Lithology and biostratigraphy of Upper Cretaceous-Paleocene carbonates in the Molenbeersel borehole (NE Belgium)

Abstract

The Molenbeersel well was drilled by the Belgian Geological Survey as a reconnaissance well in the Rur (=Roer) Valley Graben (NE Belgium). Paleocene and Upper Cretaceous (Upper Maastrichtian) carbonates were traversed between 1223--1283.17 m of which interval the major part was cored. A sedimentological and biostratigraphical analysis allows the recognition of three megasequences which correlate with thicker successions on the adjoining Brabant Massif, including the Maastrichtian type area. These megasequences testify to repeated flooding events on the inverted Rur Valley Block. Each of these is characterized by a basal conglomerate overlain by glauconite-rich deposits. In the upper two megasequences these deposits pass into pure calcareous strata. All deposits indicate shallow nearshore environments above storm wave base. Occasional emergence occurred as indicated by karstified horizons. Fossil assemblages belong to the boreal province with the exception of an immigration of Mediterranean organisms in the middle megasequence. This may be related to a period of tectonic relaxation of the Rur Valley Block during the Late Maastrichtian.