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Crossbedded fluvial sandstones and conglomerates in basal part of White Hills Member of Sagavanirktok Formation along the Toolik River. .. .. . 40. Bluff along east bank of Sagavanirktok River and southern end of Franklin Bluffs, showing contrast between Franklin Bluffs Member of Sagavanirktok Formation and brown-weathering, lignite-bearing silty mudstone of upper part of White Hills Member .

Constraining the pre-opening paleogeography of the Canadian and Alaskan margins of the Canada Basin is a fi rst-order objective in resolving the plate tectonic evolution of the Amerasia Basin of the Arctic Ocean. The most widely accepted model for opening of the Canada Basin involves counterclockwise rotation of Arctic Alaska away from Arctic Canada about a pole of rotation in the Mackenzie Delta region, although numerous other kinematic models have been proposed. The rotation model is tested using detrital zircon U-Pb geochronology of 12 samples from Middle Mississippian to Early-Middle Jurassic strata (Ellesmerian and lower Beaufortian megasequences) obtained from wells and outcrop along Alaska's North Slope. These northerly-derived strata were deposited in fl uvial to nearshore marine environments along the south-facing (present-day) shelf margin of the Arctic Alaska Basin and contain 360-390 Ma, 415-470 Ma, 500-750 Ma, 0.9-2.1 Ga, and 2.4-3.2 Ga zircon populations. Detrital zircon age populations in Ellesmerian and lower Beaufortian strata are remarkably similar to detrital zircon populations from Devonian foreland clastic wedge strata in the Canadian Arctic Islands and northern Yukon Territory. A paleogeographic setting in which Arctic Alaska received sediments recycled from the Devonian foreland clastic wedge and underlying Franklinian Basin strata is most consistent with the model of Embry (1990) in which northern Alaska lay within the foreland fold and thrust belt of the Franklinian mobile belt prior to the opening of the Canada Basin.The sequences that are inferred to have been the long-lived source region for Ellesmerian and lower Beaufortian strata were uplifted by Paleozoic (predominantly Late Devonian) deformation that has been documented along the Canadian and Alaskan margins. Triassic and Jurassic strata deposited along the Arctic Canada, Arctic Alaska, and northern Yukon shelves have detrital zircon ages that are signifi cantly older than the youngest detrital zircon ages (Mesozoic) in coeval strata that were deposited west of Hanna Trough and north of the Sverdrup Basin axis, supporting continuity of these bathymetric features prior to opening of the Canada Basin.

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