Williams et al. (2009) report on new multibeam sonar bathymetry and underwater video data collected from submarine canyons and seamounts on Australia's southeast continental margin to 'investigate the degree to which geomorphic features act as surrogates for benthic megafaunal biodiversity' (p. 214). The authors describe what they view as deficiencies in the design of the Marine Protected Areas (MPAs) in the southeast region of Australia, in which geomorphology information was employed as a surrogate to infer regional-scale patterns of benthic biodiversity. This comment is designed to support and underscore the importance of evaluating MPA designs and the validity of using abiotic surrogates such as geomorphology to infer biodiversity patterns, and seeks to clarify some of the discrepancies in geomorphic terminologies and approaches used between the original study and the Williams et al. (2009) evaluation. It is our opinion that the MPA design criteria used by the Australian Government are incorrectly reported by Williams et al. (2009). In particular, we emphasise the necessity for consistent terminology and approaches when undertaking comparative analyses of geomorphic features. We show that the MPA selection criteria used by the Australian Government addressed the issues of false homogeneity described by Williams et al. (2009), but that final placement of MPAs was based on additional stakeholder considerations. Finally, we argue that although the Williams et al. (2009) study provides valuable information on biological distributions within seamounts and canyons, the hypothesis that geomorphic features (particularly seamounts and submarine canyons) are surrogates for benthic biodiversity is not tested explicitly by their study.

Steep terrain affects optical satellite images through both irradiance and BRDF effects. To obtain corrected land surface reflectance and detect land surface change through time series analysis over rugged surfaces, it is necessary to remove or reduce the topographic effects. In this paper, a physical based BRDF and atmospheric correction model for both flat and sloping surfaces in conjunction with the 1-second SRTM (Shuttle Radar Topographic Mission) derived DSM product was applied to conduct BRDF, atmospheric and terrain correction. The model was applied to 8 Landsat scenes covering different seasons and terrain types in eastern Australia. Initial visual assessment showed that the algorithm removed much of the topographic effect and detected deep shadows in all 8 images. Indirect validation based on the change in correlation between the data and terrain slope showed that the correlation coefficient between the surface reflectance factor and the cosine of the incident (sun) angle reduced dramatically after the topographic correction algorithm was applied. The correlation coefficient typically reduced from 0.80 to 0.02 in areas of significant relief. The terrain corrected surface reflectance can also provide suitable input data for multi-temporal land cover classification in areas of high relief based on spectral signatures and spectral albedo, while the products based only on BRDF and atmospheric correction cannot. To ensure stability of the terrain corrected reflectance products when expert intervention in the processing workflow needs to be minimal, the paper also shows the need for additional constraints and calibration the correction algorithm. For example, to avoid overcorrection, the algorithm currently applies an angle threshold to both the BRDF model and the direct irradiance. Above all, the accuracy and effectiveness of the product is shown to depend particularly on the quality of the DSM data, its co-registration with the Landsat data and its spatial resolution.

For the first time in Australia, active present-day hydrocarbon seepage has been imaged on the tropical carbonate Yampi Shelf, in 50 and 90 m water depth. Seepage features consist of gas plumes in the water column associated with specific seabed features, such as clusters of reflective blocks, hard-grounds, pockmark fields and mounds. Seepage activity and intensity appear to vary with changes in pressure related to macro-tidal cycles. The seabed features coincide with sub-surface features such as areas of seismic signal attenuation under high amplitude reflectors, seismic discontinuities and bright spots. Hydrocarbon migration-seepage pathways appear to be controlled by the reactivation of pre-existing fractures and dykes within the basement. The types of seabed features and their preservation on a tropical carbonate shelf are strongly influenced by the coarse bioclastic nature of sediments and the high energy of macro-tidal currents and storm reworking.

Physical property measurements provide a critical link between geological observations and geophysical measurements and modelling. To enhance the reliability of gravity and magnetic modelling in the Yilgarn Craton's Agnew-Wiluna greenstone belt, mass and magnetic properties were analysed on 157 new rock samples and combined with an existing corporate database of field measurements. The new samples include sulphide ore, serpentinised and olivine-bearing ultramafic host rocks, granitoid, and felsic and mafic volcanic and volcaniclastic country rock. Synthesis of the data provides a useful resource for future geophysical modelling in the region. Several rock types in the region have sufficiently distinct physical properties that a discriminant diagram is proposed to facilitate a basic classification of rock types based on physical properties. However the accumulation of emplacement, metamorphic, hydrothermal and structural processes has complicated the physical properties of the rocks by imposing duplicate and sometimes opposing physical property trends. The data confirms that massive sulphide and ultramafic rocks have the most distinctive mass and magnetic properties but with variability imposed by their complex history. Sulphide content imposes the strongest control on densities, but can only be identified when comprising > 10 vol. % of the rock. The pyrrhotite-rich Ni-sulphide assemblages generally have similar magnetic properties to the host ultramafic rocks, but can have much lower susceptibilities where the thermal history of the rocks has favoured development of hexagonal pyrrhotite over monoclinic pyrrhotite. In ultramafic rocks that contain < 10 vol. % sulphides, density and susceptibility are primarily controlled by serpentinisation, with olivine breaking down to serpentine and magnetite in the presence of water.

For the first time, the distribution of seabed geomorphic features has been systematically mapped over the Australian margin. Each of 21 feature types was identified using a new, 250 m spatial resolution bathymetry model and supporting literature. The total area mapped was >8.9 million km2 and included the seabed surrounding the Australian mainland and island territories of Christmas, Cocos (Keeling), Macquarie and Norfolk Islands. Of this total, the shelf is >1.9 million km2 (21.92%), the slope >4.0 million km2 (44.80%), and the abyssal plain/deep ocean floor >2.8 million km2 (32.20%). The rise covers 97,070 km2 or 1.08% of the margin. A total of 6,702 individual geomorphic features were mapped on the Australian margin. Plateaus have the largest surface area and cover 1.49 million km2 or 16.54%, followed by basins (714,000 km2; 7.98%), and terraces (577,700 km2; 6.44%), with the remaining 14 types each making up <5%. Reefs, which total 4,172 individual features (47,900 km2; 0.54%), are the most numerous type of geomorphic feature, principally due to the large number of individual coral reefs of the Great Barrier Reef. The geomorphology of the margin is most complex where marginal plateaus, terraces, trench/troughs and submarine canyons are present. Comparison with global seabed geomorphology indicates that the Australian margin is relatively under-represented in shelf, rise and abyssal plain/deep ocean floor area and over-represented in slope area, a pattern that reflects the mainland being bounded on three sides by passive continent-ocean rifted margins and associated numerous subsided marginal plateaus. Significantly, marginal plateaus on the Australian margin cover 20% of the total world area of marginal plateaus. The Australian margin can be divided into 10 geomorphic regions by quantifying regional differences in diagnostic features that can be used to infer broad-scale seabed habitats. The present study has application for the future management of Australia's ocean resources.

No abstract available

Gold deposits in the Archaean Eastern Goldfields Province in Western Australia were deposited in greenstone supracrustal rocks by fluids migrating up crustal scale fault zones. Regional ENE-WSW D2 shortening of the supracrustal rocks was detached from lower crustal shortening at a regional sub-horizontal detachment surface which transects stratigraphy below the base of the greenstones. Major gold deposits lie close to D3 strike slip faults that extend through the detachment surface and into the middle to lower crust. The detachment originally formed at a depth near the plastic-viscous transition. In orogenic systems the plastic-viscous transition correlates with a low permeability pressure seal separating essentially lithostatic fluid pressures in the upper crust from supralithostatic fluid pressures in the lower crust. This situation arises from collapse in permeability below the plastic-viscous transition because fluid pressures cannot match the mean stress in the rock. If the low permeability pressure seal is subsequently broken by a through-going fault, fluids below the seal would flow into the upper crust. Large, deeply penetrating faults are therefore ideal for focussing fluid flow into the upper crust. Dilatant deformation associated with sliding on faults or the development of shear zones above the seal will lead to tensile failure and fluid-filled extension fractures. In compressional orogens, the extensional fractures would be sub-horizontal, have poor vertical connectivity for fluid movement and could behave as fluids reservoirs. Seismic bright spots at 15-25 km depth in Tibet, Japan and the western United States have been described as examples of present day water or magma concentrations within orogens. The likely drop in rock strength associated with overpressured fluid-rich zones would make this region just above the plastic-viscous transition an ideal depth range to nucleate a regional detachment surface in a deforming crust.

A significant problem for ground-based gamma-ray spectrometric surveys is the effect of emanation radon on estimated uranium concentration estimates. Radon gas (a daughter product in the U238 decay series) escapes from rocks and soils near the earth?s surface into the lower atmosphere. Under early morning, still-air conditions, radon concentrates as a thin layer near the earth?s surface. If ground radiometric surveying is undertaken before this radon layer is mixed into the lower atmosphere, large errors in U concentration estimates result. This paper shows the effect of early-morning radon accumulation on a quad-bike gamma-ray spectrometric survey near Boorowa, NSW. Paddocks surveyed early-morning show much higher apparent uranium concentrations than those surveyed later in the day. We demonstrate the radon diurnal effect by recording the apparent U concentration at a fixed site over several weeks. Typically, there is a build-up of radon near the earth?s surface overnight. Radon concentration reaches a maximum at about 7 am before slowly dispersing over a period of 2-3 hours. The diurnal data also show the effect of rainfall on apparent U concentrations. Rain precipitates radioactive daughter products of atmospheric radon onto the ground resulting in a significant increase in apparent U concentration. These short-lived daughter products decay to insignificant concentrations within about 3 hours. Ground surveys should not be conducted within 3 hours of rain, or under early-morning, still-air conditions.

Although the positional accuracy of spatial data has long been of fundamental importance in GIS, it is still largely unknown for linear features. As early as 1987 the US National Center for Geographic Information and Analysis identified accuracy as one of the key elements of successful GIS implementation. Yet two decades later, while there is a large body of geodetic literature addressing the positional accuracy of point features, there is little research addressing the positional accuracy of linear features, and still no accepted accuracy model for linear features. This research aims to address some of these shortcomings by exploring the effect on linear feature positional accuracy of feature type, complexity, segment length, vertex proximity and 'scale'. A geographically sensible error model for linear features using point matching from a test line to a reference line of higher accuracy is developed and a case study undertaken using well-regarded and commonly used Australian topographic datasets. Half a million points are matched between test and reference lines for a range of topographic feature types at a spectrum of 'scales' and summary statistics are generated that shed light on the relationships between positional accuracy and 'scale', feature type, complexity, segment length, and vertex proximity. It is found that (a) metadata for the tested datasets significantly underestimates the positional accuracy of the data; (b) positional accuracy varies with 'scale' but not, as might be expected, in a linear fashion; (c) positional accuracy varies with feature type, but not as the rules of generalisation suggest; (d) complex features lose accuracy faster than less complex features as 'scale' is reduced; (e) the more complex a real-world feature, the worse its positional accuracy when mapped; and (f) accuracy mid-segment is poorer than accuracy end-segment.

This paper explores the effect of correlation on the statistics of separation of two lines when using regularly-spaced offsets. In a case study the positional accuracy of a test coastline feature is determined with respect to a representation of the same coastline at a much larger scale using regularly-spaced perpendicular offsets. The paper uses two methods to show how adjacent offsets are correlated and how this degrades the precision with which the positional accuracy of the test coastline can be determined. These methods and findings make offset models of positional accuracy for linear features more explicit and attractive.