School of Earth Sciences - Theses

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Start date: 2020 × End date: 2022 × Subject: Fault × Author: Mahon, Elizabeth ×

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    Stratigraphic and structural evolution of the Gippsland Basin, Late Cretaceous to Miocene, Australia
    Mahon, Elizabeth ( 2021)
    Deposition in the Gippsland Basin from the Late Cretaceous to the Miocene was characterised by extensive, wave-dominated shorelines in front of lower coastal plain peatlands. Using depositional architecture evident on seismic data, these deposits have been interpreted to consist of 23 discrete packages. Shoreface morphology ranges from progradational beaches to large, aggradational beach-barriers. While some of these beach-barrier-coastal plain units are progradational, on a multi-million-year timescale they retrograde. Transgression occurred from the Late Cretaceous to the Oligocene, with the main driver for this transgression likely basin subsidence. Despite large changes in paleoclimate, basin tectonics and ocean chemistry, the depositional style remains remarkably consistent. The Gippsland Basin experienced compressional tectonics which resulted in large anticlines forming across the basin. The timing of onset of compressional tectonics in the basin has been revised based on measurements of syn-tectonic sediment thickness changes across structures. These measurements indicate extensional growth faulting was occurring from the Late Cretaceous until the Late Eocene, and compressional structures did not begin growing until the Eocene-Oligocene transition. This research has brought the previously interpreted date for the onset of compressional tectonism in the Gippsland Basin forward approximately 10-20 Ma, from the previously interpreted early to mid-Eocene, to the Eocene-Oligocene transition. From the Palaeocene-Eocene transition to the Eocene-Oligocene transition a series of large channels incised into the top Latrobe Group - the Tuna and Marlin Channels. These channels have previously been interpreted as forming via fluvial processes associated with tectonic uplift. However, this research has shown that tectonic uplift occurred after channel incision, indicating uplift did not contribute to channel down- cutting. Additionally, well data reveals a marine origin for channel fill sediments, and seismic data indicates channels are located seaward of coeval palaeoshorelines. This suggests these channels formed in a submarine environment, with the close proximity of channel heads to the shorelines indicating they were shelf-incising. A second pulse of compressional tectonics occurred in the mid Miocene, which measurements across structures indicate primarily affected the present-day onshore area. This episode of tectonic uplift corresponds to the previously documented unconformity at ~10 Ma. From the early Miocene onwards, shorelines become progradational and regressive. This is interpreted to be the result of compressional tectonics and global icehouse conditions.