A Geomorphological and Sedimentological Investigation into the Glacial Deposits of the Lake Clearwater Basin, Mid Canterbury, New Zealand.

Abstract

This thesis presents the findings of a combined geomorphological, sedimentological and geochronological investigation into the glacial history of the Clearwater Basin, Mid Canterbury, New Zealand. The study demonstrates that a thick wedge of glacial and paraglacial sediments are preserved in the valley. These are >100m thick and preserve evidence of at least 3 glacial phases (>180ka). The study presents a new and detailed geomorphology map for the Clearwater valley and adjacent areas and has added 17 new recessional positions to the local glacial record. Surface Exposure Dating (SED) has been used to directly date the moraines of the Clearwater Basin providing the first detailed chronology for glacial moraine in this area. In total 31 cosmogenic ages from 9 separate moraines are presented. The results demonstrate that the LGM advance is the Trinity moraine of Mabin (1980) and not the Hakatere moraine as previously assumed and that the LGM was achieved at or about 23ka. The Clearwater glacier receded up valley between 23 and 13ka with some indication of accelerated retreat after c.16ka. The correlation to the adjacent Lake Heron Valley is also revised.