Shoreline to Basin Transition (?) in Albian-Cenomanian Strata East of the Sagavanirktok River, Brooks Range Foothills, Alaska

By

D.L. LePain, R. Kirkham (Alaska Division of Geological and Geophysical Surveys), and P.J. McCarthy (University of Alaska, Fairbanks)

The depositional setting of Albian-Cenomanian strata east of the Sagavanirktok River on Alaska’s North Slope is poorly documented. At Slope Mountain Albian-Cenomanian strata include a thick (hundreds of meters) regressive succession of stacked outer-shelf to marginal-marine parasequences typical of the uppermost Torok and marine portion of the Nanushuk formations to the west. North of Slope Mountain, near the Lupine River, a 350-meter-thick regressive succession of Albian age displays an internal organization consisting of poorly exposed shale intervals up to 15 meters thick punctuated by numerous sharp-based sandstone bodies 2 to 10 meters thick. Sand bodies in the basal two-thirds of the section consist of amalgamated beds a few decimeters thick. Sedimentary structures include groove casts, flute casts, current-ripple cross lamination, and convolute lamination, suggesting deposition from turbidity currents. The upper third of the section includes amalgamated beds of fine- to medium-grained sandstone with plane-parallel lamination, wave ripple lamination, wave ripple bedforms, trough and swaley cross stratification, and plant debris on some bedding planes, suggesting deposition in water depths above storm wave base. Marginal- and non-marine strata are absent. Thirty kilometers east of the Lupine section, a 900-meter-thick succession of Albian-Cenomanian strata assigned to the Gilead sandstone is similar to the Lupine section, with lower sands displaying features suggestive of deposition in deeper water and higher sands deposition in shallower water. These features suggest deposition in settings more distal than at Slope Mountain, but gradual shoaling, possibly through progradation of a ramp-like basin margin that promoted delta-fed turbidity currents.

AAPG Search and Discovery Article #90008©2002 AAPG Pacific Section/SPE Western Region Joint Conference of Geoscientists and Petroleum Engineers, Anchorage, Alaska, May 18–23, 2002.