A biofacies analysis of the Gastrioceras cumbriense Marine Band (Namurian) of the central Pennines

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Abstract
SUMMARY: The Gastrioceras cumbriense Marine Band (G 1b ) is the highest marine horizon in the Namurian Series of the central Pennines and does not generally exceed 60cm in thickness. In the present paper local variations are examined at six sections along a 60km distance from west Yorkshire to south Lancashire. The initial onset of marine conditions is recorded by Lingula -bearing grey shales in the central Pennines, but by the productoid facies (Calver 1968) to the west in south Lancashire. This is interpreted as reflecting a slight shallowing of the sea towards the west, a palaeotopography that persisted throughout the marine phase. The deepest water conditions, which occurred at the acme of the incursion, produced a marked change in cephalopod and bivalve species ratios and an associated change to a black shale lithology. Euxinic conditions appear to have occurred only temporarily. Over the whole of northern England the basal marine shales record a series of distinct faunal profiles, with fully marine faunas recorded to the west of the area. The regression appears to have been more rapid than the advance, and retreat faunal facies are more sporadically developed.