Regional evolution of a fluviodeltaic cycle succession in the Marsdenian (late Namurian Stage, Pennsylvanian) of the central Pennine Basin, UK

Basinwide analysis of sedimentary facies, isopachytes and
palaeocurrents for two late Marsdenian (Pennsylvanian) sedimentary cycles
within part of the Millstone Grit Group, has led to a new sequence-stratigraphic
interpretation for the relationships between its constituent sandstone units
(currently named Huddersfield White Rock, Chatsworth Grit, Brooksbottoms
Grit, Holcombe Brook Grit, Brown Edge Flags and Redmires Flags). The
Bilinguites superbilinguis (R2c1) and Verneulites sigma (R2c2) marine bands
related to fourth-order marine highstands show faunal variations possibly
reflecting fifth-order sea-level fluctuations. The lower R2c1 cycle consists entirely
of deep water mudstone. The overlying R2c2 cycle shows an upward regressive
passage through pro-delta and delta-slope deposits to mouthbar and channel
sandstones. The latter comprises an ‘eastern inflow’ of northerly provenance,
the distribution of which was not influenced by the underlying basement
configuration, and a ‘southern inflow’ sourced from the Wales-Brabant High.
Falling sea-levels resulted in progressive narrowing of the fluvial pathway within
the main sandstone body of the ‘eastern inflow’, with a concomitant increase in
flow velocities and grainsize. At lowstand, this culminated in the Chatsworth
palaeovalley, 25 km wide, the basal surface of which can be correlated into the
interfluve areas as a leached palaeosol. Higher sandstone bodies, where
developed, are of two kinds: an earlier set present outside of the palaeovalley
was formed during regression, and a later set within the palaeovalley was
formed as sea level rose. As part of this transgressive systems tract, a Lingula
band developed across the flooded Chatsworth palaeovalley and its interfluve
margin. The transgression culminated in the highstand of the Cancelloceras
cancellatum (G1a1) Marine Band.