Community Ecology Of The Early Permian "Vegetational Pompeii" From The Wuda Coalfield,Inner Mongolia

Reconstruction of the temporal and spatial evolutions of deep-time plant communities through geologic history is one of the major goals in palaeobotany.The fidelity of community reconstruction depends on the extent of preservation of the community structure.Volcanic ash fall is one of the geological events that may lead to in situ preservation of the vegetation community.Meanwhile,the fossil plants are usually completely and well-preserved with fine structures that facilitates whole plant reconstruction.The early Permian autochthonous peat-forming forest,termed as "vegetational Pompeii",buried by volcanic ash fall from the upper part of the Taiyuan Formation in the Wuda Coalfield,Inner Mongolia is among the ideal fossil lagerstattes for detecting the community ecology of the Cathaysia Flora.The wide exposure and high quality preservation of the ash bed make it the best section so far known to investigate the Late Palaeozoic swampy forest.Moreover,the opencast coal mining provided easy access to the tuff layer creating an excellent opportunity for field investigations on the vegetation community.In this study some modern phytocommunity methods used for the extant vegetation,such as quadrat sampling and minimal area,are applied to investigate an area of 936 m2 of the peat-forming forest.The main results of the present study are:1)The peat-forming vegetation is made up of 40 species of 21 genera belonging to seven groups,including Lycopsida,Sphenopsida,Pteropsida,Pteridospermopsida,Noeggerathiales,Cycadopsida and Cordaitopsida,indicating a high diversity in composition;2)Based on the data of the species-area curve,the minimal area that sufficiently represents the pattern of such swampy forest is estimated to be 755 m2;3)The vertical structure indicates spatial heterogenity and special light-use strategies by different vegetational tiers occurred with varieties of heights and abundances;4)Various types of plant accessory structures such as trichomes,aphlebiaes,hooks,tendrils,spines and aerial roots display morphological multi-functions of water storage,protection,supporting,scrambling/climbing and defense,demonstrating a high diversity of functional structures occurring in the Late Palaeozoic coal-swamp forests.The studied community is further compared with the contemporaneous plant assemblages from the same area of fluvial and lacustrine deposits,showing that they are largely different in composition and landscape.Such assemblage differences are apparently due to taphonomic disparities and changes of environmental phases.This implies that the different growth environment and taphonomic patterns may in most cases be the cause of compositional differences.Therefore,one way to strengthen the accuracy of terrestrial stratigraphy based on mega-plant assemblages is to correlate with their living environments.Since the taphonomy and community ecology have seldom been taken into consideration in the study of Cathaysian floras,an ecostratigraphic investigation on the Late Palaeozoic of Cathaysia is advocated.