South-west England Chalk Group Lithostratigraphy: Jukes-Browne & Hill, 1903, 1904 - Lower Chalk/Cenomanian Limestone

From Earthwise
Jump to navigation Jump to search

Jukes-Browne & Hill (1903) assigned a laterally variable thickness (typically a couple of metres but ranging from less than a metre to nearly 10 m) of sandy chalk (named Arenaceous Beds) and indurated limestones (sometimes informally referred to by them as Cenomanian Limestone, and subsequently more formally used (Smith, 1957) for these indurated beds) to the Lower Chalk. The Lower Chalk was subdivided into three or four units named, in ascending order, A (locally split into A1 & A2), B and C, all of which are richly fossiliferous with ammonites, echinoids, bivalves and brachiopods in particular, many worn and phosphatised and/or glauconitised (Jukes-Browne & Hill, 1903). The latter subdivisions are laterally variable in thickness and development, so that relatively few localities show a complete succession. The base of the Lower Chalk is the unconformable contact with Lower Cretaceous or older strata, and the top is the base of a hard, gritty, quartzitic and glauconitic limestone, above which Jukes-Browne & Hill (1903) recorded hard, yellow, nodular chalk that they considered analagous to the Melbourn Rock.

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.

See: Arenaceous Beds, Cenomanian Limestone, A1, A2, B, C, Melbourn Rock