| The western area of Ordos basin, which possesses abundant oil and gas resources and should be paid more attention ,has bright prospect in oil and gas exploration.lt has been becoming one of the important tactical areas in oil and gas exploration in further ordos's research and exploration .By collecting data about outcrop, core, and many other elementary geological data, at the same time using sedimentary analyse and geological analyse, in this thesis, sequence division were applied, provenance were analysised, type of sedimentary facies were identified, the extension of sand bodies and distributing of sedimentary facies were studied and the paleogeograpby were reconstruced. Sedimentary system of Taiyuan and Shanxi were realized by the research above. Finally the favorable area were found out.Based on the primary markes of contrast in region and interface of sequence stratigraphy, stratum of Taiyuan and Shanxi Formation were divised. According to vertical association and cycle characteristics, such as weathering and denudation surface, scour surface, sudden change surface of lithologic character and lithofacies, channel incise, transfer surface between ascending and falling, combine with production of other people, mid-term cycle of Taiyuan Formation can be divided into 2 short-term cycles, namely Tai2,Tai1; mid-term cycle of Shanxi Formation can be divided into 3 short-term cycles, namely Shan2,Shan12,Shan11 in ascending order.The western area is far-flung and have more than one sediment source. From palaeo-structure pattern, distribution of sedimentary system, depositional structure and texture, composition characteristics of debris, cathodoluminescence of quartz, characteristics of heavy minerals, characteristics of rare earth element and trace element, sediment source of study area was discussed. It indicated there are two sections in the area and that debris material of northern area mainly derived from Yimeng and Alashan ancient promontory; The southwest sediment source is late-proterozoic metamorphic rock, with volcanic rock and magmatic rock.Based on outcrop observation, core description, single well-log and sequence analysis, connecting-well section, combined with analytic result of plane configuration of sandstone , characteristics of lithology and log displays of all substratum, Taiyuan formation are composed of beach-barrier system and neritic-shelf system. Flat, branching-bay, barrier bar, barachois, beach deposit were identified in Taiyuan formation.Delta system and fluvial system were identified in Shanxi formation, Delta system is mainly composed of delta plain and delta front, while pro-delta is not well developed. Delta front were controlled by the line of lakeshore. Fluvial system is distributed at the north part of the study area, developed during early and late period of Shanxi formation. Fluvial system is dominated by meandering river, while braided river is not only confined within small area, but short time as well. The extension of stand bodies were controlled by distributing of sedimentary facies. Stand bodies of foreshore, barrier bar and distributary channel are researchful target.Base on the connecting-well section and combined with the synthetic study ofgeological back ground of the study area, the paleogeographic evolution was reconstructed. Qilian sea transgression happened in western area of late-Carboniferous. Till Permian Taiyuan, Qilian sea converged with eastern sea, paralic inland sea appeared. From north to sourth, delta, lagune and barrier bar appeared in order. In the period of Shanxi, sea regressed and climate becomed warm so that delta-fluvial system deposition appeared, coal bed are formed for peat swamp and pit developed.Through analysis of oil depression, reservoir, blanket, trap, we consider that gas and oil concentration is mainly controlled by distribution of sand bodies and source bed, four comparatively favorable area were found out: Tekesumiao area, Tianshenl-Yuantanl area, Huianbu area and Pingliang area.
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