Predicted and observed Holocene sea-levels on the Australian coast: What do they indicate about hydro-isostatic models in far-field sites?

Abstract

Data relating to Holocene sea-level elevations and ages, obtained by radiocarbon dating of relict calcareous skeletons of intertidal organisms from widely spaced parts of the Australian coast, a far-field region of comparative tectonic stability, are divisible into two sets, namely: pre- and post- ca. 3600 yr BP. The older ages are from material consistently between 1.5 m and 2.2 m higher than present sea-level, whereas the younger ages (ca. 3600-1500 yr BP) generally cluster around 1 m above present sea-level. The elevations do not display any decline in amplitude from north to south over an extensive transect, contrary to predictions by hydro-isostatic models. Also, there appears to be little difference between time-elevation results for the coasts of North Queensland, New South Wales and the Bass Strait region adjacent to Tasmania, despite differences in the width of the continental shelf in these three locations, and the expectation of some hydro-isostatic warping of the continental shelf subsequent to the onset of the Holocene transgression. Results from the south and southwest coasts of Western Australia also display similar elevations to the east coast for the same time periods. There is sufficient evidence extending over 20° of latitude to suggest that north-south differences related to hydro-isostatic influence is limited or non-existent. There is insufficient data to test hydro-isostatic models across continental shelves. Hydro-isostasy, and the lithological elasticity it reflects, may not be as pronounced in far-field sites with narrow continental shelves as models predict. Stable far-field passive continental margins may be the best place to measure the ratio of inputs of eustatic and hydro-isostatic influences on Holocene relative sea-levels.