U-series ages measured by thermal ionisation mass spectrometry (TIMS) are reported for a LI (=Last Interglacial) fossil coral core from the Turtle Bay, Houtman Abrolhos Islands, West Australia. The core is about 33.4 m long of which are about 4 m a.p.s.l. (=above present sea level). From the 232Th concentrations and the reliability of the U-series ages two core sections can be distinguished. Calculated U/Th ages in core section I (3.3 m a.p.s.l to 11 m b.p.s.l) vary between 124±1.7 ka (m a.p.s.l.) and 132.5±1.8 ka
(m b.p.s.l.), respectively, and those of section II (11 to 23
m b.p.s.l.) between 140±3 ka and 214±5 ka, respectively. The ages of core section I are in almost perfect chronological order whereas for section II no clear age-depth relationship of the samples can be recognised. Further assessments applying the 234U(T) criteria reveal that none of the samples of core section II give reliable ages whereas for core section I several samples can be considered as to be reliable at least within 2 ka. However, we recognise that even samples which were considered to be unreliable are following the correct chronological order. Therefore we conclude that the 234U(T) criteria is necessary but not sufficient to all samples and do not allow robust constraints on the reliability of U/Th ages. Thus, the only logically consistent criteria available for the Turtle Bay core is the correct chronological order within the core. The data of the Turtle Bay core compend and extend our previous work (Zhu et al., 1993) from the Houtman Abrolhos showing that the sea level reached a height of about 4 m b.p.s.l at about 134 ka B.P. (=Before Present) and a sea level heighstand of at least 3.3 m a.p.s.l. at about 124 ka B.P.. Sea level dropped below its present position at about 116 ka B.P.. A detailed comparison reveals considerable differences between the Holocene (Eisenhauer et al., 1993) and LI sea level rise as monitored relative to the Houtman Abrolhos Islands. These observation put further evidence to the ongrowing set of data that the LI sea level rise started earlier and persisted longer (about 13±2 ka) than recognised by the Milankovitch theory of climate change. However, a strict screening of all U-series ages (TIMS) available for LI corals on a global scale reveals that only a few provide reliable U-series ages according to the 234U(T) criteria. Thus, we yet do not argue that our data provide robust constraints on the limits of the LI sea level rise until better criteria are available which may provide final verification of the U/Th ages.
Eisenhauer, A., Wasserburg, G.J. , Chen, J.H., Bonani, G., Collins, L.B., Zhu, Z.R., & Wyrwoll, K.H., Earth Planet. Sci. Lett. 114, 529-547 (1993).
Zhu, Z.R., Wyrwoll, K.-H., Collins, L.B., Chen, J.H., Wasserburg, G.J. & Eisenhauer, A., Earth Planet. Sci. Lett. 118, 281-293 (1993).