Kunk M J, Izett G A, Haugerud R A, Sutter J F
Science. 1989 Jun 30;244(4912):1565-8. doi: 10.1126/science.244.4912.1565.
The mineralogy of shocked mineral and lithic grains in the Cretaceous-Tertiary (K-T) boundary claystone worldwide is most consistent with a bolide impact on a continent. Both the concentrations and sizes of these shocked grains are greatest in the western interior of North America. These data suggest that the Manson impact structure in north-central Iowa is a viable candidate for the K-T boundary impact event. Argon-40-argon-39 age spectrum dating of shocked microcline from the crystalline central uplift of the Manson impact structure indicates that there was severe argon-40 loss at 65.7 +/- 1.0 million years ago, an age that is indistinguishable from that of the K-T boundary, within the limits of analytical precision.
全球白垩纪 - 第三纪（K - T）边界黏土岩中冲击矿物和岩石颗粒的矿物学特征与小行星对大陆的撞击最为相符。这些冲击颗粒的浓度和尺寸在北美中西部地区最大。这些数据表明，爱荷华州中北部的曼森撞击构造是K - T边界撞击事件的一个可能候选地点。对曼森撞击构造结晶中央隆起处的冲击微斜长石进行的氩 - 40 - 氩 - 39年龄谱测年显示，在6570±100万年前存在严重的氩 - 40损失，在分析精度范围内，这个年龄与K - T边界的年龄无法区分。
