Zhengchuang Hui

Late Tertiary reorganizations of deformation in northeastern Tibet constrained by stratigraphy and provenance data from eastern Longzhong Basin

The deformation of the Tibetan Plateau is central to unraveling the process and mechanism of continental tectonics. Although most agree that crust shortening and plateau growth were protracted throughout the Cenozoic Indo-Asian collision, particular deformation histories relating to tectonic kinematics and dynamics are still incomplete due to sparseness of diagnostic geological information from plateau margin. Here we present combined investigation of stratigraphy, magnetostratigraphy, and provenance for the eastern margin of Longzhong Basin to show two reorganizations of basin formation and tectonic regime during the late Tertiary. First, the depocenter migrated from the dispersed Paleogene sequences to the Wushan-Tianshui foreland sequence during the earliest Miocene (circa 22 Ma), accompanied by shift of sedimentary provenance from double sources including the eastern Qilian block and eastern West Qinling terrain to single source within the West Qinling. It suggests reorganization of deformation from NW-SE extension to NE-SW contraction and initial uplift of the eastern West Qinling. Second, massive coarse-grained fluvial beds were revived in the Wushan Basin during the late Miocene (circa 10 Ma), associated by eastward depositional expansion and another shift of sedimentary provenance toward northeast. It reflects thrusting up of the northern edge of the West Qinling and Liupan Shan Mountains linked with relocation of crust shortening from NE-SW direction to ENE-WSW direction and accelerated deformation of northeastern Tibet. These transitions of deformation regimes imply variation of geodynamic mechanisms during the process of plateau growth.

Diversity of Moschidae (Ruminantia, Artiodactyla, Mammalia) in the middle Miocene of China

Abstract. In this paper, we describe newly discovered and previously collected fossil moschid specimens from the middle Miocene of China. Besides the previously reported Hispanomeryx andrewsi, we recognize four additional fossil species in two genera of Moschidae in the middle Miocene of China based on dental morphology: Micromeryx cf. flourensianus, Micromeryx sp., Hispanomeryx sp. 1, and Hispanomeryx sp. 2. The specimens are of Tunggurian age (Neogene Chinese Land Mammal Age), corresponding to European MN6-MN7/8. The records show a diversity of fossil moschids in the middle Miocene of China comparable with the contemporaneous diversity in western European faunas.

Understanding Miocene climate evolution in Northeastern Tibet: Stable carbon and oxygen isotope records from the Western Tianshui Basin, China

To investigate climate evolution during the Miocene, especially during the Middle Miocene climate transition on the northeastern Tibetan Plateau, stable oxygen and carbon isotopes of carbonates from a 288-m-thick lacustrine-fluvial sediment sequence covering the period from 17.1 to 6.1 Ma from Tianshui Basin, China, were analyzed. The relatively low stable oxygen isotope values indicate the prevalence of wet climate conditions during the period of 17.1–13.6 Ma, an interval corresponding to the well-known Middle Miocene Climate Optimum. The interval between 13.6 and 11.0 Ma (i.e., the late Middle Miocene) is marked by a progressive increase in the δ18O values, indicative of a decrease in precipitation, probably linked to the expansion of the East Antarctic Ice Sheet and global cooling since about 14 Ma. The climate in the study area continued to get drier as shown by the enrichment of the heavy oxygen isotope from 11 Ma. We attribute these stepwise climatic changes as revealed by our carbonate δ18O record from the northeastern Tibetan Plateau to the sustained global cooling that may have reduced moist transport to Central Asia, which in turn led to a permanent aridification.