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.