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

From Earthwise
Jump to navigation Jump to search

The Bastion Steps Beds, c. 8 - 9 m thick locally in Sussex, are marked by the Meeching Paired Marls at the base and the upper Castle Hill Marl at the top (Mortimore, 1986a). These beds comprise mostly soft, flinty chalk with marl bands, but beds of hard, iron-stained, spongiferous chalk also occur (Mortimore, 1986a). The Meeching Marls are a closely spaced pair that have interconnecting marl wisps through the 0.3 to 0.5 m of intervening nodular chalk (Mortimore, 1986a). Above a distinctive band of tubular and finger flints (Tavern Flints) is a group of four thin marls in the middle of the succession, named the Telscombe Marls (Mortimore, 1986a). A bed of hard, spongiferous chalk in the higher part of the succession is named the Arundel Sponge Bed, overlain by the Arundel Flints, and then by poorly flinty chalk up to the Castle Hill Marls.

The fauna of the Bastion Steps Beds is characterised by the echinoids Offaster pilula, O. pilula planata, Echinocorys scutata (large, thick-tested morphotype of Gaster, 1924), and Hagenowia blackmorei. In Wiltshire, the belemnite Belemnitella locally occurs in this interval (Bailey et al., 1983).

Macrofossil Biozonation: top O. pilula Zone and basal G. quadrata Zone

Correlation: see (table #) for correlation with other Southern Region Chalk Group classifications, & (table #1) for correlation with other UK Chalk Group successions

References[edit]

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

GASTER, C T A. 1924. The Chalk of the Worthing District, Sussex. Proceedings of the Geologists' Association, Vol. 35, p. 89-110.

See: marl, flint, Arundel Sponge Bed