Southern Region Chalk Group Lithostratigraphy: Sussex lithostratigraphy of Mortimore (1986a) - Melbourn Rock
An indurated, feature-forming horizon, comprising several closely spaced beds of dense, nodular, typically iron-stained limestone, with thin marls and mineralised hardgrounds. Glauconite occurs as coatings to some of the chalk nodules, especially in the hardgrounds.
The Melbourn Rock was originally recognised in Cambridgeshire (Penning & Jukes-Browne, 1881), and although its base (coincident with the top of the Plenus Marls) has been traced over much of southern England, the top of the unit has not been consistently recognised in sections. Mortimore (1986a) proposed that the top of the Melbourn Rock in southern England be standardised at the lowest of a group of marls he named the Meads Marls, and named parastratotype sections at Beachy Head [TV 588 964], Willingdon [TQ 583 025], Beddingham [TQ 441 062] and Southerham [TQ 432 092]. As such, the Melbourn Rock is typically 3 to 4 m thick, the thicker intervals ascribed to this unit at Eastbourne (7m) and Dover (10 m) by Jukes-Browne & Hill (1903) being due to the inclusion of stratigraphically higher horizons. Mortimore (1986) recognised three marls that could be used to correlate sections: the Foyle Marl (at the base), the Old Town Marl and the Pilot Inn Marl.
The fauna of the Melbourn Rock is characterised by acmes of the heteromorph ammonite Sciponoceras and the asteroid Crateraster quinqueloba (Gale, 1996), and coarsely ribbed examples of the bivalve Inoceramus pictus also occur (Mortimore, 1986a)
Macrofossil Biozonation: M. gelinianum Zone (pars) & N. juddii Zone (pars)
Correlation: see Correlation with other Southern Region Chalk Group classifications
see Correlation with other UK Chalk Group successions
GALE, A S. 1996. Turonian correlation and sequence stratigraphy of the Chalk in southern England. In HESSELBO, S P & PARKINSON, D N (eds), Sequence Stratigraphy in British Geology, Geological Society Special Publication, No. 103, pp. 177-195.
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.
MORTIMORE, R N.1986a. Stratigraphy of the Upper Cretaceous White Chalk of Sussex. Proceedings of the Geologists' Association, Vol. 97(2), 97-139.
PENNING, W. H. & JUKES-BROWNE, A. J.1881. Geology of the neighbourhood of Cambridge. Memoirs of the Geological Survey of England & Wales.
See: Plenus Marls, hardground