Transformation Of Cenozoic Sedimentary And Riginal Consrast In Western Qaidam Basin

The turn of Paleogene and Neogene is an important transforming period of the Cenozoic sedmentary in Northern Tibetan Platean. Qaidam Basin is surrounded by the Qilian Mountains, Altun Mountains and Eastern Kunlun Mountains. The formation and evolution of the basin was closely related to these orogenic belts, so that the sedimentary records in Cenozoic in this basin can provide direct evidence for the uplifting time series of these orogenic belts. By sedimentary research on measured sections in the field, combined with indoor thin section analysis and Statistics, supplemented by the inspection of cathodoluminescence, the source of sediments has been confirmed and the speculation that there was a sedimentary transformation in the time of 22Ma of the Qaidam Basin has been verifyed. In a larger area, the Tarim Basin,Hoh Xili Basin and Kumukuli Basin have been compared with. Conclusions are as follows:(1) In Cenozoic there were 8 sets of main sedimentary strata in Qaidam Basin, form bottom to top layer: Palaeocene Lulehe Formation, Eocene Xiagancaigou Formation, Oligocene Shanggancaigou Formation, Miocene Xiayoushashan Formation and Shangyoushashan Formation, Pliocene Shizigou Formation, Pleistocene Qigequan formation and Holocene sedimentary strata. The sedimentary paleoenvironments include the paleo-river and four subenvironment: lakes delta, lakeshore, shallow lake and deep lake.(2) The Qaidam Basin had experienced at least two completely third-level cycles of lake regressions and transgressions in Cenozoic, the first cycle occurred in Paleogene, and the second occurred in Neogene. Algal limestone began in the late Oligocene, flourished in the early Xiayoushashan period, declined in the late of this period. This period may be the humid time in Cenozoic in the Qaidam Basin. Argillaceous dolomite and Gypsum-salt mainly developed in middle and late Eocene and Oigocene, the environment might be relatively dry in this period. (3) During the deposition period of Xiagancaigou Formation to Shangyoushashan Formation, rock debris of sedimentary stone is dominant in the whole debris, indicating that Altun Mountains was the main source area of the western Qaidam Basin at least(4) A lot of metamorphic rock debris, irruptive rock debris and effusive rock debris were found at the bottom of the Xiayoushashan Formation, implying that Altun Mountains has been experienced an important tectonic events in the turn of Paleogene and Neogene( 22Ma ).(5) The turn of Paleogene and Neogene is an important transforming period of the Cenozoic sedmentary in Northern Tibetan Platean. During this period the souce area of the Qaidam Basin changed; paleoclimate of the Hoh Xili Basin changed form the hot and dry to an unusually wet; marine depositional system transformed to a continental depositional system in the southwest of Tarim Basin; the paleaclimate of the Kumukuli Basin changed from half-dry to wet.