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

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 arc 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 implications of K-Ar glauconite dating of the Diest Formation on the paleogeography of the Upper Miocene in Belgium

The glauconite-rich Diest Formation in central and north Belgium contains sands in the Campine subsurface and the hilly Hageland area that can be distinguished from each other. The Hageland Diest Sands member contains no stratigraphically relevant fossils while in the Campine subsurface dinoflagellate cysts are common and show a stratigraphic range covering the entire Tortonian stage. K-Ar dates were determined for glauconite from 13 selected samples spread over both areas. A glauconite date corresponding to the earliest Tortonian indicates newly formed glauconite was incorporated into a greensand at the base of the Diest Formation in the central Campine area. All other dates point at reworked glauconite and can be organized in two groups, one reflecting a Burdigalian age and another reflecting a Langhian age. These data and the thickness and glauconite content of the Diest Formation imply massive reworking of older Miocene deposits. The paleogeographic implications of these data lead to the tentative recognition of two Tortonian sedimentary sequences. An older one corresponding to dinoflagellate biochron DN8 comprises the Deurne Member, part of the Dessel Member, the Hageland Diest member, the eastern Campine Diest member and some basal sands of the Diest Formation in the central Campine. A younger sequence corresponding to dinoilagellate biochrons DN9 and 10 was strongly influenced by the prograding proto-Rhine delta front in the Roer Valley Graben to the northeast. The subsiding Campine basin was filled from east to west during this second cycle

Essai d'application de la méthode radiométrique au strontium aux glauconies du néogène: le problème du traitement de l'échantillon avant analyse

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The implications of K-Ar glauconite dating of the Diest Formation on the paleogeography of the Upper Miocene in Belgium

The glauconite-rich Diest Formation in central and north Belgium contains sands in the Campine subsurface and the hilly Hageland area that can be distinguished from each other. The Hageland Diest Sands member contains no stratigraphically relevant fossils while in the Campine subsurface dinoflagellate cysts are common and show a stratigraphic range covering the entire Tortonian stage. K-Ar dates were determined for glauconite from 13 selected samples spread over both areas. A glauconite date corresponding to the earliest Tortonian indicates newly formed glauconite was incorporated into a greensand at the base of the Diest Formation in the central Campine area. All other dates point at reworked glauconite and can be organized in two groups, one reflecting a Burdigalian age and another reflecting a Langhian age. These data and the thickness and glauconite content of the Diest Formation imply massive reworking of older Miocene deposits. The paleogeographic implications of these data lead to the tentative recognition of two Tortonian sedimentary sequences. An older one corresponding to dinoflagellate biochron DN8 comprises the Deurne Member, part of the Dessel Member, the Hageland Diest member, the eastern Campine Diest member and some basal sands of the Diest Formation in the central Campine. A younger sequence corresponding to dinoflagellate biochrons DN9 and 10 was strongly influenced by the prograding proto-Rhine delta front in the Roer Valley Graben to the northeast. The subsiding Campine basin was filled from east to west during this second cycle.status: publishe