Origin and age of erosion surfaces in the upper drainage basin of Waiapu River, northeastern North Island, New Zealand

Abstract

In the upper drainage basin of Mata River, a tributary of the Waiapu River, hilltop height accordances at two levels, 500–580 m and 560–640 m above sea level, are observed. Both hilltop height accordances are inferred to represent erosion surfaces developed over folded Neogene rocks. The lower erosion surface is estimated from geomorphological position relative to the Mangamaunu Upland and tephrochronology to have been formed during a period of 25 000–30 000 years from prior to c. 35 000 years ago to c. 12 400 years ago (late Otiran). This lower erosion surface is not an elevated peneplain but was originally formed at a high level similar to its present altitude. The lower erosion surface was probably formed by cryoplanation under cooler and slightly drier climatic conditions than present with a sparse vegetation cover. The age of the higher erosion surface is not known but it must be much older than c. 35 000 years.

Keywords:

• erosion surfaces
• fluvial features
• terraces
• late Pleistocene
• Otiran
• uplifts
• rates
• denudation
• climate
• vegetation
• Waiapu River
• periglacial environment