The neogene of the Lower Tagus Basin (Portugal)

Abstract

The Tertiary Lower Tagus Basin (LTB) occupies a large area in Portugal and constitutes a symmetric basin of the oriental huge Upper Tagus Basin, centered at Madrid (Spain). The LTB was an endorreic basin during the Paleogene.  Marine connection occurred at the Lower Aquitanian; at the Lisbon – Setúbal Peninsula region the sedimentation was in the ocean/continent interface, with several changes in the coast line. Apparently, the first marine transgression came from South, originating a gulf with a N-S coral reef that attained the Lisbon area. Occidental communication to the sea was established after the Burdigalian.The sedimentary and palaeontologic record of the distal sector of the LTB (Lisbon–Setúbal Peninsula) is related to sea level changes. The fossil richness – dinoflagellates, spores, pollen, plant macrorremains, foraminifera, ostracoda, molluscs, echinids, fishes, reptiles, mammals – and O and C isotopes, constitutes a large source of information for environmental and palaeogeographical reconstitutions, as well as for the establishment of correlations between marine and continental deposits. The analysis and the integration of a large amount of lithological and biostratigraphical data joined with isotopic ages (K/Ar and 87Sr/86Sr), allow the establishement of a chronostratigraphic framework for the distal part of the Miocene of the LTB and the definition of 10 depositional sequences, in part agreeing with the Haq’s 3rd order eustatic cycles. Climatic evolution during the Miocene has been also characterized. At continental environments, the faunas and floras point out to an alternation of moist and dry episodes, the dryest one at the Langhian