Geochemistry Characteristics of Middle-Lower Jurassic Clastic Rocks in the Northern Margin of Qaidam Basin and Their Geological Significance(PDF)
《地球科学与环境学报》[ISSN:1672-6561/CN:61-1423/P]
- Issue:
- 2017年第06期
- Page:
- 721-734
- Research Field:
- 基础地质与矿产地质
- Publishing date:
Info
- Title:
- Geochemistry Characteristics of Middle-Lower Jurassic Clastic Rocks in the Northern Margin of Qaidam Basin and Their Geological Significance
- Author(s):
- DU Jian-jun; ZHANG Shi-an; XIAO Wei-feng; JIANG Wan
- 1. Key Laboratory of Neotectonic Movement and Geohazard of Ministry of Land and Resources, Beijing 100081, China; 2. Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China
- Keywords:
- geochemistry; clastic rock; Jurassic; sedimentary rock; paleoclimate; provenance; paleogeography; Qaidam Basin
- PACS:
- P588.21;P595
- DOI:
- -
- Abstract:
- Middle-Lower Jurassic in the northern margin of Qaidam Basin is the focus of oil and gas exploration in the medium-small basins around Qaidam Basin. In order to provide a basic geological support for Jurassic oil and gas exploration in the northern margin of Qaidam Basin, the Middle-Lower Jurassic palaeogeography and paleoenvironment were discussed according to the geochemistry characteristics of clastic rocks. These rocks are similar in major oxide compositions to the upper continental crust (UCC), but have slightly lower contents of MgO, Na2O and K2O. They have moderate abundance of REE with patterns, which are identical to that of the upper continental crust. The trace elements are characterized by medium depletion of large ion lithophile element (LILE), medium depletion of compatible element and weak-rare depletion of high field strength element (HFSE). The Middle-Lower Jurassic clastic rocks display medium to high weathering, suggesting a warm and humid palaeoclimate for the northern margin of Qaidam Basin during Early-Middle Jurassic, which is consistent with previous palaeontology studies and the location of the study area in the mid-latitude of the northern Tethyan ocean. The insignificant sedimentary cycle in the clastic rocks suggests the inexistence of intensive sedimentary cycle for their provenance. The characteristics of trace elements can objectively reflect those of the provenance, and the detritus of the rocks are predominantly derived from Post-Archean upper continental crust mainly consisting of intermediateacid magmatic rock. The water environment discrimination of ancient lake basin manifests a hypoxic-reducing environment for the northern margin of Qaidam Basin during Early-Middle Jurassic, and the reducing condition is gradually weakened from Early Jurassic to Middle Jurassic. It may be related to the different prototype basins of the different stages; the graben basin formed in Early Jurassic is small and deep water, and is characterized by enclosed lake basin; whereas, the graben basin formed in Middle Jurassic is large and shallow water.
Last Update: 2017-12-15