Geologica Belgica

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Rik HOUTHUYS

A sedimentary model of the Brussels Sands, Eocene, Belgium

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Annexes

Mots-clés : Brussels Sands, sedimentary model, lateral accretion, breaching, flow section restriction.

Abstract

New observations in the central Belgian Brussels Sands (transition Lower to Middle Eocene) allow to build a consistent model of the sedimentary processes and facies relationships of the deposit. The Brussels Sands fill a 120 km long and 40 km wide lowstand complex valley incision, correlated with the Yp10 50.0 Ma global lowstand. A marine transgression penetrated into the incised valleys transforming them first into estuaries and then into a tidal marine embayment. The sediment fill has a highstand signature. Filling started at the western bank, probably fed by a continuous coastal drift inferred to have existed along the southern North Sea coast. The West to East lateral progradation of the embayment shore created the “westerly lateral accretion” arrangement which dominates the Brussels Sands sedimentary record. This arrangement contains many gravity flow deposits, thought to be caused by breach failure. That mechanism conveyed coarser-grained sand from the embayment shore environment to the embayment floor. As the hydraulic section of the embayment narrowed, “flow-section restriction” events became more frequent, on either local or regional scale, depending on the presence and magnitude of intraformational relief and inherited paleorelief highs. Due to the section restriction, flow currents were increased locally causing lateral and vertical erosion to generate a short-lived accommodation space increase. Sedimentation outpaced the space creation rate and the narrowing channels and scour pits were filled with thick cross beds. Each time after filling the local space, the westerly lateral accretion resumed. The embayment closed with the deposition of the coarse glauconite sands in the East of the basin. A successive sea-level rise, following Lu1 at 48.1 Ma, caused a marine ravinement to truncate at least 10 to 20 metres of the top of the Brussels Sands.

To cite this article

Rik HOUTHUYS, «A sedimentary model of the Brussels Sands, Eocene, Belgium», Geologica Belgica [En ligne], volume 14 (2011), number 1-2, URL : http://popups.ulg.ac.be/1374-8505/index.php?id=3205.

About: Rik HOUTHUYS

geoconsultant, Suikerkaai 8, B-1500 Halle, E-mail: rik.houthuys@telenet.be