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Geological Society, London, Special Publications
Palaeogene volcanism: the sedimentary record in
Denmark
O. B. Nielsen and C. Heilmann-Clausen
Geological Society, London, Special Publications 1988, v.39;
p395-405.
doi: 10.1144/GSL.SP.1988.039.01.35
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Palaeogene volcanism: the sedimentary record in Denmark
O. B. Nielsen & C. Heilmann-Clausen
SUMMARY: Approximately 200 volcanic ash layers are known from Palaeocene and
Eocene marine clays in Denmark. The oldest layers are present in the upper part of the
Upper Palaeocene and are sporadic, thin and acidic in composition. The main volcanic
phase took place at the Palaeocene-Eocene transition. During the main phase, a supply from
the N to NE is indicated, while a few layers probably had a source to the NW or W. A later
volcanic phase is represented by thin and more sporadic ashes in the Lower to Middle
Eocene. These are almost totally transformed to smectite.
In the Upper Palaeocene, and partly in the Lower Eocene, smectite is a highly dominant
clay mineral in the interbedded clays. Zeolites of the heulandite--clinoptilolite type are also
present, while cristobalite is sporadically present in the lower part. A major supply of
smectite from the N Atlantic may be indicated. Below the ash-bearing sequence the only
evidence for volcanic activity is the presence of very smectite-rich, zeolitic clays with
scattered opal-CT and slightly silicified horizons. Calculated chemical compositions of
smectites from both ash layers and clay layers between ash layers and below the ash-bearing
sequence are almost identical, indicating a volcanic source for the smectite.
The conspicuous black, sandy layers of the
Danish Palaeogene Fur Formation were known
already by Forchhammer (1835) and their identity
as volcanic ash layers was revealed more than a
century ago, by Prinz & van Ermengem (1883).
Since then, Palaeogene ash layers have been
found in several other Danish formations and all
over the North Sea Basin. It is the purpose of this
study to describe the Danish Palaeogene ashes
and associated clays and discuss their age and
provenance.
Since their recognition the ash layers, in
particular those of the Fur Formation, have been
subject to many different analyses. B~ggild (1918),
Andersen (1937) and Norin (1940) analyzed their
thickness and grain size, while B~ggild (1918),
Madirazza & Fregerslev (1969) and Pedersen et
al. (1975) also focused on their petrographic and
chemical composition. Nielsen (1974) and Pedersen (1981) discussed depositional environments
and Heilmann-Clausen et al. (1985) and Pedersen
& Surlyk (1983) established a modern lithostratigraphy for the ash-bearing sequence. The deposits
have been dated primarily by means of dinoflagellate cysts (Hansen 1979; Heilmann-Clausen
1982, 1983, 1985; Nielsen & Heilmann-Clausen
1986) and calcareous nannofossils (Perch-Nielsen
1967, 1971 ; Thiede et al. 1980). A biostratigraphic
study of silicoflagellates (Perch-Nielsen 1976)
from the Fur Formation also gives information
on the age.
Localities studied and discussed in the present
work are shown in Figure 1. The stratigraphy
and chronology of the Danish ash-bearing deposits and their North Sea equivalents are shown in
Figure 2.
Methods
Ash and clay layers were subject to: (1) grain-size
analysis, after disaggregation by shaking in water
for 72 hours and repeated ultrasonic treatment,
by combined sieving and settling in Andreassen
settling tubes; (2) determination of total organic
carbon (TOC), sulphur and carbonate in a LECO
induction furnace; (3) chemical analysis of whole
rock samples by atomic absorption spectroscopy
(AAS); (4) bulk mineralogical composition by
means of X-ray diffraction (XRD) and quantified
using the principles described by Schultz (1960);
(5) clay mineralogy of the < 2 vm fraction (XRD).
XRD analyses were performed on a Philips
diffractometer, with Cu K~ radiation and an
automatic divergence slit. The clay fraction was
investigated using oriented smear-slide preparations (Gibbs 1971). Records were made of airdried, of glycolated (24 hours at 60 ~
and of
heated (to 300 ~ and to 550 ~ for two hours)
preparations respectively. The minerals were
determined according to Brindley & Brown
(1980). The semiquantitative estimate of the clay
mineral composition is carried out using peak
areas corrected with empirically estimated correction factors from the glycolated diffractograms.
Preparations for dinoflagellate biostratigraphy
were produced following normal palynological
techniques (for details, see Heilmann-Clausen
1985).
The biostratigraphy of Danish Upper Palaeocene to Middle Eocene sediments is mainly
based on dinoflagellates, since calcareous microfossils are usually absent. The only exception is
From MORTON,A. C. & PARSON,L. M. (eds), 1988, Early Tertiary Volcanism and the Openingof
the NE Atlantic, Geological Society Special Publication No. 39, pp. 395-405.
395
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396
O. B. Nielsen & C. Heilmann-Clausen
......
f
I" "i GEOpHYSiCAL
! ANOMALY
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a SALT
/~&
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EALAN
FIo. 1. Map of Denmark and surroundings with localities.
DINO-ZONES
MA
AGE
NP
Denmark
NW Europe
North Sea
numbers
52- MID. EOC.
of
Beggild
(1918)
53
EARLY
GROUP
{PART)
12"
g
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~:
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y LILLEB/ELT
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LITHOSTRATIGRAPHY
Denmark
Ash layers
NNW (Fur)
rl
_
_
_
_
L1
_
R6
ROSN/ES
CLAY
FM.
11"
D.varielongitudum
56-
R4
.....
10
Knuds~ovedMb.
BALDER
FORM. ',s ~ s ;
SELE
FORM
9
A.hyperacant hum
8
D.
/~,.
speciosa//m-argarita
LATE
PAL EOC.
60-
O.simile
W. ast ra'+ ~/. meckelfe~d.
D. oebisfeld. /
Acme
J
58
59-
R5
EOCENE
7
LISTA
FORM.
.
R1- R3
~'[]ILIIiLIa,~,,~I;I]IIIJl]IiJH!ILJIIIEIIH
.... i~
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91--FUR
FM.
K n u d e k l i n t Mb.
"series'-33-
V. . . . Idb.
OLST FORM.'
I ~
Haslund Mb.
GREY CLAY
HOLMEHUS
FORM.
( PART )
3
GREY
CLAY (PART)
FiG. 2. Stratigraphy and age of the Danish ash-bearing deposits and their North Sea equivalents. The
lithostratigraphy of Denmark is from Heilmann-Clausen et al. (1985) and Pedersen & Surlyk (1983). The North
Sea stratigraphy is from Deegan & Scull (1977). Dinoflagellate zones of Denmark and correlations between
Denmark and the North Sea are from Heilmann-Clausen (1985). NW European dinoflagellate zones are from
Costa et al. (1978) and Knox et al. (1981). Only calcareous nannoplankton zones (NP Zones) marked with an
asterisk are identified in Denmark, other NP Zones are inferred from the dinoflagellate zonation. The calibration
between absolute ages and NP Zones is from Berggren et at. (1985).
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Palaeogene sedimentary record in Denmark
the Lower Eocene Rosna~s Clay Formation, in
which the age is evaluated based on both
calcareous nannofossils and dinoflagellates.
The age is given in terms of standard calcareous
nannoplankton zones (NP Zones) in the Rosn~es
Clay Formation. In the non-calcareous formations, the equivalent NP Zones may in some
cases be inferred based on dinoflagellate zonation.
The dinoflagellate biostratigraphy of the Upper
Palaeocene to Middle Eocene in the North Sea
Basin (including Denmark) is developed by, in
particular, Costa & Downie (1976), Costa et al
(1978), Knox & Harland (1979), Knox et al.
(1981), De Coninck (1975, 1977, 1981) and
Heilmann-Clausen (1985). The zonation of Heilmann-Clausen (1985) integrates previous zonations covering the Upper Palaeocene and
lowermost Eocene and is used here. For the
Lower to Middle Eocene the zonation of Costa et
al. (1978) is adopted. Additional information is
taken from Nielsen & Heilmann-Clausen (1986)
regarding identification of the Lowe~Middle
Eocene boundary.
Results and discussion
The evidence for volcanism
The main evidence for volcanism is the presence
of ash layers, and the best proof for a volcanic
ash layer is the presence of volcanic glass.
Ash layers containing glass as well as argillized
ash layers, in which the glass has been transformed, are known in the Danish Palaeogene.
The ash-bearing deposits are shown in Figure 2.
The ashes may be separated into three phases:
(1) The layers of the earliest phase occur in the
top of the Holmehus Formation and lower
part of the Gist Formation and Fur Formation. Most of the sequence was numbered -1
to -39 by Boggild (1918), and is known as the
'negative series' (see Fig. 2).
The layers in the 'negative series' generally
contain considerable amounts of glass. They
have a variety of compositions--basaltic,
dacitic, Iiparitic and peralkaline (Pedersen et
al. 1975)--and are often partly transformed
to clay minerals and zeolites. The composition
of the few, thin ashes from the Holmehus
Formation is not yet known.
(2) The middle phase, which is the main phase
of the Palaeogene volcanism, is present in the
upper part of the Fur and (311st Formations.
The ashes of this phase, the 'positive series'
(3)
397
of Boggild (1918), are numbered + t to + 140
(see Fig. 2).
The layers in the main phase generally
contain considerable amounts of glass, they
are thick, frequent and appear fresh and
unaltered. Their composition is generally
basaltic.
The later phase includes approximately 19
thin layers in the Rosn~es Clay Formation
and the lower part of the Lilleb~elt Clay
Formation. These layers are argillized and
only contain little, if any, glass. They probably
had a basaltic composition as they, like the
basaltic ashes below, have a relatively high
Ti content (Gersner 1980). These altered ash
layers still have very sharp boundaries and
usually show graded bedding (Fig. 3).
Another line of evidence for volcanism can be
found in the interbedded clay and in the clays
above and below the ash-bearing sequence. The
mineralogy of these clays is well known (Nielsen
1974; Thiede et al. 1980; Heilmann-Clausen et
al. 1985; Nielsen & Heilmann-Clausen 1986).
Smectite is the dominant mineral, but zeolites of
the heulandite-clinoptilolite type are always
present in the Gist Formation and occasionally
present below, besides other minerals. Cristobalite is sporadically present in the (01st Formation,
as sand-sized grains in the clay, and as a
diagenetic cement in silicified horizons. Silicified
layers are also common in the clay below the
Holmehus Formation. Mfiller (1967) has proposed that smectite, mainly nontronite, zeolites
and free silica, which might lead to cristobalite
formation, is a typical mineral paragenesis
formed by transformation of basaltic material.
However, this mineral paragenesis may also
develop from non-volcanic precursors,
Figure 4 shows the average smectite content of
the clay fraction ( < 2 Ixm) in the upper part of the
FIO. 3. Argillized ash layer from the Rasna~sClay
Formation. The match is 4.7 cm long.
Downloaded from http://sp.lyellcollection.org/ at Universitetet i Oslo on June 20, 2013
398
O. B. Nielsen & C. Heilmann-Clausen
E
ta
z-
z
NW
~~j
s,Ls....
i~J
~
.~-
,.lalwo
E
::L
Z
~ t=~
u~
8
8
o
~
e l . , L.,E.
.oJ
z_
z
-----e
_
I
J
NW
J
SE
~o.
_z
,I,",-
a
~c
ASH
LAYERS
o_o_
o.
O.
c0
O
O-
o
,ILTRUP
NW
OLST
I:II~JLE
ULSTRUP
SE
FIG. 4. NW-SE profile showing: Total thickness in cm, average median in Fm and average smectite content in
of all identified clay layers. Total thickness in cm, average median in I.tmand average sand content in ~ of all ash
layers identified with certainty at the four localities (mainly thick basaltic layers in the main phase).
Olst Formation from three localities. The average
mineral composition of the clay from the Holmehus Formation and of transformed ash layers
from the Rosna~s Clay Formation is shown in
Figure 5. Pyrite and carbonates are not included.
It is obvious that the whole rock composition is
very similar in the two types of layers, strongly
suggesting a volcanic origin of both.
The chemical composition of smectites in
argillized ashes from the Rosnms Clay Formation
is compared to the chemical composition of
smectites in the Holrnehus Formation (Fig. 6).
The whole-rock chemical composition was
subject to different calculations in order to
determine the chemical composition of the
smectites, which make up 85-90~ of the wholerock mineralogy. Carbonates, pyrite, quartz,
feldspars, kaolinite and illite were quantified
partly by means of chemical analyses, and partly
by X-ray diffraction; a proportional amount of
the relevant chemical composition was subtracted
from the whole-rock composition. The remaining
chemical components were recalculated to 100~
(water-free).
It is evident that the composition of the
smectites from the two different types of layers is
almost identical, and relatively close to the
nontronitic composition, mentioned by Miiller
(1967) as the normal mineral formed by alteration
of volcanic material. Thus, the mineralogical and
chemical composition of the Holmehus Formation suggests a volcanic origin for the smectites
from this unit, though only few ash layers are
present. It is most likely that smectites from the
clays and marls underlying the Holmehus Formation also have a volcanic origin, since, apart
from being carbonate-bearing, they have a very
similar mineralogical composition. A nontronitic
Downloaded from http://sp.lyellcollection.org/ at Universitetet i Oslo on June 20, 2013
Palaeogene sedimentary record in Denmark
399
FIO. 5. Average whole-rock mineralogical composition, based on XRD, of the Holmehus Formation and some
argillized ash layers in the R~sn~es Clay Formation from Danish outcrops and borings. Recalculated to 100~
after subtraction of carbonates and pyrite.
FIG. 6. Average chemical composition of smectites from the Holmehus Formation and some argillized ash layers
in the R~sn~esClay Formation from Danish outcrops and borings. Recalculated to 100~ waterfree.
composition of these smectites has not, however,
been proved.
Age
The biostratigraphy and the age of the Danish
late Palaeocene to Middle Eocene is summarized
in Figure 2. The oldest ash layers in the top of the
Holmehus Formation occur on the islands of
Mors and Fur in northwestern Jutland (see Fig.
1). The ash layers on Fur belong to dinoflagellate
Zone 5 of Heilmann-Clausen (1985), probably
near the oldest part of the zone. Dinoflagellate
Zone 5 may correlate to the upper part of the
Lista Formation in the North Sea and to Sables
d'Erquelinnes in Belgium (see Heilmann-Clausen 1985). The latter unit contains calcareous
nannofossils clearly indicating the NP9 Zone (De
Coninck et al. 198 I). The correlation with Sables
d'Erquelinnes therefore suggests that the oldest
ashes in Denmark are of late Palaeocene age,
time-equivalent to the NP9 Zone.
The overlying ash sequence in the Olst and Fur
Formations contain the ashes numbered from
- 3 9 to + 140 by Boggild (1918) (see Fig. 2). The
lowermost of these, Nos - 39 to - 33, belong to
dinoflagellate Zone 6 of Heilmann-Clausen
(1985), while the overlying main part, at least
above ash layer - 19b, belongs to zone 7. Zone 6
is equivalent to the lower part of the Apectodinium
(formerly Wetzeliella) hyperacanthum Zone of
Costa & Downie (1976), while Zone 7 corresponds
to the Deflandrea oebisfeldensis acme interval of
Knox & Harland (1979) (see Fig. 2). In the North
Sea Zone 6 is present in the lower part of the Sele
Formation, and Zone 7 in the upper part of the
Downloaded from http://sp.lyellcollection.org/ at Universitetet i Oslo on June 20, 2013
400
O. B. Nielsen & C. Heilmann-Clausen
Sele Formation and in the Balder Formation (see
Heilmann-Clausen 1985). In terms of silicoflagellate biostratigraphy the Fur Formation may
be referred to as the Naviculopsis constrieta Zone
(Perch-Nielsen 1976).
The exact age of the Olst and Fur Formations
and their North Sea equivalents is uncertain,
Most likely, they are of latest Palaeocene to
earliest Eocene age, and there is some evidence
to suggest that the Palaeocene-Eocene boundary
is located close to the base of the Fur Formation.
Various ages for these formations have previously
been proposed and their chronostratigraphical
position will therefore be discussed below. The
current use of the Palaeocene-Eocene boundary
as equal to the boundary between the calcareous
nannofossil Zones NP9 and N P I 0 (e.g. Berggren
et al. 1985; Martini & M/iller 1986) is adopted
here.
A correlation between the ash sequence in the
Fur Formation, in the North Sea and the N
Atlantic is proposed by Knox (1984) based on
variations in the chemical composition of feldspars in the ash layers. According to Knox (1984)
the N Atlantic Deep Sea Drilling Project (DSDP)
Site 550 contains an ash sequence that may be
correlated to the Danish ash series from ash layer
No. - 17 to the top of the Fur Formation. The
entire ash sequence in Site 550 is included in the
lower part of the NP10 Zone, i.e. in the earliest
Eocene, and the NP9/NP10 boundary is situated
approximately eight metres below the presumed
ash layer - 17 in Site 550. In the Fur Formation
ash layer - 17 is present in the lower part, and
consequently most or all of the Fur Formation
may be referred to the NP10 Zone. However, this
conclusion is completely dependent on the correct
identification of the ash layer - 17 from Site 550.
The location of the Palaeocene-Eocene boundary
in Denmark is thus based on a long distance
correlation, and should therefore be considered
with caution.
Heilmann-Clausen (1982) previously used the
W. astra dinoflagellate Zone as a base Eocene
marker, following Costa & Mfiller (1978). On this
basis the Palaeocene-Eocene boundary should
be located immediately above the Fur Formation.
However, the validity of using the W. astra Zone
as a basal Eocene marker has been questioned by
Morton et al. (1983).
The ash layers in the Rosna~s Clay Formation
may be confidently dated as Early Eocene, based
on calcareous nannoplankton and dinoflagellate
assemblages. The calcareous beds of this formation, R4 and R5, are referred to NP Zones 11 and
12 (Thiede et al. 1980). The W. astra and W.
meckelfeldensis zones are identified in the basal
Knudshoved Member and bed R1 (Heilmann-
Clausen 1982; Nielsen & Heilmann-Clausen
1986) while the Dracodinium simile, D. varielongitudum and Kisselovia coleothrypa Zones are
identified in beds R4 and R5 (Heilmann-Clausen
1983; Nielsen & Heilmann-Clausen 1986).
The youngest ash layers occur in the Lower
Lilleb~elt Clay (beds L1 to L3). Nielsen &
Heilmann-Clausen (1986) correlated the dinoflagetlate assemblages of these units with assemblages in Belgium, the Netherlands and southern
England. They indicated that the Lower-Middle
Eocene boundary lies within beds L1 to L3. This
is based in particular on the first occurrence of
Areosphaeridium diktyoplokus in bed R6 and the
last occurrence of Eatonicysta ursulae in bed L4.
Consequently, the latest ash layers, known from
Denmark, were deposited approximately at this
boundary, i.e. near the NP13/NP14 boundary.
The source of the ash layers
The source, dispersal and deposition of the ashes
have been the subject of much discussion. The
ashes are all well sorted and well graded. The
thickness of ash layer No. + 62 (Fig. 7) and other
similar isopach maps have been used to conclude
(Andersen 1937), that the volcanoes were situated
in Skagerrak (see Fig. 1). Geophysical anomalies
(Am 1973) and basalt dredged from the area
(Noe-Nygaard 1967) support this hypothesis.
Fig. 8 is a profile from NW to SE in Denmark,
showing grain sizes and thicknesses from N W to
SE in Denmark for ash layer No. + 62 and for
I i i i i I
0
5 0 km
/
/
ASH LAYER +62
ISOPACHe, MAP IN CM
FIG. 7. Isopach map of ash layer No.
from Andersen 1937).
-I-
62 (modified
Downloaded from http://sp.lyellcollection.org/ at Universitetet i Oslo on June 20, 2013
Palaeogene sedimentary record in Denmark
40 I
~u
r
Z
Z
~
,
ULSTI~
OLST
I
-
ROJLE
I
NW
ULSTRUP
;
SE
('4a~
_z
~=
o
~
ASH
LAYER
+62
~.
o
2
I
i
i
SILSTRUP
HARRE
OLST
i
R EI'JLE
!
ULSTRUP
SE
FZG. 8. NW-SE profile of ash layer No. + 62 and clay layer between ash layers Nos. + 62 and + 63, showing the
variation in grain size, thickness and srnectite content.
NW
the clay layer between ash layer Nos + 62 and
+ 63. Fig. 4 shows the same profile, in which the
total thicknesses and average grain-size parameters and smectite contents (only for clay layers)
are plotted for all ash and clay layers identified at
selected localities.
In the following, the regional variations in
thickness and grain size of ash layers and
interbedded clay layers will be compared. The
thickness patterns outside the Limfjord area and
their relations to the Limfjord area as a whole
will be discussed first, and afterwards the detailed
distribution within the Limfjord area will be
described and interpreted.
Outside the Lirafjord area
It is evident from Fig. 8 that the ash layer No.
+ 62 is coarsest in the Limfjord area and much
finer grained to the SE. The thickness is greatest
at Olst and decreases to the S or SE. In the clay
layer between ash layers Nos + 62 and + 63 the
same decrease in grain size and thickness is seen.
The decrease in the grain size is expressed as an
increase in smectite content because of the smaller
size of smectite particles compared to other clay
minerals. The pattern for ash layer No. + 62 and
for the clay layer between ash layers Nos + 62
and + 63, seems to be characteristic of most of
the ash and clay layers. As seen from Fig. 4 the
thickness, grain size and smectite patterns for all
ash and clay layers identified at four localities
(see Fig. 6) are similar from 131st towards the S
and SE. The clay layers were deposited by settling
in the sea water and the patterns of parameters
seem to indicate a supply from the N and N W
and a dispersal by water currents to the S and SE.
As the ash layers show the same trends outside
the Limfjord area, it is suggested that the supply
and dispersal mechanism for the ash layers S and
SE of the Limfjord area were the same, i.e. a
transport from N and N W to S and SE by a
current.
The Limfjord area
The maximum grain size of the ashes in the
Limfjord area is ca. 0.5 mm, with an average size
Downloaded from http://sp.lyellcollection.org/ at Universitetet i Oslo on June 20, 2013
402
O. B. Nielsen & C. Heilmann-Clausen
of 0.1 mm. The relatively coarse grain size in the
Limfjord area (mean=100 ~tm) and its rapid
decrease to Olst (mean=13 ~m) indicates a
relatively short distance to the source of the
volcanic material. It is suggested that the main
transport mechanism from the volcanic centre(s)
to the Limfjord area was the generally northerly
winds, overprinted by a water current transport
becoming successively more dominant with decreasing grain size. The increase in thickness
from Silstrup to Olst is interpreted as indicating
that the original ash contained a considerable
amount of silt-sized fractions relative to the sand.
The silt-sized ash particles were more subject to
water-current transport than the sand, and are
therefore deposited further away from the volcano(es). The very good degree of sorting in most
ashes supports the hypothesis of silt winnowing.
Within the Limfjord area the grain-size and
thickness distribution of the ashes show characteristic trends (Boggild 1918; Andersen 1937;
Pedersen et al. 1975). According to these authors
the thickest and coarsest layers are generally
found on Fur. Both parameters decrease towards
the NW, S and E, indicating that the windborne
supply of coarse ash particles was located to the
N and N N E (see Pedersen et al. 1975).
As indicated on Figure 1, there may have been
more volcanic centres in the Skagerrak. Maim et
al. (1984) also suggested a source in the Skagerrak
region for the main part of the basaltic ashes in
Denmark. It is most likely, however, that some
of the acidic and more fine-grained ashes, as for
example No. + 19, have had another source,
possibly the British volcanic province.
In the North Sea Basin the clay mineralogy of
the Palaeogene section from the Norwegian Wells
30/5-1, 15/6-2 and 2/8-2, located in the central
parts of the Viking and Central Grabens, have
been analyzed (Sorensen & Nielsen 1981a, b, c).
In the Danish offshore sector the Wells B-l, C-l,
D-I, E-l, F-l, M-2x (Nielsen 1980), Lulu-1 and
Inez-1 were analyzed in this study. Onshore the
borings Harre, Viborg-1 (Thiede et al. 1980),
LB 38, D G I 83101 (Nielsen & Heilmann-Ctausen 1986), the wells T~nder-3 and P16n in W
Germany, besides several outcrops (Nielsen
1974; Heilmann-Clausen et al. 1985) have been
included in the project.
Smectite is a dominant, but variable, component in the clay fraction in the Palaeocene and in
parts of the Eocene sediments. This variation is
due in part to changes in the supply of other
minerals, i.e. the dilution effect. In order to find
an absolute measure for smectite deposition the
sedimentation rates for smectite have been
calculated.
Comparing these sedimentation rates for smec-
tites in different regions of the North Sea (Fig. 9)
quite distinct differences are revealed. In the
Central Graben, the Norwegian-Danish Basin,
on the Ringkobing-Fyn High and in the N
German Basin, the sedimentation rates were
small and with only small variations, although
there is an overall southward decrease in thickness. In the Viking Graben the sedimentation
rate was much greater. This might have been
caused by a shorter distance to main volcanic
centres in Scotland and in the opening N Atlantic.
FIG. 9. Average sedimentation rates in mm/ka for
smectites in different regions of the North Sea from
top Ekofisk Formation/top Danian Limestone to top
Balder Formation/top Fur and ~lst Formations.
Conclusions
(1) The evidence for the Palaeogene volcanism
is provided by:
a) The presence of more than 200 ash layers.
Downloaded from http://sp.lyellcollection.org/ at Universitetet i Oslo on June 20, 2013
Palaeogene sedimentary record in Denmark
b) The mineralogy of the sediments, and
especially the similarity in mineralogy of
argillized ash layers and interbedded
clays, i.e. the dominance of smectite and
presence of zeolites and cristobalite.
c) The almost identical chemical composition of smeetites from argillized ash layers
and the interbedded clays and the clays
of the Holmehus Formation indicates
that a volcanic origin for the Palaeogene
smectites is probable.
(2) The proposed ages for the Danish Palaeogene pyroclastic phases are:
a) The earliest recorded volcanic ash layers
are of late Palaeocene age, belonging to
the Danish dinoflagellate Zones 5 and 6
(probably equivalent to the NP9 Zone).
The ashes are present in the Holmehus
Formation and in the lower part of the
Olst Formation.
b) The age of the main phase in the Fur
Formation and upper part of the ~Olst
Formation is still unknown, but there is
some evidence for suggesting an early
Eocene (NP 10 Zone) age.
c) The latest phase is of Early Eocene age,
and terminated near the Early-Middle
403
Eocene boundary (i.e. during NP13 or
NP14).
(3) The provenance and transport mechanism of
the volcanic sediments are deduced as
follows:
a) The grain-size and thickness variations
suggest a relatively short distance to the
eruption centres, and that they were
situated N of the Limfjord area.
b) In southern Denmark both the ashes and
the interbedded clays show evidence of
transport by water currents from N W to
SE.
c) The deposition rate of smectite in the
Viking Graben is six times greater than
in the remaining part of the North Sea,
indicating a supply from a volcanic source
to the N or W, closer to the region than
the Skagerrak volcano.
ACKNOWLEDGEMENTS: Samples for this study were
kindly placed at our disposal by Norwegian Petroleum
Directorate, Geological Survey of Denmark, M~ersk
Olie & Gas A/S and Deutsche Texaco A/G. Financial
support has been given by the Danish Natural Science
Research Council.
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