Cenozoic Sedimentary Evolution Of The Western Tarim Basin

Retreat of Tethyan realm and uplift of Tibet plateau are important geological issues occurred in the Cenozoic era, which play important roles in driving the Asian interior aridification and the Asian monsoon change. However, the issues of how and when these events occurred, and the relations between the events and climate changes are still in hot debates due to either lack paucity of continuous sedimentary sequence across the Cenozoic era or accurate chronology constrain. In the western tarim basin, over 3000 m Cenozoic sequences, consisting of the marine strata in the bottom, continental clay and fine sand in the middle, and molasse sequence in the upper part, record continuous paleoenvironmental evolutions of the area from shallow marine to arid land and finally to high altitude like today. The Taklimakan desert in the Tarim basin is the largest desert in Euraasia, and was regarded as one of the major dust sources of the North Hemisphere. Well exposed late Cenozoic strata in the central area preserves direct evidence on the evolution of Taklimakan desert. In this work, a systemic investigation was developed to the Cenozoic sequence of the western Tarim basin, and six typical sections including Ulukeqiati section, Aertashi section, Tageshan section, Hongbaishan section, Simhana section and Kangsu section were selected to developed chronological and paleo-envrionmental investigations. Magnetostratigraphy, ESR dating and biostratigraphy were conducted to found geological time framework. Facise analysis and multi-proxy indices including grain size, magnetic susceptibility and color index were used to reconstructing the paleoenvironment evolution of the region. Accordingly, further discussions of the geological and climatic events, i.e. retreat of Tethyan realm, interior aridification, uplift of Tibet-Pamir plateau, were developed based on the high-resolution paleoenvironmental records. The following points mark the main conclusions of this thesis.1) Four major Paleoenvironmental evolution stage of the western Tarim basin were identified:-65-33.9 Ma was characterized by alternating of shallow marine and continental environment;-33.9-23 Ma dominanted by arid plain environment, whereas,-23-5.3 Ma was characterized by alluvial and fluvial plain, and finally, from-5.3 Ma alternating to intermountain environment.2) The Tarim gulf was formed in the late Cretaceous. Uppermost marine strata terminated in-33.9 Ma, which indicate the eastern edge of the Tethyan realm finally retreat from Tarim Basin at this time. We argued the global sea level fluctuation is the major forcing factor, On the other hand, the tectonic activities also played important role.3) Aridification of Interior-Asian, as indicated by the Aeolian deposits, initiated at the very beginning of the Cenozoic, and significant enhanced at ～33.9,～25-23,～16-14,～5.3,3.4 and 2.8 Ma.4) Accumulation of the molasse sequence and deformation of the strata record two main tectonic activities of the area, which in turn suggest two tectonic episodes of the north Pamir Plateau. The last and more significant one, which led to the final deformation of the strata, occurred in the middle to late Pleistocene.