JIA Ze-nan1，TIAN Ya-ming1*，LIU Ming1，LI Wen-qing2，LU Zong-qiang1
(1. College of Earth Science，Chengdu University of Technology，Chengdu 610059，China；
2. Exploration and Development Research Institute of PetroChina Changqing Oilfield Company，Xi’an 710018，China)
Abstract: The analysis of trace elements and rare earth elements (REE) for mudstones from Chang-7 and Chang-8 members of the Upper Triassic Yanchang Formation in the northern Jiyuan area of the Ordos Basin has been carried out in this paper. This study reveals that mudstones of the Chang-7 and Chang-8 members are characterized with rich in REE, obviously negative anomaly of Eu, Their REE distribution patterns reflect a distinct differentiation of LREE and HREE, with steep right-declined curves in the La-Eu section but flat curves in the Gd-Lu section. Combined with the analysis of parameters including Sr/Cu, Sr/Ba, V/(V+Ni), and Ceanom, it is believed that mudstones of the Chang-7 and Chang-8 members were formed in the sedimentary environment of humid, low salty, and reduced water body. The geochemical parameter of (La/Yb)N of the mudstones indicates that suspended particles were general slowly deposited with deposition rates varying from relatively high to low for mudstones in beds from bottom to top of the profile. Meanwhile，the δCe, δEu values and La/Lb-∑REE discrimination diagram indicate that mudstones of the Chang-7 and Chang-8 members are sourced from major granites and minor alkaline basalt which were formed in a tectonic setting of the continental margin.
Keywords: Mudstone; geochemical characteristics; Yanchang Formation; the northern Jiyuan area; Ordos Basin
ACTA MINERALOGICA SINICA Vol. 39, No.5, 2019, page 549-558
