Ancient Submarine Canyons. and Fans of the Carson Basin, Grand Banks, Offshore Newfoundland, Canada

Abstract

The Carson Basin lies beneath the Grand Banks, offshore Newfoundland, and is composed of several depocenters, the deepest of which holds over 7 km of Mesozoic and Cenozoic strata. To date only four exploration wells have been drilled. The basin lies to the southeast of the more intensely studied and developed Jeanne d'Arc Basin, which contains the Hibernia production platform and other developing oil-fields. A basement high separates the Carson Basin from the southern Jeanne d'Arc. The basins formed in response to the opening of the North Atlantic Ocean in a complex series of rifting events. Submarine canyons and erosional scours have been recognized in the northern end of the Carson Basin at depths of 1100 m, and are buried and filled by the Banquereau Formation. The canyons were mapped using industry seismic reflection profiles. Two canyon complexes, informally named the Bonnition and St. George Canyons, incise an interpreted paleocontinental shelf-break. The upper reaches of the Bonnition Canyon carve a V -shaped erosional notch at least 6.5 km wide, with canyon walls dipping as 1nuch as 34.5 degrees. The Bonnition Canyon is over 39 km long, and trends roughly northwest-southeast. The St. George Canyon is over 30 km long and also trends northwest-southeast. Both canyons have deposited submarine fans basinward over a wide area, with a maximum thickness of approximately 900 m. Synthetic seismograms created from well logs, along with biostratigraphic studies, indicate that the canyon incision correlates with a basinwide erosional unconformity that occurred in the Early Eocene. The Early Eocene Unconformity corresponds with a relative drop in sealevel on the shelf adjacent to the canyons, resulting in a change in marine environment from outer neritic to nearshore marine. Early Eocene erosional channels and gullies of the Jeanne d'Arc Basin have previously been interpreted as submarine canyons. The Early Eocene erosion and deposition occur stratigraphically higher than the ridge separating the Jeanne d'Arc Basin from the Carson Basin, indicating possible interaction between the two basins. With the recognition of large submarine canyons and fans to the southeast in the Carson Basin, the Early Eocene erosional features of the Jeanne d'Arc Basin may be interpreted as subaerially exposed incised valleys. The northwest -southeast direction of transport for the East and West Cormorant Canyons is very similar to the Bonnition and St. George Canyon trend. A prograding clastic wedge at the outlet of the Cormorant Canyons was deposited on the high between the two basins. The prograding package may be the primary source of unstable material ultimately transported to the submarine fans of Carson Basin. The Carson Basin is relatively underexplored when compared to other basins on the Grand Banks. The submarine fans of the Carson Basin are areally extensive, thick deposits which may act as both reservoir and trap for hydrocarbons present in the basin. Stratigraphic pinchouts and salt tectonism create favourable conditions for hydrocarbon plays, however the deep water environment and questionable source rock potential will continue to curtail exploration in the near future.