Floristic changes indicate a cooling climate in the Eocene of southern England

Abstract

A major climatic cooling at the close of the Eocene (the ‘terminal Eocene event’) is suggested by studies of leaf floras in North America^1,2; and by oxygen isotope studies, of mollusc shells from the North Sea³ and of planktonic and benthic foraminifera from the North and South Pacific⁴. Climatic fluctuations in the French Palaeogene^5–8 inferred from palynological studies, are difficult to interpret in terms of this single event. The Pacific faunal studies⁴ and preliminary palynological evidence from the Isle of Wight, southern England⁹ indicates an onset of cooling earlier in the Eocene. We have therefore examined fossil floras (fruits, seeds, pollen and spores) from the Palaeogene deposits of the London and Hampshire Basins of southern England which form a continuous sequence from the early Eocene. We find no evidence for a sudden climatic change at the end of the Eocene (taken to be near the base of the Bembridge Marls in the Hampshire Basin¹⁰). Our evidence, in the form of two major periods of floristic change, suggests a more gradual cooling, commencing in the latest early Eocene.