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Detailed Geologic Mapping and Overview of Structural and Stratigraphic Studies in the East-central North Slope Foothills, Alaska

Trystan M. Herriott1, Marwan A. Wartes1, Robert J. Gillis1, Paul L. Decker2, Wes Wallace3, Andrea M. Loveland1, Rocky R. Reifenstuhl1, and David L. LePain1
1Alaska Division of Geological & Geophysical Surveys, Fairbanks, AK.
2Alaska Division of Oil and Gas, Anchorage, AK.
3Department of Geology and Geophysics, University of Alaska, Fairbanks, AK.

The Alaska Division of Geological & Geophysical Surveys regularly conducts 1:63,360-scale geologic mapping in structurally and stratigraphically complex areas of northern Alaska to further establish the region’s framework geology and provide constraints on petroleum system evolution. During the past five years, we mapped ~6,2002 km in three areas along the North Slope’s east-central foothills belt. This region notably hosts two undeveloped gas discoveries and holds significant future exploration potential.

The Sagavanirktok River map area lies entirely north of the Brooks Range and spans the main transportation and pipeline corridor of northern Alaska. Despite typically persistent tundra cover, mapping along curvilinear ribs of resistant Brookian sandstone delineates variable plunge along several km-scale folds, highlighting the potential for structural traps in the foothills area. Additionally, a several-km-thick succession of marine to nonmarine Upper Cretaceous strata crops out along riverbanks and records northeastward progradation and infilling in this sector of the foreland basin. These regionally important exposures—which in part exhibit a strong hydrocarbon odor—serve to correlate key Brookian sequence stratigraphic surfaces to the west (more proximal) and east (more distal).

Farther east, the Echooka and Kavik rivers map areas permit observation of Mississippian-Paleocene strata in the Ellesmerian, Beaufortian, and Brookian sequences near the northeastern Brooks Range mountain front. In these areas, the alpine topography is dominated by basement-involved structures and km-scale detachment folds. This structural style contrasts with the generally thin-skinned deformation to the north, characterized by a structurally complex foreland fold-and-thrust belt. The mid-Cretaceous Gilead succession (informal usage) crops out southwest of the Echooka River and comprises a >850-m-thick, sand-rich, deep-water package deposited in a toe-of-slope to basin-axis environment; this setting may have prospective subsurface equivalents to the west.

Furthermore, a probable genetically correlative unit (“Juniper Creek sandstone”) is observed to the east in the Kavik River map area, providing new constraints on the extent of this depositional system. These deep-water sandy units thin and fine markedly to the north, condensing entirely into basinal Cretaceous Hue Shale. The organic-rich Hue Shale in the Echooka River area is regionally separated by an intervening tongue of sand-prone, strongly petroliferous Upper Cretaceous Seabee Formation.

Our long-term goal is to publish 1:63,360-scale geologic maps along the entire foothills belt. This effort aims to incorporate our growing understanding of the region’s structural and stratigraphic evolution while employing modern stratigraphic nomenclature. These first-order geologic data provide a sound basis for future exploration in northern Alaska.

 

AAPG Search and Discovery Article #90130©2011 3P Arctic, The Polar Petroleum Potential Conference & Exhibition, Halifax, Nova Scotia, Canada, 30 August-2 September, 2011.

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