Holocene heavy mineral assemblages in a coastal compartment in eastern Australia

Heavy minerals along the east coast of Australia form part of a northward transport pathway that moves sediment from southern New South Wales to Queensland, Australia. The proportion and occurrence of heavy minerals from non-local source rocks reflect reworking of quartz sand from the outer-shelf to the inner-shelf and coastal environments during the post-glacial marine transgression. The northward transport system is disrupted by a prominent headland to preserve a locally derived pyroxene-rich heavy mineral suite in the Kiama coastal compartment. The heavy mineral assemblage indicates derivation from multiple Neoproterozoic and Palaeozoic sources in southern Australia and possibly Antarctica, including the Lachlan Fold Belt and Sydney Basin in southeastern Australia. The common pyroxene was derived locally from coastal Permian latite units in the Sydney Basin, Mesozoic tinguaites and the Eocene Robertson Basalt. Five identified mineralogical facies are controlled by spatial variability of heavy mineral assemblages rather than the textural characteristics of the sediment. The upper river facies is dominated by catchment-derived augite. The Minnamurra spit and back-barrier facies has the highest heavy mineral content with abundant ultrastable and metastable minerals consistent with their accumulation as prograding coastal barriers. The two high-energy sand-dominated inner-shelf facies contain a mix of ultrastable and metastable heavy minerals with pyroxene being more common in the inner zone while zircon, rutile, garnet, epidote, andalusite and monazite/apatite are more common in the outer zone where they are affected by the regional northward sand migration. The low-energy mid-shelf facies (depth >55 m) is finer grained and contains the highest proportion of micaceous minerals and hornblende. The adjacent probable tsunami sandsheets at Dunmore have very similar heavy mineral signatures to the coastal barrier and inner shelf deposits and were probably derived from them.