Acraman - Hypervelocity Impact Crater

Alternate Names
Local Language
Coordinates 32° 0' 57" S; 135° 26' 20" E
Notes
  1. Acraman Crater is located in the Gawler Ranges, ~170 km E of Ceduna.
Country Australia
Region South Australia
Date Confirmed 1986
Notes
  1. The date is confirmed based on the presence of shatter cones, PDFs in quartz, and intensely shattered dacite outcrops (Williams, 1986). The large, circular structure is also easily observed.
Buried? No
Notes
  1. Alluvium fills the depression surrounding Lake Acraman (Williams, 1986).
Drilled? No
Target Type Crystalline
Notes
  1. The target properties consist of coarsely porphyritic Yardea dacite with minor rhyolites and basalts of the Middle Proterozoic Gawler Range volcanics (Williams, 1986).
Sub-Type Volcanics
Notes
  1. Coarsely porphyritic Yardea dacite with minor rhyolites and basalts of the Middle Proterozoic Gawler Range volcanics (Williams, 1986).
Apparent Crater Diameter (km) 90 km
Age (Ma) ~541 - 635
Notes :
  1. ~541-635 Ma determined stratigraphically by presence of distal ejecta in Ediacaran Bunyeroo Formation 300 km east of the structure [Ediacaran Period was 541-635 Ma, Bunyeroo Formation is ~590 Ma by whole rock Rb-Sr] (Gostin et al., 1986). Previous age constraints: Inconclusive zircon U-Pb SHRIMP of impact melt rock (Pb-loss during post-impact event) and 40Ar/39Ar data of shocked target rocks and impact melt rock (alteration ages) (Schmieder et al., 2015). Late Neoproterozoic age yielded by palaeomagnetic data on melt dyke (Schmidt and Williams, 1996). Minimum estimate of ~450 Ma (Late Ordovician) yielded by K-Ar and 40Ar/39Ar ages of impact melt rock, regarded as minimum estimate because melt rocks affected by authigenic replacement and devitrification (Baldwin et al., 1991).

Method :
  1. Stratigraphy
Impactor Type Chondrite
Notes
  1. Cosmogenic Ir is found in ejecta deposits linked to the crater (Gostin et al., 1989). The impact is attributed to a chondritic asteroid about 4.7 km in diameter (Williams, 1994) (Williams et al., 1996) (William and Gostin, 2010).

Advanced Data Fields

Notes

Erosion
7
  1. The shattered bedrock within Lake Acraman is eroded below the level of the crater floor, >2-2.5 km and perhaps up to twice that thickness has been eroded (Williams, 1990).
Final Rim Diameter
Unknown
Apparent Rim Diameter
90 km
Rim Reliability Index
3
  1. The crater morphology consists of a probable central uplift within Lake Acraman, a surrounding inner depression about 30 km in diameter, an intermediate ring 90 km in diameter, and a possible outer ring at 160 km (Williams, 1986). The central uplift diameter was first estimated as 10 to 12 km (Williams, 1986) (Schmidt and Williams, 1991) and later suggested as 20 km (Williams et al., 1996); however (Hawke, 2003) suggested 18km.
Crater Morphology
Complex
Central Uplift Diameter
18-20km
Central Uplift Height
Unknown
Uplift Reliability Index
4
Structural Uplift
Unknown
Thickness of Seds
Target Age
Precambrian
Marine
No
Impactor Type
Chondrite
  1. Cosmogenic Ir is found in ejecta deposits linked to the crater (Gostin et al., 1989). The impact is attributed to a chondritic asteroid about 4.7 km in diameter (Williams, 1994) (Williams et al., 1996) (William and Gostin, 2010).
Other Shock Metamorphism
Shocked zircon
  1. Timms et al. (2017) reported the presence of FRIGN zircon in impact melt rock from Acraman. The presence of FRIGN zircon indicates the former presence of reidite, which records P> 20 GPa in crystalline target rocks.
Shatter Cones
Yes
  1. Poorly developed shatter cones (~5 cm in length) in dacite which consist mainly of feldspar phenocrysts in a granophyric matrix (Williams, 1986). The shatter cones have sizes ranging from <3 cm to up to 15 cm in length and are only located in the central part of the structure (Williams, 1994) (Williams, 1996). Small shatter cones (~1 cm in length) in a 12 cm dacite block from an ejecta layer are located at about 250-300 km away from the Acraman structure (Gostin et al., 1986). The impactites are comprised of brecciated and shatter cone-bearing Yardea Dacite in an autochthonous lithic breccia, and a 12 m-long and 3 m-wide dike of fine-grained crystralline impact melt rock (Schmieder et al., 2015).
Planar Fractures
No
Planar Deformation Features
Yes
  1. PDFs are present in quartz grains (Type C, ~15 GPa) (Williams, 1986) (Gostin et al., 1989) and zircon (Gostin and Zbik, 1999). PDFs also present in quartz in partially to fully digested clasts of Yardea Dacite and sub-planar and planar fractures in zircons (Schmieder et al., 2015).
Diaplectic Glass
No
Coesite
No
Stisovite
No
Crater Fill
  1. The ejecta blanket is widely dispersed, covering 20,000 km2 within the Adelaide Geosyncline. Shattered mineral grains and local abundance of altered, tektite-like spherules are found in the outermost locality at ~470 km NW of Acraman structure (Wallace et al., 1990), anomalous for Ir and other PGE values (Gostin et al., 1989) (Wallace et al., 1990). Ejecta in the sedimentary column are present over an area of 20,000 km2. The most distal ejecta are ~540 km NW of structure. Environmental effects were documented in (McKirdy et al., 2006). Microtektites and suevite were reported in the ejecta in (Arouri et al., 2000), and melt rock occurs within dykes in the central uplift according (Schmidt and Williams, 1991). The impactites are comprised of brecciated and shatter cone-bearing Yardea Dacite (target rock) in an autochthonous lithic breccia, and a 12 m-long and 3 m-wide dyke of fine-grained crystralline impact melt rock (Schmieder et al., 2015). The ejecta layer (Bunyeroo ejecta horizon in the Banyeroo Formation) contains seawater-reworked cobble to sand-sized fragments of Yardea Dacite, shocked quartz grains, altered impact spherules and glass shards, and tsunami-deposited sandstones (Schmieder et al., 2015). Crater-fill impactites are not preserved.
Proximal Ejecta
    Distal Ejecta
    S
    1. Ejecta in sedimentary column over an area of 20,000 km2. Most distal is ~540 km NW of structure. Had environmental effects (McKirdy et al., 2006).
    Dykes
    M
    Volume of Melt
    Depth of Melting

    References

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    V A Gostin, G E Williams (1986) Dispersed ejecta breccia linked to major impact structure in the late Precambrian of South Australia, p. 123, Canberra, Australia (AUS): Bur. Miner. Resour., Geol. and Geophys., Canberra, url, doi:10.1126/science.233.4760.198

    J B Garvin (1986) Australian impact structures; geomorphology from LEC images, Eos, Transactions, American Geophysical Union 67(16), p. 300, Washington, DC, United States (USA): American Geophysical Union, Washington, DC, url

    V A Gostin, P W Haines, R J F Jenkins, W Compston, I S Williams (1986) Impact ejecta horizon within late Precambrian shales, Adelaide Geosyncline, South Australia, Science 233(4760), p. 198-200, url, doi:10.1126/science.233.4760.198

    G E Williams (1986) The Acraman Impact Structure Source of Ejecta in Late Precambrian Shales, South Australia, Science 233(4760), p. 200-203, pubmed, doi:10.1126/science.233.4760.200

    G E Williams (1987) The Acraman structure; Australia's largest impact scar, Search (Sydney) 18(3), p. 143-145, Sydney, N.S.W., Australia (AUS): Australian and New Zealand Association for the Advancement of Science (ANZAAS), Sydney, N.S.W.

    V A Gostin, R R Keays, M W Wallace (1989) Iridium anomaly from the Acraman impact ejecta horizon: impacts can produce sedimentary iridium peaks, Nature 340(6234), p. 542-544, doi:http://dx.doi.org/10.1038/340542a0

    V A Gostin, R R Keays, M W Wallace (1989) Iridium anomaly from the Acraman impact ejecta horizon; impacts can produce sedimentary iridium peaks, Nature (London) 340(6234), p. 542-544, London, United Kingdom (GBR): Macmillan Journals, London, url, doi:http://dx.doi.org/10.1038/340542a0

    M W Wallace, V A Gostin, R R Keays (1989) Geological Note: Discovery of the Acraman impact ejecta blanket in the officer basin and its stratigraphic significance, Australian Journal of Earth Sciences 36, p. 585-587, doi:10.1080/08120098908729511

    V A Gostin, R R Keays, M W Wallace (1989) Iridium anomaly from the Acraman impact ejecta horizon Impacts can produce sedimentary iridium peaks, Nature 340

    M W Wallace, V A Gostin, R R Keays (1989) Discovery of the Acraman impact ejecta blanket in the officer Basin and its stratigraphic significance, Australian Journal of Earth Sciences 36(4), p. 585-587, doi:10.1080/08120098908729511

    R Walker (1990) An investigation of the Acraman Eject Horizon and the host shales of the Bunyeroo formation located between Bunyeroo Creek and Brachina Creek, central Flinders Ranges (includes map), An investigation of the Acraman Eject Horizon and the host shales of the Bunyeroo Creek and Brachina Creek, central Flinders Ranges, p. 89, url

    M W Wallace, V A Gostin, R R Keays (1990) Acraman impact ejecta and host shales: Evidence for low-temperature mobilization of iridium and other platinoids, Geology 18(2), p. 132-135, doi:http://dx.doi.org/10.1130/0091-7613(1990)018<0132:AIEAHS>2.3.CO;2

    M W Wallace, R R Keays, V A Gostin (1990) Diagenetic enrichment of iridium and other platinoids: evidence from the Acraman impact ejecta horizon and host shales, Abstracts - Geological Society of Australia 25, p. 66-67, Sydney, N.S.W., Australia (AUS): Geological Society of Australia, Sydney, N.S.W., url

    V A Gostin, M W Wallace (1990) Sedimentology and geochemistry of the Bunyeroo impact ejecta horizon, South Australia, LPI Contributions 746, url

    M W Wallace, V A Gostin, R R Keays (1990) Acraman impact ejecta and host shales: Evidence for low-temperature mobilization of iridium and other platinoids, Geology

    M W Wallace, V A Gostin, R R Keays (1990) Spherules and Shard-Like Clasts from the Late Proterozoic Acraman Impact Ejecta Horizon, South Australia, Meteoritics, url, doi:10.1111/j.1945-5100.1990.tb00991.x

    M W Wallace, V A Gostin (1990) The Late Proterozoic Acraman Impact-Towards an Understanding of Impact Events in the Sedimentary Record, Mines and Energy Review South Australia 157, p. 29-35, url

    G E Williams (1990) The Acraman Impact Structure, South Australia, Abstracts for the International Workshop on Meteorite Impact on the Early Earth, url

    R R Keays, M W Wallace, V A Gostin (1991) Mobilization of platinum metals by diagenetic fluids along the Lake Acraman meteorite ejecta horizon, South Australia, Record - Bureau of Mineral Resources, Geology and Geophysics, p. 43-44, Canberra, A.C.T., Australia (AUS): Geoscience Australia, Canberra, A.C.T., pdf

    S L Baldwin, I McDougall, G E Williams (1991) K/Ar and 40Ar/39Ar analyses of meltrock from the Acraman impact structure, Gawler Ranges, South Australia, Australian Journal of Earth Sciences 38(3), p. 291-298, url, doi:10.1080/08120099108727973

    G E Williams (1992) Acraman: a major impact structure from the Neoproterozoic of Australia, Special Paper - Geological Society of America 293, B O Dressler, R A F Grieve, V L Sharpton (ed.), p. 209-224, Boulder, CO, United States (USA): Geological Society of America, doi:10.1130/SPE293-p209

    K Dowling, R R Keays, M W Wallace, V A Gostin, Burkhard O Dressler, V L Sharpton (1992) Mobilization of the platinum group elements by low-temperature fluids; implications for mineralization and the iridium controversy, LPI Contribution 790, p. 23, Houston, TX, United States (USA): Lunar and Planetary Institute, Houston, TX, url

    V A Gostin, R R Keays, M W Wallace (1992) The Acraman impact and its widespread ejecta, South Australia, Lunar and Planetary Inst., International Conference on Large Meteorite Impacts and Planetary Evolution, url

    George E. Williams (1992) Acraman: A major impact structure from the Neoproterozoic of Australia, Geological Society of America Special Papers, p. 209-224, url, doi:10.1130/SPE293-p209

    P Lee (1993) Briny lakes on early Mars? Terrestrial intracrater playas and martian candidates, LPI Technical Report 93-03, Par, S Squyres, J Kasting (ed.), p. 17, Houston, TX, United States (USA): Lunar and Planetary Institute, Houston, TX, url

    E P Gurov (1993) The Acraman impact structure Estimation of the diameter by the ejecta layer thickness, Abstracts of the 24th Lunar and Planetary Science Conference, held in Houston, TX, url

    G E Williams (1994) Acraman, South Australia; Australia's large meteorite impact structure, Proceedings of the Royal Society of Victoria 106, p. 105-127, Melbourne, Victoria, Australia (AUS): Royal Society of Victoria, Melbourne, Victoria

    V A Gostin, M Zbik (1994) "Flindersites", distant ejecta impactites from South Australia, Lunar and Planetary Science Conference 25, Part 1, p. 447-448, Houston, TX, United States (USA): Lunar and Planetary Science Conference, Houston, TX, url

    G Williams (1995) Magnetic signature and morphology of the Acraman impact structure, Geophysics Down Under 21, p. 30-31, Canberra, A.C.T., Australia (AUS): Geological Society of Australia, Specialist Group on Solid-Earth Geophysics, Canberra, A.C.T., url

    G E Williams, P W Schmidt, M Boyd (1996) Magnetic signature and morphology of the Acraman impact structure, South Australia, AGSO Journal of Australian Geology and Geophysics 16(4), Andrew Y Glikson (ed.), p. 431-442, Canberra, A.C.T., Australia (AUS): Australian Geological Survey Organisation, Canberra, A.C.T., url

    E P Gurov, A F Khmel'Nitskii (1996) Occurrence and Preservation of Ejecta from Impact Structures: the Boltysh and Acraman Craters, Solar System Research 30(1), p. 16-20, url

    P W Schmidt, G E Williams (1996) Palaeomagnetism of the ejecta-bearing Bunyeroo Formation, late Neoproterozoic, Adelaide fold belt, and the age of the Acraman impact, Earth and Planetary Science Letters 144(3-4), p. 347-357, Amsterdam, Netherlands (NLD): Elsevier, Amsterdam, url, doi:http://dx.doi.org/10.1016/S0012-821X(96)00169-0

    M W Wallace, V A Gostin (1996) Sedimentology of the Neoproterozoic Acraman impact-ejecta horizon, South Australia, AGSO journal of Australian geology & geophysics , url

    V A Gostin, M Zbik (1999) Petrology and microstructure of distal impact ejecta from the Flinders Ranges, Australia, Meteoritics & Planetary Science 34, p. 581-592, Meteoritical Society, url

    B M Simonson, M Hornstein, S Hassler (2000) Particles in late Archean Carawine Dolomite (Western Australia) resemble Muong Nong-type tektites, Impacts and the Early Earth 91, I Gilmour, C Koeberl (ed.), p. 181-213, url

    K R Arouri, P J Conaghan, M R Walter, G C O Bischoff, K Grey (2000) Reconnaissance sedimentology and hydrocarbon biomarkers of Ediacarian microbial mats and acritarchs, lower Ungoolya Group, Officer Basin, Precambrian Research 100, p. 235-280, url, doi:10.1016/S0301-9268(99)00076-5

    K Grey, A C Hill, M R Walter, Jack D Farmer, R Blankenship (2002) Plankton and isotope changes at the late Neoproterozoic Acraman impact ejecta layer, Astrobiology 2(4), p. 499-500, Larchmont, NY, United States (USA): Mary Ann Liebert, Larchmont, NY, url

    K Grey (2002) Towards Neoproterozoic biozonation in Australia, Abstracts - Geological Society of Australia 68, Glenn A Brock, John A Talent (ed.), p. 70, Sydney, N.S.W., Australia (AUS): Geological Society of Australia, Sydney, N.S.W., url

    K Grey (2002) A sixth great extinction and recovery event? The Ediacarian Acraman bolide impact, Abstracts - Geological Society of Australia 67, V P Preiss (ed.), p. 33, Sydney, N.S.W., Australia (AUS): Geological Society of Australia, Sydney, N.S.W., url

    R Nowak (2003) Rock and ice vie for credit complex life, New Scientist (1971) 178(2393), p. 17, London, United Kingdom (GBR): Reed Business Information, London, url

    K Grey, M R Walter, C R Calver (2003) Neoproterozoic biotic diversification: Snowball Earth or aftermath of the Acraman impact?, Geology, p. 459, url, doi:10.1130/0091-7613(2003)031<0459:NBDSEO>2.0.CO;2

    P J Hawke (2003) A re-evaluation of the size of the Acraman impact structure, Australia, Meteoritics & Planetary Science 38, pdf

    K Grey (2004) The significance of the ca. 580 Ma impact event, Abstracts - Geological Society of Australia 73, Jocelyn McPhie, Peter McGoldrick (ed.), p. 232, Sydney, N.S.W., Australia (AUS): Geological Society of Australia, Sydney, N.S.W., url

    L Webster, D M McKirdy, K Grey, K R Arouri, V Gostin (2004) Biomarker and sedimentological signals of concerted environmental stress on the late Neoproterozoic palaeo-Pacific Ocean, Cameron McIntyre (ed.), North Ryde, N.S.W., Australia (AUS): Commonwealth Scientific and Industrial Research Organisation (CSIRO) Petroleum, North Ryde, N.S.W., url

    A C Hill, P Gorjan, M R Walter (2004) Carbon, nitrogen and sulfur stable-isotope changes before and after the approximately 580 Ma (late Neoproterozoic) Acraman impact event, Abstracts - Geological Society of Australia 73, Jocelyn McPhie, Peter McGoldrick (ed.), p. 233, Sydney, N.S.W., Australia (AUS): Geological Society of Australia, Sydney, N.S.W., url

    K Grey (2004) The Acraman impact and its relation to the snowball Earth and biotic diversification, Abstracts with Programs - Geological Society of America 36(5), p. 321, Boulder, CO, United States (USA): Geological Society of America (GSA), Boulder, CO, url

    L J Webster, A C Hill, K Grey, V A Gostin (2004) Neoproterozoic Acraman ejecta in the Officer Basin, Australian Journal of Earth Sciences 51(1), p. 47-51, url, doi:10.1046/j.1400-0952.2003.01044.x.001

    P J Hawke (2004) The geophysical signatures and exploration potential of Australia's meteorite impact structures, p. 1-314, pdf

    G Webb (2005) Crisis and Recovery: The Acraman impact event and its biostratigraphic significance, Journal of the Virtual Explorer 20, doi:10.3809/jvirtex.2005.00143

    K Grey, J Laurie, J Gehling (2005) The "new" Ediacaran Period, Aus Geo News 80, p. 0-unpaginated, Canberra, Australia (AUS): Australian Geological Survey Organisation, Canberra, url

    K Grey (2005) Ediacaran palynology of Australia, Memoir of the Association of Australasian Palaeontologists 31, p. 439, Sydney, N.S.W., Australia (AUS): Association of Australasian Palaeontologists, Sydney, N.S.W., url

    G E Williams, V A Gostin (2005) Acraman - Bunyeroo impact event (Ediacaran), South Australia, and environmental consequences: Twenty-five years on, Australian Journal of Earth Sciences 52(4-5), p. 607-620, doi:10.1080/08120090500181036

    A C Hill (2006) The Ediacaran Acraman impact event; did it affect the long-term carbon cycle?, Geochimica et Cosmochimica Acta 70(18S), p. 1-A250, New York, NY, International (III): Elsevier, New York, NY, url, doi:http://dx.doi.org/10.1016/j.gca.2006.06.504

    D M McKirdy, L J Webster, K R Arouri, K Grey, V A Gostin (2006) Contrasting sterane signatures in Neoproterozoic marine rocks of Australia before and after the Acraman asteroid impact, Organic Geochemistry 37(2), p. 189-207, url, doi:10.1016/j.orggeochem.2005.09.005

    L Webster (2007) Terminal Proterozoic biomarker assemblages in the Centralian Superbasin before and after the Acraman meteorite impact, Terminal Proterozoic biomarker assemblages in the Centralian Superbasin before and after the Acraman meteorite impact, p. 47, url

    L J Webster, D M McKirdy, K Grey (2007) Biogeochemical anatomy of the Acraman bolide impact, 23rd International Meeting on Organic Geochemistry 23, p. 257-258

    G E Williams, V A Gostin (2010) Geomorphology of the Acraman impact structure, Gawler Ranges, South Australia, Cuadernos do Laboratorio Xeoloxico de Laxe 35, p. 209-220, url

    V A Gostin, D M McKirdy, L J Webster, G E Williams (2010) Ediacaran ice-rafting and coeval asteroid impact, South Australia: insights into the terminal Proterozoic environment, Australian Journal of Earth Sciences 57(7), p. 859-869, London, United Kingdom (GBR): Geological Society of London, London, url, doi:10.1080/08120099.2010.509408

    C Hallmann, K Grey, L J Webster, D M McKirdy, K Grice (2010) Molecular signature of the Neoproterozoic Acraman impact event, Organic Geochemistry 41(2), Evelyn S Krull, David M McKirdy (ed.), p. 111-115, International (III): Elsevier, url, doi:http://dx.doi.org/10.1016/j.orggeochem.2009.11.007

    Christian Hallmann, Kathleen Grey, Lynn J Webster, David M McKirdy, Kliti Grice (2010) Molecular signature of the Neoproterozoic Acraman impact event, Organic Geochemistry 41(2), p. 111-115, url, doi:10.1016/j.orggeochem.2009.11.007

    G E Williams, V A Gostin (2010) Geomorphology of the Acraman impact structure, gawler Ranges, south Australia, Xeolóxico de LaxeCoruña 35, p. 209-220

    V A Gostin, D McKirdy, G Williams (2011) Ice, an asteroid impact and the rise of complex life, Australasian Science (Hawksburn) 32(4), p. 34-36, Hawksburn, Victoria, Australia (AUS): Control Publications, Hawksburn, Victoria, url

    Sebastian Willman, M Moczydłowska (2011) Acritarchs in the Ediacaran of Australia — Local or global significance? Evidence from the Lake Maurice West 1 drillcore, Review of Palaeobotany and Palynology 166(1-2), p. 12-28, url, doi:10.1016/j.revpalbo.2011.04.005

    M Schmieder, E Tohver, F Jourdan, S W Denyszyn, P W Haines (2012) The Acraman Impact Melt Rock Revisited, Meteoritics and Planetary Science Supplement, url

    M Schmieder, E Tohver, S W Denyszyn, F Jourdan, P W Haines (2013) Shock-metamorphosed zircons from the Acraman impact structure (South Australia) - tracers of multi-stage impact crater evolution, 44th Lunar and Planetary Science Conference, url

    M Schmieder, E Tohver, F Jourdan, S W Denyszyn, P W Haines (2015) Zircons from the Acraman impact melt rock (South Australia): Shock metamorphism, U-Pb and 40Ar/39Ar systematics, and implications for the isotopic dating of impact events, Geochimica et Cosmochimica Acta 161, p. 71-100, Elsevier Ltd, doi:10.1016/j.gca.2015.04.021

    N E Timms, T M Erickson, M A Pearce, A J Cavosie, M Schmieder, E Tohver, S M Reddy, M R Zanetti, A A Nemchin, A Wittmann (2017) A pressure-temperature phase diagram for zircon at extreme conditions, Earth-Science Reviews 165, p. 185-202, Elsevier B.V., doi:10.1016/j.earscirev.2016.12.008