A botanical analysis of a late-Pleistocene and Holocene profile in the Rhine Delta

The post-Glacial history of the forests in the Netherlands has been reconstructed fairly well by pollen analysis of several bogs. At the same time stratigraphical investigations shed some light on the way in which these bogs had been built up, i.e. on the plants by which, in the various forest periods, peat was formed. Though these data are quite interesting, they do not give a good impression of the entire synchronal herbaceous flora, as they are limited to the peatbuilding plants. As yet very little is known of the rest of the vegetation (water-, marsh- and land-plants) of the late-Pleistocene and Holocene periods. We must look for their remains in other deposits, particularly in clay and sand, wherein however few land plants will be found, as their chance of preservation is very small. The best strata for an investigation of this kind he, as a rule, beneath the groundwater level, and this is a great handicap for collecting samples. Deep pits have been dug lately by the “Rijkswaterstaat” (Government office for the maintenance of dikes and canals) and as they are kept dry by intensive pumping, they are very useful for our purpose. The construction of a lock near Wijk bij Duurstede, province of Utrecht, gave us an opportunity for studying a profile extending from 4.70 m —NAP (i.e. 4.70 m below Ordnance Datum of Amsterdam) to 3.75 m + NAP (i.e. 3.75 m above O.D.). From this ± 8.5 m high profile, a complete set of samples was taken for pollen analysis, and larger quantities for macroscopical investigation. A special word of thanks is due to the technical staff of the “Rijkswaterstaat” for their kind assistance at the field work. Wijk bij Duurstede is situated in the Rhine delta, where the “Kromme Rijn”, now but a backwater of a formerly important river arm of the Rhine, branches off to the NW (see map, fig. 1). The youngest sediments consist of river clay, deposited in the broad valley of the Rhine, measuring here ± 25 km in width. About 6 km to the NE the Utrecht hill range, a push moraine dating from the Riss glacial epoch, rises up.