The lithostratigraphy and biostratigraphy of the Chalk Group (Upper Coniacian to Upper Campanian) at Scratchell's Bay and Alum Bay, Isle of Wight, UK

Abstract

The Scratchell"s Bay and southern Alum Bay sections, in the extreme west of the Isle of Wight on the Needles promontory, cover the stratigraphically highest Chalk Group formations available in southern England. They are relatively inaccessible, other than by boat, and despite being a virtually unbroken succession they have not received the attention afforded to the Whitecliff GCR (Geological Conservation Review series) site at the eastern extremity of the island. A detailed account of the lithostratigraphy of the strata in Scratchell"s Bay is presented and integrated with macro and micro biostratigraphical results for each formation present. Comparisons are made with earlier work to provide a comprehensive description of the Seaford Chalk, Newhaven Chalk, Culver Chalk and Portsdown Chalk formations for the Needles promontory.The strata described are correlated with those seen in the Culver Down CliffsWhitecliff Bay at the eastern end of the island that form the Whitecliff GCR site. This provides an overall correlation for the Upper Coniacian to Upper Campanian Chalk strata on the island.The influence of the Purbeck -Wight structure (Sandown and Brighstone periclines) on the Chalk Group strata is discussed and the conclusions drawn demonstrate that movement on this structure is diachronous across the island.