Ordovician Sedimentary Facies Of Central Guizhou Uplift And Its Adjacent Area

Central Guizhou Uplift is in a state of relative uplift in the long-term, and there is plenty of oil and gas (asphalt) along the south edge of uplift, so it is necessary to systematically research the ordovician sedimentary facies of Central Guizhou Uplift and its Adjacent Areas to guide the oil and gas exploration in the future.Based on sedimentology and sequence stratigraphy theory, the combination of field geological investigation and indoor analysis, and geology and geophysics, as well as the analysis of the sequence framework are adopted. Besides, the detailed study of sequence stratigraphy was carried out with outcrop,10three level sequence boundaries were identified in the Ordovician, and divided them into9three level sequences, of these interfaces, OSB1,OSB3,OSB4,OSb5and OSB9are type Ⅰ sequence boundary, and other sequence boundaries are type Ⅱ sequence boundary.The formation time of Central Guizhou Uplift was studied by using the sequence stratigraphic classification, and it is found that the Central Guizhou Uplift formation was done by repeated times, so the earliest time was the Ordovician Tongzi Period, it was underwater uplift stage. But it first exposed on the water until the early Meitan Formation, then it was flooded by seawater, and rose out of the water again in the late Meitan Formation. Finally, the Central Guizhou Uplift was lifted into land until the late Wufeng Formation.With a large number of outcrop section,4kinds of sedimentary system were identified,that is coastal deposition system,shelf sedimentary system,carbonate platform sedimentary system and slope-basin sedimentary system and each sedimentary system was further subdivided.By taking outcrop sequence stratigraphy as the guidline,and taking the three system tracts as time unit,the floor plan of sedimentary facies of Ordovician was established based on division and correlation of the sequence,depositional systems,and sedimentary connected well correlation. The Central Guizhou Region exposed out of the water surface for the first time during the OSQ3HST period, and during the OSQ4HST and the Central Guizhou Uplift was exposed out of the water surface again.When it came to the OSQ9TST period, the Central Guizhou Uplift was completely uplifted into land, and it was connected with Southern Guizhou to become Dianqiangui ancient land.The hydrocarbon source rocks of ordovician in the Central Guizhou Uplift and its Adjacent Areas hardly developed. The carbonates in Lower Ordovician were seen as reservoirs mainly including dolomite of Tongzi Formation and limestone of Honghuayuan Formation,and Lower Ordovician was platform edge-platform facies in study area.What is more,there was1sets of local seal,that is the Middle Ordovician mudstone class remained in Guiding-Sandu-Huangping Area in southern Guizhou. The regional seal and local seal had formed some sets of reservoir combination.