Southern Region Chalk Group Lithostratigraphy: Sussex lithostratigraphy of Mortimore (1986a) - Portsdown Chalk Member

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The Portsdown Chalk Member (Holostratotypes: Whitecliff, Isle of Wight [SZ 639 856], Farlington Redoubt, Portsdown [SU 686 064]), the lowest c. 30 m of which were described by Mortimore (1986a), is marked by the Portsdown Marl at the base. This is the highest chalk exposed on Portsdown beneath the Tertiary erosion surface. The member comprises very soft, pure white flinty chalks, with regularly developed marl seams, named in ascending order: the Portsdown Marl, Scratchell's Marls, Bedhampton Marls, Farlington Marls and the Shide Marl (Mortimore, 1986a). The trace fossil Zoophycos, typically preserved as orangey-brown skinned spikey flints, is common in the lower part of the member. Mortimore (1986a) assigned the whole of the exposed chalk on Portsdown to the Redoubt Beds.

The fauna of the Portsdown Chalk consists of the belemnites Belemnitella and Gonioteuthis, which are common and co-occur in the lower part, and the echinoids Echinocorys brydonei and E. subconicula (Mortimore, 1986a; Bailey et al., 1983). Inoceramid shell is locally very common, and associated with some of the marl seams.

Macrofossil Biozonation: Post Applinocrinus Beds (sensu Christensen, 1991) (pars) & B. mucronata Zone (pars)

Correlation: see Correlation with other Southern Region Chalk Group classifications

see Correlation with other UK Chalk Group successions

References[edit]

BAILEY, H W, GALE, A S, MORTIMORE, R N, SWIECICKI, A & WOOD, C J. 1983. The Coniacian-Maastrichtian stages of the United Kingdom, with particular reference to southern England. Newsletters on stratigraphy, Vol. 12, 29-42

MORTIMORE, R N.1986a. Stratigraphy of the Upper Cretaceous White Chalk of Sussex. Proceedings of the Geologists' Association, Vol. 97(2), 97-139.

See: flint, marl