Vol. 8 pp 1-32, Geol. Surv. Denmark and Greenland Bulletin

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Geological Survey of Denmark and Greenland Bulletin 8

Keywords

Norther n Jylland, Denmark, Weichselian, glacial geology, glaciotectonics, thin-skinned thrust faulting, balanced cross-section, thrust-
fault dynamics, imbricate duplexes, mud diapirs, piggyback basins.

Cover
The coastal cliff (99 m high at its highest point) at Rubjerg Knude on the west coast of Vendsyssel, northern Denmark. The lower

two-thirds of the cliff, beneath the prominent dark sub-horizontal surface, for ms part of the cross-section through the Rubjerg
Knude Glaciotectonic Complex displaying imbricated thrust sheets composed of the Lønstrup Klint Formation (bluish-grey colour)

and the overlying Rubjerg Knude Formation (yellow colour), both of Late Weichselian age. The thrust sheets are truncated by a
glaciotectonic unconformity (the prominent surface), upon which the Kattegat Till Formation is only preserved as a boulder bed

due to subsequent aeolian erosion of the till matrix. The upper third of the cliff comprises recent aeolian dune sands that have
accreted over the last 100 years and now encroach on the Rubjerg Knude lighthouse, the top of which is just visible above the

clifftop. Photo: Stig A. Schack Pedersen (August 1984).

Chief editor of this series: Adam A. Garde

Editorial board of this series: John A. Korstgård, Geological Institute, University of Aarhus; Minik Rosing, Geological Museum,

University of Copenhagen; Finn Surlyk, Geological Institute, University of Copenhagen

Scientific editor of this volume: Jon R. Ineson
Editorial secretaries: Esben W. Glendal and Birgit Eriksen

Illustrations: Benny M. Schark and Alice Rosenstand
Digital photographic work: Benny M. Schark

Graphic production: Knud Gr@phic Consult, Odense, Denmark
Printers: Schultz Grafisk, Albertslund, Denmark

Manuscript submitted: 8 August 2003
Final version approved: 11 February 2005

Printed: 15 December 2005

This monograph has been accepted by the Faculty of Natural Sciences, University of Copenhagen, for public defence of the degr ee
of Doctor of Science.

ISSN 1604-8156

ISBN 87-7871-168-1

Geological Survey of Denmark and Greenland Bulletin

The series Geological Survey of Denmark and Greenland Bulletin replaces Geology of Denmark Survey Bulletin and Geology of
Greenland Survey Bulletin.

Citation of the name of this series

It is recommended that the name of this series is cited in full, viz. Geological Survey of Denmark and Greenland Bulletin.
If abbreviation of this volume is necessary, the following for m is suggested: Geol. Surv. Den. Green. Bull. 8, 192 pp.

Available from

Geological Survey of Denmark and Greenland (GEUS)
Øster Voldgade 10, DK-1350 Copenhagen K, Denmark

Phone: +45 38 14 20 00, fax: +45 38 14 20 50, e-mail: geus@geus.dk

Danmarks og Grønlands Geologiske Undersøgelse (GEUS), 2005

Contents

Abstract 9
Introduction 11

History of the present investigation 11
Objectives 14

Glacial tectonics - concepts and models 14

Previous conceptual models 14
Thin-skinned thrust faulting: the concept 16

Thrust-fault modelling 16

Test model 1 19
Test model 2 19
Test model 3 21
Test model 4 21
Test models: concluding remarks 22

Concept of balanced cross-section 22

Location and construction of the Rubjerg Knude cross-section 23

Location 23
Photogrammetric work 23
Digital editing 25
Construction of the balanced cross-section 26

Geological setting 27
Lithostratigraphy . 33

Skærumhede Group 33

Stortorn Formation 35
Lønstrup Klint Formation 39

Upper Weichselian lithostratigraphic units 43

Rubjerg Knude Formation 43
Kattegat Till Formation 48
Ribjerg Formation 50
Mid Danish Till Formation 53
Vendsyssel Formation 55

Structural description of sections 60

Ulstrup Section 60

Tectonic architecture 61

Sedimentary units 62
Lønstrup Klint Formation 62
Rubjerg Knude Formation 63

Structures and breccias 63

Thrust-zone breccias 64
Foreland-dipping hanging-wall flat faults 64
Collapse structure in the Ulstrup Rende 66

Interpretation of structural development 66

Stensnæs Section 70

Tectonic architecture 70
Sedimentary units 72

Lønstrup Klint Formation 72
Rubjerg Knude Formation 73

Structures 73

Imbricate duplex folding 73
Extensional faults 73

Interpretation of structural development 78

Martørv Bakker Section 78

Tectonic architecture 79
Sedimentary units 80

Lønstrup Klint Formation 81
Rubjerg Knude Formation 81

Structures 82

Imbricate duplexes 82
Normal fault 82
Hydrodynamic brecciation 82

Interpretation of structural development 82

Kramrende Section 84

Tectonic architecture 85
Sedimentary units 86

Lønstrup Klint Formation 87
Rubjerg Knude Formation 87

Structures 87

Thrust faults 87
Kramrende diapir 88
Reverse faults 88

Interpretation of structural development 89

Brede Rende Section 90

Tectonic architecture 90
Sedimentary units 93

Lønstrup Klint Formation 93
Rubjerg Knude Formation 94

Structures 94

Diapir structures 96
Brede Rende normal fault 97
Frost wedges 97

Interpretation of structural development 97

Sandrende Section 99

Tectonic architecture 99
Sedimentary units 101

Lønstrup Klint Formation 101
Rubjerg Knude Formation 101

Structur es and breccias 103

Normal faults 103
Diapir structures 104
Frost wedge 104

Interpretation of structural development 104

Stenstue Rende Section 105

Tectonic architecture 106
Sedimentary units 107

Lønstrup Klint Formation 107
Rubjerg Knude Formation 108

Structures 108

Thrust-fault structures 108
Hanging-wall anticlines 109

Normal faults 110
Slump folding 110

Interpretation of structural development 110

Grønne Rende Section 111

Tectonic architecture 112
Sedimentary units 112

Lønstrup Klint Formation 112
Rubjerg Knude Formation 112

Structures 113

GR01 thrust sheet 113
GR02 thrust sheet 114
GR03 thrust sheet 114
GR04 thrust sheet 114
GR05 thrust sheet 115
GR06 thrust sheet 115
GR07 thrust sheet 116
GR08 thrust sheet 116
GR09 thrust sheet 116
GR10 thrust sheet 116
GR11 thrust sheet 117
GR12 thrust sheet 117
GR13 thrust sheet 117

Interpretation of structural development 117

Rubjerg Knude Fyr Section 118

Tectonic architecture 118
Sedimentary units .121
Structures 122

Anastomosing thrust-fault brecciation 122

Interpretation of structural development 122

Stortorn Section 122

Tectonic architecture 123

ST01 thrust sheet 123
ST02 thrust sheet 123
ST03 thrust sheet 123
ST04 thrust sheet 123
ST05 thrust sheet 124
ST06 thrust sheet 124
ST07 thrust sheet 124
ST08 thrust sheet 124
ST09 thrust sheet 125
ST10 thrust sheet 125

Sedimentary units 126
Structures 126
Interpretation of structural development 126

Moserende Section 128

Tectonic architecture 128

MR01 thrust sheet 129
MR02 thrust sheet 130
MR03 thrust sheet 130
MR04 and MR05 thrust sheets 130
MR06-MR08 thrust sheets 131

MR09 thrust sheet 132
MR10 thrust sheet 132
MR11 thrust sheet 132
MR12 thrust sheet 132
MR13 thrust sheet 133

Sedimentary units 134

Lønstrup Klint Formation 134
Rubjerg Knude Formation 134

Structures 134

Diapir structures 135
Thrust faults 135
Footwall synclines 135

Interpretation of structural development 136

Mårup Kirke Section 137

Tectonic architecture 138

MK01 thrust sheet 139
MK02-MK04 thrust sheets 139
MK05-MK07 thrust sheets 139
MK08-MK10 thrust sheets 140
MK11-MK20 thrust sheets 140

Sedimentary units 141
Structures 141
Interpretation of structural development 141

Fault-bend-fold model for duplex units 141
Characterisation of thrust duplex MK11-MK20 143
Discussion of structural development 143

Ribjerg Section 144

'Store Blå' and 'Lille Blå' 144
Tectonic architecture 145
Sedimentary units 146

Skærumhede Group 146
Blå-unconformity 146
Ribjerg Formation 146
Mid Danish Till Formation 147
Vendsyssel Formation 147

Structures 147
Interpretation of glacial geology and stratigraphic development 147

Dynamic development of the thin-skinned thrust faulting

148

Moserende Section 148

Moserende Section: summary data 149

Stortorn Section 149

Stortorn Section: summary data 156

Rubjerg Knude Fyr Section 156

Rubjerg Knude Fyr Section: summary data 156

Grønne Rende Section 156

Grønne Rende Section: summary data 157

Stenstue Rende Section 157

Stenstue Rende Section: summary data 161

Sandrende Section 161

Sandrende Section: summary data 163

Brede Rende Section 163

Abstract

Pedersen, S.A.S. 2005: Structural analysis of the Rubjerg Knude Glaciotectonic Com-
plex, Vendsyssel, northern Denmark. Geological Survey of Denmark and Greenland
Bulletin 8, 192 pp.

The Rubjerg Knude Glaciotectonic Complex is a thin-skinned thrust-fault complex that was
formed during the advance of the Scandinavian Ice Sheet (30 000 - 26 000 B.P.); it is well
exposed in a 6 km long coastal profile bordering the North Sea in northern Denmark. The
glaciotectonic thrust-fault deformation revealed by this cliff section has been subjected to
detailed structural analysis based on photogrammetric measurement and construction of a
balanced cross-section. Thirteen sections are differentiated, characterising the distal to proxi-
mal structural development of the complex. The deformation affected three stratigraphic units:
the Middle Weichselian ar ctic marine Stortorn Formation, the mainly glaciolacustrine Lønstrup
Klint Formation and the dominantly fluvial Rubjerg Knude Formation; these three formations
are formally defined herein, together with the Skærumhede Group which includes the Stor-
torn and Lønstrup Klint Formations. The Rubjerg Knude Formation was deposited on a regional
unconformity that caps the Lønstrup Klint Formation and separates pre-tectonic deposits below
from syntectonic deposits above.

In the distal part of the complex, the thrust-fault architecture is characterised by thin flat-

lying thrust sheets displaced over the footwall flat of the foreland for a distance of more than
500 m. Towards the pr oximal part of the complex, the dip of the thrust faults increases, and
over long stretches they are over-steepened to an upright position. The lowest décollement
zone is about 40 m below sea level in the proximal part of the system, and shows a systematic
step-wise change to higher levels in a distal (southwards) direction. The structural elements
are ramps and flats related to hanging-wall and footwall positions. Above upper ramp-hinges,
hanging-wall anticlines developed; footwall synclines are typically related to growth-fault
sedimentation in syntectonic piggyback basins, represented by the Rubjerg Knude Formation.
Blocks and slump-sheets constituting parts of the Lønstrup Klint Formation were derived from
the tips of up-thrusted thrust sheets and slumped into the basins. Mud diapirs are a prominent
element in the thrust-fault complex, resulting from mud mobilisation mainly at hanging-wall
flats and ramps.

Shortening during thrust-fault deformation has been calculated as 50%. Only about 11% of

the initial stratigraphic units subjected to thrust faulting has been lost due to erosion. The
thrust-fault deformation was caused by gravity spreading of an advancing ice sheet. Over-
pressur ed mud-fluid played an important role in stress transmission. The average velocity of
thrust-fault displacement is estimated at 2 m per year, which led to compression of a 12 km
stretch of flat-lying sediments, c. 40 m in thickness, into a thrust-fault complex 6 km in length.
The thrust-fault complex is truncated by a glaciotectonic unconformity, formed when the
advancing ice sheet finally overrode the complex. When this ice sheet melted away, a hill-
and-hole pair was formed, and meltwater deposits derived from a new ice-advance (NE-Ice)
filled the depression. The NE-Ice overran the complex during its advance to the main station-
ary line situated in the North Sea. When this ice in turn melted away (c. 19 000 - 15 000 B.P.),
the glacial landscape was draped by arctic marine deposits of the Vendsyssel Formation (new
formation defined herein).

_________________________________________________________________________________________

Author's address

Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark.
E-mail: sasp@geus.dk

Introduction

Glaciotectonic studies in Denmark have a long tradi-
tion, and an important part of structural geology stud-
ies in Denmark concern glacial tectonic deformation
resulting from the southward advance of the Scandi-
navian Ice Sheet in the Pleistocene (Fig. 1). The descrip-

tion of the geological structures dates back to Pug-
gaard (1851), who made one of the first extensive and

detailed Danish structural analyses of a tectonic com-
plex and provided a classic cross-section of Møns Klint.
Johnstrup (1874) established the concept of glacial
deformation. The next milestone in glacial tectonic
studies in Denmark was by Jessen (1918, 1931), whose
detailed survey of Lønstrup Klint (Fig. 1) included a

structural analysis and an attempt at a glaciodynamic
interpretation of the deformation structures observed.
The Lønstrup Klint coastal section includes the Rubjerg

Knude Glaciotectonic Complex, which is the subject
of this study (Fig. 2). A Danish school of glaciotecto-

nic studies subsequently developed (Madsen 1916; Jes-
sen 1931; Gry 1940, 1941; Rosenkrantz 1944; Berthelsen
1973, 1975, 1978, 1979; Sjørring 1974, 1977, 1981, 1983;
Rasmussen 1975; Petersen 1978; Houmark-Nielsen
1987, 1988; Pedersen 1987, 1993, 1996, 2000; Peder-
sen & Petersen 1988, 1995, 1997; Pedersen et al. 1988;
Klint & Pedersen 1995; Jakobsen 1996), which has
naturally been stimulated by geologists working with
glaciotectonic structural geology internationally (Ban-
ham 1977, 1988; Stephan 1980; Aber 1982, 1993; Ehlers
1983; van der Wateren 1985, 1992; Boulton 1986; Boul-
ton & Hindmarsh 1987; Croot 1987, 1988; Meer 1987;
Goldthwait & Matsch 1988; Aber et al. 1989; Hart 1990;
Hart & Watts 1997; Bennett 2001).

The similarity in structural geometry between gla-

ciotectonic terrains and orogenic belts has led to pro-
longed debate. Are glaciotectonic terrains scale mod-

els for orogenic deformation? Or does the soft and
synsedimentary nature of glaciotectonics differ in prin-
ciple from that of fold belt deformation? Arguments
for deformational similarity have been put forward by
Berthelsen (1978, 1979), Banham (1988), Aber et al.
(1989), van der Wateren (1992) and Pedersen (1987,
2000). These structural geologists share the opinion that

the terminology of structural geology related to oro-
genic belts is applicable in the description and dis-
cussion of glaciotectonic complexes. The main differ-
ences between deformation in metamorphically altered
rocks and glaciotectonic deformation of soft sediments

are: (1) the presence of 'free' water, which enables
liquefaction and fluidisation, (2) the velocity of the
deformation, and (3) the shallowness of penetrative
deformation. In contrast, deformation of metamorphic
rocks commonly involves alteration and recrystallisa-
tion of minerals, processes that never apply to glacio-
tectonics.

The advantage of a study of glaciotectonic complexes

is that the structures are at a scale that allows them to
be studied in a single exposure, in contrast to fold
belts where extensive field mapping and expensive
geophysical investigations are typically r equired for
adequate documentation of the structures. Further-
more, many glaciotectonic complexes are geological-
ly young, which means that the upper structural levels
ar e still preserved and interpretation of the full dyna-
mic development of structural complexes is possible.
The structural architecture of glaciotectonic complexes
may therefore serve as inspiration for the interpr eta-
tion of thin-skinned structural relationships in fold belts
and thrust-fault deformation terrains. The structural
analysis of the Rubjerg Knude Glaciotectonic Com-
plex is presented as a mesoscopic model of a thin-
skinned thrust-fault complex (Plates 1, 2).

History of the present investigation

This study focuses on the structural framework and
dynamic development of the glacial tectonic thrust-
fault complex at Rubjerg Knude, Lønstrup Klint. It is
based on twenty years of investigations of the Løn-
strup Klint cliff section. The author took up the study
of glacial tectonic thrust-fault structures after having
concluded a Ph.D. thesis on thin-skinned thrust fault-
ing in the North Greenland fold belt (Pedersen 1979,
1981, 1982, 1986a, 1987). A large part of the study of
the fold belt structures in Peary Land, North Green-
land, was photogrammetric mapping (Pedersen 1979,
1981), undertaken at a time when geological map-
ping by computer-assisted photogrammetry was under
development in Copenhagen. This project was an inte-
grated collaboration between the Geological Survey
of Greenland, the Institute of Surveying and Photogram-

metry of the Technical University of Denmark (DTU),
the Geological Museum (GM) and the Geological Insti-
tute (GI) of the University of Copenhagen. In the years

up to 1990, techniques of geological mapping and
construction of geological cross-sections based on multi-

model photogrammetric analysis were developed and
made available at DTU (Dueholm 1992). Initial inves-
tigations in co-operation with K. Dueholm (DTU) and
A.K. Pedersen (GM) proved the applicability of multi-
model photogrammetry in the study of glaciotectonic
cross-sections in Denmark by an examination of the
Møns Klint cliff section (Pedersen 2000). Subsequent-
ly, the photogrammetric investigation of the Rubjer g
Knude cliff section was initiated, and forms the basis
of the present work.

Objectives

The objectives of the study of the Rubjerg Knude Gla-
ciotectonic Complex can be summarised as follows.

1. A description of an exceptionally well-exposed gla-

ciotectonic complex, which can be taken as an ex-
ample of a very low friction thrust-fault wedge, pre-
sented as a detailed cross-section based on multi-
model photogrammetric measurements of the Ru-
bjerg Knude cliff section.

2. A demonstration of the techniques of balanced

cross-section construction that per mit interpretation
of the unexposed parts of the thrust-fault complex.

3. The construction of a model for the dynamic de-

velopment of the proglacial thrust system that dem-
onstrates the sequential evolution of increasing de-
formation intensity and the interplay with syntec-
tonic depositional processes.

4. An interpretation of deformation processes within

the framework of Danish glacial stratigraphy in the
late Pleistocene (late Middle to Late Weichselian c.
30 000 - 20 000 years B.P.).

Previous conceptual models

The basic concept of glacial processes acting as the
deformation agent was formulated by Johnstrup (1874).
His concept was primarily focused on the Formation
of the spectacular cliffs at Møns Klint in south-eastern
Denmark and on Rügen in north-eastern Germany.
However, subsequently Johnstrup (1882) also includ-
ed the formation of the steeply inclined floes exposed
in the Lønstrup Klint cliff section in the classic exam-
ples of glacial deformation in Denmark. (The term
floes is frequently used in the old glacial geology lite-
rature inspired by the idea that the dislocated sheets
were ground- or permafrozen; in a structural geologi-
cal context, floes are identical to thrust sheets or thrust-
sheet segments.) Johnstrup's main conclusions con-
cerning the glaciotectonic origin of the deformation
at Lønstrup Klint were: (1) the dislocations are super-
ficial without extending down to a deep root zone,

and are restricted to surface phenomena, (2) the di-
rection of movement indicated from the dip of the
dislocated floes corresponds to a uniform direction of
ice advance, and (3) the dislocated floes formerly con-
stituted one undisturbed area. The detailed mapping
and construction of the cross-section was presented

by Jessen (1918) in his geological description of the
Vendsyssel map sheet. However, the final detailed de-
scription of the dislocations at Lønstrup Klint was pub-

lished later (Jessen 1931).

In 1927, George Slater included a study of the Løn-

strup Klint section as part of his thesis for a D.Sc.
degree at the University of London, which also in-
cluded a study of glacial deformation at Møns Klint.
The most striking conclusion was that the glacial defor-
mation at Lønstrup Klint was caused by englacial defor-
mation. Slater (1927, p. 312) summarised thus: "... 2.
The deposits represent the final positions of englacial
material after the melting of the interstitial ice. 3. The
type of structure is analogous to that seen in decaying
Arctic glaciers, and is due to the arresting of move-
ment of the frontal part of an overloaded ice-sheet. 4.
The structure has been built up in the reverse direc-
tion to the line of movement." Slater (1927) interpre-
ted the Lønstrup Klint section as a variety of glacial
tectonics he termed 'the stagnant-glacier type'.

Subsequently, Axel Jessen and Karl Gripp exchang-

ed ideas about proglacially formed glaciotectonic struc-

tures, and concluded that the structures Jessen had
observed at Lønstrup Klint were similar to those that
Gripp (1929) described from the foreland of the ad-

Glacial tectonics - concepts and models

vancing Holmströms Gletscher on Spitsbergen. In his
detailed and comprehensive description of his inves-
tigations, Jessen (1931) concluded that the disloctions
cannot have formed englacially, but must be the result

of pressure building up due to loading at the margin
of the advancing ice. This pressure spreads out later-
ally into the clayey units, which in the foreland react
by splitting up into fractured dislocation sheets com-
pressed in front of the advancing ice masses.

Jessen (1931) also discussed the difficulty related

to the displacement of the sheets without fracturing
of the lithological units resulting in a complete col-
lapse during deformation, and he pointed out that
Johnstrup (1882) had suggested that the deformed
layers could have been ground-frozen. Jessen's (1931)
more subjective arguments against Slater's work con-
cern the fact that Slater (1927) did not refer to Jessen's
(1918) substantial work on Vendsyssel and in particu-
lar his published cross-section of Lønstrup Klint. Jes-
sen pointed out that major anticlines in Slater's cross-
section between Mårup Kirke and Rubjerg Knude Fyr
do not exist, and that Slater's (1927) misinterpretation
must be ascribed to his superficial investigations which
did not allow him to check the way-up relationship of
each limb in the fold structure (Jessen 1931).

In his work on the glaciotectonic deformation of

Palaeogene diatomites with ash layers in the Limfjor-
den region, Gry (1940) compar ed these with the de-
formation at Lønstrup Klint and supported the progla-
cial deformation concept of Gripp (1929) and Jessen
(1931). Furthermore, Gry proposed a gravity-spread-
ing model for the deformation and attempted a very

early balanced cross-section in the consideration of
restoration of the dislocated thrust sheets (Fig. 3). How-

ever, Gry (1940) proposed a cylindrical model for the
thrust surfaces, and in his 'back-stripping' cross-sec-
tion the floes were displaced along circular fault lines.
Thus, in his dynamic consideration the floes were as-
signed a standing position with their frontal parts 'up
in the air' (Fig. 3), and he consequently concluded
that more than 80% of the upper sand-series at Løn-
strup had been eroded away by the advancing ice.

In contrast to this point of view, Pedersen (1987)

suggested that a large proportion of the upper sand-
series was deposited syntectonically; this removed the
requirement that a large part of the floes or thrust sheets

had been eroded away. Pedersen (1987) interpreted
the glaciotectonic thrust-fault complex as an example
of gravity-spreading deformation, viewed in the light
of the gravity-spreading experimental model presen-
ted by Bucher (1956) and with reference to compa-

rable gravity-spreading deformation in soft sedimen-
tary rocks exemplified by the mudlumps in the Missis-

sippi Delta (Morgan et al. 1968). Furthermore, the
mudlumps or mud diapirs in the Lønstrup Klint imbri-
cate fan were described, and interpreted as an integral

part of a conceptual dynamic model for thrust-fault

related mud diapirism and syntectonic sedimentation
(Fig. 4).

Sadolin et al. (1997) elaborated on the model of

syntectonic sedimentation in the Lønstrup Klint sec-
tion. Based on detailed sedimentological studies, they
pointed out the importance of the unconformity that
separates the lower muddy units (their unit A), from

Diluvial sand

Yoldia clay

Fig. 3. A model for structural balancing

of the dislocated floes in the Lønstrup
Klint section suggested by Gry (1941).

In his model, the displacement surfaces
were regarded as cylindrical sections

and due to the suggested amount of
displacement about 80% of the dislocat-

ed floes was subsequently eroded
away.

the upper sandy units (their units B-D). The lower
unit A was interpreted to have been deposited in a
lake isolated from the former marine Kattegat-Ska-
gerrak basin by either a damming of the advancing
ice, in accordance with ideas also presented by Jes-
sen (1918, 1931), or simply by isolation of the lake
basin due to lowering of sea level in the late Pleis-
tocene (Sadolin et al. 1997). The unconformity was
interpreted to reflect a major drainage event of the
lake basin before a shallow lacustrine basin was es-
tablished, characterised by incursions of glaciofluvial
deposition (units B-D of Sadolin et al. 1997). During
the deposition of units C and D, glaciotectonic thrust-
ing commenced contemporaneously with the rise of
mud diapirs and the formation of normal faults due to
mass adjustments in the mobilised mud in the subsur -
face (Sadolin et al. 1997; Fig. 5).

The conceptual model presented here aims at an

interpretation based on the concepts of thin-skinned
thrust-fault tectonics. Although the scale is an order
of magnitude smaller than in typical orogenic belts, it
has not been found appropriate to introduce special
terminology for the deformation structures in the Ru-
bjerg Knude Glaciotectonic Complex. The concept of
thrust-fault deformation and related structures is sum-
marised in the following chapter.

Thin-skinned thrust faulting:
the concept

It is difficult to judge exactly when the concept of
thin-skinned thrust faulting nucleated, as it represents
a gradual evolution of ideas over the last 25 years or
more. However, Boyer & Elliot (1982) appear to have
been the first to give a conceptual introduction to the
basic principle of thin-skinned thrust faulting. Suppe
(1983, 1985) improved the concept by defining and
describing the geometry and kinematics of fault-bend
folding. Jamison (1987) and Schirmer (1988) contri-
buted with further improvements of geometric analy-
sis of fold development in overthrust terranes and
thrust-fault hanging-wall successions. McClay (1992)
presented a glossary of thrust tectonic terms, and Erick-
son & Jamison (1995) demonstrated viscous-plastic
finite-element models of fault-bend folds. In 1997, an
entire volume of the Journal of Structural Geology
was devoted to thrust-fault tectonics. Among the pa-
pers that particularly inspired and supported this study
of glaciotectonic thrust faulting were those of Contre-

ras & Sutter (1997), Medwedeff & Suppe (1997) and
Mitra & Sussman (1997).

Thrust-fault modelling

To better understand the range of possible configura-
tions of different structural frameworks of thrust-fault
complexes, a series of computer models were tested
with the aid of the program AUTOFAULT, a 'Balanced
Cross Section Program' within the AutoCAD system
frame (Ozkaya 1994). Four of these test models are
demonstrated here to illustrate the thin-skinned thrust-
fault concept (Figs 6-9).

The basic function of the model is to define and con-

struct a layer package onto which a thrust fault is add-
ed and given a certain displacement. The program
then calculates the configuration of the thrust sheet

Fig. 4. A four-stage model for the development of mud diapirs

related to thrust faulting in Lønstrup Klint suggested by Peder-
sen (1987). Note that in the model the thrust zone of the hang-

ing-wall ramp constitutes mobilised mud and that syntectonic
deposits accumulate 'piggyback' between the thrust sheets.

Fig. 5. The structural and depositional development of the Sandrende Section suggested by Sadolin et al . (1997). The model
summarises four stages of development initiating with the formation of the regional erosional unconformity ( 1 ). Unit B was

deposited in topographic lows above the unconformity, and thrust faulting initiated contemporaneously with the deposition of unit
C ( x₁-y₁ and x₂-y₂ denote same reference points separated by the thrusts, where x = footwall syncline and y = hanging-wall

anticline) ( 2 ). Propagation along the thrust faults continued and unit C was deposited during increasing tilting of the thrust sheet.
Normal-fault fractures formed in connection with the incipient diapirism ( 3 ). The Sandrende diapir rose during deposition of unit D

and normal faulting propagated. In the proximal part of the thrust sheet, a network of conjugate extensional faults developed and
interference between a new-formed satellite thrust and the normal faults affected the complex. The tip of the thrust sheet was bent

due to drag along the side of the rising diapir ( 4 ). Star symbol provides a reference point through the development stages.

Step 1

Step 2

Step 3

Step 4

Step 5

Step 6

Hanging-wall
block

Ramp

Footwall block

50 m displacement

100 m displacement

150 m displacement

200 m displacement

300 m displacement

400 m displacement

Lower flat

Axial surface

Upper flat = top surface

Lower ramp hinge

Upper ramp hinge

Hanging-wall anticline

Hinterland-dipping limb

Foreland-dipping limb

Hanging-wall flat

Hanging-wall ramp

Upper footwall flat

Foot

wall

ramp

Décollement or lower footwall flat

100

200

300

400 m

Fig. 6. Test model 1 of thrust-fault deformation constructed with the computer program AUTOFAULT (Ozkaya 1994). The model
demonstrates the development of simple ramp propagation given increasing displacements. In the first four steps, the displacement

is sequentially incr eased by 50 m, whereas a displacement of 100 m is added to steps 5 and 6. Note that a 'typical upright anticline'
develops when the displacement is about twice the thickness of the layer package displaced. Moreover, the model illustrates the

terminology applied in the text and defined in Appendix 1.

for the specific model constructed. Thus the program
gives the 'differential' calculation model to an induced
'integration' solution configuration. Further thrust faults
can be added, and be given new displacements, such
that rather complex models can be constructed. How-
ever, a few limitations of the program hamper realistic
comparisons with nature.

Thus the program cannot

handle inclinations exceeding 60°. In general this is
not a problem as ramp angles typically range between
10° and 35° and for rock mechanical reasons never
exceed 45° (Ozkaya 1994). However, the problem of
steep inclinations becomes important in complexes
including superimposed deformation. A second limi-
tation is that testing with superimposed displacements
requires a construction with an upper flat located with-
in the model. This results in an unrealistically high
number of shallow upper flats in the models, as illus-
trated below in test model 4 (see Fig. 9). Thirdly, the
program cannot accommodate cross-cutting thrust-fault
relationships, which limits the spacing and dip of
ramps. Nevertheless, the test models give a good in-
troduction to the thrust-fault concept, and demonstra-
tion of models with basic layer package dimensions
approaching the scale of thrust sheets involved in the
Rubjerg Knude Glaciotectonic Complex can be achie-
ved.

A glossary of the thrust-fault terms used here is

given in Appendix 1; note that only contractional
thrust-fault structures are considered.

Test model 1

The first AUTOFAULT model displays a simple thrust
fault with one ramp connecting a lower and an upper
flat (Fig. 6). The development of thrust-fault structures,

in particular the fault-bend folding of the hanging-
wall anticline, is demonstrated in six steps with increas-
ing displacement. The ramp angle is 25°, and the layer

package constitutes a lower unit 25 m thick where the
lower flat (or the décollement zone) is located. Above
this, one 25 m and two 20 m thick layers have been
constructed, with a 30 m thick uppermost layer (Fig.
6). The model approaches the assumptions of parallel
behaviour with preservation of layer thickness, no net
distortion where layers are horizontal, and conserva-
tion of bed length (Suppe 1983).

Step 1 shows the gentle hanging-wall anticlinal fold-

ing after 50 m displacement. Note the flat-topped na-
ture of the hanging-wall anticline, which makes it al-
most insignificant. The backlimb of the anticline dips

toward the left, parallel to the ramp, and the axial
surfaces defined by the bend above the lower ramp
hinge and the bend of the hanging-wall anticline de-
fine two kink bands dipping steeply to the right. By
comparing steps 1 and 2 it can be seen that the spac-
ing between the kink bands increases with increasing
displacement.

Step 2 gives the configuration after 100 m displace-

ment. Here the for elimb dipping towards the foreland
to the right starts to be a significant part of the struc-
ture. Note the increase in spacing between the kink
bands in the backlimb structure. The kink bands de-
fine minor zones of weakness, which could develop
into small reverse faults as in the thrust model dem-
onstrated by Wiltschko (1979). These are referred to
as back thrusts.

Step 3 shows the structural development after 150

m displacement. Note that the flat-topped hanging-
wall anticline now has a more angular upright for m,
where the kink bands fanning up from the positions
near the upper ramp hinge approach each other. How-
ever, in the model the anticline maintains its flat-topped
structure and retains two axial surfaces (kink bands).

Step 4 demonstrates the formation of the upright,

angular hanging-wall anticline, where the amount of
displacement is close to the length of the thrust-fault
ramp. Due to the geometric adjustments the hanging-
wall ramp is shorter than the footwall ramp. The dis-
placement is 200 m corresponding to about two times
the thickness of the thrust sheet.

Step 5 shows the structural development after 300

m displacement. The hanging-wall anticline becomes
even more flat-topped and the space between its axial
surface kink bands increases. Note that the for eland-
dipping forelimb is linked to the hanging-wall ramp
displaced along the footwall flat, and the hinterland-
dipping backlimb corresponds to the hanging-wall flat
bent up along the footwall ramp.

Step 6 , with a displacement of 400 m demonstrates

that the main structural configuration is maintained,
except for the increase in spacing between the back-
limb and the forelimb.

Test model 2

The second AUTOFAULT model demonstrates the
propagation along a thrust fault differentiated into a
décollement zone, a lower ramp, an intermediate flat,
an upper ramp and an upper flat bringing the thrust
fault up to the top surface (Fig. 7). The model is con-

structed with two lower units, 40 m in thickness; the
décollement zone is located in the second layer. The
lower layers mimic the lower clay units of the Løn-
strup Klint stratigraphy, and two c. 25 m thick layers
overlie them. The top layer is 50 m thick, but while
not comparable to any part of the stratigraphy in the
Lønstrup Klint section, its construction yields a better
demonstration of the development envisaged. The
lower ramp is given a dip of 25° and the upper ramp
a dip of only 15° to reflect the principle of increasing
angle of fracturing with increasing depth (Hobbs et
al. 1976; Pedersen 1996). The distance between lower
and upper ramps along the inter mediate flat is c. 250
m, and three steps are presented in Fig. 7.

Step 1 is given 50 m displacement and two hang-

ing-wall anticlines immediately appear. The steep ramp
clearly initiates the formation of an upright anticline
with steeply dipping limbs. Between the two hang-
ing-wall anticlines, an intervening syncline forms above

the intermediate flat. The involute sur face of the syn-
cline provides the location for a broad, shallow basin.

Step 2 shows the structural development after 100

m displacement. This demonstrates clearly that the
intervening syncline is an obvious site for a piggy-
back basin to develop. Note that the steeply dipping
forelimb of the hanging-wall anticline above the lower
ramp would be the obvious site for erosion and the
source of material feeding into the piggyback basin.

Step 3 demonstrates that with a displacement of 200

m, the piggyback basin becomes narrow and is ele-
vated to a higher position as a consequence of the
displacement up along the upper ramp; it is eventual-
ly lifted out of the position for being a centre of depo-
sition. With increasing displacement, the frontal part of

the thrust sheet develops into a wedge-shape structure.

Hanging-wall
block

Lower hanging-wall ramp

Lower ramp

Upper ramp

Upper flat

Upper hanging-wall ramp

Footwall block

50 m displacement

100 m displacement

200 m displacement

Piggyback basin

Intermediate flat

Lower flat

Fault-bend folding

Step 1

Step 2

Step 3

100

200 m

Fig. 7. Test model 2 of thrust-fault deformation constructed with the computer program AUTOFAULT. The model demonstrates the
development of thrust-fault propagation along a lower and an upper ramp and the connecting flats. Note in this model the

formation of two anticlines divided by a syncline, the depression of which is the obvious location of a piggyback basin.

Test model 3

The third AUTOFAULT model aims at constructing an
imbricate complex by branching faults fanning up from
the same décollement level (Fig. 8). The model is con-
structed with a lower 20 m thick unit in the top of
which the décollement zone is located. Above the dé-
collement zone, three units with a combined thick-
ness of 50 m form the lower part of the thrust sheets,
and the succession is capped by an upper 20 m thick
unit. In three sequential steps, the principle of piggy-
back thrusting is demonstrated (Fig. 8).

Step 1 shows 100 m displacement along a deep-

rooted ramp dipping 30°. Note the normal ar chitec-
ture of the hanging-wall anticline results from the
ramping (compare with Fig. 6, step 3).

Step 2 demonstrates the re-orientation of the piggy-

back thrust sheet by the introduction of 100 m displace-

ment along a 18° dipping ramp in front of and below
the first thrust fault. Note that the accumulated dis-

placement of the first thrust sheet amounts to c. 200 m.

Step 3 shows an additional 100 m displacement along

a low-angle 12° dipping ramp. Although the model

demonstrates the main architecture of the imbricate
fan illustrated by Pedersen (1987), it is a fairly simple
model which may have only little relevance to natural
conditions.

Test model 4

The final AUTOFAULT model demonstrates the more
likely formation of a steeply dipping imbricate fan or
duplex (Fig. 9). The model is given the same strati-
graphic units as in Test Model 3 (Fig. 8). A longer dé-

collement zone is located in the middle of the lower-
most unit, in addition to an inter mediate flat in the
third layer, while the upper flats are located within
the uppermost unit. The initial steps in the construc-

100 m displacement

100 + 100 m displacement

300 m accumulated displacement

Simple ramp

Piggyback thrust sheet

Branching thrust fault

Branching thrust-fault imbricate fan

Step 1

Step 2

Step 3

100

200 m

Fig. 8. Test model 3 of thrust-fault deformation constructed with the computer program AUTOFAULT. The model demonstrates the

formation of an imbricate fan by successive thrust-fault splays branching up from the main décollement zone. The encircled
numbers refer to the sequential phase of thrust imbrication. The model is probably not comparable to structures formed in nature,

but can be regarded as an introduction to test model 4 (Fig. 9).

tion of this model are similar to the examples demon-
strated above, and hence only the final two steps are
illustrated (Fig. 9). However, these give a convincing
illustration of the increase of dips in an imbricate thrust-
fault complex.

Step 1 illustrates the final structural architecture af-

ter 140 m displacement of thrust sheet 1 along the
décollement zone, the lower ramp, the intermediate
flat, an upper ramp and onto the upper flat (dips of
ramps c. 25°). Thrust sheets 2-5 were formed by branch-

ing ramps (dip of ramps c. 15°) with a displacement
of c. 80 m added to each thrust fault. Finally, the lead-
ing thrust sheet (6) is displaced 90 m along the lower
décollement zone and a deep-rooted 30° dipping ramp.
Note that the branching ramp imbricates are carried
piggyback on thrust sheet 6. Furthermore, it should
be noted that a long trailing segment of thrust sheet 6
occurs between the décollement zone and the inter -
mediate flat. If this trailing segment becomes chopped
up into duplexes between the two deep-rooted ramps,
it will affect the overlying imbricates by vertical eleva-
tion and the formation of antiformal stacks.

Step 2 illustrates the over-steepening of the imbri-

cates stacked onto the backlimb of the hanging-wall
anticline of thrust sheet 6 arising from the addition of
100 m displacement to step 1 along the leading thrust
rooting down to the lower décollement zone.

Test models: concluding remarks

A set of principles may be derived from the test models.

1. The level of elevation of the reference surface is

directly related to the number and sizes of ramps
the thrust sheet has passed. A ramp rooting down
to a deep flat level corresponds to a high elevation
of the topmost reference surface. In contrast, if a top

reference surface is positioned at the same level as
in the foreland, the thrusting corresponds to a trans-
lation along a flat.

2. The steeper the ramp, the earlier its time of forma-

tion. Gently dipping ramps are initiated at a late stage

of deformation in areas proximal to the for eland.

3. The thickness of a piggyback basin reflects its du-

ration as depocentre. Thus a small thickness of pig-
gyback basin fill indicates an early trapping of the
basin by overthrusting of a hanging-wall block.

4. A thick succession in the piggyback basin reflects a

long period of translation of the thrust sheet along
a long flat.

Step 1

Step 2

Fig. 9. Test model 4 of thrust-

fault deformation constructed
with the computer program

AUTOFAULT. The model
demonstrates an imbricate fan

(see Fig. 8) subjected to fault-
bend folding during piggyback

translation of an underlying
hanging-wall flat propagation

along a footwall ramp. The
footwall ramp propagation will

consequently result in increasing
dips of the thrust sheets in the

imbricate fan. Encircled
numbers indicate successive

thrust sheets.

Concept of balanced cross-section

The principle of the balanced cross-section in struc-
tural analysis of thrust-fault systems was elegantly
outlined by Dahlström (1969) and further improved
by Suppe (1985). The application of balanced cross-
sections in glaciotectonics has been demonstrated by
Croot (1987), Klint & Pedersen (1995) and Pedersen
(1996).

In the construction of the balanced section, two

different functions are applied: (1) the line balance,
and (2) the volume balance, which in a 2-D cross-
section corresponds to area balance. The first func-
tion concerns the length of displacement, whereas the
second function concerns the preservation of volume
in the deformed cross-section compared with the r e-
stored undeformed cross-section (for demonstration
see Plate 2). The basic method of balancing a cross-
section (Dahlström 1969) is restoration by defining a
pinpoint to be fixed to the foreland and then restor-
ing the thrust sheets back to their initial pre-deforma-
tional position. Thus one begins at the foreland and
then by line balancing the thrust sheets are pulled
back sequentially to their position prior to displace-
ment. This requires a measure of displacement, which
is the essential, but often difficult figure to achieve
without some range of uncertainty.

Details concerning the construction of the balanced

cross-section of the Rubjerg Knude Glaciotectonic Com-

plex (Plate 2) are given below.

Location

The Rubjerg Knude cross-section is 6124 m long and
extends from the coastal cliff immediately south of
Lønstrup, Ribjerg, to about 300 m north of the ramp
leading down to the beach at Nørre Lyngby (Fig. 2,
Plate 1). The strike of the section is 17°, which is nearly
parallel to the direction of the coastline. This is also
approximately perpendicular to the main concentra-
tion of structural strikes (bedding, thrust faults and fold

axes; Fig. 10). The cross-section was consequently
constructed to fit a general plane of orthographic pro-
jection with a projection axis striking 107°.

The Rubjerg Knude cross-section covers only the

Rubjerg Knude Glaciotectonic Complex. Thus it is not
as extensive as the cross-section of Lønstrup Klint con-

structed by Jessen (1918, 1931), which extends from
the cliff at the northern fringe of Lønstrup to the north-
ern part of the beach at Løkken (see Fig. 12). The
UTM co-ordinates (zone 32, ED50) of the end points
of the Rubjerg Knude cross-section are 547512, 6370243
(N-end point) and 545251, 6364783 (S-end point).

Photogrammetric work

The cross-section of Rubjerg Knude Glaciotectonic
Complex (Plate 1) is based on a multi-model photo-
grammetric investigation of the cliff section using the
method described by Dueholm (1992). Oblique pho-
tographs were taken from a Cessna fixed-wing air-
craft with a Minolta XG2 camera with known optical
specifications, calibrated at the laboratory of photo-
grammetry at the Technical University of Denmark.
Standard 24 × 36 mm diapositive colour film was used,
and the photographs were taken with 66% overlap
from a distance of 200-300 m with an inclination an-
gle of c. 35°, which provided the basis for setting up

67 stereoscopic models. In the laboratory, the orien-
tation of the stereo-models was carried out based on
ground control points adapted from two sets of verti-
cal aerial photographs at a scale of 1:25 000, namely

D9202 G 1365-66 and KMS 9203 A509-10 taken in
May 1992.

The stereoscopic instrument used was a Kern DSR

15 analytic plotter with a DEC VMS operating system
and the special attached GEOPROGRAM developed

100

200 m

100 m displacement
on youngest thrust fault

200 m displacement
on youngest thrust fault

Location and construction of the Rubjerg Knude
cross-section

by Dueholm (1992). In the stereoscopic models, the
geological features were outlined by the floating mark
and digitised by the attached computer. The digitised
data were stored for the later construction of the cross-
section and the transformation for other programs
applied for the management of the cross-section dis-
play. The scale of the Rubjerg Knude cross-section in
the analytic plotter version is 1:500, and the accuracy
of the plotted data is about 25 cm (for further details,
see Appendix 2).

Digital editing

In order to represent the cross-section in a publish-
able display, the digitised data were transferred to ARC-
INFO at the GIS-laboratory at the Geological Survey.
Here it was transformed into an ARC-VIEW project,
which served as the computer tool for editing the cross-
section. Thus all areas were converted to closed poly-
gons, which were annotated to fit the legend of litho-
logies. During this editing, interpretations were made

to finish the display of the cross-section, in particular
interpretations of the scree-covered parts of the sec-
tion. This was carried out contemporaneously with the

construction of the balanced cross-section (see be-
low), and a few additional corrections were added to
the Rubjerg Knude cross-section. Some new exposures
along the cliff section appeared in 1997-1999, which
added to a better understanding of the structures in
the transition from the frontal part of the glaciotec-
tonic complex to its foreland. These have been incor-
porated into the ARC-VIEW project.

The final editing of the cross-section concerned the

balanced cross-section. The construction of the bal-
anced section was digitised and transfor med into an
ARC-VIEW project, and the subsequent interpretation
of the extension of the thrust-fault ramps below sea
level was added. Thus the Rubjerg Knude cross-sec-
tion comprises a display of the exposed part of the cliff

section with lithological and structural identity added
as themes. Furthermore, the cross-section includes an
interpretation of the thrust-fault structures in the sub-
surface. Finally, a balanced construction was added

2900

3000

L/R-u

Fig. 11. Illustration of the method used for estimation of the displacement for the balanced cross-section. Above the main erosional

unconformity at the top of the cliff, the extension of the thrust sheet tip is constructed by the intersection between the thrust fault
( T ) and the L/R-unconformity ( L/R-u ) based on the angle ( +/- ) between the bedding of the thrust sheet and the hanging-wall ramp.

Dm , displacement measured; Dc , displacement constructed from tip-extension; Ds , displacement estimated from the interpretation
of thrust-fault trace under the scree cover. The section illustrated is part of the Rubjerg Knude Fyr Section (Plate 1).

Table 1. The distribution of areas in the balanced cross-section (Plate 2)

Balance (Plate 2A)

Ramps (Plate 2B)

Section*

Number
of areas

Area (m

)

Section*

Number
of areas

Area (m

)

01UL

23 048

01UL

24 302

02SN

8965

02SN

8536

03MB

28 443

03MB

30 944

04KR

24 158

04KR

18 390

05BR

34 143

05BR

33 548

06SR

33 218

06SR

31 588

07SS

26 421

07SS

23 973

08GR

49 842

08GR

45 118

09RF

22 827

09RF

21 458

10ST

43 674

10ST

36 656

11MR

51 902

11MR

45 342

12MK

82 226

12MK

62 763

13BL

17 922

13BL

14 313

NrLy

5437

13RI

4405

PTR

2538

472

9818

* The annotated numbers of sections (05BR) correspond to the sequential location of each section in a distal-proximal order,
and the capitalised letters refer to the general abbreviation of the section names (see Plate 2).

to the cross-section project, such that each thrust sheet
is annotated in a balanced restored cross-section as
well as in the structural cross-section displaying the
geometry of the ramps and flats (Plate 2).

Construction of the balanced
cross-section

The construction of the balanced cross-section for the
Rubjerg Knude Glaciotectonic Complex was based on
the geological cross-section, which displays the geo-
metry of the thrust sheets in sufficient detail to allow
calculations of their displacements and cross-section-
al areas (Plates 1, 2). The method of balancing neces-
sitates that the thrust sheet closest to the foreland is
the first to be restored to its pre-deformational posi-
tion. Therefore, the balancing works backwards from
the distal to the proximal deformation area, and con-

sequently the annotation of the thrust sheets begins
with the first thrust sheet restored. In the balanced
cross-section of the Rubjerg Knude Glaciotectonic
Complex, the thrust sheets are additionally annotated
according to that part of the cliff in which they occur:
two capital letters refer to the name of the section and
a number refers to its position from leading edge to
trailing end of the section. Thus, KR01 is the thrust
sheet nearest to the foreland in the K ram r ende Sec-
tion. A thrust fault is referred to according to the thrust
sheet it displaces. However, the trailing footwall ramp
is referred to the annotation of the footwall block,
which underlies the hanging-wall ramp/flat of the
thrust sheet displaced over it. Thus the KR02 hang-
ing-wall ramp is displaced up along the KR01 foot-
wall ramp.

Although one of the basic conditions in construct-

ing balanced sections is the preservation of volumes,
which in the areas strongly affected by mud remobili-

sation and diapirism is difficult to maintain, the exer-
cise has been carried out to match a balanced section
to the mapped and interpreted thrust-fault framework.
So despite the uncertainties and the demand for inter-
pretation of the geometry and magnitude of eroded
thrust sheet tapers, the construction of the balanced
section added significantly to the understanding of the

duplex framework (Plate 2B).

In the Rubjerg Knude cross-section (Plate 1), the

displacement is measured and estimated mainly from
the distance between the intersection of the L/R-un-
conformity (the unconformity between the Lønstrup

Klint and Rubjerg Knude Formations, see below) and
the footwall ramp, and the intersection of the L/R-
unconformity and the hanging-wall ramp (Fig. 11). How-

ever, the tips of the thrust sheets are generally eroded
away, so the first approximation is from the L/R-un-
conformity footwall point to the point where the hang-
ing-wall ramp is truncated by the glaciotectonic un-
conformity at the top of the cliff. The second approx-
imation is the addition of the distance estimated from
the size of the tip eroded away. This estimate is based
on a simple geometric construction of the tip-triangle

from the dips of the hanging-wall ramp and the L/R-
unconformity, respectively (Fig. 11). This line balance
is subsequently controlled by the width of the piggy-
back basin more or less corresponding to the upper
footwall flat. All the measured displacements are strictly
restricted to the minimum distance to avoid unrealis-
tic exaggerations. Therefore the actual displacements
might be slightly greater.

The area balance is based on a calculation of all

the areas annotated in Plate 2. The computer-supported
calculation was carried out with the ARC-INFO pro-
gram, and the calculations of the areas in the bal-
anced cross-section and the ramp cross-section devi-
ate by less than 10% (Plate 2A, B). This is regarded as
a r easonable correspondence considering the various
sources of error (Table 1). In general, the sections
have a smaller area in the ramp cross-section (Plate
2B) due to the erosion of areas above the main head-
of-cliff unconformity, and in most sections the number
of areas is higher due to the increased complexity of
the geometry in the reconstructed structural cross-sec-
tion (Plate 2B).

Geological setting

The Rubjerg Knude Glaciotectonic Complex incorpo-
rates deformed sedimentary deposits that belong to
the upper part of the mainly marine succession known
previously as the Skærumhede series (Jessen et al.
1910). This succession was deposited in the northern
part of the Danish Basin in the late Pleistocene, after
the late Saalian terrestrial glaciation retreated from Den-

mark (Houmark-Nielsen 1987, 1999; Knudsen 1994).
The major source area for deposits in this part of the
Danish Basin is the Scandinavian basement in south-
ern Norway and central Sweden, that comprises Pre-
cambrian Fennoscandian granites and gneisses over-
lain by Palaeozoic metasediments, including Permian
volcanics and their related intrusive magmatic rocks
of the Oslo province (Oftedahl 1981). The extrabasi-
nal indicator boulders reflect these source areas, which
were situated between the centres of ice-cap nucleation

and the depositional basin (Milthers 1909; Smed 1995).

The boundary between the northern part of the

Danish Basin and the south-western part of the ele-

vated Scandinavian basement is covered by the Ska-
gerrak, the sea covering a deep depression (about 500
m deep) known as the Norwegian Channel (Sejrup et
al. 1987, 1994, 1998). One of the important discussions

concerning the glaciation of Denmark during the last
stadial focuses on how the ice from Norway advanced
across the Skagerrak about 30 000 years ago. The prob-

lem involves the dynamics of the ice stream along the
souther n coast of Norway, the so-called Norwegian
Channel Ice Stream, and the interaction between the
marine and terrestrial parts of the ice cap in south-
west Norway (Larsen et al. 2000). Associated prob-
lems include the filling of the deep trench in Skager-
rak, and the termination of marine conditions in Ska-
gerrak, Vendsyssel, and the northern North Sea as well
as the Kattegat (for locations, see Fig. 12).

The marine environment referred to as the Older

Yoldia Sea, which extended into the Vendsyssel re-
gion, formed in the Late Saalian, and the climatic
change from a mild climate in the Eemian to a glacial

climate in the Weichselian is recorded in a series of
wells drilled in north Jylland and the Kattegat region
(Knudsen & Lykke-Andersen 1982; Lykke-Andersen
1987; Lykke-Andersen & Knudsen 1991; Knudsen
1994). Towards the end of the Middle Weichselian the
Scandinavian Ice Sheet over southern Norway built up.

The ice streams were drained from a main spillway in
Oslo fjord moving out through the Norwegian Chan-
nel along the coastline of southern Norway (Larsen et
al. 2000). A change in the dynamics of the Scandina-
vian Ice Sheet over southern Norway forced the gla-
ciers to progress south-westward across the Norwe-
gian Channel. The ice advanced into the norther n
North Sea, where a glacial cover was established about
29 000 years B.P. and lasted until 22 000 years B.P.,

when the first recurrence of marine conditions (the
'Young Yoldia Sea') was recorded (Sejrup et al. 1994,
2000). This glacial coverage was probably closely con-
nected with the fall in sea level, amounting to 120 m
below present sea level (Fairbanks 1989; Bard et al .
1993), which could have hampered the active drain-
age of the Norwegian Channel Ice Stream. The ice
spread southward over the Skagerrak causing the Kat-

tegat basin to be dammed by the ice margin and ter-
restrial areas to be established in the central part of
the North Sea (Sadolin et al. 1997; Houmark-Nielsen
1999). As a consequence, the Kattegat-Skagerrak re-
gion began to dry up due to the general sea-level fall;
this is reflected in the progression from arctic marine
conditions in the Skærumhede series to brackish and
glaciolacustrine environments. This change took place
at about 32 000 years B.P. (Table 2), and may have
been accentuated by the addition of meltwater from
the advancing Norwegian Ice (Jessen 1918; Sadolin et
al.

1997).
The dramatic drainage of the lake basin in the Kat-

tegat towards the North Sea is recorded by a signifi-
cant erosional unconformity in the sedimentary suc-
cession at Lønstrup Klint (the L/R-unconformity), dat-
ed as close to 29 000 years B.P. (Sadolin et al. 1997).

Shortly afterwards, the basin was once again dammed
and shallow lacustrine and fluvial environments were
established while proglacial thrust faulting was initi-
ated reflecting the relatively fast advance of the ice
margin (Sadolin et al. 1997). The thin-skinned thrust
faulting in the Rubjerg Knude Glaciotectonic Com-
plex involved an accretionary wedge extending more
than 12 km to the south in front of the advancing ice
margin. The lowermost décollement level was situat-
ed in the marine clays of the Older Yoldia Sea. After a
compression of about 50%, the glaciotectonic complex

was formed (Pedersen 1987) leaving a large part of
the area between Lønstrup and Hirtshals as a depres-
sion corresponding to the 'hole' and the Rubjerg Knu-
de Glaciotectonic Complex to the 'hill', in a 'hill-and-
hole' pair in the sense of Aber et al. (1989). Subse-
quently the Norwegian Ice truncated the glaciotec-
tonic complex and the deposition of the Kattegat T ill
Formation concealed its structures. The Norwegian Ice
advanced down to a stationary line (Figs 1, 12) cross-
ing central Denmark from west to east, whose posi-
tion is inferred from the distribution of the Kattegat
Till Formation (Houmark-Nielsen 1987, 1999, 2003;
Pedersen & Petersen 1997).

After its termination at the stationary line (Figs 1,

12), the Norwegian Ice melted back. It was succeeded
by the main south-west ice advance of the Scandina-
vian Ice Sheet, which extended out to the Main Sta-
tionary Line (Ussing 1903; Houmark-Nielsen 1987,
2003; Pedersen et al. 1988). In northern Jylland, the
isostatic depression due to the loading of the ice sheet
was substantial. The termination of the glaciation in
Denmark thus resulted in interference between eus-
tatic sea-level rise and isostatic rebound with a com-
plex depositional development during the re-estab-
lishment of the Younger Yoldia Sea in the Skagerrak-
Vendsyssel-Kattegat region about 17 000 years ago.

This may be summarised as a forced regression under
progressively falling sea level due to the isostatic rise
of the Vendsyssel region (Richard 1996). The Venne-
bjerg and Rubjerg Knude hilly islands probably formed
part of a larger island archipelago extending out into
the North Sea.

Terrestrial conditions were established at the end

of the Weichselian. At Nørre Lyngby (Fig. 13), a de-
pression was formed above a neotectonic fault zone
that predated Older Dryas time (Lykke-Andersen 1992).
In this depression, lacustrine gyttja and fluvial sand of
Older Dryas and Allerød age were deposited; a large
number of mammalian remains have been found in
these deposits indicating an arctic to sub-arctic rein-

Facing page:
Fig. 12. Location map. Map ( A ) shows the main part of the

Danish Basin with the surrounding land areas. SDKT is the
position of the stationary line for the Norwegian Ice Advance

(SDKT is an abbreviation of s outhern d istribution of K attegat
T ill Fm). MSL is the Main Stationary Line for the Scandinavian

Ice Sheet at the glacial maximum in the Late Weichselian.
Map ( B ) gives the position of relevant geographical localities

in Denmark as well as the location of Fig. 13, the geological
map of Vendsyssel.

deer steppe also populated by hunters (Jessen & Nor -
dmann 1915; Aaris-Sørensen 1995 ).

During Holocene time, the Vendsyssel r egion was

affected by isostatic rebound (Mertz 1924). At Løn-
strup Klint, this resulted in a 25 m elevation of the
heterolithic sediments of the Younger Yoldia Sea. Bogs
developed in the depressions on the glacial peneplain
at the end of the Stone Age and the beginning of the
Bronze Age (Jessen 1918). Up to 1.5 m of peat accu-
mulated; when this is exposed in the cliff surface and
blocks of peat fall down onto the beach, the peat is
locally called martørv (sea-peat). The locality names
Martørv Bakker (sea-peat hill) and Moserende (bog-
gully) refer to these deposits.

The geomorphology of the cliff is strongly influ-

enced by the thrust-fault structures. The clayey parts
of the thrust sheets form ridges that form projections
along the coast between gullies that are eroded out in
the sandy parts (Schou 1949). Springs typically well
out at the sur face between the clayey and sandy units
and more incised gullies (render in Danish) are formed
where the drainage is concentrated. Although the lo-
cation of gullies and the cliff line have retreated about
100 m since A. Jessen constructed the first cross-sec-
tion of Lønstrup Klint, it has been possible to retain
his names in the present cross-section (Plate 1). The

general erosion rate of the cliff is about 1.3-1.5 m per
year (Jessen 1918; Pedersen 1986b). Landslides occur
very frequently, particularly at sites where mud dia-
pirs are located in the cliff section. Where glaciofluvi-
al deposits dominate the cliff section, there is a marked
tendency for aeolian dunes to accumulate on top of
the cliff (Pedersen 1986b). Wind action on the mo-
raine plateau on top of the cliff has eroded the fine-
grained material away from the till deposits, leaving a
stone pavement as the residual trace of the glacially
truncated surface.

Aeolian sand migration intensified about 300-400

years ago (Jessen 1918), one of the consequences being

the burial and abandonment of the Old Rubjerg Church.

The high aeolian dunes on top of Rubjerg Knude have
accumulated during the last 100 years. The Rubjerg
Knude lighthouse was built in 1900 (Bendsen 1981)
when dunes were less than 10 m high. Today the tops
of the dunes are close to 100 m above sea level corre-
sponding to a vertical dune accumulation of nearly 50
m. The present-day steep nature of the dunes was
probably stimulated by the artificial dune protection
fences. However, the steady erosion of the cliff indi-
cates that the lighthouse will fall into the sea about
ten years from now.

Table 2. Radiocarbon dates, Rubjerg Knude and Lønstrup Klint, Vendsyssel, northern Denmark

Stratigraphic unit

Vendsyssel Fm

Rubjerg Knude Fm

Lønstrup Klint Fm

Stortorn Fm

Locality

Lønstrup Klint

Sandrende

Lønstrup Klint

Sandrende

Ribjerg

Mårup Kirke

Stortorn

Lab. ID no.

K-858

K-2670

AAR-2134

AAR-2265

AAR-4066

Ua-4454

AAR-4067

AAR-4068

AAR-4069

Material

Mollusc

Plant

Mollusc

Moss

Mollusc

C age

ka B.P.

13.9

± 0.2

14.7

± 0.2

14.5

± 0.2

30.9

± 0.5

43.0

± 1.3

29.2

± 1.4

29.6

± 0.4

30.9

± 0.4

31.3

± 0.4

Calib. age

ka B.P.*

± 1

± 3

± 1

PDB+

0.6

-27.3

3.3

-29.1

1.5

1.7

1.3

Ref.

(1)

(2)

(3)

(4)

(5)

(4)

(5)

* Calibrated ages are calculated according to Bard et al. 1993 and Kitagawa & van der Plicht (1998).

+ Relative to PDB standard.

References: 1: Krog & Tauber (1974); 2: Knudsen (1978); 3: Richardt (1996); 4: Houmark-Nielsen et al. (1996); 5: this study.

www.geus.dk > Publikationer > Geological Survey of Denmark and Greenland Bulletin > Volume 8 > Siden her

Geological Survey of Denmark and Greenland Bulletin

Nr. 8 pp 1-32, Structural analysis of the Rubjerg Knude Glaciotectonic Complex, Vendsyssel, northern Denmark