New insights into the tectono-stratigraphic evolution of the Malvinas Basin, offshore of the southernmost Argentinean continental margin

• We have identified 5 seismo-stratigraphic units in the Malvinas Basin.
• The units are corresponding to the tectonic evolution of the basin.
• Rifting is bidirectional related to the Weddell Sea and the South Atlantic opening.
• Accumulation rate decreases from 4.84 to 0.8 km3/Ma × 103 in the transition phase.
• In the latest unit it increased to 8.91 km3/Ma × 103 because of the Andean orogeny.

A detailed tectono-stratigraphic analysis of the Malvinas Basin was achieved by the interpretation of around 65,000 km of 2D seismic reflection profiles. Five main seismo-stratigraphic units and their sub-units, informally named units U1 to U5 a/b, bound by major unconformities were identified and correlated with the Mesozoic to Cenozoic main tectonic phases of the basin. Unit U1 (Pre-168 Ma) represents the seismic basement. Unit U2 (168–150.5 Ma, syn rift phase) thickens and deepens southwards. Units U1 and U2 are affected by several syn-rift normal faults that exhibit a main NE–SW strike direction in the south of the basin and a NW–SE strike direction in the centre of the basin. This suggests that the Malvinas Basin may have developed initially as a rift basin with two different extensional directions: (1) a NW–SE directed extension probably linked with the opening of the Weddell Sea (Early Mid-Jurassic), and (2) a NE–SW directed extension most likely linked with the Jurassic back-arc extension of Gondwana and probably later with the onset of the opening of the South Atlantic during Late Jurassic to Early Cretaceous time. Unit U3 (150.5–68 Ma, sag phase) is mainly an aggradational wedge-shaped unit. Unit U4 (68–42.5 Ma, transtensional foredeep phase) overlies unconformable unit U3. It deepens in the south because of an N–S/NW–SE directed extensional regime. Accumulation rates decrease during units U2, U3, and U4 from 4.84, to 1.23 to 0.8 km3/Ma × 103. Units U5a and U5b (42.5–5.5 and 5.5–0 Ma, transpressional foredeep phase) finally represent a change from aggradation to progradation sedimentary pattern and to a left-lateral transpressional regime in the south. The sediment supply was considerably higher than before and a thick sedimentary wedge has been deposited until today. Accumulations rates increased in units U5a and U5b from 2.28 to 8.91 km3/Ma × 103.