Discussion on geological age and phytogeographic division of the Middle Jurassic flora in the Baojishan Basin of Gansu Province
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Abstract:
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.
