Basin Evolution and Prospectivity of the Argentine Continental Margin

Abstract

Nine Mesozoic‐Tertiary basins of different orientations lie along the Argentine continental margin, over a distance exceeding 2,000 km: these are the Salado, Colorado, Valdes, Rawson, San Jorge offshore, North Malvinas (San Julian), West Malvinas and Magallanes (Austral) Basins on the Continental Shelf, together with the Continental Slope. These basins formed following the latest Jurassic — Early Cretaceous extension that accompanied the onset of South Atlantic rifting. Strain was modified by earlier basement fabrics, with consequent transtension. The Cape Fold Belt (Permo‐Triassic) provided a NW‐SE grain to pre‐Mesozoic cover off NE Argentina. In the central‐southern sector, several phases of oblique NEwards Pacific subduction and terrane accretion during the Permo‐Triassic formed back‐arc basins and volcanic belts, producing a more variable fabric orientated close to NNW‐SSE. Atlantic basin fill, of Lower Cretaceous‐Tertiary clastics, was deposited as a result of rift‐shoulder erosion and Atlantic flooding, following eastward tilting. Basin fill thickness is typically 2–4 km, but locally exceeds 6km. The hydrocarbon potential of these basins hinges as much upon the preservation of source rocks within the pre‐rift succession as it does on that of those within the base‐rift succession, and subsequent Atlantic anoxic events.

Tectonic evolution of the Colorado Basin, offshore Argentina, inferred from seismo-stratigraphy and depositional rates analysis

“…1b) (Lopez-Gamundi and Rossello, 1998). The succession shows consistent affinity to the Great Karoo Basin of Southern Africa (Keidel, 1916;Keeley and Light, 1993;Lopez-Gamundi and Rosello, 1997).…”

“…This early extensional phase may be reflected by the lower syn-rift succession in the North Malvinas Graben (Richards & Fannin, 1997). The major Late Jurassic -Early Cretaceous crustal stretching episode is found throughout the sedimentary basins of the Argentine continental shelf (Keeley and Light, 1993).…”

“…The pre-rift deposits appear as mainly parallel seismic reflectors, both at the base of the graben structures and at the horsts ( Figure 11). It is suggested from well data, that this succession represents Late Carboniferous-Early Permian conglomerate or breccia and finer lithologies (Macdonald et al, 2003;Keeley and Light, 1993). The pre-rift succession displays a central EW-elongated graben which influences thicknesses in the overlying sequences up to the Miocene.…”

“…Keeley and Light (1993) suggested two phases of active rifting in the Late Triassic-Early Jurassic and in the Mid-Jurassic. The continental extension may have begun in isolated centres in South America…”

“…Permian time over most of Gondwana (Macdonald et al, 2003) is preserved in the area of the Colorado Basin (Keeley and Light, 1993). This was covered by dark, organic-rich shales deposited in a major fresh or brackish transgression at the end of the glaciation before a more arid continental environment established in the Triassic (Macdonald et al, 2003).…”