四川晚三叠世须家河组和早侏罗世下益门组轮藻化石的发现及其意义

DISCOVERY OF FOSSIL CHAROPHYTES FROM THE LATE TRIASSIC XUJIAHE FORMATION AND EARLY JURASSIC LOWER YIMEN FORMATION,SICHUAN PROVINCE,AND ITS SIGNIFICANCE

本文论述了发现于四川大足上三叠统须家河组和西昌地区下侏罗统下益门组的轮藻化石及其意义。迄今,记述晚三叠世和早侏罗世,尤其早侏罗世轮藻化石的文章十分罕见。文内描述的Porochara两个新种:P.dazuensis,P.xichangensis及其所在的化石组合,不仅为我国西南地区红层的划分对比提供了重要的古生物依据,而且也初次揭示了该区这一时期的轮藻植物群面貌特征,为建立我国三叠、侏罗纪轮藻化石带增添了宝贵的资料。

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.