b'AEGC 2023Short abstractsthe resolution of seismic data. In this study, a variety of datasetshas also been recorded in historic exploration wells. Previous were used to understand ecozones, sensitive animal habitats, andwork focusing on the depositional environment and vegetation with results used to rank the sensitivity of each area.tectonostratigraphic evolution within the depocenters indicates The survey area was subdivided based on terrain and habitat typethat variations in accommodation and sediment supply strongly with unique geometries assigned to each. GIS tools were theninfluences stratigraphy. To evaluate this influence, we use a utilised during design to avoid sensitive or inaccessible areas. Manylandscape and basin evolution numerical model (Badlands). different geometries were considered with a focus on reducingFirst, we generate a series of simulations with varied tectonic, the environmental footprint of the survey while maximising theclimate and erodibility parameters using a design of experiments data quality and minimising costs. To test the data quality ofmethod. From these, we select scenarios with a correspondence these geometries, decimated geometries were created from abetween the modeled and observed stratigraphy of the Crayfish high-density survey and then processed and interpreted. ResultsSub-group at specified well locations. We then propose that the demonstrated that data quality could be maintained with up to aobserved stratigraphy of the Otway Basin Crayfish Sub-group 55% reduction in linear km of seismic and equivalent reductionscan be explained by sediment supply variations caused by the in greenhouse gas emissions. The geometries also resulted in costevolution of the surrounding landscape across four phases savings due to fewer linear km of seismic and lower equipment/ which are: Phase 1: Limited sediment supply as the drainage personnel requirements. Although this method is particularlysystems start to develop in response to the rift formation. suited to areas with sensitive habitats, it can be used on any seismicPhase 2: Sediment supply peaks as high erosion in the steep programme to reduce the environmental impact, reduce costs, andrift escarpment proximal to the depocenters which increases optimise equipment layout around surface exclusions making itsediment volumes delivered to the depocenters. Phase 3: applicable to seismic programmes around the world. Sediment supply from the erosional escarpment decreases. As the valley rift escarpment migrates away from the edges of the half grabens, they evolve into shorter, shallower slopes. Phase 4: Petrophysical properties of the Cobar Province: keyDifferential sediment supply controlled by a distal and a proximal deposits to better understand magnetisation. source. Sediment from the distal escarpment is supplied at a Andreas Bjork and James Austin constant rate while proximal, high sediment supply pulses are generated when the proximal rift escarpment steepens. By CSIRO extending and quantifying existing conceptual models that link stratigraphy to sediment supply and accommodation, this The Cobar Province in NSW is renowned for its world class Au,work demonstrates how source to sink models enhance our Au-Cu and Pb-Zn-Ag deposits. Mineralisation at Cobar is inunderstanding of the complex stratigraphy within rift systems.structurally controlled lodes, with limited width and considerable depth extent. Mining operations rely on exploration as the mining proceeds, and the availability of samples through different zonesCombining seismic interpretation, gravity inversion and of the mineralisation, provides a great opportunity to investigateforward modelling finds new structures in the Otway the magnetic properties as a function of redox. Basin.The last published petrophysical work on the province was moreMatt Boyd 1 Mark A. McLean1,2 and Ross Cayley1than 20 years ago. In this detailed petrophysical work it was highlighted that some of the deposits discovered at that time hold1 Geological Survey of Victoria significant remanent magnetisation, with strengths up to eight2 University of Melbournetimes that of their induced magnetisation. More recent discoveriesThe Otway Basin in SE Australia hosts several known gas fields. such as Hera contain more non-magnetic pyrrhotite or may haveThe basin pore-space is also prospective for commodities magnetic pyrrhotite only in their halos. There has not yet been aincluding petroleum, water, geothermal energy and has full petrophysical study of the contrasts between these discoveriespotential for carbon/hydrogen storage. Prospectivity assessment and their causes in a mineral systems context. This calls for andepends on understanding basin architecture which, in a integrated petrophysical approach, that includes mineralogy andregion of poor outcrop and limited drilling, is heavily reliant petrology and addresses the influences of alteration events. on geophysical datasets. These can be used to resolve the The use of modern petrophysical techniques together withgeometries of deep (basement-hosted) crustal structures which spectral data and assessing key deposits within the Cobarcontrol the internal basin geometries closer to the surface.mineral system model will shed light on the geophysicalThis study draws several complementing studies together; variability within the province and improve future assessmentsseismic interpretation and gridded surfaces from previous of prospectively. seismic based work, gravity data from the Otway Full Spectrum Falcon airborne gravity and gradiometry survey, velocity Landscape and basin evolution modelling elucidatesmodelling, and basement and Moho surfaces generated in sediment supply and accommodation relationships ina gravity inversion study. These are used to interpret crustal the Cretaceous Crayfish Sub-group of the Otway Basin. structure from the northern limit of the Otway Basin in Victoria onshore, to offshore beyond the continental shelf.Matt Boyd 1 Tristan Salles2 and Sara Polanco2Gravity inversion and forward modelling indicates a significant 1 Geological Survey of Victoria mis-match between previous basement surfaces based on 2The University of Sydney seismic interpretations and the gravity inverted basement surface in the south-west corner of Victoria, beneath the Portland Trough.In the Otway Basin, the early Cretaceous Crayfish Sub-group infills syn-rift half grabens and has produced petroleum andTo determine the cause of this mis-match, major faults and commercial volumes of CO 2 . Naturally occurring Hydrogenhorizons were re-interpreted from the sparse seismic data, 83 PREVIEW FEBRUARY 2023'