Research On The Sedimentary Facies And Sequence Stratigraphy Of Leye Isolated Carbonate Platform, Northwest Of Guangxi

Youjiang Basin is one of the important hydrocarbon-bearing basins in the South China. Studies have shown that the basin existed mainly from Devonian to Triassic, with the Late Paleozoic as the most important period in its development. In this basin, the Upper Paleozoic is well developed, with various sedimentary types from shallow platform carbonates to deep see radiolarian chert. In this basin, there scattered a number of isolated carbonate platforms of various sizes. The Leye isolated carbonate platform is a good example for these. According to the comparison study between the characteristic sections of Gandongzi, Jingxi and Lingyun Platforms, the present study has recognized that the Carboniferous and Permian succession in the Leye platform is composed of the following units in ascending order: the early Carboniferous RaoYunling formation, Huanglong formation, the late carboniferous -the early Permian Maping formation, the early Permian Qixia formation, the Middle Permian MaoKou formation and the late Permian HeShan formation. In this paper the sedimentary faces and stratigraphic sequences of LeYe isolated carbonate platform has been studied in some details, and four main types of sedimentary faces have been recognized, including the key faces of the open platform, and others accompanied sedimentary faces of the limited-local limited platform, the shallow beach faces of the margin platform and the depression of platform from the carboniferous period to the Permian period. Altogether, 30 third-order sequences and 3 second-order sequences have been recognized from the Carboniferous to Permian for the isolate platform facies, and these sequences can be correlated quite well with those identified in the southern area of the basin. This paper has also traced the revolution of LeYe isolated carbonate platform in late Paleozoic. Three tectonic-sedimentary stages in evolutioncan be suggested for this basin: 1) the epeiric carbonate platform (early Devonian to late Devonian); 2) isolated carbonate platform (late Devonian to middle Permian); 3) submerged carbonate platform (late Permian), which has a good correlation with the evolution of Youjiang Basin, The epeiric carbonate platform stage is correspondent to shallow water sea and deep-water rift basin, isolated carbonate platform stage to the formation of ocean crust basin and the strong expanding periods of the ocean basin, and the submerged carbonate platform stage to the stage of the shrinking ocean basin in time. The study also shows that the basalt activity and their tectonic episodes in the YouJiang Basin has an important influence to the evolution of the platform and the formation of the basin. This paper has analyzed the characters and its distribution both in time and in space of the basalts in the basin. The comparison study of these basalts with the EMei Mountain basalt has suggested that they were closely related in orgin, and may be caused by the same magma process deep in the earth during the Ltae Paleozoic.