Surface lagoonal sediments on Lord Howe Island, Tasman Sea

Abstract

The lagoon on Lord Howe Island is enclosed by the southernmost coral reef in the world. The lagoon is on average 1.5 m deep and 2 km wide. Five distinct biogeological zones occur being; bare sand (65% of the lagoon area), lagoonal coral zone, gravel sheet, algal flats and patch reefs. Sedimentological studies of the surficial sediments on the lagoon floor indicate a high-energy environment where the sand and gravel is continually reworked by waves and tides. Medium-coarse sand dominates being comprised of coralline algae and micritized grains. Coral, formaminifera and molluscs are minor constituents with Halimeda being virtually absent. There is very little relation between the distribution of grain types and biogeological zonation.