Vol. 8 pp 148-192, Geol. Surv. Denmark and Greenland Bulletin

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148

Dynamic development of the thin-skinned thrust faulting

The dynamic development of the thin-skinned thrust
faulting in the Rubjerg Knude Glaciotectonic Complex

is presented as a sequence of restoration stages. Thus,
the progressive deformation of thin-skinned thrust

faulting and related syntectonic depositional devel-
opments are illustrated in sequentially restored cross-
sections beginning with the proximal Moserende Sec-
tion and concluding with the Ulstrup Section in the
most distal part of the thrust-fault complex. The basis

of each restoration sequence is the balanced profile
(Plate 2A), and the end stage is identical with the thrust-
fault cross-section (Plate 2B), including the interpre-
tation of the unexposed ramps and flats in the subsur-

face. The most proximal sections, the Mårup Kirke and

the Ribjerg Sections were interpreted individually in
the preceding chapters, and are not included here.

In a summary scheme (see Fig. 123), it is concluded

that the dynamic development was a process of con-
tinuous progressive deformation. Thus, although the
following description is concentrated on the individual

sections, it should be kept in mind that there is over -
lap between sections, and that the whole system was
mobile. Thus a displacement of 5 m on one thrust
might be followed by 10 m on a more proximal thrust
and 7 m on a more distal thrust depending on the
local conditions. This is the reason why a number of
displacements appear to be out-of-sequence, but with-
in limits that respect the lowest décollement level, and
that displacements along the most distal, leading-edge
thrusts were the last to be activated. It is therefore
also evident that displacement along a leading-edge
ramp may correspond to a translation along a flat in a
proximal section.

Moserende Section

The thrust-fault development in the Moserende Sec-
tion is regarded as normal progressive piggyback
thrusting from the proximal towards the distal part.
The MR12 thrust sheet was probably the first to be
thrust onto the relatively thinner piggyback basin on
the back of MR11 after a c. 10 m thickness of Rubjerg
Knude Formation sediments had been deposited. This
is included in the first stage of the sequential restora-
tion (Fig. 112, stage 1). A total of eight stages have
been differentiated, of which stages 1-6 are illustrat-

ed in Fig. 112. The stage preceding the deformation is
shown in Plate 2A, and the final stage terminating the
deformation is reconstructed in Plate 2B.

Moserende stage 1. The initial thrusting started with
40 m displacement of MR12 over the back of what
was to become MR11. This thrusting was rooted down
to the 20 m intermediate décollement level. During
accumulation of a 20 m thick succession of sediments
in the piggyback basins above the MR13 and MR12
sheets, the thrusting progressed with ramping of MR11
over the Rubjerg Knude Formation on top of what
was to become MR10. This thrusting involved ramp-
ing and translation of the lower segments of MR13-
MR11 from the 30 m flat level onto the 20 m flat level.
The trailing-end segments of the Moserende Section
were contemporaneously over-thrust by MK01, the
frontal thrust of the Mårup Kirke Section, which is
rooted in the 40 m décollement level. The accumulat-
ed displacement of thrusting of MR13, MR12 and MR11
is estimated at about 150 m.

Moserende stage 2. Thrusting of MR09 initiated this
stage. The MR09 thrusting ramped up from the 40 m
décollement level, and a single duplex formed during
stacking of the lower MR09 thrust segment. The MR09
sheet was displaced c. 40 m over the MR08 piggyback
basin. Contemporaneously, MR10 was thrusted over
MR09 and the MR10 hanging-wall flat extended from
the top flat level down to the 40 m décollement level.
The MR13-MR11 thrust sheets were then passively
translated on the trailing lower segment of MR10.

Moserende stage 3. Initial imbrication of the MR08-

MR05 thrust sheets resulted in an accumulated dis-
placement of c. 200 m. The ramping was rooted in the
40 m décollement level along which the main transla-
tion of the trailing-end thrust sheets of the Moser-
ende Section took place. The thrusting involved a
complex relationship between MR07 and MR06 that
may be interpreted as a connecting splay duplex (Mi-
tra & Sussman 1997). Above the L/R-unconformity,
the deposits of the Rubjerg Knude Formation probably

reached a thickness of 20 m.

Moserende stage 4. The frontal part of the section was
activated by c. 40 m translation of MR1 along the 30 m

149

décollement level over the lowermost trailing-end seg-
ments in the Stortorn Section. MR02 and MR03 fol-
lowed this translation, whereas MR04 ramped up one
level from the 40 m décollement level to the 30 m flat
level that resulted in the initial ramping of MR04 up
over the Rubjerg Knude Formation on the back of
MR03. The continued displacement consequently re-

orientated thrust sheets MR05-MR07 into more steep-
ly dipping orientations. The trailing-end thrust sheets
from MR08 and northwards were translated passively
during this displacement.

Moserende stage 5. The frontal displacement of MR01
continued along the 20 m flat level over the trailing-
end segment of the Stortorn Section. MR02 ramped
up along the footwall ramp at the trailing end of MR01
during a fault-bend rotation, which also included the
lower segment of MR01u. A vertical thrust separation
of c. 10 m brought MR02 up along the northern termi-
nation of the MR01 piggyback basin. During the pas-
sage of two intermediate ramps, an irregular anticline
formed on the back of MR02 that had significant im-
plications for the synsedimentary structures formed
in the MR02 piggyback basin (see description of the
Moserende Section, above).

During MR04 thrusting, MR03 was imbricated along

the upper 10 m flat level and the MR03b and MR03c
thrust segments started to break through the piggy-
back basin. From the rear, MR04 was pushed by MR05
which had to pass up over the fault-bend-folded seg-
ment MR04u. Together with MR06 and MR07, the MR05
thrust sheet moved up to the highest level indicated
by the L/R-unconformity, situated c. 20 m above sea
level on the back of MR06 and MR07, and their thrust
faults were steepened into a nearly vertical position.

Moserende stage 6. In the frontal part of the Moser-
ende Section, MR01 picked up a lower segment and
thrust up to the 20 m flat level, which consequently
also elevated the piggyback basin up into its present
high level. The trailing-end ramp of MR01 formed the
footwall ramp for the MR02 thrusting, which resulted
in a fault bend of MR02 as well as MR03. This was
followed by the final displacement of 18 m along the
leading MR03 thrust. Minor adjustments and re-orien-
tation of MR04-MR07 followed the ramping of MR03,
and the trailing-end thrust sheets MR08-MR13 were
passively displaced by translation along the 40 m dé-
collement level.
Moserende stage 7. During this stage, a complex du-
plex was formed by thrusting of the frontal lower seg-

ments, which also including the trailing-end segments
of the Stortorn Section.

Moserende stage 8. The final displacement along the
leading thrust-fault ramp in the Moserende Section
progressed up along the Stortorn trailing-end foot-
wall ramp. Moreover, the fault-bend folding due to
thrusting in the Stortorn Section brought the thrust
sheets into their present steeply dipping orientation.

Moserende Section: summary data

Balanced length (L₀):

1120 m

Cross-section length (L₁):

650 m

Shortening (ΔL):

470 m

Compression:

40.2%

Stortorn Section

The most important development in the Stortorn Sec-
tion was the change from the lowermost 40 m décol-
lement level to the 30 m décollement level. The ramp,
or progressive development of lower ramps, which
marked the change, is here referred to as the Stortorn
lower segment footwall ramp, and was located some-
where near the thrust between ST04 and ST03. Thus,
the ST03-ST01 thrust sheets had their lower décolle-
ment level at 30 m, whereas the thrust faults related
to ST04-ST10 were rooted in the 40 m décollement
level.

Formation of a duplex complex comprising the low-

er most thrust segments exposed the Stortorn Forma-
tion, the oldest strata involved in the thrusting. In the
frontal part of the section, a complex stacking of low-
er segments, remaining in the subsurface from dis-
placement in the Grønne Rende Section, resulted in
duplex formation that elevated ST01-ST03 about 30 m

above the reference level. Due to arguments pr esent-
ed later (see Grønne Rende Section) the duplex stack-
ing had to have been contemporaneous with the short-
ening of the Grønne Rende Section. In the Stortorn
Section, seven stages have been differentiated of which
stages 1-5 are illustrated in Fig. 113.

Stortorn stage 1. This stage is a direct continuation of
the displacement in Moserende stage 4. In the Stor-
torn Section, deformation was initiated by imbrica-
tion of ST07, ST09 and ST10 with an accumulated dis-
placement of about 50 m. This resulted in a ramping

154

up of ST10 from décollement level 40 m to flat level
30 m, along which the translation displacement took
place. Most of the ST09 thrust sheet was also ramped
up by the formation of a lower duplex structure. Both
ST10 and ST09 were affected by fault-bend folding,
which created a major distortion of the L/R-unconform-

ity surface in the upper most part of the thrust sheets.

Stortorn stage 2. During an accumulated displacement
of about 200 m related to the ST10 and ST09 thrusts,
ramping progressed with development of the first
imbrications of ST08 and ST06. Due to ramping from
the lowest décollement level to the 30 m flat level in
the trailing end of ST06, a fault bend affected the ST07-
ST10 thrust sheets that were translated piggyback on
the ST06 thrust sheet. This contributed to the steep-
ening up of the ST07-ST10 thrust structures.

In the frontal part of the section, the imbricate thrust-

ing was initiated at ST01-ST03. Accumulation of sedi-
ments referred to the Rubjerg Knude Formation
reached a maximum thickness of about 20 m, notably
in the synformal troughs of ST03 and ST09 that formed
during the pr ogress over the ramps below.

Stortorn stage 3. At this stage, ST05 was thrust about
40 m up over the footwall ramp on the back of ST04.
The ST05 thrust was rooted in the 30 m flat level, and
during a passage of a lower ramp from flat level 30 m
to 20 m, the initial fault-bend-fold resulted in undula-
tion of the L/R-unconformity at the top of the ST05
thrust sheet. The ST06 thrust sheet progressed over
the footwall flat of ST05, and both thrust faults were
rooted down to the 30 m flat level along which the
main translation of the sheets emplaced piggyback
on ST06 took place. The ST08 thrust sheet was finally
displaced along the upper flat at the top of the ST07
piggyback basin. Consequently, most of the 20 m thick
succession in this piggyback basin was preserved and
indicates the maximum level of sediment accumula-
tion in the Rubjerg Knude Formation during stage 3.
Thrusting of the ST08 sheet along the footwall ramp
on the back of ST07 resulted in a further steepening of

ST09 and ST10, while the frontal elevated parts of the
ST08-ST09 thrust sheets became subject to erosion.

The trailing-end lower segments of ST10-ST07 were

over-thrust by the frontal parts of MR01 and MR02,
corresponding to stage 7 in the Moserende Section.
The accumulated displacement in Stortorn stage 3 was
of the order of 320 m.

Stortorn stage 4. During this stage, the ST04 thrust

sheet was thrust 40 m over the piggyback basin of
ST03, and ST05 was thrust about 70 m over the upper
flat on top of the piggyback basin of ST04. During
this relatively large displacement of ST05, two lower
duplex segments were picked up from the lower 40
m décollement level. After ramping over the Stortorn
lower ramp, the duplex segments participated in the
thrusting up along the footwall ramp on the back of
ST04.

The lower trailing-end segments of the Stortorn

Section were finally thrust up along the steep foot-
wall ramp on the back of ST10 and subsequently the
frontal parts of the Moserende Section were brought
into their present upright orientation. Erosion and re-
deposition affected the piggyback basins on ST05 and
ST08, whereas thrusting over ST07 and ST04 sealed
these piggyback basins. The accumulated displace-
ment reached about 410 m.

Stortorn stage 5. A substantial displacement, in the
order of 80 m, took place along the leading thrust in
the Stortorn Section at this relatively late stage of de-
velopment of the structures at Stortorn . However, this
is only a small amount of the accumulated displace-
ment ( c. 500 m) which is of the same order of magni-
tude as that taken up by the duplex stacking of the
lower trailing-end segments of the Rubjerg Knude Fyr
and Grønne Rende Sections. The ramping and thrust-
ing of ST01-ST04 over this duplex structure explains
the high elevation of the L/R-unconformity and over-
lying piggyback basins in the frontal part of the Stor-
torn Section. The formation of the duplex stack com-
prising the lower duplex segments annotated GRu in
Fig. 113 would have taken place only after the imbri-
cate thrusting in the Grønne Rende Section developed
(see below). The combination of displacement at the
leading edge in one section and stacking of lower
duplex segments in another, indicates a continuous
progressive thrust-fault evolution.

During the propagation of ST05, the trailing end of

ST04 was involved in a duplex formation that result-
ed in fault-bend folding of the earlier formed ST05
lower duplex at the Stortorn lower ramp. The piggy-
back basin on the back of the ST05 thrust sheet was
deformed into a north-verging syncline due to steep-
ening. A similar re-orientation is seen in the thrust-
isolated piggyback basins in ST10 and ST09.

A marked diapirism and remobilisation of mud in

the ST01-ST03, ST05-ST07 and ST09 thrust sheets sug-
gests that the diapirism was related to the intensity of
ramping, especially when the ramping involved the

156

ST01 thrust sheet and the underlying duplex struc-
ture, became fault-bend-folded during the thrust pr op-
agation related to the progressive deformation in the
Rubjerg Knude Fyr Section.

Stortorn Section: summary data

Balanced length (L₀):

1125 m

Cross-section length (L₁):

570 m

Shortening (ΔL):

555 m

Compression:

49.3%

Rubjerg Knude Fyr Section

The Rubjerg Knude Fyr Section roots into the 30 m
décollement level. The most striking features devel-
oped in the Rubjerg Knude Fyr Section are the large
olistoliths in the piggyback basin that were derived
from the collapse and gravity gliding of a projecting
segment of ST04. Five stages in dynamic development
have been distinguished, which are illustrated by four
cross-sections in Fig. 114.

Rubjerg Knude Fyr stage 1. During sedimentation of
the first 10 m of sand of the Rubjerg Knude For ma-

tion, the RF05, RF04 and RF03 thrust sheets were thrust
up along their footwall ramps. RF04 was displaced 90
m along the upper flat level (10 m level) before the
frontal part propagated up along the upper ramp. With

a displacement of about 30 m, this brought the nose

of the RF04 thrust sheet up into the open air, above
the sedimentation level of the Rubjerg Knude Forma-
tion. The displacement on the other two thrusts amount-

ed to c. 20 m, implying an accumulated displacement

of 70 m.

Rubjerg Knude Fyr stage 2. The exposed nose of the
RF04 thrust sheet slumped down along a normal fault
into the piggyback basin of RF03. At the same time,
the frontal nose of RF03 was eroded away and sedi-
mentation of the Rubjerg Knude Formation onlapped
and covered these features. At the leading edge of
the section, thrusting was initiated that brought RF01
and RF02 up over what was to become the trailing-
end segments of the Grønne Rende Section.

Rubjerg Knude Fyr stage 3. The frontal imbrication of
RF01 and RF02 progressed during sedimentation up
to about 20 m above the main L/R-unconformity lev-

el. The RF05-RF06 thrust sheet ramped up onto the
intermediate flat above the trailing-end segment of
RF04. The RF04 thrust sheet was displaced about 70
m up along the relatively steep footwall ramp at the
trailing end of RF03. Due to the fault-bend folding of
RF04, the RF05-RF06 hanging-wall ramp was rotated
into a vertical position.

Rubjerg Knude Fyr stage 4. When the second 'drop' of
the frontal part of thrust sheet RF04 took place, a c. 45
m long slab of the relatively thin thrust-sheet nose
slumped down along a normal fault with a vertical
separation of more than 10 m. The 'drops' may be
regarded as two break-back sequences of the RF04
thrust sheet (in the terminology used by Mitra & Suss-
man 1997; see Figs 99, 100). Sediment accumulation
continued in the piggyback basin to a thickness of
more than 30 m, including the 'dropped' noses of RF04.
The final accumulation in the piggyback basin took
place while the displacement in the Rubjerg Knude
Fyr Section was concluded more than 500 m laterally
to the south. The translation progressed along the 20
m flat level on top of what was to become the lower
trailing-end segments of the Grønne Rende Section.

Rubjerg Knude Fyr stage 5. The continued displace-
ment of RF04 resulted in structural propagation of this
sheet above its own piggyback basin with the
'dropped' thrust noses. Stage 5 in the Rubjerg Knude
Fyr Section is interpreted to have been contempora-
neous with stage 7 in the Stortorn Section in which
compression brought the thrust sheets into their final,
steeply inclined position.

Rubjerg Knude Fyr Section: summary data

Balanced length (L₀):

525 m

Cross-section length (L₁):

260 m

Shortening (ΔL):

265 m

Compression:

50.5%

Grønne Rende Section

The impressive imbricate fan composed of 12 upright
thin thrust sheets is the essential element in the Grønne
Rende Section. As a consequence of the displacement
in the imbricate fan, 550 m of trailing-end lower seg-
ments were left behind to be stacked in a duplex be-
low the frontal part of the Stortorn Section (Fig. 113).

157

Four stages have been differentiated in the develop-
ment of the Grønne Rende Section, the first three of
which are illustrated in Fig. 115.

Grønne Rende stage 1. The initial thrust-fault frame-
work was a low-angle imbrication, about 20° on each
upper hanging-wall ramp, which rooted down to the
upper 10 m flat level. During thrusting, the upper thrust
sheets were split up into three main segments with
leading thrust faults below GR02, GR06 and GR11/
GR12 which ramped down to the main level of de-
tachment in the 20 m flat level. The initial displace-
ment of the imbricate fan is regarded to have been 20 m

on each thrust. This implies that the accumulated dis-
placement sums up to 240 m. GR01 was not affected
by thrusting in the first stage, and 240 m of its lower
trailing-end segment was consequently not displaced
during this stage.

The sediments of the Rubjerg Knude Formation at-

tained a maximum thickness of 15 to 20 m during this
stage, with decreased thicknesses on the back of the
GR06-GR08 thrust sheets, which were elevated to the
highest position.

Grønne Rende stage 2. The imbricate thrusting pro-
gressed with a displacement of 50 m on each thrust.
This implies that the hanging-wall flats were fault-bend-
folded while they passed the footwall ramps, result-
ing in a dramatic steepening of the thrust sheets. Be-
low GR10-GR12, the GR07u and GR08u lower seg-
ments formed a duplex structure that resulted in ele-
vation and complex ramp-propagation folding of the
sheets above. The accumulated displacement implies
an increase in length of the trailing-end segment of
GR01 in the order of 500 m, allowing for some adjust-
ments due to the irregular duplex deformation. Sedi-
ment thicknesses in the piggyback basin in the front-
al part of the section increased to 25-30 m.

Grønne Rende stage 3. Finally, the leading-edge thrust
was activated and GR01 was displaced 50 m up along
its footwall ramp. The GR01 thrust roots in the lower
30 m décollement level, and the displacement of the
hanging-wall flat up along the footwall ramp resulted
in steepening of all the early-formed thrust elements
(GR02-GR13).

The displacements of the individual thrust sheets

range between 60 and 70 m. The thrusting resulted in
the final, almost vertical, orientation of the thrust
sheets. In the rear part of the section, complex defor-
mation of the duplex below GR10-GR13 was reflect-

ed in unusual folding of the beds in the GR13 thrust
sheet where folds with horizontal axial planes were
formed due to gravity collapse of the piggyback ba-
sins.

Grønne Rende stage 4. This stage concluded the thrust-
ing of the leading hanging-wall ramp-and-flat over the
footwall ramp in the trailing end of the Stenstue Rende
Section and the subsequent final rotation of the GR02-
GR05 thrust sheets. In the trailing end of the section,
the RF01 and RF02 sheets concluded the displacement
by thrusting from the trailing-end segments of GR12
up over the footwall ramp onto the back of GR13.
Moreover, GR13 was rotated into an upright position
whereby the horizontal axial planes became vertically
orientated (Plate 1).

Grønne Rende Section: summary data

Balanced length (L₀):

1080 m

Cross-section length (L₁):

423 m

Shortening (ΔL):

657 m

Compression:

60.8%

Comment. The lengths are measured from the foot-
wall ramp between RF01 and GR13 to the footwall
ramp between GR01 and SS06, near the thrust trunca-
tion of the L/R-unconformity.

Stenstue Rende Section

Two markedly different structural complexes wer e
formed during the development of the Stenstue Rende
Section. They were mainly caused by the displace-
ment of the same thrust sheet (SS01) when it was dis-
placed 200 m over the upper flat on top of the piggy-
back basin in the Sandrende Section. The frontal part
of SS01 above the footwall flat of the SR04 thrust sheet
is one of the complexes. The other structural com-
plex is the chaotic breccia and gravity slumping in the
northern part of the section that formed as the piggy-
back thrust sheets were transported over a minor an-
tiformal stack in the central lower part of the section.
The progressive dynamic development in the Sten-
stue Rende Section is described in terms of five stages,
the first four of which are illustrated in Fig. 116.

Stenstue Rende stage 1. Four minor imbrications with
an accumulated displacement of 70 m initiated the

158

development in the Stenstue Rende Section. At the
leading-edge thrust, a minor connection splay sepa-
rated SS02 and SS03. Most of the thrusting was locat-
ed at the upper 10 m flat level for a distance of about
180 m, in the northern part of which it was eventually
rooted down to the lower décollement level. The dis-
placement of the SS05 thrust sheet followed the same
system, but with a smaller translation along the upper
10 m flat level. At the trailing end, SS06 was thrust up
along a steep footwall ramp, and her e the formation
of duplex structures was probably initiated. The thick-
ness of sediment (Rubjerg Knude Formation) that had
accumulated by this stage amounted to 10 m.

Stenstue Rende stage 2. The leading-edge thrusting
shifted to the SS01 thrust sheet, which was displaced
20 m up along the footwall ramp (the trailing end of
SR04 in the Sandrende Section). The SS01 thrust fault
extended down via an intermediate ramp to the 20 m
flat level, and about 200 m from the leading footwall
ramp it stepped down the lower ramp to the 30 m
décollement level. At the upper hinge of the lower
ramp, SS01 was folded into a fault-bend anticline, a
small detachment anticline. Along the foreland-dip-
ping limb of the anticline in the SS01 thrust sheet, a
normal fault was formed that displaced the tip of the
SS02 thrust sheet. Furthermore, the SS03 thrust sheet

Fig. 115. Dynamic model of progr essive
deformation in the Grønne Rende Section

illustrated in three sequential restoration
cross-sections; the final stage (4) described

in the text is not illustrated. The red lines
indicate the active displacement surfaces in

each deformation stage. Note how the
shortening due to the displacement along

the 20 m flat level resulted in the substan-
tial length of the 'left over' lower duplex

segment between the 20 and 30 m flat
level.

159

became steeply inclined, and the initial imbrication of
the thin SS03 thrust sheet resulted in the separation of
SS03 from SS04.

In the trailing end of the Stenstue Rende Section,

duplex stacking of the lower segments in SS06 result-
ed in elevation of the L/R-unconformity more than 10
m above the mean level. The accumulated displace-
ment ranged up to 160 m.

Stenstue Rende stage 3. Thrusting of SS04 progr essed
on the upper flat over the piggyback basin of SS03
with a frontal displacement of 80 m. The hanging-
wall flat of SS04 ramped up along the footwall ramp

of SS03 and during this translation the nose of SS05
became fault-bend-folded into a syncline with a steeply
dipping southern limb. The trailing end of the SS04
thrust sheet was translated along the 10 m flat level; it
was pushed from the rear by the ramping of the trail-
ing end of the SS05 thrust sheet whereby the SS06
thrust sheet also steepened up. Sediment thicknesses
in the piggyback basins increased to c. 20 m, and the
accumulated displacement ranged up to 240 m.

Stenstue Rende stage 4. The dramatic major foreland
thrusting of the SS01 thrust sheet, which included
about 200 m displacement of the hanging-wall ramp

161

over the piggyback basin of the Sandrende Section,
occurred contemporaneously with the formation of
an antiformal stack above the trailing end of SS01. The

creation of the antiformal stack had already been initia-
ted by the earlier formation of the minor detachment
anticline at the ramp splitting the lower segments of
SS01 (the SS01u segments). A duplex duplication of
the lower SS01u segments accentuated the anticline,
and finally the SS03 thrust sheet riding piggyback on
SS01 was folded into an anticline with a steep fore-
land-dipping southern limb (Fig. 90). Along this limb,
a normal fault developed that displaced the frontal
part of the SS04 thrust sheet. A chaotic soft sedimen-
tary fault breccia was formed during the stretching
and fault separation of SS04 (Fig. 91). Due to an extra
push from the rear, the SS05 thrust sheet was displaced
a further 30 m to the south, which resulted in the
formation of a huge southerly overtur ned slump fold
above the normal fault zone (Fig. 89).

The accumulated displacement totals about 470 m.

The displacement of the SS01 hanging-wall flat up
along the steeply dipping footwall ramp constrains
the sequential thrusting of the Stenstue Rende rela-
tive to the Sandrende thrusting. Thus stage 4 could
not have begun before the maximum sedimentation
in the piggyback basin was accomplished in the Sand-
rende Section. The initial SS01 thrusting could be re-
garded as a growth fault, whereby the syntectonic
accumulation of sand added to the steepening of the
footwall ramp. The present vertical to northerly over-
turned orientation of the SS01 hanging-wall flat and
ramp resulted from differential thrusting and fault-bend
of the SS01u lower hanging-wall ramp. Note also the
re-orientation of the normal fault at the tip of SS02,
which due to the same deformation was bent into a
horizontal position.

Stenstue Rende stage 5. This stage corresponds to stage
6 in the Sandrende Section, wherein the SS01 thrust
sheet riding piggyback on SR04 was displaced by
normal faulting (Fig. 117, stage 6).

Stenstue Rende Section: summary data

Balanced length (L₀):

760 m

Cross-section length (L₁):

285 m

Shortening (ΔL):

485 m

Compression:

62.5%

Comment. The lengths are measured from the foot-

wall ramp between GR01 and SS06 to the footwall
ramp between SS01 and SR04. If the compression was
calculated from the leading-edge thrust tip of SS01 to
the trailing-end footwall ramp of SS06, L₁ amounts to

455 m, ΔL = 305 m and the calculated compression

would only be 40.1%.

Sandrende Section

The dynamic development of the Sandrende Section
was formerly interpreted as a combination of diapir-
ism and normal faulting caused by volume exchange
during thrust propagation (Sadolin et al. 1997). The
model presented here aims at an explanation of the
development purely based on a thin-skinned thrust-
fault model including differential ramping and duplex
formation. Thus, the diapirism is interpreted to be an
effect of ramping and fault-bend folding growth, sim-
ilar to the model of Mitra & Sussman (1997), but also
including mud-mobilisation and exaggeration of back-
limb thrusting. The normal faulting occurring in the
Sandrende Section is interpreted as the effect of dif-
ferential ramping of a lower trailing-end segment that
created foreland-dipping features above a hanging-
wall ramp propagation along an intermediate foot-
wall flat. Six stages of dynamic development have been
dif ferentiated in the Sandrende Section (Fig. 117).

Sandrende stage 1. After initial deposition of a 3-5 m
thick succession of Rubjerg Knude Formation sedi-
ments, the SR04 thrust sheet started thrusting about
50 m over the upper flat. The dip of the footwall ramp
was relatively gentle, only c. 14°, and in the 15 m flat
level the thrust fault may be traced along a minor flat

segment on top of the lower trailing-end segment of
SR03 (SR03u). From the minor intermediate flat, the
thrust fault rooted down to the 30 m décollement lev-
el along a 20° dipping footwall ramp of SR03u. Note
that an upper and lower SR04 hanging-wall ramp was
introduced subsequently.

Sandrende stage 2. Translation of the lower SR04 hang-
ing-wall ramp along the intermediate flat established
the anticline in the central part of the SR04 thrust sheet.
The SR03 thrust sheet started to propagate towards its
foreland along the upper 10 m hanging-wall flat, and
the frontal part of SR03 was displaced 50 m over the
upper flat on top of the piggyback basin of SR02. The
tip of the SR02 thrust sheet propagated up along a
growth-fault ramp, which caused the steeply dipping

163

orientation of the northern boundary of the piggy-
back basin at the top of the SR01 thrust sheet. The accu-

mulated displacement ranged up to about 150 m, in-
cluding the initial thrusting of SR01.

Sandrende stage 3. During stage 3, the thickness of
the sediments of the Rubjerg Knude Formation reached
20 m in the piggyback basins in the Sandrende Sec-
tion. In the basin at the top of the SR04 thrust sheet,
the thickness varied considerably. The reason for this
variation is that the top of the anticline above the
SR04 lower hanging-wall ramp was subjected to ero-
sion while deposition continued in the frontal part,
south of the anticline, as well as in the basin north of
the anticline. On the foreland-dipping flank of the
anticline, minor sets of normal growth faults governed
sedimentation (Fig. 87). The tip of the SR04 thrust
sheet suffered minor erosion before deposition r e-
sumed during thrust propagation. This is document-
ed by the angular onlap relationships described by
Sadolin et al . (1997).

Sandrende stage 4 . The thrusting of SR04 continued
with 50 m further displacement. Below the trailing
end of the SR04 thrust sheet, the SR03u lower seg-
ment was picked up and displaced onto the footwall
ramp of SR02. This minor duplex and ramp thrusting
accentuated the SR04 hanging-wall anticline, and nor-
mal faulting on the foreland-dipping limb progressed.
Above the crest of the SR03u detachment anticline, a
significant normal fault complex developed. Here in
the SR04 thrust sheet, a dense network of conjugate
normal faults (Fig. 85) resulted from lateral extension
due to flexural slip bend over the upper hinge of the
lower footwall ramp.

Sandrende stage 5. The thrusting of SR01 propagated
up along the lower and intermediate footwall ramp of
the trailing segments of the Brede Rende Section. Dur-

ing this ramping, the hanging-wall flat of SR02 pro-
gressed up over the piggyback basin of SR01. The tips
of the SR03 and SR04 thrust sheets thus experienced
fault bending up along the footwall flat of SR02. The
atypical northerly overturned tip at the top of the SR02
sheet probably formed due to accentuated reverse fault-

ing along a former established back-thrust. In the trail-
ing part of the section, a minor satellite splay thrust de-

veloped, which broke through the SR04 thrust sheet

from the hanging-wall flat to the footwall flat below SS01.

Sandrende stage 6. The final development of the Sand-
rende Section was dominated by complex duplex for-
mation and fault-bend folding of the SR01 thrust sheet
below the frontal part of SR02. During the thrust pro-
pagation over the footwall ramp of the trailing-end

segments of the Brede Rende Section, a fault-bend-
folded syncline was formed in SR01, which resulted
in normal fault displacement of the SR01 piggyback
basin and the overlying frontal part of the SR02 thrust
sheet. Similar normal faulting affected the SS01 thrust
sheet, which had over-thrust the piggyback basin on
the back of SR04. Due to the intense ramping and
folding of SR01 and its underlying duplex (SR01u) into
an antiformal stack, mud of the Lønstrup Klint Forma-
tion was remobilised in SR01, which intruded through
the hanging-wall flat of SR02 to form the diapir in the
Sandrende Section.

Sandrende Section: summary data

Balanced length (L₀):

775 m

Cross-section length (L₁):

440 m

Shortening (ΔL):

335 m

Compression:

43.2%

Comment. The lengths are measured from the foot-
wall ramp between SS01 and SR04 to the footwall ramp
between SR01 and BR08, at the level where the ramps
cut the L/R-unconformity. The volume lost in diapir-
ism has not been considered, and a r educed amount
of compression would result by measuring L₁ from

the tip of the SR01 thrust sheet to the SR04 footwall
ramp.

Brede Rende Section

The development of normal faults associated with
foreland-dipping features of hanging-wall ramps trans-

Facing page:

Fig. 117. Dynamic model of progressive deformation in the
Sandrende Section illustrated by five restoration cross-

sections. Note that stages 2 and 3 include syntectonic
sedimentation of the Rubjerg Knude Formation, mainly

related to stage 2, and the thrust-fault configuration conclud-
ing stage 3. The cross-sections demonstrate the development

stages between the initial and final positions displayed in the
balanced and the structural cross-sections in Plate 2. The red

lines indicate the active displacement surfaces in each
deformation stage.

164

lated along footwall flats has already been demon-
strated in the previous sections. One of the best ex-
amples of such a normal fault relationship occurs in
the Brede Rende Section. An essential element for this
development was the formation of a long thrust sheet,
translated laterally more than 150 m along the upper
flat. This is demonstrated by the seven stages of de-
velopment recognised in the Brede Rende Section, as
illustrated by the five cross-sections in Fig. 118.

Brede Rende stage 1. The first stage differentiated her e
is the initial sedimentation of about 3-5 m of the Ru-
bjerg Knude Formation. This corresponds well with
the thickness of sediments deposited initially above
the L/R-unconformity in the Sandrende Section; this
unit is considered to represent pre-thrust sedimenta-
tion, i.e. the sediment record prior to piggyback basin
for mation.

Brede Rende stage 2. Accepting that the thinnest pre-
served section of the Rubjerg Knude Formation indi-
cates the timing of the earliest thrusting, then thrust-
ing in the Brede Rende Section was initiated with the
displacement of the BR03 thrust sheet. The frontal part
of BR03 was displaced about 50 m over the upper flat
corresponding to the relative foreland in front of the
leading edge of thrusting. The BR03 thrust fault pro-
bably rooted down to the 30 m décollement level.
However, translation in the upper 10 m flat level can-
not be excluded, and in this case the beds disturbed
by hydrodynamic brecciation might be interpreted as
thrust flats. In the trailing end of the section, the BR06
hanging-wall ramp was the next thrust to break through

and initiate the translation along the upper flat.

Brede Rende stage 3. The BR06 thrust sheet was fur -
ther displaced c. 50 m over the upper flat. The trailing
end of BR06 was separated by a splay thrust at the
footwall ramp, along which the BR07 thrust sheet prop-
agated contemporaneously with piggyback thrusting
of BR08. This stage is equivalent to the frontal thrust-
ing during stage 5 in the Sandrende Section.

Br ede Rende stage 4. Sediment accumulation in the
piggyback basins incr eased up to about 15 m. The
marked difference in thickness of deposits is clearly
seen by comparing the BR05 thrust sheet with the
BR06 thrust sheet. The roof of BR05 was obviously
capped at an earlier stage than BR06 where sediments
accumulated to more than twice the thickness of that
in BR05.

Brede Rende stage 5. With a displacement of about 60
m, the BR05 thrust sheet propagated up along the
footwall ramp of BR04 and onto the upper flat on top
of the BR04 thrust sheet. Translation of the BR06 thrust
sheet progressed c. 60 m along the upper flat. The
thrusting rooted down to the 20 m flat level on top of
the trailing-end segment of the BR03 thrust sheet
(BR03u). The accumulated displacement amounted to
150 m, including the ramping and translation of the
BR07 thrust sheet along the same 20 m flat level.

Brede Rende stage 6. After the thrusting of BR05 and
BR06 ceased, the BR04 thrust sheet was translated c.
80 m. The BR04 thrust fault included three ramps: an
upper gently dipping ramp from the upper flat to the
5-10 m flat level, an intermediate ramp-bend of the
BR03 thrust sheet due to the presence of the formerly
established BR02 footwall ramp, and a lower ramp
from the 10 m to the 20 m flat level. The translation of
the BR04 lower hanging-wall ramp along the footwall
flat of BR03 created the foreland-dipping bend that,
combined with the bend due to the BR03 ramping,
formed a syncline in front of the BR04 ramp anticline.
The normal fault created parallel to the for eland-dip-
ping features displaced the tip of the BR06 thrust sheet.
The vertical offset on the normal fault amounted to c.
20 m, which also included the displacement caused
by the offset in front of the BR05 thrust tip.

Brede Rende stage 7. Finally, the leading-edge thrust-
ing of the section propagated over the trailing end of
the Kramrende Section. Above the footwall ramp of
BR01, a minor antiformal stack was formed and sub-
sequently an irregular duplex formation affected the
BR01 thrust sheet during the last stage of deformation
in the Brede Rende Section. This phase developed
into diapirism that intruded towards the thrust fault
between BR01 and BR02.

Facing page:

Fig. 118. Dynamic model of progressive deformation in the
Brede Rende Section illustrated in five sequential restoration

cross-sections. The cross-sections demonstrate seven stages in
the development between the balanced cross-section and the

structural cross-section (Plate 2). The red lines indicate the
active displacement surfaces in each deformation stage. Note

that significant normal faulting occurred in the Brede Rende
Section during stages 5 and 6 while the hanging-wall anticline

in the middle part of the BR04 thrust sheet was formed.

166

Brede Rende Section: summary data

Balanced length (L₀):

815 m

Cross-section length (L₁):

440 m

Shortening (ΔL):

375 m

Compression:

46.0%

Kramrende Section

In the central part of the Kramrende Section, a major
diapir developed during the progressive thrusting. The
Kramrende diapir was the most distally located diapir
in the thin-skinned thrust-fault system indicating that
a certain amount of ramp propagation from a deeper
décollement level (at least 30 m flat level) was need-
ed for macroscopic-scale diapirism. South of the Kram-
rende Section, the décollement level gradually changed
to a shallower position and the intensity of ramping
decreased. Seven stages of dynamic development have
been differentiated in the Kramrende Section, as illus-
trated in the five cross-sections in Fig. 119.

Kramrende stage 1. The thrusting in the Kramrende
Section was initiated with leading-edge propagation
along the KR01 thrust fault, which constituted an up-
per footwall ramp with a dip of 10°, a minor interme-
diate flat at the 15 m flat level, and a c. 15° dipping
lower ramp connecting the thrust fault to the 30 m
décollement level. The displacement was in the order
of 100 m along the upper flat, where almost no sedi-
mentation of the Rubjerg Knude Formation took place.

Kramrende stage 2. Subsequent to the early stage

thrusting, the lower most 10 m of the Rubjerg Knude
Formation was deposited; the sediment thickness in
the KR01 piggyback basin was probably a little less.

Kramrende stage 3. The KR01 thrusting progressed
about 60 m over the upper footwall flat of what was
to become the MB04 thrust sheet, and the trailing end
of the KR01 thrust sheet was elevated to the 15 m flat
level by ramp propagation over the lower footwall
ramp of MB04. A small duplex segment (KR01s) un-
der the middle part of the KR01 thrust sheet was picked
up in the thrusting and displaced to the upper foot-
wall ramp hinge, where it formed a minor angular
anticline. In the syncline between the anticline and
the footwall ramp of KR01, the thickness of piggy-
back basin sediment accumulation increased to about
15 m before the KR02 thrust sheet propagated c. 50 m

up along the ramp, and the KR02 hanging-wall ramp
partly capped the KR01 piggyback basin. The accu-
mulated displacement ranged up to about 260 m.

Kramrende stage 4. Thrusting of the KR03 thrust sheet
was initiated up along the northerly dipping footwall
flat of KR02. The KR03 thrust fault included an upper
and a lower relatively steep ( c. 23°) ramp. The top of
the KR02 thrust sheet was probably exposed to ero-
sion, and the Rubjerg Knude Formation is thus miss-
ing in this part of the section. The piggyback sediment

pile increased to a thickness of 20 m, as indicated by
the sedimentary section preserved above the L/R-un-
conformity at the top of the KR04 thrust sheet. From
the trailing end of the KR01 thrust sheet, diapirism
intruded through the footwall ramp and irregular mud
diapirism developed in the KR02 thrust sheet.

Kramrende stage 5. With a displacement of c. 30 m,
KR03 thrusting propagated over the two ramps that
resulted in the fault-bend folding of two anticlines
separated by an intervening syncline.

Kramrende stage 6. The KR04 thrust sheet was thrust
over the fault-bend-folds formed in stage 5, simulta-
neously with limited continuation of KR03 thrusting.
Minor irregular duplex formation started to develop
into mud mobilisation at the trailing end of the KR02
and KR04 thrust sheets.

Kramrende stage 7. The final thrust propagation of
the KR03 thrust sheet concluded with a displacement
of 30 m up along the footwall flat of KR02. At the
bend between the footwall flat and the footwall ramp
of KR02, a remarkable set of r everse faults developed
(Fig. 72). The KR04 thrust sheet, carried piggyback on
KR03, was also displaced by the reverse faulting, a
fact that testifies to the relative timing of KR04 piggy-
back thrusting and KR03 ramp propagation. The re-
verse faults are regarded as back-limb thrusts similar
to the back-thrust features mentioned in stage 5 of
the Sandrende Section. Minor back-limb reverse faults

Facing page:

Fig. 119. Dynamic model of progressive deformation in the
Kramrende Section illustrated in five sequential restoration

cross-sections. The cross-sections demonstrate seven develop-
ment stages, of which stage 2 represents a purely deposition-

al phase and stage 4 only includes minor displacement. The
red lines indicate the active displacement surfaces in each

deformation stage.

168

also developed at the crest of the fault-bend-folded
KR01 thrust sheet. Polyphase diapirism evolved in the
trailing end of the KR03 and KR04 thrust sheets, such
that the primary thrust-fault framework was partially
destroyed.

Kramrende Section: summary data

Balanced length (L₀):

c. 600 m

Cross-section length (L₁):

c. 300 m

Shortening (ΔL):

c. 300 m

Compression:

c. 50%

Comment. The lengths are measured from approxi-
mate positions on the footwall ramps bounding the
Kramrende Section and the data must therefore be
regarded as tentative estimates.

Martørv Bakker Section

The development in the Martørv Bakker Section was
dominated by the translation of a thrust sheet that
was more than 600 m long and only 20-30 m thick.
During nearly 400 m of displacement towards the fore-
land, a lower segment transformed into a duplex that
ramped at a relatively late stage and created a fault-

Fig. 120. Dynamic model of progressive

deformation in the Martørv Bakker Section
illustrated in thr ee sequential restoration

cross-sections. The cross-sections demon-
strate four stages in the development

between the balanced cross-section and the
structural cross-section (Plate 2). The red

lines indicate the active displacement
sur faces in each deformation stage. Note the

significant depression formed in the hang-
ing-wall block south of the Martørv Bakker

normal fault. In this depression, diamictites
interlayered with slump-slides were depo-

sited.

169

bend-fold anticline and syncline pair. At the upper
surface of the intervening limb between the fold pair,
a foreland-dipping normal fault was formed, rather
similar to the structural complex formed in the Brede
Rende Section. Simultaneously with the sedimentation

of a diamictite, three slump-slides filled the piggyback
basin developed in a syncline created at the top of the

hanging-wall block of the normal fault. The sequen-
tial restoration stages are illustrated in three cross-sec-
tions in Fig. 120.

Martørv Bakker stage 1. Thrusting in the Martørv
Bakker Section started with foreland thrusting of MB02,
and translation of the trailing-end duplex that consti-

tuted the KR01 thrust sheet emplaced piggyback on
the MB04 thrust sheet, thrust up along the footwall
ramp of MB03. The more than 600 m long MB02 thrust
sheet was displaced c. 105 m over the footwall flat of
MB01. The MB02 thrust fault included two ramps, an
upper footwall ramp of MB01 and a lower ramp be-
tween the 20 m flat level and the 30 m décollement
level. The lower ramp was located below the central
part of the MB02 thrust sheet, where it acted as the
final step for the décollement level change to the 20
m footwall flat level. It is thought unlikely that signif-
icant sedimentation occurred in the section during this
stage.

170

Martørv Bakker stage 2. The MB01 thrust sheet was
displaced about 100 m over the foreland of the Stens-
næs Section along the leading-edge thrust. The MB01
thrust was rooted down to the 20 m flat level, and it
can be traced further on to the 30 m décollement level

by passing the central lower footwall ramp of MB02.
Minor adjustments along the hanging-wall flat result-
ed in formation of small duplexes along the thrust
fault. In the trailing end of the section, the MB03 thrust
sheet was thrust up over the footwall ramp of MB02,
whereby an antiformal stack was formed due to the
folding that also involved the MB04 and KR01 thrust
sheets. At the base of the MB03 thrust sheet, the low-
er segments formed an irregular duplex, which ac-
centuated the antiformal stack. The accumulated dis-
placement ranged up to 290 m.

Martørv Bakker stage 3. The final thrusting of the
Martørv Bakker Section was concluded by nearly 100
m displacement of the MB02 thrust sheet. The frontal
hanging-wall ramp-and-flat was thrust over the piggy-
back basin of the SN04 thrust sheet in the Stensnæs
Section. During the thrusting, the lower segment
MB02u was activated and formed a fault-bend-folded
lower duplex. Above the hanging-wall ramp of the
trailing-end segment (MB02u3), an anticline was
for med at the surface of MB02 and a subsequent syn-
cline above the hanging-wall/footwall flat became a
piggyback basin.

Martørv Bakker stage 4. The foreland-dipping limb of
the fold pair at the top of the MB02 thrust sheet devel-

oped into a southerly dipping normal fault. The c. 10
m deep piggyback basin was filled with diamictitic
deposits and slump-sheets that glided down from the
top of the antiformal stack. Deformation in the Mar-
tørv Bakker Section concluded with the steepening
up of the leading-edge thrust structures due to ramp
bending in the Stensnæs Section.

Martørv Bakker Section: summary data

Balanced length (L₀):

1065 m

Cross-section length (L₁):

675 m

Shortening (ΔL):

390 m

Compression:

36.6%

Comment. The lengths are measured from the tip of
the leading-edge hanging-wall ramp to the upper bend
of the footwall ramp of the MB04 thrust sheet.

Stensnæs Section

In the Stensnæs Section, a number of conspicuous
flexural slip folds occur which are interpreted to have
resulted from the deformation that accompanied se-
quential footwall ramp collapse and subsequent ramp
displacement of minor duplexes. It is significant that
they occur in relation to the final ramping from the
lower 20 m flat level to the upper 10 m flat level. Eight
stages have been differentiated in the development
of the Stensnæs Section, of which stages 2, 4 and 6-8
are illustrated by the cross-sections in Fig. 121.

Stensnæs stage 1. In contrast to the Martørv Bakker
Section, an initial sediment thickness of 5 m of the
Rubjerg Knude Formation is thought to have covered
the Stensnæs Section. It should be noted, however,
that typical Lønstrup Formation facies grade upwards
into typical Rubjerg Knude Formation facies in this
distal part of the Rubjerg Knude Glaciotectonic Com-
plex; the L/R-unconformity is not clearly developed,
and location of the formation boundary can be diffi-
cult. The affinities of the sediment packet referred to
above are thus debatable.

Stensnæs stage 2. Thrusting in the Stensnæs Section

was initiated with c. 100 m displacement of the SN02
thrust sheet over the upper flat. The thrust fault ramped
down to the 10 m flat level, which separated the up-
per and lower segments of the SN04 thrust sheet, si-
multaneously with stacking the SN03 thrust sheet into
a northerly dipping duplex complex along the foot-
wall ramp of SN01.

Stensnæs stage 3. Accumulation of the Rubjerg Knude
Formation incr eased to a sediment thickness of 10 m.
Sedimentation was restricted to the piggyback basin
of the SN04 thrust sheet, as well as on the foreland
south of the frontal tip of the SN02 thrust sheet.
Stensnæs stage 4. The piggyback basin on the back of
SN04 was sealed in by the overthrusting of the MB02
thrust sheet; this is equivalent to stage 3 in the Mar-
tørv Bakker Section.

Stensnæs stage 5. As a trailing-end structural complex
to the Ulstrup Section, the thrust sheets of the Stens-
næs Section were translated together with the UL02
thrust sheet over the Ulstrup footwall ramp onto the
hanging-wall flat of the foreland. During ramping, the
SN01 and SN03 thrust sheets were separated into small
duplex segments. Flexural-slip folding and polyphase

171

Fig. 121. Dynamic model of progressive deformation in the Stensnæs Section illustrated in four sequential restoration cross-sections.
The cross-sections demonstrate five of the eight stages in the development described in the text between the balanced cross-section

and the structural cross-section (Plate 2). The red lines indicate the active displacement surfaces in each deformation stage.

hydrodynamic brecciation resulted from the ramping
(Figs 53, 57, 58). The accumulated displacement ranged
up to 35 m, whereas the length of the hanging-wall
flat in the 10 m flat level amounted to 500 m. At the
leading edge of thrusting, the UL02 thrust sheet initia-
ted the thrusting up over a stepwise ramp.

Stensnæs stage 6. During this stage, about 10 m of the
Rubjerg Knude Formation was deposited in the pig-
gyback basin at the top of the SN02 thrust sheet. The

sedimentation level was probably up to 20 m above
the L/R-unconformity, inferred from the elevated po-
sition of the SN02 thrust sheet. However, this is un-
certain and the sediments were either never deposit-
ed or eroded away during later thrust elevation. In
the northern part of the section, the SN04 thrust sheet
propagated up along the footwall ramp of the earlier
created SN02-SN03 duplex. This resulted in fault-bend
folding of the SN04 thrust sheet and its piggyback
basin as well as the overlying MB02 thrust sheet. This

172

stage correlates with stages 3-6 in the Martørv Bakker
Section.

Stensnæs stage 7. The SN01 thrust sheet was displaced
about 50 m over its lower segment (SN01u), and together

they were thrust onto the footwall ramp-and-flat of the

UL02 thrust sheet. During the thrust-fault propagation

of the UL02 thrust sheet over the footwall ramp of UL01,

the SN01 and SN02 thrust sheets, piggyback translated

on UL02, were bent into c. 30° dipping position. Fi-
nally, the SN04 thrust sheet was displaced up along
the footwall ramp of SN03 during differential duplex
for mation along the SN04 hanging-wall ramp.

Stensnæs stage 8. The frontal parts of the SN01, SN02
and SN03 thrust sheets, as well as the anticlinal crest

of the UL02 thrust sheet (formed above the upper hinge
of footwall ramp of UL01), were significantly eroded,
and a local piggyback basin was formed above the
transition between the Stensnæs and Ulstrup Sections.
To the north of this piggyback basin, the elevated
and exposed tips of the SN02-SN04 thrust sheets grav-
ity-slumped out into the basin, where they were de-
posited as olistoliths, 1-5 m in size.

Stensnæs Section: summary data

Balanced length (L₀):

350 m

Cross-section length (L₁):

180 m

Shortening (ΔL):

170 m

Compression:

48.6%

173

Ulstrup Section

Thin-skinned thrusting in the Ulstrup Section involved
the remarkable translation of extensive, thin thrust
sheets over the footwall flat of the foreland. Cohesion
of the thrust sheet was probably increased by ground
frost in the upper part of the thrust sheet, while the
hanging-wall ramp-and-flat slid on a thin zone of mo-

bilised mud. During translation, piggyback sedimen-
tation varied considerably. Six stages have been dif-
ferentiated in the development of the Ulstrup Section;
stages 1-3 and 5 are illustrated by the cross-sections
in Fig. 122 (see also fig. 121).

Ulstrup stage 1. Thrusting in the Ulstrup Section initia-
ted with frontal ramping of the UL02 thrust sheet over
a two-stepped footwall ramp of what was to become

the UL01 thrust sheet. This ramping resulted in the for-

mation of two, fault-propagating folded anticlines,
which were separated by a shallow, broad syncline.
The leading edge of the UL02 hanging-wall ramp was
displaced about 25 m over the c. 5-10 m thick Rubjerg

Knude Formation deposited in the foreland (at the
top of UL01). The UL02 hanging-wall flat extended
along the upper 10 m flat level for about 400 m, ter mi-
nating to the north at the foreland footwall ramp root-
ing down to the 20 m décollement level. Thrust pro-
pagation up over this ramp formed a hanging-wall
anticline at the trailing end of the UL02 thrust sheet.
Between the anticline at the trailing end and the anti-
cline at the upper footwall ramp of UL01, a piggyback
basin formed in which glaciolacustrine sediments were
deposited to form the small, ephemeral Ulstrup lake.

Fig. 122. Dynamic model of progressive deformation in the

Ulstrup Section illustrated in four sequential restoration cross-
sections. The cross-sections demonstrate four of the eight

stages in the development described in the text between the
balanced cross-section and the structural cross-section (Plate

2). The red lines indicate the active displacement surfaces in
each deformation stage.

174

Ulstrup stage 2. Thrusting along the UL02 hanging-wall

ramp-and-flat progressed with an accumulated displace-

ment of 230 m. The glaciolacustrine deposits of the ephe-

meral Ulstrup lake participated in the ramp-propagat-
ing-folding. During translation along the upper 10 m
flat level, the trailing end of the UL02 thrust sheet was

probably covered by sediments, which subsequently

became eroded. This event in the Rubjerg Knude For -

mation corresponded to stage 6 in the Stensnæs Section.

Ulstrup stage 3. The long lateral thrusting of the UL02
thrust sheet along the upper flat resulted in 550 m of
displacement, and at the lower trailing end, the hang-
ing-wall ramp became detached to the upper footwall
ramp of UL01. Above this ramp, conspicuous flexural-
slip folds, similar to the folds developed in the Stens-
næs Section, were formed in the UL02 thrust sheet.

Ulstrup stage 4. Glaciofluvial sands were deposited
upon an erosional surface capping the Ulstrup lake
sediments (all Rubjerg Knude Formation). Depositional
base level was probably equivalent to that experienced
in stage 8 in the adjacent Stensnæs Section (see above).

Ulstrup stage 5. The final foreland thrusting took place
as the UL01 thrust sheet was thrust over the upper
ramp of the foreland and propagated about 200 m to
the south. When the anticline above the UL02 hang-
ing-wall ramp approached the footwall ramp of the
for eland, where a fault-bend formed continuously
during the propagation of the UL01 thrust sheet, a
narrow channel was formed in which coarse-grained
glaciofluvial gravel was deposited (Figs 27, 122). The
gravel also included redeposited frozen blocks of sand,
testifying to the ground-frozen conditions of the en-
vironment (Fig. 28).

Ulstrup stage 6. At the leading edge of the UL01 thrust
fault, the deformation concluded with 150 m of dis-
placement over the upper footwall flat of the fore-
land. During the translation of the UL01 thrust sheet
over a minor depression in the foreland, a sandy mud
volcano developed due to trapping of the high water
pressure close to the leading-edge thrust. The sedi-
ment extrusion r esulted in chaotic disturbances in the
central part of UL01.

Ulstrup stage 7. The last stage of development in the
Ulstrup Section involved sedimentation of the upper -
most post-tectonic deposits of the Rubjerg Knude For-
mation. The conglomerate (of stage 5) was covered

by sand, and deposition in the foreland covered the
leading-edge thrust at Tvonnet Rende (for location
see Plate 1).

Ulstrup Section: summary data

Balanced length (L₀):

c. 1350 m

Cross-section length (L₁):

c. 850 m

Shortening (ΔL):

c. 500 m

Compression:

c. 37%

Summary of dynamic development

The dynamic development of the complex is summa-
rised in Figs 123 and 124. From the scheme in Fig.
123, it is clear that the Rubjerg Knude Glaciotectonic
Complex developed in sequential progressive stages
during syntectonic sedimentation of the Rubjerg Knu-
de Formation.

The thin-skinned thrust-fault complex developed

mainly as piggyback thrusting with proximal thrust
sheets being displaced contemporaneously with acti-
vation of the distal thrust fault. During the advance of
the thrust-fault complex, the position of the décolle-
ment zone shifted progressively to deeper levels. The
dynamic development can be summarised in eight
steps that resulted in the formation of eight character-
istic thrust-fault structure types (Fig. 124).

Fig. 123. Summary scheme of the

syntectonic sedimentary development
in the Rubjerg Knude Glaciotectonic

Complex. The deformation stages for
each section, as described in the text,

are indicated here by the symbol #.

175

1. Long lateral translation of a thin thrust sheet took

place over the foreland. The ramp was rooted in
the uppermost shallow décollement level 1 at a
depth of c. 10 m from the top surface.

2. Ramps became rooted in décollement level 2, and

the increase in ramp height, amounting to about
20 m, is regarded to be the cause of the duplex
folding at ramp collapse.

3. The hanging-wall anticlines became dominant struc-

tures with hinterland-dipping piggyback thrust
sheets on the back limb. As the ramps extended
down into décollement level 3, the height of the
ramps increased and consequently the hanging-
wall anticlines increased in size.

4. The antiformal stack developed, which included

long-distance translated piggyback thrust sheets
that were folded in a hanging-wall anticline. In
relation to the antiformal stack, for eland-dipping
thrust faults occur that were accompanied by nor-
mal faults.

5. The prominent imbricate fan formed above décol-

lement level 2. The initially gently to moderately
dipping imbricated thrust sheets were re-orientat-
ed into steeply dipping positions due to lateral
translation of the imbricate fan along décollement
level 3.

6. This step involved the subsequent deformation of

the lower duplex segment not incorporated in the
imbricate fan. This lower duplex segment was im-
bricated and the sub-segments were displaced in-
to a duplex stack during push from behind by a

progressing hanging-wall ramp, rooting in décol-
lement level 3.

7. This step involved differential duplex stacking and

imbrication of thrust-fault sheets. The piggyback
basins vary in elevation due to differences in du-
plex stacking. Further more, the variation in duplex
stacking reflects the shift from décollement level 3
to 4 (corresponding to a shift in the décollement
sur face from 30 to 40 m).

8. The fault-bend-folded duplex units were formed.

The formation of these duplex units was only pos-
sible because the four thrust-fault flat levels had
developed, and thus the duplexes could be stacked
and subsequently fault-bend-folded during maxi-
mum compression and translation along décolle-
ment level 4 (Fig. 124).

The thickness of sediments that accumulated contem-
poraneously in tectonically correlated piggyback ba-
sins decreases from north to south. Thus the depo-
centre was situated in front of the last activated thrust
section, and the depocentre gradually shifted to a more
and more distal position. Correlation of the syntec-
tonic progressive development of the complex shows
that sedimentation was contemporaneous with thrust-
ing rather than there being an alternation between
periods of active thrust faulting and periods of depo-
sition. Further more, it indicates that the ice margin
was not melting back during the formation of the com-
plex but advanced in a continuous progressive gravi-
ty-spr eading process.

178

Discussion

The observations that form the basis for the descrip-
tion of the structural geology, mechanical behaviour
and dynamic development of the Rubjerg Knude Gla-
ciotectonic Complex, raise important questions with
respect to understanding the framework and nature
of thin-skinned thrusting related to glacial defor ma-
tion; seven topics have been selected for further discus-

sion below. The basis for understanding a structural
complex is to describe the tectonic architecture and
the range of structures it contains from microscopic to
macroscopic scale. The discussion of thrust-fault archi-

tecture leads to evaluation of the reliability of the balan-
ced cross-section. Consideration of thrust brecciation
and diapirism leads naturally to a focus on the thrust-
fault dynamics, and the significance of the rate of defor-
mation. The dynamics associated with the syntecton-
ic deposits and the formation of piggyback basins merit
discussion, as does the interpretation of a pr oglacial
contra subglacial deformational setting. The final topic
deals with the geological setting of the complex, inclu-

ding the timing of the event that created it.

Thrust-fault architecture

A prerequisite for understanding the thrust-fault ar -
chitecture is a familiarity with the terminology (see
Appendix 2). The macroscopic structures encountered
in thin-skinned orogenic belts are all recognisable in the

glaciotectonic complex. Mesoscopic structures such
as folds and faults are similarly recognisable. However,

small-scale structures such as joints, cleavage and fabric
ar e more difficult to recognise (except for hydrody-
namic brecciation), and this may be one of the major
differences between soft sedimentary deformation and
hard-rock deformation.

It seems likely that joints and fractures in soft sedi-

ments would be able to re-heal after deformation. Thus,

a large number of minor reverse faults must have
for med in thrust sheets during ramp propagation (Fig.
67), but appear to have disappeared again after sub-
sequent thrust sheet propagation along the flat, as
they have not been observed with the exception of the

in situ positions related to ramp bend (Fig. 85). There
is an approximation to a right-angle relationship be-
tween the footwall ramp and the back-thrust faults,

which indicates that an increase in the dip of the foot-
wall ramp results in a decrease in the dip, in the op-
posite direction, of the back thrust. Moreover, a steeper
and higher footwall ramp also corresponds to an in-
crease in displacement along the back-thrust fault. Thus
one can regard the KR01 (Kramrende) back-thrust faults

as structures related to initial faulting in the progr es-
sive deformation (Fig. 67), and the KR04 back-thrust
splay faults as a structural element related to a devel-
oped phase of progressive thrust-fault deformation
(Fig. 72). Major back thrusting at the back of SR02
(Fig. 84) represents a mature phase in the progressive
thrust faulting. The apparent lack of joints and frac-
tures reflecting ramp propagation could probably be
explained as having been absorbed in the hydrody-
namic brecciation process.

Among the structural elements analysed during the

interpretation of the balanced cross-section, the du-
plex structures create the most interesting problems.
Firstly, the interpretation of the duplex imbricates in
the Stensnæs Section provides an explanation for the
complicated fold framework. Secondly, the interpre-
tation of the duplex below the frontal part of the Stor-
torn Section links the hidden duplex segments at the
base of the Grønne Rende Section with the duplex
stacking below ST01-ST03. Thirdly, the normal faults
can be interpreted to have been related to the ramp-
ing of lower duplex segments. If the normal faults are
regarded as foreland-dipping faults or part of a for e-
land-dipping duplex, the model for duplex formation
suggested by Contreras & Sutter (1997) may be rele-
vant for the understanding of the foreland-dipping
faults. In their model for formation of foreland- or
hinterland-dipping duplexes, they considered two fac-
tors: u = distance of displacement along the upper
flat, and s = length of duplex segment. In a regime
where the ratio u/s is greater than one (u/s > 1), for e-
land-dipping duplexes are formed; in a regime where
u/s < ½, hinterland-dipping duplexes are formed. in
regimes where ½ < u/s < 1 or u/s = 1, antiformal
stacks or angular antiformal stacks, respectively, are
formed. This corresponds well to the interpr etation
presented here of the Rubjerg Knude cross-section,
where most thrust sheets are displaced by less than
their length, and consequently the main orientation
of thrust sheets is hinterland dipping. According to
the model of Contreras & Sutter (1997), foreland-dip-

179

ping duplexes are formed when a duplex segment is
displaced along an intermediate or upper flat for a
distance equal to, or more than, its length. A conse-
quence of this is that a roofing thrust sheet will be
displaced in front of the foreland-dipping upper foot-
wall flat, where normal faulting will take place. This
is interpreted to be the case for the normal faults in
the Martørv Bakker and Brede Rende Sections (see
Fig. 66). The normal fault developed in the Stenstue
Rende Section may also be regarded as an expression
of the latter regime in the suggested model. A fore-
land-dipping feature may well reflect the foreland-dip-
ping limb of a hanging-wall anticline formed above a
laterally displaced hanging-wall ramp. However, the
normal fault-displaced thrust sheet must be thrust over
the duplex segment before it was thrust faulted together

with its roofing thrust sheet, and then as translation
continued attached to the hanging-wall flat until the
displacement was concluded by the normal faulting
over the tip of the duplex segment.

The consideration of duplex formation naturally

leads to a focus on the changes in décollement levels.
When a duplex segment is formed, there would nor-
mally be an early décollement surface at a shallow
level, succeeded by a shift to a deeper level connect-
ed with a new footwall ramp. The upper décollement
level (the 10 m level or corresponding gently dipping
ramp to the leading edge) was probably the first to be
formed in the proximal part of the complex and pr ob-
ably also the last to form in the distal part (Fig. 124).
From the cross-section, it is indicated that the 10 m
décollement level extended for about 1 km, but end-
ed up with a distance of only 600 m. The 20 m décol-
lement level was the next to take over, and during the
establishment of a related ramp, footwall ramp imbri-
cation progressed, modifying the ramp transition con-
necting the two décollement levels. The length of this
décollement level might have been of the same scale,
but only c. 400 m is preserved as a lower footwall flat.
The 30 m flat level is the dominant décollement level
extending from the middle of the Martørv Bakker Sec-
tion to the middle part of the Stortorn Section, where
finally the 40 m décollement level was developed.
Note that the present-day position of the lowermost
décollement surface is at about 45 m b.s.l. due to the
regional, very gentle dip to the north of the L/R-un-
conformity that serves as the reference level, corre-
sponding to the 0 m flat level. From the cross-section,
it can be seen that the dips of the ramps increase from
gentle (5-15°) in the zone between the upper surface
flat to the 10 m flat level, to 25° dips between the 10

and 20 m levels, and reaching up to 35° between the
20 and 30 m flat levels. The ramp dips with steeper
angles in the cross-section, arise from over -steepen-
ing or superimposed tilting during ramp propagation
(Fig. 9). Thus, in the proximal part of the complex,
dips between 35° and 45° are interpreted as the pri-
mary dips of ramps rooting down to the deepest dé-
collement level at 40 m, which is incorporated in the
model for the fold-imbricate duplex units. The increas-
ing dips of ramps are interpreted to have resulted from
the increase in fracture angle as a function of increase
in normal stress (change of levels) and incr ease in
shear stress (increasing force required to move thrust
sheets). This is implied from the shape of the Mohr-
envelope in the Mohr diagram (Hobbs et al. 1976),
and it is suggested to be a basic relationship for glacio-

tectonic fracture and fault deformation (Pedersen 1996).

Balanced cross-section

In the balanced cross-section, the changes in dip ang-
les are responsible for the insertion of a number of
small triangular-shaped duplex segments, which ar e
incorporated in the geometric construction and anno-
tated as splints (horses) (Plate 2). It is not known how
many splints exist in reality. A few have been recog-
nised as structural identities (KR01_s in Kramrende),

but it is likely that space deficits or excesses have
been absorbed in mud-mobilisation or differential
small-scale anastomosing fracturing. Differential frac-
turing and thrust-fault formation with a spacing of only
1 m has been documented in the Moserende Section
(Fig. 27), indicating that the duplex segmentation does
exist. Hence it is probable that a much more differen-

tial translation took place than is indicated in the cross-

sections of the dynamic model of thrust-fault propa-
gation (Fig. 112).

The reliability of the approximations in construc-

tion inherent in a balanced cross-section is founded
in the area balance. The main calculation of the bal-
ance indicates that the shortening amounts to approx-
imately 50%, with L₀ = 12 km and L₁ = 6 km. The area

of the L₀ cross-section (L₁ multiplied by stratigraphic

thickness) amounts to 340 000 m², and the area of the

L₁ cross-section (L₁ multiplied by measured thickness

of the retrodeformed cross-section) is 382 500 m². The

difference amounts to 11%, which is interpreted as a
consequence of the erosion of the thrust sheets in the
proximal part of the complex (Grønne Rende Section
- Ribjerg Section). The detailed calculations of areas

180

for the area balance are summarised in Table 1, and
documented in Plates 2A and 2B. The amount of ero-
sion indicated from the area balance differs markedly
from the 80% erosion estimate by Gry (1941), and sup-

ports the argument that Gry's cylindrical thrust-fault
model was incorrect.

Considering the amount of erosion, the question

arises: why is the preservation potential so great? Three
factors are suggested here to answer this: (1) the steep-
ly orientated thrust sheets were partly packed by the
sand fill in the piggyback basins, (2) the thrust-fault
deformation resulted in a strain hardening that con-
solidated the complex, and (3) as the sole of the ap-

proaching ice sheet advanced across the proximal part
of the complex, the over -pressured pore water mi-
grated from the hanging-wall ramps and flats of the
thrust sheets to the hanging-wall flat of the ice sheet,
facilitating the over-thrusting of the footwall block which

subsequently comprised the thrust-fault complex.

Thrust brecciation and diapirism

In order for a thrust sheet to move, a fracture must be
cr eated that can develop into a plane of thrusting.
The initial fracture is formed when the failure limit is
reached in a system subjected to pressure (loading
and lateral compression). A recurring question, and an

apparent conflict in reasoning, is why fault planes
develop, leaving the rest of the thrust sheet preserved?
Since the sedimentary unit forming a thrust sheet is
subjected to the same amount of confining pressure,
it might be expected that a muddy mass of collapsed
sedimentary units just as well could have been the
result?

It is well known that an increase in pore-water pres-

sure results in failure and initialisation of fractures along

surfaces of anisotropy, as described for orogenic sys-
tems by Hubbert & Rubey (1959). However, in soft
sedimentary deformation with lower confining pr es-
sure and smaller shear strength, as well as smaller
coefficient of internal friction, the limits of fracture
formation and complete collapse are much narrower.
The structures developed in the Ulstrup Section re-
flect these conditions. The anastomosing jointing and
mud mobilisation at the tip of the UL01 thrust sheet
reflect the stage of near collapse (Fig. 49). The thick
zone of hydrodynamic brecciation along the hanging-

wall flat reflects the same tendency towards collapse,
and speculations about the influence of ground-fro-
zen conditions on the preservation of the thin thrust

sheets during translation over the foreland are rele-
vant. Ground-frozen conditions are interpreted to have
affected that part of the thrust sheets elevated above
the ground surface; the freezing of the sediments in
the thrust sheet may result in more brittle behaviour,
whereby cracks formed (Figs 44, 46). However, due
to the high pore pressure maintained along the hang-
ing-wall flat, the cracks were filled with sand pumped
into the cracks by the over-pressured pore water from
the base of the thrust sheet.

Hydrodynamic brecciation is evidently related to

the hanging-wall ramp-and-flat. Brecciation was ini-
tiated at an episedimentary stage with the formation
of ball-and-pillow structures due to sediment load-
ing. When the loading increased by over-thrusting,
the ball-and-pillow formation progressed further and
hydrodynamic brecciation was concentrated at the
hanging-wall flat. Small-scale mud diapirism took place,

with chaotic folding developing into polydiapirs (Figs
54, 55, 77, 78, 86, 88). Polydiapirism and mud-mobili-
sation are considered to have developed simultane-
ously and with an increasing degree of disordering
and size of diapir in progressive stages of deforma-
tion. Many of the mesoscopic diapir structures recog-
nised in the Rubjerg Knude Glaciotectonic Complex
can be compared with the multi-wavelength gravity

structures described in the model analysis by Wein-
berg & Schmeling (1992). The formation of large-scale
diapirs is suggested to have been related to thrust-
fault deformation of a deep-seated hanging-wall flat
that propagated up to surface level along a set of rel-
atively steep footwall ramps. During propagation up
along a lower ramp to an intermediate flat, and ramp-
ing from the 20 m inter mediate flat level to the 10 m
flat level, polysequential hanging-wall anticlines

formed, and were subsequently destroyed by mud-

mobilisation initiated from the deep-seated thrust zone
of the hanging-wall flat. Some of the soft sedimentary

xenoliths floating in the mud diapirs can be viewed
as relicts of anticline crests (Fig. 74). Staircase-like ramp
propagation is indicated for the Kramrende diapir and
the Sandrende diapir, but is not so obvious in the
case of the Brede Rende diapir. Intrusive remobilised
mud is evidently related to the footwall ramp propa-
gated hanging-wall flat of GR01, and the mud mobili-
sation in the thrust sheets of the Stortorn and Moser-
ende Sections are all easily identified with sequential
ramping from the deepest décollement level.

181

Thrust-fault dynamics

The difference in thrust-fault development that relates
to the upper flat level (10 m) is very marked when the
Ulstrup Section is compared to the Grønne Rende
Section. Thus the foreland regime in the latest stage
of deformation is characterised by thin, very long
sheets subjected to horizontal translation over the foot-
wall flat of the foreland. In contrast, the Grønne Rende
Section probably formed an imbricate complex of
smaller, moderately dipping thrust sheets when this
section was adjacent to the foreland. There is no ob-
vious reason for this difference, although minor dif-
ferences in lithology and differences in environmen-
tal conditions (frozen or unfrozen ground) could be
viewed as contributing factors. However, there is an
invisible condition which must be considered, name-
ly the velocity of deformation. At the initiation of any
deformation, the velocity is zero; the velocity then
increases until the displacement is brought to a halt at
the edge of the foreland during decreasing velocity.
Fast deformation results in more fractures than slow
deformation. It is therefore suggested that the imbri-
cate structures in the central part of the thrust-fault
complex were initiated during the fastest advance to-
wards the foreland and that the long-distance transla-
tion of unbroken thrust sheets relates to decreasing
velocity or slow advance.

In a discussion of the velocity of thrust-fault propa-

gation, the question of rates and timing is inevitable.
The youngest dating of the Stortorn Formation is 30 000

years B.P., while the oldest dating of the Rubjerg Knude
Formation is about 29 000 years B.P. and the oldest

dating of the Ribjerg Formation is 26 000 years B.P.

Thus, a time span of 3000 years is estimated for the
calculated shortening of 6 km, which indicates an
average velocity of 2 m per year.

The peak velocity of the deformation must evidently

have been more than 2 m per year, taking into ac-
count the acceleration and deceleration. However, the
velocity would also have been much higher if defor-
mation had progressed in periodic steps rather than
continuously. A step-like process would have involved
periods of no movement alternating with higher ve-
locity in the periods of advance. With respect to the
Rubjerg Knude Glaciotectonic Complex, the summary
of the dynamic development suggests that a continu-
ous progressive deformation process characterised the
formation of the complex (Fig. 123). Although the
developments of the sections are described separate-
ly above, the deformational overlap from one section

to the next links the sections in a continuous dynamic
development.

Syntectonic deposition

The concept of piggyback basins was originally relat-
ed to large-scale regional orogenic settings (Ori & Friend

1984; Ricci Lucchi 1986). However, as applied her e
the ter m is used for the syntectonic deposits of the
Rubjerg Knude Formation that were laid down in ba-
sins structurally overlying moving thrust sheets. The

initial depositional environment of the Rubjerg Knude

Formation was a relatively flat lowland, dominated
by shallow lakes in an outwash plain bounded by an
ice margin to the north. The plain was probably gently

dipping towards the north due to isostatic loading of
the ice cap. Judging from the variation in thickness of
the Rubjerg Knude Formation (30 m in the proximal
part to only about 10 m in the distal), the dip of the
plain was not more than 2°.

As the thrust belt propagated southwards, the plain

became separated into smaller, more or less isolated
basins characterised by steep slopes and uneven re-
lief. The most distinctive deposits in these basins ar e
the sedimentary breccias and slumped thrust sheets
derived from the tips of up-thrust thrust sheets.

Three types of syntectonic slump/slide deposits can

be differentiated. The first type involves deposition
of coarse clasts up to metre size, which were rotated
indicating transport as sedimentary clasts enveloped
by sandy mud. This deposit type is regarded as being
related to the distal part of the thrust-fault system,
and is exemplified by the piggyback basin in the Stens-
næs Section (Fig. 56). The second type is characte-
rised by isoclinally folded slump sheets interlayered
with matrix-supported coarse clastic diamictite. This
indicates that the source was very close to the depo-
centre, although the slump sheets were detached from
their roots and were transported independently by
gravity gliding into the basin. The piggyback basin in
the Martørv Bakker Section represents this deposit type
(Figs 23, 64). The third type comprises slump-folded
sheet segments that can be traced directly, or correla-
ted over short distances, back to the source of the
thrust sheet; this type is regarded as being related to
the proximal part of the system. The next step in the
development would be that of thrust sheets displaced
by normal faulting, but lacking depositional features
such as sedimentary breccias. However, this type of
dynamic development is strictly tectonic. The major

182

slump fold occurring in the Stenstue Rende Section
(Fig. 89) may be regarded as a transition from a sedi-
mentary to a tectonic regime. The deposition of recog-
nisable thrust-sheet tips in the piggyback basins sup-

ports the concept of a continuous thrust-fault process.

Proglacial and subglacial deformation

Glaciotectonic analyses distinguish between deforma-
tion generated in proglacial and in subglacial regimes
(Aber 1982; Croot 1988; Aber et al. 1989; Pedersen 1993,

1996, 2000). It has already been argued that the thin-
skinned thrust-fault deformation of the Rubjerg Knude

Glaciotectonic Complex is an example of proglacial
deformation. The key evidence for this is the presence

of intimately associated syntectonic piggyback basins.
These basins must have been situated in front of the

ice margin, with sedimentation taking place under open

water, simultaneously with thrust-fault propagation.

However, the subglacial deformation is represented

locally by the 1 m thick glacitectonite occurring below

the glaciotectonic unconformity that truncated the

thrust-fault complex. This is found in the glaciolacu-
strine beds at the top of the UL02 thrust sheet in the
northern part of the Ulstrup Section. It can be argued
that here the subglacial deformation penetrated down
a depth of c. 5 m below the glaciotectonic unconform-

ity. Mud diapirism and hydrodynamic brecciation oc-
curred in this setting, probably caused by loading when
the ice sheet overrode the sediments. The focus of
subglacial deformation is at the Blå-unconformity (Fig.
32). In the northernmost 300 m of the cross-section,
the ef fects of mud mobilisation increase to a point at
which primary sedimentary as well as early structural
features are completely destroyed. This phase of de-
formation is interpreted to have taken place while the
sole of the frontal part of the ice sheet was fixed to
the trailing end of the thrust-fault complex. This also
implies that the velocity of the thrust faulting was equal
to the advance of the ice sheet. The advance of the
ice-sheet load corresponds to the mechanics of grav-
ity spreading (Pedersen 1987). The increasing propa-
gating stress resulted in increasing mud mobilisation,
and subsequently the overpressure was transmitted
laterally by the mud fluid towards the for eland. The
mechanism might well be compared to squeezing
toothpaste out of its tube.

At a certain stage, the fluid pressure was released,

probably due to migration of all the hydrodynamic
breccias, and the mobilised mud consolidated. Sub-

sequent to consolidation, the frontal sole of the ice-
sheet released contact with the Blå-unconformity and
propagated over the thrust-fault complex formed in
the foreland of the ice margin. During this process,
subglacial shearing affected the top of the structure-
less consolidated mud, and anastomosing as well as
plane-parallel shear fractures were formed (Fig. 32).

In soft sediment structural geology, the gravity-

spreading model has been successfully applied to the
geological setting of the mud lumps in the Mississippi
Delta (Morgan et al. 1968; Pedersen 1987; Aber et al.
1989). It could therefore be suggested that a gravity-
spreading model due to clastic progradation might be
the deformation mechanism. However, there is no
known delta setting at this time/place that could have
provided the basis for this model, and furthermore,
the sand units observed here only reach a third of the
thickness of the 100 m delta-sand units in the Missis-
sippi Delta setting. Finally, the presence of the glacio-
tectonic unconformity and related glacitectonite is in-

compatible with a sand sediment-spreading process.

Although a delta setting has not been document-

ed, it might be suggested that a slope similar to that
of a megascopic delta foreset existed, and that the
deformation was caused by major gravity gliding on
this slope, or was simply due to uplift in the hinter-
land. However, this is not considered likely. The iso-
static rebound documented from the elevation of the
Vendsyssel Formation reaches 60 m a.s.l. To this must
be added the uplift due to the lowering of sea level;
the area in the hinterland was thus an area of subsi-
dence rather than uplift. Structurally, a gravity-gliding
model would provide extensional normal fault sys-
tems in the trailing end of the thrust-fault complex
(Pedersen 1987). This is not compatible with the ob-
served increase in compressional structures in the hin-
terland, as documented in the cross-section and indi-
cated by the balanced cross-section; a gravity-gliding
model for the complex can therefore be rejected.

Such larger glaciotectonic complexes are often so

impressive that some geologists suggest that they were
formed by orogenic activity (Lykke-Andersen 1992;
K. Binzer, personal communication 1997). Disregar-
ding the obvious glacial geological indications, there
are two features that distinguish glaciotectonic com-
plexes from basement-involved deformation: (1) the
superficial detachment, and (2) the rate of translation.
In the Rubjerg Knude Glaciotectonic Complex, there
are no infracrustal rocks involved and the thrust sheets
are not rooted down into a deep-seated hinterland
source. The lowermost detachment level is 40 m be-

183

low the reference level, which is more or less coinci-
dent with present sea level, and there are no indica-
tions that the deformation extended below the 40 m
level. The velocity of thrust-sheet motion in orogenic
mountain ranges is of the order of 1 cm per year (Wilt-
scko & Dorr 1983). In glaciotectonic systems, the ve-
locity can be up to 100 times as fast, as documented
by the velocity estimate of 2 m per year for the Ru-
bjerg Knude Glaciotectonic Complex.

Glacial geological conditions

The Rubjerg Knude Glaciotectonic Complex is inter-
preted to have formed due to the advance of the Nor-
wegian Ice in the late Middle Weichselian. The Nor-
wegian Ice melted back at the beginning of Late Weich-
selian time and was succeeded by a renewed advance
of the Scandinavian Ice Sheet from central Sweden. In
that part of Denmark east and north of the Main Sta-
tionary Line (Figs 1, 12), the direction of this advance
was towards the south-west and the advance is thus
referred to as the NE-Ice (Houmark-Nielsen 1987). The
eastward advance of this ice towards Vendsyssel pro-
bably formed the N-S-trending hilly landscape named
Jyske Ås, the formation of which was contemporane-
ous with deposition of the outwash plain represented
by the Ribjerg Formation. When the NE-Ice advance
reached the Rubjerg Knude Glaciotectonic Complex,
it only resulted in minor superimposed deformation.
The oblique orientation of the fold axis of the mega-
slump in the Stenstue Rende Section might be due to
such superimposed deformation, but in general very

few glaciotectonic disturbances can be related to the
NE-Ice advance. That overriding by the NE-Ice had so
little effect may be attributed to strain hardening due
to the preceding deformation, or the smoothing out
of the landscape by the former glaciotectonic uncon-
formity, which would facilitate the second overriding
of the complex. Ground-frozen conditions could also
have been a factor, since this would have prevented
drainage from the ice sheet through the substratum,
resulting in high pore-water pressures at the sole of
the ice. The effect of this would have been to facili-
tate easy and fast propagation over the complex, al-
though it by then formed a hill in the landscape.

The Norwegian Ice produced a hill-and-hole pair

with Rubjerg Knude as the hill and the depression
extending from Lønstrup northwards as the hole. Im-
mediately after the melting back of the NE-Ice, the
landscape was covered by the Vendsyssel Formation.
A contour map of the base of the Vendsyssel Forma-
tion (Fig. 125) thus provides a picture of the geomor-
phology of the young glacial landscape unaffected by
the succeeding 15 000 years of erosion. In Fig. 125,
the hill-and-hole pair is readily identified and the gen-
eral E-W morphological trends are well represented.
To the east, this trend is truncated by a strong SE-NW
hill-and-hole geomorphology, related to the NE-Ice.
The tr end of the thrust-fault belt of the Rubjerg Knu-
de Glaciotectonic Complex can be followed from the
coastline to the east for about 2.5-5 km. The eastern
fringe of the complex has been eroded down to sea
level, probably by the NE-Ice, and subsequently con-
cealed by the Vendsyssel Formation.

185

Facing page:
Fig. 125. Contour map of the pre-Vendsyssel Formation
landscape; for location, see Fig. 13. Note the depression north
of Lønstrup which represents the hole in the hill-and-hole
pair morphology of a glaciotectonic complex; the correspond-
ing hill is represented by the high at Rubjerg Knude. The map
is based on data from the GEUS well database and from Plate 1.

Conclusions

Structural analysis of the Rubjerg Knude Glaciotec-
tonic Complex, based on detailed photogrammetric
measurements and field investigations, provides a
geological cross-section through a low-friction thrust-
fault system. Interpretation of the entire thrust-fault
architecture included unexposed parts of the complex,
and is based on the construction of a balanced cross-
section. A model for the dynamic development dem-
onstrates that deformation progressed continuously
and involved formation of duplexes and mud diapirs.
Although the thrust-fault structures were formed in a
proglacial regime related to the advance of the Nor-
wegian Ice (30 000 - 26 000 B.P.), the structures can
be viewed as representing an almost complete model
of thin-skinned thrust-fault systems.

For descriptive purposes, the complex is subdivid-

ed into 13 sections, which demonstrate the structural
development from a proximal to a distal position in
the thrust-fault system. Investigation of these sections
provided the following main conclusions.

1. The structural elements in the Rubjerg Knude Gla-

ciotectonic Complex comprise ramps and flats re-
lated to hanging-wall and footwall positions, re-
spectively. Hanging-wall anticlines and footwall
synclines were formed due to thrust-fault propa-
gation. Back-thrust faults were formed during up-
per ramp-hinge propagation, and an irregular fold
framework developed in relation to sequential
duplex imbricate formation during footwall ramp
collapse. Foreland-dipping normal faults were

formed in relation to translation of duplex segments.

2. From the balanced cross-section, the shortening

during thrust-fault deformation is calculated to have
been c. 50%. About 11% of the initial stratigraphic
unit subjected to thrust faulting is estimated to have
been lost due to erosion. The décollement zone
was at its deepest position (40 m) in the proximal

sections, becoming shallower towards the foreland.
Stacking of duplex segments is correlated with space

problems created in the subsurface due to initial
displacements at the upper levels. Stacking of du-
plex segments correlates well with the elevation
of the reference level in the system.

3. Hydrodynamic brecciation was dominantly relat-

ed to the hanging-wall ramps and flats. Polydiapir-
ism and mud mobilisation characterise the thrust
zones. Mud mobilisation resulted in the formation
of larger mud diapirs, and preferentially evolved
during hanging-wall propagation from the décol-
lement level up above sets of intermediate and
upper footwall ramps.

4. Syntectonic deposition took place in piggyback

basins overlying the thrust sheets. Thrust sheets
exposed to erosion provided sediment to the ba-
sins, and in some cases major lumps derived from
the tips of thrust sheets slumped and slid as mega-
blocks into the piggyback basins.

5. The thrust-fault deformation was caused by gravi-

ty spreading at the front of an advancing ice sheet.
Over -pressur ed mud formed an important part of
the stress transfer. The average velocity of the
thrust-fault displacement is estimated to have been
2 m per year. A 40 m thick succession of flat-lying
sediments, extending for 12 km, was compressed
into a thrust-sheet complex that was 6 km in length
and up to 80 m thick.

Acknowledgements

The Geological Survey of Denmark and Greenland is
thanked for supporting this project during the last 10
years. Initial investigations were carried out while the
author held a senior stipend at the Geological Insti-
tute, University of Copenhagen. The Carlsberg Foun-
dation supported the project with a one year research
grant, which is gratefully acknowledged; the Danish
Research Agency is thanked for financial support for
printing this bulletin. Keld Dueholm and the Institute
of Survey and Photogrammetry are thanked for their
co-operation and willingness to provide time and fa-

186

cilities at the photogrammetric instrument at the Tech-
nical University of Denmark.

Frants von Platen-Hallermund is thanked for assist-

ance with the ARC-INFO transfor mation and ARC-VIEW
editing, which provided the graphic display of Plates
1 and 2. Alice Rosenstand and Benny M. Schark helped
in drafting the figures, and the staff of the Graphic

Section at GEUS are thanked for technical support.

I am indebted to A.K. Higgins for reading the first

draft of this manuscript, to two anonymous referees
and the editor, Jon R. Ineson, for their constructive
and helpful comments on the manuscript, and to my
wife, Gunver K. Pedersen, for support and inspiring
discussions during the progress of this work.

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190

Appendix 1

Thrust-fault terminology

Thrust fault : A surface along which an overlying block
is displaced relative to an underlying block. Relative to

bedding, two different elements are distinguished in
a thrust fault: the ramp and the flat.
Ramp : A thrust-fault ramp cuts up-section in the di-
rection of slip and dips towards the hinterland. The
angle between bedding and the ramp is in general
between 20° and 30° and will not exceed 45° due to
general rules of initial fracturing. A ramp is linked to a
lower flat at the lower ramp hinge and to an upper
flat at the upper ramp hinge. A ramp may become for e-

land-dipping in special cases, mainly related to trans-
port along an upper flat.
Flat : A thrust-fault flat is a bedding-parallel slip sur-
face along which lateral displacement takes place. The
lowermost thrust-fault zone in deformation complex-
es is in general referred to as the décollement surface,
décollement zone or décollement level. In the present
description the 'décollement level' is the ter m used
for the thrust fault between a thrust sheet and an un-
displaced footwall block below a footwall flat. As flats
develop at dif ferent levels, the flats above the décol-
lement level are referred to as intermediate flats and
the upper flat (identical with the roof thrust fault).
The thrust-fault flats are referred to by their depth from

the upper reference zero-level indicated from the balan-

ced section. Thus the 20 m flat level is the horizontal
thrust fault situated 20 m below the top reference level

and 10 or 20 m above the décollement level.
Thrust sheet : A thrust sheet is the block displaced
over a thrust fault. In this study, the thrust sheets ar e
annotated according to the section in which they oc-
cur with two capital letters, referring to the named
section, and a number referring to its position from
leading edge to trailing end of the section. Thus, KR01
is the thrust sheet near est to the foreland in the K ram-
r ende section. A thrust fault is referred to according
to the thrust sheet it displaces. A thrust sheet is syn-
onymous with the hanging-wall block.
Hanging-wall block : The rock mass displaced over
a thrust fault is a hanging-wall block. At the base, a
hanging-wall flat and a hanging-wall ramp bound the
hanging-wall block. At the roof, the hanging-wall block
is capped by a top sur face or a roof thrust fault. The

roof thrust fault may constitute a footwall flat as well
as a footwall ramp.
Footwall block : The rock below a thrust fault is a
footwall block. The footwall block is bounded by a
footwall ramp, and the top of the footwall block con-
stitutes a top surface and/or a footwall flat.
Hanging-wall ramp : The segment of a ramp that
bounds the hanging-wall block is a hanging-wall ramp.
At the incipient displacement along a ramp, the hang-
ing-wall ramp is thrust along a footwall ramp. When
the hanging-wall ramp passes the upper ramp hinge,
the hanging-wall ramp is thrust along a footwall flat.
A hanging-wall anticline is always formed above a
hanging-wall ramp.
Hanging-wall flat : The bedding-parallel thrust-fault
boundary below the hanging-wall block is a hanging-
wall flat. When a hanging-wall flat is thrust up along a
footwall ramp, the hanging-wall flat is re-orientated
and becomes inclined towards the hinterland. When
the hanging-wall flat is thrust along an upper footwall
flat, the thrust fault again becomes bedding parallel.
Footwall ramp : The inclined thrust-fault boundary
of a footwall block is a footwall ramp. The footwall
ramp is either the ramp boundary to the undisplaced
foreland or it forms the trailing ramp boundary of a
thrust sheet. In this study, the trailing footwall ramp is
referred to using the annotation of the thrust sheet/
footwall block that underlies it. Thus the KR02 hang-
ing-wall ramp is displaced up along the KR01 foot-
wall ramp.
Footwall flat : A footwall flat is always the top of a
footwall block. A footwall flat is more or less horizon-
tal unless it is re-orientated during the displacement
of a thrust sheet up along a ramp.
Hanging-wall anticline : When a hanging-wall block
is thrust over an upper ramp hinge, the hanging-wall
block is folded into an anticline with a foreland-dip-
ping forelimb and a hinterland-dipping backlimb. This
fold may also be termed a ramp anticline. During the
progress of thrusting along the upper limb, the hang-
ing-wall anticline develops into a flat-topped anticline.
The flat-topped anticline may alternatively be regard-
ed as a flat-lying thrust sheet with a foreland-dipping
forelimb or a frontal thrust-sheet nose. However, it is
important to note that above a hanging-wall ramp
thrust along a footwall flat, a foreland-dipping sur-
face is formed.

191

Footwall syncline : When a thrust fault propagates
up along a ramp, an anticline-syncline pair is formed
above, and in front of, the tip of the thrust fault, iden-
tical to the formation of a fault-propagation fold. When
the thrust fault finally breaks through the folded lay-
ers, the fold pair is separated into a hanging-wall an-
ticline and a footwall syncline. A footwall syncline
therefore represents the gentle deformation below the
footwall ramp; this deformation does not add signifi-
cantly to the displacement along the thrust fault. The
footwall syncline may also be regarded as a drag fold.
The case where this is the only correct interpretation
is along a growth fault. Here the sediments deposited
syntectonically up against a hanging-wall ramp are
successively bent into an overturned syncline. The
footwall syncline is identical to a trailing syncline.
Duplex : A duplex is one or more thrust-sheet seg-
ments entirely bounded by thrust faults and thus over-
lain by a thrust sheet. A thrust sheet bounded by thrust
faults is called a horse, originally regarded as a minor
rootless thrust-sheet segment. Some of the lower thrust-
sheet segments described in this study are identical to
horses, although the more neutral term 'segment' is
adopted here. The formation of a duplex is related to
the 'footwall ramp collapse' (Boyer & Elliott 1982),
whereby progressive failure during thrust-fault prop-
agation creates successively younger thrust faults be-
low older ones. A parcel of thrust-sheet segments may
be stacked to form a duplex complex.

Imbricate fan : A branching thrust-fault complex in
which the individual thrust faults r each the surfaces
or top level is called an imbricate fan. An imbricate
fan is termed a duplex if the upper boundary is a roof
thrust.
Antiformal stack : When a duplex is fault-bend-fold-
ed over a footwall ramp, an antiformal structure sim-
ilar to a hanging-wall anticline is formed. Due to the
complex stratigraphic relationship within such a struc-
ture, it is referred to as an antiformal stack.
Piggyback thrusting : When an older thrust sheet rests
on the back of a younger thrust sheet and is trans-
ported due to the displacement along the thrust faults
bounding the younger thrust sheets, it is called pig-
gyback thrusting.
Piggyback basin : Just as piggyback thrusting refers
to transport of a thrust sheet, the term is also applied
to a basin that accumulates sediments during transla-
tion on the back of an active thrust sheet: the piggy-
back basin (Ori & Friend 1984; Ricci Lucchi 1986). In
this study, the term is mainly used in the description
of an area of sedimentation between two thrust sheets.
In general, the piggyback basin is deposited between
a fault-bend thrust-sheet tip in the distal part of a thrust
structure and bounded by a hanging-wall ramp at the
proximal boundary of the basin. The term piggyback
basin can only be applied to successions identified as
having been deposited syntectonically.

192

Appendix 2

Specification of photogrammetric work

The construction of the Rubjerg Knude cross-section
(Plate 1) is based on a multi-model photogrammetric
investigation of the cliff section, with the application
of the method described by Dueholm (1992). A series
of

oblique photographs were taken from a Cessna

fixed-wing aircraft in June 1993. The camera used for
the photography was a Minolta XG2, which had been
tested and calibrated for its optical specifications at
the laboratory of photogrammetry at the Danish Tech-
nical University. The films used were standard 24 × 36
mm colour diapositive. The photographs were taken
with 66% overlap from a distance of 200-300 m with
an inclination angle of c. 35°. From the series of pho-
tographs, 70 samples were selected for setting up three
sets of templates, which included 67 stereoscopic
models.

In the laboratory, the orientation of the stereo-models

was carried out based on ground control points adapt-
ed from two sets of vertical aerial photographs at a
scale of 1:25 000, namely D9202 G 1365-66 and KMS
9203 A509-10 taken in May 1992. The strike of the
section line is N15°E from Rubjerg Knude and south-
wards. North of Rubjerg Knude, the strike is N24°E,
which is nearly parallel to the direction of the coast-
line along the beach. Fortunately, this is also a r ea-
sonable approximation of being perpendicular to the
main concentration of structural strikes (bedding, thrust
faults and fold axes; Fig. 10). A minor adjustment of
the northern and souther n section lines was subse-
quently implemented to make the cross-section fit to
the general plane of orthographic projection with a
projection axis striking 107°.

The stereoscopic instrument used for the investiga-

tion was a Kern DSR 15 analytical plotter with a DEC
VMS operating system and the special attached GEO-
PROGRAM developed by Dueholm (1992). Five dif-
ferent labels were used for the features outlined by

the floating mark: line type 1 includes bedding traces,
line type 2 includes the main unconformities, line type
3 was used for the contacts between geological units
(members and formations), line type 4 outlines thrust
faults, and finally line type 5 was used for topograph-
ic features (dunes, scree cones, strandplain, rockfalls
etc.). Digitalisation of the geological structures in the
stereo-models was administrated in data files, each
covering a plot-area. The plot-areas covered 500 m of
the Rubjerg Knude cross-section, and 13 plot-areas
were used for the analogue plotting of data digitised
in the stereo-model. The digital data were stored for
the later construction of the cross-section and the trans-
formation for other programs applied for the manage-
ment of the cross-section display.

The orientation of models and setting up the sys-

tem for the cross-section investigation took about one
week, and the photo-geological compilation work was
made over a period of three months in the autumn of
1993. The average progress was two models per day.
The benefit of the multi-model analytical stereo-plot-
ter is that features can be traced continuously from
one model to the adjacent models. Thus one is not
restricted to working model by model, but the compi-
lation can be extended over several models using the
same set of templates. By January 1994, the cross-sec-
tion could be plotted out in a normal vertical projec-
tion profile plan from the stored digital data with the
application of the program facilities prepared by Due-
holm (1992). The scale of the Rubjerg Knude cross-
section in the draft versions is 1:500, and the accuracy
of the plotted data is estimated to be better than 25
cm.

In 1995-1996, the cross-section details observed in

the photo-geological models were checked in the field,
and in 1997 the templates were set up again for cor-
rection, adjusting and compilation of details in the
cross-section.

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 148-192, Structural analysis of the Rubjerg Knude Glaciotectonic Complex, Vendsyssel, northern Denmark