The South Australia Coast and Holocene Sea-Level Transgression

Abstract

Along the South Australia coast sea level has been relatively stable since 6.5 ka B.P. Tides are generally <1 m, and sediments are predominantly shelf- and shoreface-derived carbonate detritus. Deepwater wave height is persistently moderate to high, although breaker-wave height is highly variable along the coast. Shoreface barriers range from low-energy prograding tidal flats, cheniers, and beach and foredune ridges through moderate-to-high-energy prograding-to-recessive systems of foredune-ridge pro- gradation to high-energy barriers, consisting of massive mobile dunes. Breaker-wave regime dominates location, nature, and evolution of shoreface type by influencing sediment supply and morphodynamics. ing and since the postglacial marine transgression (PMT) to provide sediment for the formation of substantial barrier-dune systems along most of the -2,000-km open coast. Because of the semiarid climate, rivers and sediments derived from them are minimal. On the high-energy open coast, shorefaces have evolved in response to sediment supply, large waves, and strong on- shore winds. At the same time protection from ocean waves in Spencer Gulf and Gulf Saint Vincent, as well as local wave attenuation and coastal con- figuration, affords a range of moderate- and low-energy sandy shoreface types. Because the entire length of the South Australia coast has essentially the same sea-level history, the area provides an ideal natural laboratory in which to examine the response of this high-energy, extremely variable coast to the PMT and the subsequent stillstand. The purpose of this article is to present seven types of sandy shoreface-barrier evolution that are representative of the low-, moderate-, and high-wave-energy sections of the coast and to discuss the implications for Holocene shoreline evolution. The Quaternary sea-level history of southern Australia is well preserved by the gentle volcanic-induced upwarp in southeastern South Australia. This uplift has resulted in the preservation of a series of more than twenty cal-