Browsing by Author "Wright, SA"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Rapid relative sea-level fall along north-eastern Australia between 1200 and 800 cal. yr BP: an appraisal of the oyster evidence
    (Elsevier, 2015-12-01) Lewis, SE; Wüst, RAJ; Webster, JM; Collins, J; Wright, SA; Jacobsen, GE
    A fast-paced post-glacial sea-level rise and subsequent mid-Holocene sea-level highstand are well documented at several far field locations away from the presence of former ice sheets but sea-level development during the late Holocene remains ambiguous. In this study, we present new data from modern and fossil oysters attached to shoreline rocks along the north-eastern Australian coastline that reveal new constraints on the nature and timing of relative sea-level change over the past 2500 yr. Surveyed elevations of various contemporary oyster zones contextualize modern oyster growth forms in relation to sea-level datum and build the reference for our fossil oyster data. Based on survey data and field observations we developed a robust set of criteria for measuring fossil oysters to determine their relative sea-level position and constrain the uncertainties associated with these reconstructions. Thick (> 10 cm) fossil oyster visors above the equivalent modern growth suggest higher relative sea-levels in the past (i.e. > 1200 cal. yr BP). Radiocarbon analyses of the modern oyster visors suggest continuous lateral accumulation over the past ~ 800 yr which implies relatively stable sea-level over this period. The modern and fossil dataset defines a distinct and rapid relative ~ 1 m sea-level fall between 1200 and 800 cal. yr BP. Whether the sea-level fall was stepped or followed a broader smooth/monotonic pattern is unclear. The timing coincides with the initiation of some inshore fringing coral reefs in the Great Barrier Reef region and other major geomorphological changes along the coastal zone. A combination of various factors may have been the driving mechanism behind this relative sea-level fall with rates between 1.0 to 5.2 mm yr− 1. © 2015, Elsevier B.V.
  • No Thumbnail Available
    Item
    Sea level change over the past 2500 years from northeastern Australia
    (Australian Geosciences Council, 2012-08-05) Lewis, SE; Wust, RAJ; Webster, JM; Collins, J; Wright, SA; Jacobsen, GE
    This study C-14 dated living and fossil oyster bed deposits (>50 cm thick) to examine when sea level fell to its present position. These thick oyster bed deposits are formed in the inter-tidal zone and are relatively long-lived features with one bed dated in this study growing for ∼1000 years. Consistent growth rates at each sampling location indicated that oyster bed accumulation over time has been continuous, although growth rates varied markedly between locations from 0.30 mm/year to 6.4 mm/year suggesting the influence of localised environmental variability in water circulation, wave exposure and boulder lithology. We will show that a rapid sea-level fall occurred between 800 and 1200 years BP where sea level fell from ∼ + 1 m to present position with rates up to 7 mm/year but no less than 2.5 mm/year. The rapid fall supports the stepped sea-level model. This rapid fall influenced the movements of indigenous people as well as coincided with the development of inshore fringing coral reefs and geomorphological changes along the coastal zone.