Thalassostatic terraces and Pleistocene chronology

Rejuvenation and aggradation are among the usual adaptations of a river under changing conditions. Terraces may result from rejuvenation, and a repeated alternation of rejuvenation and aggradation may lead, but does not necessarily so, to the formation of a sequence of terraces bordering a valley. Many agencies are involved in terrace formation. The correlation of terraces along different rivers, or even along different parts of the same river, often meet with serious difficulties. However, under certain conditions the causes involved may be of such a nature as to affect all rivers in a vast area in the same way. This has been the case for instance during the changing glacial and interglacial conditions of the Pleistocene. Their effects are well developed in the middle course of several rivers in the periglacial belt of temperate Europe. On paleontological evidence it is assumed, that the aggradation is of glacial age, and accordingly the rejuvenation is of interglacial age. Zeuner (1945, p. 26) pointed out that, to state it more exactly, aggradation began when, toward the end of an interglacial, conditions became colder, and rejuvenation set in as soon as the climate became milder again, i. e. still under cold conditions. This type of river terraces is generally known as glacial-climatic terraces. Glacial-climatic terraces have provided valuable evidence for the chronology of the Pleistocene. Their significance is hardly less than that derived from directly glacial evidence.