Microscopic planar features in quartz from Scollard Canyon, Alberta, and the Cretaceous–Tertiary boundary event

Abstract

Quartz grains separated from the Cretaceous–Tertiary (K/T) boundary clay at Scollard Canyon, Alberta, have prominent, microscopic planar features. These occur in 15–30% of the grains from the lower 1.5 cm of the boundary clay. They commonly correspond to the ω and π orientations found at known meteorite impact sites and differ from deformation features produced by other dynamic geologic processes. Basal planar features, however, are absent here and at other K/T sites. One possible explanation is that quartz at boundary sites is an incomplete sample of shocked quartz from the postulated K/T impact and unshocked detrital quartz. The source of the shocked quartz most likely was close to the point of impact and near surface. This and previous isotopic data suggest the K/T target site contained a relatively thin upper unit of quartz-bearing crystalline rocks overlying basaltic material, corresponding possibly to thinned continent or a continental margin.