Other
Scientific paper
Sep 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992lmip.conf...30g&link_type=abstract
In Lunar and Planetary Inst., International Conference on Large Meteorite Impacts and Planetary Evolution p 30-31 (SEE N93-10112
Other
Australia, Earth Crust, Ejecta, Meteorite Collisions, Precambrian Period, Shales, Anomalies, Coarseness, Geochronology, Grain Size, Iridium, Sedimentary Rocks, Sediments, Stratigraphy
Scientific paper
Discovery of a widespread horizon of shock-deformed volcaniclastic ejecta preserved in Late Proterozoic (approx. 600 Ma) shales in South Australia and its probable link to the Acraman impact structure in the Middle Proterozoic Gawler Range. Volcanics provide a rare opportunity to study the effects of a major terrestrial impact, including the sedimentology and distribution of an ejecta blanket and its precious-metal signature. The ejecta horizon occurs in the Bunyeroo Formation at many localities within the Adelaide Geosyncline, including the Wearing Hills, which are approx. 350 km northeast of the Acraman impact site. Following a search at the same stratigraphic level in other basins in South Australia, the ejecta has been located within the Lower Rodda beds of the Officer Basin, extending the limits of the ejecta to approx. 470 km northwest of the Acraman impact structure. The ejecta is therefore widely dispersed, and provides an important chronostratigraphic marker enabling precise correlation of Late Proterozoic sequences in southern Australia. In summary, the Bunyeroo ejecta is unique as the only known example of a widely dispersed, coarse-grained ejecta blanket that is, moreover, strongly linked to a known major impact structure. The marked Ir-PGE anomalies in the ejecta horizon provide support for the hypothesis that meteorite impact events can produce Ir anomalies interrestrial sediments. The findings also indicate that Ir can be mobilized and concentrated in sediments by low-temperature diagenetic processes. The identification of ejecta horizons in sedimentary rocks therefore should be based on the coincidence of shock-metamorphic features in the detritus and clear Ir anomalies.
Gostin Victor A.
Keays Reid R.
Wallace Malcolm W.
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