Evidence for a putative impact structure in Palm Valley, Central Australia

Duane Willis Hamacher, Craig O'Neill, Anthony Buchel, Tui R Britton

Research output: Contribution to conferenceAbstract

Abstract

Introduction: We present evidence supporting the impact origin of a circular structure located in Palm Valley, Central Australia (24° 03′ 06′′ S, 132° 42′ 34′′ E). The ~280 m wide structure was discovered using a combination of Google Maps and a local Arrernte Aboriginal oral tradition regarding a star that fell into a waterhole called Puka in Palm Valley, Northern Territory [1][2] (see [3] for details of the discovery). Geophysical Evidence: A survey of the structure in Septem- ber 2009 collected magnetic, gravity and topographic data. Geo- physical modeling of the data revealed the structure has a bowl- shaped subsurface morphology, as expected for a simple impact crater. Though the structure sits within the Finke Gorge system, the models do not support an erosional origin for the structure, as no buried channels are observed. Nor does the modeling fit a volcanic origin, as the density structure at depth is consistent with fractured sandstone/sediments. Geological Evidence: One channel runs out of the crater to the south, consistent with outflow from crater-filling events, but again not with an erosional origin for the structure itself. The mi- crostructure of rock samples collected from the site revealed the presence of planar deformation features in the quartz grains. The coincident angle of the fractures is consistent with the crystallo- graphic fracture directions under mild-end shocks. These grains probably represent local focusing of stress as the shock wave moved through the heterogeneous grain matrix, suggesting the conditions were right for the shock pressure to locally exceed the ~7.5 GPa required to form the features, even though the bulk of the shock pressure was much less. Conclusion: Based on the level of erosion and the absence of shatter cones and meteorite fragments, we estimate the struc- ture’s age to be in the millions of years. While the presence of shocked-quartz is a direct indicator of a cosmic impact, we can- not rule out that the quartz was transported from an older struc- ture into the Hermannsburg sandstone as it was deposited. The ~22 km wide Gosse’s Bluff impact structure, located ~40 km from Palm Valley, postdates the Hermannsburg sandstone, leav- ing a distal unidentified impact event as a possibility. However, the bowl shaped morphology of the Palm Valley structure, as well as the fractures on the structure’s walls, support an impact origin. References: [1] Austin-Broos, D., 2009, "Arrernte Past, Ar- rernte Present", University of Chicago Press, pp. 37-38. [2] Róheim, G., 1945, "The Eternal Ones of the Dream: a psycho- analytic interpretation of Australian myth and ritual", Interna- tional Universities Press, New York, p. 183. [3] Hamacher, D.W. & Norris, R.P., 2010, Falling Star at Puka: using Aborigi- nal Oral Traditions to locate meteorite falls and impact craters. In Ilgarijiri - things belonging to the sky, edited by R.P. Norris, Proceedings of the symposium on Indigenous Astronomy held on 27 November 2009 at Australian Institute for Aboriginal and Torres Strait Islander Studies, Canberra, Australia (in press).
Original languageEnglish
PagesA73
Number of pages1
Publication statusPublished - 2010
EventAnnual Meeting of the Meteoritical-Society 2010 - New York, United States of America
Duration: 26 Jul 201030 Jul 2010
Conference number: 73rd

Conference

ConferenceAnnual Meeting of the Meteoritical-Society 2010
Abbreviated titleMetSoc73
CountryUnited States of America
CityNew York
Period26/07/1030/07/10

Cite this

Hamacher, D. W., O'Neill, C., Buchel, A., & Britton, T. R. (2010). Evidence for a putative impact structure in Palm Valley, Central Australia. A73. Abstract from Annual Meeting of the Meteoritical-Society 2010, New York, United States of America.