Browsing by Author "Lewis, SE"

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    Development of an inshore fringing coral reef using textural, compositional and stratigraphic data from Magnetic Island, Great Barrier Reef, Australia
    (Elsevier, 2012-03-01) Lewis, SE; Wüst, RAJ; Webster, JM; Shields, GA; Renema, W; Lough, JM; Jacobsen, GE
    The stratigraphy of fringing coral reef environments and platforms provides unique insights into reef development and evolution. This study used twelve sediment cores from three transects across a reef flat in Nelly Bay, Magnetic Island (NE Australia), to examine its development over the Holocene. The maximum thickness of the Holocene reefal material based on seismic and bore log data was around 5 m and comparable to other fringing reefs in the Great Barrier Reef (GBR). Six different sedimentary facies were identified in the cores and two coincided with reef accretion: the lower muddy sand with coral rubble and the upper siliciclastic sand with coral rubble. Radiocarbon and U-series dates show that the Nelly Bay fringing reef initiated around 6300 yr BP on a gently sloping, unconsolidated or weakly cemented Pleistocene alluvial sedimentary facies. The ages of four massive coral heads (range between 5790 and 6290 calibrated C-14 yr BP) were almost contemporaneous with reefal initiation indicating that conditions were favourable for reef growth around this time. Vertical accretion rates for the Nelly Bay fringing reef were, on average about 0.5 mm/yr over the last 6000 yr, although rates were as high as 5 mm/yr during initiation. Average lateral accretion rates varied from 98 to 120 mm/yr, which are comparable to rates of other fringing reefs in the region. The age structure of the lower muddy sedimentary facies was consistent with the classic seaward prograding model of fringing reef development. In contrast, the upper siliciclastic sand with coral rubble facies was much younger in age (< 1100 yr BP) than the models and appears to represent an erosional unconformity between the upper and lower reefal facies possibly linked to late Holocene sea-level fall. This younger facies extends laterally across the reef flat and has no obvious prograding symmetry. Our integrated approach, using multi-proxy analyses of sediment cores from the Nelly Bay reef flat, highlights the complex development of this reef which include changes in coral composition and rubble preservation, reef evolution in response to sea-level change and changes in reef accretion rates. (C) 2012 Elsevier Ltd.
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    The implications of a relative sea-level fall along eastern Australia between 1200 and 800 Years BP.
    (Asia Oceania Geosciences Society Brisbane, 2013-06-24) Lewis, SE; Wüst, RAJ; Webster, JM; Collins, J; Jacobsen, GE
    AOGS (Asia Oceania Geosciences Society) will hold their 10th Anniversary meeting for the first time in the Southern Hemisphere at the Brisbane Convention and Exhibition Centre from the 24th to 28th of June 2013. AOGS was established in 2003 to promote geosciences and its application for the benefit of humanity, specifically in Asia and Oceania and with an overarching approach to global issues. AOGS holds annual conventions providing a unique opportunity of exchanging scientific knowledge and discussion to address important geo-scientific issues among academia, research institution and public.Asia Oceania Geosciences Society (AOGS) was established in 2003 to promote geosciences and its application for the benefit of humanity, specifically in Asia and Oceania and with an overarching approach to global issues. Asia- Oceania region is particularly vulnerable to natural hazards, accounting for almost 80% human lives lost globally. AOGS is deeply involved in addressing hazard related issues through improving our understanding of the genesis of hazards through scientific, social and technical approaches. AOGS holds annual conventions providing a unique opportunity of exchanging scientific knowledge and discussion to address important geo-scientific issues among academia, research institution and public. Recognizing the need of global collaboration, AOGS has developed good co-operation with other international geo-science societies and unions such as the European Geosciences Union (EGU), American Geophysical Union (AGU), International Union of Geodesy and Geophysics (IUGG), Japan Geo-science Union (JpGU), and Science Council of Asia (SCA). © 2013, AOGS.
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    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.
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    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.