Parent material stratigraphy of an egmont loam profile, Taranaki, New Zealand

Abstract

The Egmont loam of Taranaki, New Zealand, is regarded as a classic andosol developed in andesitic tephra (a yellow-brown loam in the N.Z. genetic soil classification or an entic dystrandept in the US. Soil Taxonomy). Variations in grain size distribution and mineralogy within a representative profile show it to consist of two distinct units, an upper unit of andesitic tephra and a lower unit, containing up to 30% quartz, which is interpreted as a tephric loess. Correlation of peaks in andesitic glass distribution within the profile with eruptions from Mt Egmont suggest an accumulation period of circa 10000 years for the tephra unit, while the presence, in places conducive to its preservation, of the Aokautere Ash, a rhyolitic ash of widespread distribution in the Central North Island, dates (NZ1056A) the base of the profile at less than 19 850 � 310 years B.P. Peaks in distribution of the minor rhyolitic glass component in the tephra unit are correlated with three major post-glacial rhyolitic eruptions from the Central North Island; the Taupo eruption of 1840 � 50 years B.P. (NZ1548A), the Waimihia eruption of 3440 � 70 years B.P. (NZZA), and the Rotoma eruption of 7330 � 235 years B.P. (NZ1199A). Variations in the rate of quartz accumulation in the silt fraction of the Egmont profile are correlated with climatic changes, a higher rate of quartz accumulation occurring during the colder climate of the last stadial, in contrast with a lower rate of quartz accumulation occurring during the warmer climate of post-glacial time.

Eolian Additions to Soils and Sediments of Japan

“…which correspond to the last glacial maximum period. In New Zealand, STEWART et al (1977) have also obtained similar results for an Egmont Ando soil developed on tephric loess.…”

Geochemical fluxes and weathering of volcanic terrains on high standing islands: Taranaki and Manawatu-Wanganui regions of New Zealand

“…These high ratios could therefore be accommodated by the dissolution of calcic andesine which has been previously identified to compose up to 20% of the fines in the Egmont Loam (Stewart et al, 1977). This preferential weathering of feldspars could be explained by the relatively thicker soil profiles for the Taranaki region compared to the Ruapehu region, which are the result of lower soil slopes and a less dissected topography for this region (Leathwick et al, 2003) that would allow more time for Si to leach out of solution (Fig.…”

“…Egmont. Mineralogically, the soil fines contain quartz (<3% in the upper layer), feldspar (present mostly as calcic andesine), andestic glass (with microlites of feldspar, mafic minerals, and titatomagnetite in a glassy matrix), rhyolitic glass, and the mafic minerals augite, hornblende, and hypersthene (Stewart et al, 1977) along with high amorphous clay allophane content ($70% of the clay fraction) (Russell et al, 1981). The presence of iron oxide pans is an additional characteristic feature of the Egmont andisols (Childs et al, 1990).…”

Towards a climate event stratigraphy for New Zealand over the past 30 000 years (NZ‐INTIMATE project)

“…Quartz in soils derived from basaltic and andesitic tephras has been demonstrated to be of aeolian origin (Mokma et al, 1972;Stewart et al, 1977Stewart et al, , 1986. Variations in the total quartz content and accumulation rate of quartz within well-dated andesitic soils (Andisols) at Taranaki on western North Island provide a proxy record of climate that has been linked with deep-sea and ice-core records of atmospherically transported sediment (Alloway et al, 1992a).…”