Vol. 8 pp 120-147, Geol. Surv. Denmark and Greenland Bulletin

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121

from the 30 m décollement level. The hanging-wall
flat of RF06 rests on the upper flat of RF05, where no
deposits of the Rubjerg Knude Formation have been
recognised. Thus the two thrust sheets occur as a block
of Lønstrup Klint Formation 60 m thick, separated in
the middle by a thrust fault. The L/R-unconformity in
the RF06 sheet is located at about 10-15 m above sea
level. Thus, the RF06 sheet was faulted up on an in-

termediate flat above the trailing edge of RF05, prob-
ably while both were transported along the lower foot-
wall flat on top of the lower trailing duplex segment
of the Grønne Rende Section.

Sedimentary units

In the Rubjerg Knude Fyr Section, the lower stratigra-
phic levels of the Lønstrup Klint Formation are exposed,

although they are commonly deformed either by mud-
mobilisation or thrust-fault shearing. The Rubjerg Knu-

de Formation above is poorly exposed, partly due to
sand scree derived in part from the formation itself,
and partly from the up to 50 m high sand dunes above
the cliff. No further description of the formations is
given here.

Facing page - upper:

Fig. 99. Normal faults displacing the top of the RF03 thrust
sheet in the Rubjerg Knude Fyr Section. Note the footwall

syncline folded below the hanging-wall ramp at the top of
the cliff section. Photograph: June 1984.

Facing page - lower:

Fig. 100. Normal fault ( NF ) displacing the tip of the RF04
thrust sheet, which prior to normal faulting was thrusted

along the hanging-wall flat of RF04 ( RF04HWF ). Photograph:
July 1994.

Fig. 101. Thrust-fault brecciation related to the lower hanging-wall ramp and flat in the Rubjerg Knude Fyr Section. The brecciation

fabric that is typical of the fine-grained sand turbidites and laminated clayey muds (compare with primary sedimentary features in
Figs 22, 23) was produced by low-angle anastomosing shearing. Photograph: September 1985.

122

Structures

Two types of deformation alter the primary sedimen-
tary architecture of the Rubjerg Knude Fyr Section. The

first type is anastomosing thrust-fault brecciation re-
lated to the zone above the hanging-wall ramp with
fine-grained turbidites. The second type is the mud-
mobilisation and mesoscopic-scale polydiapirism,
which is common in the clay-rich lower part of the
thrust sheets. These deformation types have to be
considered in the evaluation of the balance calcula-
tion. Only the anastomosing thrust-fault brecciation
will be further described in this section; descriptions
of diapirism are given under the Kramrende, Brede
Rende, Sandrende and Moserende Sections.

Anastomosing thrust-fault brecciation

The most significant mesoscopic-scale structure rec-
ognised in the Rubjerg Knude Fyr Section is related to
thrust-fault brecciation in the lower part of the Løn-
strup Klint Formation. The brecciation fabric that is
typical of the fine-grained turbidites and laminated
clayey muds was created by low-angle anastomosing
shearing. The shear surfaces and thrust-fault displace-
ments are located in the clay-rich laminae, whereas
the segments bounded by the anastomosing fractures
consist of silty mud lithologies (Fig. 101). The br ecci-
ation extends from the lower hanging-wall ramp-and-
flat up to 10 m above the sole of the sheets.

The anastomosing thrust faulting indicates that sig-

nificant differential movements developed in the sub-

surface during thrust-fault propagation, which illus-
trates the nature of the displacement-related shearing

and which may account for some of the volume prob-

lems arising from construction of the balanced cross-
section.

Interpretation of structural development

The compression (shortening) in the Rubjerg Knude
Fyr Section is about 48%, calculated from the meas-
ur ed length of the section of 270 m (= L₁) and the

balanced length of about 520 m (= L₀). This implies

that the thrust sheets in the section have been dis-
placed upwards at the ramp originally situated at the
trailing end of RF04 and transported to the position of
the footwall ramp of GR13. The lower flat is still the foot-

wall flat on top of the lower duplex segment of the

Grønne Rende Section. Thus, a considerable amount of

lateral translation is apparent in the Rubjerg Knude
Fyr Section.

The appearance of the normal fault with down-fault-

ed noses of the RF03 and RF04 sheets indicates that
differential movements, including duplex development
of the GR01-GR06 lower segments, may have occurred
to create the foreland-dipping features in the RF02-
RF03 piggyback basin.

The interesting structure in RF05 is the lower hang-

ing-wall ramp, which has to correspond to a footwall
ramp at the trailing end of RF04. The footwall ramp-
ing probably also included propagation along a foot-
wall ramp of a lower duplex segment of RF04 (RF04u).
The present orientation of the RF05 lower hanging-
wall ramp is more or less vertical, indicating three
steps of ramping. The final tilting was due to the ram-
ping of the upper footwall ramp of GR13, the middle
phase of ramping was up along the footwall ramp of
the piggyback basin in the normal fault displaced RF04,
and the initial ramping was probably a complex pro-
pagation over several smaller ramp-steps that separa-
ted RF06 from RF05.

The uppermost part of RF06 shows a marked to-

pography, indicating that at an early phase of defor-
mation it was elevated up to a level of erosion, before
subsequent sedimentation. This sedimentation was pro-

bably of relatively short duration before over-thrusting

of the Stortorn Section trapped the piggyback basin.

Stortorn Section

Stortorn is the name of the very steep and muddy cliff
in the central part of the Rubjerg Knude cliff section.
On old drawings of the beach and the coastal cliff,
Stortorn is depicted as a steep, wild looking castle-
like cliff in the distant horizon, emphasising the ro-
mantic scenery of this remote place (e.g. engraving
by C. Neumann 1884, reproduced in Vendsyssel nu og
da , 1981). In recent times, the cliff has also been the
location of major landslides, which in some cases trav-
elled more than 100 m out into the sea. In general,
the sea reaches close up to the vertical cliff, and due
to the muddy and slippery cliff surfaces and the clay
pavement in the zone of breakers, it is the most diffi-
cult place to pass along the coast.

In the Stortorn Section, the deepest level of thrust-

ing occurs where the décollement zone is located at a
depth of 40 m stratigraphically below the reference
surface of the L/R-unconformity, which is about 45 m

123

below sea level. From this deep level, the thrust sheets
were elevated up to the exposed position in the cliff
section. Coinciding with this, the thrust sheets con-
tain the deepest levels of the stratigraphy, and beds
of marine and glaciomarine clay can be identified by
the occurrences of arctic marine fossils. Moreover, the
Stortorn Section contains the key features for under-
standing the structural and dynamic problems of the
adjacent Rubjerg Knude Fyr and Grønne Rende Sec-
tions. The key features are flat-lying duplex complex-
es formed by ramping up of the relatively long, lower
thrust-sheet segments onto a high flat level. This is
reflected in an elevation of the L/R-unconformity up
to a height of c. 40 m above sea level in the cliff sec-
tion.

Tectonic architecture

The Stortorn Section is divided into ten thrust sheets
annotated ST01-ST10. The southern boundary of the
section is the frontal hanging-wall flat of ST01, which
coincides with the footwall ramp of the RF06 thrust
sheet in the Rubjerg Knude Fyr Section. The norther n
boundary is the trailing footwall thrust of ST10 along
which the frontal hanging-wall ramp of the Moserende
Section was thrust.

The southernmost three thrust sheets form a sepa-

rate group of high-level thrust sheets. The L/R uncon-
formity is here situated at an elevation of 35-40 m
above sea level. The central part of the section is
formed by a series of thick thrust sheets of clayey,
partly mobilised, mud, which are situated above hid-
den duplexes in the subsurface. This complex extends
about 150 m along the cliff section at Stortorn. In the
northern part of the section, upright mud diapir-dom-
inated thrust sheets occur with complexly developed
piggyback basins.

ST01 thrust sheet

The southernmost thrust sheet in the Stortorn Section
(ST01) is wedge-shaped, c. 160 m long, with an initial
25° dip of the frontal hanging-wall ramp. The foot-
wall ramp (FR06 trailing edge) dips at about 45°, which
creates a problem in the balancing. It is obvious that a
splint (or horse) corresponding to a triangle with an
acute angle of 20° must be hidden somewhere in the
deeper structure. The trailing end of ST01 is 30 m thick.
However, the Lønstrup Klint Formation is deeply erod-

ed in the central part of ST01, which truncates the
L/R-unconformity.

ST02 thrust sheet

The ST02 thrust sheet was also elevated to a height of
35-40 m in the cliff section. The hanging-wall ramp is
vertical and forms a right-angle with the horizontal
bedding in the piggyback basin of ST01. This indi-
cates that final up-thrusting of the frontal hanging-wall

ramp took place in an upright position during sedi-
mentation on the back of ST01. The ST02 thrust fault
was rotated at least three times before propagation
up along the footwall ramp of ST01. The initial dip of
this ramp was relatively steep, about 40°, as indicated
by the angle between the thrust fault and the bedding
in the Lønstrup Klint Formation of ST01. Furthermore,
the problem related to the change in ramp angle re-
curs. In the balancing of the thrust structure, a splint
volume must be calculated for, corresponding to the
triangle created by the initial thrust angle and the fi-
nal steeply inclined thrust fault.

ST03 thrust sheet

The ST03 thrust sheet is not elevated as much as ST01
and ST02; the L/R-unconformity is only situated at
about 30 m above sea level. The Lønstrup Klint For-
mation was deeply eroded before sedimentation in
the piggyback basin was initiated, probably due to
marked relief during ramp propagation.

ST04 thrust sheet

The lowest position of the L/R-unconformity in the ST04

thrust sheet is about 13-15 m above sea level, which
demonstrates a shallower level of ramping than in ST01-

ST03. The 45° steeply dipping thrust fault between
ST03 and ST04 roots down to the décollement zone
and propagated up along the footwall ramps of the
subsurface duplex segments beyond ST01-ST03. The
difference between initial and final angle of ramping
also created a balancing problem for ST04. The fron-
tal part of the hanging-wall ramp of ST04 only had a
dip of 18-20°, whereas the footwall ramp now dips at
c. 45°. Therefore a splint (with an area of 630 m² in

the cross-section) is envisaged in the subsurface. The
ST04 ramping over this splint is interpreted as the rea-

124

son for the elevation of the L/R-unconformity up to c.
15 m above sea level.

ST05 thrust sheet

The ST05 thrust sheet is one of the most important
structures, not only in the Stortorn Section but also in
the Rubjerg Knude Glaciotectonic Complex as a whole.
It involved thrusting of the deepest décollement lev-
el, which introduced a complex framework due to
the large number of duplex segments involved. The
ST05 thrust sheet was thrust up along the footwall
ramp of ST04. The dip of the thrust fault increases
from 35° at the beach level to 70° at the top of the cliff
section. The tip of the thrust sheet was finally dis-
placed horizontally over the top of the piggyback basin
of ST04. The thrust displacement along the hanging-wall

thrust fault is estimated to be in the order of 90 m.

The Lønstrup Klint Formation of ST05 is dominat-

ed by mud diapirism and polydiapiric structures up to
5 m in vertical scale. In the middle part of the thrust
sheet, where the thickness of the initially wedge-
shaped frontal part was 20 m, a deeply eroded trough
was formed. The L/R-unconformity on the northern
flank of this erosional depression is situated nearly 50
m above sea level. This is about the highest elevation
of the reference surface, and was caused by thrust
duplication of the thrust sheet in the subsurface du-
plex complex.

ST06 thrust sheet

The ST06 thrust sheet is poorly exposed and mud-
mobilisation and internal diapirism obscure primary
structures. The thickness of the thrust sheet is up to
40 m, measured from the frontal hanging-wall thrust
up to a small pocket of Rubjerg Knude Formation sand
that for ms the remnant of a piggyback basin. The front-
al thrust is drawn with some uncertainty, because a
large part of it is penetrated by diapirism intruding
from the back of ST05. A minimum displacement of
40 m is inferred, which is incorporated in the model-
ling of the balanced cross-section. This implies a rath-
er complex structural assemblage of the subsurface
lower duplex segments of ST05, ST06 and ST07.

ST07 thrust sheet

The ST07 thrust sheet is nearly vertically orientated
with a frontal ramp rising from 70° to vertical, along
which a displacement of 28 m is estimated to have
occurred. The L/R-unconformity surface is also steep-
ly dipping, and is even overturned at the top. The
lower part of the thrust sheet is mainly covered by
scree, but it is possible to trace the line of the uncon-
formity down to the level of the beach in the cross-
section. This implies that the thrust sheet has not been
thrust up to be displaced along an intermediate ramp
but is only tilted due to the main ramping, first along
the thrust fault of ST06 and finally on its own hang-
ing-wall ramp. The ramping is also reflected in the
deposition in the piggyback basin where three super-
posed angular discordances are recognised. The de-
posits in the piggyback basin are c. 15 m thick; at the
base of the succession, the R-onlap starts with an an-
gle of 45° and terminates with a 90° angle, indicating
deposition in the basin while the thrust sheet was
vertically orientated. In the uppermost bed, minor
slump folds are present, indicating the effect of the
ST08 thrust nose approaching from the north.

ST08 thrust sheet

A double ramp synclinal structure, similar to the one
occurring in the piggyback basin of ST05, is recog-
nised in thrust sheet ST08. The L/R-unconformity in-
cises through the Lønstrup Klint Formation and down
into the thrust-fault surface of the hanging-wall ramp.
The lateral distance between the ramps is only about
25 m and the basin is less than 10 m deep. The sedi-
ments in this piggyback basin show large-scale trough
cross-bedding accentuated by synclinal folding. The
Rubjerg Knude Formation covers a feature that repre-
sents the erosional remnants of a detachment anti-
cline on the northern limb of the basin. On the north
side of this structure, the initial stratification above
the L/R-unconformity shows clear R-onlap, corre-
sponding to the inclination parallel to the tilt of the
lower ramp. The unconformity is elevated up to 20 m
above sea level, indicating that the ST08 thrust sheet
was lifted up by at least two subsurface duplex seg-
ments. These hidden segments are annotated ST08u1
and ST08u2. The displacement along the footwall ramp
of ST08 is estimated at 78 m, mainly along the thrust
fault dipping at 30°.

125

ST09 thrust sheet

The ST09 thrust sheet is a c. 30 m thick sheet bound-
ed by a 60° dipping hanging-wall flat thrust up onto
the footwall ramp of ST08 back and the 60° dipping
footwall thrust fault of ST10, which truncates the ir-
regular structures in the upper part of the thrust sheet.
The displacement along the hanging-wall ramp is es-
timated at c. 60 m. Although the Lønstrup Klint For-
mation in ST09 is characterised by internal diapirism,
the features of a hanging-wall anticline can be recog-
nised at the top of the cliff section. During translation
of two or more footwall ramps, an irregular synform
formed and created the depocentre of a piggyback
basin. The L/R-unconformity is here elevated to 5-10
m above sea level, corresponding to propagation up
onto the ST08u2 duplex segment.

ST10 thrust sheet

The ST10 thrust sheet is about the same size as the
ST09 sheet, and also has steeply dipping bounding
thrust faults. The most remarkable structure in the ST10
thrust sheet is the structural complexity of the piggy-
back basin. The L/R-unconformity forms an isoclinal
recumbent syncline, with the upper limb formed by
the mud-mobilised Lønstrup Klint Formation, and above

this a minor synclinal trough appears. This structure
is best described as a detachment anticline, which
developed into a diapir with a reverse fault displacing
the northern limb of the structure into a mushroom-
shaped structure, similar to the diapir in the Sandrende
Section. At a late stage of thrusting, the piggyback
basin was rotated 60° and the diapir-developed de-
tachment anticline collapsed into the recumbent struc-

Fig. 102. Isoclinal upright anticline

formed in the lower part of the Lønstrup
Klint Formation in the frontal part of the

Stortorn Section. The right limb of the
anticline constitutes an imbricate duplex

formed by connecting thrust-fault splays
(white dot-and-dash lines). The fold is

interpreted as a hanging-wall anticline
developed during fault propagation and

successive imbricate stacking (compare
with Fig. 59). Photograph: August 2001.

126

ture. The L/R-unconformity is elevated up to 15-18 m
above sea level indicating a ramping of the ST08u
duplex segment as well as the trailing segment of ST09.
An estimated displacement of 73 m along the hang-
ing-wall ramp of ST10 still leaves some subsurface
segments to be balanced in the structure below the
Moser ende Section to the north.

Sedimentary units

The most important sedimentary feature in the Stor-
torn Section is the exposure of the Stortorn Forma-
tion, which is the lower most stratigraphic level in-
volved in the Rubjerg Knude Glaciotectonic Complex.
The Stortorn Formation is located at the lower hang-
ing-wall ramp of the ST05 thrust sheet, where it for ms
a duplex segment about 3-5 m thick at the base of
the cliff. To date, it has not been possible to measure
a sedimentological log of the formation at this locali-
ty, partly because the formation is strongly sheared
by anastomosing fractures, and partly because land-
slide activity precludes more detailed stratigraphic
description.

Structures

The contact between mobilised, intrusive mud and
stratified mud has been observed in many places, but
this characteristic is better illustrated in the Moserende
Section (see below). Anastomosing thrust faults and
tectonic breccias occur commonly in the ST05 and
ST06 thrust sheets. However, due to the difficult field
conditions, detailed investigations have not been car -
ried out.

In the dark clayey mud of thrust sheet ST01, an

upright nearly isoclinal anticline has been observed
(Fig. 102). This fold is considered to represent a hang-
ing-wall anticline that was subjected to an advanced
stage of deformation during ramp propagation. This
stage compares well with the model of duplex for ma-
tion described by Mitra & Sussman (1997), in which
the growth of imbricates derived from successive con-
necting splays results in steepening of antiformal stacks
for med by fault-propagation folding of duplexes. Suc-
cessive growth of duplex elements corresponds well
with the interpretation presented below.

Interpretation of structural development

The cross-section (Plate 2B) provides a model for the
structures below the frontal part of the Stortorn Sec-
tion, which requires four duplex segments forming a
duplex complex, on top of which thrust sheets ST01,
ST02 and ST03 have been thrust along the footwall
flat. The structural interpretation of a duplex stacking
of subsurface segments below the frontal part of the
Stortorn Section is based on two lines of evidence:
(1) the missing balance of the lower segments related
to the Grønne Rende Section, and (2) the high eleva-
ted position of the L/R-unconformity in this part of
the section. Thus the lower duplex complex in the
frontal part of the section is interpreted to represent
stacking of the trailing lower segment of GR01, al-
though an alternative differential duplex-segment dis-
placement is also possible.

From geometric considerations, it is evident that

the 20 m and 30 m décollement levels must have been
pervasive throughout the proximal part of the thrust
structure. Thus the duplex in the Stortorn Section con-
sists of segments c. 10 m thick. Mobilisation and the
internal polydiapirism have obscured the boundaries
of these segments, which are the lower and interme-
diate footwall and hanging-wall flats respectively.
However, in a model for reconstruction, these volumes

are regarded as solid thrust sheet, i.e. the duplex seg-
ments (represented by annotated areas in Plate 2). In
the description and solution of the structural problem
related to differential thrust faulting of the lower du-
plex segments, three main types of fault-bend-folded
segments are distinguished (Fig. 103).

Fig. 103. Schematic illustration of the three types of fault-bend
folding of duplex segments. Type 1 is referred to as an L-struc-

ture, type 2 as an S-structure and type 3 as a G-structure (G
chosen due to similarity with the Greek capital letter gamma

(Γ)). The footwall ramp dips at about 45°, the shortening be-

tween the underlying footwall ramp and the overlying hang-

ing-wall ramp is 43%, the initial length (L₀) of the thrust sheet is

c. 100 m, compared to a thrust-sheet thickness of 40 m, and a

thickness of 10 m for the individual duplex segments.

127

1. A duplex segment with one part of the segment

resting on the lower flat and the other parallel with
a ramp (L-structure).

2. A duplex segment which has the trailing part par-

allel with the lower flat, the intermediate part par-
allel with a ramp, and the frontal part parallel with
the upper flat, thus giving the shape of a S.

3. A duplex segment with the trailing part of the seg-

ment located parallel with the ramp and the front-
al part parallel with the upper flat (Γ-structure).

The stacking of the duplex below the ST01, ST02 and
ST03 thrust sheets started when the lower segments
were thrust up into the first type duplex bend during
ramping towards the footwall ramp of RF06 (trailing
end of the Rubjerg Knude Fyr Section). This probably
marked the end of the lateral translation along the
lower flat levels and the initiation of stacking along
steeply dipping thrust faults. This resulted in the rota-
tion of all the previously formed structures and crea-
ted the odd trough structures in the double ramp syn-
clinal troughs. The final up-thrusting along steeply
dipping thrust faults, which occurred contemporane-
ously with the uppermost sedimentation in the piggy-
back basins, was probably also contemporaneous with
the initiation of ramping of ST05 from the lowest level.
One way to demonstrate this is to focus on the thrust-
fault development of ST04. The ST04 thrust fault act-
ed as the ramp that pushed on the trailing end of the
duplex below ST01, ST02 and ST03. When the push
on this footwall ramp ended and the ST04 thrust sheet
was displaced up over the footwall ramp of ST03 it
resulted in a shortening of 60%. The balanced length
of ST04 is c. 200 m. Thus, the deep level ST05 ramp
must be responsible for removing the 120 m lower
long segment originally situated below ST04. There-
fore about half of the ST04 thrust sheet also involves
thrusting down to the 40 m décollement level. In the
model, this ST04u segment was up-thrust to form a
first type of duplex-segment structure as the first low-
er-segment imbricate in the subsurface of ST05.

However, it should be appreciated that a whole

unit of the thrust segments between the 20 m flat lev-
el and 30 m décollement level has to be incorporated
in a differential thrust model. The simplest model for
this is to dissect the lower duplex segments into sheets
with an average length of c. 100 m. With each seg-
ment bend in a type 2 ramping and with an equal
distribution of the frontal and trailing part on the up-
per and lower flat, a series of double ramp synclines
would be created - comparable to the piggyback ba-

sins seen in ST10, ST09, ST08 and ST05. Similar basins
may have existed in ST07 and ST06, but, if present,
were removed by glaciotectonic truncation.

One of the central problems in describing the dy-

namic development of the Rubjerg Knude Glaciotec-
tonic Complex is understanding the formation of the
lower ramp below the ST05 thrust sheet. It is known
that the hanging-wall ramp is displaced up along the
ST05 thrust fault to be exposed in the cliff section at
Stortorn. However, a central question is - where was
the footwall ramp for the lower hanging-wall ramp of
ST05 situated?

According to the balanced cross-section, the ST05

ramp should be situated about 7800 m from the front-
al ramp in the Ulstrup Section and the footwall ramp
for the lower ST05 ramping should be situated on the
far side (north) of the Lønstrup village. However, this
is not the position of the ST05 ramp. The distance to a
hidden footwall ramp can only be fixed relative to the
displacement in front of the lower ramp when it was
activated during the change of décollement level from
the 30 m level down to the 40 m flat level. The rela-
tive displacement on the ST05 thrust fault is c. 90 m,
measured from the tip of the thrust sheet along the
hanging-wall ramp-and-flat down to the lower décol-
lement sur face. The main problem is related to the
compression documented south of the Stortorn Sec-
tion. When this is considered in the balanced cross-
section, it gives the geometric point for the hanging-
wall ramp 7800 m from the frontal ramp in the Ulstrup
Section. However, the distance in the Rubjerg Knude
cross-section from this ramp to the central part of the
Stortorn Section is only 3800 m. The solution to this
problem is that the ramp was first formed after all the
former translation in the higher flat levels had passed.
To understand this, one has to imagine that the upper
part of the Lønstrup Klint Formation at Grønne Rende
( c. 3800 m from the frontal ramp in the Ulstrup Sec-
tion) was originally situated above the Stortorn For-
mation at the ST05 lower ramp. However, the ramp
was first formed when the Rubjerg Knude Fyr Section
was displaced towards the Grønne Rende Section
which itself was compressed against the Stenstue and
Sandrende Sections, which were all displaced over
the initial position of the Brede Rende and Kramrende
Sections. Only then was the ST05 lower ramp activat-
ed, and the remaining northern part of the Rubjerg
Knude Glaciotectonic Complex was displaced along
the lowermost décollement zone.

128

Moserende Section

Between Rubjerg Knude Fyr and Mårup Kirke, some
small peat-bogs occur in depressions in the dune land-
scape. This area of bog-filled depr essions formerly
extended to the west, and the present cliff section
intersects one of these bogs where peat (martørv) is
exposed in the upper most part of the cliff, similar to
the situation in the Martørv Bakker Section. A former
gully here was named Moserende, and the name is
adopted her e for the section north of the Stortorn
Section.

The most impressive feature in the Moserende Sec-

tion is the syntectonic evolution of the piggyback
basins during polyphase thrust propagation (Fig. 104).
Unusual sedimentological features are developed in
the Rubjerg Knude Formation, reflecting the tectonic
deformation, notably structures described as fissure
strata (Sjørring 1977). These are thin sedimentary beds
occurring as discordantly incised wedges in ground-
fr ozen sediment, here present in the gr owth-fault syn-
clines related to the piggyback basins (Fig. 105).

Tectonic architecture

The Moserende Section comprises 13 relatively thick
thrust sheets annotated MR01-MR13. In the section,
three larger piggyback basins are preserved, one in
the frontal, souther n part and two in the northern part
of the section. The L/R-unconformity surface at the
base of the piggyback basins was elevated to various
levels in the cliff section, reflecting the differentiated
type of ramping throughout the section.

The leading-edge thrust in the Moserende Section

is the hanging-wall ramp of MR01, which coincides
with the footwall thrust fault on the back of the ST10
thrust sheet. To the north, the section is bounded by
the hanging-wall thrust at the base of the c. 40 m
thick MK01 thrust sheet, which forms the southern front

of the Mårup Kirke Section. The MK01 thrust sheet
was thrust up along a steeply dipping footwall ramp
and subsequently displaced over the upper footwall
flat on top of the piggyback basin of MR13 in the
northernmost part of the Moserende Section.

It should be noted that the main frontal part (top-

Fig. 104. The piggyback basin of the MR02 thrust sheet. A sequentially developed growth-fault footwall syncline was formed below
the hanging-wall ramp of MR03 ( MR3HWR ). Note the fissure strata cross-cutting the bedding ( arrow ) in the growth-fault footwall
syncline. Photograph: June 1984.

129

most part) of the thrust sheets shows a marked drag
and truncation due to the formation of a glacitectonite
on top of the cliff section.

MR01 thrust sheet

In the cliff section, the MR01 thrust sheet forms a
massive unit of mobilised, structureless grey mud. The
exposed thickness close to the beach level is nearly
30 m. The hanging-wall thrust dips at about 60°N,
and the unconformity surface, which dips at about
45°, is elevated c. 15 m above sea level. This indicates
that the MR01 thrust sheet is situated above two low-

er duplex segments. According to the balancing, these
segments constitute a lower segment of the MR01 thrust
sheet (MR01u) and a segment originating from the
lowest, northern part of the Stortorn Section. The MR01u

segment, which exists as a consequence of the esti-
mated c. 46 m displacement along the 60° tilted front-
al hanging-wall ramp, is separated into two different-
ly displaced segments in the balanced cross-section.
This is a feasible explanation but not the only one of
several possible solutions for the displacement struc-
ture in the subsurface, which include differential lat-
eral displacement along each lower 10 m level as well
as mud diapirism.

Fig. 105. Detail of the fissure strata

indicated in Fig. 104, illustrating that
climbing ripple cross-laminated sands

were deposited in the initially horizontal
wedge-shaped fissure extending out into

the growth-fault syncline deposits.
Photograph: June 1984; notebook ( c. 18

cm long) for scale.

130

MR02 thrust sheet

The MR02 thrust sheet is nearly 40 m thick and is
dominated by mud mobilisation and internal chaotic
structures reflecting polydiapirism and internal flow.
The sheet is divided internally by a thrust-fault zone
with differential thrust movements, which could be
interpreted as a separation of the sheet into two indi-
vidual thrust sheets. However, as the segments are
not separated by a piggyback basin they are regarded
as a single amalgamated sheet.

The displacement along the hanging-wall ramp is

the same order of magnitude as for MR01 ( c. 47 m)
and the ramp is divided into an upper low-angle part
with an initial dip of only 20° and a lower steeply
dipping part with an initial ramp-angle of about 45°.
Due to subsequent rotation, the upper part of the ramp
is now orientated vertically while the lower part has a
steep listric dip to the south. The footwall ramp (up-
per part of MR01) has an initial dip of 45°, which cre-
ates a space problem in balancing the section and
makes it necessary to introduce a splint segment be-
tween MR01 and MR02 in the subsurface. The splint
was probably sheared and squeezed out and is likely
to have been included in the general mud mobilisa-
tion. However, it is included in the balanced profile
in order to deal with the ramp-angle-space problem
(Plate 2).

The geometry of the L/R-unconformity at the top

of the Lønstrup Klint Formation in the MR02 thrust
sheet is very irregular with a peculiar c. 8 m high ob-
stacle. This is very similar to the structure in the ST08
thrust sheet in the Stortorn Section. It was probably
formed by a detachment anticline on the northern flank
of the piggyback basin in the external part of the MR02
thrust sheet, where it was subsequently buried by the
Rubjerg Knude Formation sand. The unconformity is
elevated about 5 m above sea level, indicating that
the MR02 thrust sheet has only stepped up one level
of the lower segments from where it is bent up along
its hanging-wall ramp. The detachment anticline was
probably formed during the ramping of this lower
segment.

MR03 thrust sheet

The Rubjerg Knude Formation in the piggyback basin
on top of MR02 and MR03 is here envisaged as a sin-
gle large basin situated in the frontal part of the Mo-
serende Section. The basin extends about 70 m along

the cliff section. Three upright standing peaks repre-
sent the tips of three small thrust sheets that disturbed
the basin by small displacements. These thrust sheets
represent imbricates in the upper most part of the MR03
thrust sheet. Since the main part of the MR03 thrust
sheet can be viewed as one large sheet subjected to a
single mode of displacement, the three imbricates are
referred to as MR03a, MR03b and MR03c.

The L/R-unconformity in MR03b and MR03c can be

traced down below sea level, indicating that the main
part of MR03 was displaced along the lower décolle-
ment level prior to the displacement up along the 45°
dipping frontal footwall ramp. However, the frontal
hanging-wall ramp of MR03 is now vertical. It is only
necessary to tilt the initial ramp on another 45° dip-
ping ramp to achieve this, and although it is a very
steep inclination for ramping, there are no obvious
reasons for introducing more ramps. The steep ramp
angle of the MR03b thrust forms part of the same frame-
work. The initial dip of the MR03b hanging-wall ramp
was 18°, and the thrust fault is now vertically orientat-
ed due to the ramp-bending mentioned above. The
displacement relative to MR03a is only about 10 m
and the sand beds of the Rubjerg Knude Formation
were folded in a footwall syncline of MR03a during
the hanging-wall thrusting of MR03b.

MR04 and MR05 thrust sheets

The MR04 and MR05 thrust sheets are closely related
and only separated from each other by a relative dis-
placement of about 25 m along the hanging-wall thrust
of MR05. In contrast, the displacement along the MR04
hanging-wall thrust is about 80 m. Both thrust sheets
are dominated by mud diapirism, structures that may
have originated as one large diapir that was only dis-
placed by the late MR05 hanging-wall ramp. The thick-
ness of the Lønstrup Klint Formation in the thrust
sheets is up to 30 m in the cliff section, and the height
of the diapir is 15 m. The diapir has characteristic in-
trusive contacts with the upper and frontal part of
MR04 (Fig. 106). It is evident that the final thrust dis-
placement post-dates the diapirism, and the very steep
thrust angle indicates that the ramping is rooted in
the deepest levels of the section. The L/R-unconform-
ity is elevated up to 10-12 m above sea level. From
this it is inferred that the thrust sheets were lifted up
on the lower segments of the MR03 and MR04 thrust
sheets, although most of the lift is related to the ramp-
ing on the steep thrust faults. The thickness of the

131

Rubjerg Knude Formation in the piggyback basin of
the thrust sheets is about 15 m.

MR06-MR08 thrust sheets

The main feature of the MR06 and MR07 thrust sheets
is that they are lifted relatively high up in the cliff
section, such that only a small part of the piggyback
basins are preserved. The ramping of MR06 and MR07
is about 22 and 13 m, respectively, corresponding to
one level of elevation of the foremost MR06 thrust

sheet. The ramping is interpreted to have been a step-
wise progression up over the trailing lower part of
MR05, which is ramp-bent over the lower segment of
MR04. The displacement of MR06, MR07 and MR08 on
each hanging-wall thrust fault is about 40 m, indicat-
ing that the displacement is of the order of the dis-
tance down to the décollement surface.

The general impression is that MR06, MR07 and

MR08 initially formed one large thrust sheet, which
was stepwise separated during differential thrust move-
ments. This differential thrusting moved MR06 to the
highest position, whereas MR08 was left in the trail-

Fig. 106. Mud mobilisation and diapirism

in the Lønstrup Klint Formation in the
central part of the MR04-MR05 thrust

sheets of the Moserende Section.
Photograph: May 1985.

Fig. 107. Mobilised mud (lower left) in
the lower part of the Lønstrup Klint

Formation intruded into the bedding of
the formation. The mobilised mud

probably formed a viscous liquid that
facilitated the gravity-spreading defor-

mation mechanism. Photograph: June
1984; staff divisions are 20 cm.

132

ing part with its hanging-wall flat still r esting on the
lower décollement surface. This is implied by the ele-
vation of the L/R-unconformity, which can be traced
down to a horizontal orientation about 5 m below sea
level in MR08.

In the frontal part of the MR08 thrust sheet, a very

well-developed intrusive contact of a diapir is exposed
(Fig. 107). It is evident that the process of thrust fault-
ing was facilitated by the buoyancy and lubricating
effects of the water-saturated mud. In addition, the

mobilised mud had the effect of pushing the thrust sheets

from the rear during the gravity spreading process.

MR09 thrust sheet

The MR09 thrust sheet is a relatively thick thrust sheet.
The angle between the main part of the hanging-wall
ramp and the bedding in the Lønstrup Klint For ma-
tion within the sheet is c. 30°, and the displacement is
estimated to be about 58 m. The L/R-unconformity is
elevated to about 7 m above sea level, and the MR09
thrust sheet must be considered to have been dis-
placed along the rear part of the lower segments in
the section.

MR10 thrust sheet

The MR10 thrust sheet has the same characteristic shape

as the ST08 and MR02 thrust sheets, with an obstacle
interpreted as a detachment anticline. The final orien-
tation of the hanging-wall ramp is rather steep ( c. 70°)
implying rotation of an initially steep ramp ( c. 35°).
This corresponds well with the angle between the bed-

ding in the piggyback basin of MR09 and the MR10
hanging-wall ramp. In the cliff section, the Lønstrup
Klint Formation within the thrust sheet is up to 35 m
thick. Due to uncertainties in reconstruction of the

frontal part, the displacement is estimated to be be-
tween 30 and 65 m. The L/R-unconformity can be

traced down to about 5 m below sea level, indicating
that the main part of MR10 rests on the lower décolle-
ment surface.

The Rubjerg Knude Formation of MR10 is about 25

m thick. It contains a c. 12 m thick lower unit with
bedding dominated by R-onlap. Above this follow
three units, each developed as growth-fault footwall
synclines. To obtain the rather large accumulated thick-
ness of deposit in the piggyback basin, as well as
folding the thr ee synclines, the order of displacement

is more likely to be 65 m than 30 m. This order of
displacement also assumes that the frontal part of the
thrust sheet extended nearly 50 m further 'up in the
air' before being removed by erosion. The final impli-
cation is that the upper piggyback basin above the
anticlinal obstacle was deposited in a syntectonically
deeply eroded depression.

MR11 thrust sheet

MR11 is a small thin thrust sheet with a displacement
of 55 m along the hanging-wall ramp. The thrusting
of MR11 is another example of a thrust sheet requir-
ing the formation of a splint in the subsurface. This is
due to the low angle of the initial frontal ramp (only
15-18°), whereas the ramp angle between the hang-
ing-wall ramp and the original bedding in the piggy-
back basin of MR10 is 40-45°. The splint was probab-
ly trapped as a triangular prism along the 45° dipping
ramp, just below the beach surface.

The L/R-unconformity is elevated to about 7 m above

sea level. The model for balancing this thrust sheet
indicates that it had a lower hanging-wall flat situated
at the 30 m level (below the L/R-unconformity). From
this level, it ramped up to the 20 m level onto a foot-
wall flat on MR10, and finally developed an internal
duplex of its own lower segment, which separated
into MR11u₁ and MR11u₂ (see Plate 2).

The piggyback basin of MR11 consists of only a 10

m thick unit of the Rubjerg Knude Formation. The
sand beds show a F-bedding relationship to the L/R-
unconformity with a weak tendency for D-onlap.

MR12 thrust sheet

The exposed part of the Lønstrup Klint Formation in
the MR12 thrust sheet is about 15 m thick and was
displaced c. 58 m along a hanging-wall ramp dipping
38°. About half of the Lønstrup Klint Formation here
constitutes mobilised mud, without showing any

marked tendency towards diapirism. The Rubjerg Knu-
de Formation is typically c. 15 m thick, with the ex-
ception of increased thicknesses in growth synclines,
and the MR12 thrust sheet is regarded as only 30 m
thick. This leaves another nearly 60 m long lower seg-
ment to be added to the trailing end of the MR10u
duplex segment. The initiation of the MR12 thrusting
started relatively early compared to the thrust sheets
in front (to the south) and behind. This is based on a

133

consideration of the thickness of the Rubjerg Knude
Formation in MR11, which only reached a thickness
of about 10 m before it became trapped by the MR12
thrust sheet. In the cliff section, the MR12 hanging-
wall flat (related to the 20 m flat level) is positioned
on the footwall flat of the MR11 thrust sheet. The L/R-
unconformity is situated about 5-6 m above sea level,
which is compatible with the lift of the thrust sheet
up onto the footwall flat of its own lower segment
(MR12u).

The Rubjerg Knude Formation of MR12 was depo-

sited in one of the large piggyback basins in the proxi-
mal part of the Moserende Section. The width of the
basin is about 45 m and the accumulated thickness of
the sand succession is c. 23 m. Four units can be dif-
ferentiated in the Rubjerg Knude Formation of MR12.
The lowest of these is about 10 m thick, displays F-
bedding, and corresponds well to the lower part of
the Rubjerg Knude Formation in other parts of the
section. Above this follows a trough-shaped unit folded
in a gentle syncline. A new trough-shaped unit, which
is folded into a tight footwall syncline, truncates the
northern limb of this syncline. Finally these two growth
synclines are truncated by the upper sub-unit; the lat-
ter is mainly F-bedded, except for the northern part
which is dragged into a footwall syncline below the
hanging-wall thrust of MR13.

MR13 thrust sheet

The Lønstrup Klint Formation of the MR13 thrust sheet
forms an upright, wedge-shaped feature, which was
displaced about 42 m up along a relatively steep (70°
dip) hanging-wall ramp. This thrust surface has a re-
markable curved shape, which is interpreted to be
the result of erosion in the ramp caused by water flow
contemporaneous with the deposition of the two
growth synclines in the external part of MR12. Similar
features have been observed in places further to the
south, but this is one of the best-developed examples.

The erosion can be determined to have taken place in
the interval between deposition of the lower 10 m thick

unit of the Rubjerg Knude Formation subsequent to
c. 20 m ramping and before the final displacement
along the ramp and deposition of the uppermost unit
in the MR12 piggyback basin.

The L/R-unconformity is situated 5-6 m above sea

level. This is close to the elevation of the L/R-uncon-
formity in MR12, and the thrusting follows a similar
development style with ramping and displacement

along the flat of the lower segment of the trailing end
of the thrust sheet in front (to the south). The section
balance requires a lower segment of the MR13 thrust
sheet (MR13u) in the subsurface, bounded by the flats
at the 20 m and 30 m levels (Plate 2). The MR13u
segment accumulated on the MR10u segment leads to
a high ramping of the thrust sheet to the north, as will
be demonstrated in the following section.

The large piggyback basin in the Moserende Sec-

tion is r epresented by the c. 20 m thick succession of
the Rubjerg Knude Formation in MR13. It is nearly 60
m wide and the main part is planar parallel bedded
(F-bedded); only in the upper most, rear part of the
thrust sheet does a single footwall syncline appear.
The external part of MR13 is therefore thought to have
been deposited during a relatively long period of trans-
port along a flat, contemporaneous with the ramping
that had started in the thrust sheets in the distal part
of the section.

Sedimentary units

In the Moserende Section, only two formations involved

in the thrust-fault deformation can be studied. The
Lønstrup Klint Formation for ms the lower part of the
thrust sheets, and the Rubjerg Knude Formation forms
the fill of the piggyback basins above the L/R-uncon-
formity.

Lønstrup Klint Formation

The lower part of the Lønstrup Klint Formation typi-
cally consists of clayey mobilised mud. About two-
thirds of the thrust sheets comprise mobilised mud,
which commonly developed into diapirs, rising from
the sole thrust up into the formation, where they of-
ten truncate bedding with intrusive contacts (Fig. 107).
The upper part of the formation is composed of thin-
to medium-bedded sandy turbidites interlayer ed with
silty mud (Fig. 27). In the majority of layers, the mud
and fine-grained sands have been disturbed by ball-
and-pillow breccias or small polydiapiric water-escape
structures. During the main thrust faulting, these struc-
tures were superimposed by a dense framework of
smaller thrust faults (Fig. 27).

134

Rubjerg Knude Formation

The Rubjerg Knude Formation has a maximum thick-
ness of 25 m in the Moserende Section; such thick-
nesses are rarely attained, however, either due to over-
thrusting that sealed the deposits in the piggyback
basins before accumulation of this thickness, or to
er osion of the upper part of the formation after depo-
sition and deformation. In general, deposition was
initiated with a unit of F-bedded sand c. 10 m thick.
Above this are two or three units showing R-onlap
and locally for eland-dipping large-scale cross-bedding
(D-onlap). The upper most part typically shows R-on-
lap.

Structures

In the Moserende Section, three types of structural
elements are described and discussed: (1) diapirs, in-
cluding mud mobilisation, (2) mesoscale thrust fault-
ing, and (3) growth-fault footwall synclines, includ-
ing fissure strata. The existence of frozen sand clasts
and frost wedges that testify to the ground-frozen con-

dition of some of the sediments in the Rubjerg Knude
Glaciotectonic Complex has already been mentioned.
Further evidence for ground-frozen conditions is seen
in the presence of fissure strata (Sjørring 1977). A fis-
sure stratum is a layer of sand deposited horizontally
in a fissure that discordantly cuts into a package of
sediment (usually meltwater sand) (Fig. 105). The
implication of the occurrence of fissure strata is that
not only was the host sediment affected by (glacio)tecto-

nic deformation prior to fissure incision, but also that
the sediment must have been frozen so that the fis-
sure cavity did not collapse during deposition of the
fissure strata. As the fissure strata for m wedge-shaped
sand layers, they have also been referred to as kilelag
(wedge-layers in Danish; Berthelsen 1975). In the Mo-

serende Section, the fissure strata document an inter-
mediate phase of syntectonic deposition, as they have
been tilted into a vertical position.

Diapir structures

In the Moserende Section, the zone above the hang-
ing-wall ramps and flats often comprises mobilised
mud (Figs 106, 107). The mud-mobilisation and relat-
ed diapirs dominate in the thrust sheets from the in-
ter mediate hanging-wall ramp and towards the trail-

ing end of the sheets. The diapirs are irr egularly de-
veloped, mainly related to intrusive migration lateral-
ly into the bedding. In the example shown in Fig.
107, the intrusive mobilised mud has a contact rim of
segregated sandy mud that forms the contact to the
truncated bedding. In the thickest thrust sheets, the
larger diapirs rose from the hanging-wall thrust fault
up to 15 m above the thrust-fault surface (Fig. 106).

In the construction and calculations of the balanced

cross-section (Plate 2), the mobilised mud and poly-
diapirism create a problem of volume preservation
relevant to the approximation and evaluation of the
reliability of the balanced model. However, the vol-
umes are not lost but only reorganised and may there-
fore be treated as part of the thrust sheets and duplex
segments. The mobilisation is dominantly developed
along the lower part of the thrust sheet, from where
the mud intruded the upper part of the Lønstrup Klint
Formation of the thrust sheets. It is evident that the
thrust sheets were carried on the mobilised mud, which
with its high water pressure facilitated the displace-
ment of the sheets. Pedersen (1987) described a mod-
el for this process, and with minor modifications this
is still considered to be valid (Fig. 4). The model also
implies that the muddy liquid formed a pressure agent
in the gravity-spreading dynamics, which pushed the
thrust sheets forward towards the distal part of the
thin-skinned thrust-fault complex.

Thrust faults

In the structural cross-section, only the thrust faults
identified as carrying the major displacements are out-

lined (Plate 1). A number of smaller thrust faults and
bedding-parallel contractional faults that occur in the
Rubjerg Knude Glaciotectonic Complex are therefore
not included in the cross-section. One example of these
less significant faults was described in the Rubjerg
Knude Fyr Section (Fig. 101). In the Moserende Sec-
tion, similar thrusts occur, and were recorded during
detailed logging of the upper part of the Lønstrup
Klint Formation in the MR03 thrust sheet (Fig. 27).
Within a 7 m thick succession, ten minor thrust faults
have been recognised. The base of the succession is
the hanging-wall ramp of MR03b. Along the base of
the succession, 0-1.5 m above the hanging-wall ramp,
the clayey mud is cataclastically brecciated by anasto-
mosing shear fractures. In the overlying part of the
formation, the bedding-parallel thrust faults occur with
a spacing of 0.5-1.5 m, concentrated in the muddy

135

layers, whereas steep connecting ramps are situated
in the sandy beds.

It is likely that this type of differential bedding-

parallel thrust faulting and shear brecciation was an
important component in translation in the thin-skinned
thrust-fault system. It also implies that the stratigraph-
ic succession in a formation that appears to be well
preserved may in fact have experienced significant
lateral dislocation.

Footwall synclines

The dominant structures in the Moserende Section are
the footwall synclines, which include the growth syn-
cline basins and re-orientated fissure strata. These
synsedimentary folds were formed continuously, be-
ginning with the deposition of the sand in a trough.
As the thrusting up over the footwall ramp progressed,
the trough deepened; contemporaneous with this
deepening of the footwall block, the hanging-wall
ramp north of the trough started thrusting, which re-
sulted in a drag bend of the northern flank of the syn-

cline. Some of the synclines were trapped and over-
thrust, resulting in overturning of the northern flanks,
which in a few cases created nearly isoclinal, r ecum-
bent folds.

In the piggyback basin of the MR02 thrust sheet, an

excellent example of deposition in a growth syncline
is preserved. The width of this basin ( c. 20 m) is of
the same magnitude as the thickness of the sequence
deposited and deformed. The basin fill can be divid-
ed into four sub-units of the Rubjerg Knude For ma-
tion separated by angular discordances (Fig. 104). The
lowest sub-unit (S₁) consists of c. 5 m of trough cross-

bedded sand deposited in an erosional depression
incised into the Lønstrup Klint Formation of the MR02
thrust sheet. It could be argued that in relation to the
L/R-unconformity of MR02, this sub-unit shows R-on-
lap, but it is evident that the trough cross-bedded sand
is growth-related to an initial up-thrusting of the MR03
frontal nose.

The second sub-unit (S₂) was deposited after the

first sub-unit was tilted during ramping of the MR02
thrust sheet. The tilting also lifted the S₁ sub-unit up

to a level at which the 5 m thick sand package could
be subjected to ground-frost. This is deduced from
the occurrence of fissure strata emplaced discordant-
ly into the S₁ sub-unit. The fissure strata transecting

sub-unit S₁ show small-scale current ripples, which

demonstrates that these fissure strata were deposited

parallel to the sides of the wedge (Fig. 105). The fis-
sure strata can be traced into the second sub-unit S₂,

which consists of stratified sands characterised by
climbing ripple cross-lamination, deposited in a growth
syncline trough. The thickness of the S₂ sub-unit is 5-

10 m; this sub-unit is dominated by R-onlap in rela-
tion to the L/R-unconformity in MR02.

Deposition of the third sub-unit (S₃) was first initia-

ted after sub-units S₁ and S₂ were deformed by com-

pr essional deformation due to push from hanging-
wall thrusting of MR03 over the footwall block of MR02.
The fold structure may be described as an inclined S,
where the lower bend of the S corresponds to a foot-
wall syncline.

The S₃ sub-unit is c. 10 m thick. The base of S₃ is an

angular discordance on the folded S₁ and S₂ sub-units.

The S₃ sub-unit shows R-onlap onto the L/R-uncon-

formity of MR02 and the upper most part of this sand
package covers the detachment anticline structure of
MR02 as well as filling the depression on the northern
flank of the structure. Finally the S₃ sub-unit was fold-

ed into a footwall syncline by thrust propagation of
MR03. In the uppermost part of the basin, a small
growth syncline comprises the uppermost sub-unit (S₄).

This unit is 1-6 m thick and may be regarded as re-
cording deposition in a depression formed by a foot-
wall synclinal bend during the general northward tilt-
ing of MR02.

Interpretation of structural development

In the model for the structural development of the
Moserende Section, a distal (souther n), an intermedi-
ate and a proximal (northern) zone are distinguished.
The distal zone includes thrust sheets MR01-MR03,
which were probably displaced in similar mode. The
intermediate zone includes thrust sheets MR04-MR08,
and finally in the proximal zone thrust, sheets MR09-
MR13 probably moved sequentially in one continu-
ous displacement.

The distal MR01-MR03 zone is regarded initially to

have formed one coherent thrust sheet, which was
split up during the ramping of MR01. The main bend
during ramping took place in MR02, while the trailing
end of MR03 still rested on the décollement surface
without being elevated, and thus represents the root
zone of the MR01-MR03 segment. The sequential de-
velopment of deposition and deformation is very well
illustrated in this first segment with the key locality in
the piggyback basin of MR02. Here four depositional

136

phases (S₁-S₄) separated by four deformational phas-

es (F₁-F₄) have been identified.

Depositional phase S₁ . The S₁ depositional phase

took place during the initial thrusting. About 5 m of
trough cross-bedded sand was deposited before (or
coeval with) the first deformation phase F₁.

Deformational phase F₁ . The first fold phase culmi-

nated with the creation of the hanging-wall anticline
or detachment anticline in MR02. This folding must
be the effect of ramping up from the 20 m level (or 30
m) to the 10 m flat level, resulting in folding of the c.
10 m upper Lønstrup Klint Formation of MR02.

Depositional

phase

S₂ . During

S₂ deposition, the an-

gle between bedding in the Rubjerg Knude Forma-
tion and the L/R-unconformity is nearly perpendicu-
lar. The ramp is not indicated in the ramp cross-sec-
tion because it was destroyed by mud-mobilisation in
the lower part of MR02 (Plate 2). Deposition of S₂ also

took place during the exposure of the S₁ unit to ground

frost conditions as indicated by the presence of fis-
sure strata.

Deformational phase F₂ . The F₂ folding was related

to the hanging-wall thrusting of MR03. As this phase
includes thrust displacement of the S₁ sand and a syn-

clinal drag of the S₂ sand below the footwall ramp of

MR02, it progressed during S₂ deposition. The F₂ phase

terminated with the final folding and minor thrust trun-
cation of S₂. Thus the separation of the imbricate thrust

sheet MR02 and MR03 took place during the F₂ phase.

Depositional phase S₃ . Deposition of S₃ covered the

hanging-wall anticline of MR02, and part of S₂ is dis-

cordantly inclined relative to S₃ bedding. S₃ sedimen-

tation is characterised by F-bedding, and displacement
probably took place along the 30 m level on top of
MR01u, and also ST09-ST10u.

Deformational phase F₃ . The F₃ fold phase is re-

stricted to folding of a footwall syncline of the S₃ unit

related to the hanging-wall ramp propagation of MR03.
It might be interpreted as a continuation of F2, but
the MR03 thrusting definitely propagated after S₃ dep-

osition and its extension most likely for ms a hanging-
wall flat over the sand covering the hanging-wall an-
ticline of MR02.

Depositional phase S₄ . The uppermost growth syn-

cline in the piggyback basin of MR02 was formed by
the 5 m thick upper most unit of the Rubjerg Knude
Formation sand. It probably truncated the F3 thrust,
and is thus not interpreted to represent dislocated parts
of S₁ or S₂.

Deformational phase F₄ . The last fold phase creat-

ed the footwall syncline of the S₄ deposits. The hang-

ing-wall ramp of MR03 increased its inclination by
about 30° and propagated along a steeper satellite
thrust. The footwall syncline was initially overturned
to the south, but during the final phase of ramping
and steep tilting the syncline became re-orientated
into an upright position.

The MR04-MR08 intermediate zone initially formed
one coherent thrust sheet, comparable to the MR01-
MR03 thrust sheets, with a frontal steep ramp, hang-
ing-wall ramp of MR04, and a MR08 trailing-end sheet
with the L/R-unconformity below sea level, indicating

that this thrust sheet rooted in the décollement zone.

In the proximal zone, the MR09 thrust sheet prob-

ably propagated as an individual sheet onto the foot-
wall ramps. The main thrusting was initiated with the
MR11-MR13 sheets being thrust along a flat in the 30
m level, which is on the lower footwall flat of the
trailing end of the MR10 thrust sheet. Thus MR11-
MR13 can be viewed as thrust-sheet imbrications peel-
ing off the back of MR10. At the latest stage of thrust-
ing, the continued displacement along the décolle-
ment zone was responsible for the steepening up of
the sheets, somewhat similar to the development of
the Grønne Rende Section.

For the calculation of the displacement of the indi-

vidual thrust sheets, the erosionally removed fr ontal
parts have been reconstructed from simple angular
geometry, in the same way as the calculation of dis-
placements in the Grønne Rende Section (Fig. 11).
When the elevation of the L/R-unconformity is con-
sidered, it mainly refers to the position of the lowest
part of the L/R surface. Ideally this part should be
horizontal, to indicate the main elevation of the thrust
sheet. However, this is not always the situation, and
therefore the position of the L/R-unconformity in gen-
eral refers to its position where a hanging-wall ramp
or flat truncates it.

Mårup Kirke Section

One of the locations where landsliding at present is
most dramatic is at Mårup Kirke (the old church at
Mårup). This attracts much public attention, not least
among the local people. The back-stepping of the head
of the slides has been very rapid during the last ten
years, and it is probable that the coastal protection
measures instituted at Lønstrup have increased the
erosion of the cliff at Mårup Kirke. Over a number of

137

years the landslides have also obscured the exposures
at this location and a lot of interpretation has been
necessary to reconstruct the structural framework and
the development of the thrusting. The Younger Yol-
dia clay and Saxicava sand (the Vendsyssel Forma-
tion) cap the Mårup Kirke Section. The erosional un-
conformity at the base of the Vendsyssel Formation
acts as a drainage surface, which contributes to the
generally poor exposure conditions. However, with
the experience gained from the other sections, com-
bined with theoretical structural analysis, it is possi-
ble to present a model of the structures in the Mårup
Kirke Section.

There is a marked correlation between the occur-

rences of piggyback basins comprising the sand-rich
Rubjerg Knude Formation, and the build-up of aeo-
lian dunes above the cliff. The northern boundary of

the dune field is situated about 200 m south of Mårup
Kirke in the frontal part of the Mårup Kirke Section.
South of this area, the aeolian dunes for m features
ranging from a few metres in height to nearly 50 m
high dunes above the Rubjerg Fyr Section, which is
also the highest point of the cliff section. Thus it is
evident that the dunes are formed where a sand source
(the Rubjerg Knude Formation) is available (Pedersen
1986b). Above the main part of the Mårup Kirke Sec-
tion, no dunes are present, as this is a cliff section
that consists only of clay and mud (Fig. 108).

The most interesting feature at Mårup Kirke is the

packing of the thrust sheets into uniformly developed
thrust-fault deformed duplex segments. A theoretical
model is presented for the deformation geometry of
these duplex units, subjected to extreme compressional
development; comparisons with the observations re-

Fig. 108. The Mårup Kirke situated at the head of the cliff in the central part of the Mårup Kirke Section. Note that the flat cliff-top

surface, representing the horizontal bedding of the Vendsyssel Formation, is not covered by dunes, reflecting the fact that the cliff
consists of clay and mud. In the distance, the Rubjerg Knude Fyr (lighthouse) is being engulfed by sand dunes derived from the

sand-rich Rubjerg Knude Formation in the piggyback basins present in the sections to the south. Photograph: July 1994; note that by
2002 cliff erosion had reached the corner of the graveyard.

138

corded in the cliff section indicate a reasonable match
between the theoretical model and cliff observations.

Tectonic architecture

Due to the variation in the distribution of piggyback
basins and the general tectonic ar chitecture of com-
pressional framework, the Mårup Kirke Section is di-
vided into thr ee zones: (1) a leading zone (MK01-
MK07), (2) a transitional or inter mediate zone (MK08-
MK10), and (3) a trailing zone, including thrust-fault
duplex units annotated MK11-MK20.

In the leading zone, the first six thrust sheets have

preserved a relatively highly elevated remnant of their
strongly eroded piggyback basins. In the transitional
zone, only the thrust sheet MK10, just below the Mårup
Kirke, contains a piggyback basin. North of this thrust
sheet, the thrust-fault duplex units only comprise the

Lønstrup Klint and Stortorn Formations. In the inter-
mediate and trailing zones (MK08-MK20), the thrust
sheets are defined as duplex units, each comprising
four duplex segments, which are annotated d1-d4.
Thus the lower duplex segment in unit MK09 is anno-
tated MK09d1 and the upper thrust-sheet segment is
annotated MK09d4 (Plate 2).

The southern boundary of the Mårup Kirke Section

is the leading-edge thrust fault corresponding to the
trailing footwall thrust of MR13 and the hanging-wall
ramp of MK01. The boundary is fairly obvious, as it
separates the large piggyback basin of MR13 from the
c. 50 m thick MK01 thrust sheet. The trailing end of
the section is more loosely defined, due to poor ex-
posure and the increasing mud mobilisation of the
thrust sheets. It has therefore been defined in relation
to the unconformities above the thrust sheets. Thus
the boundary between the Mårup Kirke Section and
the Ribjerg Section to the north is placed where the

Fig. 109. Upright thrust sheets in the frontal zone of the Mårup Kirke Section (thrust fault arrowed ). The difference in lithology

between the upper and lower levels of the Lønstrup Klint Formation is illustrated by comparing the sand-rich (upper Lønstrup Klint
Formation) footwall block (to the right, south) with the mud-dominated (lower Lønstrup Klint Formation) hanging-wall block (left).

Encircled rucksack for scale. Photograph: August 1996.

139

unconformity at the base of the Vendsyssel Forma-
tion truncates the unconformity between the glacio-
tectonic unit and the Ribjerg Formation. The glacio-
tectonic unit is viewed as the unit of deformed de-
posits related to a glaciotectonic event (Pedersen 1993),
here included in the Rubjerg Knude Glaciotectonic
Complex. The defined boundary is very close to where
45° dipping thrust-fault features are obscured both by
the mud mobilisation and by superimposed, more or
less horizontal, anastomosing jointing.

MK01 thrust sheet

The first thrust sheet in the leading zone of the Mårup
Kirke Section is the nearly 50 m thick MK01 thrust
sheet. In the exposed parts of the thrust sheet, the Løn-

strup Klint Formation has a thickness of 40 m, which
indicates that the deepest level of the section includ-
ing the lower décollement zone is brought up to the
upper flat. The displacement is estimated to be 102 m;
this includes construction of the eroded tip of the thrust
sheet (Fig. 11). This corresponds well with calcula-
tion of the displacement according to the equation
d × sin α = h, where d is the displacement, α is the

angle of the thrust ramping from the lower flat to the
upper flat, and h is the distance between the two flats.
The distance between the lower and upper flats is 40
m, and assuming an initial thrusting angle of about
23°, the calculated displacement d is c. 100 m.

Most of the Lønstrup Klint Formation of MK01 is mo-

bilised and forms a diapir-like structure. Bedding is
only well preserved in the upper 7-10 m of the Løn-
strup Klint Formation in this thrust sheet. The bed-
ding is characterised here by medium-bedded sandy
turbidites.

The Rubjerg Knude Formation of MK01 comprises

a nearly 10 m thick succession of glaciofluvial sand.
The sand layers show R-onlap and are strongly de-
formed by a footwall syncline. The L/R-unconformity
is situated about 15 m above sea level, indicating an
elevation of the lower hanging-wall flat up to the 20
m level footwall flat. This corresponds well with the

balanced model for the Moserende Section, where the
trailing-end lower segments MR10u and MR13u still re-

main to be calculated for. It is thus evident that the MK01

thrust sheet was translated along the 20 m level flat.

MK02-MK04 thrust sheets

The MK02-MK04 thrust sheets are three relatively small
sheets with only minor displacements, about 30 m for
MK02 and MK03, and c. 40 m for MK04. The estimates
of the displacement for thrust sheets with erosionally
removed tips are based on reconstructions following
the same principles as applied in the Grønne Rende
Section (Fig. 11). The thickness of the Lønstrup Klint
Formation in the thrust sheets is only between 10 and
20 m, and the thrust sheets are considered to repre-
sent imbricates from the upper part of the MK01 thrust
sheet, which roots down to the décollement zone in
the 40 m flat level.

The Lønstrup Klint Formation in MK02 is completely

mobilised apart from the uppermost 1-2 m. The mud
diapir in MK02 is regarded as an extension of the large
mud diapir in MK01. In MK03 and MK04, bedding is
partly preserved, and may be compared with the up-
per sandy bedding seen in MK01.

The L/R-unconformity cuts down to at least 2-3 m

below the mean level of bedding on the back of MK02
and MK03, and given this uncertainty in location, the
position of the unconformity is at the same elevation
as in the MK01 and MK04 thrust sheets. It is therefore
inferred that the imbricate thrusting of MK02-MK04
was initiated at an early stage, prior to the subsequent
deeper-level up-thrusting of MK01.

Early development of the imbrication is further sup-

ported by the thickness of the Rubjerg Knude Forma-
tion, which in MK01-MK04 is less than 10 m. The
piggyback basin on the back of the non-imbricated
MK01 was short-lived relative to those described above
in the Moserende Section where the Rubjerg Knude
Formation is up to 25 m thick. Along the footwall ramps,

sand of the Rubjerg Knude Formation was deposited
in growth synclines indicating syntectonic develop-
ment of the small piggyback basins in the leading zone
of the Mårup Kirke Section.

MK05-MK07 thrust sheets

The MK05-MK07 thrust sheets form an imbricate set
of upright thrust sheets, now dipping more than 60°N
(Fig. 109). The thickness of the thrust sheets is about
20 m in the cliff section. The displacement is 40 m for
MK05, 28 m for MK06 and only 15 m for MK07. The
Lønstrup Klint Formation, making up most of the thrust
sheets, is characterised by a few relatively thick fine-
grained sand turbidites interbedded with dark blue-

140

grey silty mud. The bedding is strongly disturbed by
thrusting and jointing, similar to the thrust-fault frame-
work described in MR03, and small- to medium-scale
duplexes are common. In the upper half of the MK07
thrust sheet, a major footwall syncline is developed
below the hanging-wall ramp of MK08.

The Rubjerg Knude Formation is only represented

in MK06, where the L/R-unconformity is elevated up
to about 20 m above sea level. In the MK04-MK05
thrust sheets the elevations are more than 20 m, indi-
cating that these thrust sheets were lifted up and trans-
lated along an upper flat resting on three lower seg-
ments. The accumulation of these segments for ms a
subsurface duplex, probably deformed into an intense
network of anastomosing thrust faults. The duplex
segments constitute the trailing lower segments of
MK01-MK04, and for MK06 and MK07 the trailing low-
er segment of MK05 is also added (see balanced cross-
section, Plate 2).

MK08-MK10 thrust sheets

MK08 is the southernmost thrust sheet in the transi-
tional zone of the Mårup Kirke Section. The transi-
tional zone is characterised by the change from thick
continuous successions of lithologies into sheet units
comprising duplex segments bounded by footwall and
hanging-wall flats. Along these flats, lateral translation

preceded tilting and steepening during propagation
along the ramps.

The thrust fault separating MK07 and MK08 is the

trailing-end footwall ramp on top of MK07 and the
hanging-wall flat of MK08. At the top, MK08 is bound-
ed by the footwall flat and hanging-wall ramp be-
tween MK08 and MK09. The thrust fault and the gen-
eral bedding in MK08 dips at 35°N. In the exposed
cliff section, MK08 is 40 m thick, which implies that
the hanging-wall flat is a segment of the lower décol-
lement zone. Above this, four segments may be iden-
tified corresponding to the four main levels of flats
below the L/R-unconformity. Each flat-segment is
about 10 m.

The displacement along the hanging-wall thrust is

110

m, calculated from the equation d × sin α = h,

given that the height h is c. 65 m (sum of cliff section
and distance down to the décollement surface) and α

is 35°. The estimate is based on the assumption that
the tip of the hanging-wall ramp in the lowest seg-
ment (initially located at the 30 m flat level) only r each-
es up to the hinge of the footwall ramp at the top of

the cliff. In the MK08 thrust sheet, there is no record
of the Rubjerg Knude Formation.

Due to the intense development of landslides be-

low the Mårup Kirke, the MK09 thrust sheet is very
poorly exposed. The interpretation here is based on
the space relationships and the structures exposed in
MK08 and MK10. From MK08 it is known that the
frontal hanging-wall ramp of MK09 dips at 35°. The
bedding is more or less horizontal in the cliff section,
judging from the occasional features that can be picked
out from the photo-geological interpretation. The dis-
tance between the leading and trailing thrust fault is
about 70-73 m, and the displacement must therefore
be about 50-55 m. The interpretation of the MK09
framework is that the upper segment forms a type 3
fault-bend-fold structure, where the sub-segment rest-
ing on the upper flat has been eroded away and trun-
cated by the MK10 hanging-wall flat, the two segments
in the intermediate levels for m S-shaped type 2 struc-
tures, and the lower segment forms a type 1 structure
with the trailing end of the segment resting on the
lower flat (compare with the model in Fig. 103).

The MK10 thrust sheet is situated below the Mårup

Kirke, and preserves the most proximal piggyback
basin containing the Rubjerg Knude Formation. The
thickness of the Rubjerg Knude Formation is about 10
m and the basin is deformed into a recumbent foot-
wall syncline. The L/R-unconformity is situated about
10 m a.s.l., indicating elevation above two lower du-
plex segments in the subsurface. The increase in the
dip of the L/R-unconformity and bedding in the Løn-
strup Klint Formation from 20° in the frontal part to
35° in the rear part is interpreted as a bend by the
hanging-wall ramp propagating over irregularities in
the trailing part of MK09. Thus part of the subsurface
structure must include the geometric adjustments of a
splint appearing due to the ramp angle change (see
Plate 2). This is reflected in the occurrence of a hang-
ing-wall anticline in the trailing end of MK10.

MK11-MK20 thrust sheets

In the trailing zone of the Mårup Kirke Section, there
are no occurrences of the Rubjerg Knude Formation,
and the L/R-unconformity has not been identified. The
thrust faults are mainly steeply dipping, about 45°,
and at the top of the cliff section the thrust sheets are
shear-dragged southwards and reworked into glaci-
tectonites, a truncated glaciotectonic unconformity and
local till.

141

This trailing zone can be divided into ten fairly

uniform thrust-fault duplex units, each about 55 m
long (measured horizontally along the beach level)
and separated by 45° steeply dipping thrust faults.
For the characterisation and structural explanation of
these thrust-fault duplex units, a thrust-ramp-propa-
gation model is presented below (see Fig. 114).

Sedimentary units

In the Mårup Kirke Section, no significant additional
data have been obtained to supplement the sedimen-
tological descriptions. However, it is evident that the
Rubjerg Knude Formation only occurs in the south-
er n part of the section, where it is less than 10 m
thick. It is inferred, therefore, that the piggyback ba-
sin in the Mårup Kirke Section was short-lived rela-
tive to the thicker successions of the Rubjerg Knude
Formation further south. The Rubjerg Knude Forma-
tion may never have been deposited in the trailing
end of the Mårup Kirke Section.

Structures

A conspicuous feature of the Mårup Kirke Section is
the shear drag at the top of the cliff section. The main
structures formed during the subglacial drag are south-
erly overturned to recumbent synclines that developed
in a sandy glacitectonite about 1 m in thickness. The
glacitectonite is interpreted to have formed by sub-
glacial shear deformation superimposed on the pro-
glacially formed thrust-fault and duplex structures
(Pedersen 1988, 1996, 2000).

Over a large part of the Mårup Kirke Section, the

amount of mobilisation is not very high. This permits
a characterisation and interpretation of the deforma-
tion of duplex segments and stacking of duplex units,
as described below.

Interpretation of structural development

The main purpose of this section is to present an an-
alytical structural model that can be used to interpret
the thrust-fault framework developed in the Mårup
Kirke Section. The basic elements of the model are
the duplex segments, and the structural deformation
can be characterised as fault-bend folding. The result
of the deformation is a compressional stacking of

duplex segments into duplex units with a certain ge-
ometry and size. The interpretation of these structures
adds to the basis for the discussion of structural de-
velopments that concludes this section.

Fault-bend-fold model for duplex units

It was demonstrated in Fig. 103 how a duplex unit
developed with type 1-3 duplex-segment structures.
However, a number of structural configurations may
develop from the deformation of duplex segments
stacked into duplex units, depending on the amount
of displacement and the initial length of the thrust
sheet. For the interpretation of the structures in the
northern part of the Mårup Kirke Section, as well as a
major part of the Ribjerg Section, the analytical mod-
els in Fig. 110 have been constructed.

The premises for the models are: (1) the duplex

unit comprises four initially horizontal sheets with a
thickness of 10 m each, (2) the bounding leading and
trailing thrust ramps dip at 45° (maximum angle of
thrust-fractur e formation), (3) the vertical distance
between the lower and upper flat is 40 m, and (4) the
lateral compression cannot exceed the packing of the
sheets in 45° dipping imbricates. From the latter premise,

it can be predicted by simple trigonometric calcula-
tion that the lateral distance between the bounding
thrusts of the duplexes should be close to 56.5 m, and

this corresponds very well with the thrust features
recorded in the cliff section.

To illustrate the model, one ideal case is consid-

ered, namely the case where the displacement is to
the top of the ramp, which has the same length as the
maximum compression distance of 56.5 m (Fig. 110,
type 3). The displacement takes place along the low-
er footwall flat, and the lower hanging-wall flat prop-
agates up along the 45° dipping footwall ramp. The
resulting structural framework is an L-type fault-bend
folding (Fig. 103). In this case, the lower thrust seg-
ment will just reach the level of the upper flat. The
displacement is c. 42 m and the balanced length of
the duplex unit is 98.5 m, which results in a calculat-
ed compression of 43%. Due to the propagation along
the upper flat and the ramp-bend folding, a hanging-
wall anticline is for med, which can be described as a
fairly upright, angular antiformal stack.

The case described above is shown as type 3 in

Fig. 110. This case might also be called the angular
antiformal stack type. Further cases can be considered

with decreasing or increasing displacement relative

142

Fig. 110. The duplex-unit model for fault-bend folding of duplex segments. The basic elements for the constructed models are: (1)

the duplex unit comprises four initially horizontal sheets, separated by thrust-fault flats, and each sheet is 10 m thick, (2) the
bounding leading and trailing thrust ramps dip at 45° (maximum angle of thrust-fracture formation), (3) the vertical distance

between the lower and upper flat is 40 m in types 1-6, and in types 7-9 it is extended 10 and 20 m above the upper footwall hinge,
and (4) the compression cannot exceed the packing of the sheets in 45° dipping imbricates. The cases in the model are selected with

steps jumping one 10 m level from case to case. According to simple trigonometry, this will result in a displacement unit of c. 14 m,
and multiples of this. The initial dimensions (L₀) of duplex units 1-6 are given by the scale in the lower right corner. Type 1 is a

single monoclinic flexural kink fold. T ype 2 is a double monoclinic flexural kink fold. Type 3 is an angular antiformal stack. Type
4 is a flat-topped antiformal stack. Type 5 is a lateral extension of the flat-topped antiformal stack. Type 6 is a lateral extension of

the flat-topped antiformal stack, where it is demonstrated that the frontal limb in the antiformal stack retains its profile, and it is only
a lateral translation of duplex segments that responds to the further compression of the duplex unit. Type 7 is a per fect G-S-L

structure (Fig. 107). Compression of 33% in type 7, and an elevation of the ramp by two 10 m levels, results in the monoclinic
flexural kink fold. The effect of increasing compression and propagation up along the extended ramp (types 8 and 9 ), demonstrates

the development of the antiformal stack in a manner comparable to that from type 3 to type 4 . Note that the given maximum
stacking of imbricates constrains the size of the balanced length of duplex units. This is demonstrated in the diagram relating

balanced length to magnitude of compression. L₁, length after deformation; Δ, shortening; L₀, initial length; comp., compression.

to type 3. If the displacement of the lower thrust-sheet
segment is less than the height of the footwall ramp,
the duplex segments above have two ramps to pass.
Consequently, two ramp-bend folds will be created,
which may also be described as a repeated monoclin-
ic flexural kink-fold (Fig. 110, type 2). In the model,

the second ramp-bend fold will not develop until the
displacement exceeds 20%, corresponding to a displace-

ment lift of only one 10 m level (Fig. 110, type 1).

With increased compression, the hanging-wall an-

ticline formed in type 3 will develop into a flat-topped
antiformal stack (types 4 and 5). Finally, type 6 dem-

143

onstrates the lateral extension of the flat-topped anti-
formal stack resulting from 60% compression. Note
that in this case the frontal limb in the antiformal stack
maintains its profile and an increase in compression
only results in lateral translation of thrust sheets. In-
creasing compression also requires increasing length
(L₀) of the duplex unit, which is demonstrated by the

diagram in the lower right corner of Fig. 110.

In Fig. 110, the cases with an extended ramp have

also been examined. This corresponds to thrusting
above the upper hinge of the footwall ramp, which
would be the case if syntectonic sedimentary units
were deposited on the upper flat preceding ramp prop-
agation. Type 7 is a perfect Γ-S-L structure, exemplify-
ing this development. It is formed by compression of
33% and elevation of the ramp by two 10 m levels,
here creating a monoclinic flexural kink-folding.

The effect of increasing compression and elevation

of the ramp from type 8 to type 9 demonstrates the
development of the antiformal stack in a manner ra-
ther similar to that from type 3 to type 4.

Characterisation of thrust duplex MK11-MK20

On the basis of the models in Fig. 110, the MK11 thrust
sheet is classified as a type 2 structure due to the pres-
ence of two monoclinal flexures. However, the struc-
ture in MK11 must incorporate the effects of the dis-
placement of the thrust segment of MK10. Consequent-
ly, the upper segments of MK11 are stacked on each
other as relatively short duplex segments. Moreover,
the topmost part of MK11 is dragged out and sheared
over the piggyback basin of MK10. This dragged part
can be interpreted as the frontal limb of the antifor-
mal stack initially formed over the upper footwall hinge.

MK12 is the duplex unit situated north of Mårup

Kirke. All the structures dip at 45°, except for the up-
permost shear -dragged parts, which were reworked
into a local till (the Kattegat Till Formation). Thus the
structure is interpreted mainly as an L-structure, prob-
ably a type 5 or 8 structure with 55% compression
and a balanced length of c. 126 m (Fig. 110).

MK13 has an undulating flat-lying structure with

flexural drag up along the footwall ramp. It is thus
interpreted as a type 4 structure with a flat-topped
antiformal stack capping the frontal part of the lower
thrust segment, which was only displaced up to the
reference level of the L/R-unconformity. Compression
amounts to 50-55%, and the balanced length is esti-
mated to be 120 m.

MK14 is considered to be similar to MK13. It was

probably very close to the modelled type 4 structure
(Fig. 110), prior to glaciotectonic shearing and trunca-
tion of its flat-topped antiformal stack.

MK15 and MK16 are probably the closest approxi-

mation to a perfect Γ-S-L-structure of type 7 in the

model (Fig. 110). MK17 and MK18 may well be inferred

to be of the same type. However, the exposures are here

too poor for definitive structural characterisation.

In MK19 and MK20, structures with 45° steep dips

ar e displayed in the cliff section. These duplex units
can thus be interpreted as type 9 duplexes.

Discussion of structural development

Although the balanced section is subject to some un-
certainties in the Mårup Kirke Section, calculation of
the compression from the measured length of the sec-
tion L₁ = 978 m, and a balanced length of about L₀

1814 m gives 46%. As described above, the section is
divided into three architectural zones : (1) a leading
zone (MK1-MK7), (2) a transitional or intermediate
zone (MK8-MK10), and (3) a trailing zone that in-
cludes thrust-fault duplex units (MK11-MK20). The
discussion below attempts to demonstrate the proxi-
mal-distal thrust-fault development.

The fault-bend-fold model for duplex units describes

the thrust-fault structures in the trailing zone and gives
an approximation of the structural framework of the
major part of the Mårup Kirke Section. The absence of
the Rubjerg Knude Formation in the trailing zone sug-
gests that it was never deposited here. Moreover, the
thrust stacking of the duplex units started before, or
just at the beginningof, deposition of the Rubjerg Knu-

de Formation in the most proximal part of the glacio-
tectonic complex. It is further suggested that the thrust
levels rapidly shifted to lower levels in progressive
steps. So, after the first few hundred metres of peel-
ing off the upper most thrust segments, the thrusting
propagated for the next five hundred metres in the
intermediate flat levels. Finally, the main compression
started to stack the duplex units up into imbricates
during translation along the lower flat level, the dé-
collement zone, and differential displacement between
the duplex segments.

The displacements of the duplex units were limit-

ed by the maximum shortening between the 45° steep
northward-dipping ramps. It might be suggested that
the displacement was much larger and considerable
amounts of the leading part of the thrust sheets wer e

144

eroded away from the upper flat. However, this is
unlikely for two reasons: (1) the amount of compres-
sion is 50-60% which is consider ed to be a limiting
amount of compression for natural systems, and (2)
the structures discernible from the photo-geologically
interpreted cross-section support a model with c. 50%
shortening. Another suggestion could be that the du-
plex imbricates were formed subglacially, bounded
by a floor thrust (the décollement zone) and a roof
thrust situated in the glaciotectonic unconformity (the
sole of the glacier). This is disproved by the fact that
the antiformal stack above the duplex units would
have required space to be stacked up on the upper
flat. Thus, although the antiformal stacks were removed
by glacial erosion and the upper part of the Mårup
Kirke Section is shear-dragged and truncated by the
glaciotectonic unconformity (formed subglacially), the
thin-skinned thrust faulting developed in a proglacial
setting in front of a progressively advancing ice margin.

MK08 is the leading thrust sheet in the transitional

zone of the Mårup Kirke Section. It has a considera-
ble displacement, more than 100 m, and it probably
ramped up to the 20 m flat level along which it was
translated for more than 50 m before its hanging-wall
flat propagated up to the uppermost footwall flat. Thus,
all the segments in the thrust sheet were earlier trans-
lated along the various flats before MK08 was dis-
placed up along the footwall ramp on MK07. There
should therefore be a stepping down of the trailing-
end sheet in the zone. This would correspond to trans-
lation along the lower flat level of the MK09-MK10
thrust sheets, which facilitated the formation of a de-
pression above MK10, where the Rubjerg Knude For-
mation was deposited and preserved in the most prox-
imal piggyback basin of the glaciotectonic complex.

The leading zone is characterised by carrying a rel-

atively high-elevated piggyback basin, where the Ru-
bjerg Knude Formation was deposited on an uneven
erosional unconformity. During the early phase of im-

brication, this piggyback basin was separated into five
sub-basins, before they were finally trapped by over -
thrusting and deposition ceased. The accumulated dis-

placement in the leading zone is c. 180 m. The thrust-
ing probably started from a detachment level in the
upper flat (10 m level), inferred from the thickness of
MK02-MK04. Thrusting then shifted down to the sec-
ond flat (20 m level). Assuming that the first half of
the displacement started as an imbrication of the
MK02-MK06 thrust sheets, then lateral translation of
the upper 10 m thrust-sheet segment resulted in later-
al displacement of the upper thrust level in the order

of 100 m. Subsequently, the detachment surface was
lowered down to the 20 m level, and it is evident that
this detachment surface is the next flat level, along
which about 100 m lateral translation occurred. One
of the main lines of evidence that this level is another
pervasive flat level is that it acted as an upper flat for
the displacement of MK01. The propagation of this thrust

sheet probably started with a minor dislocation along
the 30 m flat level, which is known to be a pervasive

flat level from the Moserende Section, before it moved
down to be a dislocation along the lower décolle-
ment level (40 m flat level). From the lower décolle-
ment level, MK01 ramped up to the 20 m flat level along

which translation occurred over a distance of 80 m
before its hanging-wall flat and ramp was ramped up
to the surface along the footwall ramp at the trailing
ramp of the Moserende Section. During displacement,
the MK01 thrust sheet carried the MK02-MK07 sheets
piggyback resulting in over-steepening of these thrust
sheets towards the trailing end (MK05 and MK07).

Ribjerg Section

The northern termination of the Rubjerg Knude Gla-
ciotectonic Complex is the sandy hill at Lønstrup called
Ribjerg. Most of the coastal cliff below Ribjerg is now
protected, and vegetation covers the cliff exposures
at Ribjerg. However, on the south-western side of Ri-
bjerg a funnel-shaped gully has been formed by steady
erosion due to high groundwater drainage in the gla-
ciofluvial sand (Fig. 111). At the boundary between
the sand and the underlying mud, groundwater wells
up and creates quicksand. Thus, although a section
through the glaciofluvial sand is well exposed, access
is difficult and potentially dangerous. In spite of such
obstacles, a detailed log of the succession has been
measured, and the locality yields the type section of
the Ribjerg Formation. In addition, the section is the
site for studying the glaciotectonic unconformity above
the Skærumhede Group, cropping out at the 'Lille Blå'
(northernmost part of the cross-section in Plate 1).

'Store Blå' and 'Lille Blå'

North of the Mårup Kirke Section, the unconformity
above the mud-rich Lønstrup Klint Formation dips
gently to the north. Jessen (1918, 1931) named this
part of the cliff 'Det Store Blå' and 'Det Lille Blå' (the

145

big blue and the small blue, respectively, a reference
to the blue colour of the clayey mud in the mud-rich
part of the cliff section). In general, the mud is a mo-
bilised succession with only few bedding surfaces and
thrust faults preserved. In the Store Blå cliff section,
the structural features recorded accord well with the
maximum compressional model described for the du-

plex units of the Mårup Kirke Section (Fig. 110). In
the Lille Blå cliff section, the mud is structureless, and
no primary bedding surfaces are preserved. A second-
ary sub-horizontal planar fabric is recognisable, and
pebbles and boulders occur on the unconformity as
well as in the upper most metre just below the uncon-
formity. Jessen (1931) interpreted the Lille Blå as dis-
located Older Yoldia clay, which he named Portland-
ia arctica clay after the occurrence of the identified
mollusc species in the unit.

Jessen's description of the clay compares well with

the characterisation of the Skærumhede Group and
the model of glaciodynamic development presented
below. Due to the progressive deformation in the
proximal part of the glaciotectonic complex, deeper

levels of the Skærumhede Group were thrust up into
a position close to the main L/R-unconformity level,

such that an increasing proportion of the group has
been eroded.

Jessen (1931) also described another important fea-

ture related to the Lille Blå cliff section. Before 1895,
it could be observed that the unconformity was fold-
ed into a syncline with a fold axis directed N-S. This
is of course unusual since all structures described until
now are assumed to have been formed by compres-
sion directed N-S due to the advance of the ice cap
from the north, resulting in mainly E-W-tr ending struc-
tural features. The N-S-orientated fold axis is inter-
preted to be related to deformation by ice advance
from the east, an event that also deposited the Mid
Danish Till Formation.

Tectonic architecture

The Ribjerg Section is defined as the section between
the northern boundary of the Mårup Kirke Section
and the end of the Lønstrup Klint cliff section, which
terminates at the vegetation-covered cliffs below the
town of Lønstrup. The southern boundary of the sec-
tion is situated where four unconformities are super-

Fig. 111. The Ribjerg Section viewed towards the north. The sandy cliff in the centre of the figure is the type locality of the Ribjerg
Formation. Photograph: July 1994.

146

imposed upon each other. These are: (1) the L/R-un-
conformity, (2) the glaciotectonic unconformity be-
low the Kattegat Till Formation, (3) the unconformity
between the Kattegat Till Formation and the glacio-
dynamic succession related to the NE-Ice Advance,
and finally (4) the unconformity between the glacio-
dynamic successions and the Vendsyssel Formation
(Plate 1). The first three unconformities are here col-
lectively termed the Blå-unconformity.

The Blå-unconformity dips at 2-3° to the north. The

surface is relatively planar, but uneven. A few clasts
remain in depressions on the surface, but clasts pro-
truding into the surface from below are more common.

The unconformity between the Ribjerg Formation

and the Vendsyssel Formation is an erosional surface
dipping gently to the south. The main lithology in the
Vendsyssel Formation is the Saxicava Sand, which
consists of sandy heteroliths. These beds onlap the
unconformity, which probably was subaerially exposed

before inundation by the rising Younger Yoldia Sea.

Sedimentary units

In the Ribjerg Section, four sedimentary units are re-
presented: the Skærumhede Group, the Ribjerg For-
mation, the Mid Danish Till Formation and the
Vendsyssel Formation (Figs 14, 17, 33).

Skærumhede Group

The Skærumhede Group comprises two formations:
the Stortorn Formation and the Lønstrup Klint Forma-
tion. In the southernmost part of the section (at the
Store Blå), it is possible to distinguish the two forma-
tions (Fig. 17). However, in the northern part of the
Ribjerg Section, pervasive mobilisation has obliterat-
ed the primary lithological differences and the sedi-
ments may only be referred, undifferentiated, to the
Skærumhede Group.

In the southern part of the section, the Stortorn

Formation constitutes the lowermost 10 m of the cliff
section (Fig. 17). Here a cataclastic breccia separates
the Stortorn Formation from the Lønstrup Klint For -
mation above. It is inferred that this breccia repre-
sents one of the thrust-fault flats that for m the bound-
ary of the duplex segments building up the duplex
units of the section.

The Skærumhede Group is truncated by the Blå-

unconformity, above which the Vendsyssel Formation
was deposited.

Blå-unconformity

The Blå-unconformity is considered to represent three
superimposed unconformities. The first one is the L/R-

unconformity, the existence of which is only rarely
demonstrable in this section.

The second unconformity is the glaciotectonic un-

conformity below the Kattegat Till Formation. The
Kattegat Till Formation has been almost completely
eroded away from the Ribjerg Section, but is present
in small, isolated pockets (Fig. 31). However, the gla-
citectonite related to the subglacial deformation be-
low the Kattegat Till Formation is well preserved in a
zone more than 1 m thick below the Blå-unconfor m-
ity (Fig. 32). Erratic clasts are common in this zone,
probably lodged into the soft sediment from the till
above, and an indicator boulder of larvikite has been
recognised. A number of clast fabrics have been meas-
ured, which show a N-S long-axis orientation (varia-
tion from 010° to 175°). The unconformity is preserved
at the base of the Vendsyssel Formation in the north-
ern part of the Mårup Kirke Section (Fig. 37).

The third unconformity is the erosional surface upon

which the Ribjerg Formation was deposited. The crea-
tion of this surface removed much of the evidence of
the preceding unconformities; indeed, at the south-
ern extent of the unconformity, the Ribjerg Formation
is also absent, and the Vendsyssel Formation rests on
the composite surface.

Ribjerg Formation

The c. 25 m thick glaciofluvial sand of the Ribjerg
Formation dominates the Ribjerg Section (Fig. 33, Plate
1). The formation comprises fine- to medium-grained
sand, coarsening upwards into gravel-dominated beds
at the top (Fig. 33). The formation was deposited on
the erosional unconformity capping the Skærumhede
Group (the Blå-unconformity). At this surface, a re-
sidual coarse clastic bed is present, less than half a
metre in thickness, dominated by clayey clasts de-
rived from the unit below. The clayey clasts continue
to appear in the sand beds in the lowermost 5 m of
the formation.

The middle part of the formation is dominated by

trough cross-bedding, and the flow direction indicat-

147

ed from measurements of foreset beds was from east
to west.

The fill of the large channels incised into the medi-

um-grained sand package also include gravel and
slumped diamictite material. Water-escape dykes and
sand-filled cracks are common in the sand within the
large channels (Fig. 34). The formation coarsens up-
wards into a trough cross-bedded sandy gravel in the
uppermost 3 m, just below the diamictite referred to
the Mid Danish Till Formation.

Mid Danish Till Formation

The Mid Danish Till Formation is a c. 3 m thick unit of
grey brown to light yellowish brown sandy till that over-

lies the Ribjerg Formation (Figs 14, 33, 35). The till is
divided into lower and upper beds. The lower bed is
a laminated to thin-bedded, fine-grained sandy, ma-
trix-supported diamict. Lamination and bedding is
deformed into irregular intraformational slump folds
with fold axes trending N-S, indicating a slump-slide
direction towards the west, and the unit is interpreted
as a sediment gravity flow or flow till (Dreimanis 1988).
The upper bed is a massive, structureless and sandy
matrix-supported diamict (Fig. 35). The clasts, pebble
to cobble in size, occur randomly, and the till fabric
shows an a-axis orientation gently dipping towards
the east. The unit is interpreted as a basal lodgement
till (Dreimanis 1988) superposed on the flow till and
deposited by an ice stream moving from east to west.

The Mid Danish Till Formation is truncated by the

erosional unconformity upon which the Vendsyssel
Formation was deposited.

Vendsyssel Formation

In the Ribjerg Section, the Vendsyssel Formation trun-
cates the Mid Danish Till Formation, the Ribjerg For-
mation and the Blå-unconformity. The maximum thick-
ness in this part of the Lønstrup Klint section is about
12 m, decreasing towards the north, where it onlaps
the unconformity above the Ribjerg and Mid Danish
Till Formations (Fig. 33). The Vendsyssel Formation
comprises laminated mud and thin-bedded fine-
grained sandy heteroliths, which in the southern part
of the Ribjerg Section are characterised by well-pre-
served trace fossils created by the bivalve Hiatella
arctica , often with the shells preserved in life posi-
tion (Fig. 41).

Structures

In the Ribjerg Section, the most important structures
ar e the anastomosing joints related to the glacitec-
tonite below the Blå-unconformity (Fig. 32). At the
Lille Blå locality, the rhomb-shaped segments, 0.5-3
m in size, bounded by conjugate shear joints, are flat-
lying. The angle between conjugate joints varies from
10-30° and the zone-axis is orientated more or less
E-W. At the Store Blå locality, the shear joints are
more parallel with a spacing of c. 30 cm between the
almost horizontal fractures, and in the southernmost
part of the section, sand-fill intruded the fractures to
create rhomb-shaped segments in a sandy mud ma-
trix.

Interpretation of glacial geology and
stratigraphic development

In the interpretation presented here, the Blå-uncon-
formity is considered to be a modulation sur face or
deformational layer below the advancing fr ont of the
Norwegian Ice. The unconformity may even be inter-
preted as the surface onto which the sole of the ice
pressed during the propagation towards the glaciotec-

tonic complex developing in front of it. After the ice
retreated, a hill-and-hole pair formed. Rubjerg Knude
is here viewed as the hill and the depression extend-
ing to the north of the northward-dipping unconform-
ity corresponds to the hole. The hole was subsequently
filled with glaciofluvial sands (the Ribjerg Formation)
that are younger than the Rubjerg Knude Formation.
On top of the Ribjerg Formation, Jessen (1931) described

a sandy till that is here referred to the Mid Danish Till
Formation, but he also recorded a single till-bed inter-

calated in the meltwater sand. This sandy till as well
as the thin diamictite layers related to the slumps in
the troughs and channels are interpreted as precur-
sors to the flow till that initiated deposition of the Mid
Danish Till Formation. The Ribjerg and Mid Danish
Till Formations were formed as proglacial and sub-
glacial units during the advance of the ice from the
east towards the west with a source area in central
Sweden. This ice advance was also responsible for
the gentle folding of the Blå-unconformity and the
beds above it into a syncline with a N-S-trending ax-
is, as noted by Jessen (1931).

Geological Survey of Denmark and Greenland Bulletin

Nr. 8 pp 120-147, Structural analysis of the Rubjerg Knude Glaciotectonic Complex, Vendsyssel, northern Denmark

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