South-west England Chalk Group Lithostratigraphy: Jukes-Browne & Hill, 1903, 1904 - Middle Chalk

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Jukes-Browne & Hill (1903) assigned c. 43 m to the Middle Chalk near Beer, Devon. It comprises hard, nodular, yellow-stained chalk in the lower part, with sparsely developed flint nodules and locally abundant comminuted inoceramid bivalve shells (Jukes-Browne & Hill, 1903). A locally developed freestone near the base of the Middle Chalk is named the Beer Stone, and slightly higher is a locally developed hard, yellow limestone (Jukes-Browne & Hill, 1903) The remainder of the Middle Chalk is soft, white chalk with abundant , mostly small, nodular and spikey flints, forming bands and belts in coastal sections (Jukes-Browne & Hill, 1903). Beds of marly chalk and laminated marly chalk also occur; two of them lack flints and are conspicuous markers in the cliffs around Beer, and were named the 'Two Foot Band' and 'Four Foot Band' by Rowe (1903). The base of the Middle Chalk is marked by a hard, gritty limestone, overlain by, hard, nodular, yellow-stained chalk which Jukes-Browne & Hill (1903) likened to the Melbourn Rock. The top of the Middle Chalk was locally placed at the base of a bed of hard, nodular chalk with phosphatic fragments, which Jukes-Browne & Hill (1903, p. 127) likened to the Chalk Rock, or immediately below the inferred base of the S. plana Zone, which is traditionally coincident with the Middle / Upper Chalk boundary.

Macrofossil Biozonation: Recent biostratigraphical studies show that the Middle Chalk of south-west England belongs to the N. juddii Zone, Mytiloides spp. Zone (sensu Wood, 1996) and the T. lata Zone (Wright & Kennedy, 1981).

Correlation: see Correlation with other lithostratigraphical schemes for south-west England

see Correlation with other UK regions

References[edit]

JUKES-BROWNE, A J & HILL, W.1903. The Cretaceous rocks of Britain. Vol. 2 - The Lower and Middle Chalk of England. Memoir of the Geological Survey of the United Kingdom.

WOOD, C. J. 1996. Upper Cretaceous: the Chalk Group. In SUMBLER, M. G., British Regional Geology: London and the Thames Valley. Fourth Edition. (London: HMSO for the British Geological Survey).

WRIGHT, C W & KENNEDY, W J. 1984. The Ammonoidea of the Lower Chalk. Part I. Monograph of the Palaeontographical Society. London: 1-126, pls 1- 40 (Publ. No. 567, part of Vol. 137 for 1983).

See: Melbourn Rock, Chalk Rock, S. plana Zone