Terrigenous sediments as influences upon Holocene nearshore coral reefs, central Great Barrier Reef, Australia

Sedimentary studies of inner shelf reefs on the Great Barrier Reef shelf in creasingly reveal evidence for coral growth in turbid, shallow coastal envi ronments, where coral survival is aided by prevailing hydrodynamic and sedi mentological conditions. New models of coral reef growth on the Great Barri er Reef are needed which explicitly include the role of terrigenous sedimen ts in influencing sites of potential reef initiation and conditions of grow th. We outline potential interrelationships of sediment dynamics, terrigeno us sedimentation and coral reef growth on the Great Barrier Reef over the l ast 9000 years, by integrating measurements of hydrodynamic and sedimentary processes at inner shelf coral reefs near Townsville, with an assembled da taset of 324 radiocarbon-dated corals. In Halifax Bay, 'coastal turbid-zone reefs' occur in water less than similar to 4 m deep, where coastal turbidi ty is high, sometimes over 100 NTU (nephelometric turbidity units) as a res ult of wave-induced resuspension, and wind-driven longshore currents preven t accumulation of fine-grained sediment. Net accumulation of sediments at t hese sites over the last 5500 years has been less than 1 m. A model of mid- and inner shelf evolution is presented, which describes a suite of potenti al conditions and sites of reef initiation on the central Great Barrier Ree f, related to coastal geomorphology and the resulting sedimentary regime un der a rising sea-level. We distinguish progradational, erosional and indent ed island coastlines, which, by virtue of their likely sedimentary characte r, may have distinct patterns of coral reef growth in time and space. At so me stages during the transgression, the presence of inner shelf sediment we dges may have delayed initiation of nearshore reefs for a period of a few c enturies.