Quaternary river terraces in England: Forms, sediments and processes

Flights of Quaternary river terraces in south and east England have common characteristics involving low-gradient planed or irregular bedrock surfaces and single or multi-storey gravel deposits. Rather than depending on warm–cold or cold–warm transitions, it is suggested that bedrock planation, “working depths” of gravel and later-stage (relatively shallow) aggradations are all dominantly of cold-climate origin. Basal sediments show active incorporation of plucked and periglacially-shattered materials, whilst super-incumbent units incorporating up-catchment and slope-derived materials demonstrate later cold-stage sediment influx and consequent cessation of active bedrock erosion. Channel activity effecting both planation and deposition are reviewed, together with the detailed sedimentology of gravelly sediments which show evidence of both autogenic processes (bar migration, channel switching and infilling, and truncation of upper sedimentation units), cold-climate indicators (turbation, ice-wedge casts, and frozen block transport), and (specifically for the last glacial–interglacial cycle) varying sediment flux as climates changed. Both interglacial and “transitional” activities are believed to be of lesser morphological significance, whilst prior uplift is taken as enabling rather than being a generator of terrace within the timescale of a glacial–interglacial cycle. Variations within cold-stage climates, varying sediment influx and channel-belt bedrock erosion are stressed as dominating mid-catchment and mid-latitude Quaternary terracing at the glacial–interglacial scale.