The middle Pleistocene deposits at Marks Tey, Essex

Abstract
At Marks Tey, Essex, Pleistocene lacustrine sediments rest on chalky boulder clay and occupy a deep, narrow trough cut into the subglacial surface. The central deposits of the former lake basin consist of laminated clay muds, partly brecciated, overlain by laminated grey clay, which is at present exploited for brickmaking. Together these strata have a maximum proved thickness of at least 35 m. The marginal sediments of the basin are thinner and more organic, and indicate some fluctuation of water level during deposition. Palaeobotanical evidence suggests that the basin was formed during the Lowestoft glaciation, possibly by subglacial erosion, and was gradually infilled during the course of the entire Hoxnian interglacial and the earliest part of the ensuing Gipping glacial period. Pollen analysis of the lacustrine deposits yielded the first complete vegetational record throughout the Hoxnian interglacial from the Lowestoft Late-glacial to the Gipping Early-glacial periods. The vegetational and climatic development of the interglacial can be reconstructed from the palaeobotanical evidence. The grey clay of Gipping age contained a macroflora of ‘full-glacial’ aspect. Of particular note are (1) the closing zones of the interglacial (Ho III and Ho IV ), which have not been fully recorded before; (2) the occurrence during this period of such exotic plant types as Vitis, Pterocarya and Ericacf. terminalis ; and (3) a high non-tree pollen phase during subzone H o l i e similar to that recorded by West (1956) from the same subzone at Hoxne. A preliminary investigation has been made of diatomaceous lamination structures in the interglacial clay mud. This lamination, which appears to be annual, suggests that the timespan of the interglacial period was of the order of 30000 to 50000 years. The interglacial deposits rest on chalky boulder clay, corresponding to the Springfield Till of Clayton (1957, 1960). There is no sign of till overlying the lacustrine deposits. Nearby, other Hoxnian deposits at Copford and Rivenhall End, Kelvedon, rest in a similar stratigraphic position. This fact implies that all the till deposits of south-east Essex belong to the Lowestoft glaciation, and that the Gipping ice advance did not extend as far south as commonly assumed.