Borsbeek Member

The information on this page is a summary description.
The full formal description is available here: Borsbeek Member

Abbreviation DiBo
Parent unit Diest Formation
Child units
Lithological description The Borsbeek Member as introduced by Goolaerts et al. (2020) is characterised by greenish-coloured, intensely bioturbated, heterogenous glauconiferous, fine-grained sand with an important clay-silt-very fine sand fraction (<125 µm) (28–46%, 62% at base) and variable amounts of median and coarse sand (>250 mm, high and variable (11–36%) in the lower half, small and stable (7-8%) in the upper half). It has a glauconite content of 30% throughout, except for a much higher content (45–60%) in the basal part. A basal gravel with reworked phosphorites and different types of flint and flint pebbles residing in the sandy matrix occurs in the lowermost meter. Large-scale sedimentary structures are absent, except for horizontal bedding. The sediment may have a mottled appearance on mechanically dug vertical walls. An anomalously high concentration of marine mammal fossils may occur both in the lower and the upper half of the deposit. The invertebrate fauna is relatively poorly diverse, with pycnodontids and pectinids occurring in beds, while disciniscid (lower part) and lingulid (upper part) brachiopods are generally found dispersed. Terebratulid brachiopods are locally abundant.
Age The age of the Borsbeek Member is middle Tortonian (upper Miocene). Dinoflagellates indicate the Amiculosphaera umbraculum Zone of Dybkjær & Piasecki (2010) and the DN8 Zone of de Verteuil & Norris (1996). Most probably, the base falls also within the Bolboforma metzmacheri Zone, which allows to situate it in the time interval between 9.54 and 8.8 Ma (Goolaerts et al., 2020).
Thickness The Borsbeek Member has an observed maximal thickness of 4.5-5 m. Due to the erosive nature of the base with the overlying Deurne Member, the member may be locally reduced to zero.
Area of occurrence The Borsbeek Member is currently identified in a small number of temporary outcrops in the Antwerp area, located to the S and SE of Antwerp city, mostly in the municipalities of Borsbeek, Mortsel and Deurne. In many localities, it may have been partially or even completely removed by erosion with only a lag deposit with reworked bones, pebbles and sandstone remaining at the base of the overlying Deurne Member (e.g. Rivierenhof gravel).
Type locality Temporary excavations near Antwerp International Airport (AIA), section LP1-A as described by Goolaerts et al. (2020).
Alternative names Temporary excavations near Antwerp International Airport (AIA), section LP1-A as described by Goolaerts et al. (2020).
Authors Goolaerts, S.
Date 01/09/2023
Cite as Goolaerts, S., 2023. The Borsbeek Member, 01/09/2023. National Commission for Stratigraphy Belgium.
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