Genesis of red and dark brown soils on basaltic parent materials near Armidale, N.S.W., Australia

Abstract

Morphological, physical, chemical and mineralogical data are presented for contiguous euchrozem (nitosols) and chocolate soils (cambisols) developed on basaltic parent materials in the Armidale district of northern New South Wales. The genesis and distribution of the different soils classified at great soil group and series level are related to parent material and topography. The dark brown chocolate soils associated with the modern surface overlie a uniform parent material of partly weathered alkali-olivine basalt. The red euchrozem soils, although having morphological and mineralogical properties associated with intensive weathering and long term soil genesis, have also developed on the modern surface under a moderate leaching regime. They are derived from re-exposed, highly weathered, sesquioxidic, interbasaltic lapilli tuffs and underlying basalt which were probably transformed under a different climate in Pliocene—Pleistocene times. The study showed further that reddish chocolate soils are not necessarily the uppermost member of a sequence of soils developed on partly weathered basalt.