Vol. 8 pp 60-89, Geol. Surv. Denmark and Greenland Bulletin

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Structural description of sections

The Rubjerg Knude Glaciotectonic Complex is differ-
entiated into 13 structural sections, which are named
after the localities recorded in the geological cross-
section of Lønstrup Klint by Jessen (1918). The sec-
tions can be grouped into three zones within the com-
plex: a distal zone (three sections farthest to the south),
a central zone (seven sections in the middle part of
the complex), and a proximal zone (three sections farth-

est to the north). They are named, from south (near
Nørre Lyngby) to north (at Lønstrup): Ulstrup, Stens-
næs, Martørv Bakker, Kramrende, Brede Rende, Sand-
rende, Stenstue Rende, Grønne Rende, Rubjerg Knude

Fyr, Stortorn, Moserende, Mårup Kirke and Ribjerg
Sections. Three criteria were used for defining the
sections: (1) the sections had to be bordered by marked
footwall ramps, (2) each section should be character -
ised by uniform structural architecture, and (3) the
sections had to be descriptively and geographically
delimited. A good example of the first criteria is the
steep thrust fault separating the Sandrende Section
from the Stenstue Rende Section. As an example of a
uniform architecture, the Grønne Rende Section can
be mentioned, and finally the Mårup Kirke Section
includes the long barren stretch from the Mårup church
to Ribjerg at Lønstrup where the lack of geographical
markers as well as characteristic footwall ramps is sig-
nificant.

Each section is described separately, a general phys-

iographic introduction being followed by four parts:
(1) tectonic architecture, (2) sedimentary units, (3) struc-

tures, and (4) interpretation of structural development.
The first descriptive part provides a general descrip-
tion of the macro-structures. The second part presents
the sedimentary deposits, and although to some de-
gree it repeats the lithostratigraphic descriptions of
the formations (see above), the detailed observations
of syntectonic sedimentation are relevant to an ap-
pr eciation of the structural development in the indi-
vidual sections. The third part concerns the descrip-
tion of meso- and mini-structures (thrust faults, folds,
faults, shear zones, joints, fractures, breccias, polydia-
pirs etc.). The description of each section is conclud-
ed with an interpretation of the formation of the struc-
tures. This interpr etation should not be confused with
the overall interpretation of the dynamic development
of the progressive thrust-fault deformation that fol-
lows the systematic descriptions of the sections. The

organisation of the section descriptions follows the
general systematics of structural geology: the descrip-
tion of geometry, the kinematic investigation, inter-
pretation of the dynamics and finally the analysis can
be concluded by a tectonic synthesis (Dennis 1972).

The reader should note that the structural elements

are numbered from distal to proximal. This is a conse-
quence of the systematic analysis; in order to obtain
an overview, the reader can compare the structural de-

scription given for each section with the dynamic de-
velopment presented in the latter part of this bulletin.

Ulstrup Section

The southern frontal edge of the Rubjerg Knude Gla-
ciotectonic Complex is positioned in the Ulstrup Sec-
tion where the undeformed foreland is exposed be-
low the hanging-wall flat of the last displaced and
most distal thrust sheet (UL01, see Plate 2). One of
the most interesting problems addressed in the analy-
sis of this complex is the presence of two long thin
thrust sheets that were translated southwards for about
500 m from their ramps to their present positions with-
out complete internal disruption. The Ulstrup Section
represents the foreland margin of the thrust-fault com-
plex, and the two flat-lying thrust sheets extend from
the southern edge of the thrust front at Tvonnet Rende
to the steep ramp thrust separating the Ulstrup and
Stensnæs Sections (Plate 1). The Stensnæs ramp thrust
was initially regarded as the foreland thrust (Peder-
sen 1987), but new outcrops of the southern Ulstrup
thrust exposed in 1996 and 1997 clearly demonstra-
ted additional details of the frontal thrusting. Conse-
quently, the long cliff section showing horizontal bed-
ding that had previously been regarded as a primary,
undeformed sedimentary unit (Fig. 42) is now inter-
preted as a displaced thrust sheet (UL01).

The Ulstrup Section is truncated by a broadly hori-

zontal glaciotectonic and erosional unconformity
above which aeolian sand was deposited, either as
sheet sands or as small dunes, up to 10 m high.

Tectonic architecture

The Ulstrup Section comprises the two flat-lying thrust
sheets, UL01 and UL02. The tip line of the hanging-
wall ramp (the edge of the frontal thrust) is situated
on the northern side of Tvonnet Rende (for location,
see Plate 1). Unfortunately, the precise position is
obscured by late, syntectonic erosion and sedimenta-
tion at the front of the thrust-fault complex, as well as
by sand scree covering the outcrops at Tvonnet Rende.
The northern boundary of the section is the footwall
ramp and flat of the UL02 thrust sheet, which forms a
transitional zone of imbricate thrusting related to the
frontal part of the Stensnæs Section.

The frontal part of the UL01 thrust sheet was dis-

placed from the upper footwall ramp (Fig. 43) along
an upper footwall flat on the top surface of the fore-
land. At the tip of the thrust sheet, the thrust fault dips

gently towards the foreland, and a small foreland-dip-
ping ramp is also located at point 6040 m in the cross-
section (Plate 1, see Fig. 50). The ramps probably formed

due to erosion in front of the propagating thrust-fault
edge. In the central part of the UL01 thrust sheet, a
synform structure is associated with a chaotic breccia,
interpreted as the collapse of a frost mound or sand-

mud diapir below the thrust fault; the synformal de-
pression is referred to hereafter as Ulstrup Rende (for
location, see Plate 1). The trailing end of the thrust
sheet starts at the upper footwall ramp of the foreland
from where the hanging-wall flat is inferred to contin-
ue along the footwall flat to the footwall ramp at its
trailing end. The total length of the thrust sheet is
about 750 m and the displacement is estimated at 350
m, which is the distance from the footwall ramp at
point 5800 m in the cross-section to the frontal termi-
nation in Tvonnet Rende (Plate 1). The thickness of
the thrust sheet varies from 10 to 20 m, decreasing
towards the tip to the south, and increasing in thick-
ness where syntectonic deposits fill the piggyback
basin on the back of the thrust sheet. The thickness
of the Lønstrup Klint Formation is only 6 m in the
souther n part of the piggyback basin due to erosion
related to elevation during thrust faulting.

The UL02 thrust sheet is 600 m long, with the fron-

tal edge situated on the northern side of the UL01
piggyback basin at point 5900 m, and the trailing end
disappearing into the décollement zone at point 5300
m. The thrust fault consists of a more than 400 m long
footwall flat on top of UL01 extending from the foot-
wall ramp hinge at point 5360 m southwards to the

Fig. 42. The steep sandy cliff of the Ulstrup Section displays horizontal bedding of an apparently undisturbed deposit. However,
structural analysis of thrust-fault relationships to the south indicates that it is a long flat thrust sheet displaced more than 500 m

towards the foreland to the south. The cliff section is 25 m high and the view is towards the south. Photograph: June 1984.

gently dipping frontal bend at point 5780 m in the
cross-section (Plate 1). The frontal bend corresponds
to the hinterland-dipping limb of the flat-topped hang-
ing-wall anticline of UL01. This hanging-wall anticline
compares well with the structure of the thrust-fault
model in Fig. 6, and the southernmost c. 100 m of
UL02 can be regarded to have been emplaced piggy-
back on UL01 during the translation over the frontal
footwall ramp. The UL02 thrust sheet is only 5-6 m
thick above the flat-topped anticline, whereas the thick-
ness increases to 20 m at the trailing-end ramp. The
displacement along the northern thrust fault is 550 m,
with an uncertainty of 10-25 m depending on the in-
terpretation of the shape of the trailing-end ramp and
the amount of erosion of the frontal part at the piggy-
back basin at Ulstrup Rende.

Sedimentary units

The sedimentary units in the Ulstrup Section comprise
the upper part of the Lønstrup Klint Formation, ero-
sional remnants of the lower part of the Rubjerg Knu-
de Formation, and a variety of intercalations of the
Rubjerg Knude Formation distinguished here as the

Ulstrup beds. The L/R-unconformity between the Løn-
strup Klint and Rubjerg Knude Formations can be
traced along the upper part of the UL01 thrust sheet
in which it also forms the base of the piggyback ba-
sin. A few younger erosional unconformities, below
and above the Ulstrup beds, are of only local signifi-
cance within the Ulstrup Section.

Lønstrup Klint Formation

The mud-dominated Lønstrup Klint Formation forms
the main part of the thrust sheets in the Ulstrup Sec-
tion, and has an average thickness of about 10 m (Fig.
19). In the southern thrust sheet, the fine-grained sand
beds are thin and only small-scale current ripples have
been observed. A combination of load structures (ball-
and-pillow) and water-escape structures (convolution
and small-scale diapirs) are developed at certain hori-
zons. Above the hanging-wall flat, a zone about 2 m
thick takes the form of a mobilised mud breccia, which
can be characterised as a sole thrust zone. This brec-
cia is superimposed by beds affected by a brittle type
of brecciation, for ming cracks and joints in an up to 4
m thick zone in the lower part of the thrust sheet.

Fig. 43. The upper footwall ramp of the foreland (Foreland FWR) along which the UL01 thrust fault propagated ( UL01HWF : Ulstrup
thrust sheet 01 hanging-wall flat), and from where it continued for more than 300 m over the footwall flat of the foreland. The cliff

section is 25 m high and south is to the right. Photograph: May 1998.

The northern thrust sheet (UL02) displays a more

sandy part of the Lønstrup Klint Formation (Fig. 25).
Here the sand beds are up to 1 m thick and water-
escape structures, convolute bedding and flame struc-
tures commonly disturb the primary bedding. Ball-
and-pillow structures are more common towards the
trailing end of the thrust sheets.

Rubjerg Knude Formation

In the Ulstrup Section, the Rubjerg Knude Formation
comprises three different depositional units: the main
'background' sedimentation of outwash sand, the gla-
ciolacustrine Ulstrup beds (Fig. 25), and the coarse-
grained glaciofluvial Ulstrup beds (Fig. 20).

The main depositional unit is fine- to medium-

grained meltwater sand represented in the footwall
block of the foreland (Fig. 43). Small-scale current rip-
ples occur in the parallel bedded sand, which is inter-
layered with c. 0.5 m thick trough cross-stratified beds.

The glaciolacustrine Ulstrup beds for m a 3-5 m thick

unit that is only found on the back of the UL02 thrust
sheet (Fig. 25). This unit consists of dark bluish grey,
laminated clayey mud interlayered with a few sandy
beds up to 0.5 m in thickness. The unit was deposited
on a bedding-parallel unconformity, which is only
discordantly developed in the northernmost trailing
part of thrust sheet UL02. The unit thins out towards
the south, and disappears near the hinterland-dipping
limb of the flat-topped hanging-wall anticline formed
above the footwall ramp of the foreland. Intraforma-

Fig. 44. The mud-mobilised thrust-zone

breccia consists of structureless mud
with scattered clasts floating in the

matrix. Dilation cracks filled with sand
are superimposed on the mud-mobilised

brecciation fabric. This reflects two
phase of cataclastic deformation: a first

phase of water-over-pressured breccia-
tion (hydrodynamic brecciation), and a

second phase of brittle fracturing when
the mud was consolidated, dehydrated

or perhaps frozen. Handle of spade is
12 cm. Photograph: June 1997.

tional hydrodynamic brecciation, including small-scale
diapirs and slump-like features, deformed the clayey
mud; such deformation is not seen in the Lønstrup
Klint Formation below the unit.

The glaciofluvial Ulstrup beds occur in the Ulstrup

Rende depression between points 5900 and 6000 m
in the cross-section (Plate 1). This unit is a c. 8 m
thick succession of meltwater gravel fining up into
coarse-grained sand (Fig. 20). Large-scale trough cross-
bedding dominates the succession and clasts up to
boulder size occur in the lowermost 2 m (Fig. 28).
Lithologically, the clasts are dominated by flint, but
clasts of fossil frozen sand are abundant (Fig. 29).

The glaciofluvial Ulstrup beds are overlain by c. 5

m of medium- to coarse-grained sand of the Rubjerg
Knude Formation. On the north side of the Ulstrup
Rende depression, between points 5900 and 6000 m,
slump-folded sand beds and sedimentary breccias
occur in the upper part of this succession, suggesting
gravity gliding down the steep slope of the depres-
sion (piggyback basin of UL01).

Structures and breccias

The most important structures related to the thrust
faults in the Ulstrup Section are the breccias occurring
in the thrust zones above the thrust-fault surfaces. They
appear to have formed by collapse of the thrust sheet
during translation. The low-angle anastomosing faults
that developed in the most distal part of the thrust-
fault complex originated similarly during translation

and are associated with southerly dipping normal
faults. A significant collapse structure that formed be-

neath the Ulstrup Rende depression is also worthy of
note.

Thrust-zone breccias

The thrust-zone breccias occur above the hanging-
wall flat of the UL01 and UL02 thrust sheets, where
they affect the mud-dominated Lønstrup Klint For ma-
tion. The thrust zone is up to 4 m thick in the most
distal part of the thrust-fault system (souther n part of
UL01), and decr eases in thickness to 1 m northwards;
it can be traced along the hanging-wall flat of UL02

for a considerable distance. The thrust-zone breccia
consists of mobilised mud with irregular clasts of mud
scattered throughout (Fig. 44). Some patches may be
more sandy and others more clayey, and lenses and
layers of sand may be present. The mobilisation was
apparently initiated as sandy mud-fluid that developed
at the thrust-fault surface and extended up into the
sedimentary unit (Fig. 45). In many cases, the initial
hydrodynamic brecciation of the thrust zone left seg-
ments along the displacement surface of the thrust
fault, which were modified and developed into elon-
gated cataclasts along the sole of the breccia zone.
Convolute bedding and small-scale diapirism are also
present.

The mobilised mud was subsequently transected

by dilation cracks and sand-filled fissures (Fig. 46).
The dilation cracks form an irregular network and the
sand-fill was injected into consolidated mud (Figs 44,
46, 47). More or less horizontal sand-filled cracks have
been observed in the frontal part of the UL01 thrust
sheet, where they are up to 15 cm thick and appear
up to 1 m above the hanging-wall flat. The sand in
the cracks shows planar horizontal lamination and
small-scale current ripples and a few vertical sand-
filled pipes extend upwards from the cracks (Fig. 48).

Towards the frontal tip of the UL01 thrust sheet, an

increasing number of bedding parallel or low-angle
anastomosing fractures and small-scale faults appear
to be related to an increased rate of inter nal gliding.
This is an indication of how close the thrust sheet
was to disintegration and a loss of cohesion. Zones
0.2-0.5 m thick, grading into mobilised mud, occur in
between the anastomosing fractures, resulting in the
destruction of bedding (Fig. 49).

Foreland-dipping hanging-wall flat faults

In the frontal part of the UL01 thrust zone, foreland-
dipping faults become increasingly common. These
faults are either foreland-dipping (20-30°S) ramps
formed by the hanging-wall flat scouring into the foot-
wall flat (Fig. 50), or sets of 50°S dipping normal faults
with displacements of about 10 cm. These structures
are considered to be the result of partial collapse of
the tip of the foreland-dipping limb of the hanging-
wall ramp above a low-angle hanging-wall ramp trans-
lated along the footwall flat of the foreland.

Intrusive contact

Thrust-fault surface

Fig. 45. Mud mobilisation along the hanging-wall flat of the

UL02 thrust sheet. From the thrust-fault sur face, a sandy mud
fluid intruded along fractures and up into the lower part of the

thrust sheet where it formed a mud-intrusion. During the initial
hydrodynamic brecciation of the thrust zone, small relict seg-

ments remained at the thrust plane where they were modified
and developed into elongate cataclasts in the sole of the thrust

breccia zone. Photograph: July 1998; matchbox for scale.

Collapse structure in the Ulstrup Rende

Structures in the central part of Ulstrup Rende (Figs
51, 52) are interpreted to represent a collapsed diapir.
The early phase structures include thinning of the Løn-

strup Klint Formation in the thrust sheet, and forma-
tion of concave troughs in its surface. Vertically or
steeply dipping sand breccias with upward directed
flow structures cross-cut the thrust-zone breccia. The
appearance of structureless sand pockets indicates sand-

fill of mobilised sediment from an over-pressured zone
in the subsurface. The complex of breccias and re-
orientated bedding is interpreted as a collapse struc-
ture; it is considered to be responsible for the forma-
tion of the Ulstrup Rende depression, and the disrup-
tion of the thrust sheet along steeply dipping frac-
tures. In the breccia zone, steeply dipping sand-filled
cracks and normal faults formed prior to the contin-
ued deposition of the Rubjerg Knude Formation in
the depression.

On the southern side of the Ulstrup Rende depres-

sion, the muddy part of the thrust sheet is displaced
by steeply dipping normal faults. Downthrow is to the

south, synthetic towards the depression, and the faults
are thought to be related to the collapse of the diapir
structure.

Interpretation of structural development

There are two reasons why the Ulstrup Section de-
serves special attention. The first is that it represents a
foreland thrust section with long lateral transport of
thin thrust sheets, the nature of which has not previ-
ously been documented. Secondly, it demonstrates
the likely development of the initial stages of defor-
mation, which the remainder of the thin-skinned thrust
faulting in the Rubjerg Knude Glaciotectonic Com-
plex also experienced before the upper most part was
eroded. Thus the first phase of thrust-fault deforma-
tion is preserved her e whereas it is almost never re-
presented in the thrust-fault sections that have been

Fig. 47. The formation of thrust-zone breccias in the distal part of the thrust-fault complex is here illustrated in four stages of
development. ( 1 ) The initial undeformed sediment (Lønstrup Klint Formation) comprises clayey mud interlayered with thin sand

beds. ( 2 ) A mud-fluid is formed above the thrust-fault surface (line with open triangles ) from where it is injected up into the layers
above (see Fig. 45). ( 3 ) Increasing mud-mobilisation results in the formation of a structureless matrix with dispersed matrix-

supported clasts of the primary sediment (see Fig. 44). Note the small normal faults indicating an on-going process of collapse. ( 4 )
The mobilised mud becomes consolidated and the thrust-zone breccia develops into a more brittle stage; dilation cracks form into

which water-saturated sand is injected (see Fig. 46).

more intensely deformed. The interpretation of the
structural development can be summarised in the fol-
lowing nine stages.

1. Initial thrust-fault fracturing and thrust-fault propa-

gation took place during mobilisation of mud along
the hanging-wall flat. At this stage, the thrust-zone
breccia was formed due to high pore-water pres-
sure in an unfrozen stage.

2. The UL01 and UL02 thrust sheets probably started

to move along the décollement zone as one coher-
ent thrust sheet, and first separated into two thrust

sheets after the frontal part of the sheet had passed
the most distal foreland footwall ramp.

3. The ramping up of the northern UL02 thrust sheet

probably increased the pore-water pressure, and
when this increase also affected the frontal part of
UL01, diapirism was initiated under the central part
of the southern thrust sheet.

4. The diapiric uplift and erosion took place in the

elevated surface. This erosion extended through the
Rubjerg Knude Formation to locally intersect the
L/R-unconformity. The residual coarse clastic gravel

Fig. 48. A subhorizontal sand-filled

fracture occurring in the frontal part of
the UL01 thrust sheet. The sand-filled

fracture appears about 1 m above the
hanging-wall flat; the sand shows planar

horizontal lamination and current ripple
cross-lamination. The sand-filled fracture

is interpreted to have formed during
ground-frozen conditions, whereas the

vertical sand-filled pipe probably reflects
loading of the thrust sheet when it

ultimately lost its carrying pore-water
pressure and settled on its hanging-wall

flat. Photograph: June 1997.

Fig. 49. Subhorizontal anastomosing

faulting (centre left) with mud-mobilisa-
tion developed in domains between

fault fractures in the frontal part of the
UL01 thrust sheet. Photograph: June

1997.

Fig. 50. A : Foreland-dipping ramping of hanging-wall flat
formed by scouring-erosion of the footwall flat into the

top surface of the foreland. Note in the close-up ( B ) that
some hydrodynamic brecciation occurred in the footwall

ramp just below the thrust zone. Photograph: June 1997.

on the footwall flat at the surface of the foreland

in the Ulstrup Section.

7. The consequence of the diapir collapse was the

formation of the depression in Ulstrup Rende.
Redeposited coarse-grained clastic material filled
the depression, generating the glaciofluvial Ul-
strup beds. The occurrence of fossil frozen-sand
clasts implies that part of the surface, the Ru-
bjerg Knude Formation, was ground-frozen -
probably that part of the thrust sheet that had
been elevated due to the propagation up over
the central ramp. The ground-frozen condition
was probably also responsible for freezing of
the mobilised mud in the thrust zone and the
subsequent development of sand-filled dilation
cracks (Fig. 47)

bed on the unconformity surface was probably the orig-
inal source for the large amount of coarse-grained ma-
terial in the Ulstrup Rende depression.

5. The mud-sand volcano broke through to the surface, and

the mobilised mud and sand were extruded with the
release of the high pore-water pressure.

6. The surface of the diapir collapsed and gravel and sand

filled the fractured structure. The collapse was probably

contemporaneous with the loss of pore pressure through-
out the thrust zone. The release of over-pressure in the
thrust zone resulted in the final settling of the thrust sheet

8. The depression was ultimately filled by the sand of

the upper unit of the Rubjerg Knude Formation.
The frontal edge of the northern thrust sheet prop-
agated towards the northern side of Ulstrup Rende
and parts of its leading tip slumped down the steep
slope of the depression. This indicates the sequen-
tial and later movement of the northern thrust sheet.
The depression can be interpreted in part as a pig-
gyback basin that formed according to the model
demonstrated in Fig. 7.

9. Finally, the upper most sediments of the Rubjerg

Knude Formation covered the section before the
glacier advanced across the area. The uppermost
metre of sand was transformed into a glaciofluvial-
sand-glacitectonite.

Fig. 51. The Ulstrup Rende depression is interpreted to represent a combination of a piggyback basin (according to the model in
Fig. 7) and the collapse of an underlying mud diapir or frost-mound feature. Note the steep normal fault on the left side of the

depression (to the north). Photograph: June 1997; spade (lower centre) for scale.

Fig. 52. Chaotic sand/gravel breccia in the centre of the Ulstrup

Rende depression, which is interpreted as the result of the col-
lapse of the diapiric structure created in the subsurface below

the UL01 thrust sheet. Photograph: May 1998.

Stensnæs Section

The Stensnæs Section is named after Stensnæs, which
is a minor point (Danish: sten = stone; næs (pynt) =
point) at a gentle bend in the cliff section. Stones and
erratic blocks, probably derived from the up to 2 m
thick sandy till and the erosional unconformity below
the Vendsyssel Formation, were formerly abundant
on this part of the beach. The sandy till thins out south-
wards where a glaciotectonic unconformity truncates
the section.

The Stensnæs Section displays the most spectacu-

lar folds in the Rubjerg Knude Glaciotectonic Com-
plex (Fig. 53). The folds are situated at the transition
from the flat-lying beds to the south (the Ulstrup Sec-
tion) and the main thrust-fault imbrications to the
north. The fold complex is truncated by an erosional
unconformity forming a depression in which slump
slides and sedimentary breccias derived from the tip
of the thrust sheet were deposited after collapse and
gravity gliding. In general, the fold complex is well
exposed, whereas the transition further southwards is
often covered by sand scree. During the years of study
of the Rubjerg Knude Glaciotectonic Complex by the
author, variations in the degree of exposure of the
Stensnæs Section have contributed to a fuller under -

standing of the structural development of the section
that represents the foreland margin of the thrust-fault
complex.

Tectonic architecture

The Stensnæs Section comprises four thrust sheets
(SN01, SN02, SN03 and SN04, Plate 2). The southern
boundary of the section is defined by the footwall
ramp of UL02, although the trailing end of UL02 is
here included in the description of the imbricate du-
plex that hosts the fold complex. The northern boun-
dary is the hanging-wall ramp of MB01/MB02, that is
thrust up along the footwall block of SN04. The thrust
sheets comprise the uppermost part of the Lønstrup
Klint Formation and a relatively thin cover of the over-
lying Rubjerg Knude Formation sediments. Two dis-
crete piggyback basins (early and late) were formed
above the SN01 and SN02 thrust sheets.

The SN01 thrust sheet is about 30 m thick, and al-

though the thrust sheet includes a number of small
duplex imbricates it can be subdivided into upper and
lower segments. The lower segment is thrust onto the
UL02 footwall block with a displacement of about 30 m.

The displacement of the upper segment is partitioned

Fig. 53. The fold complex developed in the transitional imbricate zone between Ulstrup and Stensnæs Sections. Note that the thrust

faults acting as flexural slip surfaces in the folding continue into the bedding-parallel thrust-fault flats to the south (right). Photo-
graph: July 2000.

into a series of minor differential displacements rang-

ing from minor flexural slips along bedding surfaces in

the fold structures to imbricate offsets of about 1-3 m.

In the frontal part of the SN02 thrust sheet, the Løn-

strup Klint Formation is only a few metres thick, and
is overlain by 10 m of sediments of the Rubjerg Knu-
de Formation r esting on the L/R-unconformity. At the
trailing end of the thrust sheet, the Lønstrup Klint For-
mation is more than 15 m thick, whereas the Rubjerg
Knude Formation is cut off by the footwall ramp of
SN02 (corresponding to the hanging-wall thrust fault

for the imbricates of SN03). The accumulated displace-
ment of SN02 amounts to 88 m, including 15 m up
over the footwall ramp and 73 m along the footwall
flat of SN01.

The SN03 thrust sheet may be divided into four

imbricate segments thrust onto the footwall ramp of
SN02. The displacement along the hanging-wall thrust
fault is 45 m, but it was also carried piggyback on
SN02 during the translation along the décollement
zone, which gives an accumulated displacement of
163 m for the SN03 thrust sheet.

Fig. 54. Ball-and-pillow structures in the

Lønstrup Klint Formation in the Stens-
næs Section. Note that the size of the

structures reflects the thickness of the
sand beds involved. Photograph: July

2000; staff divisions are 20 cm.

Fig. 55. Dish-and-pillar structures
developed in the lowermost sandy bed

above the hanging-wall flat of the SN2
thrust sheet in the Stensnæs Section.

This type of water-escape structure is
interpreted to have formed during the

thrust-fault translation along a hanging-
wall flat due to the high water pressure

released from the sole of the thrust

sheet. Photograph: July 1998.

The SN04 thrust sheet is about 20 m thick, includ-

ing an up to 8 m thick unit of the Rubjerg Knude
Formation resting on the L/R-unconformity above the
Lønstrup Klint Formation; this unit increases in thick-
ness to about 15 m towards the trailing end of SN04.
Total displacement is about 45 m, including a hang-
ing-wall ramp-and-flat propagation along the footwall
ramp of SN03.

Sedimentary units

The sedimentary units that crop out in the Stensnæs
Section are dominated by the upper sandy parts of
the Lønstrup Klint Formation. A lens of a glaciolacust-
rine diamictite is preserved as an imbricate thrust sheet,
c. 3.5 m thick and 22 m long, and is tentatively inter-
preted to form part of the Rubjerg Knude Formation.
The latter is mainly represented by a 6-8 m thick suc-
cession including the residual gravel deposited on the
uneven sur face of the L/R-unconformity. An upper
unconformity truncates the SN01 and SN02 thrust
sheets, and coarse gravel beds as well as olistoliths of
the Lønstrup Klint Formation were deposited in a late
piggyback basin (SnstRu in Plate 2).

Lønstrup Klint Formation

The sedimentology of the Lønstrup Klint Formation
in the Stensnæs Section is similar to that described for
the Ulstrup Section. The maximum thickness of the
formation is about 15 m, and lithologies are dominated

by 0.2-0.8 m thick fine-grained sand beds with climb-
ing ripple lamination. Thin laminae of mud and small
amounts of detrital organic material commonly drape
the ripples. The sand beds are interlayered with thin

laminated dark grey mud beds; micro-faulting is evi-
dent in this facies. Ball-and-pillow and convolute struc-
tures are abundant (Fig. 54). In the uppermost 4 m of
the formation, the sandy beds become thinner and
the uppermost part is dominated by mud. In sand beds
inferred to be situated above the hanging-wall flat,
dish-and-pillar structures have been observed (Fig. 55)
that are interpreted to have formed by water-escape
processes related to the thrusting.

Cheel & Rust (1986) provided a model for the de-

velopment of water-escape structures in glacial out-
wash deposits from Ottawa, Canada. In their model, a
sequential development from simple load structures
through detached ball-and-pillow structures to dish
structures is demonstrated. The model predicts a stra-

Fig. 56. The piggyback basin situated above the erosional truncation of thrust sheet UL02 and SN01 in the Stensnæs Section (SNstRu
in Plate 2). Note that normal listric faults ( arr ow ) may be traced to the trailing end of the large olistoliths ( green ) deposited in the

meltwater sand and gravel. This is interpreted as the result of gravity gliding of the tip of a thrust sheet, which during propagation
from the north collapsed subsequent to thrust faulting up above the mean level of sedimentation. Photograph: July 2000; thrusts

indicated in red , unconformity indicated in purple .

tified distribution with convolute stratification at the
base of a bed, ball-and-pillow structures dominating
the main part, and dish structures formed in the up-
permost part of the bed (or unit) resulting from ex-
cess pore-water fluid pressure. The observed water-
escape structures in the Stensnæs Section as well as in
the sections further to the north compare well with
the model of Cheel & Rust (1986) (Figs 54, 55; see
also fig. 77), although they suggested the triggering
mechanism to be earthquakes or movements due to
melting of dead-ice.

Rubjerg Knude Formation

In the Stensnæs Section, two units of the Rubjerg
Knude Formation are distinguished: (1) a lower unit
dominated by fine- to medium-grained glaciofluvial
sand, and (2) an upper unit of varied sedimentary
breccias and coarse-grained clastic deposits that in-
fills the piggyback basin on top of the truncated thrust
sheets in the section (Fig. 56). The sand deposited in
the lower unit may be planar parallel stratified, or
exhibit large-scale trough cross-bedding with shallow
troughs, only 0.5 m deep. The lower unit of the Ru-
bjerg Knude Formation is estimated to be 6-8 m thick,
and although strongly affected by hydrodynamic bre-
cciation, the unit compares well with the description
of the lower part of the formation provided by Sado-
lin et al. (1997).

The upper unit was deposited on the erosional

unconformity truncating the back of the UL02 thrust
sheet, the fold and imbricate complex of SN01, and
the tip of the SN02 thrust sheet (SnstRu in Plate 2).
The central part of the basin is about 7 m thick, de-
creasing towards both the north and south forming a
relatively narrow trough. The sediments in the basin
consist of large-scale irregularly trough cross-bedded
glaciofluvial sand and gravel. Blocks of sandy mud,
which can be identified as derived from the Lønstrup
Klint Formation, were deposited as sedimentary brec-
cias in the basin. The clasts are up to 1 × 5 m in size;
blocks and clasts less than one metre in size were
commonly rotated during redeposition. Normal listric
faults in the northern part of the basin relate to the
deposition of the largest olistoliths (Fig. 56). The south-
ern part of the basin was tilted subsequent to deposi-
tion due to the fault-bend folding of the hanging-wall
flat of UL02 when it propagated along the footwall
flat during the latest phase of thrust faulting. Thus the
upper unit of the Rubjerg Knude Formation in the

Stensnæs Section is interpreted to have been deposit-
ed in a piggyback basin in which thrust-sheet tips
thrust up from the north collapsed and gravity-glided
out into the basin.

Structures

Two types of structures in the Stensnæs Section are
related to thrust faulting: (1) the folding related to
duplex imbricates, and (2) extensional faults related
to push-from-the-rear in the trailing end of a thrust sheet.

Imbricate duplex folding

The folds in the Stensnæs Section can be described as
flexural slip folds, and have amplitudes of 1-3 m and
wavelengths of 2-5 m (Figs 53, 57, 58). The folds ar e
very irregular in shape, however, and cannot be ex-
plained in terms of simple compression. Analysis of
the flexural slip surfaces shows that the folded layers
were separated into segments and that discordant re-
lationships exist between beds in neighbouring seg-
ments. By defining the segments as small imbricate
thrust sheets in a duplex, thrust-fault terminology can
be applied and hanging-wall and footwall thrusts of
the individual duplex segments defined. In Fig. 57
this has been done by identifying the footwall ramps
(FWR), thus distinguishing five imbricate thrust sheets
about 1 m in thickness. The folds in the imbricate
duplex segments include both hanging-wall anticlines
and footwall synclines. As documented by the refold-
ing of the upper hanging-wall anticline in Fig. 57, the
folds are superimposed by sequential phases of fold-
ing and thus also phases of imbricate thrusting. Fig-
ures 58 and 59 illustrate the sequential development
of imbricate thrusting; the imbrication steps forward
towards the footwall ramp of UL02 to the south. Note
also that the hanging-wall flat of each imbricate con-
tinues into an intraformational bedding-parallel thrust
fault. This can be difficult to recognise in an isolated
exposure, where the flats cannot be traced back to
the ramp structures in the imbricate duplex (Fig. 53).

Extensional faults

In the trailing part of the SN03 thrust sheet, listric ex-
tensional faults have been observed (Fig. 60). Dis-
placements along the faults are up to 0.5 m and the

spacing between the faults is 0.2-0.6 m, which creates

a boudinage-like network. The structures are interpre-

ted to have been formed by push and loading of a thrust

sheet ramping the formerly monoclinal fault-bend-fold-
ed thrust sheet, which responded to the gravity spread-
ing by displacements along the extensional faults.

Similar mini-scale extensional normal faults are rec-

ognised in the footwall block below the hanging-wall
flat of SN03 (Fig. 61). It is remarkable that the thrust-
fault deformation only weakly affects the top of the
footwall block, while the hanging-wall block is strongly
affected by hydr odynamic brecciation. A zone only
20 cm thick below the shear-laminated thrust-fault
sur face is affected by low-angle extensional faulting,
and grades down into a minor normal fault network
(Fig. 61). Isoclinal folding has been observed in the
narrow shear-laminated thrust-fault zone, adding to
the impr ession of high strain along the thrust fault.
However, it is clear that the elevated water pressures
supporting the thrust sheet were located in the hang-
ing-wall flat.

Interpretation of structural development

The formation of the imbricate duplex fold complex
in the Stensnæs Section is evidently related to ramp
pr opagation. Two footwall ramps are significant: the
footwall ramp of UL01, which can be regarded as re-
pr esenting the footwall ramp of the foreland, and the
footwall ramp of the trailing end of UL02. The UL01
footwall ramp acted as a stopping block for the for -
ward push of the imbricate thrust sheets, and the pro-
pagation of this ramp was responsible for the general
gentle northerly tilt of the structures. The UL02 foot-
wall ramp was subjected to successive thrust-fault splay
formation, and consequently imbrication and super-
imposed folding, which can be viewed as the col-
lapse of the trailing end of the UL02 thrust sheet.

The imbricate duplex fold complex of the Stensnæs

Section can be readily compared to the model for
connecting splay duplexes of the Sevier thrust belt in
the Cordilleran Fold Belt (Mitra & Sussmann 1997).
There is a close similarity with respect to the growth
of the duplex by successive connecting splays of the
thrust fault and the creation of folds by thrust-fault
propagation. Moreover, the analysis of the imbricate
duplex fold complex implies that the imbrication start-
ed at the footwall ramp in the trailing end of the sys-
tem and propagated towards the foreland. It can there-
fore be argued that the process was one of footwall

ramp collapse. A simplified model for the growth of
duplexes in a connecting splay duplex system is illus-
trated in Fig. 59.

With respect to the thrust-fault displacement, an ac-

tive and a passive stage of translation need to be dis-
tinguished. The active translation is the amount of dis-

placement of the thrust sheet arising from propaga-
tion along its hanging-wall thrust fault. The passive
translation is the amount of transport arising from the
displacement of the underlying thrust sheet which
carries it piggyback fashion. During this latter transla-
tion, the underlying thrust sheet may propagate foot-
wall ramps, which will fold the actively translating thrust

sheet as well as the piggyback thrust sheets into hang-
ing-wall anticlines. This type of deformation will cre-
ate an antiformal stack. The Stensnæs imbricate du-
plex fold complex may thus also be viewed as a meso-
to macroscopic-scale antiformal stack (Fig. 59).

A roof thrust, which is 110 m long and about 8-12

m thick covers the SN01-SN02 duplex. The accumu-
lated length of the three duplex segments is 175 m; c.
65 m is thus missing in the balance calculation of the
southern half of the Stensnæs Section. It is most likely
that part of the initial thrust sheet has been eroded
away, but up to c. 45 m of it might have been incor-
porated in a foreland-dipping frontal thrust structure
preserved in the chaotic imbricate fold complex.

Martørv Bakker Section

The name Martørv Bakker is derived from the peat
exposed in the coastal cliff (Danish: mar = sea; tørv =
peat; bakker = hills), which is covered by aeolian sand
dunes above the northern end of the section. In the
southern part of the section, the Vendsyssel Forma-
tion forms the top unit in the cliff. The Vendsyssel
Formation was deposited on an erosional unconfor m-
ity above the glaciotectonic complex. All the post-
tectonic deposits are prone to cliff erosion and the
resultant scr ee partly obscures the structures in the
Martørv Bakker Section. In addition, the unconformi-
ty at the base of the planar-bedded Vendsyssel For-
mation is a focus for groundwater seep which also
conceals details in the exposures. However, two im-
portant architectural elements have been recognised:
(1) the common appearance of minor duplexes in the
southern part of the section, and (2) the occurrence
of southerly dipping normal faults in the northern part.

The southern boundary of the section is the foot-

wall ramp of SN04 in the trailing end of the Stensnæs

Section. The northern boundary is not defined by a
simple reference point in the cross-section, but by the
trailing end of the MB04 thrust sheet which is a com-
bination of footwall ramp and footwall flat below the
leading-edge thrust fault of the Kramrende Section.

Tectonic architecture

The Martørv Bakker Section is subdivided into four
thrust sheets (MB01-MB04). The thrust sheets in the
southern part of the section are subdivided into up-
per and lower duplex segments of which only the
lower duplex segments are distinguished by separate
annotations (MB02u1-MB02u3, Plate 2). In the front-
al part of the section, smaller imbricate duplexes are
associated with syntectonically formed hydrodynam-
ic breccias and ball-and-pillow structures.

The MB01 thrust sheet is up to 20 m thick and com-

prises the upper part of the Lønstrup Klint Formation.
The frontal hanging-wall ramp was thrust up along
the 15° dipping footwall ramp of SN04, and displace-
ment is estimated at about 55 m. The bedding be-
comes steeper in the trailing end of the thrust sheet,
probably due to the relatively steep dip of the ramp
in the subsurface from the 20 m to the 10 m flat level.

The MB02 thrust sheet is long and flat-lying and

occupies more than 400 m of the section. The frontal
part is only 10-15 m thick and was displaced along its
upper hanging-wall flat along the footwall flat of MB01
for a distance of about 180 m. The trailing part of the
MB02 thrust sheet is 20 m thick, but as indicated in
the balanced cross-section it roots down to the 30 m
décollement level (Plate 2). The thrust sheet is dis-
placed by a prominent normal fault in the central part
of the Martørv Bakker Section (Fig. 62). Above the
Lønstrup Klint Formation, a marked basin developed
in the hanging-wall block of the normal fault. The

Fig. 62. The normal fault developed in the central part of the Martørv Bakker Section. In the hanging-wall block to the south, the

fluvial sands of the lower part of the Rubjerg Knude Formation are preserved in a 'fault trap' along the fault plane. Diamict
sediments were deposited above the sand in a piggyback basin that developed during the thrust faulting of the MB02 thrust sheet.

Note that the thickness of the Lønstrup Klint Formation in the footwall block decreases downwards along the normal fault drag. This
is interpreted as a foreland-dipping limb related to a hanging-wall anticline formed prior to offset by the normal faulting. The

formation of the normal fault is interpreted to be related to a foreland-dipping limb of a hanging-wall anticline at the tip of a
subsurface thrust-sheet segment (MB02u3 in Plate 2). Photograph: June 1993.

sediments in this basin were described as moraine
sand by Jessen (1918, 1931).

The MB03 thrust sheet is 30 m thick and made up

of the Lønstrup Klint Formation, which is here strong-
ly deformed by hydrodynamic brecciation and disloca-

ted by a number of bedding-parallel minor thrust faults.
The frontal part is flat-lying, whereas the dip of the bed-

ding increases to 25-30° at the trailing end indicating
a bend over an upper hinge on top of the footwall
ramp of MB02. In the exposed part of the section, the
MB03 thrust sheet is only about 120 m long, and it is
inferred that the foreland-dipping structures in the
fr ontal part reflect re-orientation due to hanging-wall
ramp propagation along the footwall flat of MB02.

The MB04 thrust sheet forms a flat-topped hang-

ing-wall anticline above the footwall ramp of MB03.

The thrust sheet is displaced along a normal fault par-
allel to the foreland-dipping bend in the top of the
frontal part of MB03. The normal fault does not dis-
place the footwall flat of MB02, and is therefore re-
garded as a structure related only to the framework of
MB03 and MB04. The structural framework in this part
of the section may be characterised as an antiformal
stack, including thrust sheets MB03 below and KR01
above MB04.

Sedimentary units

The Martørv Bakker Section is dominated by the Løn-
strup Klint Formation. However, the most important
sedimentological feature in the section is related to

Fig. 63. Hydrodynamic brecciation in the

Lønstrup Klint Formation in the north-
ern part of the Martørv Bakker Section.

Photograph: June 1993.

Fig. 64. Slump-fold structures formed in

the thin-bedded sand layers enveloped
in dark muds of the diamict sediments

in the piggyback basin in the Martørv
Bakker Section. Photograph: October

1998.

the basin developed at the top of the hanging-wall
block connected to the normal fault displacing the
MB02 thrust sheet (Fig. 62). The deposits in this basin
are regarded as an exotic part of the Rubjerg Knude For-

mation, and are described under this heading below.

The southern part of the Martørv Bakker Section is

unconformably overlain by the Vendsyssel Formation,
the initially glaciotectonic truncation being superim-

posed by a post-glacial erosional unconformity. A Holo-

cene erosional unconformity truncates the Vendsys-
sel Formation as well as the glaciotectonic unconform-

ity, and the peat deposited on this unconformity is up
to 2 m thick in the northern part of the section, where
it is covered by modern aeolian dunes up to 20 m high.

Lønstrup Klint Formation

The lower part of the Lønstrup Klint Formation is mud-
rich. It is exposed in the northern part of the section,
where it was thrust above the hanging-wall flat from
the décollement surface 25-28 m below sea level. The
upper part of the formation is dominated by 0.5-1.5
m thick sand beds interlayered with thin beds of hor-
izontally laminated mud, which typically has been
mobilised to form hydrodynamic breccias. In the south-
ern part of the section, the beds are strongly affected
by ball-and-pillow deformation (Fig. 63).

Rubjerg Knude Formation

The Rubjerg Knude Formation comprises two units:
(1) a lower 3 m thick sand unit only exposed along
the prominent normal fault in the central part of the
Martørv Bakker Section, and (2) a c. 15 m thick diamic-
tite interpreted as a glaciolacustrine mud with rede-
posited clasts. The first unit was deposited on the
L/R-unconformity, and comprises light yellowish me-
dium-grained sand (Fig. 26). The diamictite unit rests
partly on the lower sand unit, and partly on the L/R-
unconformity at the top of the Lønstrup Klint For ma-
tion. The diamictite is dark grey, and comprises weakly
laminated mud interbedded with structureless, irre-
gularly distributed matrix-supported beds containing

Fig. 65. A schematic diagram explaining the development of the hydrodynamic brecciation displayed in Fig. 63. The formation of the
structure was the result of three phases of defor mation. In the first phase, a succession of sandy turbidites interbedded with mud ( 1 )

was affected by loading to form the ball-and-pillow structures ( 2 ). In the second phase, the ball-and-pillow structures were dis-
placed by thrust faulting ( 3 ). During the third phase, the mobilised mud intruded up thorough the thrust-fault surface ( 4 ), demon-

strating the syntectonic development of the hydrodynamic brecciation.

unsorted clasts in a matrix of sandy mud (Fig. 26). In
the lower most 2 m of the diamictite succession, the
matrix-supported clasts were probably derived by re-
deposition of coarse-grained material eroded from the
L/R-unconformity to the north. About 3 m up in the
succession, a c. 1 m thick bed occurs with clay clasts
10 cm in size deposited in a weakly clay-laminated
and sand-streaked silty mud. This bed is overlain by
three 1.5-3 m thick units of isoclinally slump-folded,
thin-bedded, fine-grained sand encased in dark struc-
tureless mud (Fig. 26). These units are interpreted as
slump-folded sheets derived from the Lønstrup Klint
Formation (Fig. 64). The middle and upper slump-units

are separated by a c. 5 m thick interval dominated by
sandy mud with scattered clasts and a few thin sand
beds. The uppermost sand bed was not affected by
slumping and shows lar ge-scale trough cross-bedding.

The lower part of the diamictite succession is strong-

ly disturbed by hydrodynamic brecciation with meso-
scopic-scale diapirs rising from the top of the Løn-
strup Klint Formation and penetrating upwards into
the diamict sediments. This indicates that the diamic-
tites were part of the main sedimentation affected by
glaciotectonic disturbances.

Structures

In the Martørv Bakker Section, three types of structural

elements were studied: (1) imbricate duplexes domi-

nating the southern part of the section, (2) the normal
fault in the central part of the section, and 3) hydro-
dynamic brecciation contemporaneous with, or super-
imposed on, ball-and-pillow structures (Figs 63, 65).

Imbricate duplexes

The imbricate duplexes in the souther n part of the
section constitute rhomb-shaped segments 10 to 25 m
in

size bounded by low-angle thrust faults. Minor im-

bricates may occur along the thrust faults, but the thrust
faults are mainly narrow fracture surfaces without signi-
ficant brecciation.

A mini-scale example of duplex formation is shown

in Fig. 66. Although the structure is related to intrafor-
mational deformation of the beds, it illustrates instruc-
tively the formation of hanging-wall ramp propaga-
tion of a stacked footwall ramp. Thus the footwall ramp

is formed by the trailing edges of two duplex seg-
ments that were displaced one over the other to form

a single planar ramp for the propagation of the upper
thrust sheet. Flame-like upright minor anticlines are
interpreted as compressed hanging-wall anticlines

formed during the sequential propagation of the vari-

ous ramps. On top of the upper footwall hinge, a radial

flame structure probably indicates the site of incipient
diapirism (Fig. 66). The formation of foreland-dipping
thrust structures above the tip of a lower duplex seg-
ment is also apparent.

Normal fault

The normal fault in the central part of the section is
an uneven fault plane striking E-W with a dip of about
45° to the south. Displacement along the fault plane
is about 25 m, and a set of minor normal listric faults
displace the top of the hanging-wall block (Fig. 62).
The footwall block comprises the Lønstrup Klint For-
mation, which decreases in thickness southwards and
forms an irregularly folded drag along the fault plane.
At the top of the hanging-wall block, the diamict sed-
iments described above are discordantly superposed
on the light-coloured sand at the base of the Rubjerg
Knude Formation.

Hydrodynamic brecciation

Ball-and-pillow structures occur in the sand-rich parts
of the Lønstrup Klint Formation, where hydrodynam-
ic mud mobilisation created chaotic breccias (Fig. 63).
The initial size of the sand ball-and-pillow structures
is related to the primary thickness of the beds, but
subsequent to the sedimentary load deformation they
were distorted and deformed during thrust-fault related
mud remobilisation. In Fig. 63, the distorted ball-and-
pillow structures can be seen to be displaced by minor

thrust faults, and these thrust faults were intruded by
mobilised mud. The sequential development of this
hydrodynamic brecciation is illustrated in Fig. 65,
where three phases of deformation are recognised,
although these probably developed progressively
during thrust-fault displacement and related loading
of superposed thrust sheets.

Interpretation of structural development

The thickness of MB01 implies that the décollement
surface in the southern part of the section is situated

at the 20 m level. The thickness of MB03 is 30 m,
implying that the décollement level stepped down 10
m somewhere in the central part of the section. A
lower footwall ramp and a corresponding hanging-
wall ramp must therefore be included in the balanced
cross-section. The L/R-unconformity reference surface
on top of the MB02 thrust sheet was about 20 m above
present sea level prior to the normal fault displace-
ment, which indicates that a duplex 20 m in thickness
is situated below the trailing end of MB02. The lower
footwall ramp responsible for the fault-propagation
folding of the antiformal stack in the northern part of

the section, estimated from the bend of the trailing
ends of MB02 and MB03, must be situated below
MB02. The structural model therefore suggests that a
subsurface duplex was formed by segments of the
MB02 thrust sheet situated between the 20 and 30 m
levels (MB02u1-MB02u3). The footwall ramp thus
constitutes two 10 m thick duplex segments stacked
on top of each other.

Consequently, a hanging-wall anticline with a fore-

land-dipping limb formed above the hanging-wall
ramp of MB02 and was translated along a footwall
flat. The model further suggests that the hanging-wall

Fig. 66. A model of duplex formation is here illustrated by a mini-scale structure related to intraformational deformation of beds in

the Lønstrup Klint Formation, central part of Martørv Bakker Section. The duplex comprises two segments, which were derived from
the bed underlying the lower footwall flat (lower FWF). The footwall ramp for the segments is situated to the left outside the frame

of the figure. The lower segment is a relatively short one, which was thrust over by the upper segment during the push from the
ramping of the upper thrust sheet. During propagation up the footwall ramp, the trailing edges of the two segments were displaced

to form one planar ramp for the upper thrust sheet, which was further translated over the duplex to a foreland-dipping bend created
above the tip of the lower duplex segment. The flame-like upright anticlines are interpreted as compressed hanging-wall anticlines

formed during the sequential propagation of the various ramps. Note the radial flame structures at the upper footwall hinge
indicating incipient diapirism. The small normal faults to the left of the trowel (15 cm in size) are thought to reflect similar foreland-

dipping features in the subsurface. FWH , footwall hinge; FWR , footwall ramp; uFWF , upper footwall flat; HWF , hanging-wall flat; R ,
ramp. Photograph: June 1993.

structure is a composite feature partly constructed by
the hanging-wall anticline related to the tip of the
MB02u3 segment folded over the footwall ramp of
MB02u2, and partly by the hanging-wall anticline re-
lated to the translation of the main hanging-wall ramp
of MB02 along the 10 m level. The foreland-dipping
limb of this structure corresponds well with a 45°
south-dipping normal fault with a vertical displace-
ment of about 20 m.

It is therefore concluded that the northern slope of

the diamict sedimentary basin was formed by the nor-
mal fault reflecting the foreland-dipping limb of a
hanging-wall anticline. The souther n more gently dip-
ping slope of the basin was formed by the bend of
MB02 due to its propagation up along the footwall
ramp and flat of MB01. This footwall thrust fault is a
composite imbricate duplex, which hampers the ex-
act distinction of ramp-flat relationships. The slump-
folded units in the basin are interpreted as the result
of gravity slides derived from the crest of the hang-

ing-wall anticline or the tip of the MB04 thrust sheet
propagating from the north. The sediments filling the
basin represent redeposited material derived from the
thrust-fault elevated part of the Lønstrup Klint Forma-
tion, the coarse-grained clastics on the L/R-unconform-
ity, and the lowermost part of the Rubjerg Knude For-
mation. The basin is interpreted as a piggyback basin
with syntectonic deposition during the translation of
the MB02 thrust sheet.

Kramrende Section

From the south, the first significant macroscopic-scale
diapir occurs in the Kramrende Section (the Kram-
rende diapir). Although mobilisation features also
occur in sections farther to the south, this diapir is
regarded as the most distal in the glaciotectonic thrust-
fault complex. The thickness of the thrust sheet host-
ing the Kramrende diapir suggests it is related to the

Fig. 67. The northern part of the KR01 thrust sheet where the lithostratigraphic reference section of the Lønstrup Klint Formation

(Fig. 21) is situated. The thrust sheet is fault-bend-folded up along an initially low-angle ( c. 8°) footwall ramp, which was subse-
quently folded into the present more steeply dipping orientation. Note the reverse faults interpreted as small back-thrust faults.

Photograph: June 1993.

deep level of thrust-fault rooting, which is about 30 m
below the L/R-unconformity. The thrust sheet to the
south of the Kramrende diapir and two thrust sheets
to the north are included in the section because they
are all affected by the structures related to the diapir.
The frontal edge of the Kramrende Section is formed
by the footwall ramp beneath the first thrust sheet
(KR01, see Plates 1, 2). This thrust fault is identical
with the trailing-edge footwall ramp of the Martørv
Bakker Section, which is responsible for the marked
monoclinal fault-bend folding of the KR01 thrust sheet
(Fig. 67). The steps to the beach are situated in the
gully between the KR01 thrust sheet and the Kram-
rende diapir. The steps lead up to the summerhouse

area at Oddervej, and are referred to as the Kram-
rende steps or the Oddervej Trappe.

Tectonic architecture

The Kramrende Section consists of four thrust sheets
(KR01-KR04; Plates 1, 2). The frontal thrust sheet (KR01)

is ramped over the MB04 footwall ramp in the Mar-
tørv Bakker trailing thrust sheet. At the north end of
KR01, the L/R-unconformity is situated about c. 10 m
a.s.l., which indicates that the KR01 hanging-wall ramp
propagated along an inter mediate footwall flat (FWF).
The upper ramping along the MB04 footwall ramp is

Fig. 68. Ball-and-pillow structure

developed in the sandy turbidite bed
between 4 and 5 m in Fig. 21. The

structure is interpreted as a load
structure formed immediately after

sedimentation. Additional load struc-
tures can be seen at the base of the

sand bed, where flame structures related
to the underlying clayey bed intrude the

base of the sand bed. Above the ball-
and-pillow structure, pinch and swell

structures within the sand bed are also
interpreted as gravity load structures.

Photograph: June 1993.

Fig. 69. In the upper part of the KR04

thrust sheet in the Kramrende Section,
the Rubjerg Knude Formation forms a

piggyback basin, which is overthrust by
the BR01 thrust sheet in the souther n

part of the Brede Rende Section. The
thrust fault displayed in the photograph

is a hanging-wall flat for the thrust sheet
BR01 ( BR01HWF ) and footwall ramp of

thrust sheet KR04 ( KR04FWR ). A minor
satellite thrust fault was formed below

the main thrust at a late stage of fault
propagation after the sand of the

Rubjerg Knude Formation had been
somewhat compacted. Photograph: June

1984.

responsible for the fault-bend-fold appearance of the
KR01 thrust sheet. Above the frontal part of the MB04
footwall ramp and flat, the KR01 thrust sheet is folded
into a flat-topped anticline. In the involute part of this
anticline, a splint or horse is present (the KR01 splint).
This is a small thrust-sheet wedge torn off during thrust
propagation, which created peculiar anticlinal features
in the structural profile.

The KR02 thrust sheet takes the form of a major dia-

pir. Initially the diapir was a thrust sheet that was dis-
placed up along the KR01 footwall ramp and above
the back of the KR01 thrust sheet. The KR03 and KR04
thrust sheets situated on the back of KR02 are charac-
terised by marked dif ferences in the thickness of the
Rubjerg Knude Formation. In the KR03 thrust sheet,
the thickness is only about 8 m, whereas in KR04 the

thickness of the Rubjerg Knude Formation is up to 20
m. This indicates that the KR04 thrust sheet was thrust
over the upper footwall flat of KR03 at an earlier stage
compared to a probably longer time of deposition in
the piggyback basin of KR04. The c. 20° northerly dip-

ping inclination of the KR03 footwall flat and related
parallel structures is due to the bend caused by the
propagation of KR02 along the footwall ramp. The
main décollement level below the Kramrende Section
is situated at the 30 m level.

Sedimentary units

The description of the sedimentary units in the Kram-
rende Section is mainly based on sedimentological

Fig. 70. The KR01 footwall syncline

developed below the KR01 footwall
ramp ( KR01FWR ), which is overlain by

the KR02 hanging-wall flat ( KR02HWF ).
Note how the mobilised mud migrated

from the steeply dipping limb of the
footwall syncline up into the Kramrende

diapir, intrusively penetrating the thrust
fault. Photograph: June 1995.

Fig. 71. Mobilised mud from the lower

part of the Lønstrup Klint Formation in
the KR02 thrust sheet intruded the

turbidite sand beds in the upper part of
the formation. Photograph: June 1995.

logging of the Lønstrup Klint Formation in the KR01
thrust sheet (Fig. 21). The detailed section of the Ru-
bjerg Knude Formation at the top of this log is uncer-
tain due to poor exposure and dif ficulty of access.
The Rubjerg Knude Formation exhibits variations in
thickness throughout the Kramrende Section, and the
description herein is based on scattered observations.
A c. 1 m thick homogeneous, structureless sandy till
caps the Kramrende Section. No preferred clast fabric
has been recognised in the till, and its stratigraphic
position is uncertain, although the occurrence of rare
rhomb porphyry erratics may indicate an affinity with
the Norwegian Ice (Kattegat Till Formation).

Lønstrup Klint Formation

In the Kramrende Section, the lower part of the Løn-
strup Klint Formation mainly occurs in the Kramrende
diapir, within the KR02-03 thrust sheets. Remobilisa-
tion of the mud has obliterated primary sedimentary
structures, and the diapirism also affected the thrust
sheet KR03, so that only primary bedding is recognis-
able in the uppermost part of the formation. The pri-
mary sedimentary structures of the upper part of the
Lønstrup Klint Formation are reasonably preserved in
the KR01 thrust sheet (Fig. 20), although the sediments
here, dominantly constituting sandy turbidite beds (10-
50 cm thick), are strongly affected by hydrodynamic
brecciation creating ball-and-pillow structures (Fig. 68).

The top of the Lønstrup Klint Formation in the Kram-

rende Section is truncated by the L/R-unconformity,
which displays an erosional relief of 1-2 m.

Rubjerg Knude Formation

The Rubjerg Knude Formation varies in thickness from
only 6-8 m at the top of the KR03 thrust sheet to
about 20 m in the upper part of the KR04 thrust sheet
(it is absent in KR02). The main part of the formation
comprises thick-bedded, large-scale cross-bedded,
medium-grained light yellow-grey sand. Some beds
are rich in heavy mineral sand, which occurs in paral-
lel-laminated strata. In the KR04 thrust sheet, the heavy
mineral beds are present about 6 m above the L/R-
unconformity and again about15 m above the base.
These beds have a characteristic content of small (0.1-
1 cm), grey clayey mud-clasts, which are interpreted
to reflect erosion of muddy thrust sheet units in the
vicinity of the depocentre.

Pedersen (1987) described deposits, referred here

to the Rubjerg Knude Formation, that accumulated
syntectonically in footwall growth synclines. The de-
posits were characterised as 'banana' shaped basins,
and a similar type of sedimentary/structural featur e
occurs in the KR04 thrust sheet (Fig. 69). The Rubjerg
Knude Formation at the top of the Kramrende Section
can be regarded as a piggyback basin and the foot-
wall syncline as a growth-fault syncline. At the top of
the piggyback basin, large-scale trough cross-bedded
sand is truncated by small satellite thrust faults (simi-
lar to that shown in Fig. 69), which are truncated by
superposed c. 1 m thick trough cross-bedded sand beds.

Three succeeding developments of this inter ference
between thrusting and deposition reflect the syntec-
tonic depositional dynamics of the piggyback basin.

Structures

Structures of significance in the Kramrende Section
are described under the following headings: (1) thrust
faults, and in particular associated footwall ramps and
footwall synclines, (2) the Kramrende diapir, with the
diapiric breccias and intrusive structures formed by
mobilised mud, and (3) reverse faults, here interpre-
ted as back-thrust faults.

Thrust faults

The KR01 thrust sheet is bounded by the hanging-
wall ramp and flat (KR01HWR and HWF) at the base,
and the KR01 footwall ramp and flat at the top
(KR01FWR and FWF). The wedge-shaped geometry
of the KR01 tip implies that the KR01HWR had a low
angle of inclination, dipping about 15°N. Towards the
trailing end of the thrust sheet, the ramp passes into a
hanging-wall flat which is parallel to bedding in the
Lønstrup Klint Formation. This thrust fault now dips
at 25°N, although it is a hanging-wall flat situated on
a footwall flat. This is due to the fault-bend folding
related to the thrusting in the trailing part of the Mar-
tørv Bakker Section.

At its trailing end, the KR01 thrust sheet is folded

into a footwall syncline (Fig. 70). The bend of the
northern limb in the syncline lifted the L/R-uncon-
formity up to a position nearly 5 m higher than in the
horizontal involute part of the fold, and the bedding
in the Lønstrup Klint Formation was tilted into a near-
ly vertical position (Fig. 70).

The KR02 thrust sheet was thrust up along a c. 25°

dipping footwall ramp (KR01FWR) onto the upper
footwall flat above the Rubjerg Knude Formation of
the KR01 thrust sheet. The KR02 thrust fault is appar -
ently a hanging-wall flat which indicates a rather long
displacement for thrusting. The top sur face of KR02 is
a footwall flat upon which the KR03 hanging-wall flat
is situated, only bringing different stratigraphic levels
of the Lønstrup Klint Formation into contact. The dip
of the thrust fault is parallel to the dip of the KR02-
KR01 thrust fault. The footwall flat of the KR03 thrust
sheet is overlain by a c. 80 m long hanging-wall flat of
KR04. The Lønstrup Klint Formation is only about 8-
10 m thick above the hanging-wall flat (KR04HWF), in-

dicating a fairly long inter mediate flat (at the 10 m
level below the reference surface). At the trailing end
of KR04, the thickness increases indicating the pr es-
ence of a hanging-wall ramp at the base of the thrust
sheet, and a footwall syncline similar to that described
in KR01 is present. In the upper part of the KR04 thrust
sheet, the sediments deposited in the footwall growth
syncline became overturned along the northern limb
during translation of the hanging-wall ramp of BR01,
as described above (Fig. 69).

Kramrende diapir

The Kramrende diapir constitutes the main part of
KR02. The diapirism also affected the trailing end of
KR01 (Fig. 70) as well as some parts of KR03. As shown
in Fig. 71, mud of the lower part of the Lønstrup Klint
Formation in KR02 became mobilised and intruded
the overlying turbidite sand beds and also penetrated
upwards into the overlying KR03 thrust sheet. Figure
70 illustrates a thrust fault penetrated by intrusive mud
at the footwall ramp of KR01. Here, the mobilised mud
from the steeply inclined northern limb of the foot-
wall syncline intruded into the mud-breccia along and
above the hanging-wall flat of KR02. A large part of
the boundary between KR02 and KR03 was deformed
in a similar way and the primary layering destroyed.

Reverse faults

In the Kramrende Section, significant steeply dipping
reverse faults occur in the northern part of KR01 (Fig.
67), and in the middle part of the KR03 thrust sheet.
The displacement is only about 30-50 cm on the steep
south dipping faults in KR01; the spacing between
the faults varies from 3-9 m, and often the faults can
be traced down into the tectonic breccia above the

Fig. 72. Reverse fault-splay fan developed on the back of KR03 and also displacing the overlying KR04 thrust sheet. The structure
is interpreted as a back-thrust fault-splay formed during the KR03 propagation over the upper footwall ramp situated on the back of

KR02. Photograph: July 1994; figure at fault-splay centre for scale.

hanging-wall flat. In the KR03 thrust sheet, the reverse

faults form a fault splay fan with individual faults dip-
ping moderately to steeply to the south (Fig. 72); dis-
placement varies from about 20 cm up to about 3 m.

The reverse faults appear to have formed during

thrust-sheet propagation over a ramp hinge and are
interpreted as back thrusts. A bend over a shallow
dipping ramp will only result in minor displacement
on steeply dipping back thrusts, whereas bending over
steeply dipping ramps creates low-angle back thrusts
with potentially greater displacements.

Interpretation of structural development

The balanced cross-section indicates that the KR01
thrust sheet was about 350 m long, of which a major
part of the front tip has been eroded away. The amount
of displacement is deduced from a series of balanced
approximations to be 160 m (see Plate 2). The foot-
wall ramp of KR01 is interpreted to root in the 30 m

décollement level, which indicates that the lower hang-
ing-wall ramp of KR01 was displaced onto the inter-
mediate footwall flat above the trailing segment of
MB04. Thus the lift and steep tilt of the northern limb
in the KR01 footwall syncline is interpreted to have
formed during the displacement of the lower hang-
ing-wall ramp (KR01HWR) along the trailing-end foot-
wall flat of MB04 (MB04FWF).

The tip of the KR02 thrust sheet has been eroded

away. To avoid exaggeration, the thrust fault is inter-
preted to have continued only about 15 m up in the
air further to the south, which implies that displace-
ment of KR02 was in the order of 50 m. The main part
of the KR02 thrust sheet present in the cross-section
is above the hanging-wall flat brought up from the 30
m décollement level. It is evident that the mobilised
mud was derived from this low level and that it was
activated in diapirism during the thrust-sheet propa-
gation over the footwall ramps (KR01FWR) and its
hinge bend.

It is difficult to estimate the displacement for the

Fig. 73. The Brede Rende diapir in the frontal part of the Brede Rende Section. The frontal part of the BR02 thrust sheet was thrust

up on its hanging-wall ramp ( BR02HWR ) along the footwall ramp, which turned into the KR04 footwall flat ( KR04FWF ). At an
early stage of thrusting, probably while the hanging-wall ramp passed by a lower footwall hinge, diapirism developed. The mobil-

ised mud also intruded the L/R-unconformity and formed mushroom-shaped diapirs in the Rubjerg Knude Formation. Photograph:
June 1984.

Geological Survey of Denmark and Greenland Bulletin

Nr. 8 pp 60-89, Structural analysis of the Rubjerg Knude Glaciotectonic Complex, Vendsyssel, northern Denmark

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