GEOLOGY AND MORPHOLOGY OF A PART OF THE OOTMARSUM ICE-PUSHED RIDGE

M.W. van den Berg* and C. den Otter**

CONTENTS

I. INTRODUCTION

2. GEOLOGICAL SETTING

3. INTERNAL STRUCTURE OF THE OOTMARSUM RIDGE

4. MORPHOLOGICAL EXP RESSION OF THE LITHOLOGY

5. ABSTRACT

6. ACKNOWLEDGEMENTS

7. REFERENCES

*Soil Survey Institute and State Geological Survey, P.O. Box 98, 6700 AB Wageningen, the Netherlands **State Geological Survey, P.O. Box 58, 7240 AB Lochem, the Netherlands

35 VAN DEN BER.G DEN OTTER 36 M.W. & c.

I. INTRODUCTION 2. GEOLOGICAL SETTING

The finding of some artefacts on the western The find-spots of the artefacts are located on flank of the Ootmarsum push moraine ridge the western flank of a ridge that forms part of (Stapert, this issue) gave rise to a wish for a series of elevations that continues in a more insight into the geological setting of the northern direction, across the Dutch-German area concerned. border, into the county of Bentheim (fig. I). The Mapping Department of the State This ridge consists primarily of non-glacial Geological Survey carries out a systematic deposits, and was formed by ice-pushing in survey of the whole country. The results are the Saale period. The morpho-genetic pro­ published in a series of maps on a scale of cesses which have been of basic import­ I: 50,000. During the last days of the survey ance for the ultimate situation as we know for the sheets AlmeloJ Denekamp (28 E-29 it today can be divided into three groups: W), the above-mentioned finds were dis­ a) During the last stadial of the Saalian covered. These, as yet unpublished, survey Stage (fig. 2) (Zagwijn, 1973), the inland ice results form the basis of this short summary of sheets slided over a frozen subsoil, causing the geological outlines. More extensive data little disturbance of the subsoil. Periodically, will be published in the memoir to the sheet however, the glacier lobes of the same ice 28 E-29 W (Van den Berg, in prep.). Geomor­ sheet were able to cut deeply into the pre­ phological data are taken from an earlier glacial deposits and push them up into ridges. published Geomorphological Map of the This mechanism is not yet fully understood, Netherlands, sheet AlmeloJ Denekamp, scale although explanations have been offered by I: 50,000. Zagwijn (1975) and Jelgersma and Breeuwer

tentative m.an lumm,r temperature doling O· S· 10· IS· 20· subdivision Iyears 8,PJ of Iht conil. tundra fOll.l polOfotilhic

50.000 • •• II��' ,"f -l:., ..... -; ...... r - --' �___I �:1-7' '-..<:L :---J.. / / / I ...- /'/ /I y' / / V 1/ w / I z \ / / I c o ',[ / I u 100.000 E o Ql .ALMELO W o o

• BENTHEIM

• HENGELO 150.000 c o

10 km o L..-_--'-_-.Jf (/)

1--.:)lllZjd<;�d3D4. .. ""

1 1151::;.)161-17 200.000 Holst.inion • • Fig. 1. Physiographic picture of sheet 28E-29W and the adjacent county. of Bentheim. 1. push direction of the �'I Qdi Qh Saalian land ice lobes; 2.push moraine; push moraine, DinlHllodials 3. orinltr9tacials eroded; 4. Dutch-German border; 5. mapsheet Almelo/ Denekamp; Saalian outwash fans, partly covered by Fig. Climatic curve for the Late Pleistocene in the 6. 2. younger deposits; 7. section shown in fig. Netherlands (based on Zagwijn, 1975). 3. Geology and morphology of a part of the Ootmarsum ridge 37

w E

80 E

70 • • • • • • • • • 60

\ 50 ===== PUSH DIRECTION ',\ \ \ \ 40 E \ \ \ \ \ '\ 30 '\. \" \ c ,\ \ 20 \ � \ \ \ ...... \ \ ______,,",--.'�'.'�':".''-U. \ \ \ \ \

30

-- - ." . 40 :

50

60 i Site Middle Paleolithic 70 Artefacts o 2km ' L' __---'- __.....J 1 80

Fig. Schematic cross section through the Ootmarsum push moraine ridge. A. fine-grained Tertiary deposits; B. coarse­ 3. grained Middle Pleistocene deposits; C. ice-pushed strata; D. Saalian outwash fan; basal till of the Saalian ice sheet; F. E. Weichselian soliOuction fans.

(1975). The direction of push was, for the N-S map a very regular pattern is found on the section of the ridge, from the east; the E- W Ootmarsum ridge. This regular pattern is the section in the county of Bentheim has been response to the drumlinoid form of this part pushed up from the north (fig. I). of the ice-pushed ridge. This form is caused During the formation of the ridge, I by the overriding ice-sheet. glacial meltwater flowed over it, taking up A detailed description of the periglacial local material from the ridges, and thus processes and relat�d forms is given by many building up from this a major outwash fan on authors (e.g. Van der Hammen et al., 1967; the western flank (figs. I and 3). After the Maarieveld, 1976). Aeolian accumulation formation of the ridge and the outwash fans, forms are well known from this timespan, they the ice sheet flowed further south, meanwhile occur mainly in the lower areas between the overriding and strongly eroding the ridges; a ice-pushed ridges, and are very scarce on the basal till or the remains of it are found all over ridges themselves. Coversand accumulation is the ridges, and on the outwash fan. found on top of the solifluction fans that have b) Major erosion took place on the ridges been built up at the foot of the ridge (fig. 3), when periglacial conditions prevailed during each fan matching a-solifluction valley system parts of the Weichselian (fig. 2). The sparse (fig. 4). During part of the Late Pleniglacial vegetation cover during the sub-arctic and arc­ very severe and dry climatic conditions tic phases of this stage, together with the abun­ prevailed, presumably a polar desert; these dant snow meltwater and the strong terrain conditions are documented by a deflation level gradient on the slopes of the ridges, led characterized by an aeolized pebble and stone to the formation of solifluction valleys (figs. 4 layer. In the.lower areas this band is covered by and 5). According to the geomorphological coversand. On the Ootmarsum ridge aeolized 38 M.W. VAN DEN BERG DEN OTTER & C.

N s

497

Fig. 6. Cross section through the Mosbeek valley near the watermill of Bels. Holocene (anthropogenic) accu­ I. 494 mulation lying on top of the Weichselian basal gravel; 2. Weichselian solifluction head; ice-pushed strata. 3.

gravel and boulders, often reshaped into ventifacts, are found in the topsoil. From the detailed facies analyses of the periglacial sediments carried out by Ruegg tz2Z22l,rrr:oll:-:-:-:-:-:-:14�sl = 1.1 _-=-"�17 (1981, 1983), it appears that after the forma­ c=J2 tion of the aeolized stone layer (called: Fig. 4. Generalized distribution of different lithologies Beuningen Gravel Bed) mainly wet-aeolian outcropping on part of the Ootmarsum push moraine conditions prevailed together with permafrost ridge. Tertiary strata: heavy clay; Tertiary strata: I. 2. other lithology; basal till of the Saalian ice sheet; 4. (Maarleveld, 1976). Consequently on the 3. Middle Pleistocene coarsegrained sands; 5. Weichselian flanks of the ice-pushed ridges sheet-like valley bottom deposits; quarry; 7. Weichselian solifluc­ 6. movement of the top layer could still take tion fans. place till the end of the Pleniglacial. During the Late Weichselian the vegetation became denser (fig. 2); permafrost conditions did not occur any more and the existing surface-relief became fossilized. The drainage of the water surplus concentrated into a channel-bound system of small brooks; the effective erosion caused by t.hese brooks is very small, but it occurs. c) This erosion is evident from the third group of processes: the human interference with this drainage system. Where man has -­ �. built dams te create water reservoirs to keep I water mills going, sediment accumulated in · I 70 " , .... _/ front of these dams (fig. 6) and the reservoirs , I , '. became silted up. These ponds have frequently \ , ':/l been dug out, to retain their water storage 'n capacity. Any archeological finds within these � Ikm o 70 L-_--'-__-' , spots are possibly strongly disturbed by human activity so geological data can hardly I----} E:J2�3�' EJs r:::zJ6 [SS]7 support the archeological interpretations. Fig. 5. Part of the Ootmarsum ice-pushed ridge showing the western flank with different drainage areas near Mander. water divide; direction of solifluction mass­ I. 2. 3. INTERNAL STRUCTURE OF THE movement; contourline in metres above N.A.P. 3. 00TMARSUM RIDGE (D.O.L.); 4. a'fcheological site with Middle Palaeolithic finds; 5. Mosbeek; 6. western boundary of outcropping ice-pushed strata; 7. outcropping Saalian outwash fan, In eastern Twente only clay-rich Tertiary partly covered by a Weichselian solifluction head. sediments are incorporated into the ice- Geology and morphology of a part of the Ootmarsum ridge 39 pushed ridges. These Tertiary sediments are The first have a high infiltration capacity, the marine deposits which are characterized inter latter are very difficult to erode by running alia by the presence of glauconite, a green clay water. mineral that can turn brown when it becomes Richter et al. (1951) have drawn attention oxidized. It stains the sediments green, yellow to the conspicuous ridges with slope angles up or brown. to 15° which are determined by outcrops of Before being pushed up by the land ice materials rich in gravelly sands, that belong to sheets, the Tertiary layers were covered in the Middle Pleistocene fluvial deposits. their undisturbed position by fluviatile sands The ice-pushed Tertiary deposits can be of Middle Pleistocene age. The latter are divided roughly into two lithological units: medium fine to coarse sands rich in quartz one group consists of heavy clays (±60% and mineralogically very poor in contrast to < 2j..tm); the other group contains all the the glauconitic sediments. Because of the low other lithologies, mainly loamy green sands thickness of the fluviatile sands (less than 10 to loams. Under periglacial conditions, the m) in comparison with the Tertiary sediments first group is very sensitive to frost action that are mixed up within the ice-pushed ridge when exposed, because they tend to break up (more than 70 m) (fig. 3), the sands form only under repeated freezing and thawing. They a minor part of the internal structure of the will be only slightly effected when the role of ridge and of its surface. The ridge reveals its moisture increases and a solifl uction head internal structure at the surface (De Jong, accumulates on top of the heavy clay. The 1967), exposing strips of various types of vertical downward movement of the moisture lithology. In general these strips appear to be is prevented and the contact zone between the arranged according to the internal glaci­ solifluction head and the underlying heavy tectonical structure, parallel to the general clays will act as a slipface. As the duration of strike of the ridge and perpendicular to the the different climatic conditions during the direction of pushing (figs. I and 4). periglacial intervals (fig. 2) of the Weichselian Together with the preglacial deposits, part is not yet known in enough detail, one is only of the fluvial-glacial fan has been partly able to record the final result of all these pushed as well. Shortly after the formation of different processes active during this long the ridge, a strong surface relief must have timespan. The areas in which fields with heavy been present. This relief has been flattened out clay dominate belong to the more resistant flat by till accumulations, formed at the base of zones in the morphology (with step angles the overriding land ice sheet and mainly 1° -5°), while the second group in general is eroded from the ridge itself. Very thick reflected by wide flat depressions (slope angles accumulations have been encountered dUring 1° -2°) as is demonstrated by fig. 5; here the the survey (section in figs. I, 3 and 4). Mosbeek drainage basin is widening in eastern direction. The relatively narrow deep valley section crosses a 7.one with predominantly 4. MORPHOLOG ICAL EXPRESS ION heavy clays (fig. 4). This morphological ex­ OF THE LITHOLOGY pression of the lithology is only valid in very general terms. As appears from very detail­ The lithology of the outcropping strata ed mapping (Van del' Akker & Knibbe, 1963; appears to be related to some extent to the Richter et al., 1951) the main mapped units, as present-day morphological features visible on shown in fig. 3, are divided up into very small the Ootmarsum ridge. The effect of selective elongated sub-units, sometimes less than 20 m soil erosion can be explained primarily by the wide, caused by the internal glaci-tectonic periglacial conditions during the Weichselian. structure. Fig. 6 shows a cross section through Under a temperate climate, without man's the narrow part of the Mosbeek where it interference, a dense vegetation will protect crosses the field with predominantly heavy the soils against the eroding impact of rain. clays near the watermill of Bels. In this section Overland flow caused by heavy rainstorms the asymmetry of the valley is very striking. will only be effective on the steeper slopes, and This asymmetry is typical for many valleys those slopes tend to coincide with either the developed under periglacial conditions. The coarse gravelly sands of Middle Pleistocene south-facing slope is always steeper because age or the heavy clay of the Tertiary strata. the moisture-dominated solifluction processes M.W. VAN DEN BERG DEN OTTER 40 & C. are less active here as a result of the more abun­ Staalduinen (eds.), Toe/ichling bl} ge% gische dant sunheat received. overzichlskaarlen van Neder/and. Haarlem, pp. 93 - 103. JONG, J. D., 1967. The Quaternary of the Netherlands. In: The geo/ugica/ .ITSlems. The 5. ABSTRACT K. Rankama (ed.). Qualernary 2. New York-Lol)don-Sydney, pp. 301-426. A general outline is given of the geology and MAARLEVELD. G.c.. 1976. Periglacial phenomena and morpho-genetic processes that concern the the mean annual temperature during the last glacial area near Mander on the ice-pushed ridge of time in The Netherlands. Biu/. Peryg/acja/ny 26, pp. Ootmarsum. 57-78. RICHTER, W., H. SCHNEIDER & R. WAGNER. 195 1. Die Saaleeiszeitliche Stauchzone von Iterbeck Uelsen 6. AC KNO WLEDGE MENTS (Grafschaft Bentheim). Zeilschr!/i deulsche geo/­ ogische Ge.l'e//scha/i 102. pp. 60-75. 'RUEGG, G. H.J .. 1981. Sedimentary features and grain­ The authors are grateful to the director of the size of glacial-nuvial and periglacial deposits in The State Geological Survey and the Soil Survey Netherlands and adjacent parts of Western Institute for permission to publish this paper. Germany. Jlerhalld/ungen nalurll'issenschaji lichen Jlerein Hamburg Mrs. H.G. Meijnen-Roelofs typed the man­ N. F. 24. pp. 133-154. uscript; Mr. J. M. Smit prepared the draw­ RIIEGG. G.H.J., 1983. Periglacial eolian evenly laminated ings; Dr. J.J. Butler corrected the English text. sandy deposits in the Late Pleistocene of N. W. Europe. a facies unrecorded in modern sedi­ mentological handbooks. In: M.E. Brookfield & T.S. Alstbrandt (eds.). Eolian .I'edimel1ls alld 7. REFERENCES processes. Amsterdam. pp. 455-482. STAPERT, D., 1982. A Middle Paleolithic artefact scatter. AKKER, A.M. VAN DEN & M. KNIBI3E. 1963. Glaciale and a few younger finds, from near Mander NW of verschijnselen in de stuwwal van Ootmarsum. Boor Ootmarsum (province of O\'crijssel, the Nether­ en Spade 13, pp. 12-20. la nds). Pa/aeuhisturia 24. pp. BERG. M.W. VAN DEN, in prep. Toe/ichling bl} de ZAGWIJN, W.H., 1973. Pollenanalytic studies of Ke% gische kaarl van Neder/and Blad 1,'50,000. Holsteinian and Saalian beds in the Northern Almelo Denekamp 28 0s -29 West. Haarlem. Medede/ingen Rl}ks Ge% gische 0 l Netherlands. HAMMEN, TH., VAN DER, MAARLEVELD, J.c. Dieml G.c. 24, pp. 139- 156. VOGEL & W.H. ZAGWIJN, 1967. Stratigraphy, ZAGWIJN, W.H.,,1975. Indeling van het Kwartair op climatic succession and radio-carbon dating of the grond van veranderingen in vegetatie en klimaat. In: Last Glacial in The Netherlands. Ge% gie en W.H. Zagwijn & c.J. van Staalduinen (eds.l. Ml}nbouw 46, pp. 79-95. Toe/ichling bl} ge% gische overzichlSkaal'lell van JELGERSMA, S. & J.B. BREEUWER, 1975. Toelichting bij Neder/and. Haarlem, pp. 109-114. de kaart Glaciale verschijnselen gedurende het Saalien, 1:600,000. In: W.H. Zagwijn & c.J. van Manuscript completed in 1983.