Mid- to late-Holocene sea-level change in the northern Whitsundays Queensland

Abstract

Relic fixed intertidal biological indicators (FIBIs), in the form of calcareous tubeworms, barnacles and oysters have previously been used to identify former sea-levels for the south west and south east Australian coast and North Queensland. In this study, sub fossil assemblages of oyster and barnacle species preserved in growth position on Hook Island and Cape Gloucester, in the northern Whitsundays, provide evidence of higher than present mid to late Holocene sea-level. While evidence from relic oysters, fossil microatolls and raised beachrock has previously suggested higher than present sea-levels for the nearby Edgecumbe Bay and Bowen region, evidence of elevation from the Whitsunday Islands is sparse. Here we present the first Holocene sea-level time-elevation data recorded for Hook Island. Models of predicted hydro-isostatic rebound, along with previous radiocarbon dates from emerged fossil microatolls in North Queensland, have been used to propose a higher relative sea-level in the mid Holocene with a linear fall to present. However, time-elevation data obtained from the northern Whitsunday region appears to support an oscillating model of higher than present mid to late Holocene sea-level previously identified for the areas to the north of this region and from south-east and south-west Australia. As an understanding of present intertidal zonation and the environmental requirements of sessile marker species is essential to FIBI methodology we are undertaking extensive surveys of the current rocky shore intertidal zonation at each location. This knowledge enables a more precise interpretation of the biological associations represented within the sub fossil assemblages and therefore a better understanding of palaeo environmental conditions and change.