Exploration wells and interpretations of two-dimensional seismic surveys delineate a circular feature in the subsurface ∼12 km southeast of Barrow, Alaska. This is the Avak impact structure. It is at ∼1 km in depth, and it is ∼10 km in diameter. Displaced and chaotic stratigraphy, shatter cones, and shocked quartz occur at the Avak #1 well, which tested the central uplift of the Avak feature. To date, the age of the Avak impact has been poorly constrained.

Examinations of core holes from comparatively shallow wells drilled ∼50 km east of the Avak impact site show there is an assemblage of exotic rock fragments within a section of marine mud and sand. This is a breccia composed of angular to rounded rock fragments composed of black shale, reddish-brown argillitic siltstone, chert, and quartzite pebbles in sizes up to ∼5 cm. These lithologies are representative of the stratigraphic section that was ejected by the Avak event.

These exotic rock fragments occur within the marine mudstone of the Seabee Formation and within poorly sorted, disorganized sands lacking sedimentary structures. Palynology shows that the marine mudstone of the Seabee Formation in this area is Turonian to Coniacian in age. Palynology of the ejecta matrix provides a middle to late Turonian date for the Avak impact event.