The source rocks of Ordovician carbonate rocks in the Ordos Basin are mostly Preserved in darkgrey micrite transgtessive system tracts and early-sarge high water-level system tracts. The transgressive system tracts of Fengfeng and late Majiagou stages are two major oil-generation stages.The formation of reservoir and cap rocks was mainly related to the meteoric diagenesis

Penecontemporaneous dolomitization

and condensing evaporation during the late stage of high water-level system tracts. The upward shallowing penesequence cycles within the sequences formed a series of "self-reservoiring and near-reservoiring "souroe- rsservoir-caprock complexs. Ordovician deposition in the area underwent three platform evolution Periods: gentle-slope platform

rimmed platform and open platform Periods

and formed the main sedimental pivot belt in platform margins and secondary sedimental pivot belts within the platform. It has been proved that oil and gas distribution are related to the above mentioned pivot belts.