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Portugal Prospective Petroleum Basins, Offshore Edge of Iberia Peninsula

Abstract

Portugal Prospective Petroleum Basins, Offshore Edge of Iberia Peninsula

Abstract

The continental margin edge of the Western Iberian Margin is marked by the Portuguese rifted sedimentary margin basins. These rifted basins originated from the closure of Thetis Ocean and opening of the North Atlantic Ocean and they all have similar characteristics. The best known of these basins is the mostly onshore Lusitanian Basin where exploratory work has been consistent. The basins evolved as part of the Mesozoic evolution of the Iberia Peninsula, the petroleum geology history of the Lusitanian Basin being known through the detailed stratigraphic mapping of outcrop exposures and legacy exploratory drilling. Exploratory work have also been conducted in the onshore and shallow offshore wells have been drilled in the Algarve Basin. The lesser known basins are the western offshore basins of Porto, Peniche and Alentejo and the southernmost basins of Sagres and Algarve deeper offshore. In the last decade state of the art seismic surveys were conducted in the Peniche, in the Alentejo and in the Algarve basins. Interpretation mapping of these surveys un-covered attractive structural and stratigraphic prospects in deep-water shaped by salt tectonics.

This paper describes an overall G & G view of these marginal basins based on seismic, gravity and magnetics data. The better known onshore Lusitanian Basin developed over a Paleozoic basement terrane amalgamated during the Variscan orogeny. Triassic rift siliciclastic infill was followed by thick salt-rich clays deposited in continental and coastal evaporitic sabkhas. Marly and carbonate deposition were predominant during the Early and Middle Jurassic with marine sediments of ramp and platform environments. The late Jurassic characterizes a new rifting episode with realignment of old basement structures and erosion of the margin rift shoulders. Early Cretaceous sedimentation was marked by the break-up of the North Atlantic whereas the late Cretaceous marks the tectonic inversion of the basin and its continued deformation. Salt pillows deforming the Late Triassic date back from Early to Mid-Jurassic, whereas Late Jurassic tectonics and basin inversion are contemporaneous with the rise of salt diapirs and the massive corridor salt walls of Lusitanian Basin. The late Cretaceous piercing of diapirs and the deformation of the buried and piercing salt features are related to the Alpine compressive events. These deformations continued until recent times with the diapirism being regionally defined by seismic and basin outcrop exposures. The Peniche and Alentejo basins offshore also display thick sections of Triassic (with massive salt in the Peniche Basin), Jurassic and Lower Cretaceous sediments whereas the Algarve Basin has influences from the Atlantic and from the Pelagian Platform of North Africa in resemblance with oblique slip features of a transform margin.