Decalcification of marine clay soils connected with decalcification during silting

Abstract

The marine clay area in The Netherlands consists largely of soils which are deposited in various periods of the Subatlanticum. In the 11th century man began to protect these areas from flooding by means of dikes. A part of the soils is now decalcified to variable depths. In general, the strongest decalcification phenomena are to be found in the oldest polders. However, the length of time since enclosure cannot be considered the only or even the most important factor for these variations. Decalcification following enclosure is preceded by a more intensive decalcification during silting. During this stage both supply and leaching of CaCO 3 take place at a variable rate. The way in which they differ from place to place and the changes they are subjected to during silting are made clear by analysis. It is concluded that the variable conditions during silting are the most important cause of present-day variations in CaCO 3 content and depth of decalcification in the marine clay soils of The Netherlands.