The Late Sinemurian carbonate platform and microfossils with Tethyan affinities of the Algarve Basin (South Portugal)

A Lower Jurassic shallow-platform carbonate succession recognized at Alte, in the Algarve Basin (South Portugal), bears a typically Tethyan microfossil assemblage, which had not been documented before in Portugal and allows better dating of the succession. This is mainly composed of intertidal-supratidal sediments, with infrequent subtidal sediments and event deposits, suggesting a marginal-marine, peritidal depositional setting. The microfossil assemblage comprises benthic foraminifera, calcareous algae, porostromates, ostracods and Incertaesedis. As regards to biostratigraphy, the most important are the larger imperforate foraminifera, which include Lituosepta recoarensis, Paleomayncina termieri and Pseudopfenderina butterlini ?, among other. The vertical distribution of these species indicates that the succession may be confidently dated as Upper Sinemurian, most probably as topmost Sinemurian. The persistence of L. recoarensis at the top of the sucession indicates that these deposits do not reach the Carixian. The dasyclads are the most important group in the microflora, in particular the typical Liassic species Palaeodasycladus mediterraneus. Also most abundant is Thaumatoporella parvovesiculifera. As regards to the Algarve Basin Lower Jurassic shallow-platform formations, it is only in the levels bearing these assemblages that a biostratigraphical constraint is found. The recognition of these Tethyan assemblages also reinforces the knowledge of their palacogeographical distribution and of the correlative depositional settings in the southern Iberian Peninsula, allowing further comparisons with the North-African region.