| Abstract: | The 40Ar/39Ar ages of a sanidine clast from a melt-matrix breccia of the Manson, Iowa, impact structure (MIS) indicate that the MIS formed 73.8 ?? 0.3 million years ago (Ma) and is not coincident with the Cretaceous-Tertiary boundary (64.43 ?? 0.05 Ma). The MIS sanidine is 9 million years older than 40Ar/39Ar age spectra of MIS shock-metamorphosed microcline and melt-matrix breccia interpreted earlier to be 64 to 65 Ma. Grains of shock-metamorphosed quartz, feldspar, and zircon were found in the Crow Creek Member (upper Campanian) at a biostratigraphic level constrained by radiometric ages in the Pierre Shale of South Dakota that are consistent with the 40Ar/39Ar age of 73.8 ?? 0.3 Ma for MIS reported herein. |
| Genre: | Article |
| ProdID: | 70017993 |
| Citation Author: | Izett, G. A.; Cobban, W. A.; Obradovich, J. D.; Kunk, M. J. |
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| Citation End Page: | 732 |
| Citation Issue: | 5134 |
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| Citation Language: | English |
| Citation Larger Work Title: | Science |
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| Citation Number Of Pages: | 4 |
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| Citation Search Results Text: | The Manson Impact Structure: 40Ar/39Ar age and its distal impact ejecta in the pierre shale in southeastern South Dakota; 1993; Article; Journal; Science; Izett, G. A.; Cobban, W. A.; Obradovich, J. D.; Kunk, M. J. |
| Citation Start Page: | 729 |
| Citation Volume: | 262 |
| Citation Year: | 1993 |
| Type: | citation/reference |
| Text: | The Manson Impact Structure: 40Ar/39Ar age and its distal impact ejecta in the pierre shale in southeastern South Dakota; 1993; Article; Journal; Science; Izett, G. A.; Cobban, W. A.; Obradovich, J. D.; Kunk, M. J. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| Date Other: | Fri, 1 Jan 1993 00:00 -0600 |
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