Holocene reef growth in Torres strait

The platform and fringing reefs of Tones Strait are morphologically similar to reefs of the northern Great Barrier Reef to dr south, except that sever al are elongated in the direction of the strong tidal currents between the Coral Sea and the Gulf of Carpentaria. Surface and subsurface investigation s and radiocarbon dating on Yam, Warraber and Hammond Islands reveal that t he initiation and mode of Holocene reef growth reflect antecedent topograph y and sea-level history. On the granitic Yam Island, fringing reefs have es tablished in some places over a Pleistocene limestone at about 6 m depth ar ound 7000 years BP. Emergent Holocene microatolls of Porites sp. indicate t hat the reefs have prograded seawards while sea level has fallen gradually from at least 0.8 m above present about 5800 years BP. On the Warraber Isla nd reef platform drilling near the centre indicated a Pleistocene limestone foundation at a depth of about 6 m over which reefs established around 670 0 years BP. Reef growth lagged behind that on Yam Island. Microatolls on th e mature reef flat indicate that the reef reached sea level around 5300 yea rs BP when the sea was around 0.8-1.0 m above present. On the reef flat on the western side of Hammond Island bedrock was encountered at 7-8 m depth, overlain by terrigenous mud. A progradational reef sequence of only 1-2 m t hickness has built seaward over these muds, as sea level has fallen over th e past 5800 years. Reef-flat progradation on these reefs is interpreted to have occurred by a series of stepwise buildouts marked by lines of microato lls parallel to the reef crest, marking individual coalescing coral heads. Detrital infill has occurred between these. This pattern of reef progradati on is consistent with the radiocarbon dating results from these reefs, and with seismic investigations on the Tones Reefs. (C) 2000 Elsevier Science B ,V. All rights reserved.