Development of Dunkirk III near Alkmaar, the Netherlands

Abstract

Dunkirk III sediments (pik clay, rekere clay, and del soils) in the province of Noord-Holland lie on top of tidal-flat deposits (Calais IV and Dunkirk O) and/or Holland peat with a time stratigraphic hiatus in between. Deposition during the Dunkirk III transgression probably took place in various phases under changing environmental conditions with varying sedimentation rates between AD 1050 and 1250. This conclusion is based on geological and historical data. The initial sedimentation phase is represented by a thin layer of clay rich in organic matter, deposited under slightly brackish conditions. In the following phase of virtual non-deposition, sediment accumulated under almost freshwater conditions. Soil micromorphological, pollenanalytical, and malacological data confirm soil formation during the initial sedimentation phase while agriculture continued. Between AD 1150 and 1250 the bulk of the Dunkirk III sediments were deposited under brackish conditions. The interrelationships between pik clay, rekere clay, and del soils are discussed.