Flow in the lower continental crust as a mechanism for the Quaternary uplift of south-east England: constraints from the Thames terrace record

Abstract

The sequence of terraces of the River Thames in south-east England has been shown to date from the Early Pleistocene onwards, and to provide an indication of the Quaternary uplift history of the region. Using this evidence, supplemented by altitudes of Pliocene and Early Pleistocene marine sediments, we have determined the Pliocene and Quaternary uplift histories of five representative localities: Clacton, Colchester, and Dartford for the Lower Thames; and Cookham and Reading for the Middle Thames. These uplift histories have been modelled using a physics-based technique, which calculates the isostatic response involving flow in the lower continental crust induced by cyclic loading at the Earth's surface. Our results suggest that the Late Pliocene and Early Pleistocene part of the uplift history of our study region was initiated following the deterioration in climate starting at ∼3.1 Ma, which marked the start of upland glaciation elsewhere in Europe. The later increase in uplift rates in the Middle Pleistocene followed the start of intensified cyclic loading by very large continental ice sheets during and after oxygen isotope stage (OIS) 22 at ∼0.87 Ma. Dartford, Cookham, and Reading, in the interior of south-east England, are all shown to have begun to uplift quite rapidly, at rates of up to ∼0.1 mm a −1, following the start of forcing at ∼3.1 Ma. They have since uplifted by distances which increase gradually westward from ∼200 to ∼250 m, of which a uniform ∼70 m has occurred since OIS 22 at ∼0.87 Ma. In contrast, Clacton and Colchester, near the present North Sea coastline, experienced slow subsidence until the late Early Pleistocene, but have nonetheless uplifted since OIS 22 by similar distances to the other sites.