The Manson Impact Structure: 40Ar/39Ar age and its distal impact ejecta in the Pierre Shale in southeastern South Dakota
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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.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | The Manson Impact Structure: 40Ar/39Ar age and its distal impact ejecta in the Pierre Shale in southeastern South Dakota |
| Series title | Science |
| DOI | 10.1126/science.262.5134.729 |
| Volume | 262 |
| Issue | 5134 |
| Year Published | 1993 |
| Language | English |
| Publisher | AAAS |
| Contributing office(s) | Eastern Geology and Paleoclimate Science Center |
| Description | 4 p. |
| First page | 729 |
| Last page | 732 |
| Country | United States |
| State | South Dakota |
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