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Abstract: Permian Infilled Subglacial Gully from Bacchus Marsh Area, Previous HitVictoriaNext Hit, Australia

Richard A. Davis, Jr., C. W. Mallett

Recent investigation of a thick and narrow accumulation of polymictic conglomerate in the Permian glacial and periglacial strata from near Bacchus Marsh, Previous HitVictoriaNext Hit, has indicated that this feature represents infilling of a subglacial gully. The sediment body is 53 m thick and from 3 to 10 m wide. It is exposed on Bald Hill, 3 km northwest of Bacchus Marsh, Previous HitVictoriaTop.

The infilled gully cuts through Permian glacial and periglacial strata from which polymictic conglomerate is derived. The infilled sediment ranges from matrix to clast supported locally with clasts ranging up to 2 m in diameter. Four stages of combined erosion and deposition characterize the development of this feature which probably took place beneath an ice sheet where hydrostatic pressure was great. These stages of development are: (1) initial cutting of the steep-sided gully with some infilling of the basal 15 m from adjacent glacial till and periglacial silty sand units; (2) slight widening of the gully with much infilling from falling boulders derived from adjacent units up to 30 m above the existing gully floor; (3) collapse of large blocks from adjacent strata into the gully; 4) completion of infilling accompanied by unroofing of suprajacent tills and channel sands.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC