Atlantic Mesozoic Marginal Basins: An Iberian View

R. C. L. Wilson

In the light of theoretical models for crustal stretching that precedes ocean opening, it is unlikely that Iberian basins have mirror image counterparts beneath North American or other European continental shelves. However, certain Iberian sedimentary sequences are comparable to those found in other basins. Of particular note are (1) the almost identical prerift sequences in all these areas, (2) the development of Upper Jurassic carbonate buildups in Portugal, Morocco, and beneath the Scotian Shelf, and (3) the hydrocarbon-bearing Upper Jurassic and Lower Cretaceous synrift and postrift siliciclastics of North America, Iberia, and Aquitaine.

In the prerift sequences, Triassic red beds are capped by evaporites, which subsequently influenced the structural development of basins. Intertidal and supratidal carbonates occur at the base of the Jurassic and are overlain by Lower and Middle Jurassic limestone-shale sequences, which in places contain bituminous shales. In Portugal only, resedimented carbonates of Toarcian-Aalenian age are associated with an uplifted basement horst. In Portugal, Aquitaine, and eastern Canada, Middle Jurassic high-energy carbonate platforms developed.

Synrift siliciclastic sequences show spectacular evidence for deposition within fault-bounded basins. In Portugal, lower Kimmeridgian clastics are up to 3 km thick, but Upper-Lower Cretaceous sequences are relatively thin (ca. 1 km), in contrast to those of the Basco-Cantabrian region where they exceed 10 km. In the latter region occurs the fluvially dominated "Wealden" (Upper Jurassic-Neocomian) and "Urgonian" carbonate platforms and associated basinal sediments. In the Asturias basin, Kimmeridgian shales and fluvially dominated deltaic sandstones succeed conglomeratic fluvial sandstones of uncertain age.

Postrift Albian-Cenomanian sediments in the Basco-Cantabrian region consist of deltaic and turbiditic sequences up to 4 km thick. Off northwest Iberia, deep-sea drilling proved Albian black shales which clearly mark the onset of ocean opening between Iberia and the Grand Banks. In the Lusitanian and Asturias basins, post-Aptian sediments are relatively thin, so a characteristic postrift sequence cannot be recognized.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.