Basin History in Fracture Zone Setting: Falkland Plateau

Juan M. Lorenzo

Although virtually all passive continental margins are intersected by fracture zones, models describing margin evolution seldom include the tectonic effects of the latter. On the Falkland Plateau, whose northern margin is dominated by a large fracture zone, up to 5 km of terrigenous, transitional, and hemipelagic sediments have been deposited since the Middle Jurassic, largely under the control of a northern basement high. This high marks the Falkland fracture zone, formed during the opening of the South Atlantic in the Early Cretaceous.

The Falkland Plateau lies submerged in 2,500 m of water and can be physiographically subdivided into (1) the Maurice Ewing Bank, a broad, triangular, shallow feature on its eastern extremity, (2) a boundary steep Falkland Escarpment in the north, (3) a southern Falkland Trough, and (4) a central saddle.

Using well data (DSDP sites 511, 330, and 327) and extensive single-channel and regional multichannel seismic data, a detailed seismic stratigraphy has been developed for the Falkland Plateau. Results show four widespread depositional sequences dipping southward over both oceanic (in the west) and continental basement (in the east). Late Jurassic sapropelic black shales overlain by claystones thin and possibly crop out along the northern margin of the plateau.

Good control of structure has allowed recalculation of geophysical models, thus confirming three-dimensional basin geometry estimated seismically. Basin evolution is intimately related to the plate-tectonic setting and history, and may provide additional constraints on the breakup of Gondwanaland.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.