Middle Eocene diatoms from Whitecliff Bay, Isle of Wight, England: stratigraphy and preservation

The description of a newly discovered diatom flora from the Bracklesham Group (Eocene) sediments exposed in Whitecliff Bay (Isle of Wight, UK) is extended and the palaeogeographical implications discussed. The diatom assemblage, which includes Aulacodiscus singiliewskyanus, A. subexcavatus, Brightwellia hyperborea, Coscinodiscus morsianus, Fenestrella antiqua, Stellarima microtrias, Stephanopyxis turris, ?Thalassiosiropsis wittiana, Trinacria regina and Triceratium spp., is described from the foreshore exposures rather than the badly weathered succession exposed in the cliffs. The flora, which is preserved as pyrite steinkerns, is both diverse and abundant. Only centric diatoms have been recorded and this indicates an open marine environment. The large foraminiferid Nummulites laevigatus is also present in these glauconitic silts and sands. The distribution of these two groups of microfossils, and the associated macrofauna, is used to propose a sequence stratigraphical interpretation for this part of the Eocene succession. The Marsh farm Formation, hitherto regarded as estuarine or non-marine, is shown to be of open marine origin by the presence of marine diatom species.