distribution and intensity of glaciotectonic deformation in denmark

Distribution and intensity of glaciotectonic deformation inDenmark

PETER ROLL JAKOBSEN

DGF Jakobsen, P. R.: Distribution and intensity of glaciotectonic deformation inDenmark. Bulletin of the Geological Society of Denmark. Vol. 42, pp. 175—185. Copenhagen 1996-02-01.

Glaciotectonic deformation has a large impact on the stratigraphical andlithological variability of Quaternary deposits and the shallow subsurfacepre-Quaternary sediments. Mapping of the distribution of glaciotectonicdeformation involving pre-Quaternary and interglacial deposits has beencarried out, and the density of glaciotectonic deformation analysed, on thebasis of data from the well database ZEUS, at the Geological Survey ofDenmark.

Glaciotectonic deformation is widespread in Denmark. It is recognisedin glacial terrains within morphological well-defined glaciotectonic com-plexes, and in areas with no obvious glaciotectonic related morphology aswell as in areas covered with postglacial deposits. The dislocated bedrockis usually not transported for long distances, although rafts of pre-Quater-nary bedrock may be transported up to 50 km or more.

On a large scale, regions have been located showing high intensity ofglaciotectonic deformation. Some of these regions are in good agreementwith records from exposures and the geomorphology, others cannot be rec-ognised without well log information.

Peter Roll Jakobsen, Geological Survey of Denmark, Thoravej 8, DK2400København NV, Denmark. October 27th 1995.

IntroductionGlaciotectonic deformation has had a significant im-pact on the glacial landscape with respect to morpho-genesis and the distortion of sediments. The structuresproduced by the advancing glacier form an integratedpart of the kinetostratigraphic concept, which is usedfor the description of the glaciogeological development(Berthelsen 1978, Houmark-Nielsen 1987, Pedersen1993). The structural relationships within and betweenglaciotectonic complexes form the foundation for thereconstruction of the regional glacier advance.

In addition glaciotectonic deformation is an essen-tial feature in the study of variability of near surfacedeposits.Within the glaciotectonic deformation com-plex there is a disruption of the strata due to thrusting,and the lateral and vertical variability of sediment typeis very high. Knowledge of the existence of glacio-tec-tonics and the degree of the glaciotectonic variabilityis crucial in many aspects, as it has serious implica-tions in the fields of raw materials, hydrogeology andsoil mechanics.

Gry (1940) demonstrated the relationship betweenthe structural trend and the morphology of the ice pushridges in the Limfjord area, and explained the genesisof the structures as well as the morphology as a resultof active glacier push. Mapping of glaciotectonic fea-tures in Denmark has primarily been conducted bymeans of glaciotectonic landforms based on mor-phological studies. A genetic classification and descrip-tion of the morphology of the glacial landscape in Den-mark was first undertaken by Milthers (1948). LaterSmed (1962,1982) presented a regional morphogeneticmap of Denmark. He introduced and defined glacio-tectonic landforms in his classification, such aspushmoraines and cupola hills. An expanded classifi-cation of glaciotectonic landforms was given by Aber(1988) and Aber, Croot & Fenton (1989). They propo-sed five types of glaciotectonic landforms. These fivetypes are listed below and locations with examples ofthe five glaciotectonic landforms within Denmark areshown in Figure 1.

Bulletin of the Geological Society of Denmark 175

• • • • - ' • -

• - 1

Glaciotectonic Landforms

Hill-Hole Pair1. Odsherred (Milthers 1900)2. Munkebo-Kerteminde (Smed 1962)3. Falster (Milthers 1948)4. Mols Bjerge (Rasmussen 1977)5. Sjerring Se (Aber 1989)

Large Composite-Ridges6. Hanklit (Gry 1940, Klint & Pedersen 1995)7. Møns Klint (Hintze 1937)

Small Composite-Ridges8. Sydfynske Alper (Smed 1962)9. Røsnes (Petersen 1973)

10. Næstved (Jacobsen 1981)11. Jyske As (Jessen 1936)

Cupola Hills12. Ristinge Klint (Madsen 1916)13. Ærø (Smed 1962)14. Røgle Klint (Smed 1962)15. Hvide Klint (Aber 1979,1988)

Rafts16. Allindelille (Milthers 1943)

Concealed glaciotectonic Complexes17. Lønstrup Klint (Jessen 1931)

18. Well with DGU archive no. 38.49419. Well with DGU archive no. 172.175

Fig. 1. Sites displaying glaciotectonic landforms in Denmark according to Aber (1988) and Aber, Croot & Fenton (1989).

1) The Hill-Hole Pair is a combination of an ice-pushedridge and a discrete ice-scooped basin. The ridge issituated downglacier of the associated hole, whichis the source depression of the ice-shoved hill.

2) The Large Composite-Ridges (up to 100-200 m inheight) are a system of subparallel ridges, often ar-cuate in plan; they often include a substantial vol-ume of contorted pre-Quaternary bedrock.

3) The Small Composite-Ridges are also a system ofsubparallel ridges, arcuate in plan, but they aresmaller (< 100 m in height) than the large compos-ite-ridges; they are usually composed largely ofunconsolidated Quaternary strata.

4) The Cupola-Hill morphology is formed by a numberof conspicuous hills that lack the transverse ridgemorphology of ice-shoved hills. They generally havea smoothed dome to elongated drumlin shape, witha till cover. The glaciotectonic origin of such hillscan only be recognised with subsurface evidencefrom exposures or drilling logs.

5) The Megablocks (also called raft, floe or scale) arelarge allochthonous masses of dislocated bedrock.The megablocks are more or less horizontal, slightlydeformed, and often buried under or within thickmasses of drift. There is usually no or only littlemorphological evidence of their presence. Hencethey are very difficult to distinguish without drillinglogs or exposures.

In addition to these five types of glaciotectonic land-forms, the concealed glaciotectonic complex is an im-portant glaciotectonic feature. A glaciotectonic com-plex covered by younger sediments does not expressany glacial morphology. However the structures maybe very spectacular and result in highly deformed bed-ding and disturbed stratigraphy. Concealed glacio-tec-tonic complexes may be investigated in cliff exposures,and can be recognised in wells.

Recently, mapping of glaciotectonics in North Ame-rica has been carried out (Aber et al. 1993). The map-ping included morphological elements (ice-shoved hillsand source basins), as well as concealed structures andbasement faults related to loading/unloading of ice. Itis planned to conduct a similar mapping of glaciotec-tonics in Europe (Croot & Michalak 1993).

In many situations, glaciotectonic landforms are sig-nificantly altered by subsequent subglacial processes,or later ice advances, e.g. Ærø (Smed 1962). In othersituations such landforms might be buried under lateglacial or postglacial deposits, e.g. Lønstrup Klint(Jessen 1931). In cases where information from mor-phology and exposures are not available, informationfrom wells constitutes an important supplement.

Preliminary mapping of glaciotectonic structures andfeatures in southeast Jylland has been conducted basedon surface morphology, records of glaciotectonics fromexposures and information from well logs (Houmark-

176 Jakobsen: Glaciotectonic deformation in Denmark

Nielsen 1986); the use of well data facilitates morewidespread correlation and reveals information on con-cealed glaciotectonics.

The aim of this work is to map the distribution ofconcealed glaciotectonic deformation in Denmark,based on records from well logs stored in the well data-base at the Geological Survey of Denmark, and to ana-lyse the intensity of the glaciotectonic deformation.

Methods

Data source

The data source used in this mapping is the ZEUS welldatabase (Gravesen & Fredericia 1984) at the Geologi-cal Survey of Denmark. The ZEUS database containsinformation from about 140,000 well logs. The distri-bution of the wells is shown in Figure 2. The informa-tion from the well logs are mainly from water supplywells but also from raw material, geotechnical and sci-entific borings, The database contains details of geol-ogy, hydrogeology and well technical properties. Thegeological data are registered in a mnemo-technicalcode, with a two letter symbol, indicating the lithologyas well as the stratigraphy, which is used in the compu-terised search for concealed glacio-tectonic deforma-tion.

Recognising deformation in wellsGlaciotectonic thrusting of sedimentary rocks causesstratigraphie disruption and in some cases repetition ofthe strata. Repeated drift deposits are usually difficultor impossible to recognise in wells. However, if pre-Quaternary bedrock is involved in the thrusting, it willoften be thrusted on top of Quaternary drift, and thereby

Fig. 2. Grid map showing the distribution of wells stored inthe ZEUS database. The size of a grid cell is 5x5 km.

act as a stratigraphie marker in the deformation com-plex. This situation is exemplified by the large com-posite-ridges at Hanklit on the island of Mors (Fig. 3,for location see Fig. 1). In the Hanklit cliff, a thin-skinned thrust complex is exposed, forming a compo-site ridge system (Klint & Pedersen 1995). Within thisdeformation complex, Palaeocene-Eocene diatomite isthrusted on top of Weichselian drift. A similar sequenceis recorded by logs in the well shown in Figure 5 (DGU

Till | - , • . - . • ] Meltwaterdeposits Diatomite Thrust 100 m

Fig. 3. A section through the thin-skinned thrust complex forming a Large Composite Ridge system at Hanklit on the islandof Mors (re-drawn after Jensen 1992). In the section, Palaeocene-Eocene diatomite is thrusted onto Quaternary drift.


NW

"The white sand" Marine Eemian Thrust 10m

Fig. 4. Coastal cliff profile (Hansen 1994) exposing the interior of the Cupola Hill landscape at Bregninge Mark, Ærø.Dislocated Eemian marine deposits are repeated with intervening drift deposits

38.494

Till

172.175

Till

Paleocene-Eocene

Diatomite

MeitwatersandTill

-vi Eemian marine clay

Meitwatersand

Till

Meitwatersand

Eemian marine clay

Till

Eemian marine clay

Fig. 5. Well log profiles indicating glaciotectonic disloca-tion. In well log no. 38.494, Palaeocene-Eocene diatomiteoverlies Quaternary drift displaying a similar succession asseen in the dislocation complex at Hanklit (Fig. 3). In welllog no. 172.175, Eemian marine deposits are recorded threetimes with intervening drift, displaying a similar successionas seen in the cliff sections on Ærø (Fig. 4).

archive No. 38.494, for location see Fig. 1). In this wellEocene-Palaeocene diatomite rests on Quaternary drift,indicating that the well penetrated glaciotectonic dis-located Tertiary bedrock (Jakobsen & Pedersen 1993).

If the bedrock is dislocated as rafts or megablocks, itwill have the same implications for stratigraphie vari-ability in a well log as thrusting in thin-skinned thrustcomplexes i.e. the pre-Quaternary bedrock overliesQuaternary drift. In order to differentiate between thetwo processes, it is necessary to make an interpretationof the local geology. In any case, the presence of pre-Quaternary bedrock overlying Quaternary drift is in-dicative of glaciotectonic deformation. A search wasmade in the database for wells in which bedrock wasfound above drift and 1210 were detected.

Repetition of a well-defined unit such as interglacialEemian marine clay can also be used to recognizeglaciotectonic deformation. On the island of Ærø dis-locations of interglacial marine clay have been described(Berthelsen 1979, Hansen 1987, 1994). The Intergla-cial marine clay has been thrusted and folded duringseveral Weichselian ice advances. In a coastal cliff sec-tion near Bregninge Mark on Ærø, slices of marineEemian deposits are thrusted on top of each other, withintervening Weichselian till (Hansen 1994) (Fig. 4). Ina well situated on the island of Ærø (DGU archive no.172.175 in Fig. 5, for location see Fig. 1), interglacialmarine clay of Eemian age is repeated three times withintervening till and meltwater sand. This indicatesWeichselian glaciotectonic deformation, causing a rep-etition of the interglacial strata. On the assumption thatrepetition of the same interglacial unit in a well is in-dicative of glaciotectonic dislocation, a search was madein the database for wells with two interglacial marineclays with intervening drift and 49 were detected. Thedescription and interpretation was subsequently checkedfor each well, to ensure that it represented a repetitionof the same interglacial sequence.

Information of glaciotectonic deformation derivedfrom well logs can also be extracted from geologicalbasisdata maps. Not all wells kept in the ZEUS data-base are represented on the geological basisdata maps,


Fig. 6. Distribution of wellswith well logs in whichdislocated pre-Quaternarybedrock is recorded aboveQuaternary drift.

Kilometres

25 50 75 100Saalian glacigene

I deposits

I Weichselian glacigene| deposits

I Weichselian outwashplain

however, as it is not possible, for practical reasons, todisplay all wells on the maps.

Mapping with GISThe wells in which glaciotectonic dislocations havebeen recognized, were located in a computer search,and subsequently plotted by means of ZETA. ZETA isa computer based Geographical Information System(GIS) developed at the Geological Survey of Denmarkfor capture, management and plotting of georeferenceddata (Jørgensen et al. 1993). The wells showing a recordof concealed glaciotectonic deformation are plottedalong with the main geological features in the Quater-nary landscape, which have been digitalised fromHansen & Milthers (1954). The grid maps used to showthe distribution of wells stored in the ZEUS database

(Fig. 2) and the density of concealed glaciotectonicdeformation (Fig. 8) are computed in the statistical pro-gram SAS, and subsequently plotted using the ZETAprogram.

Distribution of concealedglaciotectonic deformationWells showing evidence of dislocated pre-Quaternarybedrock are widespread throughout Denmark (Fig. 6).They are found inside the Weichselian Main StationaryLine, as well as outside. The lithostratigraphical unitsfound as dislocated pre-Quaternary bedrock are thesame as those observed at the pre-Quaternary surfaceand the distribution corresponds fairly well with thedistribution pattern of the pre-Quaternary units (Hå-


Fig. 7. Distribution of wellswith well logs in whichdislocated interglacialmarine deposits arerepeated with interveningdrift.

kansson & Pedersen 1992). An exception, however, isthe presence of dislocated Cretaceous limestone raftsin the central part of Sjælland. They are also reportednear Allindelille (Fig. 1) by Milthers (1943) who sug-gested that the most likely provenance of the rafts wassoutheast Sjælland, with a transport distance of at least50 km. Similar far-travelled limestone rafts have alsobeen reported from Skåne, south Sweden (Ringberg etal. 1984).

Most of the recognised dislocated marine intergla-cial deposits in wells are found inside the Main Sta-tionary Line (Fig. 7). It is mainly Eemian marine de-posits, and they are restricted to areas of Eemian ma-rine deposition (Konradi 1976, Knudsen 1994). Insouthwest Jylland, outside the Main Stationary Line, adislocated sequence of marine Holsteinian deposits isrecognised (Andersen 1963, Knudsen & Penny 1987).

Outside the Main Stationary Line, the concealed de-formation is observed both in the 'hilly islands', whereSaalian drift primarily constitutes the surface geology,and they are found below the surrounding late Weich-selian outwash plain deposits which covers the Saaliandrift. The landscape within the 'hilly islands' does notdisplay distinct morphological evidence of glaciotec-tonic deformation. The morphological features seen arerelated to 120,000 years of subaerial erosion of softsediment, and deposition of eolian sand.

In the Nederlands and Germany, the Saalian ice-pushridges form distinct morphological features (Meyer1983, van der Wateren 1985, Kluiving 1994). The lackof glaciotectonic landforms in the Saalian 'hilly-islands'thus cannot be explained solely by post-Saalian suba-erial erosional processes. The landscape in the 'hilly-islands' was probably initially formed or modified by


Fig. 8. Grid map displayingthe intensity ofglaciotectonic deformationrecorded in wells. Eachgrid cell is 5x5 km.The density in each gridcell is shown as thenumber of wells withrecorded deformation inper mille of the totalnumber of wells.

Main Stationary Line

"71 East Jylland IceBorder Line

subglacial erosional and/or depositional processes. Asthe 'hilly islands' display significant concealedglaciotectonic deformation, they could be classified asmodified cupola-hill landscape.

Within the Main Stationary Line, the wells showingevidence of dislocated pre-Quaternary bedrock arefound associated with glaciotectonic landforms, as wellas in areas with no particular glaciotectonic morpho-logy, and in areas covered with post glacial deposits.They are found throughout the Danish area except inthe northern part of Jylland. This is most likely becausethe pre-Quaternary surface is situated more than 100 mbelow surface in this area, and most of the wells are notdrilled to a depth where dislocated pre-Quaternary bed-rock could be expected. Glaciotectonic dislocations inthe Quaternary strata in the northern part of Jylland areseen at Lønstrup (Jessen 1931) where marine Weich-

selian deposits are dislocated in a thin-skinned thrustcomplex. Additionally, five well logs were found wheremarine Eemian deposits are repeated (Fig. 7). Most ofthe dislocations in the northern part of Jylland seem toinvolve only Quaternary deposits.

The majority of wells drilled through dislocated Inter-glacial marine deposits occur south of Fyn on the is-lands of Ærø and Als, and in the nearby surroundingson Fyn and southeast Jylland.

Intensity of glaciotectonic deformationThe distribution of concealed glaciotectonic deforma-tion recorded in wells is widespread but shows a higherconcentration in certain areas. In order to get a general


view of the regional distribution of the density of wellsexhibiting glaciotectonic deformation, a grid is con-structed. Each grid cell is 5x5 km, and for each cell thenumber of wells exhibiting deformation are computed.As the wells in the ZEUS database are not equally dis-tributed (Fig. 2), a correction must be undertaken toaccount for this. The number of wells exhibitingglaciotectonic deformation is divided by the totalnumber of wells in each grid cell (Fig. 8). This proce-dure gives a fairly good estimation of the density ofwells exhibiting glaciotectonic deformation. In grid cellswith only a few wells there might be an over or underrepresentation of wells with concealed glaciotectonicdeformation. On a large regional scale though, a clus-ter of cells showing a high density of wells with con-cealed glaciotectonic deformation are considered sig-nificant, and it is possible to identify regions with ahigher density of wells with glacio-tectonic deforma-tions - thus with high intensity of deformation.

Comparison of well dataand record of glaciotectonicsOutside the Main Stationary Line there are several re-gions with high intensity of deformation where the wellsexhibiting glaciotectonic deformation are situatedwithin the 'hilly islands' as well as in areas covered bythe Late Weichselian outwash plane. There are manyexposures of Upper Miocene deposits recorded outsidethe Main Stationary Line, and most of them are glacio-tectonically dislocated (Rasmussen 1966). Deformationof marine Holsteinian deposits are reported from thewestern part of Jylland near Esbjerg (Rasmussen 1966,Andersen 1967) and from a well i the south westernpart of Jylland at Tornskov (Andersen 1963, Knudsen& Penny 1987) (Fig. 7).

In the western part of the Limfjord, the intensity ofglaciotectonic deformation is very high. This is in goodagreement with the numerous coastal cliff exposuresof glaciotectonic complexes and ice-push ridge systemsdescribed in this area (Gry 1940, 1979, Håkansson &Sjørring 1982, Pedersen & Petersen 1987, Pedersen1993, Klint & Pedersen 1995). The deformation com-plexes in this region usually involve pre-Quaternarybedrock, deformed during Weichselian ice advances.

East of the high intensity region in the Limfjord area,there is a region, with high intensity of glaciotectonicdeformation extending in a northwest to southeast di-rection. It coincides with the overall morphologicaltrend in this region, outlined by a northwest to south-east oriented large scale ridge (Milthers 1948). South-west of this region a similar morphological trend is seenand in this region deformation of Saalian as well asWeichselian age are described (Larsen et al. 1977,Kronborg et al. 1990).

Along the east coast of Jylland, from Djursland to

Germany, there is a very high intensity of glaciotec-tonic deformation, with the highest intensities east ofthe East Jylland Ice Border Line. Coastal cliff expo-sures in this region display extensive glaciotectonicdeformation, in which Tertiary deposits, and in thesouthern part also interglacial deposits are dislocatedalong with Quaternary drift (Jessen 1930,1935,1945,Nordmann 1958, Konradi 1976, Houmark-Nielsen1986,1987).

In the region south of Fyn, on the islands Ærø andAls, the intensity of glaciotectonic deformations is veryhigh. In this region most of the recorded deformationinvolves dislocated interglacial marine deposits. Theexposures in this region show that the interglacial ma-rine deposits were deformed during several deforma-tion phases in Weichsel, and that the deformation isextensive (Konradi 1976, Berthelsen 1979, Hansen1987,1994).

On the island of Fyn, glaciotectonic deformation ismore widespread, except in the northeast of Fyn, at theMunkebo Ice-push ridge (Smed 1962). In this regionseveral wells situated within the ice-push ridge system,exhibit glaciotectonic dislocated Palaeocene Kerte-minde Marl (Jakobsen 1993).

On Sjælland, several regions with high intensity ofglaciotectonic deformation can be pointed out. At theRøsnes peninsula a number of concealed dislocationscan be related to the ice-push ridge, constituting thepeninsula, in which Palaeocene Røsnes clay is dislo-cated (Petersen 1973). Southeast of Røsnes there is aregion showing high density of concealed dislocations,arcuate in shape, with the concave side pointing to thesoutheast. Within this region several occurrences of dis-located Palaeocene Kerteminde Marl have been re-corded (Hansen 1930).

Further to the southeast, there is an elongated north-west to southeast oriented region, with high intensityof glaciotectonic deformation. This region is situatednortheast of an iceborderline, which is limiting the highconcentration of deformation towards the southwest(Jacobsen 1981). The iceborderline is delineated by anice-push ridge system, partially developed as hill-holepair, genetically associated to a readvance from thenortheast of the ice advance which reached the MainStationary Line.

Northeast of this region, west and south west of Co-penhagen, there are two regions with high intensity ofglaciotectonic deformation.

The Copenhagen area appears as a region with highintensity. A closer inspection of the well logs reveal,however, that the majority of the pre-Quaternary unitsare locally derived limestone rafts or parautochthonousglacitectonites (Pedersen 1988), usually with a thick-ness less than one meter. In outcrops temporarily ex-posed due to construction works only minor glacio-tec-tonic deformations are seen within the Quaternary de-posits in this area. The uppermost part of the Danianlimestone is glacially tectonised (Knudsen et al. 1995)whereby the limestone rafts are detached from the pre-


Quaternary surface and incorporated in the glacial de-posits.

On the island of Møn there is a very high intensity ofglaciotectonic deformation. Coastal exposures on Mønshow extensive glaciotectonic deformation (Puggaard1851, Hintze 1937, Berthelsen et al. 1977, Aber 1979,Berthelsen 1979, Houmark-Nielsen 1994), with MønsKlint as the most impressive feature, constituting a largecomposite ridge system.

DiscussionA well drilled through a glaciotectonically deformedrock body is a point observation which is a valuablesupplement to the glaciotectonics observed in expo-sures. Much of the deformation recognised in this wayis situated below late glacial or post glacial deposits.

The vast number of wells in the ZEUS database fa-cilitates an analysis of the distribution and intensity ofglaciotectonic deformation throughout the land area ofDenmark. The possibility of detection of deformationin wells is, however, limited, as a recognisable litho-logical unit is required within the deformation com-plex. Nevertheless a large number of dislocations weredetected in well logs, widely distributed throughout thecountry.

On a large scale, regions showing a high intensity ofglaciotectonic deformations have been identified, andthey are in good agreement with reports of glacio-tec-tonics within the regions. Hence the map showing theintensity (Fig. 8) supports field observations and out-lines areas with a high degree of glaciotectonic defor-mation, and high glaciotectonic variability.

In areas with no or only few exposures, the inferenceof the high intensity of glaciotectonic deformation,based on the analysis of the well data, is consequentlyconsidered valid. In these areas, the information fromwell logs represent important data in the attempt to high-light glaciotectonic deformation and areas with highglaciotectonic variability. It should be emphasised, how-ever, that the absence of evidence of deformation inwells in certain areas, does not preclude the existenceof glaciotectonic deformation.

ConclusionsMapping of glaciotectonic deformations involving pre-Quaternary and interglacial deposits has been carriedout with the application of the well database ZEUS.Records of glaciotectonic dislocations are found wide-spread throughout Denmark. They are recognised inglacial terrain within morphological well-defined gla-ciotectonic complexes and in areas with no obviousglaciotectonic related morphology, and they are recog-

nised in areas where the glacial deposits are coveredwith younger sediments.

The pre-Quaternary surface is highly affected by thedislocation of glacier-ice movements. The dislocatedpre-Quaternary bedrock has usually not been transpor-ted long distances from source, although rafts of pre-Quaternary bedrock have in some cases been transpor-ted up to 50 km or more. The Eemian marine depositsare glaciotectonically deformed in areas affected byWeichselian ice advances, primarily southwest of Fynand in north Jylland, and dislocated Holsteinian ma-rine deposits are seen in a well in south Jylland.

On a large scale, it is possible to identify regions witha high intensity of glaciotectonic deformation. Theseare in good agreement with previous reports of glacio-tectonics and glaciotectonic landforms. Regions with-out glaciotectonic related landforms but with a highintensity of glaciotectonic deformation can also be iden-tified. In the high intensity regions, the glacio-tectonicdeformation has created a high degree of lithologicaland stratigraphical variability.

AcknowledgementsI greatly appreciate the inspiring discussions with mycolleagues at DGU, in particular Stig A. S. Pedersen,who also gave valuable criticism on the manuscript. Isincerely thank Frantz von Platen for his invaluable helpon the data management and Jon R. Ineson for improve-ments in the English language.

Dansk sammendragGlaciale forstyrrelser påfører glaciale aflejringer ogoverfladenære prækvartære aflejringer en stratigrafisksåvel som lithologisk variabilitet. Den glacialtek-toniskevariabilitet har store implikationer indenfor områdersom råstofgeologi, hydrogeologi og geoteknik, hvorfordet er af stor betydning, at vide hvor der er forstyrrelser,og at kende graden af forstyrrelserne.

Glacialtektoniske forstyrrelser kan erkendes i bo-ringsbeskrivelser, når boringen har penetreret prækvar-tære aflejringer, der hviler på glacigene aflejringer, ognår interglaciale aflejringer gentages i boreprofilet.

Der er foretaget en kortlægning af boringer der inde-holder information om glacialtektoniske forstyrrelser,ud fra oplysninger i boredatabasen ZEUS, der inde-holder boringsoplysninger fra ca. 140.000 boringer. Derer registreret 1210 boringer med dislocerede præ-kvartære aflejringer, og 49 boringer med disloceredeinterglaciale aflejringer. Boringer med oplysninger omglacialtektoniske forstyrrelser er truffet vidt udbredt iDanmark. I det glaciale landskab er de truffet indenformorfologisk veldefinerede glacialtektoniske komplek-


ser, og i områder der ikke udviser nogen karakteristiskglacialtektonisk morfologi. Derudover er de truffet iområder, hvor de glaciale aflejringer er dækket afsenglaciale og postglaciale sedimenter.

Prækvartær overfladen er stærkt påvirket af de gla-cialtektoniske forstyrrelser. De dislocerede prækvar-tære bjergarter er som regel ikke transporteret langt.Der er dog eksempler på flager der er transporteret optil 50 km. De interglaciale marine Eem aflejringer erdeformeret i Weichsel, primært i området sydvest forFyn og i Nordjylland.

I stor skala er det muligt, at udpege områder med højdensitet af boringer, der indeholder oplysninger omglacialtektoniske forstyrrelser, og dermed høj intensitetaf deformation. Mange af de udpegede områder medhøj deformations intensitet, er i god overensstemmelsemed beskrivelser af glacialtektoniske forstyrrelser, ogmorfologiske landskabsanalyser. Derudover er derudpeget områder med høj intensitet af glacialtektoniskdeformation, i områder der ikke har glacialtektoniskrelateret morfologi, som ikke ville kunne udpeges udenboringsoplysninger.

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distribution and intensity of glaciotectonic deformation in denmark

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