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Climate-controlled tephra redeposition on Pouakai ring plain, Taranaki, New Zealand

1975; Taylor & Francis; Volume: 18; Issue: 2 Linguagem: Inglês

10.1080/00288306.1975.10418202

1175-8791

V. E. Neall,

Coastal wetland ecosystem dynamics

Abstract Redeposited tephra deposits have been identified over 250 km2 of Pouakai ring plain in Taranaki, and are here termed the Katikara Formation. The deposits are discontinuous and consist of massive, blocky, sandy loam material, containing weak cross-stratification. They form mounds and sinuous ridges or dunes up to 10 m thick, which have modified the pre-existing relief, mostly between 150 and 300 m altitude. Below 150 m altitude, and between the larger deposits above 150 m altitude, the formation averages <3 m-thick and, where present, is conformable with the underlying tephras. Both air-fall and air-flow tephras are interbedded within cross-stratified redeposited tephra deposits indicative of an aeolian origin. The Katikara Formation is interbedded near its base with the Saunders Ash, radiocarbon dated (NZ942) at 16 100 ± 220 yr b.p. At most localities the Okato Tephra, dated (NZ1143 at 12 550 ± 150 yr b.p., overlies the formation. Within the Saunders Ash, charcoal at 300 m altitude has been identified as Dracophyllum sp.; this is consistent with a lowered tree line during the last stadial. Above 150 m altitude, widespread erosion breaks are often preserved beneath the base of Katikara Formation deposits, and beneath the Saunders Ash where the former is absent. The formation is thought to represent the result of widespread erosion of older tephras on the upper slopes of Pouakai volcano, corresponding in age to the earlier and later Kumara-3 glacier advances in Westland and to the deposition of the Mokai Sands in the Central North Island. It is suggested that the Lepperton surface in western Taranaki simply represents an equivalent of the Maitahi surface which was severely eroded and modified during the last glacial. Last stadial Katikara Formation deposits are apparently absent on Egmont ring plain, probably because most of the present Egmont cone has been constructed in post-glacial time.