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Enhancing rescue-archaeology using geomorphological approaches: Archaeological sites in Paredes (Asturias, NW Spain)
Geomorphology 132 (2011) 99–110
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Geomorphology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / g e o m o r p h
Enhancing rescue-archaeology using geomorphological approaches: Archaeological sites in Paredes (Asturias, NW Spain) M. Jiménez-Sánchez a,⁎, I. González-Álvarez b, O. Requejo-Pagés a, c, M.J. Domínguez-Cuesta a a b c
Departamento de Geología, Universidad de Oviedo, 33005 Asturias, Spain CSIRO, Australian Resources Research Centre, Earth Science & Resource Engineering, Kensington, WA 6151, Australia Gabinete Arqueológico, S. L., 33002 Asturias, Spain
a r t i c l e
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Article history: Received 14 October 2010 Received in revised form 17 March 2011 Accepted 27 April 2011 Available online 10 May 2011 Keywords: Rescue-archaeology Quaternary sedimentology Palaeolithic Roman Necropolis Fluvial landscape Asturias
a b s t r a c t Palaeolithic remnants, a Necropolis (Roman villa), and another minor archaeological site were discovered in Paredes (Spain). These sites were the focus of multidisciplinary research during the construction of a large shopping centre in Asturias (NW Spain). The aims of this study are (1) to contribute to archaeological prospection in the sites and (2) to develop evolutionary models of the sites based on geomorphological inferences. Detailed archaeological prospection (103 trenches), geomorphologic mapping, stratigraphic studies (36 logs) and ground penetration radar (GPR) surveys on five profiles indicate that the location of the settlement source of the Necropolis is outside the construction perimeter, farther to the southeast. The PreHolocene evolution of the fluvial landscape is marked by the development of two terraces (T1 and T2) that host the Early Palaeolithic remains in the area (ca 128–71 ka). The Holocene evolution of the landscape was marked by the emplacement of the Nora River flood plain, covered by alluvial fans after ca. 9 ka BP (cal BC 8252–7787). Subsequently, Neolithic pebble pits dated ca. 5.3 ka BP (cal BC 4261–3963 and 4372–4051) were constructed on T2, at the area reoccupied as a Necropolis during the Late Roman period, 1590 ± 45 years BP (cal AD 382–576). Coeval human activity during the Late Roman period at 1670 ± 60 years BP (cal AD 320– 430) is also recorded by channel infill sediments in a minor site at the margin of an alluvial fan located to the southeast. This work shows that a rescue-archaeological study can be significantly enhanced by the implementation of multidisciplinary scientific studies, in which the holistic view of geomorphologic settings provide key insights into the geometry and evolution of archaeological sites. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Archaeological studies are commonly undertaken in short timeframes in order to minimise economic impact or to comply with existing regulations (Thomas, 1991; Amore and Bejko, 2001; Gonçalves et al., 2008). These “rescue-archaeology” studies commonly require rapid decision-making based on incomplete datasets. Implemented techniques and protocols must be modified from their longer timeframe research counterparts in order to maximise outcomes. This short timeframe promotes innovative approaches and encourages multidisciplinary research (Macphail et al., 2004). Interpretation of the geomorphologic landscape evolution applying sedimentology and geochronology is widely used as the foundation for the understanding of the physical environment and dynamics of archaeological sites (Bruneton et al., 2001; Mercader et al., 2003; Hudson, 2004; Schuldenrein et al., 2004; Arco et al., 2006; Bettis et al., 2008; Butzer, 2008). The integration of geomorphologic
⁎ Corresponding author. E-mail address: [email protected] (M. Jiménez-Sánchez). 0169-555X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2011.04.034
criteria has been successfully applied to target the location of archaeological sites (Mercader et al., 2003; Uribelarrea and Benito, 2008). Remote sensing to locate targets is widely applied in many geological fields to assess the spatial constraints using Geographical Information Systems (GIS). Specifically, archaeological prospectivity can be assessed by combining geomorphologic variables in a GIS environment to display the relations between the landscape features and human activity in time (Chapman and Van de Noort, 2001; Guccione, 2008; Siart et al., 2008; Contreras, 2009). Central Asturias in NW Spain offered a favourable landscape for human settlement from prehistoric times to present due to the development of productive farming soils, easy access to water and a low-relief fluvial landscape. The planned construction of a large shopping centre in the Nora River Basin brought to light the existence of Palaeolithic and Roman remnants. These initial discoveries triggered an archaeological heritage study as required by regulations. Building was delayed until an archaeological study was completed. This study describes the methodology, findings and interpretation of the short-term rescue-archaeological survey based on a multidisciplinary research driven by geomorphologic approaches. The research evaluated the contribution of geomorphologic techniques to enhance
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the results of a rescue-archaeological project in two specific aspects: (1) determining the source of the archaeological remains; and (2) the development of evolutionary models for the archaeological sites. 2. Setting The study area includes a surface area of 305,000 m 2, which was set aside for the construction of a large shopping centre in the Nora River Basin, Asturias, NW Spain, ~4.6 km NE from the historic city of Oviedo (Fig. 1). Proximal to this area, three archaeological sites were previously described: (1) the Early-Palaeolithic site of Paredes (Rodríguez Asensio, 1983a,b); (2) the Roman site of “Castro La Torre” (González and Fernández-Vallés, 1976); and (3) scattered Roman surface artefacts (González and Fernández-Vallés, 1968, 1976). Due to these findings and legal regulations placed on building construction, an archaeological assessment was performed before the resumption of construction. A follow-up assessment was conducted during the building period to ensure the archaeological heritage was not damaged or lost. During the first stage of this archaeological study, archaeological artefacts were discovered between E272640, N4807625 and E273580, N4808570, and Zone 30 UTM, at 175 m a.s.l. (above sea level; Fig. 1). The site contained 50 artefacts: three crackers, one pick, one knife, three teeth, 42 chips and cuttings made of quartzite sandstone. These artefacts were attributed to Early-Palaeolithic times by correlation with previous studies (Rodríguez Asensio, 1983a,b). In the second stage of the survey, a Roman Necropolis (with crosscutting pebble-fire pits) was discovered during the excavation
(E273293, N4808337, and Zone 30 UTM). The discovery of the Roman Necropolis represented an exceptional find in the area since it is the first of its kind and one of the few examples reported in the northern slope of the Cantabrian Mountains. The Necropolis contained 36 structures related to burial and 13 to funeral ceremonies (five pebble fire-pits, five offer-pits and three ash-pits; Fig. 2). The burials were graves excavated in the sediment, covered by tegulae and imbricis. Pottery, glass and/or metallic artefacts were found at every burial site. Archaeological features from these findings (Requejo Pagés, 2007) suggested a Roman age (IV–V centuries). No human remains were described (Requejo Pagés, 1998, 2007). Previous studies reported Roman artefacts in the soil at the same area where the Roman Necropolis was located (González and Fernández-Vallés, 1968, 1976). Therefore, the initial working hypothesis suggested that the location of a Roman villa was within the construction perimeter. The villa was envisioned as the source of the population that was buried in the Necropolis. This hypothesis was strongly supported by other studies on Roman archaeology that described Roman villas located within short distances (b700 m) of their burial grounds (Toynbee, 1996; Abasolo et al., 1997). Other villae described in the region presented burials within the perimeter of the villa itself (Fernández Ochoa and Gil Sendino, 2007). In a preliminary effort to locate the Roman villa, 103 archaeological trenches were performed. Fragmented ceramic and storage containers, as well as table dowry, a large amount of fragmented tegulae and construction bricks of Roman age, were reported defining an additional archaeological site: Monte Les Muries (E272996, N4807989, and Zone 30 UTM; Fig. 1).
Fig. 1. Location of the study area (Paredes, Asturias, NW Spain) showing the perimeter of the construction area and the archaeological sites located during this research (Palaeolithical sites, Necropolis and Monte Les Muries sites).
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Fig. 2. Examples of archaeological findings in the Necropolis. (A) Details of a burial structure at the Necropolis. (B) Glass and (C) pottery artefacts associated with the burial sites.
Two archaeological teams worked separately in parallel studies on each of the sites reported. The priority was to quickly locate and collect all archaeological artefacts in the Necropolis, to constrain the genesis of the second archaeological site found (“Monte Les Muries”) and to connect this latter site to the location of a hypothetical Roman villa. In response to the complexity of this rescue-archaeological study, the designed approach included sedimentologic, geomorphologic, geochronologic and palynologic techniques.
Cartographic Service of Asturias, Spain) were used to define the main geomorphologic units. A map at a scale of 1:10,000 was produced from interpretation of the airborne photographic, trench data and road cuts through the study area. The geomorphologic map was used to interpret the landscape evolution. A genetic criterion was applied to the mapping in order to suggest a framework for the archaeological sites. Twenty-three trenches within geologic materials were located based on the geometry and inferred spatial relationships of the geomorphologic units (Fig. 3).
3. Methodology 3.3. Stratigraphy and sedimentology The central part of the study entailed the integration of a detailed geomorphologic study with GIS to characterise the present landscape and its evolution, as well as the stratigraphic and sedimentologic sequences associated with the archaeological artefacts. These techniques were coupled with 14C radiometric dating to constrain the absolute timeframe for the evolution of the landscape. 3.1. Geographical information system Topographic information at a scale of 1:1000 was integrated into GIS using the ArcGIS 9.2 software package. A raster digital elevation model (DEM) with a 5-m grid interval was built from the digital topographic contours (5 m interval) provided by the Asturias Government (Dirección General de Ordenación del Territorio y Urbanismo) in 2000. Different algorithms were applied to generate derivative terrain models: slope, aspect and hill-shade. Digital orthophotos (1995 and 2000 flights) were also integrated in the GIS at a scale of 1:10,000. The GIS provided a basis for establishing and quantifying the spatial relationships among the different geomorphologic units and archaeological findings. To define landscape influences on the archaeological sites, an area of 78.5 km 2 was outlined by a 5 km radius-circle centred at the Roman Necropolis. The terrain model variables were derived from this area. 3.2. Geomorphologic mapping The geomorphologic survey covered a 16 km 2 area that included all the archaeological sites. Airborne photographic data at a scale of 1:18,000 (1969 and 1994 flights, Diputación of Oviedo and the
The stratigraphic sequence was described for the 23 trenches previously mentioned. Due to continuous rain and high water table levels, continuous re-excavation of the trenches with bulldozers was necessary, which inhibited data collection. In addition, 17 stratigraphic columns (four at the Necropolis and 13 in the Monte Les Muries site) were described at the archaeological sites (Fig. 3). The stratigraphic sections and sedimentologic information collected included sediment colour, grain-size, geometry of different lithologic units, organic content and sedimentary structures. From the stratigraphic sequences, sedimentary processes were interpreted and the evolution of the fluvial system was described. 3.4.
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C radiometric analysis
Five samples from selected sites were collected for geochronological dating by 14C analyses (Fig. 3; Table 1). Three samples (Beta 117720, Beta 125596 and CNA351) were from the Necropolis site in order to determine the timing of human activity associated with the site. A fourth sample (Beta 117719) was taken to establish an absolute date on a key stratigraphic unit at Monte Les Muries, and to constrain the age of the archaeological artefacts located in this area. A fifth sample of wood (Beta 117718) was dated in order to constrain the maximum age for the alluvial fan described in the geomorphologic map. The 14C isotopic analyses were carried out at Beta Analytic Inc. Laboratories (Miami, USA) and the Centro Nacional de Aceleradores (Sevilla, Spain). The CNA351 sample was analysed by AMS and all the other samples by standard radiometric techniques. Calibration of
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Fig. 3. Research area showing the location of the Necropolis and Monte Les Muries archaeological sites. The location of the GPR profiles, 14C samples, trenches and stratigraphic logs is also shown.
dates and curves followed those of Vogel et al. (1993), Talma and Vogel (1993) and Stuiver et al. (1993), and were derived from the Calib radiocarbon calibration programme (Stuiver et al., 2010).
flotation on Thoulet dense liquid (Goeury and Beaulieu, 1979). Pollen data are presented as the relative frequency of pollen for each taxon applying the TILIA® and TILIA GRAPH® (© Eric C. Grimm) software (Jiménez-Sánchez et al., 2004).
3.5. Palynological analysis 3.6. Remote sensing One sample (M1) was collected for palynological analysis at the same locality as the Monte Les Muries sample Beta-117719 (stratigraphic unit C; E272995, N4807989, and Zone 30 UTM). Analysis was performed at the Department of Geology, the University of Alcalá de Henares (Spain). The preparation followed protocols outlined by Faegri and Iversen (1989) and Moore et al. (1994) and applied Table 1 Monte Les Muries and Necropolis Sample CNA351 (charred wood)
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Ground Penetration Radar is a widely applied geophysical technique (e.g., Leckebush, 2003; Neal, 2004; Nielsen and Müeller, 2009). It is frequently used to locate features buried between 0.5 and 6.0 m deep by utilising electromagnetic impulses between 1 and 3000 MHz, with two antennas (emission-receptor) in contact with
C dataset. Coordinates in UTM, Zone 30.
Location (UTM)
Necropolis (offering pit) (273293, 480837) Beta-117719 Unit C Monte (charred material) les Muries Site (272996, 4807989) Beta-117720 Necropolis (burnt wood) (pebble fire-pit) (273293, 4808337) Beta-125596 Necropolis (charred material) (pebble fire-pit) (273293, 4808337) Beta-117718 Nora River alluvial (wood) plain (SW Monte les Muries Site) (272747, 4807836)
Analysis
13 12 Conventional 14C Calibrated results Relative area Calibrated results Relative area C/ C age (years BP) (1σ 68.3% prob.) under distribution (2σ 95.4% prob.) under distribution ratio (‰)
AMS
1590 ± 45
cal AD 478–534
0.568
cal AD 382–576
1.000
− 20
Radiometricstandard
1670 ± 60
cal AD 320–430
0.797
cal AD 244–535
1.000
− 25
Radiometricstandard
5270 ± 70
cal BC 4171–4089
0.434
cal BC 4261–3963 0.984
− 25
Radiometricstandard
5430 ± 70
cal BC 4354–4230 0.921
cal BC 4372–4051 0.975
− 25
Radiometricstandard
8890 ± 70
cal BC 8217–7962 1.000
cal BC 8252–7787 1.000
− 25
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the ground at a specific distance. Dielectric and electric conductivity variations of the ground are measured and compared with time intervals of emission and reception. This technique allows the identification of contrasting properties, which may lead to identification of near-surface underground structures or anisotropies. A Pulse EKKO IV model was operated with the Sensors and Software Inc. system (Molenaar and Vreng, 2004). This equipment generated five profiles of b100 m length at specific locations (PA1–5; Fig. 3). To generate the profiles, a frequency of 200 MHz was used and the antennae were parallel and spaced 1 m apart. The propagation speed of the ground wave was determined by a common midpoint survey. For this, the transmitter and receiver antennas were moved apart from each other. With the time difference between the ground and the air wave at different distances, and obtained airwave receiving time, the ground propagation speed was calculated at 0.10 m s − 1 (García-García, 1997).
4. Results and discussion 4.1. Geomorphology and landscape: the framework of the archaeological sites Fig. 4 describes the landscape of a 78.5 km 2 area (5 km circle radius centred in the Necropolis) based on GIS. Altitude ranges from 136 to 610 m, averaging ~210 m (Fig. 4A and A′). The landscape is dominated by low-angle slopes with an average of ~ 6° and a maximum value of 55° (Fig. 4B and B′). North-facing slopes (0° to 90° and 271° to 360°) predominate (55.1%) over south-facing slopes
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(91° to 270°) (Fig. 4C and C′), with a predominant hill shade of ~ 180° (Fig. 4D and D′). Landscape features were represented in a 1:10,000 scale geomorphologic map (Jiménez-Sánchez et al., 2004). Two main topographic elevations are present in the area: Cerro Cueto at 210 m a.s.l. and Paredes at 199 m a.s.l. The Nora River is the main geomorphologic agent. Fluvial deposits that form terraces, flood deposits, alluvial fans and a torrential basin are the main landscape features. Colluvium and deposits associated with a palustrine environment, as well as anthropic deposits are identified (Fig. 5). These fluvial and colluvial deposits overlie Tertiary limestone bedrock (Gervilla et al., 1973). The Nora River has a meandering pattern with the flood plain located at 160 m a.s.l. along the south margin of the study area. The flood plain contains abandoned river channels identified by vegetation and relief scars. Two main river terrace levels are present: T1 (190–209 m a.s.l.) and T2 (170–180 m a.s.l.). T1 is located 30–32 m above the Nora River channel and is characterised by a 5–15% gradient towards the river channel. T1 sediment crops out mainly on road-cuts and is characterised by poorly sorted, subrounded quartzite gravel within a sand-sized matrix that laterally grades into silt and sand. T2 is characterised by a 1–2% gradient towards the channel of the Nora River. T2 is bounded by a 10 m high Tertiary white-limestone escarpment with a 50% slope to the east of the study area. T1 and T2 were transacted by torrential flows that produced a triangular alluvial fan on the flood plain. The A-6 and A-8 highways and constructions in the area sharply define the presence of anthropogenic deposits and scars. The Palaeolithical and the Necropolis sites are located on T2, and Monte Les Muries site is located on palustrine sequences (palustrine area, Fig. 5) at the NE margin of the alluvial fan to the south.
Fig. 4. Quantitative description of the relief at Paredes based on the DEM for the region and GIS. (A, A′) Elevation. (B, B′) Slope. (C, C′) Aspect. (D, D′) Hill shade.
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Fig. 5. Geomorphologic map of the study area, displaying the relationship between the fluvial system and the geoarchaeologic sites. Locations of the inferred situation of the Roman villa and cross sections I–I′, II–II′ and III–III′ are also shown.
Based on the distribution and features of the geomorphologic units in the area, 23 trenches were located (Fig. 5): 14 were on T2, four on the alluvial fan and five on the flood plain. The sediment exposed in the trenches located on T2 is fine sand-silt interpreted as the result of the sedimentation produced as channel-fill deposits as paleochannels. No archaeological remnants were found in these trenches. The alluvial fan that buries the flood plain of the Nora River to the south was specifically examined to search for archaeological artefacts. Four trenches were excavated following the axis of the fan (trenches 4, 5, 13′ and 5′; Fig. 5). No archaeological artefacts were found at these locations. The correlation among these four trenches and one of the trenches excavated on the flood plain (trench 12) allowed the definition of the geometry and stratigraphic relationships between the alluvial fan and the flood plain of the Nora River (line I–I′, Figs. 5 and 6). The alluvial fan buried part of the flood plain. These stratigraphic sequences of the alluvial fan are interpreted to be the result of a seasonal and/or episodic drainage system that crossed the valley bottom. The maximum thickness of each sedimentary unit is 16 cm, which includes a sequence of alternating coarse and finegrained sediment that are interpreted to represent a single episodic flooding event. The trench through the flood plain intersected a level of gravel and sand at the base (interpreted as a paleochannel) overlain by sand (interpreted as flood plain deposits). A fragment of wood among gravel deposits was located at the bottom of trench 12 at a depth of 2.5 m (Fig. 6). This wood was dated at 8890 ± 70 years BP (cal BC 8252–7787, sample Beta-117718;
Table 1 and Fig. 6), defining the maximum age for the beginning of the activity of the alluvial fan, as well as constraining the timing of the Nora alluvial plain. 4.2. Archaeological dimension of Terrace 2 (T2): evolution of a geomorphologic unit from the Palaeolithic to present Fluvial environments have always been favourable places for human settlements due to the presence of gentle slopes, proximity to water and good soil for agriculture. Therefore, fluvial terraces can be excellent locations to record human activities and different cultural environments through time. The T2 terrace deposits contain archaeological Palaeolithical and Roman remnants, whose relationships are summarised in Fig. 7. Scattered artefacts in the deposits represent the Palaeolithical record. Erosion processes such as creep and runoff have controlled the location and distribution of the artefacts across T2. Based on archaeological correlations to similar artefacts previously discovered by Rodríguez Asensio et al. (1998), their inferred chronology is 128– 71 ka. The Roman Necropolis records the oldest archaeological and chronological evidence of human activity during the Holocene in the T2 area. The archaeological research carried out in the area located 36 structures related to burial and 13 to funeral ceremonies (five pebble fire-pits, five offer-pits and three ash-pits) in a rectangular space with a surface area of 150 m 2. The burials were graves excavated in the sediment with unusual tegulae associations and covered by imbricis
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Fig. 6. Interpretative profile of the alluvial fan overlying the Nora River flood plain and Beta-117718 sample location dated for
and tegulae. Pottery, glass and/or metallic artefacts were found at every burial site (Fig. 2B and C). Four stratigraphic logs were described at lateral margins of the Necropolis. These logs identified three stratigraphic levels beneath the T2 surface. The simplified stratigraphic sequence in the Necropolis is a coarse-medium-grained sand unit eroded by a gravel unit, which is interpreted to be an alluvial origin (Unit 1; Fig. 8A). A second stratigraphic level (Unit 2) was defined by poorly-sorted, quartzite gravel which shows oriented clasts to the eastern area of the Necropolis. This unit is explained by gravity creep on the ground surface and/or anthropic deposition, and crosscuts the compacted siltstone/sandstone units underneath. At the top of the sequence, Unit 3 comprises silt–clay sediments and edaphic horizons with roots and sporadic gravels in the upper part of the sequence, interpreted as the result of gravity, runoff, edaphic and anthropogenic processes. The graves and fire-pits crosscut the quartzite gravel of Unit 2. At the eastern side of the Necropolis, some of the burials crosscut the silt–sand of Unit 1 (Fig. 8B); whereas in the western side of the Necropolis, the burials crosscut the channel quartzite gravel deposits of Unit 1 (Fig. 8C). Based on the features of excavated ceramic and glass pieces and according to chronologic and archaeometrical criteria (Isings, 1957; Mayet, 1984; López Rodríguez, 1985), we infer that human occupation associated with the Necropolis was active between the IV and VI centuries. However, the pebble fire-pits are more difficult to interpret, because several cultures spanning a wide time frame produced analogous structures related to funeral activities. Samples for carbon dating were collected from a pebble-fire-pit and an offering pit (Fig. 9). Fig. 9A shows a structure that was interpreted as a fire-pit based on its circular shape (~1.8 m diameter), depth (~45 cm) and concave profile section with quartzite pebbles at the bottom and carbonised fragments of oak, willow and hazel trees (Requejo Pagés, 2007).
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14
C (see line I–I′; Fig. 5).
Carbonised wood and organic-rich sediment samples collected from the fire-pit (Beta-12559614C and Beta-117720) were established at 5430 ± 70 (cal BC 4372–4051) and 5270 ± 70 years BP (cal BC 4261– 3963; Table 1). These results suggest an occupation and usage of this archaeological site during the Neolithic period. Fig. 9B displays charred sediment interpreted as the infill of an offering pit. The organic material was sampled (CNA351) and dated by 14C at 1590 ± 45 BP (cal AD 382–576; Table 1). This date strongly supports the Roman features of the archaeological artefacts collected in the same area. The stratigraphic logs coupled with the geochronologic observations described previously suggest a long time-span evolutionary model for human occupation on T2, in which: (1) Palaeolithical activity is first recorded in the area at about 128–71 ka (Rodríguez Asensio, 1983a,b); (2) the Roman Necropolis site area was previously occupied during the Neolithic, because at least one pebble fire-pit was excavated and used about cal BC 4261–4051; (3) afterwards, the area was reoccupied during Roman times, because at least one of the pebble fire-pit shows charred organic matter dated at 1590 ± 45 years BP (cal AD 382–576; IV–VI centuries); (4) from the IV–VI centuries to present, anthropogenic activity, gravity creep and edaphic processes originated the sediment levels that covered the archaeological structures. 4.3. Monte Les Muries archaeological record: a palustrine environment The Monte Les Muries site is located in the lower area of a palustrine zone which overlies T2 at the margins of the alluvial fan (Fig. 5). This site was discovered as a result of the archaeological prospection: one of the 103 archaeological trenches, located at the SE margin of the construction area, intersected tegulae tiles. Based on this finding, a trench (15.8 m length by 9.30 m width and 0.80 m depth
Fig. 7. Interpretative sketch showing the river terraces (T1 and T2) and the flood plain of the Nora River along an NE–SW profile (see line II–II′; Fig. 5).
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Fig. 8. Stratigraphic aspects at the Necropolis site. (A) Ideal stratigraphic sequence at the Necropolis. (B) An outcrop of the eastern area of the Necropolis showing the complete stratigraphic sequence (Units 1, 2 and 3). (C) Stratigraphic details of the southern area of the Necropolis site, where Unit 3 overlies the gravel of Unit 1; Unit 2 is missing.
with an SW prolongation of 4.5 m length by 4.3 m width and 1.5 m depth) was excavated to collect more archaeological artefacts. At this site, 493 fragments of tegulae tiles, 82 ceramic pieces, and 41 bricks, downy and storage containers were collected. These artefacts were similar to those described at the Necropolis site, and strongly suggest
Fig. 9. Archaeological structures sampled for chronological dating. (A) Pebble fire-pit with Beta-117720 (5270 ± 70 BP) and Beta-125596 (5430 ± 70 BP) samples supporting a Neolithic activity in the area. (B) Burnt wood from the fill in of an offering pit attributed to Roman occupation (sample CNA351) dated at 1590 ± 45 years BP (Cal 2σ 385 to 572 AD).
human occupation between ~ 1400 and 1700 years BP based on glass artefacts (Isings, 1957; Mayet, 1984; López Rodríguez, 1985). We sought to link the archaeological content of Monte Les Muries spatially and genetically with the settlement that built the Necropolis. To address this question, geologic data including stratigraphic descriptions, 14C chronological dates, GPR in the key profiles, and palynological analysis were integrated. Thirteen stratigraphic sections were described and correlated to characterise the geometry of Monte Les Muries (Fig. 10). Four stratigraphic units characterised by gravel, grey clay, silt and fine sand overlie the white limestone bedrock. This is described as a simplified stratigraphic sequence in Table 2. Units C and D contain the archaeological remnants extracted from this site. Units C and D display concave geometries at the base and laterally pinch out at a metric scale. Based on these features, the stratigraphic levels were interpreted as the result of infill of three small-scale paleochannels: (1) C1, draining NE–SW with a 3-m width between the stratigraphic sections 5 and 6; (2) C2, draining E–W longitudinally from the stratigraphic sections 11 and 12; and (3) C3, draining N–S asymmetric and 0.6 m in width (Fig. 10). These channels are characterised by: (1) a sharp erosional contact of the clay material with the overlying infill material — the erosional surface is not irregular and no rounded clay pebbles are incorporated in the infill, indicating erosional flow processes; (2) anthropogenic infill material without orientation and is very poorly-sorted (from gravel to pebble size), very angular, and has no sedimentary structures associated with transport and deposition in a channel; and (3) a lack of a natural catchment area linked to the channels. All the described features support an anthropogenic origin for these channels and their infill. Unit C was sampled for palynology (M1) and radiometric dating (charred sediment; Beta-117749; Fig. 10 and Table 1). The palynology results (Jiménez-Sánchez et al., 2004) portrayed a landscape of pines and chestnut trees, with some birches and moist soils supported by Salix and Alnus pollen, with minor low bush and a diversity of grass species. Human activity is suggested by the presence of Chenopodiaceae, Plantago, Rumex, Juglaris and Oleaceae pollen. Beta-117749 was dated at 1670± 60 years BP (cal AD 244–535, III–VI centuries), which strongly supports the archaeological evidence (Table 1 and Fig. 10).
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Fig. 10. Plan view of the Monte Les Muries site displaying the location of the stratigraphic columns (1 to 13), stratigraphic details of the palaeochannels (C1, C2 and C3), and sample locations of M1 (pollen analysis) and Beta-117719 (radiometric analysis).
Remote sensing ground penetration radar was used to define the lateral extension of the Monte Les Muries site, and to locate the possible remnants of the Roman villa inside the construction perimeter. For this reason, five profiles b100 m in length at specific locations were acquired (PA1–5; Fig. 3). No anomalies that could be interpreted as underground structures were detected (García-García, 1997). Further opening of specific trenches confirmed that no archaeological remains were associated with these profiles. Presence of this archaeological site in combination with the landscape evolution model, sedimentologic and stratigraphic evidence was used as the proxy to prioritise possible areas for the location of a hypothetical Roman villa. Therefore: (1) the lack of GPR anomalies in the immediate south limit of the construction ground; (2) the absence of archaeological findings to the north, west and south of the Montes Les Muries site; (3) the sedimentologic and stratigraphic evidence showing the proximity of the sediment source area; and (4) the probable location at b700 m of the Necropolis (following the pattern described in other studies such as Abasolo et al., 1997), the location of the Roman villa is interpreted to be to the East of Monte Les
Muries (b250 m), in an area of private land outside the construction perimeter (Fig. 5). Further testing of this hypothesis was not possible due to the lack of access to the private property. Based on all collected evidence, an evolutionary model for Monte Les Muries is proposed (Fig. 11): (1) Prior and/or coevally to 1670 years BP (cal AD 244–535, III–VI centuries), the alluvial fan was active in the southwest of the study area. In the eastern margin of the fan a palustrine area was developed (Fig. 11A). (2) After and/or coevally to 1670 BP (cal AD 244–535, III–VI centuries), the palustrine deposit was partially eroded and reworked by human activities and channels were excavated. These channels were subsequently filled with the anthropogenic debris. The anthropogenic activity also originated the deposits of the unit D, which covered the channel infill sediments (Fig. 11B). The inferred source area of the anthropogenic deposits (hypothetical Roman Villa?) should be to the east of the palustrine deposit, out of the archaeological research area.
Table 2 Description of the ideal stratigraphic sequence at Monte Les Muries site. Units
Lithology
Stratigraphic sequences including the units
Source
Comments
D
Silt, clay and brownish sand with oxidised organic matter; tegulae fragments and quartzitic gravel Silt, clay and grey sand with organic fragments; tegulae fragments and quartzitic gravel (A) quartzitic gravel; (A′) yellow sand Grey clay White limestone (Gervilla et al., 1973)
1, 2, 3, 4, 5, 6, 10, 11 and 12
Anthropogenic
Overlies all units
1, 2, 3, 4, 5, 6, 10, 11 and 12
Anthropogenic
1, 2, 3, 4, 5, 6, 10, 11 and 12 Base at 7, 8, 9, 10 and 13
Sediments from terrace 2 White limestone alteration
C A and A′ Ar Bedrock
Erosional over Ar Tertiary bedrock
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Fig. 11. Interpretative sequential evolution of Monte Les Muries and the hypothetical Roman villa suggested in this study (line III–III′; Fig. 5).
(3) Subsequently, the development of soil and vegetation cover preserved the Monte Les Muries site (Fig. 11C) until the construction of the shopping centre. At present, other private constructions are built over the inferred potential source area of anthropogenic sediment for the site. In summary, the Monte Les Muries site is the product of the accumulation of artefacts by direct human activity in an area of low drainage associated with a palustrine environment deposited at 1670 yr BP (cal AD 244–535, III–VI centuries). This poorly drained low area was formed by blockage as the alluvial fan developed. 5. Evolutionary model Based on all the evidence presented in the previous sections, a chronological model is proposed to integrate the landscape evolution with the archaeological sites at Paredes: (1) The pre-Holocene evolution of the area included the development of the fluvial landscape in which the first human activity is recorded at 128–71 ka in T2 (180–170 m a.s.l.). This is inferred from the artefacts found that correlate with Palaeolithic artefacts
of near sites (Rodríguez Asensio, 1983a,b). This date assigns a maximum age to this terrace, because the archaeological remnants are inferred to come from the denudation of the higher terrace level T1 (190–209 m a.s.l.). (2) The first Holocene geomorphologic evidence recorded is the emplacement of the flood plain of the Nora River (cal BC 8252– 7787). This age represents the minimum age for the alluvial plain of the Nora River and the maximum age of the alluvial fan that overlies it. (3) Human activity is associated with T2 based on the description of pebble fire-pits remains at the Necropolis site, which establishes an age range from cal BC 4372–3963. This strongly suggests occupation of the area during the Neolithic. It is unclear if this activity is product of an old funeral location that was active before the settlement of the Roman Necropolis. (4) Roman occupation in the area has been previously reported in several studies, which are supported by a comprehensive archaeological record in Central Asturias. Supported by existing research, the present study provides evidence of Late Roman occupation in Paredes. The 14C date of 1670 ± 60 years BP (cal AD 244–535, III–VI centuries) defines a maximum age for the excavation and infill in the palustrine archaeological site of
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Monte Les Muries. These channels and infill may be interpreted as artificial. The presence of archaeological artefacts and their location within the geomorphologic system strongly suggest that Monte Les Muries was directly related to activity at the Roman settlement that generated the Necropolis in equivalent stratigraphic levels but in other locations and microenvironments on the terrace river system. The Necropolis was located on T2 by 1590 ± 45 years BP (cal AD 382–576, IV–VI centuries). The 14C date overlaps that in the Monte les Muries site, and strongly argues that the source area of the Monte Les Muries infill (Roman villa) and the Necropolis were coeval during the IV–VI centuries. (5) b1590 ± 45 years BP (cal AD 382–576, IV–VI centuries) geomorphologic processes such as creep, fluvial, edaphic and anthropogenic processes preserved the archaeological sites and controlled the evolution of the area. At the present, this area has been intensely reworked by activities that include the excavation of the ground and the construction of the shopping centre. 6. Conclusions As a result of the construction of a large shopping centre in Paredes (NW Spain), a geoarchaeological study was initiated using geomorphology, stratigraphy, sedimentology, 14C geochronology, palynology, remote sensing and GIS techniques. The study has demonstrated that the location of the source area for the Necropolis and the Monte Les Muries archaeological remains was not within the construction perimeter. Although it is possible that the Roman villa is located further to the SE, this hypothesis is untested due to restrictions to access in this area. The T2 terrace records the first human activity in the area, whose inferred age, based on archaeological correlations, is 128–71 ka BP. Activity on T2, at the same location as the Roman Necropolis site, occurred during the Neolithic and has been dated ca. 5.3 ka BP. Late Roman occupation in the Paredes area is dated as 1670–1590 years BP by 14C. Subsequently, geomorphologic processes buried and preserved the described archaeological sites. Usually, rescue-archaeology studies occur in short timeframes. This commonly implies lack of regional data integration and/or a constraint on the variety of techniques applied. However, in this study, the wide variety of analytical techniques compensated for the brevity of the time available for assessment. The integration of multiscale data was shown to be a powerful and efficient approach to maximise local rescue-archaeology outputs by (1) defining strategies for archaeological prospection and targeting; (2) providing the 3D framework for the archaeological sites; and (3) establishing temporal relationships to construct a landscape evolutionary model. Acknowledgements We thank D. Távora-Vieira, T. Prokopiuk and P. Duuring for their insights on an early draft. We also thank Dr. S. Llana-Fúnez and Dr. H. Stoll for their help with the revision of this paper, and D. Ballesteros, L. Rodríguez and B. Naves for their assistance. We are especially grateful to Dr. M. Guccione, Dr. R. Whittecar and Dr. T. Oguchi, whose comments improved this paper. References Abasolo, J.A., Cortés, J., Rodríguez Aragón, F., 1997. La Necrópolis Norte de La Olmeda (Pedrosa de La Vega, Palencia). Diputación de Palencia, Palencia. Amore, M.G., Bejko, L., 2001. Recent rescue excavations in Albania. Antiquity 75, 269–270. Arco, L.U., Adelsberg, A., Hung, L., Kidder, T.R., 2006. Alluvial geoarchaeology of a Middle Archaic Mound Complex in the Lower Mississippi Valley, U.S.A. Geoarchaeology 21, 591–614.
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Geomorphology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / g e o m o r p h
Enhancing rescue-archaeology using geomorphological approaches: Archaeological sites in Paredes (Asturias, NW Spain) M. Jiménez-Sánchez a,⁎, I. González-Álvarez b, O. Requejo-Pagés a, c, M.J. Domínguez-Cuesta a a b c
Departamento de Geología, Universidad de Oviedo, 33005 Asturias, Spain CSIRO, Australian Resources Research Centre, Earth Science & Resource Engineering, Kensington, WA 6151, Australia Gabinete Arqueológico, S. L., 33002 Asturias, Spain
a r t i c l e
i n f o
Article history: Received 14 October 2010 Received in revised form 17 March 2011 Accepted 27 April 2011 Available online 10 May 2011 Keywords: Rescue-archaeology Quaternary sedimentology Palaeolithic Roman Necropolis Fluvial landscape Asturias
a b s t r a c t Palaeolithic remnants, a Necropolis (Roman villa), and another minor archaeological site were discovered in Paredes (Spain). These sites were the focus of multidisciplinary research during the construction of a large shopping centre in Asturias (NW Spain). The aims of this study are (1) to contribute to archaeological prospection in the sites and (2) to develop evolutionary models of the sites based on geomorphological inferences. Detailed archaeological prospection (103 trenches), geomorphologic mapping, stratigraphic studies (36 logs) and ground penetration radar (GPR) surveys on five profiles indicate that the location of the settlement source of the Necropolis is outside the construction perimeter, farther to the southeast. The PreHolocene evolution of the fluvial landscape is marked by the development of two terraces (T1 and T2) that host the Early Palaeolithic remains in the area (ca 128–71 ka). The Holocene evolution of the landscape was marked by the emplacement of the Nora River flood plain, covered by alluvial fans after ca. 9 ka BP (cal BC 8252–7787). Subsequently, Neolithic pebble pits dated ca. 5.3 ka BP (cal BC 4261–3963 and 4372–4051) were constructed on T2, at the area reoccupied as a Necropolis during the Late Roman period, 1590 ± 45 years BP (cal AD 382–576). Coeval human activity during the Late Roman period at 1670 ± 60 years BP (cal AD 320– 430) is also recorded by channel infill sediments in a minor site at the margin of an alluvial fan located to the southeast. This work shows that a rescue-archaeological study can be significantly enhanced by the implementation of multidisciplinary scientific studies, in which the holistic view of geomorphologic settings provide key insights into the geometry and evolution of archaeological sites. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Archaeological studies are commonly undertaken in short timeframes in order to minimise economic impact or to comply with existing regulations (Thomas, 1991; Amore and Bejko, 2001; Gonçalves et al., 2008). These “rescue-archaeology” studies commonly require rapid decision-making based on incomplete datasets. Implemented techniques and protocols must be modified from their longer timeframe research counterparts in order to maximise outcomes. This short timeframe promotes innovative approaches and encourages multidisciplinary research (Macphail et al., 2004). Interpretation of the geomorphologic landscape evolution applying sedimentology and geochronology is widely used as the foundation for the understanding of the physical environment and dynamics of archaeological sites (Bruneton et al., 2001; Mercader et al., 2003; Hudson, 2004; Schuldenrein et al., 2004; Arco et al., 2006; Bettis et al., 2008; Butzer, 2008). The integration of geomorphologic
⁎ Corresponding author. E-mail address: [email protected] (M. Jiménez-Sánchez). 0169-555X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2011.04.034
criteria has been successfully applied to target the location of archaeological sites (Mercader et al., 2003; Uribelarrea and Benito, 2008). Remote sensing to locate targets is widely applied in many geological fields to assess the spatial constraints using Geographical Information Systems (GIS). Specifically, archaeological prospectivity can be assessed by combining geomorphologic variables in a GIS environment to display the relations between the landscape features and human activity in time (Chapman and Van de Noort, 2001; Guccione, 2008; Siart et al., 2008; Contreras, 2009). Central Asturias in NW Spain offered a favourable landscape for human settlement from prehistoric times to present due to the development of productive farming soils, easy access to water and a low-relief fluvial landscape. The planned construction of a large shopping centre in the Nora River Basin brought to light the existence of Palaeolithic and Roman remnants. These initial discoveries triggered an archaeological heritage study as required by regulations. Building was delayed until an archaeological study was completed. This study describes the methodology, findings and interpretation of the short-term rescue-archaeological survey based on a multidisciplinary research driven by geomorphologic approaches. The research evaluated the contribution of geomorphologic techniques to enhance
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the results of a rescue-archaeological project in two specific aspects: (1) determining the source of the archaeological remains; and (2) the development of evolutionary models for the archaeological sites. 2. Setting The study area includes a surface area of 305,000 m 2, which was set aside for the construction of a large shopping centre in the Nora River Basin, Asturias, NW Spain, ~4.6 km NE from the historic city of Oviedo (Fig. 1). Proximal to this area, three archaeological sites were previously described: (1) the Early-Palaeolithic site of Paredes (Rodríguez Asensio, 1983a,b); (2) the Roman site of “Castro La Torre” (González and Fernández-Vallés, 1976); and (3) scattered Roman surface artefacts (González and Fernández-Vallés, 1968, 1976). Due to these findings and legal regulations placed on building construction, an archaeological assessment was performed before the resumption of construction. A follow-up assessment was conducted during the building period to ensure the archaeological heritage was not damaged or lost. During the first stage of this archaeological study, archaeological artefacts were discovered between E272640, N4807625 and E273580, N4808570, and Zone 30 UTM, at 175 m a.s.l. (above sea level; Fig. 1). The site contained 50 artefacts: three crackers, one pick, one knife, three teeth, 42 chips and cuttings made of quartzite sandstone. These artefacts were attributed to Early-Palaeolithic times by correlation with previous studies (Rodríguez Asensio, 1983a,b). In the second stage of the survey, a Roman Necropolis (with crosscutting pebble-fire pits) was discovered during the excavation
(E273293, N4808337, and Zone 30 UTM). The discovery of the Roman Necropolis represented an exceptional find in the area since it is the first of its kind and one of the few examples reported in the northern slope of the Cantabrian Mountains. The Necropolis contained 36 structures related to burial and 13 to funeral ceremonies (five pebble fire-pits, five offer-pits and three ash-pits; Fig. 2). The burials were graves excavated in the sediment, covered by tegulae and imbricis. Pottery, glass and/or metallic artefacts were found at every burial site. Archaeological features from these findings (Requejo Pagés, 2007) suggested a Roman age (IV–V centuries). No human remains were described (Requejo Pagés, 1998, 2007). Previous studies reported Roman artefacts in the soil at the same area where the Roman Necropolis was located (González and Fernández-Vallés, 1968, 1976). Therefore, the initial working hypothesis suggested that the location of a Roman villa was within the construction perimeter. The villa was envisioned as the source of the population that was buried in the Necropolis. This hypothesis was strongly supported by other studies on Roman archaeology that described Roman villas located within short distances (b700 m) of their burial grounds (Toynbee, 1996; Abasolo et al., 1997). Other villae described in the region presented burials within the perimeter of the villa itself (Fernández Ochoa and Gil Sendino, 2007). In a preliminary effort to locate the Roman villa, 103 archaeological trenches were performed. Fragmented ceramic and storage containers, as well as table dowry, a large amount of fragmented tegulae and construction bricks of Roman age, were reported defining an additional archaeological site: Monte Les Muries (E272996, N4807989, and Zone 30 UTM; Fig. 1).
Fig. 1. Location of the study area (Paredes, Asturias, NW Spain) showing the perimeter of the construction area and the archaeological sites located during this research (Palaeolithical sites, Necropolis and Monte Les Muries sites).
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Fig. 2. Examples of archaeological findings in the Necropolis. (A) Details of a burial structure at the Necropolis. (B) Glass and (C) pottery artefacts associated with the burial sites.
Two archaeological teams worked separately in parallel studies on each of the sites reported. The priority was to quickly locate and collect all archaeological artefacts in the Necropolis, to constrain the genesis of the second archaeological site found (“Monte Les Muries”) and to connect this latter site to the location of a hypothetical Roman villa. In response to the complexity of this rescue-archaeological study, the designed approach included sedimentologic, geomorphologic, geochronologic and palynologic techniques.
Cartographic Service of Asturias, Spain) were used to define the main geomorphologic units. A map at a scale of 1:10,000 was produced from interpretation of the airborne photographic, trench data and road cuts through the study area. The geomorphologic map was used to interpret the landscape evolution. A genetic criterion was applied to the mapping in order to suggest a framework for the archaeological sites. Twenty-three trenches within geologic materials were located based on the geometry and inferred spatial relationships of the geomorphologic units (Fig. 3).
3. Methodology 3.3. Stratigraphy and sedimentology The central part of the study entailed the integration of a detailed geomorphologic study with GIS to characterise the present landscape and its evolution, as well as the stratigraphic and sedimentologic sequences associated with the archaeological artefacts. These techniques were coupled with 14C radiometric dating to constrain the absolute timeframe for the evolution of the landscape. 3.1. Geographical information system Topographic information at a scale of 1:1000 was integrated into GIS using the ArcGIS 9.2 software package. A raster digital elevation model (DEM) with a 5-m grid interval was built from the digital topographic contours (5 m interval) provided by the Asturias Government (Dirección General de Ordenación del Territorio y Urbanismo) in 2000. Different algorithms were applied to generate derivative terrain models: slope, aspect and hill-shade. Digital orthophotos (1995 and 2000 flights) were also integrated in the GIS at a scale of 1:10,000. The GIS provided a basis for establishing and quantifying the spatial relationships among the different geomorphologic units and archaeological findings. To define landscape influences on the archaeological sites, an area of 78.5 km 2 was outlined by a 5 km radius-circle centred at the Roman Necropolis. The terrain model variables were derived from this area. 3.2. Geomorphologic mapping The geomorphologic survey covered a 16 km 2 area that included all the archaeological sites. Airborne photographic data at a scale of 1:18,000 (1969 and 1994 flights, Diputación of Oviedo and the
The stratigraphic sequence was described for the 23 trenches previously mentioned. Due to continuous rain and high water table levels, continuous re-excavation of the trenches with bulldozers was necessary, which inhibited data collection. In addition, 17 stratigraphic columns (four at the Necropolis and 13 in the Monte Les Muries site) were described at the archaeological sites (Fig. 3). The stratigraphic sections and sedimentologic information collected included sediment colour, grain-size, geometry of different lithologic units, organic content and sedimentary structures. From the stratigraphic sequences, sedimentary processes were interpreted and the evolution of the fluvial system was described. 3.4.
14
C radiometric analysis
Five samples from selected sites were collected for geochronological dating by 14C analyses (Fig. 3; Table 1). Three samples (Beta 117720, Beta 125596 and CNA351) were from the Necropolis site in order to determine the timing of human activity associated with the site. A fourth sample (Beta 117719) was taken to establish an absolute date on a key stratigraphic unit at Monte Les Muries, and to constrain the age of the archaeological artefacts located in this area. A fifth sample of wood (Beta 117718) was dated in order to constrain the maximum age for the alluvial fan described in the geomorphologic map. The 14C isotopic analyses were carried out at Beta Analytic Inc. Laboratories (Miami, USA) and the Centro Nacional de Aceleradores (Sevilla, Spain). The CNA351 sample was analysed by AMS and all the other samples by standard radiometric techniques. Calibration of
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Fig. 3. Research area showing the location of the Necropolis and Monte Les Muries archaeological sites. The location of the GPR profiles, 14C samples, trenches and stratigraphic logs is also shown.
dates and curves followed those of Vogel et al. (1993), Talma and Vogel (1993) and Stuiver et al. (1993), and were derived from the Calib radiocarbon calibration programme (Stuiver et al., 2010).
flotation on Thoulet dense liquid (Goeury and Beaulieu, 1979). Pollen data are presented as the relative frequency of pollen for each taxon applying the TILIA® and TILIA GRAPH® (© Eric C. Grimm) software (Jiménez-Sánchez et al., 2004).
3.5. Palynological analysis 3.6. Remote sensing One sample (M1) was collected for palynological analysis at the same locality as the Monte Les Muries sample Beta-117719 (stratigraphic unit C; E272995, N4807989, and Zone 30 UTM). Analysis was performed at the Department of Geology, the University of Alcalá de Henares (Spain). The preparation followed protocols outlined by Faegri and Iversen (1989) and Moore et al. (1994) and applied Table 1 Monte Les Muries and Necropolis Sample CNA351 (charred wood)
14
Ground Penetration Radar is a widely applied geophysical technique (e.g., Leckebush, 2003; Neal, 2004; Nielsen and Müeller, 2009). It is frequently used to locate features buried between 0.5 and 6.0 m deep by utilising electromagnetic impulses between 1 and 3000 MHz, with two antennas (emission-receptor) in contact with
C dataset. Coordinates in UTM, Zone 30.
Location (UTM)
Necropolis (offering pit) (273293, 480837) Beta-117719 Unit C Monte (charred material) les Muries Site (272996, 4807989) Beta-117720 Necropolis (burnt wood) (pebble fire-pit) (273293, 4808337) Beta-125596 Necropolis (charred material) (pebble fire-pit) (273293, 4808337) Beta-117718 Nora River alluvial (wood) plain (SW Monte les Muries Site) (272747, 4807836)
Analysis
13 12 Conventional 14C Calibrated results Relative area Calibrated results Relative area C/ C age (years BP) (1σ 68.3% prob.) under distribution (2σ 95.4% prob.) under distribution ratio (‰)
AMS
1590 ± 45
cal AD 478–534
0.568
cal AD 382–576
1.000
− 20
Radiometricstandard
1670 ± 60
cal AD 320–430
0.797
cal AD 244–535
1.000
− 25
Radiometricstandard
5270 ± 70
cal BC 4171–4089
0.434
cal BC 4261–3963 0.984
− 25
Radiometricstandard
5430 ± 70
cal BC 4354–4230 0.921
cal BC 4372–4051 0.975
− 25
Radiometricstandard
8890 ± 70
cal BC 8217–7962 1.000
cal BC 8252–7787 1.000
− 25
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the ground at a specific distance. Dielectric and electric conductivity variations of the ground are measured and compared with time intervals of emission and reception. This technique allows the identification of contrasting properties, which may lead to identification of near-surface underground structures or anisotropies. A Pulse EKKO IV model was operated with the Sensors and Software Inc. system (Molenaar and Vreng, 2004). This equipment generated five profiles of b100 m length at specific locations (PA1–5; Fig. 3). To generate the profiles, a frequency of 200 MHz was used and the antennae were parallel and spaced 1 m apart. The propagation speed of the ground wave was determined by a common midpoint survey. For this, the transmitter and receiver antennas were moved apart from each other. With the time difference between the ground and the air wave at different distances, and obtained airwave receiving time, the ground propagation speed was calculated at 0.10 m s − 1 (García-García, 1997).
4. Results and discussion 4.1. Geomorphology and landscape: the framework of the archaeological sites Fig. 4 describes the landscape of a 78.5 km 2 area (5 km circle radius centred in the Necropolis) based on GIS. Altitude ranges from 136 to 610 m, averaging ~210 m (Fig. 4A and A′). The landscape is dominated by low-angle slopes with an average of ~ 6° and a maximum value of 55° (Fig. 4B and B′). North-facing slopes (0° to 90° and 271° to 360°) predominate (55.1%) over south-facing slopes
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(91° to 270°) (Fig. 4C and C′), with a predominant hill shade of ~ 180° (Fig. 4D and D′). Landscape features were represented in a 1:10,000 scale geomorphologic map (Jiménez-Sánchez et al., 2004). Two main topographic elevations are present in the area: Cerro Cueto at 210 m a.s.l. and Paredes at 199 m a.s.l. The Nora River is the main geomorphologic agent. Fluvial deposits that form terraces, flood deposits, alluvial fans and a torrential basin are the main landscape features. Colluvium and deposits associated with a palustrine environment, as well as anthropic deposits are identified (Fig. 5). These fluvial and colluvial deposits overlie Tertiary limestone bedrock (Gervilla et al., 1973). The Nora River has a meandering pattern with the flood plain located at 160 m a.s.l. along the south margin of the study area. The flood plain contains abandoned river channels identified by vegetation and relief scars. Two main river terrace levels are present: T1 (190–209 m a.s.l.) and T2 (170–180 m a.s.l.). T1 is located 30–32 m above the Nora River channel and is characterised by a 5–15% gradient towards the river channel. T1 sediment crops out mainly on road-cuts and is characterised by poorly sorted, subrounded quartzite gravel within a sand-sized matrix that laterally grades into silt and sand. T2 is characterised by a 1–2% gradient towards the channel of the Nora River. T2 is bounded by a 10 m high Tertiary white-limestone escarpment with a 50% slope to the east of the study area. T1 and T2 were transacted by torrential flows that produced a triangular alluvial fan on the flood plain. The A-6 and A-8 highways and constructions in the area sharply define the presence of anthropogenic deposits and scars. The Palaeolithical and the Necropolis sites are located on T2, and Monte Les Muries site is located on palustrine sequences (palustrine area, Fig. 5) at the NE margin of the alluvial fan to the south.
Fig. 4. Quantitative description of the relief at Paredes based on the DEM for the region and GIS. (A, A′) Elevation. (B, B′) Slope. (C, C′) Aspect. (D, D′) Hill shade.
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Fig. 5. Geomorphologic map of the study area, displaying the relationship between the fluvial system and the geoarchaeologic sites. Locations of the inferred situation of the Roman villa and cross sections I–I′, II–II′ and III–III′ are also shown.
Based on the distribution and features of the geomorphologic units in the area, 23 trenches were located (Fig. 5): 14 were on T2, four on the alluvial fan and five on the flood plain. The sediment exposed in the trenches located on T2 is fine sand-silt interpreted as the result of the sedimentation produced as channel-fill deposits as paleochannels. No archaeological remnants were found in these trenches. The alluvial fan that buries the flood plain of the Nora River to the south was specifically examined to search for archaeological artefacts. Four trenches were excavated following the axis of the fan (trenches 4, 5, 13′ and 5′; Fig. 5). No archaeological artefacts were found at these locations. The correlation among these four trenches and one of the trenches excavated on the flood plain (trench 12) allowed the definition of the geometry and stratigraphic relationships between the alluvial fan and the flood plain of the Nora River (line I–I′, Figs. 5 and 6). The alluvial fan buried part of the flood plain. These stratigraphic sequences of the alluvial fan are interpreted to be the result of a seasonal and/or episodic drainage system that crossed the valley bottom. The maximum thickness of each sedimentary unit is 16 cm, which includes a sequence of alternating coarse and finegrained sediment that are interpreted to represent a single episodic flooding event. The trench through the flood plain intersected a level of gravel and sand at the base (interpreted as a paleochannel) overlain by sand (interpreted as flood plain deposits). A fragment of wood among gravel deposits was located at the bottom of trench 12 at a depth of 2.5 m (Fig. 6). This wood was dated at 8890 ± 70 years BP (cal BC 8252–7787, sample Beta-117718;
Table 1 and Fig. 6), defining the maximum age for the beginning of the activity of the alluvial fan, as well as constraining the timing of the Nora alluvial plain. 4.2. Archaeological dimension of Terrace 2 (T2): evolution of a geomorphologic unit from the Palaeolithic to present Fluvial environments have always been favourable places for human settlements due to the presence of gentle slopes, proximity to water and good soil for agriculture. Therefore, fluvial terraces can be excellent locations to record human activities and different cultural environments through time. The T2 terrace deposits contain archaeological Palaeolithical and Roman remnants, whose relationships are summarised in Fig. 7. Scattered artefacts in the deposits represent the Palaeolithical record. Erosion processes such as creep and runoff have controlled the location and distribution of the artefacts across T2. Based on archaeological correlations to similar artefacts previously discovered by Rodríguez Asensio et al. (1998), their inferred chronology is 128– 71 ka. The Roman Necropolis records the oldest archaeological and chronological evidence of human activity during the Holocene in the T2 area. The archaeological research carried out in the area located 36 structures related to burial and 13 to funeral ceremonies (five pebble fire-pits, five offer-pits and three ash-pits) in a rectangular space with a surface area of 150 m 2. The burials were graves excavated in the sediment with unusual tegulae associations and covered by imbricis
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Fig. 6. Interpretative profile of the alluvial fan overlying the Nora River flood plain and Beta-117718 sample location dated for
and tegulae. Pottery, glass and/or metallic artefacts were found at every burial site (Fig. 2B and C). Four stratigraphic logs were described at lateral margins of the Necropolis. These logs identified three stratigraphic levels beneath the T2 surface. The simplified stratigraphic sequence in the Necropolis is a coarse-medium-grained sand unit eroded by a gravel unit, which is interpreted to be an alluvial origin (Unit 1; Fig. 8A). A second stratigraphic level (Unit 2) was defined by poorly-sorted, quartzite gravel which shows oriented clasts to the eastern area of the Necropolis. This unit is explained by gravity creep on the ground surface and/or anthropic deposition, and crosscuts the compacted siltstone/sandstone units underneath. At the top of the sequence, Unit 3 comprises silt–clay sediments and edaphic horizons with roots and sporadic gravels in the upper part of the sequence, interpreted as the result of gravity, runoff, edaphic and anthropogenic processes. The graves and fire-pits crosscut the quartzite gravel of Unit 2. At the eastern side of the Necropolis, some of the burials crosscut the silt–sand of Unit 1 (Fig. 8B); whereas in the western side of the Necropolis, the burials crosscut the channel quartzite gravel deposits of Unit 1 (Fig. 8C). Based on the features of excavated ceramic and glass pieces and according to chronologic and archaeometrical criteria (Isings, 1957; Mayet, 1984; López Rodríguez, 1985), we infer that human occupation associated with the Necropolis was active between the IV and VI centuries. However, the pebble fire-pits are more difficult to interpret, because several cultures spanning a wide time frame produced analogous structures related to funeral activities. Samples for carbon dating were collected from a pebble-fire-pit and an offering pit (Fig. 9). Fig. 9A shows a structure that was interpreted as a fire-pit based on its circular shape (~1.8 m diameter), depth (~45 cm) and concave profile section with quartzite pebbles at the bottom and carbonised fragments of oak, willow and hazel trees (Requejo Pagés, 2007).
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14
C (see line I–I′; Fig. 5).
Carbonised wood and organic-rich sediment samples collected from the fire-pit (Beta-12559614C and Beta-117720) were established at 5430 ± 70 (cal BC 4372–4051) and 5270 ± 70 years BP (cal BC 4261– 3963; Table 1). These results suggest an occupation and usage of this archaeological site during the Neolithic period. Fig. 9B displays charred sediment interpreted as the infill of an offering pit. The organic material was sampled (CNA351) and dated by 14C at 1590 ± 45 BP (cal AD 382–576; Table 1). This date strongly supports the Roman features of the archaeological artefacts collected in the same area. The stratigraphic logs coupled with the geochronologic observations described previously suggest a long time-span evolutionary model for human occupation on T2, in which: (1) Palaeolithical activity is first recorded in the area at about 128–71 ka (Rodríguez Asensio, 1983a,b); (2) the Roman Necropolis site area was previously occupied during the Neolithic, because at least one pebble fire-pit was excavated and used about cal BC 4261–4051; (3) afterwards, the area was reoccupied during Roman times, because at least one of the pebble fire-pit shows charred organic matter dated at 1590 ± 45 years BP (cal AD 382–576; IV–VI centuries); (4) from the IV–VI centuries to present, anthropogenic activity, gravity creep and edaphic processes originated the sediment levels that covered the archaeological structures. 4.3. Monte Les Muries archaeological record: a palustrine environment The Monte Les Muries site is located in the lower area of a palustrine zone which overlies T2 at the margins of the alluvial fan (Fig. 5). This site was discovered as a result of the archaeological prospection: one of the 103 archaeological trenches, located at the SE margin of the construction area, intersected tegulae tiles. Based on this finding, a trench (15.8 m length by 9.30 m width and 0.80 m depth
Fig. 7. Interpretative sketch showing the river terraces (T1 and T2) and the flood plain of the Nora River along an NE–SW profile (see line II–II′; Fig. 5).
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Fig. 8. Stratigraphic aspects at the Necropolis site. (A) Ideal stratigraphic sequence at the Necropolis. (B) An outcrop of the eastern area of the Necropolis showing the complete stratigraphic sequence (Units 1, 2 and 3). (C) Stratigraphic details of the southern area of the Necropolis site, where Unit 3 overlies the gravel of Unit 1; Unit 2 is missing.
with an SW prolongation of 4.5 m length by 4.3 m width and 1.5 m depth) was excavated to collect more archaeological artefacts. At this site, 493 fragments of tegulae tiles, 82 ceramic pieces, and 41 bricks, downy and storage containers were collected. These artefacts were similar to those described at the Necropolis site, and strongly suggest
Fig. 9. Archaeological structures sampled for chronological dating. (A) Pebble fire-pit with Beta-117720 (5270 ± 70 BP) and Beta-125596 (5430 ± 70 BP) samples supporting a Neolithic activity in the area. (B) Burnt wood from the fill in of an offering pit attributed to Roman occupation (sample CNA351) dated at 1590 ± 45 years BP (Cal 2σ 385 to 572 AD).
human occupation between ~ 1400 and 1700 years BP based on glass artefacts (Isings, 1957; Mayet, 1984; López Rodríguez, 1985). We sought to link the archaeological content of Monte Les Muries spatially and genetically with the settlement that built the Necropolis. To address this question, geologic data including stratigraphic descriptions, 14C chronological dates, GPR in the key profiles, and palynological analysis were integrated. Thirteen stratigraphic sections were described and correlated to characterise the geometry of Monte Les Muries (Fig. 10). Four stratigraphic units characterised by gravel, grey clay, silt and fine sand overlie the white limestone bedrock. This is described as a simplified stratigraphic sequence in Table 2. Units C and D contain the archaeological remnants extracted from this site. Units C and D display concave geometries at the base and laterally pinch out at a metric scale. Based on these features, the stratigraphic levels were interpreted as the result of infill of three small-scale paleochannels: (1) C1, draining NE–SW with a 3-m width between the stratigraphic sections 5 and 6; (2) C2, draining E–W longitudinally from the stratigraphic sections 11 and 12; and (3) C3, draining N–S asymmetric and 0.6 m in width (Fig. 10). These channels are characterised by: (1) a sharp erosional contact of the clay material with the overlying infill material — the erosional surface is not irregular and no rounded clay pebbles are incorporated in the infill, indicating erosional flow processes; (2) anthropogenic infill material without orientation and is very poorly-sorted (from gravel to pebble size), very angular, and has no sedimentary structures associated with transport and deposition in a channel; and (3) a lack of a natural catchment area linked to the channels. All the described features support an anthropogenic origin for these channels and their infill. Unit C was sampled for palynology (M1) and radiometric dating (charred sediment; Beta-117749; Fig. 10 and Table 1). The palynology results (Jiménez-Sánchez et al., 2004) portrayed a landscape of pines and chestnut trees, with some birches and moist soils supported by Salix and Alnus pollen, with minor low bush and a diversity of grass species. Human activity is suggested by the presence of Chenopodiaceae, Plantago, Rumex, Juglaris and Oleaceae pollen. Beta-117749 was dated at 1670± 60 years BP (cal AD 244–535, III–VI centuries), which strongly supports the archaeological evidence (Table 1 and Fig. 10).
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Fig. 10. Plan view of the Monte Les Muries site displaying the location of the stratigraphic columns (1 to 13), stratigraphic details of the palaeochannels (C1, C2 and C3), and sample locations of M1 (pollen analysis) and Beta-117719 (radiometric analysis).
Remote sensing ground penetration radar was used to define the lateral extension of the Monte Les Muries site, and to locate the possible remnants of the Roman villa inside the construction perimeter. For this reason, five profiles b100 m in length at specific locations were acquired (PA1–5; Fig. 3). No anomalies that could be interpreted as underground structures were detected (García-García, 1997). Further opening of specific trenches confirmed that no archaeological remains were associated with these profiles. Presence of this archaeological site in combination with the landscape evolution model, sedimentologic and stratigraphic evidence was used as the proxy to prioritise possible areas for the location of a hypothetical Roman villa. Therefore: (1) the lack of GPR anomalies in the immediate south limit of the construction ground; (2) the absence of archaeological findings to the north, west and south of the Montes Les Muries site; (3) the sedimentologic and stratigraphic evidence showing the proximity of the sediment source area; and (4) the probable location at b700 m of the Necropolis (following the pattern described in other studies such as Abasolo et al., 1997), the location of the Roman villa is interpreted to be to the East of Monte Les
Muries (b250 m), in an area of private land outside the construction perimeter (Fig. 5). Further testing of this hypothesis was not possible due to the lack of access to the private property. Based on all collected evidence, an evolutionary model for Monte Les Muries is proposed (Fig. 11): (1) Prior and/or coevally to 1670 years BP (cal AD 244–535, III–VI centuries), the alluvial fan was active in the southwest of the study area. In the eastern margin of the fan a palustrine area was developed (Fig. 11A). (2) After and/or coevally to 1670 BP (cal AD 244–535, III–VI centuries), the palustrine deposit was partially eroded and reworked by human activities and channels were excavated. These channels were subsequently filled with the anthropogenic debris. The anthropogenic activity also originated the deposits of the unit D, which covered the channel infill sediments (Fig. 11B). The inferred source area of the anthropogenic deposits (hypothetical Roman Villa?) should be to the east of the palustrine deposit, out of the archaeological research area.
Table 2 Description of the ideal stratigraphic sequence at Monte Les Muries site. Units
Lithology
Stratigraphic sequences including the units
Source
Comments
D
Silt, clay and brownish sand with oxidised organic matter; tegulae fragments and quartzitic gravel Silt, clay and grey sand with organic fragments; tegulae fragments and quartzitic gravel (A) quartzitic gravel; (A′) yellow sand Grey clay White limestone (Gervilla et al., 1973)
1, 2, 3, 4, 5, 6, 10, 11 and 12
Anthropogenic
Overlies all units
1, 2, 3, 4, 5, 6, 10, 11 and 12
Anthropogenic
1, 2, 3, 4, 5, 6, 10, 11 and 12 Base at 7, 8, 9, 10 and 13
Sediments from terrace 2 White limestone alteration
C A and A′ Ar Bedrock
Erosional over Ar Tertiary bedrock
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Fig. 11. Interpretative sequential evolution of Monte Les Muries and the hypothetical Roman villa suggested in this study (line III–III′; Fig. 5).
(3) Subsequently, the development of soil and vegetation cover preserved the Monte Les Muries site (Fig. 11C) until the construction of the shopping centre. At present, other private constructions are built over the inferred potential source area of anthropogenic sediment for the site. In summary, the Monte Les Muries site is the product of the accumulation of artefacts by direct human activity in an area of low drainage associated with a palustrine environment deposited at 1670 yr BP (cal AD 244–535, III–VI centuries). This poorly drained low area was formed by blockage as the alluvial fan developed. 5. Evolutionary model Based on all the evidence presented in the previous sections, a chronological model is proposed to integrate the landscape evolution with the archaeological sites at Paredes: (1) The pre-Holocene evolution of the area included the development of the fluvial landscape in which the first human activity is recorded at 128–71 ka in T2 (180–170 m a.s.l.). This is inferred from the artefacts found that correlate with Palaeolithic artefacts
of near sites (Rodríguez Asensio, 1983a,b). This date assigns a maximum age to this terrace, because the archaeological remnants are inferred to come from the denudation of the higher terrace level T1 (190–209 m a.s.l.). (2) The first Holocene geomorphologic evidence recorded is the emplacement of the flood plain of the Nora River (cal BC 8252– 7787). This age represents the minimum age for the alluvial plain of the Nora River and the maximum age of the alluvial fan that overlies it. (3) Human activity is associated with T2 based on the description of pebble fire-pits remains at the Necropolis site, which establishes an age range from cal BC 4372–3963. This strongly suggests occupation of the area during the Neolithic. It is unclear if this activity is product of an old funeral location that was active before the settlement of the Roman Necropolis. (4) Roman occupation in the area has been previously reported in several studies, which are supported by a comprehensive archaeological record in Central Asturias. Supported by existing research, the present study provides evidence of Late Roman occupation in Paredes. The 14C date of 1670 ± 60 years BP (cal AD 244–535, III–VI centuries) defines a maximum age for the excavation and infill in the palustrine archaeological site of
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Monte Les Muries. These channels and infill may be interpreted as artificial. The presence of archaeological artefacts and their location within the geomorphologic system strongly suggest that Monte Les Muries was directly related to activity at the Roman settlement that generated the Necropolis in equivalent stratigraphic levels but in other locations and microenvironments on the terrace river system. The Necropolis was located on T2 by 1590 ± 45 years BP (cal AD 382–576, IV–VI centuries). The 14C date overlaps that in the Monte les Muries site, and strongly argues that the source area of the Monte Les Muries infill (Roman villa) and the Necropolis were coeval during the IV–VI centuries. (5) b1590 ± 45 years BP (cal AD 382–576, IV–VI centuries) geomorphologic processes such as creep, fluvial, edaphic and anthropogenic processes preserved the archaeological sites and controlled the evolution of the area. At the present, this area has been intensely reworked by activities that include the excavation of the ground and the construction of the shopping centre. 6. Conclusions As a result of the construction of a large shopping centre in Paredes (NW Spain), a geoarchaeological study was initiated using geomorphology, stratigraphy, sedimentology, 14C geochronology, palynology, remote sensing and GIS techniques. The study has demonstrated that the location of the source area for the Necropolis and the Monte Les Muries archaeological remains was not within the construction perimeter. Although it is possible that the Roman villa is located further to the SE, this hypothesis is untested due to restrictions to access in this area. The T2 terrace records the first human activity in the area, whose inferred age, based on archaeological correlations, is 128–71 ka BP. Activity on T2, at the same location as the Roman Necropolis site, occurred during the Neolithic and has been dated ca. 5.3 ka BP. Late Roman occupation in the Paredes area is dated as 1670–1590 years BP by 14C. Subsequently, geomorphologic processes buried and preserved the described archaeological sites. Usually, rescue-archaeology studies occur in short timeframes. This commonly implies lack of regional data integration and/or a constraint on the variety of techniques applied. However, in this study, the wide variety of analytical techniques compensated for the brevity of the time available for assessment. The integration of multiscale data was shown to be a powerful and efficient approach to maximise local rescue-archaeology outputs by (1) defining strategies for archaeological prospection and targeting; (2) providing the 3D framework for the archaeological sites; and (3) establishing temporal relationships to construct a landscape evolutionary model. Acknowledgements We thank D. Távora-Vieira, T. Prokopiuk and P. Duuring for their insights on an early draft. We also thank Dr. S. Llana-Fúnez and Dr. H. Stoll for their help with the revision of this paper, and D. Ballesteros, L. Rodríguez and B. Naves for their assistance. We are especially grateful to Dr. M. Guccione, Dr. R. Whittecar and Dr. T. Oguchi, whose comments improved this paper. References Abasolo, J.A., Cortés, J., Rodríguez Aragón, F., 1997. La Necrópolis Norte de La Olmeda (Pedrosa de La Vega, Palencia). Diputación de Palencia, Palencia. Amore, M.G., Bejko, L., 2001. Recent rescue excavations in Albania. Antiquity 75, 269–270. Arco, L.U., Adelsberg, A., Hung, L., Kidder, T.R., 2006. Alluvial geoarchaeology of a Middle Archaic Mound Complex in the Lower Mississippi Valley, U.S.A. Geoarchaeology 21, 591–614.
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