Source of food items in an Aboriginal midden at Little Dip, near Robe, southeastern South Australia: implications for coastal geomorphic change

At Nora Creina Bay, in southeastern South Australia, fossil shell of the in tertidal mollusc Katelysia scalarina from outcropping sediment yielded a ra diocarbon age of 5600+/-140 y cal BP. The presence of intertidal sandflat s ediments of this age, preserved in an open ocean coastal setting, implies t hat the western, mostly eroded side of Robe Range once sheltered quiet wate r embayments with intertidal sandflats. Radiocarbon ages for fossil mollusc s from marine sediments landwards of Robe Range reveal that autochthonous d eposition rook place within an extensive Holocene coastal back-barrier lago on environment from approximately 5500-4000 y BP. It was originally propose d that the shells of Katelysia cockles, gathered by Aboriginal people and n ow preserved within the archaeostratigraphic Early Horizon midden at Little Dip, had originated in this back-barrier lagoon. As the Katelysia sp. shel l from the Early Horizon midden is more than 3000 y older than Katelysia sp p. from the nearby autochthonous lagoonal sediments (e.g. at Fresh Dip Lake ), it now seems that the cockles were harvested from intertidal sandflat en vironments on the seaward side of Little Dip, probably before marine incurs ion into the low lying land behind Robe Range. These sandflats were ephemer al features, eroded as the protective outer margin of Robe Range was also r educed by the erosive force of the Southern Ocean to a linear array of smal l islands and sea stacks that characterise the present coastline.