Vol. 8 pp 90-119, Geol. Surv. Denmark and Greenland Bulletin

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KR03 thrusting. Its relationship to the footwall flat of
KR02 indicates that it was thrust along a hanging-wall
flat in the order of 60 m. However, before the KR03
thrusting was complete, the KR04 thrust sheet was
already emplaced on its back. The displacement of
KR04 can be determined in the cross-section to be 66
m. The implications of KR04 being thrust onto KR03
ar e that the sedimentation of the Rubjerg Knude For-
mation on top of KR03 ceased, and with the contin-
ued propagation of KR03 over the footwall ramp, the
back-thrust splay also affected the KR04 thrust sheet
that was being passively transported piggyback on
KR03.

Brede Rende Section

For more than a century, groundwater drainage has
been concentrated at a spring at Brede Rende. From
the spring, situated at the base of the cliff, a stream
has over the years eroded a large funnel-shaped gully
behind the cliff facing the sea. Gr oundwater erosion
successively stepping backwards is thus responsible
for the wide gully and for the locality name (Danish:
brede = wide; rende = gully). The groundwater trans-
missivity is, of course, governed by the geology of the

Brede Rende Section, such that the spring wells out
from the unconformity surface between the clayey
Lønstrup Klint Formation and the permeable sand of
the Rubjerg Knude Formation. The water initially
drained in a southerly direction, but the present north-
erly drainage system is exposing the structures of the
northern flank of Brede Rende in an isolated cliff. It is
likely that this cliff will be completely removed by
erosion by the sea as well as by the stream within the
next few years leading to the formation of a broad
gully at this location.

Important structural features currently exposed in

the Brede Rende Section comprise a polydiapiric com-
plex, the Brede Rende diapir in the frontal part, the
prominent Brede Rende normal fault (BRNF) in the
central part, and a series of duplexes stacked in the
trailing end of the section.

Tectonic architecture

The Brede Rende Section comprises eight thrust sheets,
annotated BR01-BR08 (Plate 2). The southern and
frontal boundary of the section is the footwall ramp
of KR04. The northern boundary is the thrust fault
which partly acts as the BR08 footwall ramp and flat,
and partly is the hanging-wall ramp for the SR01 thrust
sheet in the Sandrende Section.

The BR01 thrust sheet is a relatively thin sheet that

was displaced up along the KR04 footwall ramp, which
is c. 30 m thick and dips about 35°N. Above BR01, the
BR02 thrust sheet was displaced more than 50 m along
its hanging-wall ramp onto the upper footwall flat of
KR04. The lower part of the thrust separating BR01
and BR02 has been destroyed by penetrating diapir-
ism, and together with BR03 these frontal thrust sheets
in the Brede Rende Section constitute the Brede Rende
diapir (Figs 73, 74). The thrust sheets can still be re-
garded as individual coherent elements, although their

Fig. 74. Detail of the internal structure of the Brede Rende dia-
pir. Although the structure appears as a chaotic mixture of dis-

rupted sand beds 'floating' in a disorganised fashion in the
mobilised mud-matrix, some of the features could be interpre-
ted as relicts of hanging-wall anticlines (see dashed lines) formed
in a developed stage during thrusting up along steep ramps.

Photograph: June 1985.

boundaries and internal structure have been strongly
distorted by diapirism.

BR03 is the longest thrust sheet in the Brede Rende

Section, when the trailing lower segment is included
(see Plates 1, 2). This is a constructional convention
based on the consideration of which of the hanging-
wall ramps should be traced down to the décollement

surface, and thus determine the annotation of the sub-
surface duplex sheets (Plate 2, see later). The BR04
thrust sheet is about 300 m long and is displaced by
the Brede Rende normal fault (BRNF) (Fig. 75). North
of the BRNF, the BR04 thrust sheet was thrust along
an intermediate BR03 footwall flat, and south of BRNF
the upper hanging-wall ramp and flat of BR04 were
thrust over the upper footwall flat of BR03. The amount
of displacement along thrust faults in this part of the
Brede Rende Section is 50 m (measured in the cross-
section of Plate 1) for BR03 as well as BR04. In BR04,
the Rubjerg Knude Formation reaches its maximum

thickness of about 20 m in the Brede Rende Section,
whereas the cover of Rubjerg Knude Formation on the

back of BR02 and BR03 is less than 5 m thick.

The BR05 thrust sheet is relatively short and loca-

ted between BR04 and BR06. The displacement along
its hanging-wall ramp is about 80-90 m and the initial
ramp-angle was c. 12°. The thickness of the Rubjerg
Knude Formation on top of BR05 is only about 5 m,
which indicates that the thrusting of the BR06 thrust
sheet propagated early in the thrust development of
the Brede Rende Section. The piggyback thrusting of
BR06 on BR05 on BR04 is one of the best examples of
a duplex structure in the Rubjerg Knude Glaciotecto-
nic Complex.

The BR06 thrust sheet is a relative long and thin

thrust sheet. To the north, the trailing end of BR06
was thrust up over the footwall ramp of BR05. From
the footwall ramp hinge, an upper hanging-wall flat
(BR06HWF) was displaced along the upper BR05 foot-

Fig. 75. The Brede Rende normal fault ( BRNF ). The frontal part of the BR06 thrust sheet has a normal displacement of about 20 m
down through the 45° dip normal fault, which can be measured from the hanging-wall flat of BR06 ( BR06HWF ) north of the normal

fault to the BR06HWF south of the normal fault. In the footwall block of the BRNF, a series of minor normal faults make a stepwise
displacement of the downthrown hanging-wall block. In the hanging-wall block of the BRNF, the bend of the thrust-fault structures

may be characterised as a roll-over anticline. Note that the BR06 hanging-wall flat transforms into a hanging-wall ramp ( BR06HWR ),
which was thrust-displaced along the upper footwall flat of the BR04 thrust sheet ( BR04FWF ). Photograph: June 1984.

wall flat for about 200 m. As noted above, the BR06HWF

developed above the BR05 thrust sheet at an early
stage. The BR06 thrust sheet is divided into two seg-
ments by the BRNF (Fig. 75). South of the BRNF, the
upper hanging-wall ramp of BR06 was emplaced on
the BR04 upper footwall flat (Fig. 75).

The BR07 thrust sheet was thrust piggyback onto

the trailing-end segment of BR05 and propagated up
along the footwall ramp of BR06. It has very chaotic
internal structures dominated by polydiapirism. The
position of the reference surface (L/R-unconformity)

at an elevation of 20-30 m above sea level indicates
that the BR07 sheet was ramped up onto the flat above
a duplex composed of the trailing segments of BR03
and BR05 (see later). There is only a thin cover of less
than 5 m of the Rubjerg Knude Formation on the back
of BR07, which is overlain by the BR08 hanging-wall
ramp.

The BR08 thrust sheet is the northernmost and up-

permost sheet in the Brede Rende Section. It is the
smallest thrust sheet in the section, The thin frontal
tip of the thrust sheet consists of the uppermost part

Fig. 76. Ball-and-pillow structures

superimposed by chaotic hydrodynamic
brecciation in the upper part of the

Lønstrup Klint Formation in the Brede
Rende Section. The brecciation was

formed by polysequential diapirism
during thrusting of the BR06 hanging-

wall flat ( BR06HWF ) over the hinge to
the upper footwall flat of BR05

( BR05FWF ) situated in the left side of
the photograph. Photograph: June 1993.

of the Lønstrup Klint Formation, but with an up to 12 m

thick succession of the Rubjerg Knude Formation on
top of the L/R-unconformity. Due to the bend up along
the BR06 footwall ramp, the inclination of the BR07
and BR08 thrust sheets is c. 25°N.

Sedimentary units

The Lønstrup Klint Formation is strongly affected by
ball-and-pillow load structures and hydrodynamic
brecciation. The maximum thickness of the formation
exposed is only about 20 m (tentatively measured in
BR02). The thickness of the Rubjerg Knude Formation

varies from thrust sheet to thrust sheet, indicating dif-
ferential thrust-fault movement that either closed the
piggyback sedimentation and/or lifted the formation

up to a position exposed to erosion. The Rubjerg Knu-

de Formation was also subjected to hydrodynamic
brecciation. At the top of the central part of the Brede
Rende Section, a glacitectonite and associated glacio-
tectonic imbrications are interpreted to be related to
the advance of the Norwegian Ice; the sandy till is
interpreted to be the Kattegat T ill Formation.

Lønstrup Klint Formation

The lower and inter mediate parts of the Lønstrup Klint
Formation are characterised by dark clayey mud. The
interval 5 to 10 m below the L/R-unconformity is dom-
inated by a few thick beds of light coloured sandy
turbidites, and the uppermost 5 m is formed by thin-
bedded sand beds interbedded with mud. The size of

Fig. 77. Small-scale ball-and-pillow structures distorted and in-

truded by water-escape injection. Note that dish structures were
formed above the water-escape pipe. Detail of chaotic breccia-

tion in the upper part of the Lønstrup Klint Formation; frontal
part of the BR06 thrust sheet in the Brede Rende Section. Pho-

tograph: June 1998.

Fig. 78. Small-scale disharmonic undulations formed by polyse-

quential diapirism in the thinly interbedded clays, silts and fine-
grained sands of the upper part of the Lønstrup Klint For ma-

tion. Note the fold accentuation of the climbing ripple lamina-
tion in the central part of the figure. Frontal part of the BR06

thrust sheet in the Brede Rende Section. Photograph: June 1998.

ball-and-pillow structures is typically related to the
initial thickness of the sand beds, and the subsequent
hydrodynamic brecciation and chaotic structures
formed during water-escape activities (Figs 68, 76-78).

The L/R-unconformity at the top of BR04 truncates

a large ball-and-pillow structure at the top of the Løn-
strup Formation just north of the normal fault (Fig.
79). This implies that some of the load structures, and
possibly also initial water-escape dynamics, had com-
menced prior to the development of the unconformity.

It may be that this phase of ball-and-pillow Formation
was initiated by the drainage of the large lake basin
(see Sadolin et al. 1997). Thus the initiation of ball-
and-pillow formation can be viewed as the conse-
quence of vibration created by an increased water
transport over the beds. At this locality, the formation
of ball-and-pillow structures was clearly not the effect
of loading by over -thrusting, but only the result of
density variation of the primary sedimentary layers,
since the top of the Lønstrup Klint Formation was
under going erosion and the gravel bed on the L/R-
unconformity was deposited subsequently.

Rubjerg Knude Formation

The Rubjerg Knude Formation reaches a thickness of
15 m in the upper part of the BR04 thrust sheet, but in
the rest of the Brede Rende Section it is less than 10 m

thick. The relatively thin nature of the formation (3-5
m) in BR02, BR03, BR05 and BR07 is interpreted to
indicate that these basins were over-thrust or thrust-
elevated at an early stage of thrust propagation. In
contrast, deposition persisted in the piggyback basins
of BR04 and BR06 before their upper footwall flats were

overthrusted and deposition ceased in the basins.

Structures

Three types of structural features are described from
the Brede Rende Section: (1) diapir structures, includ-
ing mesoscopic-scale sequential polydiapirs and hy-
drodynamic brecciation, (2) the Brede Rende normal
fault (BRNF), and (3) frost wedges.

Fig. 79. A large ball-and-pillow structure in the upper part of the Lønstrup Klint Formation, truncated by the L/R-unconformity. This
relationship demonstrates that at least part of the loading occurred prior to the thrust-fault emplacement. Photograph: June 1998.

Facing page - upper:
Fig. 80. Normal fault network in the footwall block of the

Brede Rende normal fault developed in the BR04 thrust
sheet. Photograph: June 1998.

Facing page - lower:

Fig. 81. Frost wedges recognised in the Rubjerg Knude
Formation. The one on the right side of the spade ( A ) has

well-developed, 'upwards-fanning' small-scale normal faults,
whereas the one to the left of the spade ( B ) is a 5-10 cm

wide fracture with a sand-fill. Photograph: June 1997.

Diapir structures

The term diapir as used here follows the definition of
Weinberg & Schmeling (1992 p. 425): "Diapir is the
non-genetic geological term applied to ductile intru-
sive structures. Many diapirs may develop due to rise
of gravitationally unstable buoyant fluids through
denser overburden. Such gravitationally unstable con-
figurations consisting of viscous layers are known as
Rayleigh-Taylor instabilities." In the Brede Rende Sec-
tion, the diapir structures can be divided into two types:
(1) small- to medium-scale diapirs that developed into

hydrodynamic breccias in which primary sedimentary

lamination is locally preserved, although distorted and
irregularly folded, and (2) medium- to large-scale dia-
pirs where mobilised mud intrudes overlying strati-
graphic levels or thrust units.

The first type of diapirism corresponds to the se-

quential polydiapirs of Weinberg & Schmeling (1992).
These are initiated as small undulations or even flame
structures, that develop into irregular upright folds
with numerous minor undulations on their flanks (Figs
76, 78). When the viscous mud broke through the
bedding it formed intrusive pipes (Fig. 77), and either
spread out laterally between layers or released water,
forming dish-and-pillar structures in the overlying beds

Fig. 82. The shift in tilts of bedding in

the piggyback basin of the BR08 thrust
sheet is interpreted to reflect the

propagation of ramps. The strike is the
same (110°), but the dip of the lower

sand beds is 40°, corresponding to
deposition during propagation along a

flat, whereas the dip of beds above the
truncation surface is only 28°, corre-

sponding to deposition during ramping.
Photograph: June 1997.

Fig. 83. Back-thrust reverse faults

displacing the sand beds in the Rubjerg
Knude Formation deposited in the

piggyback basin of the BR08 thrust
sheet. These reverse faults are interpre-

ted to have formed during the thrust
propagation of the footwall ramp of

BR06/BR05. Photograph: June 1997.

(Fig. 77). In the Brede Rende Section, this type of dia-

pirism occurs commonly in the upper sand-rich part
of the Lønstrup Klint Formation and in the Rubjerg
Knude Formation. A good example occurs at the tip
of the BR05 thrust sheet, where the thrust fault
(BR04FWF/BR05HWR) is completely obscured by hy-
drodynamic brecciation.

Examples of the second type of diapirism include

the Brede Rende diapir and the Kramrende diapir. Here
the clay-rich units of the lower part of the Lønstrup
Klint Formation became mobilised by over-pressur ed
water (or gas) to form an intrusive grey, homogene-
ous mud. The diapirism in the Brede Rende Section
was formed syntectonically during ramping (Pedersen

1987). The thrusting displaced some of the feeders in
the mushroom-shaped diapirs, and some of the dia-
pirs intruded through the thrust sheets up into the
thrust sheet above. Moreover, the mushroom-shaped
diapirs penetrate the L/R-unconformity at the top of
the diapir (Fig. 73). It may also be noted that some of
the diapir feeders have been tilted by the bending
produced by ramp propagation (Fig. 4; Pedersen 1987).

Brede Rende normal fault

The Brede Rende normal fault (BRHF), in the central
part of the Brede Rende Section, is a planar fault that
strikes 100° and dips 45°S (Fig. 75). The vertical dis-
placement is c. 20 m when measured from the hang-
ing-wall (thrust-fault) flat of the BR06 in the footwall
block of the normal fault to the same flat in the hang-
ing-wall block of the BRNF. A network of smaller nor-
mal faults with minor displacements occurs in the foot-
wall block (Fig. 80) and adds to the monoclinal bend
in the footwall block of the BRNF. In the hanging-
wall block, the BR06 thrust sheet is dragged along the
fault plane and the drag is bounded by a minor splay
fault. Moreover, a weakly developed rollover-anticline
outlined by the BR06 thrust sheet occurs in the hang-
ing-wall block of the BRNF (Fig. 75). Above the north-
er n limb-bend of the rollover-anticline, a minor de-
pression ( c. 5 m deep) was formed. In this depres-
sion, a series of minor imbricate sandy mud slumps
formed, which may be viewed as syn- to epitectonic
deposits at the top of the Rubjerg Knude Formation
in BR06 related to faulting of the BRNF.

Frost wedges

Frost wedges or fossil ice wedges are recognised in
the Rubjerg Knude Formation, as preserved in the
upper part of the BR04 thrust sheet. The cliff section
here became exposed after the cross-section (Plate 1)
was drafted and is thus not included. It would have
been situated near point 3975 m in the cross-section.
The frost-wedge fractures are 5-10 cm wide and are
filled with structureless sand. Along the sides of the
fractures, the bedding in the sand is bent down to-
wards the fracture due to minor displacements along
small fanning normal faults; the vertical range of the
frost wedges is about 1-3 m (Fig. 81).

The presence of frost wedges in the Rubjerg Knu-

de Formation clearly indicates that the sand was
ground frozen, and thus also elevated above water
level in the glaciofluvial and glaciolacustrine environ-
ment that prevailed during the deposition of the for-
mation. The ground-frozen condition of the sand may
be the reason for the excellent preservation of the
normal fault network related to the BRNF.

Interpretation of structural development

The first thrust sheets to move were probably BR03
and BR06, which ramped up to the upper footwall flat
and moved southwards over a thin cover of the Ru-
bjerg Knude Formation. In the balanced cross-section,
the presence of the long, thin BR03 thrust sheet, and
especially BR06, requires that there has to be under-
lying lower and intermediate duplex sheets. The bal-
anced cross-section model favours a continuation in
the subsurface of several segments of the lower thrust
duplex. The BR03 thrust sheet is viewed as a coher-
ent thrust sheet, which from the ramp of the minor
BR02 thrust sheet, continues along the lower décolle-
ment surface at the 30 m level. The lower trailing-end
duplex segment extends northwards to the thrust fault
separating the Brede Rende and the Sandrende Sec-
tions (SR01HWR/BR08FWR). This trailing segment of
the BR03 thrust sheet is estimated to be about 300 m
long, and the remaining five thrust sheets in the Brede
Rende Section have all been ramped up onto this seg-
ment along which the allochthonous transport and
piggyback displacement took place.

The simplest model for understanding the frame-

work of the duplexes is to accept segmentation of the
trailing end of the BR05 thrust sheet. It is necessary
that BR06 was thrust over BR05 before the trailing

end of BR05 was thrust up over the footwall ramp of
BR04. The existence of the inter mediate BR04 hang-
ing-wall ramp indicates that BR04 had to ramp up two
footwall ramps in different positions of the trailing
end of BR03. Thus the model indicates that a lower
hanging-wall ramp of BR04 was emplaced along the
intermediate footwall flat of BR03. According to the
construction of the balanced cross-section, this also
necessitates a lower duplex segment to be thrust up
in front of the lower hanging-wall ramp and flat of
BR04. These differential thrust displacements provide
an explanation for the development of the BRNF. The
displacement along the BRNF is consequently consid-
er ed to be due to two factors. The first 10 m offset
was caused by normal faulting in front of BR05, where
a foreland-dipping bend of the BR06 hanging-wall flat
was created over the nose of the BR05 thrust sheet.
The next 10 m displacement was caused by a for e-
land-dipping limb of the tip of a duplex segment situ-
ated beneath the BR04 thrust sheet causing the BR04
hanging-wall flat to act as a normal fault.

At the north end of the section, the BR07 thrust sheet,

which only has 3-4 m of the Rubjerg Knude Forma-
tion at the top, was overthrust by the BR08 thrust sheet
at an early stage. The thickness of about 10 m of Ru-
bjerg Knude Formation on top of BR08 indicates that
after the two thrust sheets were thrust-separated, depo-
sition of Rubjerg Knude Formation continued in the
piggyback basin of BR08. This sedimentation proba-
bly took place while BR08 in a piggyback position on
BR07 ramped over a lower footwall ramp of BR03 and
propagated along an intermediate flat, passing over
the footwall ramp of BR05/BR06, before the tempo-
rary cessation of thrusting. In the BR08 piggyback ba-
sin, the propagation of ramps is reflected in the change
in tilt of the bedding (Fig. 82). Moreover, a number of
minor back-thrusts have been recognised in these beds
(Fig. 83), and are consider ed to have been related to
the ramp propagation.

In the dynamic development of the Brede Rende

Section, both the frontal southern and the northern
parts were involved in diapirism. In both parts, it is

Fig. 84. The Sandrende diapir developed in the SR02 thrust sheet. The arrow indicates the direction of reverse faulting, which marks

the prominent back thrust. Along the steep northern flank, the hanging-wall ramp of SR03 ( SR03HWR ) was bent. The bend of the
L/R-unconformity formed due to the fold-bend-folding of SR02 at the lower footwall ramp hinge.

evident that the diapirism was active after the em-
placement of the thrust sheets, since the hanging-wall
flats are penetrated by diapirs rising from a mobilised
underlying thrust sheet. However, it is also evident
that the diapirism ceased before the maximum com-
pression of thrust sheets had occurred. The termina-
tion of thrust compression was reached when the
maximum inclination of the flats occurred. This coin-
cided with the conclusive accumulated ramping of
piggyback thrust sheets. Thus, the inclined position
of the feeders to the mushroom-shaped diapirs indi-
cates a synthrust intrusive emplacement. It is there-
fore concluded that the diapirism was activated by
ramp propagation and that some of the diapirs can be
regarded as extr eme developments of hanging-wall
anticlines created during soft sedimentary deforma-
tion (Fig. 74).

Sandrende Section

The Sandrende Section is one of the most studied parts
of the Lønstrup Klint cliff section (Fig. 5; Houmark-
Nielsen et al. 1996; Sadolin et al. 1997). Even so, the
development of this section is not fully understood,
and some new and revised details are added her e.
The main feature of the section is a broad basin con-
taining a thick succession of the Rubjerg Knude For-
mation deposited in a piggyback basin. To the south,
a diapir distorts this basin, and to the north the basin
is over-thrust by a thrust sheet of the Stenstue Rende
Section. The central part of the section preserves a
remarkable development of normal faults. These were
formerly regarded to have formed in response to the
volume adjustments in the Sandrende diapir (Sadolin
et al. 1997), but are now interpreted as elements of a
thrust-fault propagation model with differential du-
plex segments ramping in the subsurface.

Tectonic architecture

The Sandrende Section comprises four thrust sheets
(SR01-SR04). The southern boundary of the section is
the trailing-edge ramp of BR07 and BR08 in the Brede
Rende Section, and the northern boundary is the rather
steep (> 60°) trailing-edge ramp of SR04. The bound-
ary with the Stenstue Rende Section to the north is a
combination of this trailing-edge ramp and the hang-
ing-wall flat of the frontal southernmost thrust sheet in

the Stenstue Rende Section (see below).

The transition between the Brede Rende Section

and the Sandrende Section in the subsurface is not
clear due to uncertain r elationships between BR07-
BR08 and SR01. The description below is based on
the preferred interpretation, which traces the trailing-
edge ramp of BR08 in the Brede Rende Section down
to the décollement surface 30 m below the reference
surface. This implies that the lower most trailing ends
of BR07 and BR03 remain as low-lying segments that
SR01 had to ramp over. An extra segment and some
smaller adjustment splints of the SR01 thrust sheet wer e
also left in the subsurface. This is reflected in some of
the structural features exposed in the section between
SR01 and SR02.

At the tip of the SR01 thrust sheet, the Lønstrup

Klint Formation forms a thin wedge, which indicates
that the initial hanging-wall ramp (SR01HWR) only
had a dip of about 10°. However, after ramping was
concluded, the thrust fault was steepened to the
pr esent dip of 40°N; the measured orientation of the
ramp is 108°/40°N. The displacement of SR01HWR
along the upper footwall ramp and flat of BR08 is c.
53 m. The frontal part of SR01 has a bend, and it only
dips about 25°N due to the change in thrust-fault in-
clination passing the upper footwall ramp hinge and
the subsequent introduction of a small satellite thrust
fault displacing the lower part of SR01 up over the tip-
wedge. The consequence of thrusting the thin c. 50 m
long frontal part of the thrust sheet is that in the bal-
anced cross-section, a lower duplex segment (SR01u)
must be accounted for, and that SR01u at an advanced
stage of SR01 thrust propagation was picked up in the
thrust translation (see below).

The SR02 thrust sheet was formerly interpreted as a

large-scale diapir (Sadolin et al. 1997; Fig. 84). In the
present structural analysis, SR02 is treated as one large
thrust sheet in which the mobilised mud underwent
mud diapirism at a relatively late stage. This assump-
tion permits an appr oximation of balancing the thrust
sheets, accepting that the thrust faulting is evidently
the most important part of the dynamic development.
The argument for this is based on the fact that SR02
over-thrust the back of SR01 with a displacement of
about 100 m. This 100 m of displacement has to be
compensated for by the same amount of displacement
along the lower décollement sur face, which can be
calculated to have taken place at a stratigraphic depth
of 30 m below the L/R-unconformity. The thrusting of
SR02 resulted in a considerable amount of elevation
during propagation along footwall ramps (SR01FWR
and BR03FWR), since the L/R reference surface is sit-

100

uated about 35-40 m above sea level in the cliff sec-
tion. Thus the ramping and displacement along the
upper flat took place before the final emplacement of
the lower duplex segment of SR01, indicated by the
normal fault displacement of both SR01 and the front-
al part of SR02.

As noted in the Kramrende Section description,

steep ramping creates back-thrusting at the hinge of
the hinterland-dipping limb. Thus the peculiar mush-
room-shaped structure with a wing pointing to the
north is consider ed to be the effect of reverse faulting
due to back-thrusting (Fig. 84). The reverse fault fea-
ture may have been accentuated by re-orientated in-
ternal detachment folding and irregular diapirism in
the Sandrende diapir. Furthermore, it should be noted

that the L/R-unconformity surface has a steep dip on
the northern flank of the Sandrende diapir. Near the
beach level, the L/R-unconformity bends into a gen-
tle dip indicating that in the trailing end of SR02, the
lower hanging-wall flat r ests on the lower footwall
flat coinciding with the décollement level at 30 m.

The SR03 thrust sheet is relatively small with a dis-

placement of about 75 m. The tip of the thrust sheet is
bent upwards into a nearly vertical position due to
drag along the almost vertical northern flank of the
Sandrende diapir (SR02). Thus the SR03 thrusting was
rather early, but as the Rubjerg Knude Formation is
about 10 m thick in SR02 there was a significant time
span before SR03 was thrust up on the back of SR02.

SR03 was displaced up along the upper footwall

ramp, which is exposed in the cliff section. SR03 was
also displaced along an intermediate flat situated at
the 20 m level, indicated by the thickness of the thrust
wedge. During thrust propagation, the trailing end of
SR03 was cut off and left as an isolated duplex seg-
ment, while the frontal part of SR03 was displaced
along the intermediate flat (see Plate 2).

SR03 was over-thrust by SR04 with a relatively short

time gap, as indicated by the thin (3 m) succession of
Rubjerg Knude Formation on top of SR03. The thrust
displacement of SR04 over SR03 is about 60 m, and

Fig. 85. Conjugate normal faults developed in the Lønstrup Klint Formation in the SR04 thrust sheet. An offset of about 1 m can be
recognised by correlating turbidite sand beds in the footwall block to the same beds in the hanging-wall block. The normal fault

framework is interpreted to be due to lateral extension in the SR04 thrust sheet during its propagation over the upper footwall hinge
of an underlying duplex. Photograph: May 1995; measuring staff divisions (centre) are 20 cm.

101

the accumulated displacement of the trailing end of
SR04 relative to SR02 is in the order of 135 m.

The frontal part of SR04 consists of a relatively thin

wedge of the upper part of the Lønstrup Klint Forma-
tion overlain by an up to 28 m thick succession of the
Rubjerg Knude Formation. In the central and r ear parts
of SR04, the thickness of the Lønstrup Klint Forma-
tion increases to more than 20 m, indicating the exist-
ence of a hanging-wall ramp which can be traced down
to the décollement zone, 30 m below the L/R refer-
ence surface. The central part of SR04 forms a broad
hanging-wall anticline, where a number of extension-
al normal faults cross-cut the Lønstrup Klint Forma-
tion (Fig. 85). The southernmost normal fault in this
system is considered to reflect the foreland-dipping
features formed due to displacement of the hanging-
wall anticline along the intermediate flat. Finally, it
should be noted that the piggyback basin (Rubjerg
Knude Formation) of SR04 is divided into two sub-
basins, one in the southern frontal part and one in
the northern trailing part of the thrust sheet. The area
between the sub-basins lacks the Rubjerg Knude For-
mation because it corresponds to the crest of the hang-
ing-wall anticline.

Sedimentary units

The type sections of the Lønstrup Klint and Rubjerg
Knude Formations, as defined in this bulletin and pre-
viously described by Sadolin et al. (1997), are situat-
ed at Sandrende. As defined above, this succession is
divided here into the Lønstrup Klint Formation and
the overlying Rubjerg Knude Formation, which are
separated by the L/R-unconformity (Fig. 19). The Ru-
bjerg Knude Formation is covered by an up to 1 m
thick homogeneous sandy till, which is referred to the

Kattegat Till Formation (Fig. 30).

Lønstrup Klint Formation

In the Sandrende Section, the lower exposed part of
the Lønstrup Klint Formation is composed of lamina-
ted clayey to sandy mud, intercalated with a few thin
sandy turbidites that grade up into finely laminated
clay-rich mud. In the upper part of the formation, thick-
er turbidite sand beds with climbing ripples give the
formation a banded light/dark coloured appearance
(Figs 19, 85). Only very few load structures and hydro-
dynamic breccias have been noted in the Sandrende

Section, except in the lower part of the SR04 sheet
where ball-and-pillow structures and small-scale poly-
diapirism have been observed (Fig. 86). The ball-and-
pillow features are about 20 cm in thickness, which is
probably the thickness of the original beds; they ar e
typically elongated about 50-75 cm parallel to the strike
of the bedding, suggesting they were formed during
the thrust deformation.

Rubjerg Knude Formation

The Rubjerg Knude Formation comprises three units:
(1) a lower unit c. 5 m thick consisting of trough cross-
bedded sand and gravel, (2) a middle unit dominated
by climbing ripple cross-laminated sand, and (3) an
upper unit comprising alternating beds of small-scale
ripple cross-laminated sand and trough cross-bedded
sand (Fig. 19). The units reflect the change from fluvial

to lacustrine and back to fluvial depositional environ-
ments (Sadolin et al. 1997). The Rubjerg Knude For-
mation has an onlapping relationship in the frontal
part of the SR04 thrust sheet, which reflects initial thrust
faulting during sedimentation (Sadolin et al. 1997). In
the central part of the SR04 thrust sheet, growth-fault
sedimentation along normal faults is recorded in the
lower part of the Rubjerg Knude Formation. The
growth faults coincide with the foreland-dipping limb
of the hanging-wall anticline of SR04 (Fig. 87). This
syntectonic sedimentation supports the piggyback
basin concept for deposition of the Rubjerg Knude
For mation. Moreover, a slumped block 0.5 × 2 m in
size occurs along one of the normal faults indicating
that the tip of the satellite thrust in SR04 was exposed
to erosion and slumped into the basin. Similar slumped
blocks were observed on the northern flank of the
Sandrende diapir indicating that the diapir rose above
the depositional sur face during emplacement and that
fragments of the Lønstrup Klint Formation slumped
into the piggyback basin. The synsedimentary rise of
the vertical diapir wall was also reflected in sedimen-
tation of small point-bar wedges along the vertical
flank of the Sandrende diapir.

Towards the top of the Rubjerg Knude Formation,

broad trough cross-bedding is observed. Minor thrust
faults splaying out from the tip of SS01 displace the
cross-bedded sand, and the base of some of the
troughs dramatically truncate the thrust faults, in a
similar fashion to that observed in the BR04 piggy-
back basin of Brede Rende (see above). At the top of
the Rubjerg Knude Formation, sand was deposited in a

102

Fig. 86. Mobilisation and small-scale polydiapiric features developed in the upper part of the Lønstrup Klint Formation in the
Sandrende Section (trailing end of SR04). The polydiapirs started along a bed of clayey mud as small flames (with small wave-

length), which were subsequently folded around the taller diapirs. The sandy beds above and below constitute planar laminated
and climbing ripple cross-laminated fine-grained sand with organic debris and mud draping the ripples. Locally in this sand,

hydrodynamic mobilisation has created zones of mud-free structureless sand and the accumulation of mud forming dendritic
structures. The dynamic development of the structure is illustrated in Fig. 88.

Fig. 87. Extensional normal faults with
related growth-fault sedimentation of

sand and gravel in the lower part of the
Rubjerg Knude Formation. The growth

faults are marked with arrows indicating
the direction of displacement. The top

of the Rubjerg Knude Formation in the
SR04 thrust sheet is over thrusted by the

SS01 thrust sheet. The two sheets are
separated by a thrust fault that acts as

footwall flat of SR04 ( SR04FWF ) and
hanging-wall ramp of SS01 ( SS01HWR ).

Photograph: May 1995.

103

depression above the top of the Sandrende diapir. This

depression was probably formed by relaxation collapse

of the diapir during consolidation and dehydration.

Structures and breccias

Structural investigations in the Sandrende Section fo-
cused mainly on the normal faults and their relationship

to the thrusting, diapirism in the Sandrende diapir, small-

scale incipient polydiapirism, and the record of a deep
frost wedge cutting the Rubjerg Knude Formation.

Normal faults

The Sandrende Section is an important locality for the
investigation of normal faults formed on the foreland-
dipping limb of hanging-wall anticlines. Thus, one
set of normal faults displaces the frontal parts of SR01
and SR02, and another set displaces the central part
of the SR04 thrust sheet.

In the frontal part of SR01, a hanging-wall anticline

developed due to ramping from the 10 m to the 20 m
flat level. The normal faults here displace the Rubjerg
Knude Formation of SR01 as well as the tip of SR02.
The faults now have a dip of about 45°S, but initially
probably had a much steeper dip (up to 80°) subse-
quently reduced during the final bend of the BR08
footwall flat. In the trailing end of SR01, a steep nor-
mal fault displaced SR01, as well as the over-thrust
SR02, with an offset of 10 m. This probably reflects
the influence of a sub-surface duplex, similar to the
development of the BRNF.

The normal faults in the SR04 thrust sheet can be

Fig. 88. The polydiapiric structures and hydrodynamic

breccias shown in Fig. 86 are interpreted to have developed
in the following five steps. 1 : Initial sedimentation of a clayey

mud bed in a succession of mud and fine-grained sands. 2 :
First-order formation of small flames can be regarded as

micro-diapirs with small wavelength. 3 : Second-order small
diapirs developed with increased wavelength. Small-scale

thrusting and overturned geometry indicates formation during
thrust-fault propagation. 4 : Increased mobilisation creates

small-scale domes with extensional fractures forming in the
crest. 5 : Liquefaction of the heterolithic sediment results in

segregation of the sand and mud components. The mud
accumulates in an irregular diapir from the top of which the

mud-saturated liquid intrudes laterally along the primary
parallel lamination. Some mud and fragments of sand fall to

the base of the diapir under gravity.

104

viewed as two sets of a fault framework. The first set
for med 45-60°S dipping faults with displacements of
1-3 m. The southerly dipping tilt of the L/R-uncon-
for mity is regarded as the foreland-dipping limb of
the hanging-wall anticline formed in SR04 (Fig. 87).
The faults above the foreland-dipping surface devel-
oped as growth faults associated with syntectonic sed-
imentation, as recorded in the lower part of the Ru-
bjer g Knude Formation. During displacement along
the normal faults, a minor satellite thrust cross-cut the
SR04 thrust sheet, and the tip of the satellite thrust
sheet was slump-faulted to form slumped blocks in
the growth-fault setting of the piggyback basin.

The normal fault network at the crest of SR04 is

very impressive (Fig. 85). The strike of the normal
faults is 090° with a dominant dip of 50°S, although a
small number of conjugate faults with a dip of 60-
75°N also occur. In view of the angle of conjugate
faulting, these normal faults could have formed due
to the loading of the SS01 thrust sheet emplaced above
the upper footwall flat of SR04, but could also have
formed due to necessary extensional adjustments dur-
ing propagation over the hinge of the footwall ramp.

Diapir structures

The Sandrende diapir only affected one thrust sheet
(SR02), in contrast to the Brede Rende and Kramrende
diapirs where two or more thrust sheets were involved
in the diapir formation. The most impressive feature
of the Sandrende diapir is the major back-thrust, which
has an offset of about 20 m towards the north. Initial-
ly it was probably an almost vertical reverse fault,
which was re-orientated and accentuated during thrust-
fault propagation. A number of smaller r everse faults
occur along the steep northern wall of the diapir, which
internally is composed of mobilised mud. In the up-
per part of the diapir, distorted bedding-structures iso-
lated as 'xenoliths' in the upper part of the diapir ar e
interpreted as fragments of hanging-wall anticlines.
Judging from the thickness of the diapir feeder, the
diapir formed over a hanging-wall ramp where the
SR02 thrusting ramped from the upper 10 m flat to the
lower 20-30 m flat level.

The formation of diapirs was evidently initiated by

mobilisation on a small scale. An illustrative small-scale

example of diapirism was observed in the northern
part of the SR04 thrust sheet (Fig. 86) where mobilisa-
tion and small-scale polydiapirs developed in the up-
per part of the Lønstrup Klint Formation in the San-

drende Section (trailing end of SR04). The polydiapirs
are related to beds of clayey mud deposited between
the thicker beds of sandy turbidites. Along the boun-
dary of the 25-75 cm high diapirs, small flame struc-
tures occur and the laminated sandy beds above are
irregularly folded. Locally, hydrodynamic mobilisation
created mud-free structureless sand and complex mud
structures developed. An interpretation of the dynamic
development of the structures is given in Fig. 88.

Frost wedge

A 20 m deep fracture cross-cuts the Rubjerg Knude
Formation in the central part of the southern sub-ba-
sin in the SR04 thrust sheet. The fracture is less than
10 cm across, and can be followed as an irr egular trace

downwards into the sand sequence with a number of
minor lateral jumps. This irregular fracture is one of
the few structures that can be interpreted as a frost
wedge. It does not penetrate the overlying SS01 thrust
sheet, indicating that it formed within the Rubjerg
Knude Formation from an exposed surface downwards
into a freshly frozen sand package. It can be inferred
that during the latest phase of thrusting, the SR04 thrust
sheet was elevated to a position such that the top of the

Rubjerg Knude Formation was exposed subaerially.

Interpretation of structural development

A hanging-wall anticline developed c. 40 m from the
tip of SR01 when it passed the footwall ramp and flat
of BR08. This initially created a foreland-dipping tilt
of the SR01 thrust structures, and was also respon-
sible for the formation of the normal faults described
above. However, the frontal part of SR01 has to be
accommodated with a duplex segment in the subsur-
face (SR01u). The trailing end of SR01 is rooted down
to the décollement level, where it corresponds to the
segment adjusting the c. 80 m long frontal part of SR02.

When the hanging-wall ramp of SR02 initiated the

propagation up along the footwall ramp, a hanging-
wall anticline was formed that developed into the
Sandrende diapir with its marked back-thrust. During
the SR02 propagation along the footwall ramp, the
SR01u-duplex was pushed up and created a minor
hanging-wall anticline, along which foreland-dipping
limb a normal fault developed and displaced the SR02
thrust sheet as well as sediments in the piggyback
basin of SR01.

105

The lower 10 m of the Rubjerg Knude Formation was

deposited throughout the Sandrende Section, with the
exception of the northern part of SR03, which had al-

ready been blocked by thrusting of SR04. Displacement

of the lower hanging-wall ramp of SR04 onto the in-

termediate flat of SR03 (and SR02) then took place. Sub-

sequently, the first normal growth faulting was initia-

ted at the margin of the southern part of the piggyback

basin above the foreland-dipping L/R-unconformity.

Propagation of the lower SR04 hanging-wall ramp

separated the piggyback basin into two sub-basins
where deposition of the upper part of the Rubjerg
Knude Formation took place, while the cr est of the
anticline between the sub-basins was probably sub-
jected to erosion. The souther nmost thrust of the Sten-
stue Rende Section (SS01) over-thrust the top surface
of the Rubjerg Knude Formation (SR04FWF) as well
as the eroded surface of the ramp anticline; this pre-
vented deposition in the SR04 piggyback basin.

Ramping of the lower trailing segment of SR03 was

activated in the latest stage of thrusting. The propaga-
tion of this duplex segment (SR03u) for a short dis-
tance up along the footwall ramp contributed to the
flat-topped hanging-wall anticline formed in SR04. This
final duplex emplacement may have been one of the
causes for the formation of the normal fault frame-
work in the hanging-wall anticline of SR04 (Fig. 85).

Stenstue Rende Section

In the Stenstue Rende Section, a r emarkable and dra-
matic episode of megaslumping is recorded. Forma-
tion of a very large southward-verging anticline was
accompanied by chaotic hydrodynamic brecciation
(Fig. 89). Another important element related to this
section is the c. 200 m displacement of the frontal
thrust sheet over the Sandrende Section to the south.

Fig. 89. The large slump fold in the Stenstue Rende Section. The slumping folded the SS05 thrust sheet into an overturned anticline
during displacement down the normal fault escarpment. The escarpment was formed during normal fault displacement of the tip of

SS04 parallel to the foreland-dipping limb of a hanging-wall anticline in SS03 (see Plate 2 and Fig. 90). Photograph: June 1999.

106

The Stenstue Rende Section is named after the gul-

ly situated between the Stenstue Rende Section and
the Sandrende Section leading inland from the beach.
In the northern part of the section is the gully known
as the Søndre Grønne Rende. This is reached by a
path through the pinewood connecting with the main
road between Rubjerg and Lønstrup.

Tectonic architecture

The Stenstue Rende Section comprises six thrust sheets
(SS01-SS06). To the south, the footwall ramp and flat
of SR04 in the Sandrende Section bound the section.
To the north, the boundary is defined by the footwall
ramp of SS06, which coincides with the hanging-wall
flat of the southernmost thrust in the Grønne Rende
Section (GR01).

The most important thrust sheet in the Stenstue

Rende Section is the more than 400 m long SS01 thrust
sheet, the frontal part of which over-thrust the north-
ern part of the Sandrende Section and has a displace-
ment of more than 200 m. The initial ramping of the
SS01 thrust sheet was located at a gently dipping hang-
ing-wall ramp. Subsequent to the ramping, part of the
tip was eroded away during the uplift exposure of the
hanging-wall anticline above the ramp and the final
truncation of the glaciotectonic unconformity. Due to
the increase in thickness of the SS01 thrust sheet, cor-
responding to a change from the 10 m upper flat level
to the 20 m flat level, an inter mediate hanging-wall
ramp developed about 100 m from the frontal tip. This
hanging-wall ramp rests on top of the footwall flat
(SR04FWF) above the prominent normal fault struc-
ture in the Sandrende Section. Only a small remnant
of the northern part of the upper flat structure is pre-
served, and this is not very well exposed due to its
location in the inner part of the Stenstue Rende. The
lower SS01 hanging-wall ramp (SS01HWR, ramping
from the 30 to 20 m flat level) situated in the middle
part of the SS01 thrust sheet is now exposed in a steep-
ly dipping position along the SR04 footwall ramp. The
propagation of SS01HWR was responsible for the bend
of the footwall syncline in the Rubjerg Knude Forma-
tion in SR04, and the subsequent tilting of SS01HWR
resulted in the appearance of a more or less vertical
boundary between the two sections. The vertical orien-
tation is a combination of 45° dip on the footwall
ramp added to 45° dip on the hanging-wall ramp. Note
that in the balanced cross-section, there is a c. 200 m
long lower SS01 duplex segment (SS01u) which needs

to be allowed for. This implies that after ramp pr opa-
gation, the lower hanging-wall flat of SS01 was dis-
placed along the intermediate footwall flat on SS01u.

SS02 is a small thrust sheet, thrust onto the foot-

wall ramp of SS01; this footwall is composed of the
Rubjerg Knude Formation situated in the upper part
of SS01. Note that the frontal part of SS02 has a sur-
prising vertical orientation and is displaced by a more
or less horizontal extensional fault, the cause of which
is discussed below.

The frontal part of the SS03 thrust sheet is shown

in the cross-section as a rather simple, upright thrust
structure (Plate 1). However, the SS03 thrust sheet is
in reality a chaotic load and hydrodynamic breccia
complex. At the base of the cliff section is an upright
anticline, which is regarded as a key structure in the
interpretation of the thrust development (Fig. 90).
Above the anticline, a normal fault dipping 40°S trun-
cates the c. 30 m thick Rubjerg Knude Formation.

The thin frontal part of the SS04 thrust sheet is char-

acterised by chaotic brecciation. The trailing end is c.
10 m thick, dipping 45°N, with the hanging-wall flat
thrust along the footwall flat of SS03. The tip is sepa-
rated from the trailing part of the SS04 thrust sheet by
a 40° dipping normal fault with a displacement of about
50 m. This normal fault formed an escarpment trun-
cating the Rubjerg Knude Formation on top of the
SS03 thrust sheet, upon which deposition of a coarse
clastic breccia took place (Fig. 91).

The normal fault escarpment was finally overrid-

den by the frontal part of the SS05 thrust sheet, which
slump-thrusted down the fault plane and formed a
major overturned slump fold (Fig. 89). The formation
of the megaslump fold took place after the SS05 thrust
sheet was thrust up along the footwall flat of SS04 to
the head of the escarpment from where it gravitation-
ally slid down to the depression on the back of the
SS04 tip. A soft sedimentary tectonic breccia was
formed at the transition between SS04 and SS05, which
was cross-cut by a number of minor steeply south-
ward dipping normal faults reflecting the final set-
tling of the fault-slump structure.

The SS06 thrust sheet is about 30 m thick, its lower

hanging-wall flat resting on the footwall ramp of SS05.
It has a steep dip and has been strongly disturbed by
mobilisation and internal diapirism. This thrust sheet
is included in the Stenstue Rende Section because it
involves the trailing lower duplex segments of SS05
and SS04. From the position of the L/R-unconformity
surface, about 30 m above sea level, it can be inferred
that the SS06 thrust sheet was raised up over the low-

107

er trailing segments during ramping and subsequent
stacking of a subsurface duplex complex.

Sedimentary units

The most interesting sedimentological feature within
the Stenstue Rende Section is the record of syntecton-
ic sedimentation related to normal faulting. This in-
cludes slump deposits as well as a gravel bed devel-
oped on the escarpment surface of the normal fault.
As these sedimentary features are related to deposi-
tion in the piggyback basin, they are described below
as part of the Rubjerg Knude Formation.

The sediments of the lower Lønstrup Klint Forma-

tion have been strongly affected by thrust shearing,
and the upper levels were modified by hydrodynamic
brecciation. The Rubjerg Knude Formation comprises
a confusing mixture of redeposited units together with
the main fluvial-lacustrine sediments related to the
piggyback basins.

Lønstrup Klint Formation

The lower part of the Lønstrup Klint Formation is ex-
posed in the SS06 thrust sheet, where the lower hang-
ing-wall flat is thrust up along the footwall ramp of
SS05. Here bluish grey clay alternates with dark red-
brown clay in a laminated to thin-bedded unit (Fig.

Fig. 90. The crest of the hanging-wall

anticline formed in the SS03 thrust sheet
in the Stenstue Rende Section. Photo-

graph: June 1984; the staff divisions are
20 cm.

Fig. 91. The conglomerate/breccia
formed along the fault escarpment

truncating the SS03 thrust sheet.
Photograph: June 1984; the staff

divisions are 20 cm.

108

92). It is evident from the shear structures that this
unit acted as a décollement zone during thrusting.

The main part of the Lønstrup Klint Formation ex-

posed in this section comprises the upper sand-domi-
nated part of the succession. The breccias in the SS03
and SS04 thrust sheets probably initially formed as
medium- to large-scale ball-and-pillow structures in
sand beds 20-60 cm thick during initial thrusting; the
for mation was subsequently deformed during gravity
slumping.

Rubjerg Knude Formation

Nearly 20 m of fluvial-lacustrine sand were deposited
in the piggyback basin of SS01 and SS03 during the
thrust-fault activity affecting the Stenstue Rende Sec-
tion. However, the most conspicuous unit is the r e-
markable conglomerate/breccia related to the normal
fault. The gravel bed draping the fault escarpment is
10-50 cm thick and includes clasts up to 10 cm in
size. Locally, the clasts occur in a clayey mud matrix,
but the latter has often been removed by recent ero-
sion. It is perhaps surprising that a coarse gravel bed
could have accumulated and been preserved along a
fault escarpment dipping at about 35° (Fig. 91). One
explanation may be that the escarpment was only
exposed for a very short time before the SS04 thrust
sheet was displaced down the fault plane; in this case,
the redeposited gravel rather represents a tectonic
breccia composed of the smeared-out lithologies of
the L/R-unconformity and surrounding sediments. The
breccia is thus interpreted as the residue of a brecciat-
ed thrust sheet. The source of the clasts was probably
the L/R-unconformity, and some of the material may
have been derived from the unconformity by succes-
sive erosion during exposure at the head of the fault
escarpment. This probably only occurred for a brief
period before the escarpment was covered by the
slump-slide of the SS05 thrust sheet.

The small piggyback basin on top of the SS05 thrust

sheet is a double syntectonic basin which was partly
carried on the back of a thrust sheet as well as acting
as a depression in the hanging wall of a normal fault.
A 9 m thick succession represents the fill of this basin.
The lowermost 3 m consist of large-scale cross-bedded

medium-grained sand, rich in clay and silty mud clasts.
Towards the upper part of this unit, clay drapes on
the cross-bed foresets become more common and the
beds are affected by small-scale slumping. The over -
lying 5 m thick unit comprises sand beds 30-50 cm

thick, with mud intercalations 5-20 cm in thickness.
Clay clasts are common and the sand shows small-
scale ripples. The uppermost 1 m thick bed consists
of mainly horizontal laminated sand and mud.

This piggyback basin succession is interpreted to

record a fluvial depositional environment that with
time developed into a small shallow lake. A number of

small south-dipping normal faults intersect the Rubjerg

Knude Formation up to the base of the thinly bedded
muds and sands, indicating that the lake first became
established when the fault activity ceased.

Structures

Four types of structures in the Stenstue Rende Section
deserve particular mention: (1) mesoscopic thrust-fault
structures above the lower hanging-wall flat, (2) hang-
ing-wall anticlines, notably the one in the central part
of the section, (3) normal faults, the most important be-

ing the major escarpment-producing fault, and (4) slump

folding related to the escarpment of the same fault.

Thrust-fault structures

Thrust faulting related to the décollement zone in the
Stenstue Rende Section has been observed in the lower
hanging-wall flat of the SS06 thrust sheet. Here the
décollement zone is located in the 30 m flat level,
which corresponds to the base of the 30 m thick Løn-
strup Klint Formation where lithologies are mud-dom-
inated, comparing dark blue-green-greyish, clayey or
silty mud with a few light grey coloured, fine-grained
sand laminae. Two types of structures are distinguish-
ed: imbricate duplexes and listric imbricate fans (Figs
92, 93). The duplex imbricates appear within a 1 m
thick unit bounded by thrust-shear surfaces below and
above (Fig. 92). The mesoscopic-scale duplex com-
plex consists of sheets about 0.5 m thick and 1-3 m
long. Some of the duplexes are folded into antiformal
stacks and form lensoid networks. The basal and roof-
ing thrust faults occur as 20 cm thick shear bands pen-
etrated by flat anastomosing jointing (Fig. 92). The
listric fans are outlined by 1-2 cm thick sedimentary
layers or tectonically induced sand streaks (Fig. 93).
They rise from a narrow thrust plane, recognisable as
a joint surface draped by a 1 mm thick film of black
mud, and extend upwards into the muddy lithology
where they seem to disappear before being over-thrust

109

by the next thrust joint surface about 1 m above the
basal thrust surface.

Hanging-wall anticlines

Three hanging-wall anticlines have been recognised;
the anticline in the frontal part of SS01 has been com-
mented on above. The second example is not very
obvious, but was developed above the intermediate
hanging-wall ramp of SS01. The structures related to
it were later modified by re-orientation due to the
bend of SS01 up along the SR04 footwall ramp. The

third hanging-wall anticline is the key structure in the
Stenstue Rende Section and is situated in the middle
part of the SS03 thrust sheet. The SS03 hanging-wall
anticline (Fig. 90) was folded due to the ramping in
the middle of the lower trailing duplex segment (SS01u).

This ramping took place at a mature stage of thrust-
ing, and SS01u was separated into two segments. The
anticline is upright and tight, and the onlapping sed-
imentation of the Rubjerg Knude Formation on the
northern flank indicates that the SS03 thrust sheet had
commenced transport along a footwall ramp and flat
prior to the anticlinal folding.

Fig. 92. Along the lower hanging-wall

flat of the SS06 thrust sheet, an imbri-
cate duplex complex has been recogni-

sed; bounding thrusts indicated by shear
arrows . The thrust-fault imbrication

formed in the lower most part of the
Lønstrup Klint Formation during

displacement along the décollement
surface. The trowel is c. 30 cm long.

Photograph: June 1997.

Fig. 93. An imbricate fan formed in the

lower part of the Lønstrup Klint Forma-
tion in the SS06 thrust sheet. The trowel

is c. 30 cm long. Photograph: June 1997.

110

Normal faults

Two normal faults are discussed: (1) the extensional
fault with horizontal fault plane that displaces the tip
of SS02, and (2) the major normal fault displacing the
SS04 thrust sheet.

The extensional fault affecting SS02 was for med

north of the hanging-wall anticline developed over
the intermediate hanging-wall ramp of SS01. It is inter-
preted to have formed initially as a normal fault dipping

c. 45°N on the foreland-dipping limb of the SS01 hang-
ing-wall anticline. Subsequent to displacement on the
normal fault, the SS02 thrust sheet and the fault wer e
tilted into vertical and horizontal positions, respectively,

during the fault-bend folding resulting from the SS01
propagation up along the footwall ramp. The major
normal fault displacing SS04 is also regarded as a fault
that developed on the foreland-dipping limb, here
related to the anticline in SS03. It is observed that the
L/R-unconformity dips beneath the beach level, indi-
cating that the reference surface is not elevated and
consequently that the underlying SS03 hanging-wall
flat rests on a footwall flat; the normal fault is thus
preserved with its initial orientation. The formation of
the normal fault is similar to the formation of the BRNF
in the Brede Rende Section (see above).

Slump folding

The large-scale slump fold formed by the SS05 thrust
sheet as it was displaced down the foreland-dipping
fault escarpment can be compared to the same type
of deformation described from the Martørv Bakker Sec-

tion. However, in the Stenstue Rende Section, the Løn-

strup Klint Formation is still preserved as a coherent

sheet, deformed into a major southerly overturned fold
with an amplitude of about 15 m and an irregular fold
axis orientated SE-NW ( c. 150°) (Fig. 89). During slump-

ing along the escarpment, the redeposited units were
strongly affected by hydrodynamic brecciation result-
ing in the chaotic disorganised natur e of the sediments.

Interpretation of structural development

The important question in the development of the
Stenstue Rende Section is the time of formation of the
ramp bend anticline during thrust-fault propagation.
The interpretation given here is based on the descrip-
tion above, and the balanced cross-section and mod-

el for ramping in the subsurface given in the ramp
cross-section (Plate 2B).

Firstly, it should be remembered that there is evi-

dence of a long translation along the décollement zone,
primarily indicated by the considerable distance of
SS01 transport over the upper footwall flat in the Sand-
rende Section (SR04). Secondly, the displacement of
the frontal part of SS01 must be balanced with a low-
er duplex segment (SS01u) in the subsurface. More-
over, the displacement of SS01 also affected the SS02
thrust sheet by superimposed structural development.
The superimposed model here advocated is support-
ed by the following interpretation. As the initial angle
of thrust faulting rarely exceeds 30° (Jaeger & Cook
1979), superimposed rotation must have affected the
SS02 thrust. The angle between the SS02 hanging-wall
ramp and the L/R-unconformity surface is about 30°
indicating a normal type of thrusting when the Ru-
bjerg Knude Formation was horizontal. Considering
the thrust in this pre-rotated position, it is easy to
envisage that the extensional fault offsetting the tip
of SS02 as a normal fault formed over the lower hang-
ing-wall ramp of SS01. To restore the thrust sheet into
an upright position, two phases of rotation are neces-
sary. The first one would be the SS01 ramping on the
footwall ramp of SR04, and the second would be the
re-orientation of the ramp due to the fault-bend pro-
vided by the thrusting of a subsurface segment of SR03
up along its footwall ramp in the Sandrende Section.

The initial ramping of the leading edge of SS01 prob-

ably took place during sedimentation in the lower
part of the piggyback basin of SR04. Thrust propaga-
tion of SS02 must have been initiated at the same time,
indicating that the SS03 thrust sheet in the trailing end
of SS02 also participated in the translation along the
10 m flat level (SS01 intermediate footwall flat). Dur-
ing the translation of the lower footwall ramp in the
trailing end of SS01, the 200 m long lower SS01u seg-
ment must also have been thrust, which is interpreted
to have caused the ramping in the central part of SS01u.
Above this ramp, a lower hanging-wall anticline de-
veloped, which also folded the overlying SS03 thrust
sheet into the exposed anticline in the middle part of
SS03, resulting in the foreland-dipping footwall flat of
SS03 and the initiation of normal faulting. Part of the
SS04 thrust sheet had by then already pr opagated over
the SS03 footwall flat, and was therefore subsequent-
ly displaced by the normal fault with a drag down the
fault plane. The displacement on the SS01u footwall
ramp must have been relatively small to create and
preserve an upright, close to tight anticline. If the dis-

111

placement had continued, it is likely that a more flat-
topped anticline would have developed and minor
normal fault imbricates would have been the result,
rather than the marked fault escarpment that actually
formed on the southern flank of the anticline.

The slump-thrusting of SS05 down into the depres-

sion on the hanging-wall block of the normal fault is
interpreted to have taken place shortly after the SS04
was down-faulted. Propagation of the SS05 thrust sheet
was combined with the push on its footwall ramp by
thrusting of the SS06 sheet. During this final thrusting
in the Stenstue Rende Section, the trailing lower seg-
ments were stacked into a duplex, probably analo-
gous to the mesoscopic-scale duplex structure exposed
along the hanging-wall flat of SS06 (Fig. 92).

Grønne Rende Section

In the geological cross-section of Lønstrup Klint pre-
sented by Jessen (1931), two gullies were indicated
south of the Rubjerg Knude Fyr (the lighthouse), name-
ly Søndre and Nørre Grønne Rende. By the year 2000,
the cliff profile had no obvious gullies that these names

can be attached to, although Søndre Grønne Rende
must have been close to the gully so annotated in the
northern part of the Stenstue Rende Section. The name
Grønne Rende Section is therefore adopted here to
cover the section between Stenstue Rende and Ru-
bjerg Knude Fyr.

The section comprises twelve nearly vertically ori-

entated thrust sheets, which can be characterised as a
listric imbricate fan. Only the frontal parts of the thrust
sheets are ramped up into steeply dipping positions,
and in these parts of the thrust sheets the Lønstrup
Klint Formation is thin, whereas the Rubjerg Knude
Formation is relatively thick. The general impression
of the section is of thin mud sheets alternating with
thick units of sand (Fig. 94).

The points of interest in this section are the means

of formation of an imbricate fan of uniform thrust
sheets, and the mechanism by which the sheets
reached their vertical orientation. Also of interest is
the arrangement of the now concealed duplex seg-
ments in the subsurface, where balancing of the thrust
sheets indicates shortening of about 60%.

Fig. 94. View along the Grønne Rende Section to the north where the Lønstrup Klint Formation forms thin mud sheets interleaved
with thick sand sheets referred to the Rubjerg Knude Formation. In the far distance, Stortorn forms the vertical cliff facing the sea.

Height of cliff is c. 50 m. Photograph: August 1984.

112

Tectonic architecture

The Grønne Rende Section comprises a leading-edge
thrust sheet (GR01), which consists of a 30 m thick
section of the Lønstrup Klint Formation, succeeded
above the L/R-unconformity by about 15 m of the
Rubjerg Knude Formation. North of GR01, a further
twelve thrust sheets (annotated GR02-GR13) are ex-
posed, each composed of an average thickness of c.
10 m of the Lønstrup Klint Formation overlain by about
25 m of the Rubjerg Knude Formation. To the south,
the section is bounded by the thrust fault that sepa-
rates the lower hanging-wall flat of the Grønne Rende
frontal thrust sheet (GR01) from the footwall ramp-
and-flat of the northernmost thrust sheet (SS06) in the
Stenstue Rende Section. To the north, the boundary
of the Grønne Rende Section is defined by the thrust
fault that acts both as the hanging-wall ramp of RF01,
the frontal thrust sheet in the Rubjerg Fyr Section, and
as the footwall ramp-and-flat of GR13.

In the description of the thrust sheets, it is assumed

that the thrust sheets initially involved only the Løn-
strup Klint Formation, and that the Rubjerg Knude
Formation was deposited syntectonically and separa-
ted into small piggyback basins between the sheets.
As the imbricate thrust sheets constitute the most im-
portant structural element in this section, each thrust
sheet is described separately in the structural account
below.

Sedimentary units

In the Grønne Rende Section, the Lønstrup Klint For -
mation is mainly represented by the upper levels of
the formation. The only exception is the southern-
most thrust sheet GR01, in which lower stratigraphic
levels of the formation are also exposed. In this sec-
tion, intra-Rubjerg Knude Formation erosional surfac-
es locally incise the unconformity defining the Løn-
strup Klint Formation - Rubjerg Knude Formation
boundary. This unconformity is thus composite in plac-
es but the term L/R-unconformity is retained as it clearly
still forms the boundary between these two forma-
tions. During hanging-wall ramping of the thrust sheet
tips, the gravel beds on the unconformity were partly
removed from the unconformity surface, and desicca-
tion cracks may be present (only observed in the up-
per most tips of the thrust sheets) indicating that some
of the tips were exposed above water level. The Ru-
bjer g Knude Formation mainly comprises the same

three units described in the Sandrende Section. How-
ever, a number of variations in sedimentary architec-
ture occur due to syntectonic sedimentation.

Lønstrup Klint Formation

The lower part of the formation exposed along the
hanging-wall flat of GR01 consists of dark grey lami-
nated mud with a few c. 0.5 m thick white sand turbi-
dites; these have been strongly disturbed by thrust-
ing, contortion and mud-mobilisation. The upper part
of the formation is dominated by light-colour ed sandy
turbidites up to 1 m thick, interbedded with 10 cm
layers of blue-grey clayey mud.

Rubjerg Knude Formation

It has already been noted that the Rubjerg Knude For-
mation was deposited in a number of small piggy-
back sub-basins. In the description of the piggyback
basin architecture, four depositional elements are dif-
ferentiated.

1. Flat-parallel bedding (F-bedding): initially horizon-

tal stratification of a bed deposited on a surface
parallel to a flat as well as to the mean level of the
L/R-unconformity.

2. Ramp onlap (R-onlap): horizontal stratification or

large-scale cross-bedding in a bed deposited on
an inclined unconformity surface that had been
tilted due to ramping prior to sedimentation.

3. Foreland-dipping onlap (D-onlap): initially hori-

zontal stratification in a bed deposited on an in-
clined unconformity surface dipping towards the
foreland due to the repositioning of a hanging-
wall ramp on a footwall flat.

4. Climbing ripple stratification (C-bedding): climb-

ing ripple cross-lamination in beds 20-80 cm thick,
commonly limited by F-bedding below and above
(Figs 24, 95).

The Rubjerg Knude Formation is interpreted as a gla-
ciolacustrine deposit. Sediment influx was probably
relatively constant, and the sedimentary structures de-

veloped in the individual thrust sheets were governed
by local conditions. During thrusting, the sedimenta-
ry base level changed, and the accommodation space
varied depending on the size of the piggyback basins.

Thus the flow regime fluctuated and a variety of sed-

113

imentary structures formed, which are interpreted to
reflect the thrust-fault development.

The syntectonic banana-shaped basin described by

Pedersen (1987; Fig. 4) was based on observations in
the upper part of these piggyback sub-basins. These
structures might also be characterised as footwall syn-
clines that developed as growth-fault synclines, where
deposition took place as the hanging-wall block was
thrusted up along the footwall ramp dragging the
underlying limb up along the thrust fault during the
displacement.

Structures

A systematic description of each thrust sheet in the
section is provided below, together with some refer-
ences to the syntectonic sedimentation. In general,
the thrust sheets constitute an upright hanging-wall
ramp, which initially had a dip of less than 20°. Hydro-
dynamic brecciation and mud mobilisation occurred
along the hanging-wall ramps and flats. Along the
upper footwall ramp, footwall synclines with compres-
sive deformation of climbing ripple cross-laminated
sands are very common, mainly developed as growth-
fault synclines as mentioned above. All the thrust
sheets from GR02 to GR13 can be demonstrated to
have been carried piggyback on the GR01 thrust sheet.

GR01 thrust sheet

The accumulated displacement of GR01 is estimated
to about 140 m. This includes an interpreted displace-
ment, c. 40 m, of the thrust-sheet tip. The thrust-sheet
tip was, at a post-thrust stage, eroded away by the
truncation of the glaciotectonic unconformity; calcu-
lation of the displacement of the tip follows the prin-
ciple illustrated in Fig. 11. The total displacement also
includes the c. 100 m displacement along the exposed
footwall ramp of SS06 and its consequent continua-
tion down to the décollement zone in the 30 m flat
level (stratigraphic level from the L/R-unconformity).
From the base of the cliff and down into the subsur-
face, thrusting took place along the GR01 hanging-
wall flat.

The internal tectonic structure of the Lønstrup Klint

Formation in GR01 is very similar to the thrust struc-
tures described from the SS06 thrust sheet of the Sten-
stue Rende Section (Figs 92, 93) with intraformational
duplex structures, imbrication and strong mobilisa-
tion along the hanging-wall flat. As can be seen from
the cross-section (Plate 2B), the L/R-unconformity is
traceable down to a level c. 5 m below sea level. This
interpretation is supported by field observations, al-
though the base of the cliff is often scree covered,
and implies that the hanging-wall flat can be traced
down to the décollement sur face, and that the thrust
sheet has not been elevated up onto, and translated
along, inter mediate flats in the subsurface. The L/R-
unconformity rests in its initial stratigraphic position,
and the reference level lies below sea level. The accu-

Fig. 95. Large-scale cross-bedding

displaying D-onlap overlain by planar
bedding (D-onlap) and climbing ripple

cross-laminated sand (C-bedding) of the
Rubjerg Knude Formation in the Grønne

Rende Section. Photograph: July 1999;
way-up is to the left. L/R-u , L/R-

unconformity.

114

mulated thickness of the Rubjerg Knude Formation is
c. 15 m, and the sand beds were deposited with an
onlap onto the northerly dipping L/R-unconformity
(R-onlap).

GR02 thrust sheet

The GR02 thrust sheet is the southernmost imbricate
in the imbricate fan of the Grønne Rende Section. It
consists of a 10 m thick section of the Lønstrup Klint
Formation overlain by an about 30 m thick section of
the Rubjerg Knude Formation. The main part of the
thrust dips at 55°N, whereas the upper part is some-
what steeper.

The lower 5-8 m thick unit of the Rubjerg Knude

Formation is characterised by large-scale trough cross-
bedding, and R-onlap can be recognised. F-dipping
bedding, grading up into D-onlap in the uppermost
part of the cliff section overlies this lower unit; this
indicates ramp-flat-foreland dipping relationships
during ramp and flat propagation. Above this, a mid-
dle sand unit with F-bedding was deposited, and fi-
nally the upper unit shows R-onlap, which was sub-
sequently folded in a footwall syncline below the GR03
thrust fault.

GR03 thrust sheet

In the GR03 thrust sheet, the lower part comprising
the Lønstrup Klint Formation is a wedge-shaped struc-

ture aligned along a vertical thrust fault (GR03 hang-
ing-wall ramp). The thickness varies from c. 15 m in
the lower part to c. 3 m in the upper part. Above the
L/R-unconformity, the Rubjerg Knude Formation con-
sists of a more than 30 m thick succession, which
indicates that the piggyback basin of GR03 (as well as
GR02) was a long-lived depocentre. The geometry of
the GR03 hanging-wall ramp implies that it can be
traced down to the 15 m (or 20 m) level. During ramp-
ing, a second stage of erosion affected the L/R-un-
conformity, which thinned out the Lønstrup Klint For-
mation (Fig. 96). The R-onlap in the lower half of the
Rubjerg Knude Formation probably reflects the ramp-
ing on the footwall ramp of GR02, and the middle
part of the Rubjerg Knude Formation was deposited
during the propagation of the hanging-wall ramp over
the footwall flat of GR02. The uppermost 4 m of the
GR03 thrust sheet is very disturbed, probably due to
push from the GR04 upper hanging-wall ramp.

GR04 thrust sheet

In the GR04 thrust sheet, the Lønstrup Klint Forma-
tion is relatively thick, c. 20 m in the lower part of the
cliff section and about 7 m in the top part. The GR04
hanging-wall ramp dips 70-80°N, and in the middle
part of the cliff section a small hanging-wall ramp about
5 m high is preserved. In front of this ramp, the sand
deposited at the top of the GR03 piggyback basin was
pushed forward during thrust faulting along the up-
per footwall flat, as mentioned above.

Fig. 96. The composite development of

the L/R-unconformity ( L/R-u ) resulted
in the reduction of the thickness of the

GR03 thrust sheet to a very thin horizon
interlayered with thick piles of sand

referred to the Rubjerg Knude Forma-
tion in the Grønne Rende Section. The

upper hanging-wall ramp ( GR03HWR )
displays marked relief due to erosion.

Photograph: October 2000.

115

The maximum thickness of the Rubjerg Knude For-

mation in GR04 is similar to the thickness in GR02
and GR03, but the piggyback basin is wedge-shaped
due to the footwall ramp produced by the thrusting
of GR05. The large-scale trough cross-bedded lower
part of the formation tends to show R-onlap towards
the upper part of the L/R-unconformity.

GR05 thrust sheet

GR04 and GR05 initially formed one coherent thrust
sheet, with GR05 being carried piggyback during thrust
propagation of GR04 before they were separated by
the satellite thrusting of GR05 up along the footwall
ramp of GR04. The hanging-wall ramp drops from the
5 to the 10 m flat level along a relatively steep ramp,
which lifted GR05 free of GR04. In the lower part of
the cliff section the L/R unconformity is situated about
5 m above sea level, indicating ramping to an inter-
mediate flat in the subsurface. The GR05 thrust fault

is overturned to the north, indicating that the thrust
plane dips at 75°S (Fig. 97).

The uppermost 10-15 m of sand beds in the GR05

piggyback basin are horizontally orientated. The sand
beds show large-scale trough cross-bedding and sed-
imentation is inferred to have taken place between
the GR04 and GR05 thrust tips when these were ex-
posed above the sediment/water inter face during the
latest stage of dynamic development.

GR06 thrust sheet

The Lønstrup Klint Formation of GR06 is generally a
relatively thick unit (10-15 m) although locally in this
section deep erosion is evident at the L/R-unconform-
ity. This localised deep erosion at the unconformity
was probably due to erosion of a hanging-wall anti-
cline during propagation over the footwall ramp hinge.
This suggestion is supported by the presence of R-on-
lap in the lower to middle part of the cliff. The C-

Fig. 97. The thrust-fault structures related to the GR04 and GR05 thrust sheets. The 'overturned' orientation of the GR05 hanging-
wall ramp ( GR05HWR ) is regarded as the result of repeated footwall ramping of the GR04 thrust sheet ( GR04FWR = footwall ramp

of the GR04 thrust sheet), and subsequent translation of the imbricate fan along the lower décollement surface. Photograph: July 1999.

116

bedding observed in the middle part of the Rubjerg
Knude Formation may well reflect post-ramp deposi-
tion; subsequently, sedimentation briefly took place
during displacement on the upper footwall flat. The

thickness of the Rubjerg Knude Formation is 15 m
where the unconformity is deeply incised, decreasing
to only 10 m laterally. This indicates that the basin
was partly closed by the GR07 thrust propagating along
its hanging-wall flat (back of GR06) in an early phase
of development of the section. The upper most beds
show a high-angle R-onlap to the unconformity in
GR06, demonstrating that the sand was deposited dur-

ing the final phase of upthrusting, and just before the
last c. 30° tilting of the thrust sheet into its present
upright position.

GR07 thrust sheet

The GR07 thrust sheet consists of a 10 m thick unit of
the upper part of the Lønstrup Klint Formation with
medium-bedded light grey fine-grained sand interbed-
ded with thin mud layers. The L/R-unconformity is
parallel with the hanging-wall flat in the main part of
the exposed thrust sheet giving the impression that
the sheet is of uniform thickness. The topmost part of
the sheet is wedge-shaped where the upper hanging-
wall ramp is preserved, and the irregular structures of
the tip can be interpreted as an upper hanging-wall
anticline.

The Rubjerg Knude Formation in GR07 is about 15

m thick and can be divided into three 5 m thick units,
which show the typical characteristics of sedimenta-
tion in the formation. In the uppermost part of the
piggyback basin, high-angle R-onlap, similar to the
bedding in the GR04-GR06 thrust sheets, indicates late
syntectonic deposition between the thrust-sheet tips.

GR08 thrust sheet

The lower part of GR08, comprising the Lønstrup Klint
For mation, forms a wedge-shaped structure, with a
thickness of only 3 m in the top of the cliff section and

about 10 m at the base. The basal part is characterised
by mobilised mud bounded at the thrust sole by a
vertical thrust fault. At the top, a hanging-wall anti-
cline and small diapir deformed the tip.

The Rubjerg Knude Formation of the thrust sheet

comprises three units. The lowermost unit, up to 10 m

thick, shows R-onlap in the lower part which is also

the lower part of the cliff section. Upwards, along the
steeply dipping L/R-unconformity, the dip of the R-
onlap increases. There is an angular discordance be-

tween these beds and the beds occurring above. These
beds show planar parallel bedding (F-bedding). In the
lower part of this F-bedded unit, clasts of mud occur
with sizes from cobbles to boulders (1 m size). These
boulder-sized mud-blocks are interpreted as fragments
of the GR09 thrust tip that were deposited by gravity
slumping in the piggyback basin. The middle unit of
the formation is c. 8 m thick and shows large-scale
cross-bedding with sets up to 3 m thick, and the unit
has an R-onlap relationship to the unit below. The
upper unit is c. 10 m thick and the beds show mainly
planar bedding with some trough cross-bedding towards
the top. The lower and middle units may be interpre-
ted to represent deposition during two phases of ramp-
flat propagation.

GR09 thrust sheet

The Lønstrup Klint Formation of the GR09 thrust sheet
forms a uniform c. 5 m thick unit with a vertical orien-
tation. The Rubjerg Knude Formation is about 25 m
thick and can be divided into a lower and an upper
part. The lower part displays variable large-scale cross-
bedding and the unit has a F-bedding relationship,
whereas the upper part forms one large R-onlap suc-
cession. The lower part may be interpreted as having
been deposited while the GR08 hanging-wall ramp
propagated over a footwall flat, whereas the upper
part was deposited when the GR09 thrust sheet was
displaced up along a 45° dipping ramp during a rela-
tively late phase of deformation. A number of minor
horizontal extensional faults are interpreted as fore-
land-dipping normal faults related to a hanging-wall
anticline formed over a hanging-wall ramp during an
early or intermediate phase of thrusting.

GR10 thrust sheet

The Lønstrup Klint Formation of GR10 is very thin,
only about 3-4 m thick, in the exposed part of the
cliff section. The Rubjerg Knude Formation is about
25 m thick, and the lower part shows a poorly ex-
posed F-bedding relationship. The upper part displays
marked R-onlap with a 45° dipping angular discord-
ance to the L/R-unconformity.

117

GR11 thrust sheet

The GR11 thrust sheet is irregularly orientated, but is
mainly vertical in the upper frontal part. In GR11, the
Lønstrup Klint Formation has a uniform thickness of
10 m, consisting of medium-bedded light coloured sand

interbedded with thin mud layers situated above the
steeply dipping hanging-wall flat. The Rubjerg Knude

Formation is generally not well exposed due to sand
scree, but has a thickness of about 15 m.

GR12 thrust sheet

A large part of the GR12 thrust sheet is covered by
sand scree, and detailed data from this part of the
Grønne Rende Section are limited. The Lønstrup Klint
Formation forms a c. 5 m thick unit of sand domi-
nated by thick-bedded turbidites, as is typical of the
upper part of the formation. The Rubjerg Knude For-
mation is more than 20 m thick and displays the typ-
ical depositional features of the formation. However,
it should be noted that the L/R-unconformity in GR12,
as is the case in GR11, has been lifted up to an eleva-
tion of 15-20 m a.s.l.; this indicates that these sheets
propagated over an upper flat, probably composed of
two stacked duplex segments of GR06 and GR08 in
the subsurface.

GR13 thrust sheet

The GR13 thrust sheet is also mainly covered by sand
scree at the base of cliff. However, exposur es in the
upper part of the cliff reveal a rather complex struc-
ture. The Lønstrup Klint Formation of the thrust sheet
is very thin, and in places only the unconformity is
observed; it can thus be difficult to recognise where
the stratigraphic unconformity is preserved and where
it has been completely replaced by the thrust fault,
which is now vertically orientated. Furthermore, the
Rubjerg Knude Formation has been subjected to su-
perimposed folding. The thickness of the piggyback
basin deposits in GR13 is more than 30 m and four
units of the Rubjerg Knude Formation are differenti-
ated. Unit 1 is about 5-6 m thick, and appears in the
frontal and upper part of the piggyback basin; it is
characterised by large-scale cross-bedding as well as
planar parallel stratification. Towards the trailing end
of the thrust sheet, the R-onlap in unit 1 grades up
into unit 2, which is folded into a set of overturned

folds, originally with a horizontal axial plane, but now
re-orientated into an upright position; the overturned
folds deform the bedding in unit 1. Unit 3 is charac-
terised by steeply dipping large-scale foresets that were
deposited over the recumbent folds. Finally unit 4,
about 7 m thick, is mainly planar-bedded and was
pushed in front of a hanging-wall ramp of the frontal
thrust sheet in the Rubjerg Fyr Section.

Interpretation of structural development

Two types of interpretations are considered prior to
the further description of the structural development:
(1) in order to estimate the displacement, a geometric
construction has been made for each thrust-sheet tip
subsequently eroded away at the glaciotectonic un-
conformity (Fig. 11), and (2) the position of the L/R-
unconformity below the screes has been constructed
from successive approximations (Plate 1). Interpreta-
tion of the extent of the thrust tips was carried out as
a triangular construction with a best-fit of the inter-
section of the unconformity and the thrust plane (see
Fig. 11). Where these surfaces (lines in the 2-D con-
structions in Fig. 11) were obscured, the construction
was guided by the assumption that the acute angle is
close to 18°, which from experience is a general ini-
tial thrust ramp angle. According to this geometrical
reconstruction, the average displacement of each thrust
sheet is about 70 m.

The general impression is that the thrusting of the

twelve imbricate sheets in the Grønne Rende fan-struc-
ture was broadly contemporaneous. If the experience
from the Ulstrup Section near the foreland is taken
into consideration, one would expect a long coher-
ent thrust sheet initially displaced along the upper flat
level at 10 m stratigraphic depth (from the L/R-uncon-
for mity). From this detachment level, the imbricate
thrust-fault fan propagated with fairly equal spacing,
and the thrusting progressed during sedimentation of
the Rubjerg Knude Formation. However, there are two
positions where the piggyback basin has a thinner
depositional fill, namely the basin on GR01 and on
GR06/GR07. Thus, the first longer displacement along
an upper footwall flat took place on the back of GR06
and GR01, subsequently leaving a trailing-end duplex
segment below the 10 m detachment level at the rear
of GR06 as well as at the end of GR01. When about
half of the displacement along the GR06 had taken
place, the level of detachment started to root down to
the 20 m flat level, such that the trailing duplex seg-

118

ment of GR06 was free to move along intermediate
ramps. Thus, if about 20 m of the displacement on
each of the GR07-GR13 thrusts is accumulated, it
amounts to a total displacement of about 140 m for
the GR06 trailing segment (GR06u). It is therefore ar-
gued that the GR06u segment started to ramp in the
middle phase of thrust propagation, which is reflect-
ed in a foreland-dipping tilt in the GR13 basin that
created the recumbent folding.

The sequence in ramping follows three angular

modes: initial ramping along an angle of about 18°,
intermediate ramping along an angle of 30°, and final
ramping at close to 45°. However, ramping will never
be initiated at an angle of 90°, so the problem is how
to explain the vertically orientated thrust faults.

The first c. 20° ramp is given by the upper ramping,

and progressive ramping will result in a 36-45° tilt.
This would result in progressive steepening of the
tilting from south to north, however, which is clearly
not the case. It is suggested, therefore, that the GR01
thrust jumped down to the décollement level at the
30 m stratigraphic depth, and that this caused the re-
orientation during the final displacement of GR01.
Thus, when the imbricate fan with ramp angles up to
40° was carried along with the lower GR01 thrust-
sheet segment (GR01u) towards the 45° inclined frontal
ramp, all the thrust sheets were subsequently tilted
due to a common megascopic shear. The combina-
tion of this large-scale shear tilt and the accumulated
ramp steepening is very well illustrated in the GR05
thrust sheet, which was separated from GR04 along a
satellite thrust fault. The hanging-wall ramp of GR04
was fixed with a c. 75° steep dip. Consequently the
hanging-wall ramp of GR05, which was carried piggy-
back on GR04, ended up in an overturned position
(dip of about 75°S).

In balancing the Grønne Rende Section, one prob-

lem remains to be solved, namely the fate of the trail-
ing-end segment of GR06. However, this is a minor
problem compared to the space problem created by
the GR01 thrusting along the 30 m décollement level.
The trailing-end thrust-sheet segment of GR01u (a
duplex sheet created between the 30 m and the 20 m
flat level) is consider ed below under the structural and
dynamic analysis of the Rubjerg Knude Fyr and Stor-
torn Sections.

Rubjerg Knude Fyr Section

This section is situated below the Rubjerg Knude Fyr,
and makes up the highest part of the cliff (see cover
illustration). The cliff section below the lighthouse
comprises the thickest thrust sheets, which are ramped
up to the highest footwall flat level. This means that
thrust sheets with a décollement level at a depth of
about 35 m are ramped up and thrust along a flat at
the 10 m deep level.

Normal fault structures similar to the Brede Rende

normal fault also appear in the Rubjerg Knude Fyr
Section. The tip of the prominent thrust sheet in the
central part of the section was dropped down into the
piggyback basin in front of the thrust fault, and sub-
sequently buried by sediments of the Rubjerg Knude
Formation. Structural elements related to the hang-
ing-wall ramp are well illustrated in this section.

Tectonic architecture

The Rubjerg Knude Fyr Section comprises six rela-
tively thick thrust sheets annotated RF01-RF06. The
leading-edge thrust and hanging-wall ramp-and-flat
of RF01 terminate all the imbricates in the Grønne
Rende Section. To the north, the section is bounded
by the footwall ramp of RF06 that coincides with the
hanging-wall ramp of the frontal thrust sheet in the
Storntorn Section. The thickness of the thrust sheets
is bounded by the 20 m flat level in the southern part,
and increases in the northern part down to the 30 m
flat. All the thrust sheets in the section are thrust over
the lower duplex segment of GR06 and GR01. Trans-
lation along an intermediate flat is indicated by the
dominant position of the L/R-unconformity at 20 m a.s.l.

The RF01 and RF02 thrust sheets make up an easily

recognisable thrust sheet pair that can also be located
on the geological cross-section constructed by Jessen
(1918; Fig. 98). The similarity of the remaining part of
the Rubjerg Knude Fyr Section to Jessen's cross-sec-
tion is not so obvious, probably due to the interven-
ing 80 years of cliff erosion and the present poor ex-
posure of the section due to extensive sand scree.
The dips of the footwall ramps are about 60°. The
angle between the L/R unconformity and the thrusts
is about 30°, which means that the thrusts have been
rotated about 30° during ramp propagation in the sub-
surface. This is illustrated by the angular relationship
between the L/R unconformity in RF01 and the foot-
wall ramp of RF02. The thrust-fault displacement of
RF01 and RF02 ranges from 50-65 m.

119

At the tip of RF01, a 25 m long upper hanging-wall

flat is preserved. Below this, a 5-7 m thick sheet com-
prising the top of the GR13 piggyback basin occurs.
This upper footwall flat segment of GR13 was dis-
placed an unknown distance (25-50 m) forwards in
front of the upper hanging-wall ramp of RF01.

The Rubjerg Knude Formation in RF02 is poorly

exposed due to sand scree at the base of the cliff, but
it is interpreted to be 20 m thick. From the L/R-uncon-
formity up to the overlying thrust fault, the thickness
of the piggyback basin is about 40 m. However, it is
inferred that a thrust fault situated in the middle part
of the basin is responsible for repetition of the Ru-
bjerg Knude Formation, and that a normal fault simi-
lar to the BRNF, is located in the upper levels of the
RF02 sheet. The normal fault is asymptotic, fading out
towards the L/R-unconformity in the RF02 thrust sheet.

The RF03 thrust sheet is a small sheet with a trun-

cation structure. The nose of this thrust sheet was

obviously exposed to normal faulting at an early stage
of development (Fig. 99). After fault displacement, the

RF03 tip was eroded away and the top of the thrust
sheet erosionally truncated to form an unconformity,
which cut off the sheet at a very steep angle (> 70°).
The normal fault at the tip of RF03 is the first of two
normal faults displaced down on to the piggyback
basin of RF02. In the second phase of normal fault-
ing, the c. 45 m long tip of the RF04 thrust sheet was
displaced c. 35 m down a normal fault plane (Fig.
100), which had an angle of 70-90° relative to the
thrust fault and the L/R-unconformity of RF04. The
normal faulting may have been initiated by differen-
tial translation of hanging-wall ramps along interme-
diate flats related to one or more subsurface duplex
segments. In a late phase of thrust faulting, the trailing
part of RF04 was thrust up over the piggyback basin
of RF04/RF03/RF02, which brought the nearly 45° dip-
ping lower hanging-wall ramp of RF04 into contact
with the footwall ramp of the displaced tip of RF04.
The final phase of fault-bend folding tilted this ramp
into a 70°S dipping position.

The RF05 and RF06 thrust sheets were thrust up

Fig. 98. The thrust sheet pair exposed below the Rubjerg Knude Fyr. To the right, the RF01 thrust sheet is thrust faulted along its

hanging-wall ramp ( RF01HWR ) along the footwall ramp in the trailing end of the Grønne Rende Section. RF01 forms the footwall

block for the propagation of the hanging-wall ramp of RF02 ( RF02HWR ). Note the elevated position of the L/R-unconformity
indicating that the thrust sheets were thrusted up on duplex segments in the subsurface. Photograph: July 1999.

Geological Survey of Denmark and Greenland Bulletin

Nr. 8 pp 90-119, Structural analysis of the Rubjerg Knude Glaciotectonic Complex, Vendsyssel, northern Denmark

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