Dorne Formation
Dorne Formation NEW
Name: Dorne, ancient hamlet of Opoeteren; the borehole site is located in the fields and woods (former Dornerheide) on the Campine plateau heights to the southeast of Dorne.
Synonyms: Benzenrade Member of the Vaals Formation, by Felder & Bosch (2005); Pre-Valkenburg strata (Gulpen Formation) , by Felder et al. (1985).
Stratotype: borehole KS22 (63E222, X 238822, Y 191259, Z 91 m), depth range 411-499 m
Stratotype of the synonymous Benzenrade Member of the Vaals Formation in South Limburg: outcrop near De Dael on the Putberg between Benzenrade and Ubachsberg (Dutch Geological Survey number 62B-376, Dutch coordinates 195.800 - 318.820) (Felder & Bosch, 2005).
Lithological description in the type section (borehole KS22):
411-418 m: Light-grey chalk with dark laminae; lithified and/or silicified bands with thicknesses 10 to 20 cm. Moldic porosity associated with coquina beds.
418-431 m: Light-grey chalk and silty chalk, with grey marly beds and bioturbations. Coarse dispersed glauconite grains in lower 1.50 m, above basal gravel, 2 cm thick.
431-439 m: Alternating beds of light-grey silty and marly chalk, becoming more sandy in lower half, with dispersed coarse quartz grains. The glauconite content increases downward, leading to light-greenish bioturbated marly sandstone beds; burrowings full of glauconite near the base. Basal layer with thickness 4 cm, composed of quartz granules floating in dark green clay.
439-450 m: Compact light-grey sandy chalk with dispersed coarse quartz grains and downward increasing glauconite content. Glauconite lenses and large desintegrating mollusc shells in the lower part. Basal gravel bed composed of rolled belemnites in clay matrix. Slightly reduced carbonate and clay contents with a minimum in the midst of the unit, fewer bedding planes as deduced from microresistivity log, generally high compressive strength, further characterise this unit. The reduced carbonate content is a feature shared with the underlying units.
450-469 m: Light greenish-grey marl with compact very sandy beds and strongly bioturbated less cohesive marly beds; large weathered mollusc shells. Frequent coarse-grained quartz lenses between 457-462 m and at base of unit.
Noteworthy is the clear eastward sedimentary dip observed in this unit, contrary to the random dip observed in the overlying sequences.
469-481 m: Light greenish-grey sandy marl to marly sandstone, with strongly bioturbated marly intervals; large weathered mollusc shells. An overall fining upwards trend may be deduced from gamma-ray and spectrometric readings with smaller jumps at 469 and 474 m.
481-487 m: Coarse-grained bright-green poorly consolidated calcareous sand. This very distinctive unit with low compressive strength is interpreted as a basal sequence of the overlying unit, composed of reworked material from the underlying unit.
487-499 m: Light greenish-grey marly sandstone. Frequent gravelly quartz lenses and glauconite-enriched burrows. This unit is mainly distinguished from the underlying units by the more irregular clay distribution in a basal coarsening-up sequence followed by two fining-up sequences. The more sandy beds possess higher porosity and less strength than the more clayey beds.
Possibly, the upper contact could be situated at the 490 m level: geophysical well logs show twin peaks characterised by higher clay and carbonate contents and better cementation, indicative for a hardground.
Geographical distribution: Eastern Campine mining district, laterally interfingering with the Gulpen Formation in the western Campine mining district; absent in the Rur Valley Graben, north of the Heerlerheide and Dilsen Faults. Continuing into Dutch South Limburg but width of subcrop, hence transition to the 'normal' Gulpen facies is variable.
Thickness: between 50 m in the east (Maasmechelen) and 100 m in the northwest (Meeuwen-Gruitrode).
Boundaries: gravel bed at the top of the formation; frequent gravel beds within the formation down to its base, which is possibly associated with a perforated hardground.
Underlying unit: Vaals Formation in the eastern Campine mining district. The contact is marked by a gravel bed overlying a hardground.
Overlying unit: Kunrade Formation, the lower part of which is equivalent to the Lanaye Member of the Gulpen Formation. The top is inconspicious, without much evidence for an erosive level which might correspond to the Lichtenberg Horizon (base Maastricht Formation in type locality).
Age and stratigraphic correlation: Upper Campanian to early Upper Maastrichtian, based on bioclast Ecozones II, extending into Ecozones III and IV (Felder, Bless & Meessen, 1985; Felder 1994, 2001). Jagt et al. (1987) assigned ammonites from the Benzenrade Sand to the Upper Campanian.
Although the lithofacies is different from the chalky type area, a series of events related to sea-level rise and fall or temperature equally affects both type area and Campine mining district. Based on these events, a tentative correlation of the units encountered in borehole KS22 with classical members of the Gulpen Formation would allow recognition of the following equivalents, corroborated by the bioclast zonation of Felder (xxxx):
- Lixhe Member (411-431 m), with gradual increase of marly and sandy components and basal gravel;
- Upper Vylen Member (431-439 m), containing already high-energy sediment components and another basal gravel;
- Lower Vylen Member (439-450 m);
- Beutenaken 2 (chalk) member (450-481 m);
- Beutenaken 1 (marl) member (481-487 m);
- Zeven Wegen Member (487-499 m).
The upper part of the Dorne Formation (411-439 m), as well as the lower part of the Kunrade Formation (assumed to be the Lanaye equivalent) coincides with Ecozone IV, possibly including the top of Ecozone III. The interval 439-450 m correzsponds to Ecozone III. The Beutenaken Members correspond to Ecozone IIc and the Zeven Wegen Member to Ecozone IIb.
Depositional environment: Marine calcareous and glauconitic silt in irregular sequences, with storm layers characterised by quartz gravel beds, and punctuated by hardgrounds, which can be correlated with hardgrounds affecting the Gulpen Formation or the contact with the Vaals Formation further south.
The upper sequence (411 - 419 m) is transitional to the overlying Kunrade Formation.
The upper part of the Dorne Formation (411 - 439 m) still displays the regularly bedded silty chalk facies, fairly well comparable to the type area. The base of this unit constitutes the sharp basis of a sequence characterised by intensive bedding planes observed on microresistivity logs. This most striking feature is typical for the eastern Campine basin and has been recognised on every dipmeter survey performed in this area. The top of the continuous bedding sequence is at 398 m, already within the Maastricht Formation, suggesting a continuous sequence from Gulpen to Maastricht Formation in this area. Beds average 25 cm in thickness but are rather irregular. Sedimentary bedding dips are well expressed but highly erratic, a phenomenom shared with the silex-rich lower part of the Kunrade Formation, from level 383 m downwards (assumed to correspond to the Lanaye Member).
Horizons corresponding to unit tops at 411, 418, 431 and 439 m have a hardground character. Velocity measurements provide the best evidence for this interpretation. Upwards increasing formation strenghts in the intervals between 411 and 439 m give these units a cyclic signature.
Below 439 m, the regularity of the sedimentary sequence is much less.
Low-Uranium clay appears as a minor, more regular constituent of the sedimentary column. The clay content is at a very low level in the Kunrade Formation, but slightly grades towards small gamma-ray peaks at 417 m and 439 m. An upward increasing carbonate trend is apparent in the interval 411-439 m.
The clay content as well as the Uranium level of the sediment column in the 439 - 499 m interval increase slightly, compared to overlying units. This feature will continue till the base of the Vaals Formation.
History:
The glauconiferous marly sand(stone) rich in coarse-grained sand and gravel beds forms the lateral equivalent of the chalks, corresponding to the major part of the Gulpen Formation. This facies sequence was elevated to the rank of formation next to the Gulpen Formation, based on the lithological differences, despite evidence for lateral transitional facies to more typical members of the Gulpen Formation. This peculiar sequence was previously known as "Pre-Valkenburg strata", named by Felder et al. (1985). The late P.J. Felder collaborated on the description of this formation which remained unpublished since 2001.
Coal exploration boreholes drilled early in the 20th century provided cuttings for low-quality stratigraphic interpretation of the Cretaceous overburden. Attempts of application of the established stratigraphic scale of the Mons basin, which was equally utilised in the Belgian part of the Maastricht type area, frequently resulted in correlation to the Cp3a unit (GeoDoc geological archives).
As the Dorne strata were deposited on the southern graben shoulder of the Roer Valley Graben, they inevitably continue into South Limburg (the Netherlands). In the Dutch stratigraphy, another approach was followed to classify these strata. The strata equivalent to the Dorne formation were grouped into a seventh member of the Vaals Formation, named the Benzenrade Sand, and attached to the previously established zonation of the Vaals Formation (Felder & Albers, 1975). Although the Dorne Formation is succedding to the Vaals Formation, we can not group both units and adhere to the Dutch stratigraphical nomenclature for the following reasons:
- Except for the transgressive surface at the lower boundary, there are no gravel beds within the Vaals Formation, which is more regular and uniform in its sediment distribution, testifying of a more quiescent tectonic regime.
- The sedimentary sequences of the Dorne Formation are time-equivalent to successive members of the Gulpen Formation, as may be deduced from geophysical well log correlations and Felder's ecozonation. The contact with the Gulpen Formation is not erosive as suggested in Felder & Bosch (2005), but interfingering as the proximal component of sedimentary-tectonic pulses cused by the inversion of the Roer Valley Graben punctuating the global sea level fluctuation.
Discussion: Forir (1903) already drew the attention to lateral facies variations in the Campine mining district. He described the local equivalents of the Zeven Wegen Chalk in the western and southern mining district as more detrital, more silicified; in the eastern mining district he found more facies and faunal resemblance to the Emscher Greensand of the Lower Rhine coal mining basin in Germany and even compared the facies of borehole KB10 Wijshagen-Donderslagheide to the Cenomanian of the Mons Basin.
Stainier (1926) established a subdivision for the Lower Gulpen Formation (corresponding to the succession Zevenwegen Chalk - Beutenaken Marl - Beutenaken Chalk as described in Felder et al. 1985) in the Houthalen area of the western Campine mining district but was unable to trace his subdivision into the Eisden area of the eastern Campine, where chalks were replaced by sandy sediments.
Felder et al. (1985) defined the Pre-Valkenburg strata in the eastern Campine mining district as a lateral equivalent of the Gulpen Formation. They mentioned the difference in lithology despite lateral continuity of strata, which could be deduced from seismic sections.
References
Felder, P.J. ; Bless, M.J.M. ; Demyttenaere, R. ; Dusar, M. ; Meessen, J.P. ; Robaszynski, F., 1985. Upper Cretaceous to early Tertiary Deposits (Santonian-Paleocene) in northeastern Belgium and South Limburg (The Netherlands) with reference to the Campanian - Maastrichtian. Geological Survey of Belgium Professional Paper 1985/1 N. 214: 151 p.
Lohest, M. ; Habets, A. ; Forir, H., 1903. Etude géologique des sondages exécutés en Campine et dans les régions avoisinantes. Annales de la Société géologique de Belgique 30 : M101.
Stainier, X., 1926. Le Crétacé de la Campine. Bulletin de la Société belge de Géologie 36 : 223-237.
Figure : Section of boreholes from Roer Valley Graben to the western mining district of the Campine Basin, showing gamma-ray well logs of the Cretaceous section.