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Spatial and chronological prehistoric landscape reconstruction using geo-archaeological methods in the Lower Scheldt floodplain (NW Belgium)

Jeroen Verhegge (UGent)
(2015)
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(UGent) , (UGent) and (UGent)
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Abstract
Since the last decades, well preserved Late Glacial dune formations containing numerous prehistoric sites buried deeply below peat, OM rich clays and marine clayey to sandy sediments have been discovered during extensive construction works in the harbor of Antwerp situated in the lower Scheldt river basin in northwest Belgium. Archaeological excavations have identified the first presence of the transitional Mesolithic-Neolithic Swifterbant culture, previously only known from sites in the Netherlands and one site in northwest Germany, and evidence for the presence of other Final Paleolithic to Early Neolithic cultural remains. High quality organic preservation at these sites have offered the opportunity to reliably place Swifterbant occupation within the absolute chronology of the Mesolithic-Neolithic transition in this region, as well as the reconstruction of Swifterbant subsistence practices, most notably the incorporation of cattle husbandry into a traditional hunting-fishing-gathering economy. This PhD dissertation focuses on three aspects of prehistoric occupation in the wetland region of the lower Scheldt river basin, namely (1) the development of a protocol for mapping the buried paleolandscape in view of archaeological surveys, (2) the modelling of peat rise and the dating of a short expansion of the tidal influence as a tool for assessing the gradual drowning of the area and human response and (3) the refinement and the optimization of the archaeological sampling strategies. 1. Development of a protocol for mapping buried paleolandscape Until recently, (hand-)coring used to be the main tool for mapping prehistoric landscapes in comparable wetlands. In this PhD a more effective approach, including near surface geophysical and geotechnical techniques, has been developed and tested, mainly at Doelpolder-Noord. Firstly, electrical resistance imaging and shear wave land seismics are judged to be unproductive, due to the required effort and limited results. Secondly, high resolution electromagnetic induction electrical conductivity survey provides a suitable approximation of the prehistoric landscape variability but is challenged by variations in groundwater brackishness and the presence of recent land raising or dumps. Qualitative maps of the total subsurface features could be made using single coil pair sensors. Using electromagnetic induction sensors with multiple coil spacings and configurations, the prehistoric paleotopography could be reconstructed quantitatively within the limits of the instrument’s depth of investigation. This depth model could be separated from electrical conductivity variations created by more shallow (post-)medieval landscape structures. Thirdly, cone penetration tests (CPT) can provide an alternative solution beyond the instrument’s depth of investigation and in areas unsuited for electromagnetic induction survey. The use of CPT was investigated in estuarine and river floodplain environments as well as an intertidal saltmarsh. The efficiency, reliability and repeatability was evaluated against coring. These data have generally allowed highly accurate mapping of the paleo-topography of the transition from Pleistocene sediments to overlying Holocene peat sequences. Thin OM rich clay intercalations within the peat layers could often still be identified. Additional pore pressure, conductivity and seismic velocity data (from CPT-U, CPT-C and CPT-S) did not add much crucial information and their main use seems to lie in the added value for the interpretation of electromagnetic induction, electrical resistance imaging and shear wave land seismic survey results. 2. Modelling peat rise and dating of a short expansion of tidal influence After developing a geological mapping strategy, chronological evolution of the re-gional prehistoric landscape was reconstructed and related to its contemporaneous land use. As a case study, the influence of hydrological dynamics in the occurrence of the Swifterbant culture in these wetland regions of the lower Scheldt floodplain is investigated. This is carried out by employing a Bayesian chronological modelling approach to integrate stratigraphic as well as radiometric chronological data from accurately datable archaeological remains and key horizons in peat sequences. An age-depth model has been developed of the peat formation driven by the rising groundwater and the timing was determined of a Middle Holocene increased tidal influence, resulting in a short period of OM rich clastic sedimentation. Two different site types could be identified between the six excavated sites – dune and natural levee sites – which had contemporaneous periods of occupation, but different occupation histories. The integration of the archaeological and paleoenvironmental dates from both site types suggests a Swifterbant settlement system in the area. This could explain the specific tempo and trajectories of cultural and economic change in the Scheldt basin during the neolithisation well over a millennium later than in the nearby loess region. This land use model consists of larger, more continuously occupied camps on natural levees or point bars along the river valley, resulting in complex palimpsest sites on the one hand and relatively specialized and temporarily inhabited cattle and hunting-fishing camps on the floodplain dunes on the other hand. Moreover, Bayesian chronological modelling suggests that the Swifterbant occupation of the dune sites has occurred shortly after the emergence of a brackish (supra-)tidal landscape replacing a freshwater marsh. The dated sites of Deurganckdok-Sector B and M were left shortly before being covered with organic sediments, which fits within the regional age-depth model of initiating peat formation. The chronological relation between the end of the occupation of the dune sites and the disappearance of the (supra-)tidal landscape is still unclear due to a lack of dated dune sites with higher elevations. Therefore the area of Doelpolder-Noord suitable for prehistoric occupation was determined using the modelled subsurface. 3. Refinement and optimization of archaeological sampling strategies Since the 90s and particularly in Dutch and Belgian wetland research, archaeological sampling using Dutch augers has increasingly become important for the detection of covered prehistoric hunter-gatherer sites, comprised mainly of scatters of lithic artefacts of variable size and find density. The archaeological results of eleven cored sites are analysed to develop a core sampling strategy for prospecting a broad range of prehistoric sites. The results indicate that augering within a 10m grid with a 10cm to 12cm diameter core and sieving through 1mm to 2mm meshes allows the detection of nearly all identified sites, even with a small area and a low find density. A two-step gridding approach is recommended to increase discovery rates. This approach was followed at the reconstructed dune in Doelpolder-Noord. Part of it was archaeologically sampled in using the proposed methodology by Dutch hand augering on the top and Sonic Drill Aqualock coring on the flanks. Archaeological indicators for prehistoric occupation, such as burnt bone and flint fragments, were retrieved from these samples after sieving.

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Citation

Please use this url to cite or link to this publication:

MLA
Verhegge, Jeroen. “Spatial and Chronological Prehistoric Landscape Reconstruction Using Geo-archaeological Methods in the Lower Scheldt Floodplain (NW Belgium).” 2015 : n. pag. Print.
APA
Verhegge, J. (2015). Spatial and chronological prehistoric landscape reconstruction using geo-archaeological methods in the Lower Scheldt floodplain (NW Belgium). Ghent University. Faculty of Arts and Philosophy, Ghent, Belgium.
Chicago author-date
Verhegge, Jeroen. 2015. “Spatial and Chronological Prehistoric Landscape Reconstruction Using Geo-archaeological Methods in the Lower Scheldt Floodplain (NW Belgium)”. Ghent, Belgium: Ghent University. Faculty of Arts and Philosophy.
Chicago author-date (all authors)
Verhegge, Jeroen. 2015. “Spatial and Chronological Prehistoric Landscape Reconstruction Using Geo-archaeological Methods in the Lower Scheldt Floodplain (NW Belgium)”. Ghent, Belgium: Ghent University. Faculty of Arts and Philosophy.
Vancouver
1.
Verhegge J. Spatial and chronological prehistoric landscape reconstruction using geo-archaeological methods in the Lower Scheldt floodplain (NW Belgium). [Ghent, Belgium]: Ghent University. Faculty of Arts and Philosophy; 2015.
IEEE
[1]
J. Verhegge, “Spatial and chronological prehistoric landscape reconstruction using geo-archaeological methods in the Lower Scheldt floodplain (NW Belgium),” Ghent University. Faculty of Arts and Philosophy, Ghent, Belgium, 2015.
@phdthesis{6851184,
  abstract     = {Since the last decades, well preserved Late Glacial dune formations containing numerous prehistoric sites buried deeply below peat, OM rich clays and marine clayey to sandy sediments have been discovered during extensive construction works in the harbor of Antwerp situated in the lower Scheldt river basin in northwest Belgium. Archaeological excavations have identified the first presence of the transitional Mesolithic-Neolithic Swifterbant culture, previously only known from sites in the Netherlands and one site in northwest Germany, and evidence for the presence of other Final Paleolithic to Early Neolithic cultural remains. High quality organic preservation at these sites have offered the opportunity to reliably place Swifterbant occupation within the absolute chronology of the Mesolithic-Neolithic transition in this region, as well as the reconstruction of Swifterbant subsistence practices, most notably the incorporation of cattle husbandry into a traditional hunting-fishing-gathering economy.
This PhD dissertation focuses on three aspects of prehistoric occupation in the wetland region of the lower Scheldt river basin, namely (1) the development of a protocol for mapping the buried paleolandscape in view of archaeological surveys, (2) the modelling of peat rise and the dating of a short expansion of the tidal influence as a tool for assessing the gradual drowning of the area and human response and (3) the refinement and the optimization of the archaeological sampling strategies.
1. Development of a protocol for mapping buried paleolandscape
Until recently, (hand-)coring used to be the main tool for mapping prehistoric landscapes in comparable wetlands. In this PhD a more effective approach, including near surface geophysical and geotechnical techniques, has been developed and tested, mainly at Doelpolder-Noord.
Firstly, electrical resistance imaging and shear wave land seismics are judged to be unproductive, due to the required effort and limited results.
Secondly, high resolution electromagnetic induction electrical conductivity survey provides a suitable approximation of the prehistoric landscape variability but is challenged by variations in groundwater brackishness and the presence of recent land raising or dumps. Qualitative maps of the total subsurface features could be made using single coil pair sensors. Using electromagnetic induction sensors with multiple coil spacings and configurations, the prehistoric paleotopography could be reconstructed quantitatively within the limits of the instrument’s depth of investigation. This depth model could be separated from electrical conductivity variations created by more shallow (post-)medieval landscape structures.
Thirdly, cone penetration tests (CPT) can provide an alternative solution beyond the instrument’s depth of investigation and in areas unsuited for electromagnetic induction survey. The use of CPT was investigated in estuarine and river floodplain environments as well as an intertidal saltmarsh. The efficiency, reliability and repeatability was evaluated against coring. These data have generally allowed highly accurate mapping of the paleo-topography of the transition from Pleistocene sediments to overlying Holocene peat sequences. Thin OM rich clay intercalations within the peat layers could often still be identified. Additional pore pressure, conductivity and seismic velocity data (from CPT-U, CPT-C and CPT-S) did not add much crucial information and their main use seems to lie in the added value for the interpretation of electromagnetic induction, electrical resistance imaging and shear wave land seismic survey results.
2. Modelling peat rise and dating of a short expansion of tidal influence
After developing a geological mapping strategy, chronological evolution of the re-gional prehistoric landscape was reconstructed and related to its contemporaneous land use. As a case study, the influence of hydrological dynamics in the occurrence of the Swifterbant culture in these wetland regions of the lower Scheldt floodplain is investigated. This is carried out by employing a Bayesian chronological modelling approach to integrate stratigraphic as well as radiometric chronological data from accurately datable archaeological remains and key horizons in peat sequences. An age-depth model has been developed of the peat formation driven by the rising groundwater and the timing was determined of a Middle Holocene increased tidal influence, resulting in a short period of OM rich clastic sedimentation.
Two different site types could be identified between the six excavated sites – dune and natural levee sites – which had contemporaneous periods of occupation, but different occupation histories. The integration of the archaeological and paleoenvironmental dates from both site types suggests a Swifterbant settlement system in the area. This could explain the specific tempo and trajectories of cultural and economic change in the Scheldt basin during the neolithisation well over a millennium later than in the nearby loess region.
This land use model consists of larger, more continuously occupied camps on natural levees or point bars along the river valley, resulting in complex palimpsest sites on the one hand and relatively specialized and temporarily inhabited cattle and hunting-fishing camps on the floodplain dunes on the other hand. Moreover, Bayesian chronological modelling suggests that the Swifterbant occupation of the dune sites has occurred shortly after the emergence of a brackish (supra-)tidal landscape replacing a freshwater marsh. The dated sites of Deurganckdok-Sector B and M were left shortly before being covered with organic sediments, which fits within the regional age-depth model of initiating peat formation.
The chronological relation between the end of the occupation of the dune sites and the disappearance of the (supra-)tidal landscape is still unclear due to a lack of dated dune sites with higher elevations. Therefore the area of Doelpolder-Noord suitable for prehistoric occupation was determined using the modelled subsurface.
3. Refinement and optimization of archaeological sampling strategies
Since the 90s and particularly in Dutch and Belgian wetland research, archaeological sampling using Dutch augers has increasingly become important for the detection of covered prehistoric hunter-gatherer sites, comprised mainly of scatters of lithic artefacts of variable size and find density. The archaeological results of eleven cored sites are analysed to develop a core sampling strategy for prospecting a broad range of prehistoric sites. The results indicate that augering within a 10m grid with a 10cm to 12cm diameter core and sieving through 1mm to 2mm meshes allows the detection of nearly all identified sites, even with a small area and a low find density. A two-step gridding approach is recommended to increase discovery rates.
This approach was followed at the reconstructed dune in Doelpolder-Noord. Part of it was archaeologically sampled in using the proposed methodology by Dutch hand augering on the top and Sonic Drill Aqualock coring on the flanks. Archaeological indicators for prehistoric occupation, such as burnt bone and flint fragments, were retrieved from these samples after sieving.},
  author       = {Verhegge, Jeroen},
  language     = {eng},
  pages        = {XXXVI, 247},
  publisher    = {Ghent University. Faculty of Arts and Philosophy},
  school       = {Ghent University},
  title        = {Spatial and chronological prehistoric landscape reconstruction using geo-archaeological methods in the Lower Scheldt floodplain (NW Belgium)},
  year         = {2015},
}