The Paleogene Eagle Butte meteorite impact and dikes of seismic wave mobilized tuff in western Canada

Abstract

Meteorite impact‐induced mobilization of a volcanic ash tuff resulting in 100s of m long lithified clastic dikes is a novel mechanism in the geologic record. The Paleogene Eagle Butte impact event in southeastern Alberta, western Canada, resulted in a 10–17 km diameter central peak crater, now partially eroded and buried without expression at the surface. Impact shock waves, degraded to elastic waves, mobilized sediment 10s of km beyond the crater and resulted in a cluster of 100s of m long, 10–20 cm thick, dikes consisting of volcanic ash. It is not well understood how effective meteorite impact‐induced waves would be as triggers for sediment mobilization at areas 10s of km distant from an impact crater. Emplacement of the Manyberries dike cluster provides insight into this issue and confirms that shock waves, degraded to elastic waves, can indeed liquefy and mobilize sediments at distances as much as 5 crater radii beyond an impact site. These impact‐induced waves triggered liquefaction and mobilization of a shallowly buried Campanian‐Maastrichtian deposit of volcanic ash and injected the tuff sediment along impact‐induced faults. The lithification of the dike tuff, consisting of the cristobalite–tridymite groundmass, resulted from partial dissolution of glass shards and precipitation of opaline cement. These weathering resistant dikes of indurated tuff sediment extend for as much as 800 m on recessive Campanian‐Maastrichtian shale ridges of the badlands topography.