The palaeoenvironment of eastern West
Transcription
The palaeoenvironment of eastern West
The palaeoenvironment of eastern West-Frisia: a critical review W. K. van Zijverden Palaeogeography, West-Frisia, Bronze Age, environment In the second half of the twentieth century, several large-scale excavations were carried out in West-Frisia. A habitation model was developed based on the results. Based on recently excavated sites, some adjustments to the model have to be made regarding the location of settlement sites, the paleoenvironment and the cause of the rise in the ground water level. In this article, it is argued that not only the creek ridges but also the former mud flats were used for settlement sites. The environment should be characterised as a patchwork of lakes, alder cars, willow shrubs, marshy grasslands, dry nutrient-rich arable fields and riparian forests, instead of as an open, almost treeless freshwater environment. During the Late Bronze Age, marine influxes occurred resulting in brackish environments in the vicinity of the settlement sites. It is argued that the rise of the local ground water level was due to fluctuations in the flood basin effect caused by changes in the morphology of tidal inlets and tidal basins. An earlier opening of the Vliestroom in the Middle Iron Age or the end of the Early Iron Age is proposed based on the apparent marine influxes and the change in the settlement pattern. Die Paläo-Umwelt des östlichen Westfriesland: Ein kritischer Rückblick Paläogeografie, Westfriesland, Bronzezeit, Umwelt In den 70er und 80er Jahren des letzten Jahrhunderts wurden zahlreiche Ausgrabungen in Westfriesland durchgeführt. Anhand der Forschungsergebnisse hat man ein Siedlungsmodell für die Bronzezeit entwickelt. Aufgrund neuer Ausgrabungen ergeben sich Anpassungen des Modells, in Bezug auf die Wahl der Siedlungsstandorte, die Paläoökologie und die Ursache für den beobachteten Anstieg des Grundwasserspiegels. In diesem Artikel wird behauptet, dass nicht nur die höher gelegenen ehemaligen Priele, sondern auch die ehemaligen Seemarsche besiedelt wurden. Die natürliche Umgebung in diesem Zeitraum kann als ein Mosaik aus Seen, Erlenwäldern, Weidengebüschen, Feuchtgrünland, Äckern und Auwäldern mit Eiche und Esche bezeichnet werden, statt einer offenen, fast baumlosen Landschaft mit Süßwasserseen und Sümpfen. Während der Späten Bronzezeit ist ein mariner Zustrom aufgetreten, wodurch Brackwasser-Biotope in der Nähe der Siedlungen entstanden. Die Höhe des Grundwasserspiegels ist abhängig von den Schwankungen im Hochwasseraufnahmegebiet. Auf der Grundlage des deutlich marinen Einflusses und der Änderung der Siedlungsstruktur in der Mittleren Eisenzeit, lässt sich die Entstehung des Vliestroomes an den Anfang der Mittleren Eisenzeit datieren. Studien zur nordeuropäischen Bronzezeit, Band 1, 161–169 161 W. K. van Zijverden Introduction In the second part of the twentieth century, large-scale re-allotments were carried out in West-Frisia (fig. 1). Soil surveys were conducted prior to these re-allotments. In the eastern part of West-Frisia, an abundance of archaeological remains dating from the Middle and Late Bronze Age were found in the subsoil. Rescue excavations were carried out by the University of Amsterdam and the State Service combined with systematic field surveys and a survey through aerial photography (see Roessingh in this volume). Apart from the bone assemblage of the excavation Bovenkarspel Het Valkje, an assessment of the botanical remains and a selection of the survey by aerial photography of the re-allotments “Westwoud” and “De Streek”, nothing has yet been published (IJzereef 1981. Buurman 1996. De Vries-Metz 1993). Based on the assembled data, a model was published in 1983 for the rise and fall of Bronze Age civilisation in West-Frisia in relation to the development of the landscape (Van Geel et al. 1982/1983). This model plays a major role in planning archaeological research. Since 2000, several large-scale excavations have been carried out indicating that the model is incorrect to some extent (Lohof/Vaars 2005. Schurmans 2010. Roessingh/Lohof 2011). In this article, the palaeogeography of West-Frisia will be described, including the new coastal development model. The habitation model, which has been used over the last 35 years, is briefly described. New data derived from the excavations of Hoogwoud, Medemblik-Schepenwijk and Enkhuizen-Kadijken is presented (fig. 1). Based on the new data, the habitation model is critically reviewed and placed in a regional palaeogeographic context. Fig. 1. Study area, sites and re-allotments mentioned in the article A: West-Frisia, B: Westwoud, C: De Streek, D: sites 1 Opperdoes 2 Medemblik-Schepenwijk 3 EnkhuizenKadijken 4 Bovenkarspel Het Valkje, 5 Hoogwoud, E: other excavated Bronze Age sites. 162 The palaeoenvironment of eastern West-Frisia: a critical review. Palaeogeography The palaeogeography of West-Frisia is relatively well studied due to extensive soil mapping for agricultural purposes. After World War II, the government decided that the food production in The Netherlands had to be self-sufficient. Therefore, large-scale re-allotments were planned and carried out. Prior to these re-allotments, a large-scale soil mapping programme was carried out. Based on the data derived from the soil mapping programme, a first reconstruction for the genesis of the landscape of North Holland was published (Pons/Wiggers 1959; 1960). A slightly revised palaeographic model was published in the early eighties, providing an overwhelming number of radiocarbon dates (De Mulder/Bosch 1983). In this reconstruction, the transgression-regression theory was used as an explanation for changes in sedimentation and erosion within the tidal basin. According to this theory, slight differences in the pace of the relative rise of sea levels cause changes in sedimentation and erosion. At the end of the twentieth century, a new theory for the development of tidal basins was published (Van der Spek 1994). According to this theory, the morphology of the tidal inlet and the morphology of the tidal basin in combination with the relative rise in sea levels are the main factors controlling the sedimentation or erosion rates. Van der Spek applied this theory to reconstruct the development of the Bergen basin (Van der Spek 1994, 152– 180). In 2011, a new series of palaeogeographic maps for The Netherlands was published (fig. 2). Fig. 2. Palaeogeography of the study area according to Vos et al. (ed.) 2011 a: West-Frisia, b: sites mentioned in article, c: beach barrier and dunes, d: beaches, e: tidal basin, f: peat, g: brackish and salt water, h: freshwater, i: rivers, A: Bergen inlet, B: Oer-IJ estuary, C: Flevo Lagoon, D: Vliestroom, 1: river Vecht, 2: river IJssel. 163 W. K. van Zijverden The Bergen basin is situated at the location of the Pleistocene river valley of the river Rhine. In this area, the ri vers Vecht and Eem debouched at the start of the Holocene. Due to a rapidly rising sea level, the Pleistocene river valley “drowned” and a large-scale tidal basin was formed. Between 7000 and 5500 BP, the rate of the relative rise in sea level diminished, leading to a closure of the Dutch coast with beach barriers and coastal dunes. The tidal basin can be compared with the modern Wadden Sea for this period. Between 5500 BP and 3700 BP, the tidal basin can be described as an area dominated by large tidal creeks with high levees accompanied by marine crevasse splays and vast open basin areas (fig. 3a). In this landscape, man’s presence is prominent. Excavated sites dating from this period are the subject of investigation in the project “Unlocking North Holland’s Late Neolithic Treasure Chest”.1 Around 3700 BP, the Bergen basin diminished due to a disconnection with the drainage basin area of the river Vecht. Within the Bergen basin, this led to a rise of the mean high water level and an increase in the sedimentation rate. In this period, the landscape changed into a mudflat area comparable to the present day mudflat area “Verdronken land van Saeftinghe” (Fig. 3b). Around 3300 BP, the Bergen inlet closed causing a drop in the groundwater level within the tidal basin. The eastern part of West-Frisia can be described as a former mudflat area which is characterised as a freshwater environment with a patchwork of lakes, marshy areas and arable soils with a high natural fertility. Around 50 AD, the drainage pattern in the hinterland changed dramatically. The Vliestroom originated in this period, draining the lakes in the central part of The Netherlands and connecting the freshwater lakes with the marine environment of the Wadden Sea. The habitation model The model for Bronze Age habitation of West-Frisia is interlinked with the palaeogeographic model. After the closure of the Bergen inlet, the creek ridges were colonised by far mers. The first house plans in eastern West-Frisia date from between 1400 and 1500 BC. There is almost no evidence for human presence in the area prior to this date. Different dates are mentioned for the end of the habitation period. The latest houses in the Bronze Age settlement areas date from between 850 and 750 BC. In West-Frisia, settlement sites dating from the Early Iron Age (750–500 BC) are absent. Settlement sites dating from the Middle Iron Age and Late Iron Age are rare but not unknown, and are, with a few exceptions, situated at different locations from the Late Bronze Age sites (Woltering 1985, 225. Van Wijk 2008). Based on multi-proxy evidence from the excavations from the seventies, it has been argued that at the beginning of the exploitation of the landscape, the vegetation could be 1www.singlegrave.nl 164 characterised as an open, almost treeless area. Based on algae derived from ditches, the landscape can be characterised as a pure freshwater environment throughout the Middle and Late Bronze Age (Woltering 1985, 225. Van Wijk 2008). The fish bone assemblages of the old excavations also indicate a freshwater environment, excluding the possibi lity of brackish water in the vicinity (IJzereef 1981, 126). During the Bronze Age, the plants cultivated changed from wheat to barley, suggesting wetter environments. Also at the end of the Bronze Age, the number of weeds that preferred more humid conditions was substantially higher. Moreover, molluscs, mostly snails derived from ditches, indicate a more humid environment at the end of the Bronze Age compared to the start of the Bronze Age (Buurman 1997, 151). In addition, it has been suggested that the attested change from meat to dairy production is an indication of wetter conditions (Buurman 1996, 192). A final indication of wetter conditions is the exploitation of smaller habitats by small mammals, such as mice, in the later period (Buurman 1996, 148–149). In the nineties, the theory of solar forcing as the explanation for the sudden disappearance of man in West-Frisia was introduced (Van Geel et al. 1996). Based on a peat remnant under the Westfriese Omringdijk and the Engbert dijksveen in the eastern part of The Netherlands, a change was attested from Sphagnum species which favour dry summers to species favouring cooler, wetter and cloudier conditions. This change in Sphagnum species coincides with a change in the delta 14C-value, indicating a period with a substantially smaller number of solar flares. A direct link was suggested between the abandonment of West-Frisia around 750 BC and the change in solar radiation. It is suggested that this change led to a faster pace of peat formation. At the end of the Bronze Age (around 800 BC), West-Frisia should have been covered entirely by raised peat bogs. Due to land clearances and selnering in medieval times, the peat has disappeared almost completely. Only under mounds, dikes, churches and castles can remnants of this extensive peat cover be found (Borger 1975, 221). New data In the first decade of this century, three large-scale excavations were carried out: Hoogwoud, Medemblik-Sche penwijk and Enkhuizen-Kadijken (Fig. 1). Each of these sites contributed data which do not fit easily into the model described above. Hoogwoud The site of Hoogwoud is, according to the excavation report, situated on a creek ridge. The settlement site dates from the Middle and Late Bronze Age (1300–1000 BC). This is the only Bronze Age site which is situated in the western part of West-Frisia. The molluscs in the features represent freshwater or terrestrial environments. The molluscs derived from the sediment indicate a marine fauna. The large faunal re- The palaeoenvironment of eastern West-Frisia: a critical review. a Fig. 3. a: Tidal basin characterised by tidal creeks. Photo: Peter Scholle, Image courtesy Earth Science World Image Bank. b: Tidal basin characterised by mud flats. Photo: Willy Metz. b 165 W. K. van Zijverden mains, like all other sites in West-Frisia, consist of domestic animals with the exception of elk or deer (Cervus elaphus or Alces alces). The small faunal remains consist of three different species of duck (Anas platyrhynchos, Anas crecca or querquedula and Anas penelope) and five species of mice, indicating habitats from very wet and open environments to dry and shady environments. The fish remnants of this site comprise specimens indicating full marine environments (Atlantic cod and sting ray), brackish environments (European flounder and thinlip mullet) and freshwater specimens (cyprinids and Northern pike). Approximately 75 % of the fish remnants represent a brackish environment. The conditions for uncharred plant remains were poor. The charred remains comprise barley (Hordeum vulgare) and emmer wheat (Triticum dicoccum). Weeds from dry to very wet environments are present. The different species indicate a freshwater environment ranging from nutrient-rich dry arable soil to very wet pastures in the direct vicinity of the settlement sites. Mainly brackish environments, but also freshwater and marine environments, were present within reach of the settlement sites, and were exploited accordingly. No additional information on the palaeoenvironment was gained from bones of game. Medemblik-Schepenwijk The site of Medemblik-Schepenwijk is situated on a small 110 meter-wide creek ridge. The settlement site dates from the Middle and Late Bronze Age (1450–800 BC). Features and pottery dating from between 1100 and 900 BC seem to be absent. Apart from domestic animals, large faunal remains of goose, elk, deer, wild boar, fox and beaver are present from the Middle Bronze Age. From the Late Bronze age, duck (Anas crecca or querquedula), swan, crow, wild cat and otter are also present. A very special specimen present from the Late Bronze Age is the eagle owl. In the Middle Bronze Age, the fish remains indicate a full freshwater environment with mostly northern pike, cyprinids and several other species. From the Late Bronze Age, a few remains of European flounder and mullet are present, indicating brackish environments or at least a connection with a marine environment. Palynological research has been carried out on samples from water wells, ditches, ard marks and a coprolite. The pollen samples all indicate an open, almost treeless landscape, which is no surprise considering the locations that were sampled. In the samples from the ard marks, alder makes up to 25 % of the sample. The coprolites from dogs lack any indicators for brackish environments and water plants. Pollen and macro-remains from arable fields and freshwater swamps were present in the coprolites, as well as a relatively high percentage (7 %) of willow, which is a poor pollinator. The macrobotanical remains dating from the Middle Bronze Age represent different habitats ranging from dry nutritious arable land to marshy grasslands. Remnants of common saltmarsh grass (Puccinellia) and glasswort (Salicornia) indicate the presence of a brackish or marine environment. Poorly preserved wood from oak, alder and willow was only present in features dat- 166 ing from the Late Bronze Age. The macrobotanical remains dating from the Late Bronze Age comprise a few indicators for brackish environments and indicators for shrubs (or possibly woods), such as seeds of bramble and elder. The different species of animals and plants indicate for both periods a freshwater environment ranging from nutrient-rich dry arable soil to very wet pastures in the direct vicinity of the settlement site. For both periods, indications of lakes are lacking. Brackish environments were present within reach of the settlement sites. These indications are stronger for the Late Bronze Age than for the Middle Bronze Age. For both periods, there are distinct indications for the pre sence of shrubs and woodland. There was probably a wider range of environments within reach of the settlement in the Late Bronze Age than in the Middle Bronze Age. Enkhuizen-Kadijken The site of Enkhuizen-Kadijken (see Roessingh in this volume) is situated on a former mud flat. The settlement dates from the Middle and Late Bronze Age (1600–800 BC). The research regarding the environment did not result in a distinct change of the environment over time. The faunal remains consist of wild boar, brown bear, elk, deer and beaver. The small faunal remains consist of ducks, geese and water rail, indicating open water. The remains of the northern goshawk and the woodcock are interesting, both being indicative of woodland and shrubs. The fish remains are similar to the remains from Medemblik-Schepenwijk: mainly “freshwater” fish, a few mullets and large numbers of eel. Remnants of six different species of mice indicate a wide variety of biotopes ranging from shrubs and marshy grasslands to dry and arable land. The remnants of the grass snake are an indication of the presence of open water. Palynological research has been carried out on a soil horizon and a ditch. The pollen analysis indicates an open, almost treeless landscape with (marshy) grassland, which again is no surprise considering the location of the samples. The presence of spores indicative of cow dung is to be expected. The macrobotanical analysis produced distinct indications for seepage in the Middle Bronze Age. There are only few indications for seepage in the Late Bronze Age, indicating a rise in the groundwater table over time. A change in cultivation from wheat to barley could not be confirmed, while both species were present in Middle and Late Bronze Age contexts. Wooden objects made of oak, alder, ash, birch, willow and pine (one object) were found. In a few samples, an indication of brackish environments was present, for example the seeds of pickle weed. A blueberry (Vaccinium species) indicates the presence of acidic soils. At some locations within the site Enkhuizen-Kadijken, the original soil profile was intact. At two locations, a sample was taken for a micromorphological analysis. The main goal of this analysis was to answer the questions concerning the genesis of a pitch black A-horizon and the peat growth after the abandonment of the site. The black colour of the A-horizon was caused by repeatedly burning the surface. The The palaeoenvironment of eastern West-Frisia: a critical review. charcoal in the soil horizon comprised mainly epidermis of grasses and sedges, but also vascular tissue of trees. After the abandonment of the settlement site, renewed sedimentation took place. At first, the regular burning of the surface was continued. Distinct layers of charcoal particles alternate with very small silt particles. After a while, the sedimentation took place in a back swamp environment, uninterrupted by burning activities. No peat growth occurred. The different species indicate a freshwater environment in the vicinity of the settlement area throughout the Middle and Late Bronze Age. The game, the small mammals and the birds are particularly indicative of the presence of woodland and shrubs, but also dry arable land, marshy grasslands and open water. The wide range of tree species, represented by the wooden objects, also indicates different types of woodland within reach of the settlement site. The fish and macrobotanical remains indicate the exploitation of brackish environments within reach of the settlement site. The micromorphological analysis was especially valuable, providing proof of the absence of peat after the abandonment of the settlement site and indication of renewed sedimentation in a back swamp environment. For all the sites, the supposed change from meat to dairy production could be neither validated nor invalidated. A small increase in sheep remains from the Late Bronze Age compared to the Middle Bronze Age was established for Medemblik-Schepenwijk and Enkhuizen-Kadijken, but was lacking for the site of Hoogwoud. An increase in sheep remains is used by IJzereef as a complementary argument for a change from meat to dairy production and a wetter environment (IJzereef 1981). Discussion The natural landscape of the eastern part of West-Frisia has been described in the habitation model as a very open freshwater environment. The new data, however, present indications of a much more differentiated landscape than previously thought. A patchwork of lakes, marshy grasslands, dry arable fields alternating with patches of woodland and shrubs must have been present. Based on the wood species found in the excavations, willow shrubs were present as well as alder carrs. Apart from these types of shrubs and woodlands, riparian forests with ash and oak must have been present as well. The game assemblage with wild boar, brown bear, northern goshawk and woodcock is consistent with the presence of these specific woodland biotopes. The fish assemblage differs in composition for almost every site: Hoogwoud represents a brackish environment, Medemblik-Schepenwijk represents a freshwater environment with a distinct brackish influence, or at least a direct connection to marine environments. Enkhuizen-Kadijken represents an almost entirely freshwater environment, while the nearby site Bovenkarspel Het Valkje represents an en- tirely freshwater environment. The macrobotanical remains are in accordance with this picture. Of particular interest are the indications for a slight change into a more brackish environment at Medemblik-Schepenwijk based on fish remains as well as macrobotanical remains. The question is how one should interpret these indications of brackish environments. One problem is that there are no good pollinators within brackish and marine environments which give a clear signal in the pollen sample locations used in the archaeological research, such as peat bogs, ditches, ard marks and water wells. Only the coprolites could give an indication depending on the environments exploited by the animal during a day. It is a pity that only three of these have been analysed for pollen and are therefore of no use in this discussion. The differences may be interpreted as representing different environments in the vicinity of the settlement sites during the habitation. It implies at least the occurrence of marine influxes in various parts of West-Frisia during Bronze Age habitation. The habitation model assumes a rise of the groundwater table. A macrobotanical analysis of Enkhuizen-Kadijken in particular demonstrates a diminishing number of indicators for seepage from the Middle Bronze Age to the Late Bronze Age, indicating a rise of the groundwater level during this period. Indications of wetter conditions as stated in the model, a change from meat to dairy production, a change from wheat to barley and an increase of weeds indicating wetter conditions could be neither validated nor invalidated. The habitation model assumes that the creek ridges were the only place suitable for settlement sites. The excavation of Enkhuizen-Kadijken clearly proves that settlement sites also occur on mudflat deposits. It also proves that this mudflat was in use as a settlement site until 800 BC. The model assumes extensive peat growth due to higher precipitation leading to abandonment of the settlement sites. The micromorphological analysis proved the absence of peat growth and a gradual change to sedimentation in a back swamp environment. Brackish environments in the eastern part of West-Frisia can be easily explained if a connection with the Oer-IJ estuary was present from the start of the Middle Bronze Age. Actually, there is no indication that such a connection did not exist. A change to more brackish circumstances towards the Late Bronze Age can be explained with an earlier connection to the Wadden Sea (Vliestroom) or the occurrence of events such as storm surges. The marine-brackish environment for the site of Hoogwoud is difficult to explain. The closure of the Bergen inlet was possibly not as complete as expected. Marine sediments dating after 3300 BP are unknown in the western part of West-Frisia, however, the available dates for the sediments are mainly based on radiocarbon dates from molluscs. A rise in the groundwater level is easily explained as being due to the rise of the relative sea level. However, this does not explain the renewed habitation in the Middle and Late Iron Age, for instance at sites such as Opperdoes (Woltering 167 W. K. van Zijverden 1985, 225. Van Wijk 2008), and therefore additional explanations are needed. Changes in the drainage basin effect in the Flevo Lagoon can cause rapid rises and falls of the surface water level leading to changes in the groundwater level. For example, the surface water level in the Flevo Lagoon was approximately 15–60 cm below mean high water around 3700 BP due to the drainage basin effect. Around 3300 BP, the surface water level was approximately equal to mean high water (Van de Plassche et al. 2005). Sedimentation in a back swamp environment and the lack of peat growth fits very well into the idea of temporarily higher water levels in the Flevo Lagoon. Another factor leading to a rise in groundwater level is differential local subsidence due to oxidation of organic matter, compaction and auto loading. An extensive ditch system was maintained in the Middle Bronze Age. Based on the mollusc analysis, these ditches were dry during a large part of the year. The ditches probably also had an important function for an enlargement of surface runoff. The large number of water pits at the site Enkhuizen-Kadijken in the ditch systems supports this idea. Digging ditches leads to drainage of the soil and therefore to subsidence, hence the rise of the relative groundwater level. The sedimentation in a back swamp environment at Enkhuizen-Kadijken leading to the abandonment proves that there was a significant rise in the surface water level. Moreover, the lack of a proper date of this phase does not help to move the discussion forward. The closing of the Bergen inlet resulted in erosion in the Oer-IJ estuary due to an enlargement of the tidal basin (Kok 2008, 85). Between 550 and 400 BC, the Oer-IJ estuary silted up, probably due to the appearance of an opening towards the Wadden Sea (Kok 2008, 91). A date for the connection to the Wadden Sea at the start of the Middle Iron Age fits very well with the renewed habitation in eas tern West-Frisia. It also explains the oxidation of a vast peat area in the lower reach of the river IJssel and the occurrence of sites dating from the Middle Iron Age at locations in the cover sand area which had already been abandoned at the end of the Middle Bronze Age (Kok 2008, 91). AMS dates derived from a marine gully in the Flevo Lagoon indicating marine activity in the Flevo Lagoon at the end of the Early Iron Age are also in accordance with an earlier connection to the Wadden Sea (De Moor et al. 2009). Conclusions After 35 years, the habitation model for West-Frisia needs to be revised. Recent excavations have proven the presence of settlement sites at a mudflat which was thought to be uninhabitable. The natural environment showed more variety than expected. At least at the site of Enkhuizen-Kadijken, peat growth did not cause the abandonment of the settlement. Sedimentation in a back swamp environment was the actual cause. A rise in the groundwater level has been confirmed by recent excavations. This rise was probably triggered by regional changes in the morphology of the tidal inlets and 168 tidal basins influencing the flood basin effect. In addition, differential subsidence due to the maintenance of extensive ditch systems from the Middle Bronze Age onwards led to a higher relative groundwater level. An enlargement of the precipitation due to a decrease in solar activity is still likely to have contributed to the abandonment. However, it is definitely not the cause of a wetter environment, but could have been the last straw. Brackish environments can be explained by marine influxes due to storm surges. An earlier opening of the Vliestroom around 550 BC rather than 50 AD fits very well into the regional site distribution and is supported by the observation of marine sediments dating from the latter part of the Early Iron Age in the Flevo Lagoon. Literature Borger, G. J. 1975: De Veenhoop. Een historisch-geografisch onderzoek naar het verdwijnen van het veendek in een deel van West-Friesland. Dissertation, University of Amsterdam. Buurman, J. 1988: Economy and environment in Bronze Age West-Friesland, Noord Holland (from wetland to wetland). In: P. Murphy/C. A. I. French (ed.), The exploitation of wetlands British Archaeological Reports 186. Oxford 1988, 267–292. Buurman, J. 1996: The eastern part of West-Friesland in later prehistory. Dissertation, Leiden University. 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J. van der 1994: Large scale evolution of Holocene tidal basins in the Netherlands. Dissertation, Utrecht University. Vos, P. C./Bazelmans, J./Weerts H. J. T./Meulen, M. J. van der (eds.) 2011: Atlas van Nederland in het Holoceen, landschap en bewoning vanaf de laatste ijstijd tot nu. Amsterdam 2011. Vries-Metz, W. H. de 1993: Luchtfoto-archeologie in Oostelijk West-Friesland. Dissertation, University of Amsterdam. Wijk, I. van 2008: Definitief archeologisch onderzoek (DAO) van de leidingsleuven en het wegtracé te Opperdoes-KluitenZuid, ArchOL rapport 97, Leiden 2008. Woltering, P. 1985: Prehistorie en Romeinse Tijd in West-Friesland. West-Frieslands Oud & Nieuw 52, 1985, 199–232. Addresses of the author Wilko K. van Zijverden Leiden University Faculty of Archaeology PhD student Postbus 9515 NL-2300 RA Leiden [email protected] Saxion University of Applied Sciences HBO-Archeologie Lecturer Archaeology Postbus 501 NL-7400 AM Deventer [email protected] 169 170