An Early Oligocene oil seepage at the southern rim of the North Sea Basin, near Leuven (Belgium)

Abstract

A prominent chocolate-coloured horizon at the top of the Kerkom Sand (Oligocene, Tongeren Group) near Pellenberg in the Leuven area (Belgium), has traditionally been interpreted as the illuvial zone of a podsol type soil. Observed features however are equally compatible with an origin as an oil-saturated reservoir sand. In fact, organic geochemical analyses indicate strongly that a fossil oil seepage is the most likely interpretation. The time of oil impregnation may be related to an important tectonic re-arrangement, which started at the very end of the Eocene, and probably triggered the leakage and migration of oil from traps in the southwest of the Netherlands. The oil migrated through porous sands up the gentle northern flank of the Brabant Massif, guided by clayey seals till it reached the surface. The presence of a fossil oil seepage in the Leuven area, means that possible traps, downdip of the Pellenberg outcrop, may contain accumulations of oil.