justificação do valor científico
The Albufeira diapiric structure, a salt-wall, is sketched on Fig. 8 in map view and cross section. The morphological depression west of Albufeira corresponds to the core of the salt diapir that is presently covered by a cap rock, probably of Quaternary age. Outcropping evaporites with gypsum mylonites and proto-mylonites containing Jurassic limestone relicts can be observed at the Praia da Baleeira scarp.
Like the Loulé salt-wall (Terrinha et al., 1990), the Albufeira salt-wall formed at the intersection of an E-W and an approximately N-S fault, the Baleeira and Albufeira faults, respectively. Both faults are of Mesozoic age and were extensional structures during the Mesozoic extensional phases and diapirism. The shape of the diapir was controlled by the intersection of the two Albufeira and Baleeira Faults as it can be seen by the triangular shape of the salt body.
A study of the internal geometry of the salt diapir is impossible to carry out, because the diapir is covered by a cap rock. Thus its kinematics are inferred from the relative geometries and deformation structures in the surrounding country rocks, i.e. the small outcrop of Hettangian evaporates (mainly gypsum), the Upper Jurassic, the Lower Cretaceous, the Middle Miocene and the cap rock (pedogenic calcareous crusts of probable Quaternary age). All the above mentioned rocks show some degree of deformation. The evaporites are extremely deformed (they are folded, sheared and mylonitized), the Jurassic and Cretaceous carbonates are folded and thrust, the Miocene is not folded and is extensively cross cut by normal faults and the cap rock only shows micro-faults with strike-slip striae.
The geometry of the structures and the stratigraphy observed along a N-S transect through the diapir and adjacent margins suggest that the original geometry was that of a normal fault dipping to the north. To the north of the diapir, in the hanging-wall, the structure has the shape of a roll-over, probably due to extension followed by compression. To the south, in the foot-wall, the structure is more compatible with folding and flattening against a buttress, probably the foot-wall of a normal fault. It is speculated that diapirism could be of post-Kimmeridgian to pre-Albian age, because the Albian limestones seem to onlap unconformably on top of previously extended Kimmeridgian dolomites.
Evidence for Pliocene-Quaternary compression is the fact that the Miocene erosion surface that is preserved in the foot-wall of the Baleeira Thrust has no equivalent on the hanging-wall, although this erosion surface truncates previously folded and thrust beds.
TERRINHA, P.A.G.,, COWARD M.P.; RIBEIRO, A. (1990) - Salt tectonics in the Algarve Basin: the Loulé diapir, Comunicações dos Serviços Geológicos de Portugal, 76: 33 – 40.
TERRINHA, P., RIBEIRO, C., KULLBERG, J. C., ROCHA, R.; RIBEIRO, A. (2002). Compression episodes during rifting and faunal isolation in the Algarve Basins, SW Iberia. Journal of Geology, 110: 101 - 113.