The Middle and Upper Pleistocene sequence in the Lower Thames: a record of Milankovitch climatic fluctuation and early human occupation of southern Britian. Henry Stopes Memorial Lecture

Abstract

The Middle and Upper Pleistocene sequence in the Lower Thames: a record of Milankovitch climatic fluctuation and early human occupation of southern Britain. Proceedings of the Geologists' Association, 117, 281-305. The sequence of Pleistocene river terraces in the Lower Thames, long recognized as an important repository of evidence for Palaeolithic human activity, can now be interpreted in the context of the last five Milankovitch (100 ka) climate cycles, beginning with cold marine oxygen isotope stage (MIS) 12, when ice sheets blocked an earlier Thames course in Hertfordshire and Essex. This interpretation stems from empirical evidence from the Lower Thames deposits, in which the preservation of faunal and archaeological remains is unusually common. These deposits were laid down as climatically generated river terraces, formed in synchrony with the climatic cycles, although the progressive incision to ever-lower valley-floor levels is a response to background uplift. Interpretation of this evidence is revised here for the Dartford-Purfleet area in recognition of a phase of minor downcutting at the ends of interglacials. Previously regarded as insignificant, it is now realized that this erosion phase has resulted in interglacial sediments forming the higher of two facets within each terrace in the Lower Thames. Guided by this revision, the Lower Thames (Thames-Medway) terrace sequence further downstream, in eastern Essex, is reappraised in the light of the better preserved and better understood record from the Dartford-Purfleet area. It is concluded that Thames-Medway drainage northwards to the Clacton area (NE Essex) persisted until after the Hoxnian (MIS 11), so that the Clactonian (Palaeolithic) type locality lay in the main Thames valley at the time when the Clactonian knappers were operating. Despite its relegation in recent years from the earliest British Palaeolithic culture to little more than a curious anomaly, with doubts expressed about its separate existence, recent interpretations of the Clactonian hold that it appeared within the Thames sequence on two separate occasions, both coincident with a glacial to interglacial transition. These separate Clactonian occupations, at the MIS 12-11 and 10-9 transitions, together with the first appearance of the Levallois technique at around the MIS 9-8 boundary, can be linked to the chronology and to the cyclic climatic record that together underpin the Lower Thames sequence.