The Diest Formation: a review of insights from the last decades

Abstract

Research conducted since the 1960s on the upper Miocene Diest Formation in NE Belgium is reviewed and integrated. Their lithology unites the deposits of the glauconiferous Diest Sand in one formation, though biozones and internal sedimentary structures strongly suggest the formation may agglomerate the deposits of two separate, successive sedimentary cycles. The lowermost cycle is thought to have deposited the "Hageland Diest sand" during the early or middle Tortonian. It contains the Diest Sand in the main outcrop area in Hageland, Zuiderkempen and central Limburg, and probably also the Deurne Member near the city of Antwerpen. It furthermore includes the lower part of the Dessel Member in the central Kempen and in the Belgian part of the Roer Valley Graben (RVG). The Hageland Diest cycle represents the infill of a large tidal inlet tributary to the southern North Sea bight, then situated over the southern Netherlands and the Lower Rhine embayment. The Hageland Diest sand has the composition of a marine deposit, yet the confined area of occurrence and the presence of tens of metres deep incisions at the base, set it apart. The confinement of the embayment, strong tides and a steady supply of coastal‐marine sand are invoked as the main driving forces that resulted in the distinctive geometry and internal architecture of the unit. The upper cycle is associated with the "Kempen Diest sand", which is found in the subsurface of the RVG and the Noorderkempen. It has a late Tortonian to earliest Messinian age with progressively younger ages occurring to the NW. It encompasses the upper part of the Dessel Member and the overlying, coarser Diest Sand, and correlates to most or all of the thickly developed Diessen Formation in The Netherlands. It is the deposit of a prograding marine delta, containing both marine components and continental components fed by the palaeo‐Meuse/Rhine river mouths. Accommodation space kept increasing during deposition, due to subsidence of the deposition area, especially inside the RVG but also in the Noorderkempen. Although there is a fair consensus on the above, many concrete points about the geometry and depositional history of the Diest Formation and even a definitive decision on its single or dual character remain to be sorted out. In addition, this review excludes the Flemish Hills sand and the Gruitrode Member from the Diest Formation.

The upper Miocene Deurne Member of the Diest Formation revisited: unexpected results from the study of a large temporary outcrop near Antwerp International Airport, Belgium

“…The Deurne Member outcrops generally expose marginally thin sequences, ranging from 0.2 up to 1 m and exceptionally up to 2 or 3 m, thus considerably thinner than the Diest Formation sequences of the Campine and Hageland areas, where sequences of more than 200 m are known (Houthuys et al, 2020). The by far thickest ever described interval attributed to the Deurne Member was exposed in an outcrop of 5.60 m and described by Bosselaers et al (2004) from observations made at the construction site of a new wing of the Maria Middelares (Monica) Hospital in Deurne in 2001, where, unfortunately, only the topmost 2.60 m could be studied and sampled.…”

A proposal for an updated and revised stratigraphical framework of the Miocene in the Achterhoek (eastern Netherlands)

“…14). Houthuys et al (2020) describe the top of the Belgian Diest Formation, deposited during the late Tortonian, Zone DN9 (Fig. 4).…”

Downstream Distribution and Postdepositional Mobilization of Cadmium in Alluvial Soils

“…In the present paper, we will use the term "Winterbeek" to refer to the river as a whole, and the names "Grote Beek," "Zwart Water," and "Hulpe" when reference is made to specifc stretches of the river. Te subsoil consists of the Diestian Formation, containing on average between 35 and 40% glauconite [39]. Although the region is characterized by the occurrence of sandy soils, mainly peat soils are found along the stream (Figure S1), as a result of waterlogging.…”