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Late Quaternary sea-level highstands in the Tasman Sea: evidence from Lord Howe Island

by C.D. Woodroffe, C.V. Murray-Wallace, E.A. Bryant, B. Brooke, H. Heijnis, D.M. Price
Marine Geology ()

Abstract

Lord Howe Island, situated 600 km east of Australia, provides a unique opportunity to evaluate Late Quaternary highstands of sea level in the Tasman Sea. The mid-ocean island, which is the site of the southernmost coral reef, is composed of basalts of late Tertiary age, and calcarenites derived from bioclastic reefal carbonates. Both erosional and depositional evidence of Late Quaternary highstands of sea level is preserved. Uranium-series disequilibrium dating of coral clasts from a calcarenite beach facies at Neds Beach on the northeast of the island yielded a mean age of 136,000 yr B.P. Thermoluminescence dating of the quartz sand fraction from the same deposit, using fine-grained and coarse-grained methods, yielded ages of 138,000 and 116,000 yr B.P., respectively. These ages are interpreted to indicate that this beach unit, within which fossil bones and eggs of the extinct horned turtle, Meiolania, are found, formed during the Last Interglacial when the sea was 2-4 m above present. Benches and platforms developed on Tertiary basalt and on Late Pleistocene calcarenite on the more sheltered lagoonal shore on the west of the island indicate a sea level up to 1.5 m higher than present during the Holocene. Cemented boulder conglomerates (ca. 3000 yr B.P.) at North Head, and emergent mollusc-rich carbonate muds (ca. 900 yr B.P.) within an embayment fill at Old Settlement Beach, further support this interpretation. These palaeo-sea-level data from the Tasman Sea support previous estimates of the height of the Last Interglacial sea surface relative to eastern Australia, and supplement a growing body of evidence for a higher sea level in the region during the mid to late Holocene.

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