1 10 3 https://theses.otagogeology.org.nz/files/original/9ab157748022883d669156956347c62c.pdf 3f094b4597fa4ccf1fa11b47cf62cb55 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Geology theses OU Geology thesis Thesis or dissertation completed by University of Otago Geology students Location WKT (WGS84) The location stored in WKT (WGS84) format MULTIPOLYGON (((174.070746110104 -42.097846706775,174.354811926306 -41.725481753094,175.0229096855 -41.4743803795098,175.182786764833 -41.635287225184,175.298698689571 -41.656856048084,175.786393378181 -41.4345819385547,176.220194151376 -40.9848036585385,176.816067254341 -41.7147376789169,175.521928819304 -42.2842059042345,174.284381302374 -42.3381111532636,174.070746110104 -42.097846706775))) Author last name Last name of the Author Fraser Project type Is it an MSc, PhD, BSc(Hons) or PGDipSci? PhD Advisers Who supervised/advised this student Gorman, A.R. Pecher, I. Abstract The Abstract for this thesis The Pegasus Basin off the east coast of New Zealand's North Island is a frontier basin that hosts a large gas hydrate province. The basin has a large amount of faulting, which has lead to the creation of many interesting and unique accumulations of gas hydrates. In 2009/2010, petroleum industry standard 2D seismic data were acquired across the basin by New Zealand Petroleum and Minerals (a New Zealand government agency) to generate interest in exploration of this basin for conventional oil and gas. This seismic data set presents an unique opportunity to examine the basin's gas hydrate systems with the aim of determining the economic potential of the gas hydrates in the basin while improving our understanding of how observed gas hydrate features were formed. The seismic data were reprocessed to optimise the imaging of features related to gas hydrates. When the data were examined, there were numerous gas hydrate features found, so only a selection are presented in this thesis. With the assistance of seismic attributes, Bottom Simulating Reflections (BSRs) and blanking zones are examined. High-density velocity analysis is used to characterise areas of hydrate (higher velocity) and free gas (lower velocity). The high-density velocity analysis proved to be a very effective technique for examining the structure of gas migration chimneys. Two of the most interesting features identified in the data set include a blank dome shape with a gas chimney at its centre and a text book hydrate/free gas phase reversal that is examined in detail using amplitude vs offset (AVO) and inversion analysis techniques. The model for fluid flow and how the free gas from a chimney at the centre of the blanking zone is converted to hydrate is discussed. The hydrate and free gas phase reversal that is observed was formed by localised fluid flowing from depth into the gas hydrate stability zone (GHSZ). As the BSR becomes shallower, the sea floor deepens at this location. Without a localised fluid flow, the BSR would increase in depth with the increasing depth of the sea floor. Gas hydrate saturation and volumetric analyses were performed for one target. Concentrations were determined using empirical saturation formulae, confirming a potential target. The question of how much gas hydrate potentially is present in the basin, is discussed based both my work and that of others. OURArchive handle The handle from the Otago University Research Archive (OURArchive) <a href="http://hdl.handle.net/10523/7372">http://hdl.handle.net/10523/7372</a> OURArchvive access level Abstract Only Department The department where the student is studying primarily. Geology Named locality Named locality describing the field area location. Pegasus Basin Hikurangi Margin Thesis description Number of pages, maps, CDs, etc. 289 pages A4 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Identifier An unambiguous reference to the resource within a given context 2017Fraser Creator An entity primarily responsible for making the resource Fraser. Douglas Date A point or period of time associated with an event in the lifecycle of the resource 2017 Title A name given to the resource Seismic characterisation of hydrate and shallow gas systems associated with active margin sediments and structures in the Pegasus Basin, Hikurangi Margin, New Zealand Subject The topic of the resource Geophysics gas hydrates Pegasus Basin Seismic https://theses.otagogeology.org.nz/files/original/5618d6f92d4dfd3e735b7a4557f306f3.pdf eb649742c83fdc21f12b22ee0d49c1c1 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Geology theses OU Geology thesis Thesis or dissertation completed by University of Otago Geology students Location WKT (WGS84) The location stored in WKT (WGS84) format MULTIPOLYGON (((180.0 -44.339562710309906,178.642311413012322 -44.335253643114314,178.614551266778079 -43.764996330785578,180.0 -43.770672694190807,180.0 -44.339562710309906)),((172.437795548386504 -46.226325799176706,170.956219220779843 -46.20943619974814,171.074125411950234 -45.18267442813459,172.367596856769353 -45.159056922324673,172.437795548386504 -46.226325799176706)),((174.235065676561049 -44.334767485195819,173.518248259879925 -44.340269274720178,173.487607941161571 -43.844918705194296,174.30335489562475 -43.819468426881102,174.235065676561049 -44.334767485195819)),((-180.0 -43.770672694190765,-179.807242288648126 -43.771462447569967,-179.764229615031809 -44.340311004463089,-180.0 -44.339562710309878,-180.0 -43.770672694190765))) Author last name Last name of the Author Hillman Project type Is it an MSc, PhD, BSc(Hons) or PGDipSci? PhD Advisers Who supervised/advised this student Gorman, A.R. Pecher, I. Moy, C. Abstract The Abstract for this thesis Seafloor depressions are widespread on the present-day continental slope along the south-east coast of New Zealand's South Island. The depressions appear to be bathymetrically constrained to depths below 500 m and above 1100 m. Similar depressions observed on the Chatham Rise are interpreted to have formed as a result of gas hydrate dissociation, primarily due to the correlation of the depth range to the predicted gas hydrate stability zone in the region. This lead to the hypothesis that a similar origin can be applied for the depressions investigated in this study. However, this investigation has found limited geophysical or geochemical evidence to support this hypothesis. The objective of this study is to examine whether a causal relationship can be established between potential mechanisms of depression formation and observations based on existing and newly acquired data. This has been done using newly acquired data from the R/V Sonne, R/V Polaris II and R/V Tangaroa, in combination with existing data sets from previous surveys in the region. A combination of multiple geophysical survey techniques have been utilised in this study to conduct the first detailed investigation of these structures. Multibeam bathymetry and backscatter have been used to produce high resolution maps of the seafloor geomorphology and to carry out automated supervised segmentation of substrate classes. Sediment samples and underwater images have been used to ground truth substrate classifications. Sediment samples have also been used to conduct geochemical analysis to assess whether evidence of paleogeochemical methane is present. Subsurface profiles in the form of multichannel boomer seismic, parasound seismic, 2D and 3D seismic lines have been used to investigate underlying structural controls such as polygonal fault systems and understand the stratigraphic framework of the seafloor depressions. Although the results of our analysis do not preclude that the seafloor depressions formed as a result of gas hydrate dissociation, neither does our geophysical or geochemical evidence support the theory. Therefore, we propose that an alternative mechanism may have been responsible for the formation of these structures. The morphometric variability of the seafloor depressions on the Otago Shelf and Chatham Rise indicates that either these structures were formed as the result of the influence of multiple mechanisms, or that they formed at different times and are at different stages in formation. Based on the evidence presented in this study, we propose that the interaction of multiple mechanisms is the most likely explanation for the formation of these seafloor depressions. Multiple mechanisms have played a role in the formation of these structures, including fluid and / or gas venting, groundwater flux and subsurface structural controls. We propose that the primary mechanism of formation for the smaller seafloor depressions is groundwater flux related to artesian seepage of meteoric groundwater, however this mechanism cannot fully explain the formation of the giant structures observed on the Central Chatham Rise. We therefore propose that in this area gas venting from hydrates or other sources may have been a factor. Subsequent to their initial formation the seafloor depressions have been modified and maintained by the action of regional oceanic currents. OURArchive handle The handle from the Otago University Research Archive (OURArchive) <a href="http://hdl.handle.net/10523/5612">http://hdl.handle.net/10523/5612</a> OURArchvive access level Abstract Only Department The department where the student is studying primarily. Geology Named locality Named locality describing the field area location. Chatham Rise Canterbury Basin Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Identifier An unambiguous reference to the resource within a given context 2015Hillman Creator An entity primarily responsible for making the resource Hillman, Jess Irene Tsahai Date A point or period of time associated with an event in the lifecycle of the resource 2015 Title A name given to the resource Investigation of seafloor depressions east of New Zealand Subject The topic of the resource Geophysics backscatter bathymetry Canterbury Basin Chatham Rise gas hydrates geomorphology methane multibeam New Zealand Otago Submarine Canyon Complex pockmarks seafloor depressions Seismic https://theses.otagogeology.org.nz/files/original/9495590c8411f40a5d5fb56626cd4931.pdf 5e3a05fdf87366fae4b9bd3b482bbbb3 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Geology theses OU Geology thesis Thesis or dissertation completed by University of Otago Geology students Location WKT (WGS84) The location stored in WKT (WGS84) format POLYGON ((178.189965462119233 -38.863310658084821,178.213566482367384 -38.852727762863481,178.65061489207946 -38.832342239737642,178.471748811707158 -39.355394283144101,178.151705384889823 -39.674966726527757,177.276143398406418 -40.663652830499828,176.861882499895756 -41.288242103898355,175.9215715266198 -41.73535977174889,175.623468691335489 -41.914120546579973,175.532047997518902 -42.183042784196843,175.232106900289295 -42.398953965604996,174.666058806046948 -42.389519317493985,174.508176471270076 -42.239205771516176,175.066056475445635 -42.039886512178725,176.293384875468064 -41.039055900275919,176.882716191914483 -40.353519057175518,177.248382786290705 -39.825983942313066,177.400800530404268 -39.696393707251517,177.649307901742247 -39.538972587482299,177.844538405440602 -39.426155008635753,177.944971044102346 -39.36950671816038,178.10937396705998 -39.267096204667425,178.174292666826972 -39.149875720943896,178.209418926898707 -38.962495035786453,178.189965462119233 -38.863310658084821)) Author last name Last name of the Author Crutchley Project type Is it an MSc, PhD, BSc(Hons) or PGDipSci? PhD Advisers Who supervised/advised this student Gorman, A.R. Pecher, I. Abstract The Abstract for this thesis New Zealand's Hikurangi Margin hosts a large gas hydrate province that is receiving increased research attention on a global scale. Recent efforts have targeted 1) the potential of the province as an alternative energy resource, 2) methane cold seeps and 3) slope stability issues. Seismic Line 05CM-38 was used for identification and characterisation of potentially highly-concentrated deposits of gas hydrate ("sweet spots"). Two potential sweet spots within anticlines were inspected with a lD fullwaveform inversion routine to determine fine-scale velocity structure. At Western Porangahau Ridge, a high-amplitude feature within the gas hydrate stability zone (GHSZ) was characterised as a high velocity zone overlying a low velocity zone. High and low velocities are interpreted as being caused by gas hydrate and free gas, respectively. At Eastern Porangahau Ridge, results revealed low velocity zones associated with the bottom simulating reflection (BSR) that are much more pronounced near the centre of the ridge compared with further west in the limb of the anticline. At both anticlines, inversion results suggest a localised increase in fluid flow into the GHSZ - a process that is likely to encourage the deposition of relatively highly concentrated hydrate deposits. A network of cross-cutting seismic lines were analysed to reveal plumbing systems that supply gas to three general areas where methane seepage has been observed on the sea floor of the uplifted Rock Garden ridge. At the first area ("1M3"), seismic data reveal gas migration through the G HSZ that appears to be influenced by faulting in the hanging wall of a major thrust fault. At the second area ( "Weka"), data show a distinct convergence of the BSR with the sea floor. Gas supply to this seep is predicted to be focused upwards along the underside of the base of the GHSZ. The third area (the "Faure" site) is associated with a prominent arcuate slump feature. Gas migration appears to be channelled along dipping sedimentary layers that link the BSR with the sea floor. Collectively, these seep sites reveal a range of geological phenomena that are important in establishing fluid flow pathways between gas reservoirs and the sea floor. Regional erosion of the Rock Gar;den ridge top has previously been linked to the gas hydrate system. 2D numerical fluid flow simulations were conducted to investigate the potential influence of gas hydrate-induced permeability reductions and shallow gas pockets on hydro-fracturing _,a process that could lead to regional erosion. Steady-state simulations indicate that anomalous fluid pressure can develop close to the sea floor in response to lower-permeability hydrate-bearing sediments and the underlying gas pockets. Transient simulations suggest that large-scale cycling of fluid overpressure may be occurring on time scales of years to tens of years. It is predicted that regions of intense hydro-fracturing preferentially develop beneath the ridge top rather than beneath the ridge flanks, due to more pronounced overpressure generation and migration of gas through the GHSZ. Department The department where the student is studying primarily. Geology Named locality Named locality describing the field area location. Hikurangi Margin Thesis description Number of pages, maps, CDs, etc. xvi, 196 leaves, [7] leaves of plates (folded) : ill. (some col.), maps ; 30 cm. + 1 CD-ROM (4 3/4 in.) Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Identifier An unambiguous reference to the resource within a given context 2009Crutchley Creator An entity primarily responsible for making the resource Crutchley, Gareth James. Date A point or period of time associated with an event in the lifecycle of the resource 2009 Title A name given to the resource Gas hydrates on New Zealand's Hikurangi Margin : the importance of focused fluid flow for highly-concentrated deposits, methane seepage and sea floor erosion Subject The topic of the resource Geophysical Maps gas hydrates Hikurangi Margin