Tillites, diamictites, and ballistic ejecta of large impacts

The primary evidence for the temporal and spatial distribution of glaciation prior to the Cenozoic is the occurrence of tillites. These are diamictites and associated deposits, which have features considered diagnostic of glacial action. Fallout of ballistic ejecta from the impact of large asteroids or comets can also create large-scale debris flows with simultaneous rainout of debris. Recent calculations of the predicted volume and distribution of impact-generated diamictites suggest that they should be common in the geologic record. The possible confusion between glacial and impact diamictites suggests that a review of the properties of diamictites of various origins is required. Evidence of shock deformation in diamictites is the most important criterion for determining an impact origin. -from Author