The lithostratigraphy of the Coralline Crag (Pliocene) of Suffolk

A series of 7 boreholes (3 rotary and 4 shell and auger) were drilled by the British Geological Survey through the main outcrop of the Pliocene Coralline Crag Formation between Gedgrave and Aldeburgh in Suffolk between 1982 and 1985. The boreholes proved three members distinguished on the basis of grain size, sorting, carbonate content and fauna. The oldest, the Ramsholt Member, rests unconformably on the Palaeocene-Eocene London Clay Formation. It comprises a basal phosphorite-rich gravel with shelly mud-rich sands above. The Sudbourne Member unconformably overlies the Ramsholt Member and consists of cross-stratified, well-sorted carbonate sands, laid down as a tidal sand ridge. A third member, the Aldeburgh Member is found only in the northern part of the outcrop where it overlies the Ramshot Member. It consists of mud-poor, moderately sorted carbonate sand, and is probably the offshore (deeper water) equivalent of the Sudbourne Member.