|Litostratigrafie van de kwartaire afzettingen in de overgangszone tussen de kustvlakte en de Vlaamse Vallei in Noordwest-België|
De Moor, G.; Heyse, I. (1975). Litostratigrafie van de kwartaire afzettingen in de overgangszone tussen de kustvlakte en de Vlaamse Vallei in Noordwest-België. Natuurwet. Tijdschr. 56(1-4): 85-109, 1 map
In: Natuurwetenschappelijk Tijdschrift. L. Walschot/Natuur- en Geneeskundige Vennootschap: Gand. ISSN 0770-1748, more
Lithology; Quaternary; Sediment analysis; Stratigraphy; ANE, Belgium [Marine Regions]
A large number of borings along a profile between Zomergem and Damme allows the authors to establish a local and non-hierarchic lithostratigraphy of the Quaternary sediments in the transition zone between the coastal plain and the Flemish Valley. That zone also marks a transition from the system of deep but filled Pleistocene thalwegs of the Flemish Valley and the coastal plain, to the hilly region of central West-Flanders where the Tertiary substratum rises up steeply. The sedimentology and the chronostratigraphy of the lithostratigraphic units have been studied; the extension and the superposition of these units are useful arguments for the morphogenesis and the morphochronology of the Flemish Valley. The following lithostratigraphic units have been recognized : -the formation of Zoetendale (Z of the section, Pl. I) : a complex of fan sediments of Rissian I age; -the formation of Adegem (A): a fluvio-periglacial sediment of Rissian I age and consisting mostly of reworked Tertiary sands; -the formations of Kaprijke (K), of Moerkerke (MO) and of Meetkerke (ME) : different facies of marine Eemian sediments, the top sequence of which still reaches the +2,5 level; -the formation of Oostwinkel (0): a complex of fluviatile, partially perimarine sediments of Eemian age, interdigitating with tidal-flat sediments of the Meetkerke formation; -the formations of Ronsele (R) and Darome (DA): a fan sediment of Eowürmian age; -the formation of Eeklo (E): a facies of the fluvio-periglacial sediments of Würmian pleniglacial age in the Flemish Valley; -the formation of Maldegem (MA): a complex of niveo-eolian and eolian Neowürmian sediments (cover sands) and of tardiglacial and Holocene eolian sediments (dune sands), principally of local origin; -the formation of Burkel (B): a complex of tardiglacial and Holocene brooklet and depression sediments; -the formation of Nieuwmunster (N): belonging to the Holocene surface peat of the coastal plain; -the formation of Dunkirk (DU): a complex of marine post-Atlantic sediments. An important incision occurred before the deposition of each of the formations of Zoetendale and Adegem, before that of the complex of the formations of Kaprijke- Moerkerke-Meetkerke-Oostwinkel, just as before that of the formation of Ronsele-Damme. Each of those incisions may have affected the Tertiary substratum, the surface of which has a polychronic character. Within the area, the period of maximal deepening and of most important scooping preceded the deposition of the formation of Adegem. During the Eowürmian incision the surface of the Eemian formations has been deeply eroded there. A minor incision occurred at the end of the tardiglacial and in the beginning of the Holocene. The incision of the base of the formation of Kaprijke reached the level -25, probably because of the tidal currents in the large, digitated bay of the Flemish Valley during the Eemian high-sea level. The other incisions are glacio-eustatic and occurred while permafrost did not exist, either at the beginning of a glacial period with a falling sea level or at the end with a low but raising one. The morphologic impact of those incisions has been influenced by the intensity and the duration as well as by the speed of the oscillation. During humid and periglacial periods of Rissian and Würmian age, important climatic sediments have filled up the thalwegs in the Flemish Valley. The Eemian deposits have a eustatic origin. The Würmian aggradation did not stop after the filling up of the Eowürmian incisions by means of alluvial fan deposits, but continued, getting a more and more fluvio-periglacial character, and reached a level far above the top of the Eemian deposits. In such a manner a sandy and flat surface has been formed dipping gently to the north. By the deposition of the cover sands and the formation of sandy ridges (formation of Maldegem), the level of that surface has been heightened so that the Holocene marine transgression did not penetrate the Flemish Valley as far as the Eemian one did.The Flemish Valley may be considered as a region which, at least since the beginning of the Rissian, corresponds to a network of deep scoured thalwegs and interfluves and wherein the top of the Tertiary substratum always remained lower than in the surrounding regions. At present, that network is covered by a bulk of polychronic and polygenetic sediments. However, the accumulation surface, essentially of fluvio-periglacial origin and of Neowürmian age, remains below the level of the surrounding interfluves, except where small tributary valleys reach the Flemish Valley (as it is the case for the Depression of Beernem near Durmen).