Paleoclimate archives from Southern Portugal: An overview

Abstract: Paleoclimate events, either short or long in time, can be recorded in a variety of archives along the geologic timescale, several of which are present in Southern Portugal where the geologic history spans almost the last 400 Ma. The type of paleoclimate archives will define both the type of paleoclimate event that can be studied and the resolution of the proxy used to study it. In the Algarve Region, the most abundant paleoclimate archives correspond to metasedimentary and sedimentary rocks, representing depositional environments ranging from Devonian to Quaternary periods. Several proxies such as lithology, mineralogy and organic geochemistry and biology, have been used on these archives to describe paleo-environmental changes, as for instance oceanic anoxic events and sea-level variations linked to glacial cycles. Other proxies, such as the fossil content and isotopic signatures, have also been analyzed for documenting paleoclimate systems. Concerning the Quaternary period climate record, the Algarve has no ice or lake archives, but it has continental deposits, such as estuarine sediments, calcareous tufas and speleothems, as well as archeological and historical archives, allowing reconstructing more recent paleoclimate conditions. Studying all these possible archives and paleoclimate records is a demanding task and it is thus still a work in progress. Nevertheless, significant scientific contributions in this research area already exist and are being used as a geological heritage for the Loulé-Silves-Albufeira Aspiring UNESCO Global Geopark. Indeed, the territory encompassing the Loulé-Silves-Albufeira Aspiring UNESCO Geopark has several archives and records across the geological timescale that are worth presenting. As a first example, this territory has a unique record of Triassic rock formations, the Silves Sandstone succession (known as Grés de Silves sensu lato) in which a recently discovered amphibian species, Metoposaurus algarvensis, has recently been described for the first time, based on a large concentration of bones (Brusatte et al., 2015), and new fossil remains of Henodontidae are under determination. All the studied proxies describe a transitional continental environment, characterized by arid conditions that led to the existence of temporary ponds, and ultimately the formation of evaporites, in the transition to the Jurassic, after a short marine incursion into the basin (Fechner, 1989). The coral and echinoid fossils from Jurassic limestones formation can be presented as a second attractive example of this territory paleoclimate record, allowing documenting the tropical sea conditions existing at that period. Finally, a third example of the paleoclimate archive included in the aspiring Geopark territory, is linked to the extensive and magnificent karstic landscape near Loulé, that presents speleothems and springs, with calcareous tufas, in which preliminary isotopic and palynological studies are very promising.