Impactitelevel resolution

The Alvarez discovery led to the ultimate temporal resolution currently possible in the rock record. Making the well-supported assumption that the K-T boundary recognized by Alvarez is an impactite allows global marine and nonmarine correlation at resolution of less than one year (Figure 2.2). This was a paradigm-altering breakthrough at a time when one-million-year resolution was not guaranteed by any other method. In the future, perhaps one of the most important uses of the K-T boundary will be as a test of high-resolution geochronology.

In the best-preserved K-T boundary sections (our discussions do not include K-T impactites preserved in marine strata), the extinction horizon and the anomalous concentration of iridium are found in association with a unique claystone layer of kaolinitic and smectitic composition. The concentration of cm 130

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