Chapter 21 - Vertic Features

Abstract

Vertic features result from shrink-swell processes, vertical mixing and lateral shearing, in swelling clay materials under alternating wet and dry conditions. They are recognised in Vertisols and vertic subgroups of other soils, from boreal to tropical environments. Vertic features are very prominent and easily identifiable in thin sections. The most relevant are striated b-fabrics, an open porphyric c/f-related distribution pattern, a blocky microstructure, a heterogeneous groundmass with incorporated dark aggregates, Fe/Mn oxide pedofeatures and, in more arid regions, carbonate and/or gypsum pedofeatures. Good indicators for the recognition of soils with vertic behaviour include the presence of surface-derived granular aggregates preserved in deep cracks or as part of a heterogeneous groundmass, as well as the occurrence of striated b-fabrics and abundant complex disorthic nodules. Diagnostic vertic features are well preserved and easily identifiable in palaeosoils.