The Lessines borehole was drilled in the Dender valley. Sedimentary rocks of this borehole are subdivided in four informal lithostratigraphic units. Units I and II, dated as Uper Ordovician (graptolites, chitinozoans, acritarchs), show a progressive transition from thin- to medium-bedded mudstone-siltstone rhythmic alternations to black shales. These sediments were mostly deposited by turbiditic flows (high and low density) in a deep clastic lower slope to basin plain setting. Unit III, formed by thin- and wavy-bedded siltstone ("quartzophyllades') of Tremadocian age (acritarchs), is interpreted as a fine-grained turbidite sequence on a depositional slope. Unit IV, represents a rather uniform claystone facies from the Lower or Middle Cambrian age (acritarchs). Correlations with outcrops at the southern border of the Brabant Massif are proposed. -English summary ; info:eu-repo/semantics/published