Evolution Features and Controlling Factors of Depositional Systems of Paleogene-Neogene in Maxian Area, the Northern Margin of Qaidam Basin

According to the comprehensive detailed analysis of data such as, drilling core, logging and outcrop section, four kinds of sedimentary facies, namely, proluvial fan, braided river, shallow water braided river delta, and oxidative lacustrine, are recognized in Paleogene-Neogene of Maxian area in the northern margin of Qaidam basin. The evolution features of the sedimentary systems were analyzed in details: at the early forming stage of the lake basin (Paleocene-Eocene), proluvial fan -braided river depositional systems were developed in the study area. At the middle flourishing stage of the lake basin (Oligocene-Middle Pliocene), the main sedimentary systems were braided river-shallow braided river delta-oxidative lacustrine. Then the study area was dominated by proluvial fan-braided river-oxidative lacustrine depositional systems in the regression stage of the lake basin (Late Pliocene). The range of the depositional systems in low frequency sedimentary cycle was controlled by the multi-cycle tectonic uplifts and squeezing action of mountains around the study area. Paleoclimate and ancient landform controlled the high frequency change of the lacustrine level and supplied an advantage for the development of shallow braided river delta and oxidative lacustrine facies.