Kunrade Formation
Kunrade Formation NEW
Name: Named after Kunrade, village in South Limburg.
Stratotype limestone quarry Kunderberg at Kunrade, commune of Voerendaal (NL South Limburg). Dutch geological survey outcrop 62B-9 and coordinates 195450 - 320.210.
Other quarries in the Dutch type area include the Schaelsberg section atSchin-op-Geul (Dutch geological archive 62A-236) and the geological monuments Midweg in Voerendaal (62B-79) (Felder & Bosch, 2005).
Parastratotype: borehole KS22 (63E222, X 238822, Y 191259, Z 91 m), depth range 362-411 m.
Lithological description: The Kunrade limestone consists of an alternation between compact and soft limestone beds, of unequal distribution through the formation. In the outcrop area the hard beds are affected by randomly oriented vertical cleavage planes. Their thickness reaches 75 cm. The hard beds are strongly cemented. Hard beds are used as building stone (Kunrader stone), debris of hard beds and soft layers are used in limestone kilns.
Lithological description in the parastratotype section in borehole KS22:
362-374 m: Alternation between yellowish-white compact and porous mostly fine-grained calcarenite. Irregular black laminae, composed of organic-rich Uranium-bearing clay.
The calcarenite shows many bioturbations (cylindrical decapod burrowings 1-3 cm wide and possibly decimeters long, with 1-2 mm thick white marly wall). Bioclasts are sorted according to grain-size variations; larger molluscs (pectinidae) were observed. Glauconite is rare.
374-383 m: Grey mostly fine-grained bioturbated calcarenite, with centimetric to decimetric coarser grained layers; alternation of poorly consolidated and more lithified bands; rare dark brown clayey laminae (origin for discrete silicifations) and lithified nodules; moldic porosity (mostly dissolved mollusc shells). At 381 m fossiliferous horizon rich in serpulids, echinoderms and molluscs. This interval most closely resembles the typical Maastrichtian "tufkrijt/tuffeau" calcarenite in the Kunrade facies.
383-393 m: Yellow fine-grained porous calcarenites with dark laminae, alternating with lithified bands affected by joints and incipient stylolites. Silicification becomes more apparent in the form of grey-coloured silicified bands and dark-grey to black flints. Admixture of grey marly laminated calcilutite. The compact bands are strongly bioturbated, displaying abundant burrowings filled with loose calcarenites and moldic porosity.
The crumbly, porous calcarenites disappear at the base of this unit.
393-398 m: Transition zone to chalk facies, with similar lithologies, except for yellow porous calcarenites, as the overlying interval.
398-411 m: Light-grey calcilutite to chalk with dark laminae; frequent lithified and partly silicified bands with thickness 10 to 35 cm.
Geographical distribution: The Kunrade Formation spans the same area as the underlying Dorne Formation in the eastern Campine mining district and is laterally grading into the Gulpen Formation in the western Campine mining district. The Kunrade Formation is also present in the Belgian part of the Roer Valley Graben. The formation continues into Dutch South Limburg, where the type locality is located. Interfingering with the Maastricht Formation and Lanaye Member of the Gulpen Formation complicates the mapping of the Kunrade Formation.
Thickness: ca 50 m.
Boundaries: Upper boundary: Hardground contact with the overlying Houthem Formation, corresponding to the Vroenhoven Horizon. The contact between the Houthem and Kunrade Formations occurring in the parastratotype KS22 at depth 362 m coincides with the highest gamma-ray peak in an interval with high gamma-ray signature, (based on Felder et al., 1985).
Lower boundary: rather inconspicuous transition to Dorne Formation, with increase in terrigenous fraction. In the Roer Valley Graben some residual sandy deposits, which can be assigned to the Dorne Formation, are underlying the Kunrade limestone.
Age and stratigraphic correlation:
Total range of the Kunrade Formation includes a major part of the Lanaye Member equivalent of the Gulpen Formation in the type area, and the lower part of the Maastricht Formation, up to the Emael Member (Felder & Bosch, 2005, p. 73). In the eastern Campine basin, the upper part of the Maastricht Formation (Nekum and Meerssen Members) is lacking, the remaining parts (equivalent to Emael to Valkenburg Members which cannot be distinguished as individual members) being expressed under the form of the Kunrade facies. The long-lasting hiatus at the end-Cretaceous is confirmed by the absence of the bioclast zonation: ecozones Vc-d, corresponding to the Nekum-Meerssen Members of the Upper Maastricht Formation in the Maastricht type area (Felder, 1994). The core of the Kunrade beds is probably developed in beds assigned to the Gronsveld member of the Maastricht Formation in the Maastricht type area.
Depositional environment and diagenetical significance:
The Cretaceous - Paleogene boundary at the top of the Kunrade Formation.
Differences in lithification between the Kunrade and Houthem Formations indicate a long hiatus in the sedimentation rate at the base of the Houthem Formation in the Campine Basin. A succession of comparable, but obviously diachronous, early diagenetic stages of lithification affect both Kunrade and Houthem Formations and developed during the periods of non-deposition and emersion respectively at the end of the Maastrichtian and of the Dano-Montian (cf. Swennen & Dusar, 1997). Swennen & Dusar (1997) described pervasive zoned equant calcite cementation in a shallow phreatic environment, developing after initial meteoric dogtooth cementation, dissolution and compaction, and predating the deposition of the overlying Houthem Formation. This phase is the cause for the repeated but non-cyclic bedding of the compact limestones in the Kunrade Formation. The upper boundary of the Kunrade Formation marks a sudden increase in compressive strength (bulk compressibility CB from 3 to 1, Poisson's Ratio increasing from 0.1 to 0.27, Young's Modulus E from 10 to 15 gPa; Schlumberger Mechanical Properties Log). As a result the compact beds in the Kunrade Formation are much harder than those in the Houthem Formation an by far surpass those of the Maastricht Formation. However, low-density low-velocity beds make up 60% of the total rock volume.
Weathering and diagenesis by meteoric waters is particularly affecting the 356-374 m interval, across the Cretaceous-Paleogene boundary and indicative of irregular deposition at the base of the Houthem Formation. It results in a characteristic spectrometric signature, influenced by organic-rich clays, with decimetric alternation of compact and porous beds.
Correlation of the 362 m gamma-ray peak with the Vroenhoven Horizon is tentative. The presence of a series of hardgrounds and clay layers within the 356-374 m interval leaves open the problem of the Cretaceous-Paleogene boundary in view of the findings at the Geulhemmerberg C/P boundary section (Jagt et al., 1996; Jagt, 1997), but the hiatus will only be greater on top of the Kunrade Formation.
The Kunrade Formation consists of creamy white calcarenites with finer texture than observed in the overlying Houthem Formation. Alternating compact and weak diagenetic bands are typical for the Kunrade facies. The two-fold subdivision at 374 m in the upper part of the Kunrade Formation (362-383 m) is based on diagenetic modifications, due to karstification accompanying the hiatus at the end of the Maastrichtian.
Silicified bands characterise the lower part of the Kunrade Formation (383-411 m), not unlike the lower Maastricht Formation and underlying Lanaye Member of the Upper Gulpen formation of the Maastricht-Visé type area. These occur at about one-meter intervals and make up to 25% of the total volume [because of the diameter of the cores it is not possible to determine the bedded or nodular character of the flint].
The etched surfaces of building stones display cross-bedded laminations, often perturbated by burrowings, occasionally with coarser-grained bioclast layers, not unlike the Brussels and Gobertange building stones of Eocene age.
Discussion:
Umbgrove (1926) provided the first detailed petrographic description of the 'Kunrader formatie' as distinctive from the Maastricht Formation, despite the fact that thicker 'tuffaceous' calcarenites not unlike the Maastricht Formation are intercalated in the Kunrade Formation.
Because of the transitional character between the calcarenite with flints and the calcarenite with lithified beds, this unit was described as the 'Kunrade facies of the Maastricht Formation' in Felder & Bosch (2005, p. 111). However, Felder & Bosch (2005, p. 113-114) provided the stratotype section.
The Kunrader stone is a durable building stone, widely used in South Limburg but unknown in Belgian Limburg. It is known as Vetschauer Kalk in the Aachen region.
The Kunrade 'facies' was erected again towards formation status, because of the difference in sedimentary facies, diagenesis and geotechnical properties, compared to the Maastricht Formation. Moreover, the Kunrade and Maastricht Formations are not stratigraphically equivalent, as the Kunrade Formation straddles the lower Maastricht Formation and Lanaye Member of the Gulpen Formation. The depositional area seems connected to the extension of the Dorne Formation and influenced by the inversion history of the Roer Valley Graben.
Parish house of St.-Lambertuskerk Maastricht: usual appearance of Kunrader building stone.
Kunrader stone with traces of lamination destroyed by bioturbation, St.-Lambertuskerk Maastricht
Cross-bedding in Kunrader stone at St-Dionysisuskerk Nyswiller
Additional references:
Swennen, R. & Dusar, M., 1997 - Diagenesis of Late Cretaceous to Paleocene carbonates in the Rur Valley Graben (Molenbeersel borehole, NE-Belgium). Ann. Soc. Géol. Nord, t. 5 (2ème série): 215-226.
Umbgrove, J.H.F., 1926. Bijdrage tot de kennis der Stratigraphie, Tektoniek en Petrographie van het Senoon in Zuid-Limburg. Leidsche Geologische Mededeelingen deel I aflevering 2: 255-332.
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