Stratigraphy and Petrography of North-East Otago Loess

Abstract

Abstract An extensive loess mantle up to 36 ft thick, but generally less than 15 ft thick, covers much of north-east Otago, especially on the intermediate and high-level terraces south of the Waitaki River from Duntroon to the coast, and in the vicinity of Cape Wanbrow, near Oamaru. This loess is a pale yellow, angular, poorly sorted, positively skewed, medium silt. It is composed predommantly of quartz, feldspar (andesine?), accessory muscovite, and about 4% heavy minerals. The minerals are consistent with derivation from either a greywacke or schist terrain. Both slope-wash deposits and loess are discussed, because on steeper slopes slope-wash replaces loess deposition when the climate is severe. Hence, from Livingstone, a sequence of three loesses and two slope-wash deposits are described, and an attempt is made to correlate these units with loesses at Five Forks, and Maheno. The sequence of terrace gravel, loesses, and slope-washes, with soil development at one major and one minor horizon, is interpre...