DISCOVERY OF FOSSIL CHAROPHYTES FROM THE LATE TRIASSIC XUJIAHE FORMATION AND EARLY JURASSIC LOWER YIMEN FORMATION,SICHUAN PROVINCE,AND ITS SIGNIFICANCE
Liu Junying (Institute of Geology Chinese Academy of Geological Sciences, Beijing) Chen Zhongliang (Panxi Geological Party, Sichuan Bureau of Geology and Mineral Resources, Xichang)
This paper describes the fossil charophytos collected from the Late Triassic Xujiahe Formation in Dazu and Early Jurassic Lower Yimen Formation in Xichang, Sichuan Province, including two new species of Porochara: P. dazuensis and P. xichangensis. In the Xujiahe Formation elements of Porochara prevail together with those of Aclistochara with a wide and short neck, namely Porochara nanjingensis Huang, P. dazuensis (sp. nov.), Aclistochara maanshanensis Liu, A. sichuanensis Liu, A. youpingensis (Z. Wang et al.), d. abshirica (Kyansep-Rom.). In the Lower Yimen Formation there predominate Aclistochara members, accompanied by a number of Porochara and some Stenochara. Among species of the genus Aclistochara, A. sichuanensis is a major element, while A. maanshanensis Liu and A. brevis S. Wang et Zhou are next in abundance and A. nuguishanensis (Z. Wang et al.) and Porochara xichangensis (sp. nov.) are scanty. The above two florae are of a character transitional from Triassic to Jurassic. Based on the features of the charophytes from both the Xujiahe and the Wayaobao Formations in Tongchuan, Shanxi Province (Wang Zhen et al., 1978) as well as the Tanzhuang Formation in Jiyuan, Henan Province (Li Zuwang, 1985), it is reasonable to regard the Late Triassic charophytes in China as being composed of the assemblage of Cuneatockara tongchuanensis Z. Wang et Huang-Stellatochara jiyucanensis Li-Porochara dazuensis Liu et Chen; and according to the characteristics of the charophytes of the Lower Yimen Formation and the Xiangxi Group in Hubei Province (Zhang Jiefang et al., 1982; Wang Zhen, 1982), Ghina's Early charophytes comprises the assemblage of Porochara xichangensis Liu et Chen-Aclistochara sichuanensis Liu-Stenochara xiangqiensis Lu.