for the chemical sequence stratigraphic division.The division are the elements assemblages of Al-K-Ti-Mg-Rb-Cr-Zr related to terrigenous input intensity, the elements assemblages of Ca-Mn-Ba-Co related to autogenetic precipitation intensity, and the elements assemblages of V-Ni-Mo-U-Cu-Zn related to organic matter adsorption and deoxidation intensity. The Wufeng Formation is thus divided into LCW 4th-order sequence; and the lower part of Longmaxi Formation is divided into MCL1-1, MCL1-2, MCL1-3, MCL1-4 4th-order sequences accordingly from bottom to top. The total amount of major and trace element combinations related to the terrigenous input intensity is relatively high near the sequence boundary but relatively low near the most oceanic flooding surface, with the characteristics of decreasing-increasing cyclic changes of total elements. Autogenetic precipitation, organic matter adsorption and deoxidation intensity is generally lower near the sequence boundary and higher near the maximum flooding surface with the characteristics of increasing-decreasing cyclic changes of the total amount of elements.