Given their extraordinary abundance in the Iberian Peninsula since the Plio-Pleistocene, but especially after the Neolithic (Allué and Renault-Miskovsky 1999), the sediments associated with palaeontological, and archaeological open-air sites have traditionally been tested for palynology (Table 6). Reports of pollen occurrence in these sites, predominantly with coarse clasts and high lime concentration, are numerous in Spain (López-García 1991; Mariscal 1991a-c; 1992; Davis and Mariscal 1994; Castro et al. 1999; Fuentes et al. 2005; 2007; Postigo et al. 2007), but because of the high profile of some archaeological excavations, failures are highlighted.
Purely sandy and gravel-based layers are expected to be usually sterile or contain poor, contaminated, or non-significant pollen spectra. This is the case for the Chalcolithic sites of Los Molares (megalithic necropolis), Los Millares (Burjachs 1991a), La Pijotilla, Canaleja I (López-García and López-Sáez 1994a; 1994b), Buzanca I and Huerta de los Cabreros (Mariscal 1996), the Bronze Age of Monte Aguilar (Iriarte 1992), San Blas, San José, Venta Quemada I, Sevillejas, San Bernardo, La Calzadilla, El Prado (López-García 1991) and Cabezo Redondo (Fumanal et al. 1996), the Iron Age/Iberic sites of El Molón, San Miguel de Atxa (Iriarte 1994), Villasviejas de Tamuja, El Castillejo, Puente Largo del Jarama (Muñoz 2000), Castilmontán, Fuente Saúco (Mariscal 1994), Molinicos (López-García 1991) and Castro Follente (Table 6). Sandy sediments also parallel the lack of pollen in the open-air, historical sites of Castro de Vigo and Pedra Moura in Galicia (Aira-Rodríguez et al. 1988), Teatro Romano of Cartagena and Las Monjas and Torrerroja in Alicante. In other cases, sterility is in tandem with gypsum, as in the Neolithic site of Casa Montero, the Bronze Age site of San Bernardo, and the Visigothic site of San Martín de la Vega (López-García 1983).
Sands and red clays are associated with sterile palaeosols in central Spain: Urda in Toledo and Pedro Bernardo in Ávila (Table 6). In wetter climates, old soil horizons associated with settlement sites can, however, contain a lot of pollen and spores (van Geel et al. 1983; 2003) which are probably locked up in some form of humic complex (Dimbleby 1985). Slope deposits of Barranco Hondo, Las Lenas, Valmadrid, and the Portuguese Vale da Cerva at Guarda still show partial sterility and evidence of contamination by recent pollen (González-Sampériz et al. 2003a; González-Sampériz 2004a; Valero-Garcés et al. 2004) (Table 6).
Palaeontological sites can be also associated with doline infills, and fluvial and lakeshore terraces. Polliniferous layers sometimes result from areas that became buried in a general waterlogged phase, such as in the famous hominid site of Florisbad in South Africa (Scott and Nyakale 2002). Similarly, in all the palynological trials in Cal Guardiola (Tarrasa, Barcelona), the darker, more organic layers showed palynomorphs and plant macroremains, including timber (Postigo et al. 2007). The remaining layer suffered from oxidation and so lacked pollen (Burjachs 2000a; Peregrina 2003). Other sites were found to be fully sterile, like the mid-Pleistocene San Quince del Río Pisuerga and the early Pleistocene palaeontologically rich doline infilling of Incarcal (Girona) (Villalta and Vicente 1972; Galobart et al. 1990; Suc 1980; Geurts 1977; 1979; Leroy 1990) (Table 4).
Exposed tufas and travertines of Alós (Lérida), the margins of the Guadalquivir River in Córdoba, Tajo de Ronda (Málaga), the Eemian from Río Matarraña (Beceite, Teruel), and the Lower Pleistocene of Sierra de Quíbas (Murcia) were barren of pollen, despite the presence of preserved macroremains in abundance suitable for detailed palaeobotanical studies (Martínez-Tudela 1986) or palaeontological ones (Montoya et al. 2001) (Table 6). Travertines, like breccias, can be polliniferous (Weinstein-Evron 1987; Vermoere et al. 1999). When dealing with these deposits, the possibility of contamination by recent or sub-recent pollen has to be kept in mind, as in Sterkfontein and other southern African hominin-bearing sites (Carrión and Scott 1999).
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