Case Studies:Case study 10
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[edit] Prehistoric and Roman gullying in the European loess belt
Vanwalleghem et al. (2006) recorded gully erosion phases in the Meerdaal Forest of central Belgium. Evidence for gullies forming before the fourteenth century is rare in NW Europe because the probability is that it has been destroyed by subsequent erosion phases. However, the ancient Meerdaal forest offers a unique setting to study older gully erosion phases, as this forest in the loess belt has fossilized badlands with large gullies. From historical documents the area has been forested since the fourteenth century, yet the spatial distribution and morphology of these gullies are indicative of small, local clearings of the forest cover. Such gullies forming under cropland are characterized by a rapid cycle of incision and infilling. If their catchment remains under cropland, they are usually completely filled in. This renders the situation in Meerdaal forest even more unique since reforestation of the gully catchment area stabilized the old gully channels. In the Meerdaal forest, there is thus a unique archive of old gullies, which are most probably human-induced. To date, however, no dating of the gully activity phases has been done.
A preliminary stratigraphy with relative ages was made and detailed drawings of the vertical walls of each trench were made. Sediment units were characterized in the field (based on colour, field texture and structure) and by additional laboratory analysis on some selected samples (texture, dry bulk density, pH, carbon, nitrogen and phosphorus content). Radiocarbon dates were established with the AMS method and artefacts were dated by archaeologists.
During the Pleistocene loess was deposited and during the late glacial to Holocene the upper layer was decalcified, after which clay could migrate to form a clay illuviation horizon. The largest part of the gully infill consists of silty to sandy loam, with some fine layering and intercalated with several bands of coarser material. At several depths in sediment, charcoal, Roman brick fragments and late Roman pottery were found. On top of the previous layers and over the entire width of the transect, a sandy loamy colluvium layer is found. This sediment unit is much less dense than the rest of the profile.
From the transects through both gullies, several indications were found that support the hypothesis that these gullies were caused by a human-induced land use change from forest to cropland in the gully catchment area. The fact that no undisturbed, loess derived soil profile is found on top of the Tertiary sands in the thalweg of the gully is the first evidence that this gully is not of periglacial origin. Further evidence for the anthropogenic origin of the gully is given by the various artefacts found in the transects and the dating of the charcoal fragments to two phases of gully activity and agriculture in the catchment: a first one during the Bronze Age and a second one at the end of the Roman period. Silty layers slid in from the gully walls just after the first incision of the gully, when these walls were still very unstable. The infilling must have been a rapid process since no indications of a stable phase with humic horizon development within the sediment deposited was found. This is further supported by the relatively steep gully walls. Field observations at the nearby Kinderveld site confirm that the infilling of a gully of several metres deep can occur within a few decades when its catchment is continuously under cropland. It is possible that artefacts and charcoal fragments were at the soil surface for a long time before the gullies incised. Therefore, the age of the datable material found in the gully infills, strictly speaking, only provides a maximum estimate of the age of the gully.
The full article is Vanwalleghem, T., H.R. Bork, J. Poesen, M. Dotterweich, G. Schmidtchen, J. Deckers, S. Scheers and M. Martens (2006) Prehistoric and Roman gullying in the European loess belt: a case study from central Belgium The Holocene 16, (3) 393-401. This can be found at http://hol.sagepub.com/cgi/reprint/16/3/393
Keywords: Loess, gully erosion, cropland, Bronze Age, Roman, Belgium
