Abstract: There are many fossils of Bivalvia in the marl of Feixianguan formation of Lower Triassic in Beibei,Chongqing.The shells' arrangement is regular.In the samples under study,the bisectors of the shells which pass through their beaks are parallel to the palaeocurrent sirection,and the beak indicates the current direction.After measuring 53 shells at random,we calcalated the palaeocurrent direction,which is 294,with mathematical statistics mathod,and proved these shell members ' sedimentary envirment to be tidal ditch on tidal flat of lagoon.

Key words: Paleobiologic fossil, Bivalvia, Palaeocurrent direction, Chongqing