SEDIMENTOLOGY OF AN UPPER CAMBRIAN TURBIDITE SUCCESSION, SMITHTON BASIN, NORTHWEST TASMANIA

Two lithofacies associations are recognized in an Upper Cambrian siliciclastic turbiditic succession occurring near the top of the Smithton Basin at Stony Point in northwestern Tasmania: a thin-bedded association of fine- or very fine-grained sandstone, siltstone and mudstone and a coarse-grained association of thick-bedded coarse- to very coarse-grained sandstone, pebbly sandstone and granule conglomerate. The rocks are considered to have been deposited within a submarine basin-floor turbidite-fan complex. The coarse-grained association is interpreted as a succession of channel-fill deposits and the thin-bedded association as overbank deposits consisting predominantly of mud turbidites. Palaeocurrents from both associations are directed toward the north and are statistically indistinguishable; it is suggested that the palaeocurrents may have run parallel to the basin axis. Petrographic data indicate that the sandstones were derived predominantly from magmatic are material from both felsic and mafic volcanoes, but that a metamorphic source similar to that currently observed in Tasmanian Precambrian terrains was a supplier of some sediment.