Southern Region Chalk Group Lithostratigraphy: Sussex lithostratigraphy of Mortimore (1986a) - South Street Beds

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The South Street Beds, 6-9 m thick in the Lewes district (Lake et al., 1987), are marked by the Lewes Marl at the base, and by the base of the Snowdrop Flint at the top (Mortimore, 1986a). They comprise massive, medium-soft, weakly nodular chalk with marls (including the South Street Marl) in the lower part, passing up into a succession of hard, very nodular chalk with hardgrounds, named the Lewes Nodular Chalks (Mortimore, 1986a). Large nodular flints occur throughout, and two of these horizons are named South Street Flint 1 and South Street Flint 2 (Mortimore, 1986a).

The fauna of the South Street Beds is characterised by large flattened forms of the inoceramid bivalve Mytiloides, resembling species that occur in the Holywell Beds (Lake et al., 1987). The Lewes Marl at the base contains common Micraster leskei (large form), that is upwardly replaced a short distance above this marl by Micraster precursor (sensu Drummond, 1983) (Mortimore, 1986a).

Macrofossil Biozonation: upper S. plana Zone

Correlation: see Correlation with other Southern Region Chalk Group classifications

see Correlation with other UK Chalk Group successions

References[edit]

DRUMMOND, P V O.1983. The Micraster biostratigraphy of the senonian White Chalk of Sussex, southern England. Géologie Meditérraneenne, Vol. 10 (3-4), 177-182.

LAKE, R D, YOUNG, B, WOOD, C J & MORTIMORE, R N. 1987. Geology of the country around Lewes. Memoir of the British Geological Survey.

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

See: marl, flint, nodular chalk, hardground, Holywell Beds, Lewes Marl