Baarlo Formation

Formal (Van Adrichem Boogaert & Kouwe 1995).
Lithological description

Succession of dark-grey, brownish-grey or black mudstones, grading into grey or buff siltstones and very fine-grained sandstones. Large number of stacked coarsening-upward cycles of 20 to 300 meter thick, with a coarsening-upward overall trend. The mudstone intervals in the base of some cycles contain open-marine or brackish-water fossils (goniatites, Lingula). Fine- to medium-grained, (sub-)angular, moderately- to well-sorted sandstones are restricted to the tops of some of the cycles. In the Peel area and Gelderland certain sandstone intervals consist of coarse-grained sand and conglomerates. Coal seams typically restricted to the uppermost parts of depositional cycles and can be up to 2 m thick, but generally fall in the dm-range.

Depositional setting

Marine incursions, followed by delta progradation.
Overall regression reduced the deltaic realm to the basin centre. It was succeeded by coastal- and fluvial-plain deposition. Coal seams developed in delta-plain swamps. Clays, silts and very fine-grained sands were deposited in the distal part of the basin, and on the delta plain as overbank sediments.

Definition of lower boundary

Placed at the base of the lowermost coal seam and contact with the Geul Subgroup.

Definition of upper boundary

Placed at the base of the sandstone or sandy siltstone bed which truncates the top of the uppermost thick coarsening-upward sequence. It coincides with a shift in log patterns (GR, sonic, resistivity, etc.) to combined bell-funnel-shaped patterns. The transition into the overlying Ruurlo Formation is marked by the transition of thick coarsening-upward sequences into thinner, combined fining- and coarsening-upward cycles.

Thickness indication
Up to 876 m in LTG-01.
Geographical distribution
Regional correlation
UK: Westoe Coal Formation; GER: Witten and Bochum Formations; BEL: Chatalet Formation.
late Bashkirian.
Depth (thickness) AH:
2134 - 2927 m (793 m)
Depth (thickness) AH:
3777 - 4500 m (723 m)
Depth (thickness) AH:
2675 - 3216 m (541 m)
Origin of name
Named after the village of Baarlo in the south of the province of Limburg. The name corresponds to a former coal-mining unit, representing the Lower Westphalian A. This interval constitutes the bulk of this unit.
Previous name(s)
Reviewed by (date)
Tom van Hoof (2017).
Van Adrichem Boogaert, H.A. & Kouwe, W.F.P. 1995. Stratigraphic nomenclature of The Netherlands, revision and update by RGD and NOGEPA, Section C, Silesian. Mededelingen Rijks Geologische Dienst, 50, 1-40.
Cite as
TNO-GDN ([YEAR]). Baarlo Formation. In: Stratigraphic Nomenclature of the Netherlands, TNO – Geological Survey of the Netherlands. Accessed on [DATE] from