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4.2.4. Achterbos Member v 15012016

4.      Achterbos Member

Authors: present ones, this volume

Description: The Achterbos Member consists of (dull) greyish-yellow very well-sorted and loosely packed fine sand (mode between 125-250 µm) displaying cm- to dm-scale bedding caused by subtle variations in grain-size. Individual sublayers may contain up to 10% coarse sand (> 0.5 mm) or up to 10% silt and clay (< 63 µm). The origin of these sands can be traced back to deflated Podzols and the (aeolian) parent material they were formed in. The lower boundary of the unit is very clear if it overlays older aeolian deposits with soil development but less clear if the soil had been removed by aeolian deflation. In sedimentary sequences the unit is always laying on top; often an incipient soil can be observed in the top of this unit.

Stratotype: Interfluve between the Kleine Nete and the Breiloop (Kleine Nete catchment; N51°12'57", E5°05'27"), where these sands have produced a distinct morphology known as a drift sand landscape (Achterbos, Mol).

Area: Belgian sand belt

Thickness: From a few dm up to several meters.

Age: (late) Holocene (Derese et al., 2010a; Beerten et al., 2012, 2014)

Remarks: The Achterbos Member replaces the Kalmthout Member as defined in Gullentops et al. (2001). Aeolian sands (drift sands) belonging to this member are described in Beerten et al. (2012; 2014).