Origin and genesis of calcrete in the Murray Basin

Abstract

Calcretes and other terrestrial carbonate accumulations have formed throughout the Murray Basin during the Quaternary, particularly in far western regions. Ooids and grain coatings of CaCO3 by infiltrating carbonate saturated solutions indicate calcrete has formed through pedogenic processes. Based on different morphologies and spatial relationships calcretes historically have been identified as either the younger Bakara or older Ripon Calcrete. The congruence of different stratigraphic calcretes, particularly the Bakara and Ripon Calcretes, was shown by clay mineralogy and the ratio of immobile elements. Three distinct sedimentological units were differentiated through zircon/rutile ratios of the heavy mineral fraction (>2.9 g/cm3); the underlying Blanchetown Clay and two differing aeolian units including the Woorinen Formation. The strontium isotope signature in all of the calcretes and carbonate material in the profile is believed to be due to an aeolian source from a marine environment. A model of calcrete development was constructed that incorporated illuviation of carbonate saturated solutions and other pedogenic processes synchronous with an aeolian deposition of highly calcareous material.