AAPG Bulletin, V. 82 (1998), No. 4 (April 1998), P. 596-636.

Structural and Stratigraphic Evolution of the Western Malvinas Basin, Argentina¹

José Sebastián Galeazzi²

©Copyright 1998.  The American Association of Petroleum Geologists.  All Rights Reserved

¹Manuscript received March 26, 1996; revised manuscript received March 6, 1997; final acceptance October 22, 1997.
²Astra Capsa, Tucumán 744, Capital Federal, (1049) Argentina. Present address: Total S.A., 24 Cours Michelet, 92069 Paris, La Defense Cedex France; e mail: [email protected]

The core of this paper was prepared and presented as my Master’s thesis at Rice University. This work would not have been possible without help from my advisors at Rice University: P. R. Vail, A. W. Bally, R. M. Mitchum (Mitchum Exploration, Inc.), and D. Sawyer. The manuscript also benefited from constructive discussions with G. Vackarcs, M. Uliana, L. Legarreta, R. Porta, and S. White. Previous versions of this paper were improved by the comments of reviewers M. Uliana, I. Dalziel, A. Kovas, and former AAPG Elected Editor K. Biddle. The data sets for this study were kindly provided by Astra Capsa, by Exxon for the Malvinas Basin, and by Total for the Magallanes Basin. Paleontologic reports from seven wells within the Malvinas Basin were provided by Exxon, and were mainly produced by D. K. Goodman, J. C. Hanna, and R. C. Wright, and also by G. Blechschmidt, J. L. Lamb, L. A. Smith, and F. M. Weaver. I thank the management of Astra Capsa for permission to publish this paper. Astra Capsa and Rice University provided financial support for this work. 

Abstract

The Malvinas Basin is one of the few basins on the Argentine continental shelf that contains a proven petroleum system; however, uneconomical oil discoveries keep the basin at a frontier exploration status.

The Malvinas Basin evolved through three main tectonic phases: rift, sag, and foredeep. The sedimentary fill of the basin is closely related to its tectonic history. Middle Jurassic rifting resulted in north-northwest-oriented grabens that filled with volcanic and pyroclastic continental rocks. Diminished faulting and generalized subsidence during the Late Jurassic-Neocomian early sag phase were accompanied by deposition of a basal transgressive marine wedge. The Aptian- Maastrichtian interval was characterized by tectonic quiescence and deposition of offshore mud-prone sediments. Southerly localized early Paleogene transtensional tectonism accompanied the early development of a foredeep trough. Outer shelf glauconite-rich sandstones, basinal claystones, and localized carbonate buildups partially filled the basin. By the middle Eocene-Oligocene, a strong deepening event marked the initiation of the foredeep sensu stricto phase. This phase resulted in the full development of the Malvinas foredeep and the formation of compressional structures in the foreland. The foredeep basin was replenished by a westerly derived offlapping siliciclastic wedge of Oligocene-Miocene age.

Noncommercial hydrocarbon discoveries in 5 of the 17 wells drilled in the basin suggest the presence of an undercharged Lower Inoceramus- Springhill petroleum system.