湘南地区晚奥陶世的江西笔石(Jiangxigraptus)*

本文对甘肃宝积山盆地中侏罗世植物群地质时代及植物区系进行了探讨, 共统计植物大化石 18 属 53 种, 主要包括银杏纲 10 属 24 种, 真蕨纲 5 属 22 种, 苏铁纲 1 属 3 种, 松柏纲 1 属 2 种, 楔叶纲 1 属 2 种。该植物群在组成特征上表现为银杏类、真蕨类植物繁盛, 其他植物类群相对贫乏。基于该植物群特征与国内其他植物群的对比, 提出其地质时代为中侏罗世 Aalenian 期–Bajocian 期。通过哈曼、欧式距离、罗杰斯–塔尼莫特和索卡尔–施尼斯 4 种方法对宝积山盆地及中国北方其余 11 个中侏罗世植物群进行系统聚类分析, 在此基础上进一步划分了中国北方植物区系。通过计算属、种相似性系数，探讨宝积山邻近植物区系间的亲缘关系, 结果表明宝积山植物区系与同属西北地区的华亭植物区系关系较为亲近。

Jiangxigraptus Yu and Fang 1966 from the Upper Ordovician of southern Hunan Province

In this paper, we discuss the geological age and phytogeographic division of the Jurassic flora in the Baojishan Basin of Gansu Province, Northwest China. Totally 53 species of 18 genera of plant fossils are recoginzed from this flora, indicating that it was dominated by Ginkgophyta (24 species of 10 genera), Pteridophyta (22 species of 5 genera), Cyeadophytes (3 species of 1 genera), Coniferopsida (2 species of 1 genera), and Spheanoposida (2 speciesof 1 genera). The composition of the flora is dominated by Ginkgophyta and Pteridophyta, with relatively few other plant taxa. Based oncomparisons with other related floras, we suggested that the age of the flora is early Middle Jurassic, i.e., Aalenian to Bajocian. The phytogeographical position of Baojishan flora belongs to the Northern China Phytoprivince. Additionally, the Middle Jurassic floras of northern China are further analyzed and divided by cluster analysis. By calculating the similarity coefficient of genus and species among adjacent paleofloras near the Baojishan Basin, the results show that the paleofloras of Baojishan and Huating are relatively more closer in phytogeographical context.