New constraints on the early Paleozoic history of Arctic Alaska and its bearing on Arctic tectonic reconstructions

Arctic Alaska is a large composite terrane that underlies the North Slope of Alaska and makes up the majority of the E-W-trending Brooks Range. Neoproterozoic and early Paleozoic connections between Arctic Alaska and Laurentia have been questioned because of the proposed differences in stratigraphic architecture, faunal affinities of mega- and microfossils, and various geochronological data. These studies have largely regarded Arctic Alaska as a single crustal fragment (i.e., Arctic Alaska-Chukotka microplate) with the majority of Neoproterozoic and early Paleozoic comparisons being drawn from the southern Hammond and Seward subterranes of Arctic Alaska. A combined approach of geological mapping and logging of detailed stratigraphic sections integrated with chemostratigraphic, biostratigraphic, and geochronologic analyses from the North Slope subterrane enables new interpretations of the pre-Mesozoic geologic history of Arctic Alaska. Specifically, we 1) disprove the existence of an angular unconformity between the Neoproterozoic Katakturuk Dolomite and Cambrian-Ordovician Nanook Limestone, 2) recognize and divide the Nanook Limestone into two new informal members separated by a major hiatus, and 3) provide evidence for a significant tectonically-driven exposure event prior to deposition of the Lower Devonian Mt. Copleston Limestone. Based on its stratigraphic architecture and faunal affinities, we suggest that the North Slope subterrane is parautochthonous to northern Laurentia and was separate from the exotic southern subterranes of Arctic Alaska until at least the latest Ordovician. Furthermore, we posit that the North Slope subterrane was juxtaposed and eventually incorporated into the composite Arctic Alaska-Chukotka microplate when this large crustal fragment collided with the northern margin of Laurentia during the Silurian-Devonian Innuitian and Ellesmerian orogenies. Future work will continue to unravel the complex Neoproterozoic-early Paleozoic geologic history of Arctic Alaska and shed light on the tectonic evolution of the Arctic realm.