Sedimentological aspects of the KIT boundary at Geulhemmerberg, Zuid Limburg, the Netherlands

Abstract

Traditionally, the K/T boundary in Zuid Limburg is placed at the Hardground of Vroenhoven between the Maastricht and Houthem Formations. The finding in the Curfs quarry and Geulhemmerberg of possible Paleocene microfossils below this hardground in a coarse-grained, well-bedded calcarenite unit with thin clay intercalations or clay pebbles excited new interest in the mode of deposition of this unit. The latter fills an irregular paleorelief, developed as a heavily burrowed hardground (Hardground of Berg en Terblijt), marking a hiatus at the top of the Maastichtian calcarenites. In galleries in the Geulhemmerberg, the fill of this paleorelief consists of a thinning-up and fining-up sequence of 1) coarse-grained fossil hash with thin clay intercalations, 2) debrisflow-like coarse calcarenites, 3) well-laminated HCS-like calcarenites, and 4) alternating clay and calcarenitic flaser-bedding. The inferred process of infilling is episodic storm-wave activity in ca 20-40 m waterdepth. The scarcity of burrowing in the unit below the traditional K/T boundary in an otherwise heavily burrowed section of Maastrichtian and Paleocene calcarenites, and the preservation in the unit of delicate sedimentary structures and relatively thick clay layers point to extraordinary sedimentary circumstances. These are difficult to explain, but not incompatible with deposition shortly after the Chicxulub impact.