THE ARCTIC ALASKA-CANADA CONNECTION REVISITED

Since A. Wegener published his reconstruction of Gondwana geologists have looked for markers that link conjugate margins that have rifted apart. Yet even where seafloor magnetic anomalies allow for precise restoration of continents, unambiguous piercing points are rare. We have identified a set of such piercing points which link the present-day North Slope margin of Alaska to the Canadian Arctic islands. Although many plate configurations have been proposed for the opening of the Amerasia basin, the preferred model involves the counterclockwise rotation of Arctic Alaska away from the Canadian Arctic islands. Recent aeromagnetic and satellite gravity data have leant support to this model. In addition, both the stratigraphy and the tectonic history of the North Slope are comparable to those of the Sverdrup basin of Arctic Canada. The most specific piercing point previously identified is obtained by matching the axis of the Sverdrup basin (located near Brock Island) to the Hanna trough of Arctic Alaska (located west of Barrow). More precise piercing points can be found by mapping in detail the geometry of Late Paleozoic-Early Mesozoic basin fill in both areas using seismic and well data. Strata of the Carboniferous through Jurassic Ellesmerian Sequence of Arctic Alaska progressively on-laps onto a Pre-Mississippian unconformity from south to north. This can be viewed as a set of paleo-shorelines prograding to the north as the Ellesmerian basin subsided. The Carboniferous paleo-shoreline intersects the coast at about 160°W, while the late Triassic paleo-shoreline does so at 157°W, just southwest of Point Barrow. A matching set of paleo-shorelines of the same ages, in the same order, and with similar spacing, can be mapped in the Canadian Arctic islands. These paleo-shorelines approach the edge of the continental shelf on the northwest coast of Prince Patrick Island between 119°W and 122°W. This geometry establishes a compelling link between the northern margin of Arctic Alaska and the Canadian Arctic islands and confirms the rotational model for the opening for this part of the Amerasia Basin. However, whether this simple model applies to the central Arctic Basin, which is underlain by the Alpha-Mendeleev ridges, and how to fit the Chukotka portion of the Arctic Alaska-Chukotka microplate into the model, remain unresolved.