Palaeoshorelines on the Australian continental shelf: Morphology, sea-level relationship and applications to environmental management and archaeology

Palaeoshorelines that lie submerged on stable continental shelves are relict coastal depositional and erosional structures formed during periods of lower sea level. An analysis of the well-dated Late Quaternary (0-128 ka) sea-level record indicates that the most persistent (modal) lower sea levels were at 30 - 40 m below present, which occurred between 97 and 116 ka and at approximately 85 ka and 10 ka. A secondary modal position was at 70-90 m that occurred mostly during a period of fluctuating sea level between 30 and 60 ka, as well as at around 87 ka (70 - 80 m only) and 12−15 ka. For the tectonically stable Australian continental shelf, we show that a range of shorelines formed at each of these sea level modal positions and their morphology and degree of preservation depends on composition (carbonate vs siliciclastic) and oceanographic setting (wave, tide and wind energy). These ancient coasts record a range of oceanographic and geological regimes that existed during relatively long periods of lower sea level and provide a guide to the general depth zones in which similar features likely occur on other shelves globally. Australian palaeoshorelines represent distinctive benthic habitats that strongly influence the distribution of biodiversity across the shelf. Accurate mapping of these features provides a robust geospatial framework for investigations of marine species distributions and environmental change monitoring. These data also enable the better targeting of relict coastal areas that potentially include sand resources and sites of human occupation during periods of lower sea level.