Differentiation of late Pleistocene terrace outwash deposits using geomorphic criteria: Tekapo valley, South Island, New Zealand

This paper reassesses the geological interpretation of outwash deposits of different ages based on new data on terrace elevation and gradient, loess thickness, preserved paleochannel networks, and specific gravity of clasts of outwash deposits in the Tekapo valley, South Island. The results have shown no significant difference in these measures between the Wolds and Pattersons Terrace deposit, suggesting that they both represent the oldest, highest, steepest, most weathered, and most modified formation in the Tekapo valley. Significant differences have emerged between the Wolds/ Pattersons Terrace Formation and the lower Balmoral Formation, which exhibits a thinner loess cover, higher specific gravity values, and a distinctive dendritic drainage network. The Balmoral Formation is significantly differentiated from the Mt John Formation, which has little loess cover and is traversed by complex braided paleochannel networks. The measures adopted do not discriminate between the Mt John and Tekapo Formations, although loess cover is thinner on the latter. The combined use of these measures of landform, paleochannel pattern, and clast characteristics, has proved a valuable objective means of discriminating between glaciofluvial terrace outwash deposits.