Topography and ground conditions were important factors in controlling the distribution of individual Columbia River Basalt Group (CRBG) flows in western Oregon. The Columbia trans-arc lowland, the Yakima fold belt, the Portland Hills–Clackamas River structural zone, and Cascadian volcanism largely controlled the distribution of CRBG flows across the Miocene Cascade Range. The first flows to cross the Miocene Cascades into the Willamette Valley encroached onto a low-relief topography generally consisting of eroded Tertiary-age marine sedimentary rocks deformed along northwest-trending structural zones, volcanic highs, and estuaries. No north-south trough affected the distribution and thickness of the CRBG in the Willamette Valley, but an incipient Coast Range acted as a leaky barrier to the Oregon coast. Water-saturated sediments rapidly extracted heat from advancing CRBG lava flows, producing narrow, abnormally thick lobes extending along existing topographic lows. Deformation along the northwest-trending Portland Hills–Clackamas River structural zone produced a major topographic barrier early and late in the incursion of CRBG flows. The CRBG thins across this zone from 600 to 150 m. This zone diverted the earliest Grande Ronde flows into and through the Portland Basin. Some of the succeeding R 2 and N 2 Grande Ronde flows were able to cross this zone and followed another structural low, the Sherwood trough, to the Oregon coast. The total thickness of CRBG along the Sherwood trough is approximately 300 m, about twice that on either side. Paleodrainage developed during time intervals between emplacement of CRBG flows. The positions of these drainage courses were influenced by the position of the CRBG flow margins and/or structural lows. A longer hiatus between flows (> 100,000 yr) enabled rivers to develop major canyons by headward erosion, which served to channelize subsequent CRBG flows.

Abstract Basin evolution of the U.S. Chukchi shelf involved multiple phases, including Late Devonian–Permian rifting, Permian–Early Jurassic sagging, Late Jurassic–Neocomian inversion, and Cretaceous–Cenozoic foreland-basin development. The focus of ongoing exploration is a petroleum system that includes sag-phase source rocks; inversion-phase reservoir rocks; structure spanning the rift, sag, and inversion phases; and hydrocarbon generation during the foreland-basin phase. Interpretation of 2-D seismic and sparse well data documents the presence, in the south-central part of the shelf, of a series of en-echelon, north-south trending monoclonal fold limbs that display up to 1+ km (3,300 ft) of structural relief. These folds, which are located above the tips of rift-phase normal faults, are interpreted as inversion structures formed by maximum compressive stress oriented obliquely to the strike of rift-phase normal faults. Erosional relief on a Jurassic unconformity, growth strata in the overlying Upper Jurassic to Neocomian strata, and east-dipping clino-forms in a high accommodation depocenter east of the inversion structures indicate profound structural influence on sedimentation. Oil-prone source rocks, reservoir-quality sandstone, migration pathways, and structural closure are linked intimately across the Jurassic unconformity, which reflects inversion. Thus, all these key petroleum systems elements were in place when Triassic source rocks entered the oil generation window during Cretaceous–Cenozoic stratigraphic burial.

Abstract The US Chukchi Shelf is a proven petroleum province similar to the prolific hydrocarbon-bearing region in the adjacent North Slope of Alaska. This shelf is part of the Arctic Alaska plate that was presumably connected to the Canadian Arctic Islands until the opening of the Canada Basin. A new data set (3130 km) of deep 2D seismic reflection profiles, acquired in 2006 and depth processed to 40 km, provides excellent images of the drillable ( c . 8 km depth) stratigraphy as well as of deeper structures. The data also permit regional mapping of the tops of crystalline basement and the Moho discontinuity. The area has a tectonic history of multiple phases of rifting: a pre-Late Devonian phase that culminated in inversion and thrusting; a Late Devonian–Mississippian phase that accommodated Ellesmerian sedimentary deposits as a sag sequence; and a Jurassic to Early Cretaceous phase that is contemporaneous with the opening of the Canada Basin. Hanna Trough is recognized as a Palaeozoic basin with a multistage history while the North Chukchi Basin formed in early Cretaceous as an extensional basin. Only five wells have been drilled in the area; hence numerous opportunities for further exploration exist in the Chukchi Shelf.

Abstract Well data analysis and the interpretation of 2D and 3D seismic reflection data provide valuable insights into the distribution and timing of fault activity within the Central Irish Sea Basin (CISB). Structural and stratigraphic relationships have been used to constrain the timing of fault movements and to interpret the mapped fault patterns in terms of the tectonic evolution of the area. Four main fault trends are identified at the Top Lower Triassic Sherwood Sandstone Group level: I, a NE–SW fault trend that parallels the basin-bounding faults and is believed to be of Mesozoic age; II, a pervasive system of north–south-trending faults that cross-cut the earlier NE–SW-trending faults, which manifests evidence of later Mesozoic extension followed by post-Oligocene transpressional fault reactivation; III, a NNE–SSW-trending, steeply dipping, fault set; IV, a WNW–ESE-trending conjugate extensional set that formed perpendicular to the NNE–SSW-trending transpressional faults during Late Tertiary dextral shearing. Early Tertiary axial centred basin inversion and regional exhumation have resulted in the elevation of the Sherwood Sandstone reservoir to shallow structural levels within the basin. Continued fault reactivation into Late Tertiary time has resulted in the compartmentalization of mapped structural closures and suggests that trap integrity is a major exploration risk factor in the CISB.