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Stratigraphic Architecture of Hunter River Valley Fill, SE Australian Margin


The Hunter Valley, located on the Cainozoic Eastern Australian passive margin, contains a complex stratigraphic architecture that has been investigated using active and passive seismic, gravity, resistivity, rotary and sonic coring as well as multiple dating techniques. The valley is around 90 m deep and 30 km wide at the current shoreline. It has been filled by Tertiary and Quaternary marine, estuarine and fluvial sediments including shelf, shoreline, tidal delta, bay head delta, estuarine central basin, fluvial channel and floodplain settings. Continuous rotary coring of ten boreholes enabled stratigraphic units to be determined, and samples extracted for Uranium series, thermoluminescence, amino acid, radiocarbon and palynology dating, yielding ages from present day to around 240,000 years BP. The oldest sediments in the valley are Tertiary, and occupy the valley floor in a relatively narrow axial thalweg fill. Later fills follow at least two full sea level cycles, ranging from ~6m above, to around 120 m below present sea level. Four episodes of transgressive deposition were each followed by a regressive erosional phase and sea level lowstand. Coastal sandy barriers of Oxygen Isotope Stage 5e and 5a age occur landward of a Holocene barrier, with estuarine muds and sands behind them and fluvial lowstand sands below them. The valley fill follows the models of Dalrymple, Boyd and Zaitlin (1994) and these models were used to predict facies geometry and character away from cored boreholes. To test the models and their predictive capability, a new set of investigations were conducted, initially using innovative gravity and passive seismic methods (data derived from background seismic energy rather than an active source), followed by cone penetrometer and sonic drilling techniques. Results from these tests, combined with the earlier data enabled 3D distributions of stratigraphic units to be generated, providing detailed information on groundwater aquifers, and hydrocarbon reservoir exploration models.