Late Pleistocene geology of the Kowai River Valley, mid-Canterbury
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
The Kowai River Valley, a formerly glaciated tributary of the Waimakariri River, drains the eastern side of the Torlesse Range in the vicinity of Porter’s Pass. A study of the glacial deposits and stratigraphy was made, investigating three specific but complimentary aspects: (1) Mapping of the glacial stratigraphic succession for the purpose of correlation with that established for the Waimakariri River System (Gage, 1958); (2) a detailed comparative textural analysis of outwash gravels from two glacial advances to determine whether any significant differences exist, that can be directly related to environmental processes operating during transportation and depositon of these materials; (3) a clay mineral study of weathering products as a potential tool for age determination and correlation. From logitudinal terrace profiles, a distinct surface and moraine system was found for each of the Woodstock, Otarama, Blackwater I and II and Poulter Glacial Advances, from which their magnitude and maximum extension were interpreted. The stratigraphy and glacial history of the Kawai River reflects that of the Waimakariri River very closely, but, several anomalous topographical features indicate that the Kawai Valley traverses a zone of active tectonism. The principal sites of movement were identified and something of the tectonic history was deduced. Parameters measured for the gravel analysis included size distribution, composition, sphericity and shape factor. Correlations between parameters were sought. Comparisons of parameters between samples were made. Variations in size distribution between samples were explained in terms of local hydraulic conditions during deposition, selective sorting and abrasion by ice and subsequent fluvial transportation. Variations in compositional types between samples resulted from (1) increase or decrease of other rock types, (2) relative abundance and availability in source area. (3) influx of new material and (4) local sample variation. Similarity of sphericity values and dominance of disc-shaped particles for both samples reflects the importance of the mechanisms and processes during transportation within a glacial environment. Clay samples from five stratigraphic sections of Late Pleistocene glaciofluvial deposits; representing all the major advances, were analysed using X-ray diffraction and infra-red spectroscopy techniques. Differentiation between units of gravel was attempted using the relative intensities and peak area measurements of (001) basal reflection. The 7A°:14A° intensity ratio was used as an indicator of the degree of weathering with moderate success. The clay mineral assemblage within distinct gravel units is not sufficiently characteristic to be used as a consistent and accurate means of correlation, unless the duration of a particular glacial episode is such as to enable the clays to develop specific characteristic attributes prior to burial. In conclusion the main contributions of this study have been: (1) the recognition of the extent and activity of the Porter's Pass Fault Zone and the importance of taking this into account when correlating glacial deposits across this zone elsewhere, (2) The establishment of a detailed body of textural data on glacial outwash gravels for future comparative purposes, and (3) an indication that there is potential to further investigate weathering products as a correlative tool.