Depositional environments of the Triassic Gosford formation, Sydney basin

Abstract A matrix of the primary sedimentary features of modern depositional environments has been used as a key for the interpretation of the environments of deposition of the Gosford Formation, which comprises the uppermost 212 m of the Triassic Narrabeen Group on the Central Coast of New South Wales. The formation is interpreted as a fluvial deposit in in‐channel and floodplain environments. The in‐channel environments recognized include channel floor, channel bar, point bar, and abandoned channel. The floodplain environments are not so strongly differentiated but include levée, backswamp, marsh, and crevasse splay. The vertical succession of depositional environments is consistent with predictions based on accepted palaeogeographic models. The channel bar sands and associated floodplain deposits are the product of low‐sinuosity low‐braiding streams. The point bar sequences and their associated floodplain deposits were formed by streams of greater sinuosity. The Gosford Formation is probably the distal equivalent of the Hawkesbury Sandstone.