Blandijnberg

Millions of years ago, during the Paleogene and Neogene, most of our region was submerged by the sea. Today, the subsurface around Ghent is primarily composed of Eocene deposits - around 50 million years old. They belong to the Gentbrugge Formation, a package that is well known in the subsurface of West and East Flanders. After the formation of these packages, the deposition in the Eocene Sea did not stop. Layer after layer, more sand, silt, and clay deposits were laid down, totaling hundreds of meters thick. The last time the sea flooded most of Flanders was during the late Miocene, the so-called "Diestian Sea." From then on, the sea retreated towards the northeast, and younger marine sediments can still be found in the region of Antwerp and in the Kempen. After the retreat of the sea, during the Pliocene and especially the Quaternary, continental processes began, including a river system that started to cut into the former seabed. With this information, we can return to the story of Blandijnberg. If we look at which sedimentary formations are present in Blandijnberg, the pieces of the puzzle come together. According to the geological map (or take a look at the 'virtual boring at https://www.dov.vlaanderen.be/portaal/?module=verkenner), we find that in the hill the formations of Aalter, Lede, and Maldegem can be found, each younger than the Gentbrugge Formation that we find around Blandijnberg. The core of the story is that Blandijnberg is a witness hill. These younger formations were originally deposited over a much larger area, which you can also see when you trace the colors back to the first map. It is the later erosion that has removed a large part of these packages. This erosion presumably corresponds to the formation of the river basins of the Leie and the Scheldt. Typical of rivers in this type of substrate, they have relatively flat and wide valleys, which further emphasizes the relief of Blandijnberg. The formation of the hill is primarily a matter of not having been eroded yet. The hill bears witness to the presence of these formations. Sometimes, it is also referred to as a remnant hill. Possibly, at this location, the packages were just a bit more resistant than what was surrounding them, making them less easily eroded. Indeed, at the top of Blandijnberg lies a heavy clay (Maldegem Formation). A clearer example of this can be found in the hills of the Flemish Ardennes and the Hageland, where iron sandstones from the late Miocene form a protective capstone on the tops of the hills.

Pascal Brackman