The introduction of geological concepts in 3D modeling results from ongoing subsurface mapping of the Cretaceous in Flanders. The Flemish Government, Department Environment, Nature and Energy has given VITO the assignment to expand this 3D model to the whole subsurface of Flanders. The main objective is to make it available via the free web application "Databank Ondergrond Vlaanderen" (http://dov.vlaanderen.be/).
First, all available data related to the Cretaceous in the study area were put into a relational data base. The latter contains descriptions of outcrops, borehole cores and cuttings and well logs. Existing maps were digitized, evaluated and relevant data were integrated. Where Cretaceous rocks were missing (e.g. Cenozoic sediments lying directly on Paleozoic basement), extra observation points were added. As the top of the Cretaceous becomes deeper to the N and NE, the well data become scarcer here. Therefore, additional data were retrieved from 2 seismic campaigns. Using this data base, a first 3D model for the top and base of the Cretaceous was generated using a fully automated interpolation. This model was used to detect errors in the data base. Secondly, 2 different geological concepts were introduced to guide the computer generated 3D modeling:
(1) A subdivision in fault blocks in the Cenozoic Roer Valley Graben and the adjacent zone. Within each fault block a directional interpolation was performed using a search ellipse with a preferential orientation, the size of which is defined by the width of each fault block and the distance between the observation points.
(2) A paleorelief at the top of the Lower Paleozoic Brabant Massif resulting from pronounced differential erosion. For each of the areas influenced by this paleorelief a directional interpolation was performed using a search ellipse and an anisotropy factor with a preferential orientation and a size determined by structures of the aeromagnetic survey map of Belgium.
Since not all fault blocks or specified areas contain sufficient amounts of data, manual correction and smoothing was necessary. Thirdly, the Cretaceous outcrop area was mapped by combining the Digital Elevation Model with a 3D model for the thickness of the Quaternary. As the base of the Quaternary coincides here with the top of the Cretaceous, the arithmetic difference of the latter with the generated 3D models for the top and base of the Cretaceous results in a thickness model and ultimately in the distribution contours for the Cretaceous.
Now the challenge lies within appending the remaining geological data to this 3D model in order to obtain a complete model for the subsoil of Flanders. The latter will make it possible to test the reliability of the data offered in the "Databank Ondergrond Vlaanderen".
