Profile descriptions of Quaternary basaltic volcanogenic soils of the Mount Gambier area, southeast South Australia

The volcanoes of southeast South Australia form the western extension of the Newer Volcanics province of Victoria, and comprise two distinct groups: a northern Pleistocene group of 15 eruption centres in the Mount Burr range, and a southern Holocene group of two isolated eruption centres at Mounts Gambier and Schank (Fig. 1). All the volcanoes are basaltic and are formed predominantly of explosively-erupted fragmental (pyroclastic) products including ash, lapilli, and scoria; lava is less common and is rarely soil-forming (Irving & Green, 1976; Sheard, 1978; 1983a, b; 1986; 1990). Mounts Gambier and Schank are aged about 4000-5000 years old and are the youngest volcanoes on the Australian mainland (Fig. 2) (Barton & McElhinny, 1980; Barbetti & Sheard, 1981; Blackburn et al., 1982; Sheard, 1990). They were erupted through consolidated calcareous sands of the Bridgewater Formation, and the resultant pyroclastic deposits may contain up to 25% of non-volcanic material, chiefly limestone fragments (Sheard, 1990)