Palaeoenvironmental evolution of the Santo André lagoon (SW Portugal): Palaeobotanical contribution

Depositional systems such as lagoons and estuaries are natural archives of information on environmental changes that occurred in the recent past and on coastline evolution. For the Portuguese coastal fringe, based on geological and paleoecological data from the Santo Andre lagoon (SW Portuguese coast, 80 km south of Lisbon), an evolutionary model has been proposed which comprises a transgressive phase until the middle Holocene, followed by a forced regression, despite the continuous positive eustatic signal. However, so far no palaeobotanical proxies were included in the evolutionary models. To improve the knowledge of the present models, a 4.96m-long core (LSA4) has been collected from the permanently lagoonal flooded domain. The sedimentological analysis and 14C dating of cored material, allowed us to identify four major lithostratigraphical units, accumulated after 6.3 ka cal BP. Presently the palynological analysis focused on the lower units, before 5000 BP, namely LSA4 Unit I (bioclastic muddy peats) and LSA, base of Unit IIA (muds). The presence of Mediterranean trees (evergreen <em>Quercus</em>) and shrubs (<em>Olea</em>, <em>Pistacia</em>), in the Santo André basin during the first half of the Holocene, reflects the development of a local <em>Quercus </em>forest with Mediterranean shrubland. The vegetation reflects the development of a freshwater pond (<em>Botryococcus</em>,<em>Pediastrum</em>,<em>Nymphaea</em>, <em>Myriophyllum</em>) as a consequence of the formation of a costal barrier, but with some sea water influence as reflected by the presence of dinoflagellate cysts of <em>Spiniferites </em>and occurrence of <em>Cymatiosphaera</em>. The presented results represent a contribution, from palynological science, to the evolutionary models already proposed in the literature (and based on other proxies) in what concerns palaeoclimatological and human-induced contributions to modulate coastal responses.