Origin of a late Eocene to pre-Miocene buried crater and breccia lens at Fohn-1, North Bonaparte Basin, Timer Sea: A probable extraterrestrial connection
Date
2000
Authors
Gorter, John
Glikson, Andrew
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University of Arkansas
Abstract
Seismic reflection data and an at least 350 m thick, PGE-rich carbonate breccia lens intersected by the Fohn-1 exploration well in the Timor Sea off northern Australia, are interpreted in terms of a buried 4.8 km-diameter impact crater of late Eocene to pre-Miocene age. The crater displays the classic elements of impact structures, including a central uplift, ring syncline, and upraised rims. The presence in the breccia of redeposited Campanian and Maastrichtian microfossils suggests rebound of strata from levels deeper than 1250 m below the pre-Miocene unconformity. Morphometric modelling suggests an original crater at least 1400 m deep, which is consistent with the excavation of Cretaceous strata. Stratigraphic and palaeontological evidence suggests that the impact occurred between 36 and 24.6 Ma. The breccia contains a pseudotachylite component enriched in the inert Pt group elements (PGE) (Ir, Ru) by factors of 5-12 above the values of common sediments. The more mobile PGE (Os, Pt, Pd) show a wide scatter and terrestrial-type values. Opposite geochemical/stratigraphic trends pertain to different PGE species-the relatively inert Ir-Ru group shows an overall concentration at the base of the section, whereas the more mobile Os shows peaks at median levels of the section-suggesting upward diagenetic leaching. The near-chondritic PGE patterns at the base of the breccia pile are accompanied by near-chondritic Ni/Cr, Co/Cr, Ni/Ir, Ni/Pt, and Cu/Pd ratios. Departure from these values related to alteration at higher levels in the breccia pile is accompanied with high S levels (~1%).
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Keywords: crater; impact structure; Tertiary; Indian Ocean
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Meteoritics and Planetary Science
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Journal article
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2037-12-31
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