Selenium Content of Soil-Forming Rocks

Abstract

Low amounts of selenium occur in granites, rhyolites, rhyolitic pumices, limestones, and schists. High amounts occur in andesites (particularly ashes), Upper Cretaceous argillites, and basalts. The selenium content of soil-forming rocks averages 0 42 p.p.m. Se; this value is strongly influenced by the large areas covered by sedimentary rocks having a clay component and it is higher than an average based upon igneous rocks. Weathering processes at the soil surface result in a retention of selenium and prevent a recycling of the element via the marine environment. Tuffaceous greywackes of the Kawhia and Southland regions have selenium values that are above average for greywacke. Re-sorting of greywacke by river systems results in bouldery and sandy alluvia that are low in selenium, silt loam al1uvium and loess that are average in selenium, and clay loam al1uvium that is above average in selenium. © 1967 Taylor & Francis Group, LLC. All rights reserved.