GEOCHEMISTRY AND PROVENANCE OF THE MID-PERMIAN SUCCESSIONS IN THE SOUTHERN JUNGGAR BASIN AND TURPAN BASIN: IMPLICATIONS FOR THE PALEOCLIMATE AND PALEOGEOGRAPHY

The mid-Permian successions in the southern Junggar-Turpan Basin are characterized by unconformities across the formation boundaries. However, the origin of the unconformities remains ambiguous. Two sections, namely the Xiaolongkou section in the southern Junggar Basin and the southwest (SW) Tarlong section in the Turpan Basin, have been systematically studied for detrital zircon and bulk-rock geochemistry analyses. Detrital zircon and geochemistry analyses indicate that within each section, the Lucaogou, Hongyanchi and Quanzijie Formations display similar age distributions as well as rare earth elements (REE) and high field strength elements (HFSE) characteristics, suggesting no significant changes in provenance during their deposition. However, the provenances of the two sections are different from each other; the Xiaolongkou section is rich in felsic components, with two peak ages in detrital zircon age spectra, while the SW Tarlong section contains more mafic components, with a single peak age in detrital zircon age distribution. This suggests a highly partitioned nature of the greater Junggar-Turpan Basin with poly-depocenters during the mid-Permian. Meanwhile, field observations and geochemistry indicate that the Lucaogou and Hongyanchi Formations were generally deposited under arid-semiarid conditions, with low CIA values and Th/U ratios as well as low Rb/Sr ratios and high Sr/Cu ratios, and have abundant mudcracks and ripple marks, whereas the Quanzijie Formation was deposited in semiarid-semihumid conditions, which display relatively higher CIA values and Th/U ratios, higher Rb/Sr ratios and lower Sr/Cu ratios. Therefore, we suggest that these unconformities were rather not generated by tectonic uplift, which would have caused significant changes in source-to-sink system, but were most probably resulted from the increasing aridity that led to catastrophic spill-point lowering in poly-depocenter landforms. The mid-Permian unconformities were the combined results of the arid paleoclimate and highly partitioned paleogeography.