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  • 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.

  • ABSTRACT The island of Tasmania in southeast Australia consists of a number of stratotectonic elements. The relationships between these elements are largely obscured by younger cover of the Tasmania Basin, which contains extensive dolerite sills that limit the ability of potential field techniques to map basement. Therefore the development of a robust tectonic model for Tasmania has been inhibited. To assist in the development of a tectonic model, a deep seismic reflection program undertaken offshore around the entire island was designed to map the large-scale structures of Tasmania at depth. The airgun seismic energy was also recorded at a number of seismographs deployed across the island, allowing low resolution 3D tomographic imaging. Short reflection profiles were recorded onshore across structures which could not be imaged by the offshore profiling. This paper focuses on eastern Tasmania. In the seismic sections, the Proterozoic basement in the southeast is mostly featureless, except for large rotated blocks with weakly reflective boundary faults, indicating extension of the Tyennan Element by block faulting. The deposition of the sedimentary succession of the Adamsfield-Jubilee Element was related to this extensional event. In the northeast, a reflective lower crust is interpreted to represent thrust slices of previously highly extended continental crust and possibly fragments of oceanic crust. The Early Palaeozoic sedimentary succession of the Northeast Tasmania Element formed across the inverted margin. The apparently complex geology of eastern Tasmania therefore fits into an extensional model where continental extension eventually led to the formation of very thin continental crust and possibly oceanic crust to the east. The extension was probably related to Late Neoproterozoic extension recorded elsewhere in Australia. The region was subsequently shortened, probably in a ...............................

  • Low-pressure (P) high-temperature (T) metamorphism previously attributed to crustal thickening accompanying nappe emplacement in the Paleoproterozoic Willyama Supergroup at Broken Hill is reinterpreted as a response to crustal extension (D1) and bimodal magmatism commencing circa 1700 Ma. D1 deformation occurred under amphibolite-granulite facies conditions, producing layer-parallel fabrics (S1) and metapelitic mineral assemblages in which andalusite dominated over sillimanite. Crustal extension ceased soon after 1640 Ma to be followed by crustal thickening, higher-pressure metamorphism, and northeast vergent recumbent folding (D2) attendant on inversion of the original D1 extensional structures. D2 recumbent folding has previously gone unrecognized but probably peaked around 1600 Ma before further amphibolite facies metamorphism between 1600 and 1590 Ma accompanying upright folding and northwest directed thrust faulting (D3). In the light of this revised tectonothermal history, geodynamic models erected to explain elevated thermal gradients and low-P-high-T granulite facies metamorphism in tectonically thickened crust may not be as relevant to Broken Hill as once thought. Above average crustal temperatures and low-P-high-T metamorphism in the Willyama Supergroup more likely occurred in response to voluminous magmatic intrusion accompanying crustal thinning, mantle upwelling and emplacement and unroofing of midcrustal rocks along a major detachment surface. A second major structural and/or stratigraphic break in the Willyama Supergroup is indicated by the absence of D1 fabrics from the uppermost part of the sequence.

  • An integrated analysis of both airborne and field short-wave infrared hyperspectral measurements was used in conjunction with conventional field mapping techniques to map hydrothermal alteration in the central portion of the Mount Painter Inlier in the Flinders Ranges, South Australia. The airborne hyperspectral data show the spatial distribution of spectrally distinct minerals occurring as primary minerals and as weathering and alteration products. Field spectral measurements, taken with a portable infrared mineral analyzer spectrometer and supported by thin-section analyses, were used to verify the mineral maps and enhance the level of information obtainable from the airborne data. Hydrothermal alteration zones were identified and mapped separately from the background weathering signals. A main zone of alteration, coinciding with the Paralana Fault zone, was recognized, and found to contain kaolinite, muscovite, biotite, and K-feldspar. A small spectral variation associated with a ring-like feature around Mount Painter was tentatively determined to be halloysite and interpreted to represent a separate hydrothermal fluid and fluid source, and probably a separate system. The older parts of the alteration system are tentatively dated as Permo-Carboniferous. The remote sensing of alteration at Mount Painter confirms that hyperspectral imaging techniques can produce accurate mineralogical maps with significant details that can be used to identify and map hydrothermal activity. Application of hyperspectral surveys such as that conducted at Mount Painter would be likely to provide similar detail about putative hydrothermal deposits on Mars.

  • This paper presents a 3D geomechanical modelling study of the Iona gas storage facility in the state of Victoria, Australia. The results provide important information pertaining to gas storage, which can then be used to understand certain geomechanical aspects of CO2 storage. A key finding in this paper is that significant changes to the horizontal stress magnitudes are imparted by changes to the fluid pressure due to gas injection or withdrawal. This effect, known as the reservoir stress path, significantly influences fault stability by counteracting the changes to effective stress. In the case of Iona, pressurization of the field results in a stress path which is parallel to the failure criterion rather than towards it, as would be expected in a classical treatment which does not incorporate complex poro-elastic effects. Another output of interest relates to reservoir deformation, which would be manifested at the ground surface as heave or subsidence. During periods of peak gas withdrawal and injection, surface ground movement is predicted to be on the order of -9 mm and + 2.5 mm, respectively. These numbers are similar to the surface deformation observed at the In Salah CO2 injection project, but much smaller than the subsidence observed in some producing hydrocarbon fields.

  • Australia boasts arguably the richest Late Neogene to Quaternary faulting record anywhere in the world's stable continental region (SCR) crust. Variation in Quaternary fault scarp length, vertical displacement, relation to other faults and topography justifies the division of the continent according to fault character. Six onshore 'neotectonic domains' are recognised, while an additional offshore domain is proposed by analogy with the eastern United States. Each domain relates to a distinct underlying crustal type and architecture, which can be broadly considered to represent cratonic, non-cratonic and extended crustal environments. In general, greater topographic expression associated with faults occurring in extended crust relative to non-extended crust suggests a higher rate of seismic activity in the former setting, consistent with observations worldwide. Using the same reasoning, non-cratonic crust might be expected to have a higher rate of seismic activity than cratonic crust. This distinction, together with the variance in fault character between domains, should be recognised in attempts to identify analogous systems elsewhere in the world. A common characteristic of large (paleo)earthquake occurrence in Australia appears to be temporal clustering. Periods of earthquake activity comprising a finite number of large events are separated by much longer periods of seismic quiescence. In several instances there is evidence for deformation at scales of several hundred kilometres switching on and off over the last several million years. What is not clear from the limited paleoseismological data available is whether successive active periods are comparable in terms of slip, number of events, magnitude of events, etc. Irrespective, this apparent bimodal recurrence behaviour poses problems for probabilistic seismic hazard assessment (PSHA) in that it implies that large earthquake recurrence for long return periods is not random (i.e. Poissonian). The points critical to understanding the hazard posed by SCR faults, and modelling this hazard probabilistically, become: 1) is the fault in question in the midst of an active period, or in a quiescent period; 2) how many large events might constitute an active period, and how many ruptures has the fault generated so far in its current active period (should it be in one); and 3) what is the mean recurrence interval in an active period, and what is the variability around this mean? Keywords: intra-plate, neotectonics, paleoseismology, temporal clustering