The Western Malvinas Basin, Argentina: Stratigraphy, Structure and Keys to Hydrocarbon Exploration

J. Sebastian Galeazzi

The Malvinas Basin developed adjacent to the southern margin of the South American plate, tightly linked to its evolution from a Mesozoic extensional regime into a Cenozoic compressional and strike-slip stage. The basin formed in the early Mesozoic by crustal extension of a Paleozoic sialic basement. Regional intraplate sagging and a southward tilting of the slab continued during the Cretaceous to Paleogene. Finally, the inception of the Magellan-North Scotia mobile belt during the Oligocene-Neogene induced the overprint of transpressional deformation associated with the deposition of a foredeep wedge.

Major regional unconformities define five megasequences: 1) Dogger-Malm Megasequence: non marine and volcanic, onlapping and aggrading infill of isolated troughs. 2) Oxfordian(?)-Aptian Megasequence: shallow to deeper shelfal marine, onlapping and backstepping infill of a sag basin. 3) Aptian-Maastrichtian Megasequence: aggrading to starving distal shelfal drape. 4) Paleocene-Eocene Megasequence: deep water onlapping and aggrading clastic deposition of an underfilled asymmetric basin. 5) Oligocene-Pliocene Megasequence: deep to shallow marine, onlapping-downlapping and forestepping encroachment of an asymmetric underfilled to infilled basin.

The style of deformation includes a complex array of extensional, inverted and compressional features. Jurassic to Neocomian pervasive normal faulting trend mainly NW. Paleocene-Eocene E-W normal and strike-slip faulting deformed the southern part of the basin and was overprinted by Oligocene to Neogene thrusting and inversion of older normal faults which trend parallel to the E-W oriented portion of the southern Andean Orocline.

The integrated description of the basin suggests unprospected plays in addition to the known Malm-Neocomian Springhill transgressive sandstone. Slope and basin floor Miocene sandy turbidites are the most important alternative. Other possibilities are the mound shaped carbonatic buildups of Maastrichtian-Eocene age and the northward pinch-out terminations of the Paleogene section of the Glauconitic Sandstones Formation.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995