New data on the chronology of the Vale do Forno sedimentary sequence (Lower Tejo River terrace staircase) and its relevance as a fluvial archive of the Middle Pleistocene in western Iberia

Abstract

a b s t r a c tThe Vale do Forno archaeological sites (Alpiarça, central Portugal) document the earliest human occupation in the Lower Tejo River, well established in geomorphological and environmental terms, within the Middle Pleistocene. In a staircase of six fluvial terraces, the Palaeolithic sites were found on the T4 terrace (þ24 m, above river bed) which is made of a basal Lower Gravels unit (LG) and an overlying Upper Sands unit (US). Geomorphological mapping, coupled with lithostratigraphy, sedimentology and luminescence dating (quartz-OSL and K-feldspar post-IRIR 290 ) were used in this study. The oldest artefacts found in the LG unit show crude bifacial forms that can be attributed to the Acheulian. In contrast, the US unit has archaeological sites stratigraphically documenting successive phases of an evolved Acheulian. Luminescence dating and correlation with the Marine Isotopic Stages suggest that the LG unit has a probable age of ca. 335 to 325 ka and the US unit an age of ca. 325 to 155 ka. This is in contrast to previous interpretations ascribing this terrace (and lithic industries) to the Last Interglacial and early phases of the Last Glacial. The VF3 site (Milhar os), containing Micoquian (Final Acheulian) industries (with fine and elaborated bifaces), found in a stratigraphic level located between the T4 terrace deposits and a colluvium associated with Late Pleistocene aeolian sands, is younger than 155 ka but much older than 32 ka.© 2016 Elsevier Ltd. All rights reserved. IntroductionUnderstanding of the Palaeolithic occupation of Northern Europe has been substantially based on evidence from rivers (e.g. Bridgland et al., 2006). For Western Europe and specifically in Iberia, insights into the Palaeolithic occupation is similarly derived from its major rivers (from north to south: Douro, Tejo/Tagus, Guadiana, Guadalquivir) (e.g. Santonja and Villa, 2006). Within this context, the Vale do Forno archaeological sites (Alpiarça, in central Portugal; Fig. 1) provide the earliest and most well documented human occupation in the Lower Tejo (the Portuguese part of the Tejo basin). Lower Palaeolithic bifacial sites are common, often well represented by lithic industries. Their local stratigraphy and technological characteristics indicate successive phases of what is commonly named as the Acheulian. However, they were chronologically poorly constrained.From the Spanish border to the Atlantic coast, the Tejo crosses major faults which provide a natural geomorphological subdivision of the river into a series of valley reaches (I to V;Cunha et al., 2005). * Corresponding author.E-mail addresses: pcunha@dct.uc.pt (P.P. Cunha), aam@uevora.pt (A.A. Martins), jabu@dtu.dk (J.-P. Buylaert), anmu@dtu.dk (A.S. Murray), 3raposos@sapo.pt (L. Raposo), paolo.mozzi@unipd.it (P. Mozzi), m.stokes@plymouth.ac.uk (M. Stokes).

The Lowermost Tejo River Terrace at Foz do Enxarrique, Portugal: A Palaeoenvironmental Archive from c. 60–35 ka and Its Implications for the Last Neanderthals in Westernmost Iberia

“…In this area, geomorphological evidence for late Cenozoic tectonics arises from interpretation of valley asymetry and drainage patterns, fault scarps, tectonic lineaments, fracture-controlled valleys, and vertical displacement of planation surfaces and terraces [26]. The sedimentary controls for the formation of the Lower Tejo terrace staircase (mainly glacio-eustasy and differential uplift) are different from those affecting the Middle and Upper Tejo, because of separation (between the Middle and Lower Tejo) by a lengthy knick zone through hard basement [27,28]. Previous dating of the Pleistocene litostratigraphic divisions was undertaken using Uranium-series, Thermoluminescence (TL), Optically stimulated luminescence on quartz (Quartz-OSL) and infra-red stimulated luminescence (IRSL) on K-feldspar.…”

“…In Reach I of the Tejo, IRSL dating provided a first temporal framework for the Lower Tejo terraces [26], but at that stage of research T5 and T6 were not yet separated as distinct terraces. Recently, T4 in Lower Tejo Reach IV was dated to c. 340 to 155 ka, using post infra-red stimulated luminescence (pIRIR) [28].…”

“…The oldest archaeological evidence in this region appears in the basal deposits of T4, which are dated as older than 280 ka and perhaps as old as c. 340 ka [26,28]. A large Acheulean quartzite assemblage, with handaxes, cleavers, very large flakes and respective cores, was recovered from Monte do Famaco (Vila Velha de Ródão), in a colluvium resulting from the erosion of basal T4 deposits [58].…”

Los terremotos del Bajo Valle del Tajo (Portugal): Lisboa 26 de Enero de 1531 y Benavente 23 de Abril de 1909

“…190 m in the NE region of the basin and decreasing in height towards the SW. The regional uplifting that occurred since the Lower Pleistocene lead to entrenchment of the present fluvial network and the generation of a staircase of fluvial terraces (Martins 1999, Martins et al 20092010, Cunha et al 2016. Along the present alluvial plain of the Tagus River occurs a thick (up to 70 m) Upper Pleistocene to Holocene alluvial cover.…”

Aplicação de métodos de luminescência e da ressonância de spin electrónica na datação de unidades sedimentares quaternárias e da evolução das paisagens

“…Em paralelo prosseguiu a caracterização litostratigráfica e sedimentológica dos depósitos de terraço, bem como a utilização de técnicas de datação absoluta, principalmente por U-Th (ex. Raposo, 1995), por LOE (Martins et al, 2009(Martins et al, , 2010a(Martins et al, , 2010bCunha et al, 2008Cunha et al, , 2012Cunha et al, , 2016Cunha et al, , 2017, mas também por ESR (Rosina et al, 2014) (Fig. 3).…”