Honours Thesis Abstract
THE AGE AND ORIGIN OF TERRA ROSSA SOILS
IN THE COONAWARRA REGION OF SOUTH AUSTRALIA
Aija C. Mee
Flinders University, SA
2001 AIG Honours Bursary Winner
The origin of Terra Rossa soils in the Mediterranean is a matter of controversy and has
been addressed by a number of studies. Many strongly suggest that the Terra Rossa soils
contain a significant percentage of aeolian material, as opposed to being simply an
accumulation of insoluble constituents from the underlying limestone. The study
presented here supports the concept of an aeolian origin for Terra Rossa soils in the
Coonawarra region of South Australia by providing evidence both against the residual
origin theory and for an aeolian accumulation.
Burial dates obtained by optically stimulated luminescence dating of a Terra Rossa
profile within the Coonawarra region suggest that the soil has been present in its current
location for at least 100ka. The low percentages of insoluble residue in the limestone
underlying the Terra Rossa mean that the dissolution and weathering of huge
thicknesses of the calcareous material would be necessary to produce the observed soil
profiles. Considering the stability of the landscape in southeast South Australia over the
last 800ka this amount of limestone dissolution is unfeasible, therefore implying an
alternative source of soil parent material. Analysis of strontium isotopes, clay
mineralogy and Ti/Zr ratios indicate that the Terra Rossa soil and the insoluble
limestone residue are genetically different, therefore providing further evidence against
the theory of a residual origin for the Terra Rossa soils.
The very strong degree of weathering implied by mass balance calculations using the
insoluble limestone residuum as the parent material does not match the moderate degree
of weathering suggested by the clay mineralogy (smectite clays and a low percentage of
iron-oxides) in the main soil profile. Using an aeolian lunette sample from the nearby
active Bool Lagoon system as an alternative parent material, mass balance calculations
imply an extent of weathering much more akin to that suggested by the clay mineralogy.