Aminostratigraphy and electron-spin-resonance dating of Quaternary coastal neotectonism in Tasmania and the Bass Strait islands

Tasmania and the Bass Strait islands (King and Hinders) preserve a widespread but fragmentary Quaternary coastal record. Quaternary coastal sediments occur in a range of morphostratigraphic settings, typically contain well-preserved and diverse molluscan fossil assemblages of shallow water origin, and provide evidence for varying degrees of neotectonic uplift over contrasting temporal and spatial scales. Holocene and Late Pleistocene (last interglacial) coastal strata occur most extensively in this region, as revealed by amino acid racemization, electron spin resonance and radiocarbon dating. Radiocarbon dates for marine molluscs from Holocene coastal strata range between 790 to 7120 a and relate specifically to the interval since the culmination of the post-glacial marine transgression. Holocene coastal sediments in this region do not provide convincing evidence for a higher sea level during the last 7000 years. The last interglacial coastal sediments in Tasmania represent the highest topographic occurrences of coastal strata of this age on the Australian continent (+11 to +32 m above present sea-level) and consistently occur above the de facto global ‘eustatic’ sea level datum of +6 m for oxygen isotope substage 5e. Thus, tectonic processes must be considered for their anomalously high elevation. In contrast, sediments of last interglacial age on King Island and Hinders Island do not provide evidence for uplift. Neotectonic uplift is indicated, however, by the elevation of Early and Middle Pleistocene coastal strata in this region. A southerly migration in the locus of neotectonic uplift is suggested, such that uplift occurred earlier in the Bass Strait islands than in Tasmania. The nature and precise timing of neotectonic uplift remain unresolved. © 1995, Taylor and Francis Group, LLC.