Radiocarbon measurements and soil micromorphology as guides to the formation of gilgai at Kaniva, Victoria

Profiles from mound and depression at two apparently comparable gilgai sites provided samples for 82 radiocarbon measurements and other studies of profile variation, including micromorphology and swelling capacity. Comparable trends of apparent mean residence time (AMRT) of soil humus with depth were found for both profiles at Miram, with gradual increase to approximately 8500 years at 2 m. This contrasts with results for Lillimur, where the maximum AMRT for the mound profile is almost 6000 years but that for the depression profile is only 2000 years. Interpretation of the AMRT values is complicated by evidence of layering and the probability of a buried soil at each site. Downward movement of soil is shown by micromorphological features and by AMRT values taken in conjunction with evidence of layering. Evidence was sought on churning with a marked lateral component and on fossil gilgai, but without firm conclusions. It is probable that at both sites gilgai formation involved the upward movement of the mass of soils constituting the mound, at a time when it still retained relatively sandy top soil. Leaching of carbonate may have increased the microrelief.