Development of a Terra Rossa soil profile on marbles of the Cambrian Normanville Group at Delamere, South Australia

Abstract

The genesis of Terra Rossa soils is still a matter of controversy. The two leading theories are: (1) that the soil is derived from the insoluble residue of the underlying limestone; or, (2) that contributions from some outside source account for large portions of the soil. Through morphological, analytical and mineralogical studies of a Terra Rossa soil profile at Delamere, South Australia, the insoluble residue of the underlying dolomite and a texture contrast profile from upslope, the major contributors to the soil’s development were determined. Also, field emission scanning electron microscopy (FESEM) of the coarse sand fraction was employed to determine the origin of coarse quartz grains in the soils. The Terra Rossa was discovered to be receiving considerable contributions from upslope via creep and/or colluvial movement, a feature that was most apparent in the upper horizons of the profile. The deeper horizons, however, appear to be largely derived from the insoluble residue of the dolomite, indicated by the mineralogy, particle size distribution, micromorphology and quartz grain morphology.