Abstract Amerasia Basin is the product of two phases of counterclockwise rotational opening about a pole in the lower Mackenzie Valley of NW Canada. Phase 1 opening brought ocean–continent transition crust (serpentinized peridotite?) to near the seafloor of the proto-Amerasia Basin, created detachment on the Eskimo Lakes Fault Zone of the Canadian Arctic margin and thinned the continental crust between the fault zone and the proto-Amerasia Basin to the west, beginning about 195 Ma and ending prior to perhaps about 160 Ma. The symmetry of the proto-Amerasia Basin was disrupted by clockwise rotation of the Chukchi Microcontinent into the basin from an original position along the Eurasia margin about a pole near 72°N, 165 W about 145.5–140 Ma. Phase 2 opening enlarged the proto-Amerasia Basin by intrusion of mid-ocean ridge basalt along its axis between about 131 and 127.5 Ma. Following intrusion of the Phase 2 crust an oceanic volcanic plateau, the Alpha–Mendeleev Ridge LIP (large igneous province), was extruded over the northern Amerasia Basin from about 127 to 89–75 Ma. Emplacement of the LIP halved the area of the Amerasia Basin, and the area lying south of the LIP became the Canada Basin.

Abstract High-resolution multichannel seismic reflection data, exploration industry three-dimensional (3-D) seismic data, and heat-flow measurements collected on the southeast side of a mini basin (Casey basin) in the northern Gulf of Mexico continental slope have been used to characterize a bottom-simulating reflector (BSR). The BSR, which covers a small area of about 15 km 2 (6 mi 2 ), is identified by crosscutting relationships with seismic stratigraphy. Two mounds are identified. The larger Alpha mound is structurally formed at the junction of three arms of the structural high east of the mini basin. The smaller Beta mound may be a seep site. Conventional heat-flow measurements yield higher gradients (39–49 mK/m) to the northeast of the structural high and lower values (30–38 mK/m) to the south and west along the edge of the mini basin, which is separated from the structural high by the eastern Casey fault zone. When the near-sea-floor thermal gradients are extrapolated to the depth of the BSR, the resulting temperatures are generally too low if the BSR marks the base of the hydrate stability zone in a methane-only gas-hydrate system. Plausible changes in pore-water salinity or gas composition cannot account for this disparity, and thermal perturbations caused by fluid down welling, mass wasting, or depth-dependent thermal conductivity variations might best explain the low predicted BSR temperatures. The recognition of a BSR in the study area provides geophysical evidence that a hydrate stability zone with trapped free gas at its base exists in the northern Gulf and that minibasins can be locations for finding subsurface hydrate-associated free gas and probable gas hydrate.

Abstract Alaska faces the Canada Basin of the Arctic Ocean along an arcuate continental margin, gently concave to the north, that stretches unbroken from the Mackenzie Delta, near 137°W to North wind Ridge of the Chukchi Borderland near 162°W. (Marine geographic features mentioned below can be found on Plates 1 and 11 of Grantz and others, 1990a.) This margin, with an arc-length of about 1,050 km, marks one side of a continental rift along which the Canada Basin opened by rotation about a pole in the Mackenzie Delta region during middle Cretaceous time. The rift-margin structures, which lie beneath the inner shelf and coastal plain in the eastern Alaskan Beaufort Shelf and beneath the outer shelf in the western Beaufort and Chukchi Shelf, are now buried by a thick middle Lower Cretaceous to Holocene progradational continental terrace sedimentary prism. We divide the Arctic continental margin of Alaska into three sectors of strongly contrasting geologic structure and physiographic expression. In the Barter Island sector (see Figs. 3 and 4) the structure is dominated by the effects of Eocene to Holocene convergence and uplift, and the continental slope is upwardly convex; in the Barrow sector the structure is dominated by the effects of middle Early Cretaceous rifting and continental breakup, and the continental slope is upwardly concave; and in the Chukchi sector the structure is controlled by an easterly trending middle Early Cretaceous rift, and the continental slope abuts the Chukchi Borderland. Physiographically, the Alaska continental margin is expressed by the Alaska continental rise and slope