CARBONIFEROUS AND PERMIAN FLORA IN THE NORTHERN PART OF THE HELAN MOUNTAINS

The fossil plants studied in this paper were collected from the Carboniferous and Permian strata in the northern part of the Helan Mountains. The flora is composed of 104 species in 39 genera, which may be divided into five plant assemblages in ascending order as follows:(1)the early Late Carboniferous Bothrodendron circulare-Mesocalamites cistiformi assemblage;(2)the middle Late Carboniferous Lepidodendron subrhombicum-Conchophyllum richthofeni assemblage;(3)the late Late Carboniferous Lepidodendron szeianum-Neuropteris ovata assemblage;(4)the early Early Permian Lepidodendron posthumii-Callipteridium koraiense assemblage;(5)the late Early Permian Caulopteris wudaensis-Paratingia datongensis assemblage. Their typical formations are the Hongtuwa Formation, the Yanghukou Formation, the Lower Taiyuan Formation, the Middle and Upper Taiyuan Formation, and the Shanxi Formation respectively. The geological ages of the five plant assemblages may approximately correspond to the Namurian B-C, Westphalian, Stephanian, Asselian, Sakmarian and Aritinskian. The Carboniferous and Permian flora contains typical Cathaysian elements and it is a typical Cathaysia flora. The flora can be compared with contemporaneous floras in the Cathaysian province. In addition, the evolution of the flora is discussed in this paper.