Quaternary aminostratigraphy of eolianite on Lord Howe Island, Southwest Pacific Ocean

Abstract

Amino acid racemization (AAR) dating of the eolianite on Lord Howe Island is used to correlate several disparate successions and provides a geochronological framework that ranges from Holocene to Middle Pleistocene time. The reliability of the AAR data is assessed by analysing multiple samples from individual lithostratigraphic units, checking the stratigraphic order of the D/L ratios and the consistency of the relative extents of racemization for a suite of seven amino acids. Three aminozones are defined on the basis of the extent of racemization of amino acids in land snails ( Placostylus bivaricosus) and ‘whole-rock’ eolianite samples. Aminozone A includes Placostylus from modern soil horizons (e.g. mean D/L-leucine ratio of 0.03±0.01) and whole-rock samples from unconsolidated lagoonal and beach deposits (0.10±0.01–0.07±0.03). Aminozone B includes Placostylus (0.45±0.03) and whole-rock samples from beach (0.48±0.01) and dune (0.45±0.02–0.30±0.02) units of the Neds Beach Formation, deposited during OIS 5. The oldest, Aminozone C, comprises Placostylus recovered from paleosols (0.76±0.02) and whole-rock eolianite samples (0.62±0.00) from the Searles Point Formation, which indicate the formation was likely deposited over several Oxygen Isotope Stages (OIS), during and prior to OIS 7. These data support independent lithostratigraphic interpretations and are in broad agreement with U/Th ages of speleothems from the Searles Point Formation and corals from the Neds Beach Formation, and with several TL ages of dune units in both formations. The AAR data reveal that eolianite deposition extends over a significantly longer time interval than previously appreciated and indicate that the deposition of the large dune units is linked to periods of relatively high sea level.