Sedimentary Facies Characteristics And Distribution Of The Upper Ordovician Lianglitage Formation In The Western Part Of The Tarim Basin

Guided by theories and methods of sedimentary petrology,sedimentology,geostatistics,geophysics and well logging,aimed at insufficient carbonate sedimentary facies research of inner platform of Upper Ordovician Lianglitage Formation in western Tazhong Area.This paper analyzed tectonic evolution overview,divided and contrasted layers intensively,classified depositional microfacies,and studied longitudinal and lateral regularities of distribution of this area with integrated drilling,logging,core and seismic data and combined microscopic and macroscopic applications interdisciplinarily,and based on which,evolutionary patterns of sedimentary facies distribution in various depositional ages were established and favorable facies distribution of Upper Ordovician Lianglitage Formation in western Tazhong Area was simply analyzed.Major knowledge recognized in this paper is as followings:Lianglitage Fm of study area was divided into pelitic belts carbonate member,packstone member and marly member including 12 single layers from top to bottom,and thickness of formation ranged from 10m to 50m.Formation thickness gradually thickened from inner platform to platform margin and was well contrastive.Main sedimentary rocks were packstones,biogenic limestones,wackstones and micritic limestones,and intrusions were intercalated locally.Lianglitage Fm of study area was open platform sediments and developed subfacies of inner platform shoal(IPS),inter-shoal sea(ISS)and mud mound(MM)with proportions of 62.5%,29.4%and 8.1%separately.Longitudinal characteristics of sedimentary facies were multicyclic sedimentation of IPSs,ISSs and MMs forming multi-set deposits of ISSs and IPSs and mound-shoal complexes.MMs and IPSs were stripped and distributed nearly parallel along the Tazhong No.1 Slope Break.High landforms of open platform were mostly occupied by IPSs and MMs,relatively low-lying parts developed ISSs with predominant micritic limestones and pelitic micritic limestones depositing in lower hydrodynamic conditions.During depositional period of Lianglitage Fm,the sedimentary process was characterized by transgression-regression sequence.In the plane,IPSs were far more developed than ISSs and MMs and emerged as strips distributed from northwest to southeast.Scope and scale of MMs were smaller but developed earlier than IPSs.