A Paleobiogeographic Study of Paleozoic-Early Cretaceous Fossil Fauna and Flora of the Arctic Alaska Terrane

Blodgett, Robert

This report provides a synoptic overview and digital database of the Arctic Alaska terrane faunas and floras of Cambrian to Early Cretaceous age in order to better constrain speculation as to the paleogeographic origin of the terrane, host to the largest petroleum province in North America. At present the two most popular models for its origin include: 1.) a counter-clockwise rotation out of the Canada Basin (commonly referred to as the “Windshield-Wiper” model) originating from a putative late Mesozoic rifting event; and 2.) an Eurasian origin whereby it represents a rift fragment of the Siberian paleocontinent (or associated pericratonic terrane) or less likely of Baltica. Cambrian-early Late Devonian (Frasnian) marine faunas show a strongly consistent Siberian affinity, although a few occurrences of Cambrian trilobites with North American affinities have also been previously noted (A.R. Palmer recently indicates these earlier alleged North American trilobite faunas should be re-examined, as more modern work shows closely similar forms to exist as well in Siberia). Early Mississippian marine faunas have very strong linkages with faunas from the western and mid-continent portions of North America, but this may reflect the broad, cosmopolitan condition of marine faunas of this time as many of these species names are also recognized in the Russian Platform. The Late Mississippian was apparently a time of greater provincialism, and it is during this time that strong Eurasian linkages are again noted among the brachiopods (especially in the presence of gigantoproductids, unknown anywhere in Laurentia) and in Angaran Floral Realm plants found in the region near Kurupa Lake. Little is known of Pennsylvanian faunas, but they, too, also seem to be Eurasian in character. Permian marine fauna are distinctly of Arctic Permian (or Boreal) cast, but need more intense study at the species level. The low diversity (or near absence) of Early Permian fusulinids (in contrast to their relative abundance in the Canadian Arctic Islands) is consistent with a Siberian origin (or alliance) as they are also almost totally lacking there during this time. Late Triassic bivalves, brachiopods, and to a lesser degree the ostracodes indicate a very strong alliance with northeastern Siberia. Likewise, Early Jurassic bivalves (notably the species Otapiria tailleuri Imlay which is extremely abundant in Sinemurian strata across the breadth of this terrane) suggest closer ties with northeastern Siberia (where it is present), rather that with the Canadian Arctic Islands (where it is absent). By Middle Jurassic time, bivalves and ammonite faunas of the Arctic Alaska terrane are very closely similar to those in Arctic Canada (and southern Alaska as well), suggesting that this terrane had more or less attained its present geographic position relative to North America. Late Jurassic and Early Cretaceous marine faunas, likewise, indicate a nearly identical taxic content with that found in adjoining Arctic Canada and the northern part of the Cretaceous Interior Seaway. In summary, this overview of paleobiogeographic affinities of the Arctic Alaska terrane fossil biota suggest that it represents a continental margin sequence that was rifted away from, or in close proximity to, the present-day northern or northeastern margin of the Siberian continent. Much further work remains to be done with determining the paleobiogeographic affinities and ecology of Arctic Alaska terrane faunas, and numerous suggestions are made herein as to areas which I feel could be addressed that would further held resolve the paleogeographic origin of this terrane.