Salt Distribution and Morphology in the Offshore Algarve Basin
Published:December 01, 2005
Hugo Matias, Webster Mohriak, Paulo Menezes, Frode Sandnes, Valéria C.F. Barbosa, Luis Matias, Fernando Santos, 2005. "Salt Distribution and Morphology in the Offshore Algarve Basin", Petroleum Systems of Divergent Continental Margin Basins, Paul J. Post, Norman C. Rosen, Donald L. Olson, Stephen L. Palmes, Kevin T. Lyons, Geoffrey B. Newton
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The Algarve basin developed as an extensional basin during the Mesozoic, associated with northwest- southeast transtension in ending at the Azores-Gibraltar plate boundary. Several main episodes could be identified in the evolution of this plate boundary: Triassic rifting and mid-Atlantic extension until the Early Cretaceous; fracturing and strike-slip movement along the Azores-Gibraltar Fracture Zone, from Early Jurassic to lower Eocene; continental convergence between Europe and Africa, beginning in the Late Cretaceous, reaching its culmination during the Neogene.
The study of the Algarve basin began with the interpretation of 2D MCS seismic profiles generating structural and isopach maps. These maps show the geometry of the basin to be asymmetric, associated with a depocenter striking northeast-southwest and located very close to Guadalquivir ridge.
Two salt units are interpreted in the Algarve basin: an older one of Triassic age and another of as Late Jurassic age. The latter salt formation is described initially as an evaporitic layer deposited during one of the Jurassic uplift episodes. However, seismic data character suggests that it might not be autochthonous salt and could be allochthonous salt sourced from the Triassic. Salt is also distributed differently throughout the basin: the Triassic salt extends over nearly the entire basin while the Jurassic evaporites are limited to the central and eastern area.
Jurassic salt structures are associated either with extensional tectonics, such as salt-rollers with associated listric faults, or compressional geometries resulting from the reactivation of listric faults as reverse faults during the compressive episodes of the Tertiary. Morphologically, the Triassic salt is characterized mainly by a number of salt piercement features occurring as circular salt diapirs or elongate salt ridges. Although the time of initiation of salt movement cannot be determined, final movement occurred during Miocene time.