The information on this page is a summary description.
The full formal description is available here: Dorne Formation
| Abbreviation | |
| Parent unit | Chalk group |
| Child unit | |
| Lithological description | 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. |
| Age | 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. |
| Thickness | Between 50 m in the east (Maasmechelen) and 100 m in the northwest (Meeuwen-Gruitrode) |
| Area of occurrence | 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. |
| Type locality | 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) |
| Alternative names | Benzenrade Member of the Vaals Formation, by Felder & Bosch (2005); Pre-Valkenburg strata (Gulpen Formation), by Felder et al. (1985) |
| Authors | Dusar, M. & Lagrou, D. |
| Date | 01/01/2012 |
| Cite as | Dusar, M. & Lagrou, D., 2012. The Dorne Formation, 01/01/2012. National Commission for Stratigraphy Belgium. http://ncs.naturalsciences.be/lithostratigraphy/Dorne-Formation |
