Uranium?series ages of coralline terrace deposits in Western Australia

Abstract

Emerged marine erosion terraces and associated terrace deposits showing various degrees of warping are preserved at Cape Range and in the Lake MacLeod‐Cape Cuvier area of Western Australia. Uranium‐series age determinations on corals occurring in the terrace deposits gave the following results: a mean age of 123 000 for the youngest of the terrace deposits (Tantabiddi Member) at Cape Range, which has a maximum elevation of 5.5 m above present sea level (MLWS); mean ages of 123 000 years and 131 000 years for deposits overlying two morphologically distinct marine erosion terraces, with elevations ranging from 3 to 7.4 m and from 9.4 to 10.5 m, respectively, at Cape Cuvier; a mean age of 128 000 years for marine deposits occurring between —0.5 and 1.3 m on the west shore of Lake MacLeod. From these data we propose that the Tantabiddi Member at Cape Range (123 000 years) and the terrace deposits in the Lake MacLeod‐Cape Cuvier area (average age = 128 000 years) were formed at the peak of the last interglacial, for which an age of 125 000 years is now generally accepted. Although the field evidence, coupled with the radiometric ages at Cape Cuvier, appears to be consistent with the notion of a bipartite rather than a single high sea stand at the peak of the last interglacial, the two sea stands inferred are so closely spaced in time that they strain the resolution of the uranium‐series method. The observation of local warping of the dated deposits argues against crustal stability along the coast of Western Australia during Late Quaternary time. However, the net emergence of the coast since the last interglacial cannot be assessed with any confidence until a more reliable determination of the 125 000 year palaeo‐sealevel datum has been made.