The phytocoenosium from the upper Carboniferous Taiyuan Formation of Wuda Coalfield, Inner Mongolia
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Abstract:
The Wuda Coalfield in Inner Mongolia yields over 40 coal seams within approximately 1500-meter-thick strata spanning from the Carboniferous to the Permian. The high-precision dating of volcanic tuff between No. 6 and No. 7 coal seams indicates an age of 298.34 Ma, nearly on the Carboniferous-Permian boundary. Taking advantage of the well exposure of the Taiyuan Formation in the Wuda Coalfield through open-pit mining, fossil plants have been extensively collected from No. 8 to No. 15 coal seams. Six plant-fossil bearing beds have been recognized, and 26 species of 14 genera of fossil plants have been identified. Based on sedimentological analyses, the plant assemblages of the upper Carboniferous Taiyuan Formation have been constrained well in palaeoecology, showing a typical phase of the middle stage of the Cathaysia Flora. The underclay of coal seams Nos. 12, 12upper, 10, and 9 contain allochthonous plant fossils that indicate vegetation growing nearby the peat-forming swamp, whereas the roof shale of coal seam No. 8 yields autochthonous or parautochthonous plant fossils that represent the last phase of the coal-forming vegetation. The floristic difference between the floor beds of coal seams No. 12 to No. 9 may indicate that there exists the boundary of the traditionally well-known lower and upper plant assemblages of the Taiyuan Formation between coal seams No. 12upper and No. 10. Moreover, the floristic difference between the roof shale of coal seam No. 8 and the volcanic tuff sandwiched between coal seams No. 7 and No. 6 indicates that the main peat-forming plants may vary with environmental changes during different stages of coal swamps–fossils in the underclay or roof shale may reflect the peat-forming vegetation or surrounding plant communities during the early or late stages of peat formation, whereas fossils found in the mid-stage of peat formation may differ in composition.
