Stratigraphy and integrated facies analysis of the Saalian and Eemian sediments in the Amsterdam-Terminal borehole, the Netherlands

Abstract

The Amsterdam glacial basin was a major sedimentary sink from late Saalian until late Eemian (Picea zone, E6) times. The basin's exemplary record makes it a potential reference area for the last interglacial stage. The cored Amsterdam-Terminal borehole was drilled in 1997 to provide a record throughout the Eemian interglacial. Integrated facies analysis has resulted in a detailed reconstruction of the sedimentary history. After the Saalian ice mass had disappeared from the area, a large, deep lake had come into being, fed by the Rhine river. At the end of the glacial, the lake became smaller because it was cut off from the river-water supply, and eventually only a number of shallow pools remained in the Amsterdam basin. During the early Eemian (Betula zone, E1), a seepage lake existed at the site. The lake deepened under the influence of a steadily rising sea level and finally evolved into a silled lagoon (late Quercus zone, E3). Initially, the lagoon water had fairly stable stratification, but as the sea level continued to rise the sill lost its significance, the lagoon becoming well mixed by the middle of the Corylus/Taxus zone (E4b). The phase of free exchange with the open sea ended in the early Carpinus zone (E5), when barriers developed in the sill area causing the lagoon to become stratified again. During the Late Eemian (late E5), a more dynamic system developed. The sandy barriers that had obstructed exchange with the open sea were no longer effective, and a tidally-influenced coastal lagoon formed. The Eemian sedimentary history shown in the Amsterdam-Terminal borehole is intimately connected with the sea-level history. Because the site includes both a high-resolution pollen signal and a record of sea-level change, it has potential for correlation on various scales. Palaeomagnetic results show that the sediments predate the Blake Event, which confirms that this reversal excursion is relatively young. The U/Th age of the uppermost part of the Eemian sequence is 118.2 ± 6.3 ka.