| The Tianshui - Qin'an area is located at the convergence of Liupan Mountains and west of Qinling Mountains on the north margin of the Tibetan Plateau, and is the connection between the Tibetan Plateau and the Loess Plateau. Sediment in the basin has perfectly recorded the process of weather, denudation, transition and deposition in river system in orogenic belt, so the sediment not only can reflect the dynamic properties in filling process and the basic characteristics of the surrounding orogenic belt, but also record the climate and environmental change information in all kinds of geological processes. Based on wide field investigation, data analysis, synthesized various kinds of indices and correlative data, we have mainly obtained the following findings:1 Tianshui basin has experienced three stages of tectonic evolution, stage 1: Lithospheric thinning by the rotate and Stretch, sediment in Tianshui basin is brown alluvial fan red sandstone the kamafugitic series lava from mantle eruption out.Stage2:Tian shui Basin Lithospheric stretching stop to depress basin evolution and causes the Paleogene strata intense tectonic deformation in Neogene. A uniform basin has been formed between west Qinling and Huajia Mountains . Neogene strata formed and unconformably overlaped on the Paleogene sandstone. Note that at least that time India and Eurasia plate collision effects of the long-distance transmission has arrived in the area .Stage3: Tianshui basin enter the the Qinghai-Tibet Campaign A stage 3.6Ma ago, the southern region of Tianshui Basin again Depression.2 Tianshui Cenozoic sedimentary basin under the sedimentary structure of construct features were divided into 21 facies and the alluvial fan, wide-shallow lakes, flood plains, rivers four sedimentary environment,Neogene strata division into the "lower red bed", "zebra bed" "upper red bed" "upper red bed" of the four lithology Stage Magnetostratigraphy era is 15.6-9.23Ma, 9.23-7.1Ma .1-3.6Ma, 3.6Ma-1.4Ma respectively.3 the appearance of Guojia Neogene section is similar to the Loess-paleosol series, However based on the grainsize, geochemistry and microstructure analysis of the sediment deposited during 22-6.2Ma in Guojia, Qin'an, suggested that this set of red beds was it should be an alternative series which is composed of finegrain lake shoal mudflat deposition on the margin of the basin, floodplain deposition and those products of pedogenensis in the air.4 The Paleogene red coarse clastic rocks with the characters of piedmont alluvial fan facies were deposited in Tian shui basin Local area. The thickness of the Neogene deposition decreased rapidly from west Qinling piedmont depression to the broad floodplain in the basin. The sediments become finer and the horizontal difference of sediments facies is obvious. The deposition evolution experienced the following stage since 15.6MaB.P.:15.6-9.23Ma: floodplain and fluvial deposition, the "lower red bed" consists of red mudstone and calcareous mudstone or calcrate with alternate appearance; 9.23-7.1Ma, the lake invasion took place in the basin broadly, the "zebra bed" consists of celadon marlite interbeded with red mudstone; Since 7.1Ma, the lake began to shrink in large scale and floodplain developed in vast area of the basin. 7.1-3.6M, "upper red bed" came into being and consisted mainly of red argillaceous beddings and siltstone beddings, moreover, gypsum-salt deposition has been found at the top of "upper red bed" in some area; About 3.6Ma, affected by the Tibetan Plateau uplift, the south part near the west Qinling Mountains in the basin downfaulted and became lake again; 3.6Ma-1.4Ma, "upper green bed" came into being and consists of celadon mudstone interbeded with offwhite marlite; About 1.4Ma, affected by the intense uplift of the Tibetan Plateau, the development history of the lake in the study area ended. After that, the study area began to experience uplift ,denudation, river terraces development and eolian Loess deposition.
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