Contr. Tert. Quatern. Geol. 36(1-4) 59-72 15 figs, 1 tab Leiden, December 1999 The Campine clays and sands in northern Belgium: a depositional model relates to sea level fluctuations Frieda Bogemans Vrije Universiteit Brussels, Belgium Bogemans, Frieda. The Campine Clays and Sands in northern Belgium: a depositionalmodel related to sea level fluctuations.— Contr. Tert Quatem. Geol., 36(1-4): 59-72,15 figs, 1 tab. Leiden, December 1999. contributions in the northern area the discusses the conditions The first in a series of on Quaternary deposits Campine (Belgium), present paper of and well and the these deposition processes involved, as as a reconstruction of sedimentary palaeoenvironments stratigraphic position of strata within the the of these these consist of Quaternary sequence. Only sedimentary characteristics of the lowermostportion deposits are outlined; sandy-clayey sediments, reaching a thickness of more than 40 metres. Five sedimentological units are recognised; each unit accumulatedeither in an estuarine or in a fluvial-aeolianenvironment.The succession ofpalaeoenvironments occurs in an alternating pattern, with fluvial-aeolian The between these the result of level fluctuations within that deposits following upon estuarine strata. transitions are primarily sea particular stratigraphic interval. In contrast, the continuous evolution within estuarine deposits is tectonically induced. Key words — Lower quaternary estuarine environment, fluvial and aeolian deposits, sea level fluctuations. Dr F. Bogemans, Vrije Universiteit Brussel, Department ofGeography, Pleinlaan 2, B-1050 Brussels, Belgium. Contents interpretation of these deposits; he first of all pointed out addition that they displayed a complex composition. In to clay also sand, gravel and an alternation of sandy and Introduction p. 59 60 clayey sediments were observed. Delvaux interpreted these Study area p. as of a vast delta, in which constant physical changes Description of sedimentological units p. 60 part either marine fluvial conditions Reconstruction of environments 65 occurred; or predominated. depositional .... p. Rutot (1897) elaborated on Delvaux's data, and as- Discussion and conclusions p. 67 69 signed these deposits to a fluvio-lagoonal environment, Acknowledgements p. formed in the Meuse delta. References p. 70 Lorie's (1907) work is a milestone in geological studies of the Campine area. On the basis of field work data col- Introduction lected in 46 clay pits, he introduced four lithological units, discussed their mutual relationship and reconstructed the palaeosedimentary setting. With the exception of the The lowermost portion of the Quaternary sequence in the unit, which was considered to be marine in northern Campine area, known as the Campine Clays and uppermost Lorie favoured estuarine environ- Sands (Tavernier, 1942, 1954; Paepe & Vanhoorne, 1970, origin, an depositional 1976), has been a matter of dispute for over a century. ment. in the of the These strata consist of sandy and clayey sediments, and A change interpretation Campine area with Tavernier's reach a thickness of more than 40 metres in most areas deposits came (1942, 1954) papers: no were these considered to be estuarine or marine, but (Bogemans, 1994, 1997, 1998). The controversy concerns longer fluvial. How he arrived this conclusion is both the genesis and stratigraphic position of these depos- at not explained its. In the is made to reconstruct in the cited present paper, an attempt papers. their origin and the evolution of the sedimentary environ- Dricot (1961) rejected this interpretation. The large ment within the interval represented. The stratigraphic concentration of Chenopodiaceae, in combination with position ofthese strata within the Quaternary sequence will phanerogamic halophytes, that occur in the clay facies discussed in full in suggests the of a coast, more of a salt a forthcoming paper. vicinity precisely marsh. characteristics biotur- Delvaux (1891) was one of the first to present an Besides, granulometric and 60 bation traces in the underlying micaceous stratified fine Brabant) bordering in the north. In the southern Nether- sand pointed to a tidal flat depositional environment. lands and northern Belgium the Campine Clays and Sands Paepe & Vanhoorne(1970) bundled a series of obser- predominate in the Quaternary sequence. vations made in several clay pits, down to depths of 10 With the exception of the most southeasterly part of the metres. Two clay units were introduced, separated by a study area, the Cenozoic substratum is the Lillo Formation sand unit. In the uppermost clay unit at least three phases (de Meuter & Laga, 1976), which consists of grey and found be These sands. The lower is and of deposition were to distinguishable. are greyish brown shelly part clayey separated by phases of gully incisions, infill and peat contains several shell layers. In the upperpart, clay content formation. The whole series is situated in a tidal flat envi- gradually decreases as does the shell content. In the ronment. The underlying sand unit is offluvial and aeolian southeasterly part of the area either the Poederlee or Mol and is origin typified by peat horizons and periglacial formations form the upper part of the Cenozoic sequence. The lowermost unit has Formation is sand phenomena. clay sedimentary The Poederlee a fine, slightly glauconitic features identical to those of the uppermost unit; here only with small lenses of clay in the lower part, and a base of two clay members were observed. gravel of rounded quartz, flint and silicified carbonates. The Geys (1975, 1978) again introduced the fluvial origin upper part is occasionally strongly oxidised and contains interpretation, on the basis of granulometric analyses limoniticsandstones with shell moulds. The Mol Formation with His together microscopy of quartz grain morphology. contains pure white medium-fine to coarse sands, with conclusions, however, lack accuracy. lignitic horizons and lenses of micaceous clay; these are the The work is that of Kasse famous sands used in the most recent (1988, 1990), quartz glass industry. who followed the tripartite subdivision introduced by In between the above-mentionedCenozoic substratum Paepe & Vanhoorne (1970, 1976), as well as their genetic and the Campine Clays and Sands is the Merksplas Forma- interpretation, although he went into more detail here. On tion (de Meuter & Laga, 1976; Bogemans, 1994, 1997, basis of concluded of medium- the of a study heavy minerals, Kasse 1998), consisting grey, to coarse sands, spo- that both the and lower units had an unstable radically medium fine (180-250 fim), occasionally con- upper 'clay' heavy mineral association, supplied by the River Rhine. A taining gravel, shells and shell fragments. Silty to clayey stable heavy mineral association, derived from central lenses or layers, whether or not organic, as well as wood interca- scattered facies Belgium by rivers such as the Scheldt typifies the fragments are all over (Bogemans, 1994). lated unit. His observations involved section of The of the is situated in a to depths most easterly part study area more or less 30 metres, so that still portions of the Campine the borderregion ofthe Roer Valley Graben, which started Clays and Sands were not reached and remained uninter- to develop during the Cenozoic in response to the Alpine preted. stress regime (Ziegler, 1978). Tectonic units which have a the the direct impact on the geological history of area are Eastern and Western Campine Blocks, which are regions of STUDY AREA intermediatesubsidence to the west and southwest of the graben (Geluk et al., 1994). As a consequence, sedimentary thickness in the study area remained rather limited in comparison to the active graben itself. DESCRIPTION SEDIMENTOLOGICAL UNITS Unit A - a sandy complex Unit A is the lowermost memberof the Campine Clays and and is the Sands, present all over study area, reaching a of This size thickness 30 metres. sandy complex has a grain distribution from fine to medium fine ranging very sand, medium sand being less common. In some restricted places, mud deposits dominate. Besides typical minerals such as micas and glauconite, also vegetation remains, peaty dots, peat lumps and wood fragments are part of the general composition of Unit A. Within this unit two distinct facies Location of the Fig. 1. study area. are recognised: — Fades I: consists of fine to medium fine in very sand, which less than 63 distinct. These The study area is situated in northern Belgium, in the particles jum are are province ofAntwerp (Fig. 1), being known as the northern deposited as layers or are part of a stratum, the latter Campine area, with the Netherlands (province of Noord- forming wavy bedding or flasers (Fig. 2). 61 Fig. 3. Sedimentological description of Facies II of Unit A; for legend see appendix. — be thick with sand Fades II: may very (Fig. 3), gener- ally fine to medium fine. Medium sand, if present, is in a basal position, occasionally resulting in fining-up se- quences. The wavy bedding as well as flasers are strongly reduced. The horizontal stratification and planar cross bedding are. occasionally vague and containwater escape structures. Very typical in this facies is the presence of several reactivation surfaces. Where this facies is found at Fig. 2. Sedimentological description of Facies I of Unit A; for the of Unit soil horizon is sometimes legend see appendix. top A, a developed. Unit B - of successions Other typical structures are horizontal stratification, mas- a complex fining-up sive bedding, and low-angle and planar cross stratification. of Unit this unit is restricted the The orientation of planar cross stratification changes over Resting on top A, to limited depths. Scour structures, microfaults and deforma- southerly portion of the study area and may reach a thick- of9 metres there. It consists of successions tion structures also are very common. Less frequent are ness fining-up which from 2 to than with the bioturbation traces, small-scale ripple bedding and organic the numberof ranges more 7, vertical extension of succession 1 horizons. As noted above, in some restricted places of the mean a being metre.