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

From Earthwise
Jump to navigation Jump to search

The Upper Chalk , which Jukes-Browne & Hill (1904) considered to be c. 30 m thick, comprises hard, nodular chalk, with hardgrounds, marl seams and common bands of nodular flint. Subsequent research has shown that Jukes-Browne & Hill (1904) underestimated the thickness of Upper Chalk in SE Devon, by failing to recognise additional younger strata at Pinhay Cliffs [SY 312 906] (Jarvis & Tocher, 1987). The chalk is locally very fossiliferous, characterised particularly by the echinoid Micraster, but brachiopods and inoceramid bivalves are also locally common . The base of the Upper Chalk is marked by either an indurated, phosphatic bed, which Jukes-Browne & Hill (1904) considered to be the local equivalent of the Chalk Rock, or the inferred base of the S. plana Zone (traditionally considered to be coincident with the Middle / Upper Chalk boundary). The top of the Upper Chalk is the Palaeogene erosion surface. Jukes-Browne and Hill (1904) recorded a conspicuous nodular flint (probably the Annis' Knob Flint of Jarvis & Tocher (1987)), that they regarded as marking the junction of the S. plana and M. cortestudinarium zones.

Macrofossil Biozonation: Only S. plana Zone & M. cortestudinarium Zone recognised by Jukes-Browne & Hill (1904); M. coranguinum Zone subsequently recognised by Jarvis & Tocher (1987)

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

see Correlation with other UK regions

References[edit]

JARVIS, I & TOCHER, B A. 1987. Field Meeting: the Cretaceous of SE Devon, 14 - 16th March, 1986. Proc. Geol. Ass., Vol. 98 (1), 51-66.

JUKES-BROWNE, A J & HILL, W.1904. The Cretaceous rocks of Britain. Vol. 3 - The Upper Chalk of England. Memoir of the Geological Survey of the United Kingdom.

See: marl, flint, hardground, Chalk Rock,