The Late Pliocene marine formation at St Erth, Cornwall

Abstract

New excavations were made in the long-abandoned sand and clay pits at St Erth, Cornwall, from which rich collections of marine mollusca and foraminifera have come in the past. The sediments and stratigraphy revealed are described, and the results of detailed studies of the fossils (mollusca, foraminifera, ostracoda, and plants) in the marine clay are given. The sand member is well sorted, and in places contains two fine-sand populations, one of beach and the other of dune origin. The clay member was probably deposited not far below low-water mark in a sea whose water temperature was higher than that of Cornwall today, at the time that the final Boytonian beds of the Pliocene Coralline Crag were being deposited in East Anglia, and the Pliocene marnes à Nassa were being deposited at Bosq d ’Aubigny in Normandy. Sea level appears to have been lowered by about 45 m to its present level since the marine clay was deposited. The possibility of crustal movement in Cornwall is referred to.