Heist-op-den-Berg Member

The information on this page is a summary description.
The full formal description is available here: Heist-op-den-Berg Member

Abbreviation KlHe
Parent unit Kasterlee Formation
Child units
Lithological description In its type area around the hills of Heist-op-den-Berg and Beerzel up to Olen more to the north, the Heist-op-den-Berg Member can be easily recognized by the yellow-brownish, due to oxidation, well-sorted fine-grained sand with a very low glauconite content and the occurrence of thin grey and thick purple clay intercalations. The base of the member can be placed at the base of the first thick purple clay layer (>10 cm). The glauconite content of the sandy layers in the Heist-op-den-Berg Member is similar to the underlying Beerzel Member sand (2–4%, glauconite/quartz ratio of 0.03–0.05). Also the grain size distribution of the sandy intercalations is very similar to the Beerzel Member, well sorted with a mode at ~185 µm, though with a slightly larger fine fraction. Both feldspar content (5–6%, feldspar/quartz ratio of 0.07–0.08) and content of dioctahedral 2:1 Al-rich layer silicates (7–9%, 2:1 Al-clay/quartz ratio of 0.09–0.12) are similar to the Beerzel Member. In contrast to the Beerzel Member, The Heist-op-den-Berg Member sand layers contain more kaolinite (5–7%, kaolinite/2:1 Al-clay ratio of 0.6–1.0) indicating an increased component of continental sediment supply. The clay layers are mainly composed of 2:1 Al-clays (32– 44%, 2:1 Al-clay/quartz ratio of 0.9–2.3) and kaolinite (20–25%, kaolinite/2:1 Al-clay ratio of 0.5–0.6), and a considerable amount of goethite is present as well (2–4%, goethite/glauconite ratio of 0.3–0.7). The Heist-op-den-Berg Member also occurs consistently north and northeast of its type area, where it is buried deeper under younger Neogene and Quaternary sediments and can only be sampled in cores. There as well, the member is characterized by an alternation of fine sand and grey clay layers. In contrast to the type area, the sandy intercalations have a green colour due to an increased glauconite content (Vandenberghe et al., 2020). Both on CPT’s and borehole logs the sand-clay alternation can be easily recognized based on the fluctuating qc and gamma-ray signals.
Age Dinoflagellate cyst biozone DN10 was identified in the Heist-op-den-Berg Member (ON-Dessel-2 borehole 031W0338 / kb17d31w-B299), attributing a late Tortonian to Messinian Miocene age to this member.
Thickness In the type section, the Heist-op-den-Berg Member is cut off by a Quaternary cover and does not represent the initial thickness. Based on CPT’s near the type section, approximately 4 m of Heist-op-den-Berg Member is present on top of the hills (Verhaegen et al., 2020). Towards the north, the thickness fluctuates between 2 and 5 m, with an apparent general decrease towards the northeast where the overlying Retie Member strongly increases in thickness.
Area of occurrence The Heist-op-den-Berg Member occurs consistently in the southern, northern and northeastern sections of the Kasterlee Formation occurrence area. Only in the northwestern area, west of Kasterlee, the member is absent.
Type locality The proposed type section of the lower three members of the Kasterlee Formation, including the Heist-op-den-Berg Member, is the sunken lane atop the hill of Heist-op-den-Berg (DOV TO-20140919 and TO-20190617). The type section is described in detail in Verhaegen et al. (2014) and Verhaegen et al. (2020). The member name was originally proposed after a study of this section by Fobe (1995).
Alternative names ‘Clayey Kasterlee’ unit (Vandenberghe et al., 2020), formerly part of the at the time not yet subdivided Kasterlee Formation sensu De Meuter and Laga (1976) and Laga et al. (2001).
Authors Verhaegen, J. & Vandenberghe, N.
Date 01/09/2023
Cite as Verhaegen, J. & Vandenberghe, N., 2023. The Heist-op-den-Berg Member, 01/09/2023. National Commission for Stratigraphy Belgium. http://ncs.naturalsciences.be/lithostratigraphy/Heist-op-den-Berg-Member
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