Science. 1981 Dec 18;214(4527):1341-3. doi: 10.1126/science.214.4527.1341.
An iridium abundance anomaly, with concentrations up to 5000 parts per trillion over a background level of 4 to 20 parts per trillion, has been located in sedimentary rocks laid down under freshwater swamp conditions in the Raton Basin of northeastern New Mexico. The anomaly occurs at the base of a coal bed, at the same stratigraphic position at which several well-known species of Cretaceous-age pollen became extinct.
在新墨西哥州东北部拉顿盆地的淡水沼泽条件下形成的沉积岩中，发现了铱异常，其浓度高达背景值（4 到 20 万亿分之 1）的 5000 倍。该异常出现在煤层底部，与几个著名的白垩纪花粉灭绝物种所处的地层位置相同。
