Browsing by Author "Welsh, KJ"

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    Life and death of Holocene reefs of Moreton Bay, Queensland, Australia
    (Australian Geosciences Council, 2012-08-05) Nothdurft, LD; Major, J; Leondard, ND; Zhao, JX; Price, GJ; Welsh, KJ; Webb, GE; Hua, Q
    Dead fringing coral reefs of Moreton Bay are the southernmost fringing reefs in eastern Australia and are significant examples of marginal environments for subtropical reef growth. Two sites were investigated in the western part of the bay at Wellington Point and Cleveland Point. Seven auger cores and 5 surface transects were made across the dead reef flats to record spatial data on coral distribution and elevation and to provide samples for dating to test the timing and potential causes of reef termination. A total of 78 coral samples were dated using 230Th/U and 14C techniques. 230Th dates were determined by TIMS U-series, and MC-ICP-MS and 14C dates by AMS. Dates of framework corals indicate that reef growth initiated at different elevations by ∼7000 ybp and was predominantly vertical with little or no lateral progradation. Reef growth was continuous until termination at ∼5800 ybp. Micro-atolls (6523, 6680 ybp) suggest a sea level of ∼+1.3m above current lowest astronomical tides and elevated sea level persisted through that interval. Small incipient coral colonies on the dead reef surface range in ages between ∼4850 and 4700 ybp suggesting conditions were again suitable at that time for a recolonisation of the reef flat, but reef growth was not reinitiated. No younger ages were recorded. Temporal changes in Moreton Bay conditions have resulted in periodic phase shifts between favourable and unfavourable conditions for reef growth, coincident with a small sea level fall ∼5800 ybp and including potentially cooler temperatures and decreased water quality within the bay.