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

Abstract

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.

Radiocarbon Age of Vertisols and Its Interpretation Using Data on Gilgai Complex in the North Caucasus

“…For example, the 14 C data of the Bkss horizon changes from 5610 ± 180 BP on the microhigh to 3720 ± 180 BP in the microslope and to 3170 ± 110 BP in the microlow. A similar trend of 14 C age of humus in soils of microlows when compared with gilgai microhighs was noticed in Australia (Scharpenseel and Pietig 1973b;Blackburn et al 1979).…”

“…Later, investigations of Yaalon and Kalmar (1978), Wilding and Tessier (1988) have shown the priority of shear planes formation under pedoturbation. It was shown by profile distribution of physico-chemical and morphological properties (Wilding et al 1990), as well as by radiocarbon dating (Yaalon and Kalmar 1978;Blackburn et al 1979). Also, in case of a gilgai microrelief a strong spatial differentiation was found (Beckmann et al 1970;Wilding et al 1990; Kovda et al 1992).…”

Hamburg University Radiocarbon Dates III

“…Samples of all four profiles coll and subm 1977 by G D Hubble, CSIRO, Cunningham Lab, St Lucia, Queensland. Vertisol dates comply quite well with former Australian Vertisol profile dates from Caniva dist, Victoria (R, v 15, p 258-263), which were interpreted with help of conventional analysis and micromorphology data (Blackburn, Sleeman, & Scharpenseel, 1979). Dates will be used for soil organic matter decomposition model, which attempts to integrate fast exponential and slower steady-state decomposition phases.…”

Carbon Dynamics in Vertisols as Revealed by High-Resolution Sampling

“…Characteristic evidence for this pedoturbation are stress cutanes ("slickensides") found on aggregate surfaces below the zone of the cracks which are formed by the shear forces. Under certain circumstances, pedoturbation in Vertisols also leads to lateral inhomogeneity with elevated and depressed areas, a micro-relief called Gilgai after an Australian aborigines term (Blackburn et al 1979;Kovda et al 2001). In the soils studied here, however, no Gilgai phenomenon was observed.…”