Neolithic occupation and mid-Holocene soil formation at Encosta de Sant’Ana (Lisbon, Portugal): a geoarchaeological approach Diego E. Angelucci a, * , Anto ´nio Monge Soares b , Luı ´s Almeida c , Rui Brito d , Vasco Leit~ ao d a Instituto Portugue ˆs de Arqueologia, Av. da I ´ ndia 136, P-1300-300 Lisbon, Portugal b Instituto Tecnolo ´gico e Nuclear, Estrada Nacional 10, P-2686-953 Sacave ´m, Portugal c Departamento de Geologia, Faculdade de Cie ˆncias, Universidade de Lisboa, Campo Grande, Edifı ´cio C6, P-1749-016 Lisbon, Portugal d Museu da Cidade, Campo Grande 245, P-1700-091 Lisbon, Portugal Received 26 July 2006; received in revised form 28 November 2006; accepted 5 December 2006 Abstract Excavations at the archaeological site of Encosta de Sant’Ana (Lisbon, Portugal) uncovered a mid-Holocene buried alluvial soil associated with early Neolithic occupation layers. Routine laboratory analyses and micromorphological observations were undertaken on the soil material. Humic acids from its Ab horizon, as well as Neolithic ecofacts, were radiocarbon dated. The dates obtained indicate that soil was formed be- tween c. 8.0 and 6.0 cal ka BPand that the pedological evidence fits the record of the North Atlantic Holocene IRD events (‘‘Bond events’’) and the so-called ‘‘Holocene climate optimum’’. The geoarchaeological record reveals that Neolithic inhabitants settled upon a stable surface, still affected by soil formation that was suddenly interrupted by slope wasting, probably in correspondence to Bond event 4, at c. 6.0 cal ka BP. Ó 2006 Published by Elsevier Ltd. Keywords: Neolithic; Mid Holocene; Radiocarbon dating; Humic acids; Soil formation; Holocene IRD events 1. Introduction The archaeological site of Encosta de Sant’Ana (from now onwards: ESA) is located in downtown Lisbon, Portugal, along a slope crossed by the 14th century town wall. Its co- ordinates are 38  43 0 02 00 N and 09  08 0 02 00 W (European Datum); its altitude ranges from 15 to 20 m (Fig. 1). Salvage excavation at the site began in 2002 and, after a short interruption, was recommenced in 2004. Fieldwork un- covered an impressive archaeological succession that includes Neolithic and Bronze Age dwellings, part of the Roman town’s cemetery, Islamic layers and features, medieval houses, and the rubble of the 1531 and 1755 earthquakes, which strongly affected this part of Lisbon (Angelucci, submitted; Angelucci et al., 2004; Muralha et al., 2002). The oldest human traces observed at ESA are the Neolithic accumulations of shells in stratigraphic unit SU 5, which are embedded in a buried Ab horizon, and the occupation floor of SU 4, which rest on top of the same horizon. Charcoal frag- ments from SU 4 were dated to 5420  45 BP (Sac-1893) and 5140  140 BP (Sac-1894; see Table 1 and Angelucci et al., 2004). The Ab horizon is part of a buried alluvial soil profile. Here we present the radiocarbon dates obtained on the shell fragments of SU 5 and on the humic acids of the Ab horizon. These new dates are relevant for reconstructing the chronology of the process of Neolithization of the Lisbon region and the development of the environment in mid-Holocene times. 2. Site presentation Lisbon is on the northern shore of the River Tagus’ estuary, at a short distance from its opening into the Atlantic Ocean, in the Portuguese Estremadura region. Downtown Lisbondthe so-called Baixa Pombalinadoccupies a small alluvial plain * Corresponding author. Tel.: þ351 21 361 6500; fax: þ351 21 361 6559. E-mail address: diego@ipa.min-cultura.pt (D.E. Angelucci). 0305-4403/$ - see front matter Ó 2006 Published by Elsevier Ltd. doi:10.1016/j.jas.2006.12.002 Journal of Archaeological Science 34 (2007) 1641e1648 http://www.elsevier.com/locate/jas