Fluvio-lacustrine cyclothems from the Oligocene of Hampshire

Abstract

Each fluvio-lacustrine cyclothem may include the following lithotypes (in ascending order): (a) irregularly laminated silts and muds; (b) regularly laminated muds and silts; (c) muds with or without molluscan partings and bands; (d) colour mottled muds. Each cycle reflects a change from flowing water conditions (fluvial) to non-flowing water conditions (lacustrine), culminating in some cases with the formation of marsh. Each lithotype is thought to represent the environmental changes which resulted from the silting up of inter-channel depressions on a flood plain. Successive cyclothems possibly reflect renewed flooding following an increase in river level during more pluvial periods.