Abstract
AbstractThis paper presents new geological data from two terp excavations at Englum and Ezinge, in the Dutch province of Groningen, and compares them to similar data from the western part of Friesland, in particular from the terp of Wijnaldum-Tjitsma. This terp is situated at a salt marsh ridge of the same height and thickness as Englum and Ezinge, although habitation started 650 years later at Wijnaldum. The measured levels of the tidal-flat/salt-marsh boundary underneath these terps make it possible to reconstruct palaeo-Mean High Water (MHW) levels. These sea-level index points show that palaeo-MHW in the Groningen part of the Wadden Sea was at the upper limit of the range of palaeo-MHW that has been reconstructed for the Dutch Wadden Sea on the basis of data from its western part. The deviating levels indicate that there are differences between regions of the Wadden Sea; this has earlier been established for the German section of the Wadden Sea. In the eastern part of the Dutch Wadden Sea, MHW nowadays is considerably higher than in the western part of the Wadden Sea; the data suggest that this may have been the case already in the 1st millennium BC. Salt marsh levels under dated terp layers make it possible to establish the rate of sedimentation of the developing salt marsh, at 23–91 cm per century for the pioneer zone and low marsh. This rate of development slowed to 4–5 cm per century for the middle marsh and 3–4 cm per century for the high salt marsh.
Highlights
Geological research has been part of most archaeological excavations in the northern Netherlands during recent decades; this has been the case since the 1991–1993 excavations of the terp Wijnaldum-Tjitsma in the province of Friesland
The boundary between the top of the tidal-flat deposits and the deepest crinkly lamination characteristic of salt marsh deposits, which represents the start of salt marsh formation, is 20 ± 5 cm below palaeoMHW level (Roep & Van Regteren Altena, 1988: 226)
That it represents the start of salt marsh formation is supported by the occurrence of unbroken diatoms of the species Scoliopleura tumida, which belongs to the zone just below or around palaeoMHW level, in the lower part of the salt marsh deposits at Wijnaldum (Vos, 1999: 49)
Summary
Geological research has been part of most archaeological excavations in the northern Netherlands during recent decades; this has been the case since the 1991–1993 excavations of the terp Wijnaldum-Tjitsma in the province of Friesland. Geology benefits from archaeology because it offers the opportunity to acquire detailed data and dates on palaeo-levels and on the development of the salt marsh and the coastal region in general. This paper will present and discuss the data on the start and development of salt marsh formation from two excavations in the northwestern part of the province of Groningen, the terps of Englum and Ezinge, and compare them to similar data from the excavation in the terp of Wijnaldum-Tjitsma in northwestern Friesland (Fig. 1). The comparison between Ezinge, Englum and Wijnaldum reveals similarities and differences between these locations that must be related to (1) similar processes of salt marsh formation, and (2) differences in
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