The Study Of Longwu River Group At Eastern QingHai Province

Longwu River group is turbidite facies sedimentary rocks which widely distributed inthe west Qinling Tongren,Qing Hai Province-Xiahe, Dangchang,Liangdang, Gansu Provinceand the area south of Shaanxi Fengxian, Lithology is mainly for coarse-grained sandstone,Slate, thin-layer of limestone, mudstone and thin-layer instability stratigraphic sequences ofconglomerate, the overlying and underlying strata are separated to unconformities on the topand bottom.Study area is located in southern West Qinling and Qilian junction, is orogenic beltwhich has a complex ocean-continent transition process and the northern margin of thePaleo-Tethys Ocean at Triassic, in the band there are a series of micro-continental block andmany archipelagic oceanic basin. Central West Qinling rift occurred in the early Paleozoic,the forming the South,middle and the north three sedimentary zones, the Aulacogen closed inthe early Mesozoic, Eventually in indosinian-yanshanian extrusion forming miogeosynclinefold belt in the West Qinling. Longwu river groups are located in the middle area of thesedimentary zone, the band was a late Paleozoic-Mesozoic aulacogen, Most of the areascovered by Triassic sediments filling, edge of the both sides covered by upper Paleozoic deepto semi-deep water turbidite, in the aulacogen central zone is deep-water mudstone and siltyslate deposition, edge slopes covered turbidites and thin limestone.This article based on the theory of multiple stratigraphic division and correlation, byusing the lithostratigraphy, biostratigraphy and chronostratigraphy to the division and regionalcomparison of Longwu river group. According to the analysis, Longwu river group is thesubmarine fan turbidite sedimentary on the environment of continental slope, formationsediment thickness huge, rhyme significantly, dividing the formation unit signs not obvious,Previous researchers have divided formation-level lithostratigraphic unit, actually it isdifficult to identify them in the field, We propose that the group-level lithostratigraphic ofLongwu river group should be restore, use formation-level lithostratigraphic unit in a smallarea: Gulangdi formation, Jiangligou formation, Guomugou formation. Under Longwu rivergroup is a limestone, clastic rock assemblage, temporarily named Ganjia formation.According to the face mode of submarine fan, in Longwu river group,it can be identified inner-fan face of turbidite fan, middle-fan face of turbidite fan, outside-fan face of turbiditefan, sedimentary microfacies include A: conglomeratic sandstone face B: Sandstone faceC: fine sandstone face-silicalite face D: muddy rock face.