NGF-Trondheim inviterer til foredrag med Erik Lundin (Statoil)

The Canada Basin and Gulf of Mexico – North American siblings

Tirsdag 9. februar klokka 19.00

Auditorium G1 "Geologen", NTNU Gløshaugen, Høgskoleringen 6A

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The Canada Basin and Gulf of Mexico – North American siblings

Lundin, E.R. & Doré, A.G.

The Canada Basin (CB) and Gulf of Mexico (GOM) represent an unusual type of back-arc basin, by having formed at a high angle to the paleo-Pacific subduction zone. Both basins are underlain by oceanic crust or exhumed mantle, but their oceanic substrates never connected with that of the Atlantic despite having formed in concert.  Both basins opened by ca 70° counter-clockwise rotation of microcontinents away from the North American craton. The distal ends of the pie-shaped basins are marked by major continent-ocean transforms. We argue that this geometry was pre-destined to periodic confinement from the World’s oceans, but tectonic forcing also likely played an important role to the confinement.  These small oceans re-opened Late Paleozoic orogens and represent examples, although unusual, of the Wilson cycle.

GOM likely opened in the Middle Jurassic and was clearly a confined basin in which a thick succession of Callovian evaporites accumulated.  Of particular industrial interest is the basinwide deposition of Upper Jurassic source rocks, which we interpret to be a result of basin confinement. However, several other base level changes can be invoked to relate to periodic choking of marine connections rather than to whole scale basin subsidence/uplift or eustacy. CB is here interpreted to have opened in Early Cretaceous time, following a Barremian unconformity of regional extent. Known mainly from the North Slope of Alaska, the Barremian-Early Aptian Pebble Shale and Hue Shale rest on the unconformity, and are candidate confined basin source rocks. Probably, the Arctic Basin was confined throughout much of its history, until opening of the Fram Strait in Middle Miocene time.  A well-known period of confinement is represented by the Middle Eocene Azolla bloom. This remarkable plant has been proposed to have caused massive CO2 sequestration, at a scale possibly sufficient to have flipped the Earth’s climate from the preceding super-greenhouse into the icehouse we still experience. Accumulation of organic-rich sedimentary in confined basins is thus not only of industrial interest, but also has climatic implications.

Being located at either end of North America when viewed from the Pacific or Atlantic, it is not surprising that the basins also contain analogous tectonostratigraphic successions, particularly the influx of Cenozoic siliciclastic sediments driven by erosion of the Laramide orogen and subsequent uplift of the Colorado Plateau. The analogous Mesozoic oceanic crustal substrate, confined basin source rocks, and Cenozoic influx of siliciclastic sediments have resulted in interesting parallels of the petroleum systems. Differences also exist, such as paleo-latitude, which allowed evaporites and carbonates to form in GoM in contrast to siliciclastics only in CB. The basin fill in both basins has dominantly been deformed by gravity-driven tectonics, but the presence of the Callovian evaporites in GoM yielded substantially more deformation.

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