Search for evidence of impact at the Permian-Triassic boundary in Antarctica and Australia

Life on Earth was almost destroyed some 250 m.y. ago in the most profound of all known mass extinction events. We investigated the possible role of impact by an extraterrestrial bolide through chemical and mineralogical characterization of boundary breccias, search for shocked quartz, and analysis f...

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Bibliographic Details
Published in:Geology (Boulder) 1998-11, Vol.26 (11), p.979-982
Main Authors: Retallack, Gregory J, Seyedolali, Abbas, Krull, Evelyn S, Holser, William T, Ambers, Clifford P, Kyte, Frank T
Format: Article
Language:English
Subjects:
Antarctica
Australasia
Australia
bolides
exploration
Extinction
geochemical anomalies
Geological time
Geology
Graphite Peak
impactites
impacts
iridium
Lower Triassic
mass extinctions
Mesozoic
metals
metamorphic rocks
metamorphism
meteorites
meteors
Mount Crean
paleogeography
Paleozoic
Permian
Permian-Triassic boundary
platinum group
shock metamorphism
stratigraphic boundary
Stratigraphy
Triassic
Upper Permian
Wybung Head Australia
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Summary:Life on Earth was almost destroyed some 250 m.y. ago in the most profound of all known mass extinction events. We investigated the possible role of impact by an extraterrestrial bolide through chemical and mineralogical characterization of boundary breccias, search for shocked quartz, and analysis for iridium in Permian-Triassic boundary sections at Graphite Peak and Mount Crean, Antarctica, and Wybung Head, Australia. Thin claystone breccias at the isotopically and paleobotanically defined boundary at all three locations are interpreted as redeposited soil rather than impact ejecta. The breccias at all three locations also yielded shocked quartz, but it is an order of magnitude less abundant (0.2 vol%) and smaller (only as much as 176 µm diameter) than shocked quartz at some Cretaceous-Tertiary boundary sites. Faint iridium "anomalies" were detected (up to 134 pg·g-1). These values are an order of magnitude less than iridium anomalies at some Cretaceous-Tertiary boundary sites. Furthermore, peak iridium values are as much as 1 m below the isotopically and paleobotanically defined boundary. The idea that impact caused the extinctions thus remains to be demonstrated convincingly.
ISSN:0091-7613
1943-2682
DOI:10.1130/0091-7613(1998)026<0979:SFEOIA>2.3.CO;2