Pre-Devonian stratigraphy and structure of the Prion Beach-Rocky Boat Inlet-Osmiridium Beach coastal section, southern Tasmania

Abstract

The pre-Devonian stratigraphy of the Prion Beach to Surprise Bay area is composed of four stratigraphic units. The oldest is a (?) Precambrian, slightly metamorphosed, massive dolomite. This is in part the source area for three overlying units of the Denison Group (Late Cambrian to Early Ordovician). The Tyler Creek Beds are highly serpentinitic conglomerate, sandstone and siltstone. The Point Vivian Formation is a sequence of dolomitic siltstone and matrix rich polymictic conglomerates with a wide range of depositional features including channels, graded bedding and slump structures. It was probably deposited in a slope environment. The overlying Wierah Formation (Denison Group) is composed of quartz-rich pebbly sandstones and quartz arenites which formed in a high energy environment possibly above wave base. Two shear zones cut across this stratigraphy producing transposed layers and boudins. At least one of these shear zones was active during sedimentation and forms the western limit of the Point Vivian Formation in this area.