Chalk Group Lithostratigraphy: Marlborough Downs/Berkshire Downs/Chilterns - Melbourn Rock
The Melbourn Rock was first recognised by Penning & Jukes-Browne (1881), and was subsequently adopted by the Geological Survey as a marker for the base of the Middle Chalk (Hill & Jukes-Browne, 1886; Jukes-Browne & Hill, 1903). It comprises typically 3-4 m of 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. Hopson et al. (1996) recently described the Melbourn Rock at Ashwell Quarry [TL 2687 3945], near Royston, the only currently available stratotype, but the relationship of this exposure to the original concept of Hill & Jukes-Browne (1886) is uncertain. Recently, Mortimore (1986a) has redefined the Melbourn Rock for application to the Southern Region, in which it is a much less conspicuously developed feature.
Macofossil Biozonation: M. geslinianum Zone (pars), N. juddii Zone, Mytiloides spp. Zone (pars) (Wood, 1996)
Correlation: see Correlation with other parts of the UK
HILL, W & JUKES-BROWNE, A J. 1886. The Melbourn Rock and the Zone of Belemnitella plena from Cambridge to the Chiltern Hills. Quarterly Journal of the Geological Society of London, Vol. 42, 216-31
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: marl, hardground, Melbourn Rock (Southern Region)