Origin of quartz in selected soils and sediments, North Island, New Zealand

Abstract

Quartz from two marine shales has δ¹⁸O values indicative of low-temperature crystallisation. In a Mangakahia Group shale, the lowtemperature quartz is confined to the silt fraction and is a result of diagenesis; in the Whangai Shale, it occurs as clastic chert in a range of grain sizes. Quartz in soils formed from andesitic and basaltic parent materials is of eolian rather than pedogenic origin. However, quartz in the sand fractions of soils formed from a range of parent materials, including volcanic, has a δ^I8O value indicative of high-temperature formation and was probably a component of rhyolitic tephras from central North Island. Similar δ¹⁸O values for quartz in beach sands from the west coast of Northland indicate a predominantly rhyolitic source, and higher δ¹⁸O values of quartz in east coast beach sands indicates the presence of additional locally derived sediment. Only one example of low-temperature quartz was found in the soils investigated but this was found to be of eolian origin. Quartz from albic horizons of three podzols had δ^I8O values which clearly indicated that the quartz was not of pedogenic origin.

Keywords:

• quartz
• oxygen
• isotopes
• soils
• sediments
• genesis
• podzols