Evidence from cathodoluminescence for non-volcanic origin of shocked quartz at the Cretaceous/Tertiary boundary

Abstract

Bohor et al.1 have described shocked quartz, displaying one or more sets of planar elements indexed to rational crystallographic planes, associated with anomalous siderophile abundances at the Cretaceous/Tertiary (K/T) stratigraphic boundary in eastern Montana. Shocked quartz has subsequently been shown at several K/T boundary sections around the world, and has been attributed to the effects of impact on crustal rocks2–7. This impact may have occurred within the scenario of comet (or meteor) collision8,9 or, alternatively, shocked quartz at the K/T boundary could be the product of volcanic eruption, rather than bolide impact10–14. Here we describe a cathodoluminescence study of shocked quartz at the K/T boundary in southeastern Colorado that reveals a diversity of luminescence colours not present in quartz from known volcanic ejecta, but typical of quartz in crustal/supracrustal lithologies. Cathodoluminescence colour diversity indicates that the grains were originally derived from a variety of igneous, metamorphic, and sedimentary rocks subsequently overprinted with planar shock features. These observations lend support to the hypothesis of bolide impact at the end of the Cretaceous period.