Analysis Of Sedimentary Facies Characteristics And Provenance Of Upper Permian To Middle Triassic In North Qiangtang,Tibet,China

The study area,including Upper Permian Rejuechaka Formation,Lower Triassic Kanglu Formation,Lower Triassic Yingshuiquan Formation,Middle Triassic Kanglu Formation,is located in the central of Qiangtang Basin,which is a stable sedimentary strata.These sedimentary facies is a continuous sedimentary facies sequence,consisting of Marine-continetal transitional facies-Coastal phase-Mixed continental shelf facies-continental slope facies.Rejuechaka Formation consists of coarse sandstone,silstone,shale,mudstone,carbon mudstone,including brachiopods,plant fossils.Sedimentary facies mainly is delta front-neritic-Delta plain facies.The Kanglu Formation consists of sandstone,siltstone,marl,containing a large number of bivalve fossils,sedimentary facies is coastal phase.Yingshuiquan Formation consists of limestone,marl,sandstone,shale,producing bivalve fossile.Kangnan Formation consists of abundant ammonites,bivalves,belonging to slope facies.Incomplete turbidite sequences are present.Rejuechaka Formation feature a high sandstone quartz content(average 81.6%),feldspar(average 7.79%)and cuttings(average 10.62%)less content,higher cuttings roundness.Provenance cast mainly fall in recycled orogenic region.Kanglu Formation fature high cuttings(average 24.27%),feldspar(average 44.7%)content,quartz content is relatively small(average 31.03%),the main source area investment figure falls in arc cutting area;Yingshuiquan Formation fature high feldspar content(average 55.64%),cuttings(average 9.2%),quartz(average 35.15%)were relatively small,provenance cast figure fell into cutting arc and basement uplift area.Detrital zircons in Kanglu Formation were determined by LA-ICP-MS.Lower Member obtaines 9 Zircon ages,peaking in 3246?3126Ma,2498?2417Ma,2102?1803Ma,1787?1620Ma,1261?1106Ma,973?956Ma,747?542Ma,493?459Ma,283?244Ma.The upper Member only get a peak age of 255?246Ma.Speculately,there was a huge volcanic event in-255Ma,provided sedimentary for this area.From the Late Permian-Middle Triassic,because of the magma eruption,the provenance area changed greatly.Detrital zircon ages statistics show that the study area has a cathaysia source features.