Geological Survey of Denmark and Greenland Bulletin
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Nr. 4, Review of Survey activities 2003, pp. 41-44 |
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41
Until recently, studies of the regional distribution of seabed
sediments off the littoral zone of the Danish North Sea coast
had been concentrated on the Jutland Bank area (Fig. 1; Leth
1996, 1998). Knowledge on the sedimentary conditions and
processes along the entire west coast of Jutland has, however,
significantly increased as a result of 2000 km of newly
acquired high-resolution seismic and side-scan sonar data,
supplemented by about 100 vibrocores. These data were col-
lected by the Geological Survey of Denmark and Greenland
(GEUS) during joint projects with the Danish Coastal
Authority between 1998 and 2001 (Leth et al. 1999; Larsen
& Leth 2001).
sediments off the littoral zone of the Danish North Sea coast
had been concentrated on the Jutland Bank area (Fig. 1; Leth
1996, 1998). Knowledge on the sedimentary conditions and
processes along the entire west coast of Jutland has, however,
significantly increased as a result of 2000 km of newly
acquired high-resolution seismic and side-scan sonar data,
supplemented by about 100 vibrocores. These data were col-
lected by the Geological Survey of Denmark and Greenland
(GEUS) during joint projects with the Danish Coastal
Authority between 1998 and 2001 (Leth et al. 1999; Larsen
& Leth 2001).
The coastal zone off west Jutland displays a highly
dynamic environment, where sediment transport is governed
by strong tidal and wave-induced currents. The net wave-
generated current is south going, while the coastal current
has a net direction towards the north (Knudsen et al. 2002).
The direction of the net littoral drift is southward from the
outlet of Limfjorden to Blåvands Huk, with net erosion
north of Nymindegab and aggregation to the south; the off-
shore part of this depositional system has recently been stud-
ied (Larsen & Leth 2001).
by strong tidal and wave-induced currents. The net wave-
generated current is south going, while the coastal current
has a net direction towards the north (Knudsen et al. 2002).
The direction of the net littoral drift is southward from the
outlet of Limfjorden to Blåvands Huk, with net erosion
north of Nymindegab and aggregation to the south; the off-
shore part of this depositional system has recently been stud-
ied (Larsen & Leth 2001).
Seabed geology
The present coast between Nymindegab and Limfjorden is a
highly erosive, wave-dominated, high-energy barrier coast
subdivided by glacial headlands. The natural retreat of the
coast profile is in the order of 25 m/year. Mapping of the
geological substratum reveals a complex range of lithologies,
of which five types are dominant: (1) Weichselian glacial till,
(2) Saalian till, (3) Weichselian outwash deposits, (4) Eemian
marine deposits and (5) Miocene sediments (Fig. 2). The
development of the coast and sand transport has been closely
linked to the subsurface geology since the onset of the
Holocene transgression and up to the present (Leth 1996,
1998; Anthony et al. in press).
highly erosive, wave-dominated, high-energy barrier coast
subdivided by glacial headlands. The natural retreat of the
coast profile is in the order of 25 m/year. Mapping of the
geological substratum reveals a complex range of lithologies,
of which five types are dominant: (1) Weichselian glacial till,
(2) Saalian till, (3) Weichselian outwash deposits, (4) Eemian
marine deposits and (5) Miocene sediments (Fig. 2). The
development of the coast and sand transport has been closely
linked to the subsurface geology since the onset of the
Holocene transgression and up to the present (Leth 1996,
1998; Anthony et al. in press).
Distribution and transport of mobile sand
North of Nymindegab the thickness and regional distribu-
tion of the upper layer of fine- to medium-grained marine
sand have been mapped (Fig. 3). The accumulations can be
tion of the upper layer of fine- to medium-grained marine
sand have been mapped (Fig. 3). The accumulations can be
considered as positive morphological forms. Twelve samples
from the sand have yielded dates from 150 to 835 years B.P.
(calibrated C-14 radiocarbon ages). The sand unit is there-
fore regarded as mobile sand representing the recent to sub-
recent hydrographic regime. A regional erosional uncon-
from the sand have yielded dates from 150 to 835 years B.P.
(calibrated C-14 radiocarbon ages). The sand unit is there-
fore regarded as mobile sand representing the recent to sub-
recent hydrographic regime. A regional erosional uncon-
Sediment distribution and transport in the shallow
coastal waters along the west coast of Denmark
coastal waters along the west coast of Denmark
Jørgen O. Leth, Birger Larsen and Dennis Anthony
Fig. 1. Location map of the studied
offshore coastal zone covering
approximately 2300 km
2
. The two
boxes (red) mark the key areas for
the study. The depth interval is 5 m.
Geological Survey of Denmark and Greenland Bulletin 4, 4144 (2004) © GEUS, 2004
42
Fig. 2. Map showing the seabed geology below the mobile sand layer.
Fig. 3. Map showing the thickness and distribution of the mobile sand
layer.
formity underlying the sand layer suggests that the hydrody-
namic energy level in the coastal zone may have increased
within the past millennium. As the unit is less than 0.5 m
thick in most of the study area, the sand available for sedi-
ment transport in the area is obviously limited. However, the
mobile sand occurs as NESW-trending shoreface-connected
ridges close to the coast between Nymindegab and Bovbjerg
(Anthony & Leth 2002) that extend into large sand-bodies
farther offshore. The formation of two large sand accumula-
tion areas, 15 and 30 km long and with a NNWSSE trend,
is not clearly understood (Fig. 3). Their existence is most
likely due to a combination of a hydrographically controlled
sediment transport pattern and the presence on the nearby
seabed of sandy outwash deposits. Due to the young age of
the deposits and the shape of present bedforms, it is suggested
that the Jutland coastal current is the major agent responsible
for the reworking and redistribution. The overall oblique
form of the sand relative to the coast is explained by the fact
that the offshore NNW-directed tidal flood current is
stronger than the tidal ebb current. That the northern sand
body is much larger than the southern seems to reflect the
general northwards decrease of the tidal strength, leading to
a decrease in tidal current sediment transport capacity
towards the north, and thus net deposition. It is probable that
a sediment transport system interacting between the study
area and the adjacent area further west exists, but to test this
more research is needed.
namic energy level in the coastal zone may have increased
within the past millennium. As the unit is less than 0.5 m
thick in most of the study area, the sand available for sedi-
ment transport in the area is obviously limited. However, the
mobile sand occurs as NESW-trending shoreface-connected
ridges close to the coast between Nymindegab and Bovbjerg
(Anthony & Leth 2002) that extend into large sand-bodies
farther offshore. The formation of two large sand accumula-
tion areas, 15 and 30 km long and with a NNWSSE trend,
is not clearly understood (Fig. 3). Their existence is most
likely due to a combination of a hydrographically controlled
sediment transport pattern and the presence on the nearby
seabed of sandy outwash deposits. Due to the young age of
the deposits and the shape of present bedforms, it is suggested
that the Jutland coastal current is the major agent responsible
for the reworking and redistribution. The overall oblique
form of the sand relative to the coast is explained by the fact
that the offshore NNW-directed tidal flood current is
stronger than the tidal ebb current. That the northern sand
body is much larger than the southern seems to reflect the
general northwards decrease of the tidal strength, leading to
a decrease in tidal current sediment transport capacity
towards the north, and thus net deposition. It is probable that
a sediment transport system interacting between the study
area and the adjacent area further west exists, but to test this
more research is needed.
The prograding coast
The coast south of Nymindegab is aggrading at about 0.52
m/year. Over a distance of 25 km it has prograded some 3 km
westwards in the form of a beach ridge system during the last
3000 years (Nielsen et al. 1995; Larsen & Andersen in press).
The development of the back-barrier area from 8000 to 3000
years B.P. is not well known because of the 510 m thick
cover of aeolian sand. Most of the deposition in this area took
place in lagoons, like that of the present day Ho Bugt, in lakes
dammed between the littoral deposits and the Saalian land-
scape, or in the form of large dunes and cover sands. The
south-east-trending peninsula Skallingen is a very young
(after A.D. 1600) analogue to a barrier island. The westward-
protruding bank of inner Horns Rev belongs to the same sys-
tem. Blåvands Huk forms the centre of a major sand
accumulation area some 25 km long, 515 km wide and
1525 m thick, with a total volume of about 6 km
m/year. Over a distance of 25 km it has prograded some 3 km
westwards in the form of a beach ridge system during the last
3000 years (Nielsen et al. 1995; Larsen & Andersen in press).
The development of the back-barrier area from 8000 to 3000
years B.P. is not well known because of the 510 m thick
cover of aeolian sand. Most of the deposition in this area took
place in lagoons, like that of the present day Ho Bugt, in lakes
dammed between the littoral deposits and the Saalian land-
scape, or in the form of large dunes and cover sands. The
south-east-trending peninsula Skallingen is a very young
(after A.D. 1600) analogue to a barrier island. The westward-
protruding bank of inner Horns Rev belongs to the same sys-
tem. Blåvands Huk forms the centre of a major sand
accumulation area some 25 km long, 515 km wide and
1525 m thick, with a total volume of about 6 km
3
. This
Holocene spit complex is built out onto an erosional, very flat
platform at about 20 m below present sea level, west of the
old Saalian glacial landscape. The whole complex has accu-
mulated steadily throughout the past 8000 years, and is still
very active.
platform at about 20 m below present sea level, west of the
old Saalian glacial landscape. The whole complex has accu-
mulated steadily throughout the past 8000 years, and is still
very active.
Inner Horns Rev is a 6 km wide and 20 km long bank pro-
truding westwards from Blåvands Huk (Fig. 4). New investi-
gations indicate that it is highly dynamic, with active sand
accumulation particularly on the slopes. The direction of
progradation suggests longshore sediment transport (Fig. 4).
C-14 datings suggest that it has prograded some 3.5 km west-
wards during the last 800 years.
gations indicate that it is highly dynamic, with active sand
accumulation particularly on the slopes. The direction of
progradation suggests longshore sediment transport (Fig. 4).
C-14 datings suggest that it has prograded some 3.5 km west-
wards during the last 800 years.
The shape of the Blåvands Huk spit complex is due to a
combination of wave-dominated longshore sediment trans-
port from the north, tidal influence and the partial shelter
from the offshore banks at Horns Rev. According to recent
estimates by the Danish Coastal Authority (Kystdirektoratet
2001), some 2.3 million m
port from the north, tidal influence and the partial shelter
from the offshore banks at Horns Rev. According to recent
estimates by the Danish Coastal Authority (Kystdirektoratet
2001), some 2.3 million m
3
of sediments are supplied annu-
ally to the system from the north.
A second accumulation system is located at the outer
Horns Rev to the south-west (Fig. 4). This is separated from
the inner Horns Rev by the channel Slugen. The base of
Horns Rev is an erosional unconformity on top of Eemian
marine silt in the central part, and on Saalian glacial deposits
further to the west. A wide valley has been cut into Eemian
deposits and subsequently filled with Weichselian glacioflu-
vial deposits, with remnants of small Lower Holocene bogs
on the top (Fig. 5).
the inner Horns Rev by the channel Slugen. The base of
Horns Rev is an erosional unconformity on top of Eemian
marine silt in the central part, and on Saalian glacial deposits
further to the west. A wide valley has been cut into Eemian
deposits and subsequently filled with Weichselian glacioflu-
vial deposits, with remnants of small Lower Holocene bogs
on the top (Fig. 5).
From the present study it is now clear that Horns Rev con-
sists of Holocene sand with gravel deposited after the sea
transgressed the area in Early Holocene time, about 8500
years B.P., and is not a Saalian terminal moraine as has been
previously proposed. Precisely how the outer Horns Rev has
formed is not clear, but all sediment structures suggest west-
erly sediment transport. At southern Horns Rev the lower
transgressed the area in Early Holocene time, about 8500
years B.P., and is not a Saalian terminal moraine as has been
previously proposed. Precisely how the outer Horns Rev has
formed is not clear, but all sediment structures suggest west-
erly sediment transport. At southern Horns Rev the lower
43
Fig. 4. Sediment transport directions for the Holocene marine sand deter-
mined from direction of sediment structures, distribution of sediment
thickness and modelling of recent sediment transport by the Danish
Hydraulic Institute. A: section shown in Fig. 5.
44
part is a complex of gravel-rich spits that have grown towards
the east-north-east. Prograding reflectors and sand waves also
suggest a net eastward aggradation. This is in agreement with
the annual average direction and magnitude of recent sedi-
ment transport, as modelled by the Danish Hydraulic
Institute (DHI). On a day-to-day basis the sediment trans-
port is very variable, in response to the strong tidal currents
and the breaking waves. Sediment transport from a west-
south-westerly direction is also indicated by the direction of
progradation and the now buried spits in the up to 15 m
thick Holocene successions further to the north. The net
direction of sediment transport based on this evidence is
shown in Fig. 4.
the east-north-east. Prograding reflectors and sand waves also
suggest a net eastward aggradation. This is in agreement with
the annual average direction and magnitude of recent sedi-
ment transport, as modelled by the Danish Hydraulic
Institute (DHI). On a day-to-day basis the sediment trans-
port is very variable, in response to the strong tidal currents
and the breaking waves. Sediment transport from a west-
south-westerly direction is also indicated by the direction of
progradation and the now buried spits in the up to 15 m
thick Holocene successions further to the north. The net
direction of sediment transport based on this evidence is
shown in Fig. 4.
The Blåvands Huk Horns Rev area has been a major
depocenter for sediments transported southwards along the
west coast, as well as material presumably eroded from the
floor of the North Sea, in spite of the very exposed setting.
west coast, as well as material presumably eroded from the
floor of the North Sea, in spite of the very exposed setting.
References
Anthony, D. & Leth, J.O. 2002: Large-scale bedforms, sediment distribu-
tion and sand mobility in the eastern North Sea off the Danish west
coast. Marine Geology 182, 247263.
coast. Marine Geology 182, 247263.
Anthony, D., Leth, J.O., Konradi, P. & Andersen, L.T. in press: Shallow
seabed geology and paleogeography off the Danish North Sea coast.
Boreas.
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Knudsen, S.B., Laustrup, C., Madsen, H.T. & Christensen, E.D. 2002:
Sediment transport in the outer part of the coastal profile, 113. 28th
International Conference on Coastal Engineering, Cardiff, Wales.
International Conference on Coastal Engineering, Cardiff, Wales.
Kystdirektoratet 2001: Kystdirektoratets program for undersøgelser og
udvikling, 19982001, Slutrapport, 36 pp. Lemvig: Kystdirektoratets
Kysttekniske Afdeling.
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morphogenesis in the eastern North Sea: Horns Rev and Fanoe Bay
area and its relation to onshore geology. Netherlands Journal of
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Geosciences.
Larsen, B. & Leth, J.O. 2001: Regionalgeologisk tolkning og en samlet
vurdering af aflejringsforholdene i området mellem Nymindegab og
Horns Rev. Danmarks og Grønlands Geologiske Undersøgelse
Rapport 2001/96, 83 pp.
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Bank and the initiation of the Jutland Current, NE North Sea.
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processes of the Jutland Bank region, NE North Sea, 173 pp.
Unpublished Ph.D. thesis, University of Aarhus, Denmark.
Unpublished Ph.D. thesis, University of Aarhus, Denmark.
Leth, J.O., Anthony, D., Andersen, L.T. & Jensen, J.B. 1999: Geologisk
kortlægning af Vestkysten. Regionalgeologisk tolkning af kystzonen
mellem Lodbjerg og Nymindegab. Danmarks og Grønlands
Geologiske Undersøgelse Rapport 1999/75, 29 pp.
mellem Lodbjerg og Nymindegab. Danmarks og Grønlands
Geologiske Undersøgelse Rapport 1999/75, 29 pp.
Nielsen, S.T., Andreasen, F. & Clemmensen, L.B. 1995: The middle and
late Holocene barrier spit system at Vejers, Denmark: structure and
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Authors' addresses
J.O.L. & B.L., Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. E-mail: jol@geus.dk
D.A., Royal Danish Administration of Navigation and Hydrography, Overgaden o. Vandet 62 B, P.O. Box 1919, DK-1023 Copenhagen
K, Denmark.
J.O.L. & B.L., Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. E-mail: jol@geus.dk
D.A., Royal Danish Administration of Navigation and Hydrography, Overgaden o. Vandet 62 B, P.O. Box 1919, DK-1023 Copenhagen
K, Denmark.
Fig. 5. Geological cross-section of outer Horns Rev. Location shown on Fig. 4. The numbers above each borehole indicates displacement relative to
cross-section.
