River terraces and their loessial cover beds, Awatere River valley, South Island, New Zealand

Abstract

Loessial cover beds on river terraces were examined to determine the age of key terraces and the timing of latest major fluvial events. Six terrace sets or terraces are defined. Loessial cover beds on terraces are named after the terrace sets which represent fonner floodplains that the river occupied during sedimentation of each layer. Volcanic glass from c. 21 000 year old Aokautere Ash (Kawakawa Tephra) found within the loess has been used to date the last major river aggradation, which culminated about 17 000 years ago. A major change in river regimen occurred about 12 000 years ago, in which downcutting succeeded aggradation. This change is considered to mark the end of the Last Glacial.