T0 Early Permian coal-forest preserved in situ in volcanic ash bed in the Wuda Coalfield, Inner Mongolia, China

Abstract

An early Permian tuff bed between Coal 7 and Coal 6 of the Wuda Coalfield in Inner Mongolia bears T0 peat-forming vegetation preserved in situ. Documentation of the fossil record uncovered in an area of about 80 m2 shows 14 morphotaxa representing 11 whole-plant species with a wide variety of growth forms. The uncovered phytocoenosis is interpreted as a forest dominated by cordaites as the tallest trees, the remains of which covered over 50% of the excavated area. Marattialean tree ferns represent the lower canopy that was not taller than about 3 m. This storey fills gaps between cordaites and covers over 20% of the area. A rare element of lower canopy taxa was the cycadophyte genus Pterophyllum represented by a single plant. Poorly developed herbaceous groundcover includes Sphenophyllum oblongifolium, and four small fern species mostly with sphenopteroid type of foliage. Although members of the herbaceous layer covered only 7% of the excavated area, it was the most diverse storey of the peat-forming forest. Considering the small area excavated, along with the higher diversity known from the same tuff bed in the adjacent, former opencast mine, it appears that species richness in the forest was comparable to some of the less diverse Westphalian peat-forming floras in Euramerica.