Landscape history of the Oer-IJ tidal system, Noord-Holland (the Netherlands)

Abstract

AbstractThe prehistoric Oer-IJ tidal system in the coastal area of Noord-Holland, between Castricum, Uitgeest, Velsen and Amsterdam, was the successor of the Haarlem tidal system when this was silted up around 3000 BC and large peat bogs formed in the Zaanstreek and Haarlemmermeer areas. Since then the Oer-IJ has been the natural outlet to the sea, draining the peat hinterlands. About 800 BC the Oer-IJ system was connected to the fluvial system of the Utrechtse Vecht and became the northern branch of the river Rhine. During the Late Iron Age, when the Flevo lakes in the IJsselmeer region and the Utrechtse Vecht were connected with the Wadden Sea, the Oer-IJ lost its discharge function. The tidal area silted up and was closed between 200 and 100 BC by a barrier ridge. The settlement history of the Oer-IJ system and the archaeological heritage in the subsurface is closely related to the geological and hydrological development throughout the ages. The shape and location of the continuously migrating outlet determined the opportunities for human settlements and activities. The best locations were beach ridges, higher, silted-up salt marshes and marginal zones of the peatland. In the Late Iron Age the sand flats also became habitable since tidal activity had stopped. In the Early Roman period there was no direct connection from the harbour of Castellum Flevum at Velsen to the North Sea, but ships could navigate from the Oer-IJ channel between Velsen and Amsterdam, through the Flevo lakes and the Utrechtse Vecht to the Wadden Sea, and to the Roman border (Limes) along the Oude Rijn. Here the data used for the palaeogeographic landscape reconstruction of the Oer-IJ are presented and explained, and the most important landscape-forming processes, which led to the emergence and closure of the Oer-IJ, are described. The landscape reconstructions give a new perspective on the migration of the main tidal channel and the formation of the tidal-inlet system near Castricum, which was the result of the progradation of the beach ridges south and north of the Castricummerpolder (Binnendelta according to De Roo, 1953). The geological and archaeological observations in the Binnendelta prove that the Oer-IJ was closed from the open sea in the early Late Iron Age.