Orbital cyclicity in sedimentary sequence and climatic indications of C-O isotopes from Lower Cretaceous in Qingxi Sag, Jiuquan Basin, NW China

作     者：Siding Jin Haiyang Cao Hua Wang Michael Wagreich Sylvain Richoz 

作者机构：State Key Laboratory of Oil and Gas Reservoir Geology and ExploitationChengdu University of Technology College of Energy ResourcesChengdu University of Technology Institute of Sedimentary GeologyCenter for Post-doctoral StudiesChengdu University of Technology Key Laboratory of Tectonics and Petroleum ResourcesChina University of Geosciences Department of Geodynamics and SedimentologyUniversity of Vienna Institute of Earth SciencesNAWI GrazUniversity of Graz 

出 版 物：《Geoscience Frontiers》 (地学前缘（英文版）)

年 卷 期：2019年第10卷第2期

页      面：467-479页

核心收录：

学科分类：07[理学] 

基　　金：the support of a Chinese Scholarship Council’s overseas student scholarship to enable her to visit the University of Vienna for 24 months supported by Research Institute Exploration and Development, PetroChina Yumen Oilfield Company The China National Key Research Project (No. 2017ZX05009-002-003) supported this study 

主　　题：Jiuquan Basin Qingxi Sag Xiagou Formation Orbital cyclicity Stable isotope 

摘      要：Sedimentary deposits of the Lower Cretaceous Xiagou Formation form the most significant potential hydrocarbon reservoirs in the Qingxi Sag, Jiuquan Basin(NW China). Zircon U-Pb ages of the dated basalts at the top of the Xiagou Formation give an isochron age of 115.6 Ma, and the sedimentation interval of the Xiagou Formation was speculated to range from about 125/124 Ma to 115 Ma based on paleontological research and stratigraphic correlation analysis. Here we use GR logging data as a palaeoenvironmental and palaeoclimatic proxy to conduct a detailed cyclostratigraphic study of five selected wells. Power spectra, evolutionary fast Fourier transformation and wavelet analysis all reveal significant sedimentary cycles in the Xiagou Formation. The ratios of cycle wavelengths in these stratigraphic units are 33.82 m : 7.91 m : 3.06 m : 1.79 m, which is similar to the ratio of orbital targets of 20 : 5 : 2 : 1. The ratio of 20 : 5 : 2 : 1 is interpreted as Milankovitch cycles of 405 kyr long eccentricity,100 kyr short eccentricity, 37 kyr obliquity, and 22 kyr precession cycles respectively. A high-resolution astronomical time scale is constructed by tuning the stratigraphy into target curves of orbital cycles respectively. Based on the astronomical time scale, the absolute ages of 55 samples were estimated,which are used for subsequent stable carbon and oxygen isotope stratigraphy analysis. The analysis results of the five studied wells in the Qingxi Sag indicate:(1) a negative trend of δ^(13)C values upwards in the Xiagou Formation, and(2) negative δ^(18)O values with a positive trend upwards. Both relatively heavy values and pronounced covariances of δ^(13)C values and δ^(18)O values indicate an arid-evaporationcontrolled climate during the sedimentary period of the Lower Cretaceous Xiagou Formation, Qingxi Sag, Jiuquan Basin. Moreover, positive covariances of SQK_1g_(2+3) indicate extremely high temperature, and negative covariances of SQK_1g_1 indicate a relatively l