CRETACEOUS FLOODING OF THE BRABANT MASSIF AND THE LITHOSTRATIGRAPHIC CHARACTERISTICS OF ITS CHALK COVER IN NORTHERN BELGIUM
Chalk is the most characteristic facies type of the Upper Cretaceous in Belgium and the only Cretaceous rock type found on the central and northern parts of the Brabant Massif. Marine Cretaceous deposits gradually encroached the Brabant Massif from the south during transgressive pulses starting in the Cenomanian - Turonian, displaying chalk facies from the Coniacian onwards. The chalk cover on the northern part of the Brabant Massif and in the Campine basin was not installed until the late Santonian and Campanian, while inversion of the Rur Valley Graben prevented any sedimentation. The base of the chalk deposit is diachronic and may be laterally equivalent to more detrital, continental- marine facies. Flooding was gentle, covering a peneplanated landscape, while partly preserving the saprolitic paleosol and thus not influencing the chalky nature of the sediment. Peneplanation did not erase all irregularities in paleotopography, leading to differences in timing of the onset of marine sedimentation, in accommodation space and sediment thickness across the axis of the Brabant Massif. Subsequent uplift of the Brabant Massif relative to the Campine Basin led to progressive disappearance of the Maastrichtian and erosion cutting into the chalk in a southern direction. South of the axis of culmination of the Brabant Massif, in the southern half of West-Flanders, the chalk forms the latest Cretaceous formation, partially preserved. North of the axis of culmination, in the northern part of West- and East-Flanders and the westernmost part of the province of Antwerp, the chalk forms the earliest Cretaceous formation, equivalent to the more detritic sediments of the Campine basin which were supplied by the inverted Roer Valley Graben. In contrast to the Mons sedimentary-tectonic basin to the south, where the standard lithostratigraphical scale of the Belgian Cretaceous has been established, the Coniacian to Campanian chalk deposits on the Brabant Massif cannot be differentiated lithologically. A formal lithostratigraphic unit, the Nevele Formation, is introduced comprising all chalk deposits on the Brabant Massif.