Chalk Group Lithostratigraphy: Marlborough Downs/Berkshire Downs/Chilterns - Cambridge Greensand
The Cambridge Greensand is a thin (c. 1m or less) bed of glauconitic, micaceous marl with abundant phosphatised pebbles, terminating abruptly south-westwards against a fault or monoclinal flexure near Barton-le-Clay (Wood, 1996). It contains many phosphatised fossils derived from the underlying Gault (Upper Albian), particularly large brachiopods, bivalves (especially Aucellina) and ammonites, and an indigenous, non-phosphatised basal Cenomanian fauna that also includes the bivalve Aucellina, plus small brachiopods (Wood, 1996).
Macrofossil Biozonation: M. mantelli Zone, N. carcitanense Subzone (indigenous fauna) (Morter & Wood, 1983)
Correlation: see Correlation with other parts of the UK
WOOD, C. J. 1996. Upper Cretaceous: the Chalk Group. In SUMBLER, M. G., British Regional Geology: London and the Thames Valley. Fourth Edition. (London: HMSO for the British Geological Survey).