Sequence-Stratigraphic Framework And Its Palaeogeographical Background For The Ordovician System Of The Central Guizhou Uplift And Its Adjacent Areas

The Ordovician System in Guizhou and its adjacent areas contains the Tongzi Fm., Honghuayuan Fm., Meitan Fm., Shizipu Fm., Baota Fm., Jiancaogou Fm., Tonggao Fm., Guotang Fm., Wufeng Fm. and Guanyinqiao Fm.. From the northwest to the southeast, the sedimentary outline of the Ordovician here has been found out. It is: the whole Ordovition is far from the Central Guizhou uplift; erosion partly happened in the southeast of the deep-water area, and there is not sedimentation just arround the central uplift. Form lith-facies succession to meter-scale cycle and from sedimentary-facies succession to third-order sequence, the Ordovician in studied area can devided into 8 third-order sequences, they are OS1～OS8, which can be grouped into two second-order sequence. Tongzi Fm. with Dolimites compose the first third-order sequence OS1; biology classtic limestone of Honghuayuan Fm. compose the second third-order sequence OS2; Meitan Fm. compose third-order sequence OS3 and OS4; Shizipu Fm. and Baota Fm. separately compose third-order sequence OS5 and OS6; Wufeng Fm. and Guanyinqiao Fm. compose third-order sequence OS7 and OS8. According to two types of facies-changing srufaces and two types of diachronisms in the stratigraphic records, surfaces-stratigraphic divisions at each main logged section become the basis to establish the sequence-stratigraphic framework and the correspinding palaeogeographical maps. As a whole, the features of the papaeogergraphical in study areas is that the distributing of facies in the southeast is more deeper than that in the northweat before the Aijiashanian epoch. and then, the background changed just because the uplifting of the old land.