Controls on deltaic sedimentation in glacio-eustatic cycles of late Marsdenian (Namurian R(2b)4 to R(2c)1, Pennsylvanian) age in the UK Central Pennine Basin

摘要

Evolution of the succession between the Bilinguites eometabilinguis (R(2b)4) and Verneulites sigma (R(2c)2) marine bands of Marsdenian (Pennsylvanian) age in the Central Pennine Basin, and its offshore extension into the North Sea Basin, is discussed. Five separate marine bands are now recognized. Two closely spaced marine bands, B. eometabilinguis and B. metabilinguis, occur at the base of the R(2b)4 cycle and a higher B. metabilinguis band occurs at the base of the R(2b)5 cycle. The overlying B. superbilinguis and V. sigma marine bands define an additional thinner and much simpler cycle (R(2c)1). These three cycles are all of glacio-eustatic origin. A new sequence-stratigraphic interpretation examines the relationship between the constituent sandstone units (currently named the Hazel Greave Grit, Beacon Hill Flags, Guiseley Grit, Ashover Grit, Roaches Grit, plus local names and unnamed units). Different types of fluvial-deltaic sequences were deposited in different phases of the cycle and some cycles lack coarse clastic lithologies. The succession in parts of Yorkshire and Lancashire contains a major non-sequence in the R(2b)5 cycle. A revised interpretation of the incised deep channels in the Roaches Grit in Staffordshire, suggesting river channel adjustment to a post-glacial climate rather than infill of a pre-eroded palaeovalley, is also presented. Many of these different features can be explained by climatic variations associated with the Carboniferous Ice Age. Variations in basin bathymetry and fault related subsidence exercised more localized controls.