Discussion on fault activity and sedimentation in a marine rift basin (Upper Jurassic, Wessex basin, UK)

Abstract

Scientific editing by John Howell. J. K. Wright writes: I was interested to read the recent paper by ⇓Newell (2000) which incorporates a sequence stratigraphic synthesis of the Corallian of the Wessex Basin. This is an aspect of the Dorset Corallian which I investigated some years ago (⇓Wright 1986) when I subdivided the succession on a lithostratigraphic basis. Newell’s sequence stratigraphic subdivisions consist of sequences of strata bounded by major erosion surfaces. Lithostratigraphic and sequence stratigraphic units do not normally coincide, but may be coincident under special circumstances (⇓Murphy & Salvador 1999). Such circumstances occur when there is a substantial change in lithology between lithostratigraphic units that are bounded by unconformities. I would submit that this is the case in the Oxfordian of the Dorset coast, and that with some revision to the lithostratigraphy, the formation boundaries coincide with the sequence boundaries and therefore have chronostratigraphic significance. In setting up a revised stratigraphy for the Dorset Corallian Group (⇓Wright 1986), I defined formations within the group as sequences of strata bounded by erosion surfaces—in effect sequence stratigraphy. Each of these formations contained a sedimentary cycle comprising a transgressive succession followed in some cases by a regressive succession. In this way I defined six formations (sequences) although as a number of the boundaries …