Fig. 2:
Palaeogeographic map of the southern Pennine Basin during the Namurian. (J. Hunter, adapted from Smith et al, 2005)
Sedimentation was dominantly of clastic material (i.e. gravel, sand, silt and mud), derived from the upland areas, in contrast to the carbonates of the Visean below. This is thought to be due to renewed uplift of the source areas in the ancient continental area to the north, perhaps accompanied by increased rainfall and run-off from the land, compared to more arid conditions and lower surrounding land in the Visean. Early Namurian deposition consisted mainly of deep water marine muds, which accumulated very slowly, to judge from the numerous bands of evolving goniatites. Later sedimentation reflected the gradual advance of a major river delta from a broadly northerly source, bringing at first distal muds and silts, to be followed by turbidites and coarsening-upwards sequences, culminating in the coarse grits of successive delta tops. Later, successive uplift/subsidence events resulted in the return of deep water conditions and the deposition of shales. As the sedimentation continued and water depth decreased, sands were again deposited in delta systems. Some of these briefly even became land areas, marked by localised erosion and the deposition of thin coal seams.