Study On Petrology And Sequence Stratigraphy On Longwuhe Formation Of Lower-middle Triassic In The Wenbadi Area Of Qinghai Province

The Gonghe Basin is a foreland basin developed in Wenbadi area of Qinghai Province,since Indosinian period in the early Triassic.Because of lacking in data,there is little geological research in this basin.In recent years geological research has been focused on regional mineral resources and magmatic activities.This paper described excellent outcrops from a 9.5km long.field section named PM12 and several adjuvant field sections of Longwuhe Formation.Based on the previous research results,combining petrology,sedimentology,geochemistry and sedimentary basin analysis theories and methods.In this paper,the strata are measured,divided and contrasted,and sequence stratigraphy is studied.The Longwuhe Formation in study area is located in the close to the mountain side of the basin dynamic edge.It is a sea facies sedimentary strata which formed the age of basin range transition.In it's deposition process,turbidity current deposits,clastic flow deposits and storm deposits were happened.All the evidence,with palimpsest deposition structures,shows that it was formed in depositional environment at the deep sea to the coast.Based on it's petrological characteristics and sedimentary characteristics,i finished study of the protolith recovery and divided lithofacies type which include mud facies,silt-stone facies,sandstone facies and conglomerate facies.Geosphere of Longwuhe Formation shows obvious cyclicity.The lithofacies are superimpos-ed according to a definite rule on perpendicular orientation.Those constitutes sedimentary cycle sequence.This paper on the basis of different sedimentary stages,about sedimentary characte-ristics and cycles about lithofacies assemblage,and combines the theory of sequence stratigra-phy of the foreland basin and active continental margin sequence stratigraphy,founded series of sequence and system tract.Study of sequence stratigraphy shows,in early-MiddleTriassic,this geosphere experienced sea and land changes with tectonic subsidence and sediment supply,appears sandstone increment and particle sizecoarsens upward.