Southern Region Chalk Group Lithostratigraphy: Traditional Classification - 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 several parastratotype sections in Sussex. 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. Named marls in the Melbourn Rock of southern England, of value for section correlation, are the Foyle Marl (at the base), Old Town Marl and Pilot Inn Marl. Because of uncertainties in the correlation of the top of the Melbourn Rock in the type area with coastal exposures in southern England, Gale (1996) proposed that the Melbourn Rock of southern England be replaced by a slightly broader stratigraphical interval (ranging to the highest of the Meads Marls of Mortimore, 1986a) termed the 'Ballard Cliff Member'.

The fauna of the Melbourn Rock is characterised by acmes of the heteromorph ammonite Sciponoceras and the asteroid Crateraster quinqueloba.

Macrofossil Biozonation: M. geslinianum Zone (pars) & N. juddii Zone Zone

Correlation: see Correlation with other Southern Region Chalk Group classifications see Correlation with other UK Chalk Group successions