Steven D. May

Sediment thickness in the southern Canada Basin

Abstract Multichannel seismic reflection data are used, in conjunction with deep crustal seismic refraction data, to estimate the thickness of sediments in the southern Canada Basin of the Arctic Ocean north of Alaska. The sediments are interpreted to be of Hauterivian (mid-Early Cretaceous) to Holocene age. Comparison of the seismic reflection character of seismic reflections in the study area with that in other basins indicates that a base-of-sediment—top of oceanic layer 2 reflection is not present above the depth at which the water-bottom multiple obscures all deeper arrivals, which is in conflict with the conclusions drawn from aeromagnetic, refraction, and other reflection studies. Seismic velocity structure, determined from the reflection data, indicates that the reflections above the multiple are from sedimentary strata. In the absence of seismic reflection evidence for the top of layer 2 above the multiple, we estimate total sediment thickness by using the layer 3 refractions and subtracting an average assumed layer 2 thickness from the top of layer 3. Assuming that an average thickness of oceanic layer 2 (1.4 km) overlies layer 3 in the southern Canada Basin, sediment thickness in the study area is estimated to range between 6.5 km where water depth is 3.8 km to greater than 11 km where the water depth is 2 km. This is nearly double that of any previous estimates and should have a significant effect on calculations such as the age of Canada Basin, regional heat flow, and long-term sedimentation rates.

Observations of anomalous oceanic crust in the Canada Basin, Arctic Ocean

Abstract We present a seismic reflection frofile and coincident refraction data in deep water north of the Northwind Ridge, in the Canada Basin. The reflection profile shows a package of bright events, which are locally nonparallel and discontinuous, about 2.5 s below the seafloor. These bright reflectors are of interest because previous reflection profiles in the Canada Basin have not penetrated the coherent flat-lying events, which are typical of bedded sedimentary rocks. These prominent reflections are recorded on the refraction profile as wide-angle reflections, and the locally nonparallel and discontinuous event as a refraction. On the refraction profile the nonparallel and discontinuous event exhibits lower frequencies and has an associated refraction with a velocity of 4.5 km/s and a high gradient. This event is interpreted as representing the top of oceanic layer 2, which is observed for the first time in the Canada Basin. Three kilometres beneath layer 2 a velocity of 7.2–7.5 km/s is measured. This layer could represent either a high-velocity layer 3 or serpentinized mantle. Based on comparison with the eastern Grand Banks and the west Iberian and Labrador Sea margins the interpretation of serpentinized mantle is preferred.

Implications of Offshore Northern Alaska Geology for Origin of Canada Basin, Arctic Ocean: ABSTRACT

Geologic mapping and petroleum exploration in northern Alaska and seismic surveys offshore suggest that 2 pulses of rifting created the Canada basin. Mississippian to Triassic miogeoclinal rocks in northern Alaska, derived from a now-displaced northerly source land, correlate with similar strata in the Canadian Arctic Islands. Underlying Ordovician and Silurian argillite and graywacke may correlate with the clastic succession in Heezen trough of the Arctic Islands. Closing Canada basin about a Mackenzie delta pole would rejoin these correlative rocks and recreate a unified pre-Jurassic Arctic paleogeography. Rifting began in earliest Jurassic time, creating a west-northwest-trending trough beneath the Beaufort Shelf and probably the southern Canada basin. The main rifting pulse, however, began in late Neocomian time, and the main post-rift progradational sedimentary prism off Alaska is Aptian or Albian and younger. Apparently both late Neocomian and Laramide rifting thinned the crust beneath North Chukchi basin. Marked basinward thickening of Cretaceous strata records the earlier event, and extensional faulting and basinward thickening of Tertiary strata record the later one. The high-standing, north-trending ridges and troughs of the Chukchi borderland, which trend into the North Chukchi basin from the north, may represent localized Laramide(?) crustal extension subparallel to that which created the Laramide(?) and Cenozoic Makarov and Eurasia basins of the Arctic Ocean. This model requires crustal shortening between the Chukchi borderland and Canada basin and transform faults north and south of the borderland. North of our seismic lines, the southern transform may be buried by Tertiary sediment of the North Chukchi basin. End_of_Article - Last_Page 259------------

Geologic Framework and Petroleum Potential of United States Chukchi Shelf North of Point Hope, Alaska: ABSTRACT

A reconnaissance grid of 24-channel seismic-reflection data indicates that most of the United States Chukchi shelf north of Point Hope, Alaska, is prospective for petroleum. The prospective rocks, which consist of four stratigraphic sequences, rest on the Arctic platform, a regional erosional surface cut across mildly metamorphosed lower Paleozoic rocks in Late Devonian time. The Eo-Ellesmerian sequence, interpreted to contain mainly Mississippian nonmarine deposits, is 5+ km (16,500 ft) thick and fills local sags and faulted depressions in the Arctic platform. Mississippian to Neocomian stable shelf clastic and carbonate beds of the Ellesmerian sequence, 0 to 7.7+ km (25,000 ft) thick, underlie most of the shelf but are absent from Barrow arch and the outer shelf of the ortheastern Chukchi Sea. Albian and Upper Cretaceous intradelta and prodelta deposits of the lower Brookian sequence, which thicken from 250 m (800 ft) on Barrow arch to 7.5+ km (24,500 ft) to the southwest, northwest, and north, underlie most of the shelf. The upper Brookian sequence, inferred to consist of marine and nonmarine clastic deposits of mainly or entirely Tertiary age, is 0 to 5.6+ km (18,500 ft) thick. It occurs only in Nuwuk and North Chukchi basins and locally as canyon fill beneath the central Chuckchi shelf. The northern Chukchi shelf contains seven provinces of contrasting tectonic origin and structural style. Nuwuk basin, a progradational clastic prism containing 12+ km (39,500 ft) of lower and upper Brookian strata and numerous growth faults, overlies a rifted margin of Neocomian age beneath the outer shelf and slope of the northeastern Chukchi Sea. North Chukchi basin, which underlies the outer shelf west of Nuwuk basin, contains Ellesmerian beds and 12+ km (39,500 ft) of lower and upper Brookian strata. It may also overlie a Neocomian rifted margin, but was deepened by Laramide extensional rifting. South of these basins, shelf structure is controlled by the geometry of the Arctic platform, which slopes gently southwest from a depth of 0.25 km (800 ft) on Barrow arch to about 13 km (4 ,650 ft) off Point Lay. In the central part of the shelf, the platform is somewhat faulted and folded and descends to a depth of 10+ km (33,000 ft) to form the north-trending Hanna trough. West of the trough the platform rises to within 1 km (3,300 ft) of the seabed and is broken by numerous normal faults. The southern part of the platform contains a thick lower Brookian section with numerous northwest-striking, northeast-verging detachment folds. The fold province is bounded on the southwest, off Cape Lisburne, by the northwest-striking Herald arch overthrust belt at which one or more southwestward-dipping thrusts brought Ellesmerian and older strata to the seabed. The seismic and extrapolated onshore data suggest that Nuwuk and North Chukchi basins, Hanna trough, and the Arctic platform east and west of the trough could contain significant deposits of oil or gas. The potential of the fold belt, however, is modest, and of Herald arch slight. Small areas on Barrow arch and the Arctic platform west of Hanna trough lack potential because they are underlain by less than 1 km (3,300 ft) of prospective section. End_of_Article - Last_Page 474------------