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Comparative Interpretation of Regional Seismic Profiles Offshore Portugal, West Iberian Margin

Abstract

The West Iberian Margin embraces portuguese rifted basins. These are grouped as inner basins such as Porto, Lusitanian and Algarve and outer basins such as Peniche, Alentejo and Sagres offshore. These rifted basins that originated from the closure of Thetis Ocean and opening of the North Atlantic Ocean have similar characteristics. The best known 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 Lusitania basin being known through the detailed stratigraphic mapping of outcrop exposures and legacy exploratory drilling. Exploration has also been conducted in the Algarve basin where shallow water wells have been drilled. The lesser known basins are the western offshore basins of Porto, Peniche and Alentejo and the southernmost basins of Sagres and Algarve deepwater. Knowledge on the deepwater basins are essentially derived from seismic stratigraphic comparisons with Lusitanian and Algarve basins. The Lusitanian basin is developed over a Paleozoic basement terrane. Triassic rift deposits were blanketed by thick salt-rich clays. Carbonate deposition was predominant during the Early and Middle Jurassic, and Late Jurassic is characteristic of a younger rift. A Late Jurassic basin inversion is contemporaneous with the rise of salt diapirs and the rising of massive corridor salt walls. Early Cretaceous sedimentation was marked by the break-up of the North Atlantic. The Late Cretaceous tectonic inversion, Diapirs and deformation of salt features relate to Alpine compression. Deformation continued with diapirism being regionally defined by seismic and basin outcrop exposures. The Peniche and Alentejo basins offshore have thick sections of Triassic (with salt in Peniche basin), Jurassic and Lower Cretaceous sediments. Algarve basin display influences of the Atlantic and of the Pelagian Platform of North Africa in resemblance with oblique slip features of a transform margin. This paper details the interpretation of regional seismic lines over portuguese basins these clearly outlines main events such as breakup unconformities, pre-salt section, Triassic salt, Early and Upper Jurassic carbonates and Lower and Upper Cretaceous sediments. The regional interpretation differences of basin evolution were restored by computer focusing on events with salt structures, Lusitanian and Peniche, and of basins without massive salt.