Loess of the Dunedin district

Eden, D. N.

Loess of the Dunedin area from Warrington to Blackhead is described. Two textural types of loess are recognised - a coarse textured loess (poorly sorted, fine skewed, medium to fine sand) is restricted to the seaward slopes of the Otago Peninsula and one locality in Blueskin Bay. The location of the coarse textured loess suggests derivation from adjacent beaches. Fine textured (poorly sorted,fine skewed,medium silt) loesses of varying thickness occur throughout the remainder of the region. The bimodal grain size of some of these deposits adjacent to the coast suggests an origin from the continental shelf. Mineralogy in the loesses is fairly uniform, [quartz, alkali feldspar (mostly albite) are the main two minerals; other minerals include epidote, hornblende, augite (derived from the local volcanic sequence), hypersthene, actinolite. muscovite, plagioclase and chlorite] except for a higher proportion of heavy minerals in the coarse textured loesses. Sponge spicules are also found in the loess. Mineralogy does not appear to be a useful criterion for distinguishing between loesses of different age. Stratigraphic studies reveal few sequences involving two or more loesses in succession. These are given special attention and interbedded beach sands are related to altitude for regional Pleistocene correlation and age determinations. The loess sequences within the region span the latter part of the Pleistocene, with the oldest loess possibly representing the antepenultimate (Waimaungan) glaciation. Much of the loess is thought to have originated mainly from the continental shelf during periods of low sea level, as suggested by Raeside 1964. However uniformitarian considerations and some mineralogic data suggest a secondary inland origin.

80 leaves : illus. (part col.) maps (1 fold in pocket) ; 26 1/2 cm.

1970Eden

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