Fossils within accreted terranes are typically used to describe the age or origin of the exotic geologic blocks. However, accretion may also provide new pathways for faunal exchange between previously disconnected landmasses. One such landmass, the result of accretion, is Beringia, that entity encompassing northeastern Asia and northwestern North America and the surmised land connection between the two regions. The present concept of Beringia as a Quaternary subcontinent includes a climatic component in the form of glacial advances and retreats driving changes in sea level. These changes may have facilitated exchanges of marine biota between the Pacific Ocean and Arctic Basin, or exchanges of terrestrial faunas and floras between Asia and North America. The Beringian ecosystem includes specializations of the flora and fauna, especially in the vertebrate fauna. A review of tectonic reconstructions and the striking taxon-free parallel patterns in data on the Cretaceous and Quaternary fauna and flora suggest that a generalized concept of Beringia should be formally extended back in time to the Cretaceous. A significant shift in emphasis of defining variables occurs with this extension. Climate, in the form of meteorological phenomena, and geologic history are important variables in the previously recognized definition of Beringia. The extension of Beringia into the Cretaceous implies that Beringia is rooted in its accretionary rather than its climatic history; in other words, the geographic pattern as the result of tectonics is the defining parameter for Beringia.

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.