Sedimentary Characteristics And Tectonic Evolution Of Late Devonian To Early Carboniferous In Funing Area,Southeast Yunnan

The paper mainly focuses on the basic geological research of Funing area in southeast of Yunnan.On the basis of investigation of previous research,the stratigraphic profiles measured in the field are used to as the main basic data to study the sedimentary characteristics of the Late Devonian—Early Carboniferous in Funing area,southeast of Yunnan and their vertical and horizontal distribution rules.Based on the study of main section and sequence stratigraphy,following the principle of "basin controlled by structure and facies controlled by basin",three lithofacies palaeogeographic maps of Frasnian and Famen Age of Late Devonian,and Early Carboniferous are drawn by using isochronous dominant facies mapping method.Taking the stratiform siliceous rocks from the Middle—Upper Devonian Liujiang Formation and the Carboniferous Shundianhe Formation as examples,the geochemical characteristics of the major elements and rare earth elements of the siliceous rocks are mainly studied.Combined with the regional tectonic background,the genesis and sedimentary environment of the siliceous rocks are discussed,and then the change process of the sedimentary environment at the intersection of Devonian and Carboniferous in Funing area is explored.Integrated with the characteristics of carbon and oxygen stable isotope,paleobiostratigraphy and lithostratigraphy of carbonate rocks of Late Devonian to Early Carboniferous in Funing area,the features and tectonic significance of the D/C interface are discussed.The following achievements are obtained:1.From the perspective of lithostratigraphy,the lateral distribution and vertical variation characteristics of the late Devonian—Early Carboniferous strata in Funing area,the phase change relationship among the strata in different sedimentary environments,and the corresponding evolution characteristics of the paleotectonic environment are re-recognized.2.Combined with the previous research,the lithofacies paleogeographic features of Late Devonian—Early Carboniferous in Funing area are further modified and refined through the main section and stratigraphic research,and three lithofacies palaeogeographic maps of Frasnian and Famen Age of Late Devonian,and Early Carboniferous are drawn.3.The geochemical characteristics of major elements of siliceous rocks show that the Liujiang formation of Devonian fomred in the continental margin rift basin environment.The silicon in the sediments mainly comes from hydrothermal fluid,and the silicon of top part is biogenetic.The Shundianhe Formation of Carboniferous also formed in the continental margin rift basin environment,and the environment may be changed to the ocean basin from then on.The silicon at the bottom comes from the volcanic ash or siliceous organism,and the silicon of top part comes from the hydrothermal fluid.The REE geochemical characteristics of siliceous rocks from two formations are similar to those of "Atlantic type",according to Murray et al.(1992),with a trend of transition to "Pacific type",which is consistent with the sedimentary environment indicated by the major elements.4.The D/C boundary in Funing area was in a transitional environmental trend from isolated platform facies to slope—basin facies,i.e.from parallel unconformity to comformity.The carbon and oxygen isotopes of carbonate rocks show different degrees of negative migration at the boundary,consistent with the paleoenvironment and paleoclimate shown by petrology and sequence stratigraphy,so they can be used as an important indicator for stratigraphic division and comparison.