SEA-LEVEL CONTROL OF STACKED LATE QUATERNARY COASTAL SEQUENCES, CENTRAL GREAT-BARRIER-REEF

Lithofacies analysis, pollen assemblages and radiocarbon age dates of 20 stratigraphic drill holes are used to develop an evolutionary histo ry for late Quaternary sedimentation in two coastal embayments landwar d of the central Great Barrier Reef. Different physiographic settings of the embayments result in two contrasting styles of sedimentary sequ ence: (a) an exposed, moderate energy, beach barrier-lagoon system (Wy vuri Embayment) and (b) a protected, low energy, muddy inlet fill sequ ence (Mutchero Inlet). Despite sharp contrast in sequence style, simil ar depositional cycles occur in both embayments in response to late Qu aternary sea level fluctuations including: (1) a last interglacial hig hstand (+2 m; c. 125 000 yr BP) beach barrier (Wyvuri); (2) an early t o mid-Holocene (8000-6100 yr BP) transgressive beach barrier-lagoon (W yvuri) and estuarine infill (Mutchero); and (3) mid-Holocene to presen t highstand beach barrier (Wyvuri) and estuarine (Mutchero) progradati on. Preservation of such cycles in the stratigraphic record would prod uce a series of vertically stacked and offset linear barrier sands sur rounded by lagoonal mud and fine grained shoreface sediment juxtaposed to muddy, estuarine infills. Sea level elevations are well recorded b y the upward transition from Rhizophora-dominated intertidal mangrove mud to freshwater swamps (clearly identified by pollen analysis) and b y the basal contacts of beach barrier sediments which sharply overlie the upper shoreface. Transgressive sedimentation is interrupted in bot h embayments by a constructional beach barrier (Wyvuri) and abbreviate d progradation (Mutchero) corresponding to a -5 m pause in relative se a level rise at c. 6800 yr BP. Sea level control of fine scale coastal sedimentation patterns is beginning to be widely recognized and provi des an accurate analogue for stacked ancient sequences.