Structure and petroleum potential of the Yakutat segment of the northern Gulf of Alaska continental margin

Abstract

Major structural features of the Yakutat segment of the continental margin, between Cross Sound and Icy Bay in the northern Gulf of Alaska, are delineated by multichannel seismic reflection data. A large structural high centered on Fairweather Ground lies at the edge of the shelf from Cross Sound to west of the Alsek Valley. A basement uplift, the Dangerous River zone, along which the seismic acoustic basement shallows by up to 2 km, extends north from the western edge of Fairweather Ground toward the mouth of the Dangerous River. The Dangerous River zone separates the Yakutat segment into two distinct subbasins. The eastern subbasin has a maximum sediment thickness of about 4 km, and the axis of the basin is near and parallel to the coast. Strata in this basin are largely of late Cenozoic age (Neogene and Quaternary) and approximately correlate with the onshore Yakataga Formation. The western subbasin has a maximum of at least 9 km of sediment, with about 4.5 km of Paleogene strata overlain by late Cenozoic strata. The Paleogene strata are truncated along the Dangerous River zone by a combination of erosion, faulting, and onlap onto the acoustic basement. Within the western subbasin, the late Cenozoic basin axis is near and parallel to the coast, but the Paleogene basin axis appears to trend northwest, diagonally across the shelf. Sedimentary strata throughout the Yakutat segment show regional subsidence and only minor deformation except in the vicinity of the Fairweather Ground structural high, near and along the Dangerous River zone, and at the shoreline near Lituya Bay.Seismic data across the continental slope and adjacent deep ocean show truncation at the continental slope of the shelf Paleogene strata. Up to 6 km of undeformed or mildly deformed abyssal sedimentary section are present at the base of the slope, and in part onlap the slope. Faulting may have occurred along a relatively narrow zone along the slope or at the base of the slope. Observed deformation at the base of the slope is primarily related to the late Cenozoic uplift of Fairweather Ground and to Quarternary folding perpendicular to the Pacific-North America relative-convergence vector. No accretionary section or major deformation is observed along the continental slope. The absence of these features suggests that no major subduction of the Pacific plate beneath the Yakutat margin has occurred during the late Cenozoic.However, transform faulting has most likely occurred along the base of the slope, because probable Oligocene oceanic basement is juxtaposed against Mesozoic and Paleogene sedimentary strata of the Yakutat slope. This juxtaposition most likely occurred during late Oligocene and Miocene time.During much of the late Cenozoic, and especially during Pliocene and Pleistocene time, the Yakutat segment has apparently been moving northward with the Pacific plate.Dredge samples from the continental slope recovered potential petroleum source and reservoir rocks from the Paleogene sedimentary sequence. Most of the organic matter from these ...