Upland ecology of some Late Carboniferous cordaitalean trees from Nova Scotia and England

Permineralised logs and charcoal fragments composed of Dadoxylon-type wood and derived from cordaitalean trees are described from the Upper Carboniferous (Westphalian) of Nova Scotia and England. They exclusively occur in sandstone bodies interpreted as the deposits of braided, meandering and anastomosing river channels. The architecture and ecology of this type of cordaitalean has not yet been satisfactorily described. Estimates of tree height using an allometric approach suggest that the largest trees attained an approximate height of ca 45 m. The absence of true growth rings in the logs indicate that they grew under non-seasonal humid tropical conditions. However, the presence of charred wood fragments implies that droughts of sufficient intensity to permit wildfire did occasionally occur. The charcoal fragments are usually associated with incised, poorly-sorted, chaotically-bedded channel facies, interpreted as flood deposits. Dramatic increases in runoff and sediment discharge are known to follow the destruction of vegetation in modern wildfire events and the high energy charcoal-bearing channel facies described may represent a similar geomorphic response to cordaitalean vegetation fires. Geomorphic sensitivity to fire is greatest for steeply sloping terrains and it is therefore probable that the cordaitaleans described in this paper occupied upland settings. This palaeoecological interpretation is supported by occurrence of the cordaitalean remains in river channel deposits immediately downstream of regions of palaeo-upland and by the palynological record. The presence of upland forests in Late Carboniferous times has important implications for numerical modelling of global geochemical cycles.