Kasterlee Formation

The information on this page is a summary description.
The full formal description is available here: Kasterlee Formation

Abbreviation Kl
Parent unit
Child units Hallaar Member, Beerzel Member, Heist-op-den-Berg Member, Lichtaart Member
Lithological description The main properties allowing to identify the classical Kasterlee Formation in its type area are undoubtedly the fine sand grain-size compared to the medium sand grain-size of the underlying Diest Formation and a moderate to low glauconite content giving the sand a colour from grey to green depending on the content. No grain-size contrast with the overlying Poederlee Sand exists but the boundary is marked by the characteristic Hukkelberg Gravel layer at the base of the latter. Where the Kasterlee Formation is almost devoid of glauconite grains and overlain or laterally bordered by Mol Sand, the boundary can be debatable. The Kasterlee Formation contains no carbonate and calcareous fossils are absent. Dinoflagellate cysts do occur. Muscovite flakes are common. A basal flint gravel is only observed at southern locations while otherwise no basal gravel is present. Recent comprehensive studies of the Kasterlee Formation since the earlier review by Laga et al. (2001) have justified the subdivision into members. A thin basal part with reworked coarser Diest Formation sand, containing a larger amount of glauconite pellets and a bimodal grain-size distribution, is generally recognised and named the Hallaar Member. A clayey facies occurs in the east and south of the formation, named the Heist-op-den-Berg Member; it is characterized by an alternation of cm- to dm-scale fine sand and grey clay layers. A fine sand unit with low glauconite content named the Beerzel Member only occurs locally between the Hallaar and Heist-op-den-Berg members. In the east of the formation distribution area, a pale grey quartz sand practically without glauconite pellets occurs systematically above the Heist-op-den-Berg Member. In the archives of the Geological Survey of Belgium this facies was incorporated into the Kasterlee Formation although its colour and quartz composition relate it lithostratigraphically to the Mol Sand. The difference with the classical Mol Sand can be made by the presence of a coarser size fraction in the latter. The name of Retie Member is proposed for this pale grey facies which for geometrical, paleogeographical reasons, and for stratigraphical nomenclature continuity, could be grouped in the Kasterlee Formation. However it is chosen to rank the Retie Member as a lithostratigraphic member of the Mol Sand Formation because of its pale grey colour and its quartz composition (for a discussion see Vandenberghe et al., 2020). In this subdivision of the Kasterlee Formation, the classical fine-grained and pale green sand type of the previous Kasterlee Formation definitions, in the northwest of the formation occurrence area, needs to be defined as a member within the formation and the name Lichtaart Member is proposed for it.
Age Dinoflagellate cyst biozone DN10 was identified in the Lichtaart Member (Rees borehole, 017E0399; kb8d17e-B495) and in the Heist-op-den-Berg Member (ON-Dessel-2 borehole 031W0338 / kb17d31w-B299), attributing a late Tortonian to Messinian Miocene age to the Kasterlee Formation.
Thickness In the type area Herentals-Lichtaart-Kasterlee a thickness of about 15 m is interpreted in sections drafted by Laga and Gulinck and confirmed by a CPT log interpretation ( 10-CPTE-138). In the boreholes Gierle (017W0158/kb8d17w-B14) and Rees (017E0399/kb8d17e-B495), in which only the Lichtaart Member occurs underlying the Poederlee Formation, thickness is reduced to 8 to 10 m. East of Kasterlee, with the Hallaar and Heist-op-den-Berg members, thicknesses between 5 and 10 m are interpreted in boreholes. In the Beerzel and Heist-op-den-Berg outcrops the thickness is 8 m and in the Olen outcrop 5 m; in both outcrops the Kasterlee Formation is overlain by Quaternary sediments.
Area of occurrence The paleogeographical map shows the distribution of the Kasterlee Formation and its Lichtaart (open marine), Beerzel (barrier sand) and Heist-op-den-Berg (clayey facies) members (Figure 28 1). The Hallaar Member with marked reworking of underlying Diest Formation sand occurs where the latter is most strongly eroded, namely in the coastal marine realm. The Retie Member distribution is similar to that of the Heist-op-den-Berg Member.
Type locality The type section of the Kasterlee Formation selected in the Lithostratigraphic scale of Belgium (2001) are occasional outcrops in the flanks of the hills between Herentals, Lichtaart and Kasterlee on the right bank of the Kleine Nete valley. In this stratotype area the Lichtaart Member is observed and overlain by Hukkelberg Gravel at the base of the Poederlee Sand. The base of the formation cannot be observed in these outcrops. However, a CPT on the hill near Kasterlee (10-CPTE-138) shows the base of the Lichtaart Member at +4.25 m TAW and the base of the formation at -2 m TAW. As the other members occur laterally of the classical Lichtaart Member, type sections for these are also relevant and discussed in these member descriptions. For the Hallaar, Beerzel and Heist-op-den-Berg members the sunken lane in Heist-op-den-Berg is proposed (TO-20140919 / TO-20190617).
Alternative names
Authors Verhaegen, J. & Vandenberghe, N.
Date 01/09/2023
Cite as Verhaegen, J. & Vandenberghe, N., 2023. The Kasterlee Formation, 01/09/2023. National Commission for Stratigraphy Belgium. http://ncs.naturalsciences.be/lithostratigraphy/Kasterlee-Formation
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