Allocycles in the upper part of the limestone coal group (pendleian, E1) of the glasgow‐stirling region viewed in the light of sequence stratigraphy

Abstract

AbstractSequence stratigraphy has produced a number of new concepts and terms which have been described and defined in the Wilgus et al. (1988) volume. Many of these concepts and terms can be applied to the two orders of allocycles present in the non‐autocyclic parts of the Limestone Coal Group. The longer‐period allocycles responsible for major Namurian marine transgressions correspond in their duration to ‘sequences’. The shorter‐period allocycles of the distal facies association in the upper part of the Limestone Coal Group correspond in their duration to ‘parasequences’. However, they include deeply incised fluvial channels similar to those cut into shelf sediments at ‘Type 1 sequence boundaries’, and are best regarded as unusually short‐period depositional sequences. The deep fluvial channels, which relate to lowstands, were incised when the rate of fall in sea level (probably glacial‐eustatic) exceeded the local rate of tectonic subsidence.The bulk of the distal facies association belongs to the ‘highstand systems tracts’ and ‘transgressive systems tracts’ of sequence stratigraphy. Lowstand deposits are poorly represented. Erosional breaks within two‐storey sheet sandstones probably reflect scouring by fluvial channels in the prograding ‘highstand systems tracts’ during the early stages of eustatic falls. Coals mostly relate to the rising water table conditions associated with ‘transgressive systems tracts’ and each seam may be preceded by a depositional hiatus. Extensive penecontemporaneous lowstand deposits may be found in the turbidite‐fronted deltas of the Pennine Millstone Grit.