ABSTRACT

An unusual sediment accumulation in the glaciogene Permian near Bacchus Marsh, Victoria is interpreted as representing the development and infilling of a subglacial channel. This polymictic conglomerate has a thickness of more than 50 m and rests within glacial and periglacial Permian strata. Clasts are as large as 5 m in diameter and can be related to adjacent strata from which they were derived. The stratigraphy within the polymictic conglomerate indicates four phases in the development of the feature: 1) dominantly vertical erosion (about 45 m) with the bottom 15 m filled in with clasts derived from units which form the channel walls, 2) widening and infilling of the lower half of the channel, 3) widening and infilling of the upper half of the channel with large boulders jamming th top of the gulley, and 4) finally the completion of the infilling with a sandy ablation till accumulating over the adjacent land surface. This deep, steep-walled channel was cut very rapidly by discharging glacial meltwater.