Terraces of the Hurunui River, New Zealand

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Abstract
Coarse gravel terraces of the Hurunui River valley fall into five groups: high warped surfaces, probably early Pleistocene but younger than Kowai Gravels; high urlwarped surfaces, one level of which is traceable to a moraine (Three Trees) of early Otiran or Waimaungan age; intermediate (Main) surfaces correlative with the Sisters Stream Moraines of Otiran age; low terraces correlative with the late Otiran moraine enclosing Lake Sumner; a few lower postglacial terrace remnants close to present river level. The higher terrace remnants are up to 800 ft above present river level, though the most continuous terraces of Sisters Stream and Lake Sumner age lie within 300 ft of river level in the upper valley and within 125 ft in the lower. The principal and highest terrace surface in each group is of aggradational origin; lower associated surfaces appear to be due to degradation. The terraces of Lake Sumner age pass beneath present river grade h:llf way to the sea, but the Sisters Stream and Three Trees Terraces extend to the coast well above present stream level, though presumably deposited when ~ea level was hundreds of feet lower than now. Their position indicates upwarp of the coastal belt since they were formed. The course of the Hurunui River, in part adjusted to and in part transverse to structure, may l'eflect superimposition from a widespr.ead cover of Kowai Gravels near the beginning of the Kaikoura Orogeny. One cannot rule out, however, the possibility of an antecedent origin from an eastward course consequent upon the Cretaceous—Miocene marine strata, if they emerged before Kaikoura folding took place.

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