b'Letter to the EditorLetter to the EditorRe: Comments on the Deniliquinare not intended as a criticism of theirIt was once suggested to me, by the ImpactCrater work but rather some ideas to strengthenwell-known geophysicist, Hugh Rutter Dear Lisa theirhypothesis. (now deceased), that the trends of gold The most significant of these is themineralisation in Ordovician rocks at In 2000, when I was Head of theunfortunate fact that Glickson andBallarat and Bendigo in Victoria could Geophysical Mapping group ofYeates (2022) were unaware of thehave been related to radial fractures of Geoscience Australia (GA) I mentionedTectonophysics publication of Kirkby et al.the impact structure.to Tony Yeates, a colleague at GA, that(2020), which presents various inversionsThere were apparently five mass a large circular magnetic anomaly inof GA magnetotelluric data in New Southextinctions of life during the Earths western New South Wales could beWales. This paper displays various datasetshistory (not including the Noahs ark evidence of an asteroid impact crater.showing that something strange is goingepisode). The best documented of these Tony got very excited and as a result weon in the vicinity of the possible impact.is the extinction of the Jurassic dinosaurs jointly published a paper (Yeates et al.Fig. 5c of their paper, a resistivity modelrelated to an asteroid impact in the 2000). I was not entirely convinced withfrom an inversion routine, shows a clearYucatan Peninsula in Mexico. There was Tonys estimated diameter of 1240 kmdoughnut type circular feature (depth 25a mass extinction in the Ordovician. Was for this feature plus all his explanationskm) circling the centre of the Deniliquinthis due to the Deniliquin impact? Was for its other influences on Australianmagnetic high. This could be imaging thethis the reason graptolites never took geology. The subject was dormant untiledge of an impact crater. It seems that thisover the world?Tony teamed up with Andrew Glickson,paper was in press at much the same time who was at GA at the sametime as Tonyas the Glickson and Yeates paper. Peter Gunn and me and is now an Associate ProfessorGentleman geophysicistat the University of NSW. One of AndysThe second criticism is that some ofE gunngeo@iprimus.com.auimpressive achievements has been co- their geophysical images may not authoring a book on Australian impacthave displayed data in an optimal craters (Glickson and Pirajno 2018). Inway to support their case. Most ofReferencesrecent times Andy has been collaboratingtheir images of magnetic data do not with Tony Yeates and they recentlyshow reduced to the pole (RTP) results.Glickson, A.Y., and F. Pirajno. 2018. Asteroid published a paper in TectonophysicsReduced to the pole data, that correctimpacts, crustal evolution and related mineral (Glickson and Yeates 2022) presentingfor distortions of the inclination of thesystems with special reference to Australia. Mod. a very good case for the existence ofearths magnetic field, normally showAppr. Solid Earth SCI. 14.a large impact structure centred onclearer outlines of magnetic features andGlickson, A.Y., and A.N. Yeates. 2022. Deniliquin. Their paper has receivedtrends. A RTP image of NSW presentedGeophysicsand origin of the Deniliquin considerable attention in various mediain slide2 of Gunn (2021), an ASEG Youmultiple ringed feature Southeast Australia. outlets (just Google check DeniliquinTube presentation, shows a clearerTectonophysics 837: 229454impact crater). They had access to bettercircular feature at Deniliquin than theGunn, P.J. 2022. An explanation for the and more geophysical datasets than Tonyoriginal total magnetic intensity imagedistribution of Broken Hill style mineralisation. and I had back in 2000. of Glickson and Yeates. ApplicationASEG YOU TUBE talk. https://www.youtube.com/ of vertical derivative operators to thewatch?v=dRoLP-UMWhQ The Glickson and Pirajno, (2018) bookgravity data and even the seismic depthKirkby A, L. et al. 2020. Lithospheric architecture mentioned Deniliquin as the site of aresults may have imaged structures thatof a Phanerozoic orogen from magnetotellurics: major asteroid impact. The main evidencefurther supported the theory. AusLAMP in the Tasmanides, southeast Australia. for an impact feature is a large multi- Tectonophysics 793: 228560ringed magnetic anomaly with possibleElevation images of Australia show aYeates, A.N., T.J. Meixner, and P.J. Gunn. 2000. An radial fractures, a ringed gravity featurelarge regional topographic low overinterpreted 1240 km diameter impact structure coinciding with the magnetic featureDeniliquin. This could be the result of thebeneath the Deniliquin region, southeastern and a local uplift of the crust underneatharea being flanked to the east and southAustralia. In D. Denham ed. Exploration Beyond the gravity and magnetic anomalies. Asby the Great Dividing Range but may be2000: Conference handbook. Australian Society explained by Glickson and Yeates (2022),a residual sag over the impactcrater. of Exploration Geophysicists. Preview 84: 81-82these features are expected from a major impact feature. Drilling in the area has not been deep enough to identify shock metamorphic features expected from a major asteroid impact. I note that theThe ASEG in social mediainterpreted impact feature now has an interpreted diameter of about 520 km. The probable date for the impact appearssocial sow+shlFollow all our socialsto be during theOrdovician. for the latest updates!The following comments on datasets,[adjective]Relating to society or its organisationnot accessed and processing routines[noun]Social media sites, applications or accounts E C D Q M knot used, by Glickson and Yeates (2023) 4 PREVIEWFEBRUARY 2024'