The Characteristics Of Residual Strata And Lithofacies Palaeogeography Of Upper Paleozoic In Weihe Basin And Its Adjacent Region

In recent years,as the demand for global resources increasing,the most of scholars have paid more attention to the Weihe basin due to lower exploration level.In this paper,combined with the regional geological background,we identify the late Paleozoic strata distribution and accomplish stratigraphic division and comparison by method of strata profile,drilling data,geophysical data in the Weihe basin and its periphery.Further,based on the sedimentary source area,sandstone thickness,sedimentary features,we divided the sedimentary facies and lithofacies paleogeography of the late Paleozoic in the Weihe basin.The thickness of residual strata reveals that the strata of Shihezi Formation in the study area are distributed widely,which is characterized by thick in the south and west,thin in the north and east.The thickness of coal-bearing strata in Gushi sag is larger than that of Xi'an sag,and the maximum thickness is close to the south.Methane gas from the source rocks can be transported to the reservoir by a large number of faults in the basin and into a closed trap structure eventually.The results of petrology,heavy mineral,Main-Trace elements and U-Pb ages of zircons suggested that both of the southern Ordos and northern Qinling area have a similar sedimentary source area during the Permian,which mainly derived from metamorphic clastic rocks in Kuangping Group,volcanic-sedimentary rocks in Erlangping Group as well as subducted granites formed in the late Paleozoic.The sedimentary facies of upper Paleozoic Carboniferous-Permian can be divided into lake,meandering river delta,barrier island and continental shelf,and it can divided into 7 subfacies and 9 microfacies further.In the sedimentary period of Benxi formation,the subsidence in the northeast of the study area is so small that the sea water invades from the west,the study area belongs to the low energy environment under the tide.The sedimentary area is gradually spread from depositional period of Taiyuan formation,and the boundary of tidal flat and shallow continental shelf back from the Heyang-Yongji-Lingbao to the Hejin-Yuncheng-Sanmenxia.The Shanxi formation,Shihezi formation and Shiqianfeng formation of Permian in the southern part of the study area all developed shallow lake facies,barrier island and lagoon subfacies.From the old to the new,the sedimentary pattern is basically unchanged,the marine sedimentary range is gradually smaller,and the delta front subfacies deposits are developed in the southwest.