The Depositional Systems Characteristics And The Evolution Of Sequence-Stratigraphic Framework In Platform Margin During The Middle-Late Permian In Southwest Guizhou

The Southwest of Guizhou was located on the junction of Yangtze Platform and Youjiang basin, the carbonate platform margin deposition character is obvious in Guizhou Permian System,which mainly grows the platform margin beach,platform margin reef and platform margin slope turbidity current sediment. Through the characteristics of rocks and biological groups, divid the platform margin depositional system into three subfacies: the platform margin biological beach, platform margin reef and the platform edge slope.In the Qxia period and early period of Maokou the carbonate platform margin were developed the the platform margin biological beach, the main sedimentary was gray-dark gray, thinck layer, sparry bioclastic limestone, some limestone content more than 50% bioclastic in it. The platform margin reef was main developed in the late period of Maokou and Changxing, it was developed on the basis of the platform margin biological beach, it was distributed along Xingyi, Anlong, Ceheng, Ziyun, Wangmo and Luodian. But it was not continiuous. The platform margin slop facies was developed in the Sidazhai formation of the Mddle Permian and the Shaiwa formation of the Upper Permian, with the main characteristic of all kinds of gravity flow deposits sendimentary, the types of gravity flow deposits include debris flow, turbidity, particle flow, landslide sedimentary and algal limestone accumulation etc. The growth of the platform margin reef beach has experienced repetitious circular development which included platform margin beach-platform margin reef-transgression submerge,The platform margin slope is evolved from sedimentary type to by-pass type,which is charactered by the growth of various sedimentation of gravity flow.The whole platform margin reef and flat facies of Permian is controlled by the movement of regional contemporaneous faults,and it desultory grow at the side of upthrown block of the active belt. Use the outcrop sequence stratigraphy reaserch methods, on the basis of the sequence division on the typical profile and characteristic study, we can identified 12 the third sequences in the whole Permian of the Southwest of Guizhou. he PSQ1 was missing of the Longlin step in the Late Permian; there were 6 third sequences (PSQ2~PSQ7) in the Middle Permian, there were three in Qixia step (PSQ2, PSQ3, PSQ4) , among the Maokou step were (PSQ5, PSQ6, PSQ7);There were 5 third sequences in the Upper Permian (PSQ8~PSQ12), there were three third sequences in Wujiaping step (PSQ8, PSQ9,PSQ10), among the Changxing step were two third sequences (PSQ11, PSQ12). The whole 12 third sequences superpositiong the two second sequences SS1 and SS2, the SS1 include the PSQ1~PSQ7, the SS2 include the PSQ8~PSQ12. Based on what are writhen above all, a systematic study has been made on the characteristic of the development of the platform margin depositional system in the sequence stratigraphic framework.