Middle Jurassic Plant Diversity And Paleoclimate In The Ordos Basin, China

Ordos Basin, reaching out to the Yinshan and Daqingshan on the north, the Qinling on the south, the Helanshan and Liupanshan on the west, the Lvliangshan and Taihangshan on the east, is one of the largest continental sedimentary basins and the major production areas of coal, oil and gas resources in China. The Middle Jurassic Yan’an Formation in the basin contains abundant coal resources and fossil plants, but the knowledge of the fossil plants needs further research. Based on phytomorphology and phytotomy, the fossil plants from the Middle Jurassic Yan’an Formation are described systemicly in this paper. According to the floral composition and representative elements, we can further determine that the geological age of the flora from the Yan’an Formation should be the Middle Jurassic. Moreover, the flora can be compared with the others of the Middle Jurassic Eurasia, and also provides valuable information for the study of palaeoclimate and palaeogeography in the Middle Jurassic.The Middle Jurassic flora of the Ordos basin is well diversified and is composed of various members of pteridophytes, gymnosperms. The flora contains 40 species belonging to 26 genera(including 1 new genus and 7 new species). They are recognized as: Bryopsida(2 genera, 2 species), Sphenopsida(4 genera, 4 species), Filicopsida(4 genera, 10 species), Cycadopsida(2 genera, 4 species), Ginkgopsida(10 genera, 16 species) and Coniferopsida(4 genera, 4 species). According to the composition of the flora, it shows that Ginkgopsida is a dominant group, and Filicopsida constitutes a higher position. Coniferopsida is also an important group in this area, associated with a lower amount of Cycadopsida and quite a few percentage of Bryopsida. In general, the composition feature of the flora is keeping well with those of the Siberia Floristic Region in the Eurasia in the same period. And it is obvious different to those of the Euro-Sinica Floristic Region, which is dominated by Filicopsida and Cycadopsida, accompanying Coniferopsid and Ginkgopsida.The floral composition feature, the characteristics of the epidermal structure and the analysis of sedimentary environment indicate the region associated with a warm and humid climate with seasonal changes in the middle Jurassic, this may be related to the climatic conditions of the Early- middle Jurassic global warming, which may be the result of the a strong greenhouse effect, the monsoon circulation and volcanic activity during that period.