The Correlation of the Lower Chalk of South-East England
Abstract
The Lower Chalk of south-eastern England is a richly fossiliferous sequence 54-104 m. thick, spanning most of the Cenomanian Stage. It rests with a slight break or without interruption on Upper Albian dispar-perinflatum Sub-zone sediments of Gault or Upper Greensand facies. The upper limit as here adopted is marked by a slight break at the base of the Cenomanian-Turonian plenus Marls (Metoicoceras gourdoni Zone), the sub- plenus erosion surface of Jefferies (1962, 1963). Of the many groups of fossils present, the ammonites provide the most useful means of subdivision and correlation. The distribution of these, and of other originally aragonitic fossils, is largely controlled by preservation, and there are levels at which there is evidence of seafloor dissolution of aragonite. Nevertheless, three ammonite zones can be recognised:
Zone of Calycoceras naviculare Zone of Acanthoceras rhotomagense Zone of Mantelliceras mantelli Within the M. mantelli Zone three assemblages are identified, characterised by: (a) Hypoturrilites carcitanensis, (b) Mantelliceras saxbii, (c) Mantelliceras gr. dixoni. There are also three assemblages in the Zone of A. rhotomagense, characterised by: (a) Turrilites costatus, (b) Turrilites acutus, (c) Acanthoceras jukes-brownei. The C. naviculare Zone is not subdivided. These zones are comparable to those proposed by Hancock (1959) for the type Cenomanian, and are equivalent to the Lower, Middle and Upper parts of the Stage. Bivalves, corals and brachiopods also have a use in correlation, and even fragments of the commonest fossils- Inoceramus and Holaster-are of local use.- Publication:
-
Proceedings of the Geologists' Association
- Pub Date:
- 1969
- DOI:
- 10.1016/S0016-7878(69)80033-7
- Bibcode:
- 1969PrGA...80..459K