Mass-movement phenomena in an upper carboniferous greywacke-argillite sequence in North-Eastern New South Wales

Abstract

Thick slump breccias, interbedded with greywackes and argillites, are well exposed in shore platforms and cliffs at Halliday's Point, 230 km north of Sydney. They are unusual in two respects. Firstly, they were formed by submarine slumping of marine sediments initially deposited by turbidity currents and pelagic sedimentation. The slumping was initiated by minor tilting of the sea floor perhaps brought about by faulting or by volcanic activity. Secondly, it was the coarse sandy layers which proved the more unstable lithology and which failed by viscous fluid flow. The finer grained interbedded layers in the slump mass fractured and remained as blocks and slabs, some large in size, in a matrix of coarser sediment. The rocks at Halliday's Point were derived predominantly from a volcanic source. Measurement of slump folds suggests emplacement of the breccias from a north-easterly direction.