Uplift-driven valley incision and climate-controlled river terrace development in the Thames Valley, UK

The sequence of terraces of the River Thames in southeast England has previ ously been shown to span the period from the earliest Pleistocene to the pr esent. This terrace sequence contains biostratigraphical and sedimentary ev idence that testifies to the high-amplitude climatic changes of the Quatern ary. Large-scale fluvial incision, resulting in basin-wide terrace formatio n, appears to have been concentrated at the warming limbs of the major clim atic glacial-interglacial cycles, when sediment supply was greatly reduced. This incision and subsequent valley-floor widening created the accommodati on space for the later aggradation of the terrace sediments during the foll owing warm-cold transitions and during the cold stages, when high-sediment supply conditions prevailed. Although the timing of terrace aggradation may be controlled by climate change, the progressive valley incision recorded by terrace staircases cannot easily be explained in terms of Quaternary cli matic change alone and recently developed models suggest that long-term inc ision by the Thames has been driven by uplift. This paper presents an overv iew of the available terrace data and tabulates incision amounts and rates between key stratigraphic horizons. Superimposed upon these broad changes, revealed by the complex internal sedimentary architecture of many terrace s ediments, are the geomorphological system responses to both higher-frequenc y climate-driven changes and more localized intrinsic fluvial system adjust ments. (C) 2001 Published by Elsevier Science Ltd.