Anomalous concentrations of Ir have been found in upper Eocene sediments from Ocean Drilling Program (ODP) Hole 1090B.Clear and dark-colored spherules that are believed to be microtektites and clinopyroxene-bearing microkrystites, respectively, were found in the samples with highest Ir.The peak Ir concentration in Sample 177-1090B-30X-5,105-106 cm (954 pg/g) and the net Ir fluence (14 ng/cm2) at this site are higher that at most other localities except for Caribbean site RC9-58.The Ir anomaly and impact debris are probably correlative with similar deposits found at ODP Site 689 on the Maude Rise and at other localities around the world.
The Late Devonian, and in particular the Frasnian-Famennian (F/F) boundary, records one of the five largest mass extinctions in the fossil record. Glassy spherules believed to be of impact origin are associated with the F/F boundary in two Belgian sections (Senzeille and Hony). They have also been reported in sediments deposited approximately 1.5 to 2 m.y. above the boundary in south China, and in the Canning Basin (Australia) this event coincides with a 300 pg/g Ir anomaly. In this study, the F/F boundary in the Hony section was analyzed for trace and major elements to test the possibility of an Ir anomaly associated with the spherule layer. No significant positive Ir anomaly was detected in the 2 m of section investigated. Nevertheless, chalcophile elements show an increase within the dark shale bed marking the F/F boundary. This increase is interpreted to represent a reduction in oxygen concentrations in the depo-sitional environment. This level must be equivalent to the upper part of the Kellwasser anoxic event recognized throughout the paleo-Tethys in what is now western Europe. The F/F boundary seems to be marked by a succession of major events, including impact, oxygen-depleted water on the shelf, and worldwide extinction of organisms.
Research Article| November 01, 1998 Search for evidence of impact at the Permian-Triassic boundary in Antarctica and Australia Gregory J. Retallack; Gregory J. Retallack 1Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403-1272 Search for other works by this author on: GSW Google Scholar Abbas Seyedolali; Abbas Seyedolali 1Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403-1272 Search for other works by this author on: GSW Google Scholar Evelyn S. Krull; Evelyn S. Krull 1Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403-1272 Search for other works by this author on: GSW Google Scholar William T. Holser; William T. Holser 1Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403-1272 Search for other works by this author on: GSW Google Scholar Clifford P. Ambers; Clifford P. Ambers 1Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403-1272 Search for other works by this author on: GSW Google Scholar Frank T. Kyte Frank T. Kyte 2Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095-1567 Search for other works by this author on: GSW Google Scholar Geology (1998) 26 (11): 979–982. https://doi.org/10.1130/0091-7613(1998)026<0979:SFEOIA>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Gregory J. Retallack, Abbas Seyedolali, Evelyn S. Krull, William T. Holser, Clifford P. Ambers, Frank T. Kyte; Search for evidence of impact at the Permian-Triassic boundary in Antarctica and Australia. Geology 1998;; 26 (11): 979–982. doi: https://doi.org/10.1130/0091-7613(1998)026<0979:SFEOIA>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract 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 micrometers m diameter) than shocked quartz at some Cretaceous-Tertiary boundary sites. Faint iridium "anomalies" were detected (up to 134 pgṁg−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. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
