High resolution sequence stratigraphy of the late Namurian in the Widmerpool Gulf (East Midlands, UK)

Abstract

Analysis of facies stacking patterns and stratal surfaces within late Namurian deltas of the Widmerpool Gulf has revealed 10 high frequency (fourth-order) depositional sequences. Sequence correlation is based on the characteristic ‘marine band’ fauna of their condensed sections. In many instances, sequence boundaries are difficult to recognize unless there is clearly demonstrable lowstand incision. Consequently, it is often difficult to separate late highstand from falling stage progradation with any degree of confidence. Sequence thickness variations and the dominance of particular stratal surfaces and systems tracts were controlled by a longer period (third-order) cycle of relative sea-level rise and fall during the Marsdenian-Yeadonian. Major fluvio-deltaic sand bodies in the Widmerpool Gulf were formed by distributary channel progradation (e.g. Chatsworth Grit) during the late highstand and/or falling stage systems tracts, and by the filling of incised valleys (e.g. Ashover Grit and Rough Rock) following marked sea-level falls. Channel belt and valley fill orientation was initially influenced by differential compaction, but this influence decreased during the late Namurian. The recognition of incised valley fills within the late Namurian has implications for estimating the magnitudes and periodicities of Carboniferous relative sea-level change.