The carbonate platform sedimentary model of southern Ordos basin

Abstract：The characteristics of the strata, the sedimentary rock combination and the ancient landform demonstrate that the local early Ordovician Majiagou stage in southern Ordos basin can be divided into three depositional unit areas, i.e., the north-eastern area primarily with the dolomite—evaporite combination, the southern area with dolomite and minor evaporite combination, the western area mainly with limestone. Correspondingly，the north-eastern area mainly grew the intra-platform basin—basin-marginal flat, the southern area grew hollow-platform flat-platform edge-trough, and the western area grew the platform edge-trough. The surface occurrence and the well drilling core sample observation as well as the regional material research indicate that the southern edge of Ordos basin is approximately located along the Luonan Wayaogou-Xi'an-Baoji zone. On the whole, the depositional model of Majiagou stage in the study area is ‘west trough, south hollow, east flat, north basin’ in the transverse direction and ‘salty-fresh water alternation’ in the longitudinal direction. The calcareous rock-dolomite-evaporite belt is spread in the transverse direction, but shows alternate deposition with nonuniform thicknesses in the longitudinal direction.