Abstract: Geologically, the southern area of the central doming of or-dos basin is called Weibei flexural fold. Its width is about 100km from south to north. The Qinling through was in the southern ordos basin. The area was s distally steepening carbon-ate ramp in Ordovician. In the time of high sea level, the cli-mate was moist and warm, and the seawater could communicate with open seawater. In this period, the main sediments were micite, some bioclast limestone, calcarenite, calcisilte lime-stone, reef et al. In the time of low sea level, climate was be-coming more and more scorching and dry. It was difficult for the communication of seawater on the ramp with open sea. In this period, the main sediments were mud-sized crystalline dolo-stone, silt-sized crystalline dolostone, some grain mud-silt-sized crystalline dolostone, mud-silt-sized crystalline grain dolosone,strom rock et al.Because of oversaturated CaSO4or NaCl in some hollows,there were some gypsiferous dolostone and saline
rock deposited on the peritidal are and shallow ramp. On the slope area out the south-ramp, there were some calcirudite and turbidite deposited.

Key words: ordos basin, ordvician, carbonate ramp, deposi-tional