A DIFFERENT OPINION ON THE GEOLOGICAL AGES OF THE LONGZHAOGOU AND JIXI GROUPS OF EASTERN HEILONGJIANG, CHINA
Sha Jingeng (Nanjing Institute of Geology and Palaeontology, Academia Sinica)
This paper discusses the ages of the Longzhaogou and Jixi Groups. The two groups are important strata of economic value as they both contain coal. Chinese geologists have made a great contribution to the division and correlation of these two groups (see Table 1 in the text). The geological ages of the two groups were previously considered to be Jurassic or mainly Jurassic as there were "Bathonian-Callovian" bivalves and ammonites in the Qihulin For- mation and "Late Jurassic Buchia'" in the Upper Yunshan Formation and the lower Chengzihe Formation. However, recent studies have revealed that the "Late Jurassic Buchia" in the Upper Yunshan and Chengzihe Formation are actually a Middle Barremian—Early Albian Aucellina aptiensis-A, caucasica-A, jeletzkii group, and all the "Middle Jurassic" bivalves and ammonites of the Qihulin Formation are forms of Early Cretaceous age rather than of Jurassic age. Consequently, the Longzhaogou and Jixi Groups are or mainly are of Early Cretaceous age, when coal measures were deposited in eastern Heilongjiang and even in Northeast China, rather than of Jurassic or of mainly Jurassic age.