Integrated stratigraphic analysis of Lower Rupelian deposits (Oligocene) in the Belgian Basin

Abstract

Information from new borehole sections and cone penetration tests in the Rupelian type area has led to a reassessment of Lower Rupelian stratigraphy in the Belgian Basin. Deposits underlying the Boom Clay Formation in the type area are reclassified into the newly introduced Niel Sand Formation, including a lower Wintham Silt Member (new) and an upper Ruisbroek Sand Member (redefined). A new integrated stratigraphic framework is established for the Lower Rupelian, on the basis of grain-size, natural radioactivity, point resistance and calcareous nannoplankton data. These data are interpreted in terms of sequence stratigraphy. It is concluded that the lower part of the Rupelian stratotype is correlatable with the traditional «Upper Tongrian deposits» of Eastern Belgium, demonstrating once again the ambiguity of previous chronostratigraphic terminology.