Parent material uniformity and degree of weathering in a soil chronosequence, northwestern Italy

Abstract

The uniformity of the parent material and degree of weathering of the soils of a chronosequence developed during the Pleistocene were investigated using optical microscopy, X-ray fluorescence and scanning electron microscopy (SEM) techniques. Uniformity of the parent material was assessed by two criteria: the ratios of resistant minerals, and their specific elements, in the heavy fraction (S.G. > 2.96 g · cm −3). There was some variation between heavy mineral ratios but there was less variation between ratios from the chemical data, and on this basis it was concluded that the parent material of each of the three soils in the sequence was uniform. SEM examination confirmed that the resistant minerals had remained unaltered although some Ti-bearing minerals showed some alteration. The degree of chemical weathering, as expressed by the ratio of mobile to non-mobile elements, and by Parker's Index, increased from the youngest to the oldest soil.