HIGH-PRECISION U-SERIES DATING OF LAST INTERGLACIAL EVENTS BY MASS-SPECTROMETRY - HOUTMAN-ABROLHOS ISLANDS, WESTERN-AUSTRALIA

The Houtman Abrolhos Islands, situated at the western passive margin o f the Australian continent, consist of a series of shelf-edge coral re efs. The central platforms of the reefs are Late Pleistocene in age an d are generally some 3-5 m above present sea level. The uppermost part of the Last Interglacial reefs normally has an upward-shallowing sequ ence, consisting of coral framestone, coralline algal bindstone and sk eletal grainstone to rudstone. This sequence represents deposition in water depths of less than 2 m, and provides a good indicator of sea le vel. High-precision mass-spectrometric dates of corals from the Abrolh os reefs, including dates obtained from drill cores, arological, isoto pic and stratigraphic criteria are established for the selection of su itable samples for dating and for assessing the reliability of dates. Using the screened dates and the stratigraphic evidence, the timing an d character of the sea level variations of the Last Interglacial in th e Abrolhos region are examined. The data show that sea level of the La st Interglacial in the Abrolhos was 4 m below its present height by ca . 134 ka BP and probably reached about 2 m above present height at ca. 133 ka BP. The exact time at which sea level reached its peak (6 m ab ove present sea level) cannot be determined from our data. But it is c lear that the sea level high stand of the Last Interglacial lasted unt il ca. 116 ka BP and that for much of the Last Interglacial sea level at the Abrolhos was at a height of about 4 m above its present level.