Holocene lagoonal sedimentation at the latitudinal limits of reef growth, Lord Howe Island, Tasman Sea

The southernmost limit to coral reef growth occurs on Lord Howe Island (33 degrees 30'S, 159 degrees 05'E) where a discontinuous fringing reef hanks t he western side of the island. Goring and radiocarbon dating indicate that carbonate sediments were first deposited within the lagoon around 6500 radi ocarbon years BP coincident with sea level reaching close to its modern lev el. High-energy conditions dominated the reef with robust branching corals dominating the developing reef. Growth of the reef crest between 6000 and 5 000 yr BP is inferred to have caused a reduction in the energy conditions w ithin the lagoon resulting in mud deposition. During this period, sedimenta tion occurred at average rates of around 5 mm/yr, though locally up to 10 m m/yr, which infilled almost all the available accommodation space in the la goon. By 3000 yr BP most of the lagoon had accreted to a level very close t o the modern lagoon floor having accumulated over 11 m of sediment in the n orthern part of the lagoon and possibly up to 30 m in the south. Sediments younger than 3000 yr BP form a thin veneer over these older units with the main deposition being confined to embayments, the coastal plain and the inf illing of blue-hole depressions. The reef and lagoon fringing Lord Howe Isl and appear to have developed their present form primarily during a phase of luxuriant growth in the mid-Holocene. (C) 2000 Elsevier Science B.V. All r ights reserved.