The Holocene evolution of Rheban Spit, Tasmania. Age structure, geomorphic development and sediment characteristics

Rheban Spit is a small prograded sand barrier located on the east coast of Tasmania in the lee of Maria Island. It consists of four disconformable sets of beach ridges. Shallow drilling at seven sites towards the eastern end of the spit yielded sediment samples formineralogic and granulometric analyses and detrital shell for radiocarbon dating. The latter indicates that the three oldest sets of ridges were formed about 5500,4200 and 3 100 calendar years ago, the youngest set is known to have formed this century.<br>This age structure is unusual for a coastal barrier in eastern Australia because most started to prograde at the end of the Postglacial Marine Transgression (c. 7000 calendar years ago) and ceased about 2000 years ago. Rheban Spit has been severely eroded by northeasterly waves during its formation, probably as a result of periods of increased storminess in the Tasman Sea. If the sand isthmus between north and south Maria Island was also removed during these episodes, wave refraction/ diffraction and sediment movement patterns near the eastern end of Rheban Spit would have changed significantly and this may account for the disconformable nature of the successive sets of beach ridges which form the spit.