A seismic stratigraphic and lithostratigraphic study based on seismic reflection and well log data of Paleogene strata from the southern Beaufort Sea margin of Alaska and Canada has identified major unconformities and depositional sequences. A comparison of the age of the unconformities to regional uplift events, dated with fission track analysis, shows that tectonic events were more important than eustatic changes in controlling the occurrence of regional unconformities.

Paleogene sediments were deposited in a foreland basin located north of the Brooks Range. This basin trends offshore and forms part of the southern continental margin of the Beaufort Sea. Mid-Mesozoic thrusting established the basic structure of the foreland basin, which was later filled with sediments and deformed by northward-directed thrusting. Regional unconformities occur near the Cretaceous-Tertiary boundary, within the Paleocene, middle Eocene, upper Eocene, and lower Miocene. These unconformities separate depositional units consisting of northward-prograding deltaic, slope, and turbidite facies.

Most Paleogene depositional patterns can be explained as follows: thrust loading with widespread shale deposition in distal parts of the basin and coarse clastics near the thrust front (Late Cretaceous and middle Eocene); then subsequent thrust-belt erosion and uplift with sand deposition across the basin (Paleocene and Oligocene). Latest Eocene to Oligocene subsidence of the Mackenzie delta resulted from local thrust and sediment loading.

End_Page 285------------------------

The existence of lowstand systems tracts (Kugmallit-Kopanoar sequence) on this subsiding margin suggests regional isostatic uplift or eustatic sea-level fall as a facies control.