Structure of the southern Falkland Islands continental shelf: initial results from new seismic data

Acquisition of a modern marine dataset has revealed the internal structure of sedimentary basins to the south of the Falkland Islands for the first time. The new data reveal a variety of structural styles and indicate the presence of a sedimentary section ranging from 2 to 10 km in thickness developed in three linked sub-basins. 1. (1) The eastern part of the Malvinas Basin lies south-west of the islands. A prominent regional unconformity developed throughout the area marks the top of gently folded rocks of probable Palaeozoic age and their cover of Late Jurassic volcanics. To the north-west of the island, the underlying strata approach the surface in a structural high which forms a prominent gravity low and may record the continuation of the Palaeozoic basin exposed on the islands themselves. Strata of probable Mesozoic and Tertiary age rest on the unconformity throughout the area and show a regional southward dip. These deposits increase in thickness south-westwards towards the depocentre of the Malvinas Basin midway between the islands and Argentina. 2. (2) The South Falkland Basin and Burdwood Bank lie south of the islands. Thicknesses increase towards an area of southward-dipping extensional fault blocks within the South Falkland Basin. Downdip these are buried beneath a prograding and north-vergent stack of blind and emergent thrusts at the northern margin of the Burdwood Bank, which is a structural highly lying a shallow water south of the islands. Thrust loading has resulted in the development of a foreland basin north of the thrust front. Complex antiformal structures are associated with the thrusting, whereas a shallow sedimentary basin developed on the crest of the Burdwood Bank is interpreted as a piggy-bank basin riding on, and sourced dominantly from within the thrust pile. 3. (3) The Falkland Plateau Basin lies to the east and south-east of the islands and is characterized by a varied and extensive Mesozoic to Tertiary succession of submarine fan deposits thickening eastwards into deeper water. Igneous intrusives deep in the section may correlate with Jurassic volcanic rocks present within the Malvinas Basin to the west, or may record younger rifting associated with the opening of the South Atlantic. These initial results indicate considerable structural heterogeneity in this part of the Falkland Islands Continental Shelf. In the light of the hydrocarbon discoveries already made further west, significant economic potential is likely. Stratigraphic traps may occur at regional unconformities and within submarine fan deposits, whereas potential structural traps include Mesozoic extensional fault blocks and thrust and sub-thrust structures generated by Tertiary and Quaternary compression.