Science. 1993 Oct 29;262(5134):729-32. doi: 10.1126/science.262.5134.729.
The (40)Ar/(39)Ar 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 (40)Ar/(39)Ar 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 (40)Ar/(39)Ar age of 73.8 +/- 0.3 Ma for MIS reported herein.
爱荷华州曼森撞击构造（Manson Impact Structure，MIS）中熔基质角砾岩中的一粒天河石碎屑的（40）Ar/（39）Ar 年龄表明，MIS 形成于 7380 万年前（Ma），与白垩纪-第三纪边界（6443Ma）并不一致。MIS 天河石的（40）Ar/（39）Ar 年龄比之前解释为 64 到 65Ma 的 MIS 冲击变质微斜长石和熔基质角砾岩的（40）Ar/（39）Ar 年龄谱大 900 万年。在南达科他州皮尔斯页岩的放射性年代测定约束下，在 Crow Creek 成员（上坎潘阶）中发现了冲击变质的石英、长石和锆石颗粒，这些颗粒的放射性年代与本文报道的 MIS 的 7380 万年前（Ma）的（40）Ar/（39）Ar 年龄一致。
