BIOSTRATIGRAPHY OF THE UPPER JURASSIC-LOWER CRETACEOUS BIVALVES BUCHIA AND AUCELLINA OF EASTERN HEILONGJIANG, NORTHEAST CHINA

The biostratigraphic significance of the bivalves Buchia and Aucellina in northeast China is assessed. Buchia is abundant in four assemblage s of the Dong'anzhen Formation, spanning the Jurassic-Cretaceous bound ary: B. russiensis-B. fischeriana (Middle Volgian), B. fischeriana-B. unschensis (Upper Volgian), B. volgensis-B. cf. subokensis-B. cf. oken sis-B. unschensis (Berriasian), and B. pacifica (Lower Valanginian). A ucellina is common in two Middle Barremian-Aptian assemblages: A. cauc asica-A. aptiensis-A. jeletzkii in the lower part of the Upper Yunshan Formation, Longzhaogou Group, and in the lower part of the Chengzihe Formation, Jixi Group; A. cf. caucasica-A. cf. aptiensis in the upper part of the Upper Yunshan Formation. These assemblages can be correlat ed on a global scale and are particularly significant in dating the Ea rly Cretaceous coal-bearing measures of eastern Heilongjiang.