Sedimentology, paleosols and nonmarine sequence stratigraphy of the Kekiktuk Formation, northeastern Brooks Range and North Slope subsurface, Alaska

Principal Investigator:

Paul McCarthy

The Carboniferous Kekiktuk Formation contains an estimated 366 million barrels of oil reserves and 907 bcf of gas reserves at Endicott field near Prudhoe Bay, and is a potential reservoir across much of the North Slope of Alaska including the coastal plain of the Arctic National Wildlife Refuge (ANWR) and the nearby offshore region. The Kekiktuk Formation overlies a regional angular unconformity (sub-Mississippian unconformity) in both outcrop and the subsurface, but sediments are found within two distinct tectonic and depositional settings. In the subsurface, fluvial sandstones, mudstones, paleosols and coals were deposited in a half-graben depositional setting. In outcrop, thin, discontinuous fluvial sandstones, conglomerates and coastal plain deposits that are present across the northeastern Brooks Range are widespread and unconfined by major extensional basins or structures. Although sediments of the Kekiktuk Formation are at least partly coeval in suburface and outcrop, it has been suggested that they may record deposition in separate basins characterized by different tectonic settings and regional paleogeographies.

A better understanding of regional stratigraphic controls on Kekiktuk deposition and paleogeography is important because it would allow better predictions to be made about the nature and geometry of this economically significant unit within areas of the North Slope where data are more limited. Recent developments in alluvial architectural analysis and nonmarine sequence stratigraphy have established new methods for identifying sequence boundaries, changes in accommodation and systems tracts in terrestrial rocks. These new techniques have yet to be applied systematically to Alaskan problems, but they hold promise for establishing a high-resolution subsurface-to-outcrop correlation within the Kekiktuk Formation (i.e. between Endicott field and the northeastern Brooks Range), and for clarification of the development of the sub-Mississippian unconformity, an important and controversial tectonic and stratigraphic boundary in Alaska.

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