Environmental Conditions and Paleowind Directions at the End Of

Geologie en Mijnbouw / Netherlands Journal of Geosciences 80 (2): 1-18 (2001)

Environmental conditions and paleowind directions at the end of the Weichselian Late Pleniglacial recorded in aeolian sediments and geomorphology (Twente, Eastern Netherlands)

Ko (J.) van Huissteden1'2, Jacques C.G. Schwan3 & Mark D. Bateman4

1 Vrije Universiteit, Faculty of Earth Sciences, De Boelelaan 1085,1081 HV Amsterdam, The Netherlands 2 corresponding author; e-mail 3 Mauritsstraat 35,3583 HH Utrecht, The Netherlands 4 Sheffield Centre for International Drylands Research, Department of Geography, Winter St., University of Sheffield Sheffield S10 2TN Great Britain

Manuscript received: September 2000; accepted in March 2001

Abstract

The Late Weichselian Pleniglacial wind regime in the eastern Netherlands is reconstructed by means of landform and sedimentological analysis.This analysis involves aeolian and fluvial landforms in the Dinkel river valley in theTwente region.The aeolian deposits considered here date from the Last Glacial Maximum (approximately 22 ka) to the start of the Boiling Inter- stadial at 14.7 ka. A major event in this period is the formation of a cryoturbation level caused by permafrost degradation, overlain by an erosional hiatus dated between 21 and 17 ka. Both features are attributed to a period of warmer and moister climate, causing permafrost degradation and erosion by surficial runoff. Thereafter aeolian activity prevailed under relatively arid conditions. A deflation surface was formed, the Beuningen Gravel Bed. This deflation surface is present in many Weichselian sections in the Nedierlands and the adjacent parts of Belgium and Germany. The deflation occurred concurrently with deposition of coversand at other places. The morphology of the coversand-landscape in the Dinkel valley was controlled by the relief of the pre-existing floodplain and the wind pattern. Coversand ridges consisting of low dunes accumulated near the margins of the active channel belt. Rel atively thick sand sheets occur in the leesides of the ridges, thin sand sheets are found at greater distance. Mainly westerly sand-transporting winds operated during winter and summer. In winter aeolian deposition occurred by fre quent and strong easterly winds also. On the smallest, local scale, the pattern of deposition was determined by the topography and moisture of the receiving surface. Coversand deposition came to an end with the formation of a sand sheet under relatively warm and less arid conditions. Coversand deposition continued into the Belling Interstadial; colonization of the coversand surface by vegetation probably has been delayed by nutrient-poor conditions.

Keywords: aeolian features, periglacial features, palaeoclimate, Weichselian, Last Glacial Maximum, Netherlands.

Introduction term 'coversands' is often used because the deposits tend to cover the underlying topography as a continu During the Weichselian Late Pleniglacial/Marine Iso ous mantle. tope Stage 2 aeolian deposition occurred over large Systematic studies of sedimentary environment of areas in the European lowlands bordering the ice the coversands were published by Ruegg (1983), sheet (Catt, 1977; Schwan, 1986,1988;Koster, 1988; Schwan (1986, 1987, 1988). Most of these deposits Kozarski & Nowaczyk, 1991; Kasse, 1997). Abundant have originated as sand sheets (Schwan, 1988), in sources of unconsolidated sediments, a sparse vegeta particular at the transition from the Pleniglacial to the tion and a subdued relief favoured the development Late Glacial (Kasse, 1997). Horizontal lamination or of an extensive aeolian sand belt (Kasse, 1997). The low angle cross-lamination prevails in the structure of

Geologie en Mijnbouw / Netherlands Journal of Geosciences 80(2) 2001 1

2 Geologie en Mijnbouw / Netherlands Journal of Geosciences 80(2) 2001

Downloaded from https://www.cambridge.org/core. IP address: 170.106.40.219, on 02 Oct 2021 at 21:20:50, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0016774600022277 LITHOSTRATIGRAPHY CHRONO- FACIES STRATIGRAHY van der Hammen, 1971 This paper, Van Huissteden, 1990 Younger Late Dryas Coversand II 1-8 Wierden Wierden Aeolian dunes with cross- Aller0d Usselo CD O Member Soil Member bedding and sandy texture £0 Earlier Dryas Younger B0lling Coversand I

O Aeolian sand sheets and low Lutterzand Older Lutterzand dunes with mainly horizontally Member Coversand I Member bedding and grain size ranging O Weichselian between silt and coarse sand Late Beunlngen Grcvel Bed Pleniglacial Succession of (fluvio)-aeolian Older Beverborg sands and cross-bedded Coversand I Member fluvial sands. Large cryoturbatic involutions at the top of this unit

Fig. 2. Chrono- and lithostratigraphy of the coversand deposits.

the Dutch-German border a few km north of the Lut The fluvio-aeolian sediments have been laid down as terzand. Additonal information is obtained from a overbank sediments of the river, being a mixture of small roadside exposure, Nicolaasstichting (Fig. 1). aeolian sand derived from dry channel beds and flood deposits generated during high river stages. These Coversand geomorphology in the Dinkel valley. overbank areas had a slightly higher elevation than the active channel belts. Exposures in these locations The Dinkel river is bordered to the west by ice- show an intercalation of fluvio-aeolian overbank sedi pushed ridges of Saalian age and to the east by out ments and channel deposits, suggesting frequent mi crops of shales and sandstones of Early Cretaceous gration of channel belts. A similar situation is found age. The northern part of the valley is a wide glacial in modern high arctic river plains subject to strong basin, the Nordhorn Basin, in which the Weichselian wind activity (Pissart et al., 1977, Good & Bryant, age deposits attain thicknesses of more than 25 m. On 1985, Dijkmans &T6rnqvist, 1991). The 'coversand geomorphological maps of the Dinkel valley (Maar- plains' on the geomorphological maps correspond leveld, 1971; Kleinsman et al., 1978) four main geo with these higher areas. The elevation difference be morphological elements can be distinguished on the tween coversand plains and the channel belt is still valley floor: the present river plain, coversand plains, visible as a terrain step in many locations. coversand ridges and younger (Holocene) inland dune fields (Fig.3). Based on more recent research in The present river plain. the area (Vandenberghe &Van Huissteden, 1988; Van Huissteden, 1990), the following genetical interpreta To a large extent, the course of the present Dinkel riv tion can be assigned to these units. er and its tributaries is inherited from an ancient pre cursor. The present river plain merely follows the The coversand plains. (low-lying) channel belts of the Weichselian Late Pleniglacial river system. Borehole data show that the On the 'coversand plains' the Beuningen Gravel Bed present river plain only partly originates from fluvial is covered by a thin veneer of coversand or is exposed reworking by the Holocene river system. Instead, at the surface (Van der Hammen & Wijmstra, 1971). parts are covered by only a thin veneer of Holocene Vandenberghe & Van Huissteden (1988) and Van overbank sediments overlying fluvial deposits of Huissteden (1990) re-interpreted the sediments un Weichselian Pleniglacial age, whereas locally deep derlying the BGB as fluvio-aeolian sediment deposit fluvial incisions are found that have been filled in up ed by a braided river system dating from the LGM. to the present floodplain level (Van Huissteden,

Geologie en Mijnbouw / Netherlands Journal of Geosciences 80(2) 2001 3

coversand ridge conspicuous coarse-grained coversand ridge floodplain

exposure ™ ^ urban area

1 km L Fig. 3. Geomorphological map of part of the Dinkel valley, showing the relation of morpho logical features of the coversand deposits with the river floodplain. Redrawn after Kleinsman et al., 1978. 2: Vrijdijk exposure; 3: Nicolaassrich- ting exposure. The present Dinkel river is locat ed just outside the southwest corner of the map.

1990). The fluvial incisions within the Late m), with very gentle slopes. Pleniglacial channel belt date from the Late Glacial The second phase (Wierden Member, Figs 2 & 4) (probably the Belling Interstadial) and have subse is of Late Glacial (mostly Late Dryas, 12.6-11.5 ka) quently been filled by fluvial sediments of Late age (Van der Hammen, 1971; Bateman &Van Huisste Glacial age (Van Huissteden, 1990). We consider the den, 1999). This unit consists of low dunes (Schwan, present river plain together with the previous unit as a 1988). They may overly a soil of Belling - Allered age single complex, representing a now fossil floodplain (Van der Hammen, 1971) or direcdy overly the older of Late Pleniglacial age that has been modified only coversands. In isolated locations aeolian reworking partly by later fluvial activity. may have been practically continuous, as is suggested by a Belling - Altered soil interfingering with aeolian The coversand ridges. sand in Fig 4. Dune formation and aeolian reworking during the Late Dryas was generally restricted to al This landform usually borders the Late Pleniglacial ready existing coversand ridges, generating localized channel belts on both sides (Fig. 3). Like the channel hummocky dune fields. However, on several locations system itself, the ridges have a N-S orientation in the dunes migrated onto the active floodplain, thereby southern part of the valley and NW-SE orientation in constricting or damming smaller floodplains (Van der its northern part. Two phases of coversand accumula Hammen &Wijmstra, 1971;Maarleveld, 1971). tion have formed the ridges (Van der Hammen, 1971; Fig. 4). The inland dune fields The first phase (Lutterzand Member, Figs 2 & 4) These represent landforms generated by aeolian re dates from the end of the Late Pleniglacial (Bateman working of the coversand ridges after severe land & Van Huissteden, 1999), after (or contemporaneous degradation caused by medieval farming practices with, see below) die formation of the BGB. In gener (Maarleveld, 1971).The dunes have steep slopes and al, the relief of the ridges is very subdued (less than 2 are strongly influenced by the presence of vegetation

4 Geologie en Mijnbouw / Netherlands Journal of Geosciences 80(2) 2001

Section L1 Kootwijk Formation

1 Wierden Member w ('Younger Coversands') e n ^_^_^^____^^^_ t e Lutterzand Member ('Older Coversands II')

Beuningen gravel bed

Beverborg Member

Planform Lutterzand section with subsections Legend bridge • approximate position of Late | sand nTTTTTsoM Pleniglacial channel belt margin | silt bedding planes N ILI | peat ~ silly layers 2 |° o oo gravel ! cross-lamination 10C- / '

A Shfd97065 OSL sample with age • 0.6+/-0.1 ' L3* ^3

Fig. 4. Synoptic section of the Lutterzand site showing the coversand stratigraphy and the position and ages of the OSL dates, after Bateman &Van Huissteden, 1999. Lower right: location of subsections in the Lutterzand area.

during their formation. Orientation of individual bonate and peptization using a sodium pyrophos dunes is inconspicuous, but the Lutterzand inland phate solution. dune field roughly shows a SE-NW orientation. Sedimentary features of the Late Pleniglacial Materials and methods. coversands.

The sections described below were studied by means Lutterzand section of detailed field sketches of the stratigraphy and sedi mentary structures. In the Lutterzand section, the po In the Lutterzand river-bank exposure a section of sition of subsections relative to each other and the 100 m length has been studied (Fig. 4, 5). topography of stratigraphical markers was deter mined using a tachymeter theodolite. Lacquer peels The lithostratigraphy of the section includes the Be were made at representative sites in the sections using verborg, Lutterzand and Wierden Members; the main Sigma Coatings CL33 profile varnish. Grainsize features of interest are the Beuningen Gravel Bed and analyses were carried out using a Fritsch Analysette the Lutterzand Member. Section LI is situated at the 22. laser particle sizer. The samples were pretreated margin of the active channel belt of the Late by boiling with 30 % H202 to remove organic materi Pleniglacial river, the other sections occupy positions al, followed by boiling with 10% HC1 to remove car- at former higher overbank areas.

Geologie en Mijnbouw / Netherlands Journal of Geosciences 80(2) 2001 5

SW NE N

https://www.cambridge.org/core L4 30 V -

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. IPaddress: Relief Beuningen Gravel Bed and surface Lutterzand Member Legend of section

170.106.40.219 | I lacquer peel

I | horizontal lamination/ 1 ' bedding , on [~=gj wavy lamination

02 Oct2021 at21:20:50 -ww, convolute lamination oa,.oo granule layers, gravel strings I 1 climbing adhesion 0 ' lamination r3||=| concordantly infilled wind scours , subjectto theCambridgeCore termsofuse,available at LAJ current ripple 3 ^^ cross-lamination g

Beuningen Gravel Bed o (base Lutterzand Member)

60 62 64 66 68 70 72 74 76

Fig. 5. Detailed sedimentological section of the Lutterzand Member in subsection L3 of the Lutterzand area. See fig. 4 for location of subsections. The Beverborg Member. wind scours. Also surficial running water occurred, as This is the basal unit, which consists of silty sands in indicated by small cross-bedded scours. Bedding and tercalated with cross-bedded coarse sands (not de lamination of the sand is generally even parallel, re picted in Fig. 5).This complex is of fluvio-aeolian ori sembling climbing translatant strata sensu Hunter gin, the silty sands represent fluvially reworked aeo- (1977). lian sands and the cross-bedded sands channel de In places, facies A is disturbed by cryoturbation posits. The Beverborg Member is at its top strongly and small frost fissures (up to a few cm width). The cryoturbated by large amplitude (0.5-0.8 m) cryotur- cryoturbations are discontinuous and of much small bations. The cryoturbations subsequently have been er size than those below the BGB (< 0.3 m). The disturbed by sand-filled frost cracks or sand veins presence of frost fissures testify of low (< 0%) mean (Van Huissteden et al., 2000). Both the cryoturba annual temperatures (e.g. Romanovskii, 1985). tions and cracks are truncated by the BGB. A typical Facies B is found only in section LI, just above the feature is a vertical platy structure of the finer grained gravel layer at the base of the section (Fig. 4). It con beds, indicating the former presence of permafrost sist of well-sorted sands with distinct climbing cur (Moletal., 1993). rent ripple lamination. The well-sorted material sug gest that facies B consists of fluvially reworked aeolian The Beuningen Gravel Bed. sand. The climbing ripple lamination indicates high In sections L2 through L4 the BGB is well developed, sediment supply, probably from erosion of aeolian de sloping towards the west in the direction of the pre posits upstream. sent river plain. It consists of one or a few strings of Facies C consists of well-sorted fine sands and silty gravel, with clast size rarely exceeding a centimeter. sands (Fig. 6). Locally, shallow scours filled with cross-bedded grav el occur at the base of the BGB. In section LI the It is horizontally bedded, without any significant syn- BGB in its typical facies is absent (Fig. 4). However, depositional cryogenic disturbance. Sedimentary near the base of the section a 20 cm thick layer of structures are very well preserved (Fig. 7, table 1). cross-bedded gravel occurs, which is probably a later Only at the top this facies is disturbed by cryoturba al equivalent of the BGB. The elevation of the BGB tion and ice-wedge casts probably dating from the shows considerable variations, it occurs at a lower po Late Dryas (Bateman & Van Huissteden, 1999). Indi sition near the former river channel (Fig. 5). The 'Be vidual beds show a very diverse internal structure. uningen Soil', a weakly developed arctic soil with The data of table 1 may be fitted in an idealized an fragipan charactistics (Vink & Sevink, 1971) under nual cycle of aeolian sedimentation proposed by lies the BGB. In the section it is recognized by its firm consistency, other macroscopically visible signs of soil formation are absent. 16T T7 ' 1

The Lutterzand Member. Four lithofacies types have been distinguished to cov er the variation in the sedimentary make-up of this unit. Facies A occurs at the base of the Lutterzand Mem ber in sections L2 and L3 (Fig. 5). It is generally less than 0.5 m thick, in section L2 it is the only represen tative of the Lutterzand Member. Compared to the other facies types, the material in facies A is less well- sorted. It consists of generally coarse sand with thin layers and lenses of granules and fine gravel. Com -2-1012345678 pared to the BGB, these gravel strings are discontinu grainsize phi value ous and lack the coarser (> 0.5 cm) components that are characteristic for the BGB. Frequently the coarse material is concentrated in small scours. The lenses of granules indicate the transport of quite coarse materi Fig. 6. Representative grainsize distributions of coversand deposits al at relatively high wind speeds. The deposition of ae- (two for each facies).Thin lines: horizontal parallel laminated sands from facies C; stippled: adhesion ripple sands from facies C (Lut olian sand has been interrupted frequently by defla terzand section); thick lines: coarse-grained layers with granules tion as is testified by discontinuous gravel strings and from facies D (unit C) in theVrijdijk section.

Geologie en Mijnbouw / Netherlands Journal of Geosciences 80(2) 2001 7

g: detail of lacquer peel C4: current ripple cross-lamination

b: structureless silt beds a structureless sand bed

e: gravel string h: subhorizontal parallel lamination

d: climbing adhesion ripple pseudo-cross-lamination

<— c: crinkly parallel lamination

lacquer peel C3

Fig. 7. Details of sedimentary structures in facies C of the Lutterzand Member in section L3 of the Lutterzand area. Photos show parts of lac quer peels, see fig. 5 for the lacquer peel locations in the section.

Table 1. Stratification types of facies C in the Lutterzand Member in the Lutterzand section. The letters in the column 'Stratification type' al so refer to examples in Fig. 7.

Characteristics Process Literature reference Stratification type

Structureless coarse sand Niveo-aeolian deposition Washburn, 1979; Schwan, 1986 Well-sorted, structureless silt Settling of windborne fines from suspension Schwan, 1986, 1988 Crinkly parallel lamination & Deposition on a damp surface Kocurek & Fielder, 1982 cross-lamination Adhesion ripple pseudo-cross- Deposition on a damp surface. Kocurek & Fielder, 1982 lamination Attitude of cross-lamination indicates sand transport direction Discontinuos monograin string Tractional particle transport at high This paper of fine gravel wind speed Wave-ripple cross-lamination Wave reworking in temporary, shallow bodies This paper of standing water

Climbing current-ripple Reworking of aeolian sand by local current flow This paper cross-lamination Subhorizontal parallel lamination Subritically climbing translatant strata resulting Hunter, 1977 from wind ripple migration

Schwan (1986). In winter, sand-snow mixtures have spring or summer, snow-melt and rainstorms will been deposited by generally strong winds, producing cause damp surface conditions and even standing wa- stratification type a upon melting of the snow. In ter locally. When sand-transporting winds occur coin-

8 Geologie en Mijnbouw / Netherlands Journal of Geosciences 80(2) 2001

Table 2. Stratification types of facies D. Letters in parenthesis in the colum 'Stratification type' refer to examples in Fig. 8.

Characteristics Process Literature reference Stratification type

Sand beds with subhorizontal, even lamination or Scouring and subsequent Schwan, 1986, 1988 incipient trough cross-bedding. Bed boundaries infilling by wind. with concave-upward shape and intersecting at low angles.

Trough cross-bedding in sand. The sand is Fluvial reworking of aeolian This paper distinctly coarser and dip of laminae is steeper than sand that of type i

Geologie en Mijnbouw / Netherlands Journal of Geosciences 80(2) 2001 9

j: cross-bedding of fluvial origin

5 err

microstructures attributed to sand accumulation around plant stems

i: subhorizontal even lamination/ 5 cm low angle cross-bedding

structureless coarse-grained beds alternating with parallel laminated medium sand (site 3 in fig. 1)

Fig. 8. Details of sedimentary structures in facies D of the Lutterzand Member in the Lutterzand section (section L4) and Nicolaasstichting section (lower right photo, site 3 in fig. 1). Photos from parts of lacquer peels.

Unit A. base resembles adhesion plane bed lamination cf. Ko- The basal unit A is correlative with the Beverborg curek & Fielder (1982). Because of similarity to strat Member in the Lutterzand. It consists of medium- ification type a in the Lutterzand section, the sandy coarse sand with large cryoturbations and small layers may result from (niveo-) aeolian deposition. frost fissures, similar to the top of the Beverborg The beds show convolute lamination at various Member in the Lutterzand. The upper boundary of scales (Fig 10). The small-scale convoluted lamina the unit is marked by a sharp erosive contact, trun tion indicates water-saturated conditions. However, cating the cryoturbations. This hiatus is a character the larger folds may be related to permafrost melting, istic part of the BGB although the gravel lag proper continuing after the cryoturbation and truncation of is lacking here. unit A. The erosional contact and the lowermost beds of unit B have been disturbed by a small fault, indi Unit B. cating ongoing deformation of the subsoil. The pond This unit is composed of alternating cm-thick silt and ing of water at the site may have originated from sub sand beds. The silty strata formed by settling from sidence due to ground ice thawing, and probably also suspension of windborne fines into shallow ponds. prevented gravel concentration of the BGB by runoff The grain-size of the sand increases towards the top. or deflation. The parallel lamination in the thicker sand beds at die

10 Geologie en Mijnbouw / Netherlands Journal of Geosciences 80(2) 2001

bedding plane

lamination

frost fissure

] A OSL dating sample

0.5 m

Unit C. lated to strong winds, suppressing vertical accumula In the upper unit, laminae with granule or fine-gravel tion. Also the abundant coarse grained material indi composition occur regularly in a matrix of medium to cates high wind stress besides the proximity of a coarse sand. This relatively coarse texture and preva course-grained sand source. lence of inclined bedding and scour-fill cross-bedding A lacquer peel from a similar site with the same are characteristics which this unit shares with fades D coarse-grained fades shows that the coarsest layers in the Lutterzand section. However, unit C is on aver are generally structureless, while intervening fine age distinctly coarser than fades D. Schwan (1988) grained layers exhibit parallel lamination (Nico- attributes this type of bedding to dune formation re laasstichting site, 3 in Fig. 1, 3; Fig. 8). The absence

Fig. 10. Details of the succession of units A, B and C in the Vrijdijk section, showing the hiatus between units A and B. Photo from lac quer peel. The vertical crack to the right of the centre of the peel is an artefact caused by peel handling.

Geologie en Mijnbouw / Netherlands Journal of Geosciences 80(2) 2001 11

10- SSE-NNW section f 5- E-W section

100 200 300 distance from exposure (m)

of lamination indicates a niveo-aeolian origin (Schwan, 17.6 and 13.9 kyr in both sections.The age reversal of 1986). Hence it is likely that the coarsest material was the dates in the Lutterzand section and Vrijdijk sec transported mainly in winter. tions is only apparent, since the dates in question dif The abundant coarse-grained material indicates a fer less than one standard deviation from each other. nearby, coarse-grained sand source. To check for a The datings and stratigraphic relations suggest that grain size trend within the ridge that may be indica facies C is restricted to the youngest part of the Lut tive for transport direction and location of the sand terzand Member. The top of facies D interfingers source, the ridge material has been sampled from with C (Fig. 5).The dating from facies C (13.9 kyr) is auger holes at 0.75 - 1 m below the present surface, younger than the start of the Belling Interstadial at in transects parallel and at right angles to the ridge 14.7 kyr (Van Geel et al., 1989; Kasse, 1997). Thus, strike, with a 25 - 50 m interval between the auger deposition of facies C (and part of D) continued into holes (Fig. 11). The weight percentage of coarse the Boiling interstadial s.l. grains (> 500 m) rapidly falls of going from east to The cryoturbation at the top of the Beverborg west. In the transect parallel to the ridge strike this Member, formation of the erosional hiatus and the trend is absent. formation of the BGB should be regarded as separate events. First, the cryoturbation level has been formed Discussion. (Fig. 4, section L3).The large size of the cryoturbations indicates permafrost degradation (Vanden- Chronology of aeolian erosion/sedimentation. berghe, 1988; French, 1996; Van Huissteden et al., 2000). Next, the hiatus is formed. Usually, this is as The geochronology of the sections is based on OSL sumed to be caused by the deflation that also concen dates (Bateman & Van Huissteden, 1999; Bateman et trated the BGB (Van der Hammen, 1971). However, al., in prep.; Figs. 4,8) and is summarized in table 3. at the Vrijdijk section (Figs. 9,10) a clear hiatus is The ages of the Lutterzand Member range between found while an overlying deflation lag is lacking. This

Table 3. OSL datings in ka BP in the Lutterzand and Vrijdijk sections and their relation to sedimentary facies and units. Dating results after Bateman &Van Huissteden (1999) and Bateman et al., in prep.

Lithostratigraphic Unit Observation site

Lutterzand section Vrijdijk section

Lutterzand Member Facies C: 13.9 Unit C (similar to facies D in Facies B and D: 17.6-16.1 Lutterzand): 16.4-14.8

Beuningen Gravel Bed 21-17 Beverborg Member 21.9 21.1

12 Geologie en Mijnbouw / Netherlands Journal of Geosciences 80(2) 2001

Downloaded from https://www.cambridge.org/core. IP address: 170.106.40.219, on 02 Oct 2021 at 21:20:50, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0016774600022277 demonstrates that at least part of the erosion preceded braided river channels on the active channel belt formation of the BGB deflation lag. of the river, combined with deposition of finer flu- Small gravel filled scours just below the BGB (Fig. vio-aeolian sands at slightly higher elevations on 4) suggest that surficial runoff in a dense and shallow inactive parts of the floodplain (Fig 12 A; Vanden channel network has been an important erosion berghe & Van Huissteden, 1988; Van Huissteden et process (Van Huissteden et al., 2000). Vandenberghe al., 2000) & Kasse, (1993) attribute this type of erosion to cry- 2. Permafrost degradation and formation of large opediment formation. However, at the same time cryoturbations between 21 and 17 kyr (Fig. 12B). some channel down-cutting occurred as testified by 3. Formation of a hiatus by surficial runoff (Van the coarse channel lag of probably the same age at Huissteden et al., 2000), during or shortly after section LI of the Lutterzand site. Also Kolstrup the permafrost degradation, combined with minor (1980) found evidence of channel activity associated channel downcutting (Fig. 12C). with the BGB. This indicates a phase of increased flu 4. Deflation and formation of a desert pavement (the vial activity. However, this Late Pleniglacial channel BGB) and the Beuningen Soil, partly contempora down-cutting is a minor feature compared with the neous with coversand sedimentation. Deposition deep fluvial incision that occurred during the Boiling of facies D sands as low dunes along the edge of interstadial. the active floodplain. During high river discharge, In the Lutterzand section, the age of the cryoturba- these dune sands have been fluvially reworked (fa tion level below the BGB and the BGB itself is brack cies B, intercalations of fluvial cross-bedding in fa eted between at least 21.9 kyr and 13.9 kyr, based on cies D at Lutterzand). At the same time, contin two consecutive dates in one site (Fig. 4). The forma ued deflation of the BGB, and deposition of facies tion of the cryoturbations and the hiatus occurred be A sand sheet deposits may have occurred on the tween 17 and 21 kyr (table 3). For the formation of higher terrace surfaces. During deposition of fa the BGB itself, a longer time span is assumed since cies A, frost processes in the soil were still active, ages up to 13.9 kyr have been found in sediments just but permafrost did not re-appear (Fig. 12D). above the BGB. 5. Deposition of facies C as a sheet-like sand body It is likely that deflation which concentrated the under moist conditions, and continued sedimenta gravel in the BGB occurred patch-wise, while at other tion of facies D (Fig. 12E). favourable sites coversands were deposited at the same time. Deflation has been pronounced on ex Areal pattern of distribution of the aeolian sands. posed sites, such as the 'coversand plains' or higher Combining the aeolian and fluvial morphology in Fig. areas of the Late Pleniglacial river plain, e.g. in sec 3 and the sedimentological data from the sections in tion L2 and L3 at the Lutterzand site (Bateman et al., the study area, three depositional sub-environments in prep). Also in other coversand areas of the Nether may be distinguished. These are: (i). Pudges forming lands and Belgium, the BGB is particularly well de along the active channel-margin, consisting of low veloped on higher areas such as river terraces and in- dunes without slipfaces, (ii). Relatively thick sand terfluves (Vandenberghe, 1985). At the same time, sheets in the leeside of ridges and (iii). Relatively thin terrain hollows and other favourable sites were sub sand sheets alternating with areas of deflation, at jected to rapid aeolian deposition. Thick accumula greater distance from the ridges. tions of coversands are found in headwater valleys In the Lutterzand section, the base of the Lut (Van der Hammen, 1951). terzand Member shows considerable elevation differ The so-called 'Beuningen Soil' (Vink & Sevink, ences representing terrain steps bordering the ancient 1971) formed during the deflation. The soil forma braid channel belts (Fig. 5). At the Vrijdijk section, tion postdates the cryoturbation, since the intense the same can be inferred from the present relief. The cryoturbation would have obliterated the fragipan greatest mass of the dune ridges is located on the characteristics of the soil. In the Lutterzand section higher side of the terrain slopes bordering the the soil is best developed where the BGB is also a palaeochannel in both the Vrijdijk section and Lut prominent feature. Soil formation is not in contradic terzand sections. The preferential location of the cov tion with contemporaneous erosion, if the erosion by ersand ridges along the slopes bordering the active deflation has been small as suggested above. channel belts may be attributed to 1) the presence of The following sequence of events can be recon vegetation, 2) the effect of wind velocity and sand structed for the Late Pleniglacial coversand succes transport rate reduction of these slopes (e.g. Pye & sion (Fig. 12): Tsoar, 1990) and 3) the effects of moisture differ 1. During the LGM, deposition of coarse sand in ences of the receiving surface.

Geologie en Mijnbouw / Netherlands Journal of Geosciences 80(2) 2001 13

decreasing aridity, wind strength Sand sheet deposition under moist conditions

sedimentation along rivers -17-14.7 kyr and in other topographic lows wind directions mainly deflation

Formation of Beuningen Gravel Bed, dunes, Increased aridity, strong wind activity sand sheets -21 -17 kyr

. Sheetflow erosion

downcutting?

High precipitation climatic event? Formation oferosional hiatus -21 -17 kyr

Large involutions

Climatic warming: (partial) permafrost degradation Formation of cryoturbatic level Last Glacial Maximum <21 kyr Aeolian deposition+periodic flooding

Braided river plain with distinct channel belts; fluvio-aeolian sedimentation and permafrost on inactive parts

Fig. 12. Succession of aeolian, fluvial and cryogenic processes on the Dinkel river floodplain during theWeichselian Late Pleniglacial.

Late Pleniglacial fluvial deposits rarely contain or cumulation may have occurred at the base of the ganic matter in appreciable amounts and the palyno- channel margin slopes (due to seepage and river wa logical data point to an open vegetation (Kolstrup, ter) and the flat terrace surface beyond the terrain 1980). Structures in the facies D sands do not indi steps (due to imperfect drainage). Since abundant ad cate a dense vegetation. Therefore, vegetation proba hesion ripple lamination is found at the Lutterzand bly did not play a major role in the accumulation of site, imperfect drainage is the most likely explanation the ridges. Aeolian sand accumulation on the higher for the ridge accumulation at that site. side of a terrain step can be generated by wind veloci Concluding, the combined effects of terrain steps ty reduction in the vortex on the leeside of the terrain and surface moisture distribution is the most likely step if the wind is directed upslope (e.g. the cliff top cause of coversand ridge accumulation at the upslope dunes described by Pye & Tsoar, 1990). This effect side of the channel margin slopes. This requires trans may have played a role at the Vrijdijk site. In the Lut- port of sand over the terrain steps in an upslope di terzand site the channel margin slope has been less rection, which is confirmed by the sedimentary struc steep (Fig. 5). High soil moisture promoting sand ac tures (see below).

14 Geologie en Mijnbouw / Netherlands Journal of Geosciences 80(2) 2001

Table 4. Indications for palaeowind directions in the Dinkel valley coversands of the Late Pleniglacial.

Site Sand-transporting palaeowind direction Indicator

Lutterzand section; Dinkel valley in general From west Presence of coversand ridges on (north) eastern valley sides Lutterzand section From north to southwest (facies C) Attitudes of adhesion ripple pseudo cross-lamination Dinkel valley (site 3, Vrijdijk dune ridge) From north to east Presence of coarse-grained coversand ridge to southwest and west of former channel belt

Vrijdijk dune ridge From northeast to east Grainsize trend along flowpath of wind

Geologie en Mijnbouw / Netherlands Journal of Geosciences 80(2) 2001 15

Downloaded from https://www.cambridge.org/core. IP address: 170.106.40.219, on 02 Oct 2021 at 21:20:50, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0016774600022277 transporting wind directions in summer and winter; wind strength. Syngenetic cryogenic structures are 2) Frequent easterly sand transporting winds in win absent in the subject facies.Facies D supposedly rep ter. Evidence for easterly wind directions during de resents a deposit of incipient dome dunes in which position of facies C at the start of the Boiling intersta- slip faces are absent. Although it formed in an envi dial is absent. ronment, which was distinctly drier than that of facies Christiansen & Svensson (1998, 1999) deduced a C, the soil-water regime permitted some growth of predominantly easterly wind direction from wind- vegetation. Facies D accumulations closest to the an polished boulders in Denmark. Our data suggest that cient channel belt suffered frequent reworking by strong easterly winds occasionally may have occurred flood-waters. also in the Netherlands during the Late Pleniglacial The succession of Late Pleniglacial events in the next to a prevailing westerly wind direction. The east study area is as follows: ern wind component may have been driven by the an- a) Fluvial deposition by a braided-river system and ticyclonic wind system over the Scandinavian ice cap buildup of permafrost during the Last Glacial Maxi (Meyer & Kottmeyer, 1989; Vandenberghe et al., mum; b) Permafrost degradation and formation of 1999). Based on the areal distribution pattern of loess large cryogenic involutions; c) Planation by surface and coversands in northwestern Europe, Schwan runoff; d) Formation of a desert pavement (=Beunin- (1986) and Huijzer & Vandenberghe (1998) assumed gen Gravel Bed). The establishment of this extensive wind directions from the northern quadrant for the deflation surface has been partly contemporaneous Late Pleniglacial. This general pattern of net north- with the deposition of coversand. south transport points to an additional northern com The morphology of the Late Pleniglacial cover- ponent, probably the resultant of northwesterly and sand-landscape in the Dinkel valley was controlled by northeasterly wind directions and the location of the the relief of the pre-existing floodplain. The slopes source area, the dry North Sea basin. bordering the floodplain acted as topographical barri To account for the data of table 4, three scale or ers which caused the wind to slow down and drop its ders of the process of aeolian particle transport must load. As a result, coversand ridges accumulated with be considered. Firstly, there is a net, long-term north preference near the margins of the active channel to south transport of sand and dust on a continental belt. The ridges consist of low, rather flat dunes. Rela scale, determined by both source area and prevailing tively thick sand sheets occur in their leesides. Thin wind directions. The second order process involves a sand sheets, alternating with deflation surfaces, are more limited areal context, e.g. the northern Euro found at greater distance from the ridges. pean lowland. Here, during all of the year, prevailing Palaeowind data from the study area suggest aeo westerly winds carry particles to their depositional lian particle transport from both westerly and easterly sites. In winter, aeolian sand transport is added to by directions. To account for this feature, three orders of strong easterly winds. In the third place the local pat magnitude of the process of aeolian particle transport tern of aeolian deposition is controlled by the topog must be considered. Firstly, there is a net, long-term raphy of the receiving site, i.e. by the topography of north to south transport of sand and dust on a conti the Dinkel floodplain, and also by the short-term di nental scale. The second order process involves a rectional fluctuations of high winds. more limited areal context, e.g. the northern Euro pean lowland. Here, during all of the year, mainly Conclusions. westerly winds carry particles to their depositional sites. In winter, aeolian sand transport is added to by In the study area four facies of aeolian sand and/or silt frequent easterly winds of generally great strength. In were identified. Facies A has a relatively coarse tex the third place the local pattern of aeolian deposition ture and contains deflation levels. Both of these fea will be controlled by the topography of the receiving tures suggest grain transport at high wind speed. site, i.e. by the topography of the Dinkel floodplain, Scours formed by current flow are present. Discon and also by the short-term directional fluctuations of tinuous involutions and numerous frost fissures relate high winds. to low winter temperatures.Facies B is of rare occur Our data confirm previous observations that cover rence. It consists of well-sorted sand laid down by flu sand deposition, including sand sheet formation, con vial reworking of windborne sand. Facies C is a sheet tinued during the early part of the Boiling Interstadi- like sand body with horizontal bedding and ample ev al. We suggest that nutrient-poor conditions of the idence of aeolian deposition on a damp or wet sur coversand surface may have retarded colonization by face. Laminae of coarser and finer texture tend to al vegetation, although other depositional features of the ternate and may result from seasonal variation in coversand indicate climatic amelioration.

16 Geologie en Mijnbouw / Netherlands Journal of Geosciences 80(2) 2001

Downloaded from https://www.cambridge.org/core. IP address: 170.106.40.219, on 02 Oct 2021 at 21:20:50, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0016774600022277 Acknowledgements. Kasse, C, 1997. Cold-climate aeolian sand-sheet formation in Northwestern Europe (c. 14-12.4 ka); a response to permafrost degradation and increased aridity. Permafrost and Periglacial We are indebted to Elsbeth Heijna and Edwin van Es- Processes 8: 295-311. pelo for their contribution during the fieldwork in the Kasse, C, 1999. Late Pleniglacial and Late Glacial aeolian phases Twente area. Martin Konert and his laboratory per in the Netherlands. In: Schirmer,W (ed.): Dunes and fossil soils. sonnel are thanked for performing the grainsize GeoArchaeoRhein 3: 61-82. analysis. We thank Dr. R.F.B. Isarin and Dr. M.E. Kleinsman, W.B., De Lange, G.W., Maarleveld, G.C. &Ten Cate, J.A.M., 1978. Geomorfologische kaart van Nederland 1:50.000 Donselaar for their constructive reviews. Blad 28 en blad 29 Almelo/Denekamp. Stichting voor Bodemkartering / Rijks Geologische Dienst (Wageningen/Haar- References. lem). Kocurek, G. & Fielder, G., 1982. Adhesion structures. Journal of Bateman, M.D. & Van Huissteden, J., 1999. The timing of last Sedimentary Petrology 52: 1229-1241. glacial periglacial and aeolian events, Twente, eastern Nether Kolstrup, E., 1980. Climate and stratigraphy in Northwestern Eu lands. Journal of Quaternary Science 14: 277-283. rope between 30,000 B.P. and 20,000 B.P., with special refer Bateman, M.D., Van Huissteden, J. & Kasse, C. in prep. Chronolo ence to The Netherlands. Mededelingen van de Rijks Geologi gy of cryostratigraphy and aeolian sedimentation during the Last sche Dienst 32-15: 181-253. Glacial termination in the Netherlands. Koster, E.A., 1988. 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