4.2.3. Opgrimbie Member v15012016

3.     Opgrimbie Member

Authors: present ones, this volume

Description: The Opgrimbie Member consists of homogeneous sand and silty sand. The colour is pure and bright white, to grey, yellow and brown, and is dependent on local hydro- and/or pedological processes. Massive stratification is dominant, horizontal or oblique stratification may be present. Frost cracks, frost wedges and deformation structures can be present in the sediments, as well as thin (usually one pebble-thick) gravel horizons. Intercalated soil horizons, organic-rich layers, clay-enriched lamellae are frequently observed; the intercalated soils can be weak, well-developed or degraded, and their appearance depends on the parent material in which they developed. A cultural layer is common at the top.

The Opgrimbie Member covers the Tisselt Member (if present). In sequences, it can usually be distinguished from the overlying Achterbos Member (if present), essentially on account of colour and/or an intercalated organic-rich (soil) horizon or cultural layer.

Stratotype: Opgrimbie: N50°57’13” E5°38’52”

Area: Coversand and transitional area in Flanders.

Thickness: Up to several metres

Age: Late Weichselian (MIS2) and, occasionally, Holocene (MIS1) (see e.g. Bogemans and Vandenberghe, 2011; Derese et al. 2009; 2010a; 2010b; 2012; Vandenberghe et al., 2009).

Remarks: The Opgrimbie Member thus comprises the cover- and dune sands previously defined as the Wildert Member and the Hechtel Formation (but excluding the Kalmthout Member) by Gullentops et al. (2001).