Southern Region Chalk Group Lithostratigraphy: Traditional Classification - Middle Chalk

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The Middle Chalk equates with the interval from the top of the Plenus Marls to the base of the Chalk Rock (or its inferred equivalent where it is undeveloped). A typically hard, feature-forming bed at the base of this interval is named the Melbourn Rock. This is overlain by hard, nodular, flint-free chalk, in which shell fragments of the inoceramid bivalve Mytiloides are locally common and rock-forming. Higher in the succession the chalk becomes much less shelly, softer, smooth-textured, massively bedded, and creamy-white coloured with fairly regularly developed thin (centimetre scale) marls. The first appearance of flint in the chalk of southern England is usually in the higher part of the Middle Chalk, occurring initially as sporadic bands of small nodular flints, and then more regularly developed nodular flints. Above the shell-rich lower part of the Middle Chalk there are locally common inoceramid bivalves, particularly Inoceramus cuvieri and I. lamarcki, and the small brachiopod Terebratulina lata, is locally very common.

The Middle Chalk is 26-41 m thick in Dorset, 43 m thick in Hampshire, 65 - 90 m thick in Sussex and 60-80 m thick in Kent (Rawson et al., 1978)

Macrofossil Biozonation: M. geslinianum Zone (pars), N. juddii Zone, Mytiloides spp. Zone & T. lata Zone

Correlation: see Correlation with other Southern Region Chalk Group classifications

see Correlation with other UK Chalk Group successions

References

RAWSON, P F, CURRY, D, DILLEY, F C, HANCOCK, J M, KENNEDY, W J, NEALE, J W, WOOD, C J & WORSSAM, B C. 1978. A correlation of the Cretaceous rocks in the British Isles. Geological Society of London, Special Report No. 9, 70 pp..

See: Plenus Marls, Melbourn Rock, Chalk Rock