Early Corboniferous Flora From The Taizihe River Valley Of Eastern Liaoning And Its Paleoecolagical Study

It is believed for a long time that there lacks Upper Ordovician to lower Middle carboniferous an the North China Plate. In recent years, the writers discovered and described a plentiful of fossil plants from the bottom of the Benxi Formation in Muyuzi of Huanre courty , Tianshifu of Benxi county, Niuxintai and Gaotaizi of Benxi city , eastern Liaoning. There are 42 species of 21 genera, the age of the flora being affirmed as late Early Carboniferous (i.e. Visean to Namurian A). This is an important diseovery and a first systematic research. Among the flora, Lycopsida is dominant (54.8% of the total number of species), Filices and Pteridospermopsida the second (26.4%) , the others successively Sphenopsida (9.5%) ,Semina Gymnospermarum(7.1%) and Cordaitopsida (2.4%) . This flora are composed mainly of the characteristic or frequent members of the Lepidodendropsis flora, such as Lepidodendropsis, Sublepidodendron, Archaeocalamites, Cardiopteridium and Rhodeopteridium etc. Meanwhile, there appear Lepidodendron of oriental colour and individual peculiar member of the Cathaysian flora, Conchophyllum richthofeni. Therefore the present flora is of a transitional character form the Lepidodendropsis flora to the Cathaysian flora. It may be roughly compared with the late Early Carboniferous floras in Euramerican and the other areas of China.About the age of the Benxi Formation, it is generally considered as late Middle Carboniferous. Liu Fa(1987) called its lower part the Tianshifu Formation and considered as earlyMiddle Carboniferous in age. In this paper, the writer redivides and emends the Benxi Formation according to the characteristics of rock assemblage. It is as follows from bottom to top: (l)the Muyuzi Formation, the type section being at Muyuzi of Huanren, and representing the late Early Carboniferous in this area;(2) the Tianshifu Formation, only confined to the upper part of Liu's "Tianshifu Formation", the age being early Middle Carboniferous;(3)the Benxi Formation, representing only the upper part of the original "Benxi Formation " and being of late Middle Carboniferous in age.Based on lithologic characteristics, sedimentary sequence, fossil assemblages, grain size analysis of sandstone, microelement analysis and clay mineral analysis of mudstone, the original " Benxi Formation" reveals a major change in sedimentary facies vestically. It was mainly a coastal swamp environment in late Early Carboniferous, being warm and humid in climate and suitable for plant multiplying. In Middle Carboniferous, it became gradually tt> a lagoon-gulf environment, suitable for mali?e animal. The writer considers that the general floral characteristics of the four aboved areas are identical, besed on the characteristics of plant assemblages, the habits of different taxon, the living types and burial characters. A community-the Sublepidodendron Community is thus restored. The paleotopographic differences among these localities result in some slight changes of the sedimentary environments and then the floral componenents are somewhat not alike. In view of the above, four subcommunities are subdivided: (l)the SuBlepidodendron bicostae-Rhodeopteri-dium hsianghsiangensis subcommunity, (2) the Sublepidodendron robentii-Lepidodendropsis tianshifuensis subcommunity, (3) the Sublepidodendron bicostae-Sphenopteris changduensis subcommunity and (4) the Sublepidodendron bicostae~Lepidodendron gaotaiziense subcommunity.About the late paleozoic phytogeographic divisions,Vakhrameev (1970), Chaloner and Meyen(1973), and Meyen(1987) etc considered that it had been arised from Early Carboniferous in the world. Zhang shanzhen etc. (1987) suggested a posibility of phytogeographic division in Northeast China during Early Carboniferous. Yao zhaoqi(1991) drew the boundary line between the Angara paleofloristic Province and the Euramerican paleof loristic Province in Northwest China an the north of Talirau Basin. The present discoveries from the Taizihe drainage area affords important evidence to discuss the phytogeographic division in Northeast China during Early Carboniferous. The writer considers that as a boundary line from Linxi, north to Xilamulunhe, to yanji, the north is the Argara paleofloristic Province showing a temperate-wet climate of the northern temperate zone and the south is the Euramerican-Cathaysian paleofloristic Province, being of hot-wet climate of tropic-subtropic zone. This paltern is identical with that of palaeotectonics at that time. These two paleofloristic Provinces belong to the Sibirian Plate and the North China Plate respectively. These two plates were separated by the Palaeoasian Ocean and the formation of the two floras of different characters were caused.