Characterisation of coastal fjords and buried glacial valleys at the sub-Antarctic Auckland Islands using high-frequency seismic data

• Main Author: Perkins, Edward James
• Other Authors: Gorman, Andrew Robert
• Format: Thesis
• Language: English
• Published: University of Otago 2019
• Subjects: Quaternary; geology; seismic imaging; geophysics; marine sediments; Antarctic; Antarc*; Auckland Island; Auckland Islands
• Online Access: http://hdl.handle.net/10523/9590

High-resolution seismic surveying by the University of Otago has shown that the leeward side of the sub-Antarctic Auckland Islands (51° 44'S, 166° 06'E) is dominated by Quaternary glacial landforms that extend offshore. These offshore glacial landforms, as a part of the wider glacial history at the Auckland Islands are still poorly resolved. However, over 1200 km of high-frequency seismic data from previously unsurveyed fjords, harbours and specific shelf localities are presented here with a corresponding multibeam bathymetric survey. Using a suite of high-resolution geophysical and geologic surveying techniques, this project constrains the infill stratigraphy and topographic morphology of drowned, glacially incised valleys and coastal fjords. Specifically, this thesis will (i) examine glacial extent and sedimentary regimes in fjords and drowned valleys to further understand the local glaciation and sedimentation history, (ii) identify potential submarine lacustrine deposits as future coring targets for high-resolution climate proxies, (iii) use paleo sea levels to constrain paleo shorelines during the last glacial maximum, (iv) characterise the eroded eastern shelf platform during the last glacial maximum and the corresponding sea level lowstand. First-order observations and interpretations from the data show sedimentary deposits and widespread buried topography consistent with coastal glaciation. Analysis of the processed seismic data through the evaluation of seismic velocities in combination with new seafloor bathymetry data, provide high resolution inputs into specific geologic modelling packages. This refines spatial constraints on sedimentary lithologies, valley morphologies and valley formation. These reconstructions of offshore topography and stratigraphy during glacio-eustatic lowstands help to identify localities where lacustrine deposits may occur separately from marine influences. Lacustrine deposits are to be targeted for coring with relation to high-resolution Southern Hemisphere paleo-climate proxies as a wider research objective. These methods and approaches advance understanding of glacial extent, climate parameters and the emergent Auckland Island landmass during the last glacial maximum at mid-high southern latitudes where geologic archives are sparse.