TIMING AND DURATION OF THE LAST INTERGLACIAL - EVIDENCE FOR A RESTRICTED INTERVAL OF WIDESPREAD CORAL-REEF GROWTH

We report new mass spectrometric U-series ages for eight Last Intergla cial fossil reefs along the continental margin of Western Australia. C orals were selected in growth position from localities that are charac terized by apparently low levels of diagenesis and relative tectonic s tability so that the fossil reefs provide critical information on Last Interglacial sea-levels without requiring corrections for tectonic mo vements. In addition, we have improved the constraint on the timing of onset of reef growth by recovering drill core coral from the base of the reefs. Uranium and thorium isotopes were measured with high levels of precision, leading to improvements in age resolution and allowing samples which have undergone diagenetic exchange of uranium and thoriu m to be more easily identified and discarded. These data supplement ou r previous results for Rottnest Island and Leander Point, leading to m ore than seventy mass spectrometric U-series ages from which constrain ts can be placed on the timing, duration and character of the Last Int erglacial sea-level highstand. Reliable ages show that reef growth sta rted contemporaneously at 128 +/- 1 ka along the entire Western Austra lian coastline, while relative sea-levels were at least 3 m above the present level. Because Western Australia is located far from the forme r Penultimate Glacial Maximum ice sheets and are not significantly eff ected by glacial unloading, these data constrain the timing of onset o f the Last Interglacial period to 128 +/- 1 ka, assuming reef growth s tarted soon after sea-level approached interglacial levels. A unique r egressive reef sequence at Mangrove Bay constrains the timing of termi nation of the Last Interglacial period to 116 +/- 1 ka, The major epis ode of reef building, however, both globally and locally along the Wes tern Australian coast, is restricted to a very narrow interval occurri ng from similar to 128 ka and similar to 121 ka, suggesting that globa l ocean surface temperatures were warm and/or sea-levels were stable e nough to allow prolific reef growth only during the earlier part of th e Last Interglacial. (C) 1998 Elsevier Science B.V. All rights reserve d.