Clastic rocks of the Permian-Triassic Cangfanggou Group that consist of conglomerate

sandstone

siltstone

muddy siltstone and mudrock are the main reservoir rocks in Bei Shantai area.Based on typical probability curves and their vertical combina-tion

C-M patterns and grain-size parameters combining with sedimentary sequences and their primary structures

log curves

the sedimentary environment of the group is consi-dered as follows:1.alluvial fan including braided stream and fan interval deposition;2.fluvial depositional systems containing meandering stream

low sinuosity stream and in-terfluvial lake;3.delta and lake system.It is suggested that comprehensive analysis of grain-size distribution is a useful tool in sedimentary facies identification.