Architectural analysis and fold geometry of syntectonic fluvial conglomerate in the Nanushuk Formation, Brooks Range foothills, Alaska

Abstract

The fluvial style and syntectonic deposition of conglomerate in the upper part of the Nanushuk Formation are resolved using facies architectural analysis and structural geometry. Along the Kanayut River in the northern foothills of the Brooks Range, Alaska, fluvial conglomerate is exposed as benches on the north and south flanks of the Arc Mountain anticline. Photo mosaics of each bench on the north side, along with thirty-three detailed measured sections, were used to evaluate facies architecture. Eight lithofacies were described that characterize six facies associations including longitudinal and transverse gravel bars, diffuse gravel sheets, sediment gravity flow deposits, crevasse splay and floodplain deposits, and scour fills of a gravel-bed braided river. Strata on the south limb of the anticline show characteristics of syndeformational deposition during the growth of the south limb of the Arc Mountain anticline. These structural data provide new evidence for syndepositional contractional deformation during the mid-Cretaceous at this locality in the northern foothills of the Brooks Range. These results provide clues to the character and extent of potential reservoir rocks from the Nanushuk Group that are present in the subsurface of the National Petroleum Reserve in Alaska, which is important for continued recovery of natural resources on the North Slope.