Stratigraphic framework of the Changning-Menglian belt in western Yunnan

Phanerozoic strata of the Changning-Menglian belt are distributed in N -S-trending stripes.Based on lateral distribution vertical variation of different lithologies,the stratigraphic sequences of the belt may be divided into four types:(1)clastic rocks,which upward are intercalated with limestone lenses and change into alternately occurring fine clastic rocks and cherts;(2)clastic rocks,which upward are inter-calated with limestone lenses and small amount of chert and pass to Permian basic volcanic rocks at the top;(3)clastic rocks-basic volcanic rocks-pyroclastic rocks-carbonate rocks-clastic rocks;and(4)lime-stone and dolomitic limestone-dark gray thin-bedded limestone,argillaceous limestone,and mudstone with siliceous mudstone.Clarifying the relationship of different lithostratigraphic units is the prerequisite for inter-preting objectively the evolution of the Changning-Menglian Tethys.