Abstract：This paper describes fossil bivalves found in the Guanling biota，including four species，i.e. Halobia kui Chen，Halobia planicosta Yin et Hsü，Plagiostoma sp. and Asoella sp. The specimens are well preserved. The age is Late Triassic early-middle Carnian. Based on a study of the paleoecological characteristics and environment，the authors conclude that the planktic and pseudoplanktic bivalves could be eliminated in the Guanling area due to the intermittent anoxic or dysoxic events caused by the input of large amount of fresh water during the early-middle Carnian.