Meso-cenozoic intraplate magmatism along the Australian southern margin

The eastern and south-eastern Australian passive continental margins host a series of Cenozoic basins preserved in onshore and offshore Victoria, Tasmania and South Australia. Deposition in these basins was concurrent with the Cenozoic Magmatic Province that extends along the Australian eastern and south-eastern Australian passive continental margin. Although classified as a ‘non-volcanic’ passive margin, a large record of igneous rocks is preserved within the Cretaceous to Miocene syn- and post-rift successions of the offshore basins. Previous studies have mainly focussed on onshore magmatic activity and resulting geodynamic models have proposed on mantle plumes or edge-driven convection. Offshore 2D and 3D seismic reflection datasets in the Bass and Gippsland Basins analysed in this thesis have shown that the magmatism in these areas occurred during the Late Cretaceous, Eocene to Oligocene and Miocene to Recent times. The majority of magmatism significantly post-dates continental break-up and basin rifting related to the separation of Australia and Antarctica, which started around 85 Ma. This thesis presents major and trace element and isotope geochemistry of Cenozoic igneous rocks in onshore Tasmania and in the offshore Gippsland and Bass Basins. The data presented suggest that magmas have formed over a thermal upwelling with a long time-integrated high 238U/204Pb or μ (HIMU) signature that traversed a Pacific Mid-Ocean Ridge Basalt (MORB) -like asthenosphere and interacted with the mantle lithosphere. Tasmanian lavas formed at different depths with shallow silica-oversaturated melts undergoing larger degrees of melting than deeper silica-undersaturated melts (> 20 kbar). These shallow melts have then mixed with a remnant source of Ferrar Jurassic magma, related to Gondwana break-up, residing in the lithosphere. Magmas formed in the Gippsland and Bass Basins formed under similar conditions as the shallow silica-oversaturated melts with varying Oceanic Island Basalt (OIB) to Upper Continental Crust (UCC) trace element signatures. Regional 3D seismic mapping of the Gippsland Basin reveals a laterally (>40 km) and vertically extensive magmatic plumbing system comprising more than 186 intrusions. This network of sills shallows from the central part of the basin towards the basin-bounding faults at the northern margin, where magmas were ultimately extruded onto the palaeo-surface during the Late Cretaceous. A second style of magmatic activity occurred during the Middle Eocene, resulting in a volcanic cone complex in the centre of the basin, which has likely been fed through vertical to near-vertical dykes or via faults. Palynology of surrounding sediments intersected by petroleum wells indicates that magmatic activity in the Bass Basin is generally younger than that of the Gippsland Basin with activity being most abundant during the Miocene. Cretaceous to Eocene magmatic activity mainly occurred at major normal faults near the basin margins, while Miocene magmatism is focussed in the centre of the Cape Wickham Sub-basin of the Bass Basin. In contrast to the Gippsland Basin, the main direction of magma transport through the upper crust was more vertically through dykes and/or faults. This phase of Miocene magmatic activity is characterised by a southward younging trend similar to the southward younging trends of the hotspot trails observed on the Australian mainland. Although the Gippsland and Bass Basin are adjoining basins, the magmatic plumbing styles observed differ significantly. These results provide insights into the origin, cause and plumbing into intraplate magmatism occurring along the Australian south-eastern margin and magma transport through sedimentary basins, in general.Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 201

World War I heritage in Belgium: combining historical aerial photography and EMI

Millions of aerial photographs were taken by all fighting nations during World War I. These photographs are a remarkable and previously underexploited source of information for the study of this conflict heritage. This paper describes interdisciplinary research combining archival research, the interpretation and detailed mapping of historic aerial photographs and the application of electromagnetic induction. These techniques are combined in two case studies (Geluveld & Oostduinkerke) to evaluate the archaeological heritage of World War I

Geostatistical assessment of the impact of World War I on the spatial occurrence of soil heavy metals

Previous research showed a regional Cu enrichment of 6 mg kg(-1) in the top soil of the Ypres war zone (Belgium), caused by corrosion of WWI shell fragments. Further research was required since in addition to Cu, also As, Pb, and Zn were used during the manufacturing of ammunition. Therefore, an additional data collection was conducted in which the initial Cu data set was tripled to 731 data points and extended to eight heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) which permitted (1) to evaluate the environmental impact of the heavy metals at a regional scale and (2) to assess their regional spatial occurrence by performing an optimized geostatistical modeling. The results showed no pollution at a regional scale, but sometimes locally concentrations exceeded the soil sanitation threshold, especially for Cu, Pb, and Zn. The spatial patterns of Ni and Cr were related to variations in soil texture whereas the occurrences of Cu and Pb were clearly linked to WWI activities. This difference in spatial behavior was confirmed by an analysis of coregionalization

A floating sensing system to evaluate soil and crop variability within flooded paddy rice fields

Continuous paddy rice cultivation requires fields to be flooded most of the time limiting seriously the collection of detailed soil information. So far, no appropriate soil sensor technology for identifying soil variability of flooded fields has been reported. Therefore, the primary objective was the development of a sensing system that can float, acquire and process detailed geo-referenced soil information within flooded fields. An additional objective was to determine whether the collected apparent electrical conductivity (ECa) information could be used to support soil management at a within-field level. A floating sensing system (FloSSy) was built to record ECa using the electromagnetic induction sensor EM38, which does not require physical contact with the soil. Its feasibility was tested in an alluvial paddy field of 2.7 ha located in the Brahmaputra floodplain of Bangladesh. The high-resolution (1 x 1 m) ECa data were classified into three classes using the fuzzy k-means classification method. The variation among the classes could be attributed to differences in subsoil (0.15-0.30 m below soil surface) bulk density, with the smallest ECa values representing the lowest bulk density. This effect was attributed to differences in compaction of the plough pan due to differential puddling. There was also a significant difference in rice yield among the ECa classes, with the smallest ECa values representing the lowest yield. It was concluded that the floating sensing system allowed the collection of relevant soil information, opening potential for precision agriculture practices in flooded crop fields

Combining multiple signals of an electromagnetic induction sensor to prospect land for metal objects

Buried unexploded ammunition is a major problem on arable land in former battle areas. Many battlefields of the First World War (WWI) still contain a lot of unexploded shells just below the plough layer, posing serious threats to soil editors and trenchers. Electromagnetic induction (EMI) sensors have been used for a variety of agricultural and archaeological purposes to map the natural soil variability and to locate buried archaeological remains. Besides its sensitivity to variations in soil texture and anthropogenic disturbances, EMI proves to respond strongly to metal objects in the soil. Most EMI sensors rely on a single signal, with magnitude and sign of the metal anomalies differing according to the instruments coil distance and separation. The multi-coil EMI sensor, the DUALEM-21S, provides four simultaneous apparent electrical conductivity (ECa) signals enhancing significantly the possibilities for signal processing. To calibrate our instrument, we buried different masses of metal at different depths. The four ECa measurements showed a response to the metal objects down to 1.2 m. The measurements were subtracted by their gradual trend to obtain the local anomalies (Delta ECa). A combination of these four Delta ECa's was used to amplify the signal response to metal, influenced by both depth and mass of the buried objects. At an intensively shelled former WWI battle field near Ypres (Belgium), a detailed prospection was conducted with the DUALEM-21S. Based on our multi-signal procedure, we located 40 positions, 20 where we predicted buried metal and 20 where we expected that no metal was present within 1.2 m depth. There were no false negative predictions and at the 20 locations where we expected metal, shells up to 90 kg were excavated. As a final outcome we produced a map with predictions of the mass of metal objects in the soil assuming a fixed depth and alternatively a map with predictions of the depth of metal objects assuming a given mass. Apart from their potential for agricultural and archaeological investigations, multi-ECa signals were shown to be useful for locating metal objects, like unexploded WWI shells, in the top 1.2 m of soil

Imaging a polygonal network of ice-wedge casts with an electromagnetic induction sensor

Images of the morphology of a polygonal network of ice-wedge casts are a valuable aid to paleoclimatological reconstructions. Usually such images are obtained by aerial photography showing polygonal crop marks reflecting textural differences between wedge filling and host material. Our objective was to investigate an alternative method by measuring the soil apparent electrical conductivity (EC(a)) with an electromagnetic induction (EMI) sensor. Based on an aerial photograph showing polygonal crop marks in an agricultural field in Belgium, a test area of 0.63 ha was selected. A small part of the test area (6 by 6 m) was excavated revealing a clear pattern of ice-wedge casts. The wedges penetrated clay-rich Tertiary marine sediments, covered by a 0.6-m layer of eolian sandy sediments, and were associated with the permafrost during the last glacial period. We took 94 subsoil (0.6-0.8 m) samples distributed over the test area and analyzed their texture. The results showed a clear difference between the Eocene host material (on average 21% clay) and the Quaternary wedge filling (on average 6% clay). The test area was surveyed with an EMI sensor (we used an EM38DD) which resulted in an accurate image of the polygonal network. We concluded that an EMI survey is an appropriate technique to image the morphology of a polygonal network of subsoil ice-wedge casts. A final perspective comprises the strong heterogeneity of the subsoil, since nearly half of the subsoil consists of ice-wedge material. This might open perspectives for precision agriculture in such landscapes