Turonian 2: Difference between revisions
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At Folkestone, a hardground in the higher part of the Holywell Nodular Chalk forms the sequence boundary, and the marly facies of the remainder of this formation is interpreted as a shelf margin wedge (Gale, 1996). In Devon, the shelf margin wedge is locally present in thicker developments of Holywell Nodular Chalk (e.g. Whitecliff), but it thins westwards onto a positive structure in the Beer area, and where completely absent, the Branscombe Hardground represents a combined sequence boundary and transgressive surface (Gale, 1996). In basinal areas, a bed of abundant echinoderm debris at the base of the New Pit Chalk Formation represents a transgressive surface at the base of the transgressive systems tract. The remainder of the sequence comprises much of the remaining New Pit Chalk (up to a level just below the New Pit Marls), formed in the deepest phase of the Turonian sea level highstand (Hancock, 1989), but defining the top of the transgressive systems tract is problematic; it is questionably identified at the Round Down Marl of Gale (1996). | At Folkestone, a hardground in the higher part of the Holywell Nodular Chalk forms the sequence boundary, and the marly facies of the remainder of this formation is interpreted as a shelf margin wedge (Gale, 1996). In Devon, the shelf margin wedge is locally present in thicker developments of Holywell Nodular Chalk (e.g. Whitecliff), but it thins westwards onto a positive structure in the Beer area, and where completely absent, the Branscombe Hardground represents a combined sequence boundary and transgressive surface (Gale, 1996). In basinal areas, a bed of abundant echinoderm debris at the base of the New Pit Chalk Formation represents a transgressive surface at the base of the transgressive systems tract. The remainder of the sequence comprises much of the remaining New Pit Chalk (up to a level just below the New Pit Marls), formed in the deepest phase of the Turonian sea level highstand (Hancock, 1989), but defining the top of the transgressive systems tract is problematic; it is questionably identified at the Round Down Marl of Gale (1996). | ||
Latest revision as of 07:11, 2 October 2013
At Folkestone, a hardground in the higher part of the Holywell Nodular Chalk forms the sequence boundary, and the marly facies of the remainder of this formation is interpreted as a shelf margin wedge (Gale, 1996). In Devon, the shelf margin wedge is locally present in thicker developments of Holywell Nodular Chalk (e.g. Whitecliff), but it thins westwards onto a positive structure in the Beer area, and where completely absent, the Branscombe Hardground represents a combined sequence boundary and transgressive surface (Gale, 1996). In basinal areas, a bed of abundant echinoderm debris at the base of the New Pit Chalk Formation represents a transgressive surface at the base of the transgressive systems tract. The remainder of the sequence comprises much of the remaining New Pit Chalk (up to a level just below the New Pit Marls), formed in the deepest phase of the Turonian sea level highstand (Hancock, 1989), but defining the top of the transgressive systems tract is problematic; it is questionably identified at the Round Down Marl of Gale (1996).
References
HANCOCK, J. M. 1989. Sea-level changes in the British region during the Late Cretaceous. Proceedings of the Geologists' Association, Vol. 100 (4), 565-594.
GALE, A S. 1996. Turonian correlation and sequence stratigraphy of the Chalk in southern England. In HESSELBO, S P & PARKINSON, D N (eds), Sequence Stratigraphy in British Geology, Geological Society Special Publication, No. 103, pp. 177-195.