PALEOGEOGRAPHIC AFFINITIES OF CARBONIFEROUS AND OLDER STRATA IN NORTHERN ALASKA

Paleontologic and sedimentologic studies suggest that mixed paleogeographic affinities characterize Carboniferous and older strata in northern Alaska. Cambrian-Middle Devonian rocks form two main successions. Platform carbonates crop out mostly south of 68°N latitude and contain fossil assemblages with elements typical of both Laurentian (North American) and Siberian biotic provinces. To the north, coeval strata in outcrop and subsurface are chiefly deep-water siliciclastic rocks with a cosmopolitan fauna. This basinal succession could have formed along the northern margin of the carbonate platform, but cannot be depositionally tied to that platform until Devonian time or later. Contrasts in lithofacies and biofacies of the North Alaska carbonate platform with those of coeval successions in Siberia and the Canadian Arctic Islands suggest that the Alaskan rocks may have formed on a crustal fragment rifted away from Siberia during the Neoproterozoic. North Alaskan carbonate strata have striking similarities to lower Paleozoic rocks of central Alaska (Farewell terrane) and northeastern Russia (peri-Siberian terranes), however, and likely formed near these successions.

Siliciclastic, chiefly shallow-marine and non-marine strata of Devonian and Mississippian age (Endicott Group and related rocks) overlie lower Paleozoic successions in northern Alaska. These rocks have been correlated with the Middle and Upper Devonian clastic wedge in the Canadian Arctic Islands, but no palinspastic restoration has yet been proposed that provides a completely satisfactory linkage of these depositional systems. Mainly platform carbonate rocks of the Lisburne Group (Carboniferous-Permian) depositionally (and typically gradationally) overlie the Endicott across northern Alaska. The Lisburne differs from partly coeval carbonate rocks of the Canadian Arctic Islands (Sverdrup Basin) in lacking reefs, which characterize the Sverdrup succession. Plant fossils with Siberian affinities occur in deep-water facies of both the Endicott and Lisburne Groups; other Endicott floras resemble those of Spitsbergen. Lisburne foraminifer assemblages contain both Eurasian and North American forms. Thus, Siberian affinities in northern Alaskan biotas persist from Cambrian through Carboniferous time.