Marine and Petroleum Geology 06 "1999# 090Ð007
Paleogene tu}aceous intervals\ Grane Field "Block 14:00#\
Norwegian North Sea] their depositional\ petrographical\ geochemical
character and regional implications
Helge Jarle Haaland a\ \ Harald Furnesb\ Ole J[ Martinsenc
a
Phillips Petroleum Company\ P[B[ 119\ 3945\ Tananger\ Norway
b
Geological Institute\ Allegt[ 30\ N!4996\ Bergen\ Norway
c
Norsk Hydro Research Centre\ N!4919\ Bergen\ Norway
Received 06 March 0887^ received in revised form 14 February 0888^ accepted 0 March 0888
Abstract
Paleogene volcaniclastic rocks from four wells from the Grane Field "Block 14:00#\ Southern Viking Graben on the western ~ank
of the Utsira High "North Sea#\ have been studied[ The tu}aceous intervals consist of the volcanic phase 0 "47Ð46 Ma# in the Vale
and Lista Formations\ and the volcanic phase 1 "44Ð41 Ma# in the Sele and Balder Formations[ Tu} beds of phase 0 are interpreted
as having been redeposited by turbidity currents\ whereas those of phase 1 re~ect normal settling of fall!out pyroclastics in water[
Two types of fragments occur\ the most abundant being vesicular pyroclasts with irregular shape and dark\ microlithic\ partly
vesicular granules\ representing shallow submarine\ Surtseyan!type eruptions[ The other type of pyroclastic fragments are vitric
shards\ which originate by quenching granulation during subaqueous eruptions[ The tu}aceous intervals have been subdivided into
"0# identi_ed pyroclastics based on textural interpretations\ and "1# assumed pyroclastics based on geochemical interpretations[ The
majority of the samples are sub!alkaline basalts and basaltic andesites[ The phase 0 tu}s evolved from basalts to rhyolites upwards
in the Lista Formation\ and phase 1 tu}s consist of sub!alkaline basalts and basaltic andesites of within!plate origin\ similar to the
contemporaneous Lower Basalts in East Greenland\ the Rockall Trough and the Middle Series on Faroes\ all linked to the opening
of the North Atlantic Ocean[ Þ 1999 Elsevier Science Ltd[ All rights reserved[
Keywords] North Sea^ Grane Field^ Volcanism^ Volcaniclastics^ Geochemistry
0[ Introduction
During the Palaeogene onset of sea ~oor spreading
began north of the Charlie Gibbs Fracture Zone in the
North Atlantic "Ziegler\ 0870#[ Continental rifting in the
proximity of an Icelandic plume resulted in massive
amounts of igneous rocks in the East Greenland and
along the margins of the North Atlantic Basin "White
+ McKenzie\ 0878#[ This igneous activity in the North
Atlantic Igneous Province took part in two stages\ at 51
and 42Ð45 Ma "Saunders\ Fitton\ Kerr\ Norry + Kent\
0885#[ The latter one is contemporaneous with the
tu}aceous intervals in the North Sea Basin[
The area of study is Norwegian Block 14:00\ the
Grane:Balder area[ It is located on the north!western
~ank of the Utsira High\ a basement high forming the
eastern margin of the Southern Viking Graben "Fig[ 0#[
Corresponding author[ Tel[] ¦36 41 91 08 13^ fax] ¦34 41 91 06 75[
E!mail address] hjhaalaÝppco[com "H[ J[ Haaland#
Cores from wells 14:00!04\ 14:00!05\ 14:00!06 and 14:7!
3 from the Grane Field are described in order to make a
macroscopic and microscopic identi_cation of the pyro!
clastic components also determining their chemical
characteristics[ By isolating the end!members "sandstone\
mudstone and tu}s# on the basis of the core description\
possible volcanogenic levels were macroscopically ident!
i_ed[ These have been studied petrographically in thin
sections and geochemically by XRF "X!ray ~uorescence#[
The results of this study have implications for the overall
understanding of Paleogene successions in the North Sea\
both locally and regionally[ It also gives a better under!
standing of the volcanism development\ associated with
the initiation of the PaleoceneÐEocene opening of the
North Atlantic[
1[ Stratigraphy
The lithostratigraphy in the Grane area is summarised
in Fig[ 1[ The thicknesses of the cored sections are 094 m
9153!7061:99: ! see front matter Þ 1999 Elsevier Science Ltd[ All rights reserved[
PII] S 9 1 5 3 ! 7 0 6 1 " 8 8 # 9 9 9 9 8 ! 3
091
H[J[ Haaland et al[ : Marine and Petroleum Geolo`y 06 "1999# 090Ð007
Fig[ 0[ The Grane Field is situated on the north!western ~ank of the Utsira High\ Southern Viking Graben[ The location of the Grane Field is shown
with respect to the Norwegian mainland "redrawn from Hanslien\ 0876#[ The map in the lower right corner shows the localization of the wells 14:00!
04\ 14:00!05\ 14:00!06 and 14:7!3 "redrawn from Norsk Hydro#[
in well 14:00!04\ 032 m in well 14:00!05\ 69 m in well
14:00!06 and 004 m in well 14:7!3[
The Paleogene succession in the Grane area consists
of calcareous and purely siliciclastic shale formations\
interbedded with sandstone members and tu}aceous
intervals "Fig[ 1#[ The Lista Formation rests conformably
on the Vale Formation[ The Lista shales are non!lami!
nated "massive# with randomly distributed tu} layers[
The Heimdal Member "not present in the cored interval
of well 14:00!06# consists of medium!grained sandstone
with few internal sedimentary structures\ and has a
blocky gamma ray!sonic log pattern[ The sandstone units
occur within the grey and black shales in the lower part
of the Lista Formation[
The Sele Formation is present only in the cored inter!
vals of the wells 14:00!05 "4 m# and 14:00!06 "4 m#[ The
age of the Sele Formation is Paleocene to earliest Eocene[
The rocks of the Sele Formation consist of tu}aceous\
montmorillonite!rich shales and carbonaceous\ grey or
greenish!grey\ _nely laminated siltstones[
Cores from the Balder Formation were recovered from
the wells 14:00!05 "20 m#\ 14:00!06 "12 m# and 14:7!3
"15 m#[ The Balder Formation is of early Eocene age\ and
the rocks are laminated\ varicoloured\ _ssile shales with
interbedded grey\ green or brownish yellow sandy tu}s[
Balder sands are only present in well 14:00!06[ The upper
boundary is placed at the transition to the overlying non!
laminated sediments of the Hordaland Group[ The lower
boundary is de_ned by the change in gamma log signature
from higher to lower response[
2[ The tuffaceous intervals in the North Sea
Lower Tertiary tu}s are recognised throughout most
of the North Sea "Jacque + Thouvenin\ 0864^ Knox +
Morton\ 0872#[ They are found northwards along the
Norwegian shelf as far as the Haltenbanken and Tr%na!
banken areas "Malm et al[\ 0873#\ and southwards to
Denmark and in the northern part of Germany "Morton
+ Knox\ 0889#[
Early Tertiary volcanic activity is divided into two
H[J[ Haaland et al[ : Marine and Petroleum Geolo`y 06 "1999# 090Ð007
092
Fig[ 1[ The stratigraphy "based on nannoplankton zonation# of the Grane area "redrawn after Norsk Hydro\ Mangerud et al[ "in press#\ with
additional geomagnetic data from Cande and Kent\ 0884 and the volcanic phases of Knox + Morton\ 0872#[ The lithostratigraphic nomenclature is
from Deegan and Scull "0866#[
main phases of pyroclastic deposition during the time
interval 47Ð41 Ma[ These have been further strati!
graphically subdivided by the means of dino~agellate cyst
correlation "Knox + Morton\ 0872#[ Phase 0 "47Ð46 Ma#
consists of ash layers interbedded with mudstones[ The
ash layers are normally graded and vary in thickness
from 9[4Ð4 cm[ Phase 1 "44Ð41 Ma# is divided into four
subphases[ They all have di}erent characteristics prob!
ably related to depositional mode[ Subphase 1a is rep!
resented by sporadically thin\ graded ash layers[
Subphase 1b "the main tu} zone# has more than 074
amalgamated graded layers which vary in thickness from
a few millimetres up to 17 cm[ The two last subphases\ 1c
and 1 d\ are represented by thin\ generally widely!spaced
graded layers interbedded with red and varicoloured
shales[
The geochemical compositions of the Tertiary volcanic
ash beds show a wide range "Jacque + Thouvenin\ 0864^
Knox + Morton\ 0872^ Malm et al[\ 0873^ Knox +
Morton\ 0877^ Morton + Knox\ 0889#[ Phase 0 is
reported to be of basaltic composition\ including di}er!
entiated FeÐTi tholeiites\ and its distribution would indi!
cate a Hebridean origin\ connected to the Scottish central
intrusions "Knox + Morton\ 0872#[ In some samples\
aegirine\ indicative of a peralkaline composition\ is
present[ Since aegirine appears in both the British Ter!
093
H[J[ Haaland et al[ : Marine and Petroleum Geolo`y 06 "1999# 090Ð007
tiary Volcanic Province "Bell + Emelius\ 0877^ Hawkes\
Merriman\ Harding + Darbyshire\ 0864# and in East
Greenland "Nielsen\ 0868#\ it is possible that both con!
tributed to the phase 0 deposits[
Phase 1 shows a much wider compositional range than
phase 0[ Subphase 1a encompasses ashes of tholeiitic
to rhyolitic "partly peralkaline# compositions "Pedersen\
Engell + Ro
nsbo 0864#\ whereas the tu}s of subphase 1b
are basalts only\ and those of subphases 1c and 1 d are
basaltic with some minor occurrences of intermediate
rocks "Knox + Morton\ 0877#[ The tu}aceous sediments
in the North Sea are completely altered to smectitic clay
"Knox + Morton\ 0877#[ Whole!rock XRF analyses of
some fresh samples from Denmark have been performed
by Pedersen et al[ "0864#[ On altered samples\ the primary
composition has been deduced from analyses of fresh
feldspars and amphiboles "Knox + Morton\ 0877#[ A
limited geochemical study by Malm et al[ "0873# of the
main tu} zone\ subphase 1b\ showed that the tu}s are
best comparable with {within!plate| basalts[
Morton and Knox "0889# studied {immobile| trace
elements of the tu}s from the Balder and Sele formations
in four wells in the northern and southwestern North
Sea[ Their study con_rms the geochemical results done
on the tephra layers onshore in Denmark "Morton +
Evans\ 0877#[
Subphases 1a and 1b are compositionally similar both
in the North Sea and in Denmark[ In spite of the di}erent
geochemical characteristics\ Morton and Knox "0889#
deduced them to be of the same origin indicating a rift!
related setting\ and their stratigraphic development sug!
gests an evolving volcanic centre[ The geochemical data
indicate an evolution from variably silica under!saturated
to silica!saturated magmas\ interpreted to re~ect both an
increase in the degree of partial melting and decreasing
crustal involvement "Pedersen + Jo
rgensen\ 0870#[ The
proto!Icelandic plume generating the early Paleogene
basalts of East Greenland and the Faroes was believed
to be the source of the basaltic tephras "Morton + Knox\
0889#[ During the late Paleocene this plume became
established and generated a great volume of basaltic lava
in the area between the East Greenland Blosseville Kyst
and the Faroes "Bott\ 0877^ White\ 0877#[
2[0[ The Grane Field tuffs
2[0[0[ Description
The tu}aceous layers are divided into lithofacies based
on bed thickness\ lithology\ texture and sedimentary
structures[ Normally graded tu} beds appear in wells
14:00!05\ 14:00!06 and 14:7!3 within the Balder and Sele
Formations[ They are most distinctly developed in well
14:00!06 "Fig[ 2#\ within which two successions of amal!
gamated tu}!beds "2[8 and 0[5 m#\ separated by a 5 m
thick massive Balder sandstone\ occur[ In well 14:00!05
the normally graded tu} layers sum up to 4[64 m[ In well
Fig[ 2[ Normal graded tu}!beds interbedded with laminated silt[ From
well 14:00!06\ Balder Formation[
14:7!3\ 2[79 m of the normally graded tu} beds show
alternations between hemipelagic silt and tu}\ and a
0[59 m thick succession of amalgamated tu}s[ The layers
vary in grain size from medium!grained at the base to
silt! or clay size on top[ A total of 007 beds have been
recorded in well 14:00!06\ 62 in well 14:00!05 and 73 in
well 14:7!3[ The individual beds vary in thickness from
9[4Ð08 cm[ The base of the beds are well de_ned and
show two di}erent characteristics] "i# erosion into the
underlying laminae\ or "ii# conformable character[
Macroscopically the di}erence may be subtle[ The top of
the beds are often mudstone!dominated or capped by
dark brown laminated shale[ The beds are dominantly
amalgamated[ The tu}s vary in colour[ Most of them are
yellow to light green at the base\ and darkening towards
the top[ The yellow appearance at the base of some of
the beds is due to calcite cementation[ In well 14:7!3 the
normally graded tu} beds contain several vertical cracks
which are _lled with calcite[ The Balder sandstones con!
tain fragments of undistorted tu}!beds\ implying that
H[J[ Haaland et al[ : Marine and Petroleum Geolo`y 06 "1999# 090Ð007
the total of 007 tu}!beds do not necessarily record the
complete thickness of the pyroclastic beds[
The isolated tu}s are present in all four wells and are
restricted to the Lista! and Vale Formations[ The number
of beds varies from 19Ð27 in each well\ each bed varying
in thickness from 9[4Ð01[4 cm[ There is no consistent
variation in the distance between the layers[ Commonly
they appear as single occurrences "Fig[ 3#\ but in the
lower part of the Lista Formation they are more frequent[
The recognition of this facies is based on a distinctive
colour change from the mudstones and siltstones\ in
addition to grain size changes[ A majority of the beds
are normally graded with a grain size variation from
medium!\ _ne! or very!_ne sandstone to silt and mud[
The basal contact is either distinguished by a marked
colour change in the _ne grained varieties or a sharp
contact in the coarser beds[ The sharp contacts may be
erosive or non!erosive[ The upper contacts have also a
variety of features\ such as a marked colour change or a
grain size change[ The layers are always capped by mud[
Laminated shale is not recognised[ The upper contact
094
may be either abrupt or gradational[ The colour of the
layers varies from di}erent shades of green to red[ The
thickest layers are dark green at the base and lighter
towards the top[
2[0[1[ Interpretation
Normally graded tu} beds may be emplaced by two
di}erent mechanisms of transport and deposition[ One
possibility is that they represent wind transported tephra
deposits by fallout into water settling hemipelagically
through the water column[ The other possibility is depo!
sition or redeposition by low!density turbidity currents[
After deposition the tephra beds may be further reworked
and redistributed by bottom currents "Cas + Wright\
0877#[ Of those investigated for this study\ only a few
beds have been reworked[
The isolated occurrences re~ect more episodic depo!
sition "Jacque + Thouvenin\ 0864^ Knox + Morton\
0872#[ The majority of the isolated layers are reworked[
They are deposited _rst by fallout into water and there!
after reworked by low!density turbidity currents[ Only
very few of the isolated layers seem to be una}ected by
secondary processes[
Norin "0847# classi_ed tu}s according to sharp or
di}use upper contact\ presence of vertical grading\
amount and kind of pumice and non!volcanic grains\ type
of internal lamination and grain morphology[ Evidence
indicating a turbiditic origin includes erosional bases and
partial Bouma sequences with graded beds "Watkins et
al[\ 0867#[ If the tephra contains other grains than those
of pyroclastic origin\ this is attributed to turbiditic pro!
cesses[ These characteristics apply to the majority of the
phase 0 layers\ which are of single occurrence[
The process of wind!blow\ water settled tephra is tho!
roughly described by Ledbetter and Sparks "0868#[ The
size distribution of the particles and size of a graded layer
is a function of duration of eruption\ rate of release\
residence time in the atmosphere\ settling velocity and
water depth at the site of deposition[ Tephra is ejected
into the prevailing wind system from the eruption clouds[
After wind transport\ the grains fall onto the water sur!
face and sink to the bottom\ by a process of size sorting
through the water column[ As the process continues\
larger grains will settle before earlier!erupted\ _ner!grai!
ned particles[ During one eruption there will be a thin
zone of the largest particles at the base of the tu} layer[
This process re~ects the sedimentary mechanism for the
phase 1 tu}s\ where only a small number have been resedi!
mented[
3[ Petrography
3[0[ Introduction
Fig[ 3[ Example of isolated tu} in the Lista Formation " from well
14:00!06#[
Tertiary volcaniclastic sediments in the areas sur!
rounding the North Sea were _rst described by Bo
ggild
095
H[J[ Haaland et al[ : Marine and Petroleum Geolo`y 06 "1999# 090Ð007
"0807# from onshore sediments in northern Denmark and
were later found in northern Germany "Andersen\ 0826#
and in south!east England "Elliott\ 0860#[ Jacque and
Thouvenin "0864# presented the _rst paper on the equi!
valent o}shore sediments\ in which textures of two types
of volcanogenic fragments were described[
Later work by Malm et al[ "0873# discussed the textures
of the volcanogenic fragments from well 29:1!0 in the
north Viking Graben\ in relation to a speci_c volcanic
setting[ The morphology of the grains were found to be
comparable to those produced by Surtseyan!type erup!
tion\ i[e[ explosive activity caused by water gaining access
to the top of a vent "Kokelaar\ 0875#[ The vesicular tu}
particles of these eruptions are described as dominantly
green with subordinate dark brown and yellow grains[ In
addition to the predominantly vitric particles some grains
contain microscopic quench crystals of plagioclase[ These
two types of pyroclastic grains are identical to those
described by Jacque and Thouvenin "0864# "Fig[ 4"a# and
"b##[
Based on the main constituents of the tu}!layers\ they
have been subdivided into two types] "0# Tu}s consisting
of Surtseyan!type shards "Walker + Croasdale\ 0861^
Heiken\ 0863#\ containing "i# vesicular pyroclasts with
irregular shape and "ii# dark microlithic\ partly vesicular
granules[ These clasts are typically of shallow submarine
basaltic eruptions\ during which water\ having free access
to the vent\ either becomes trapped near the magma\ or
engulfed in it[ The magma moves through a wet slurry of
clastic material\ a process referred to as {bulk interaction
steam explosivity| "Kokelaar\ 0875#\ taking place at the
magmaÐwater interface[ The water thus becomes super!
heated resulting in an explosive expansion of steam that
disrupts the magma[ Deposits consisting of these shards
are named hyalotu} "Honnorez + Kirst\ 0864#[ "1# Tu}s
consisting of aphyric\ vitric shards[ A vitric shard\ formed
subaqueously by granulation during quenching\ is com!
monly irregular with planar\ concave and convex
surfaces\ containing abundant vesicles[ Two di}erent
processes may account for the shard production "Bergh
+ Sigvaldason\ 0880#[ When the hydrostatic pressure is
high\ the resulting slow eruption rate suppresses ves!
iculation and results in pillow lavas[ Shards with low
vesicularity may be fragmented from the outer rim of the
pillows[ With a low hydrostatic pressure and initial high
content of volatiles\ the resulting eruption rate is high[
The fragments formed are more vesiculated[ The related
deposits are termed hyaloclastite "Rittman\ 0859#[
3[1[ Microscopic facies description
Based on detailed thin section studies of 27 samples
and depositional interpretations\ the tu}aceous layers
have been divided into di}erent microscopic facies[ Those
facies containing grains of volcanic origin have been
classi_ed as "0# primary volcaniclastic layers\ "1# sec!
ondary volcaniclastic layers\ "2# volcaniclastic shale and
"3# volcaniclastic mud[ The relative abundance of the
di}erent grain types is estimated at the base of the layers[
The grain size is measured across the widest part of a
grain[
3[1[0[ Primary volcaniclastic layers
A deposit characterised by a sharp non!erosive base\
normal grading\ consisting of dominantly volcaniclastic
grains\ has been classi_ed as a water!lain primary vol!
caniclastic layer[ The abundance of volcanic shards varies
from 69Ð84)\ the rest representing calcite cement and a
minor fraction of hemipelagic clay[
Two types of Surtseyan!type shards\ having partly
similar characteristics\ are present[ The size of the shards
ranges from 9[4Ð0[9 mm at the base to 9[94 mm in the
upper part of the layers[ Their original shape is identical
and both have microlithic plagioclase needles[ Apart
from the microlites\ some have plagioclase crystals larger
than 9[0 mm[ One shard type is de_ned as dark microlithic
vesicular\ irregularly shaped granules "Fig[ 4"c##\ with
scattered microlithic plagioclase needles[ Some of the
vesicles are _lled with clay minerals and calcite[ The other
shard type de_ne vesicular\ transparent pyroclasts with
irregular shapes that vary from subrounded to suban!
gular[ The vesicularity ranges from few to abundant\
irregular to spherical vesicles\ _lled with clay minerals
and to a lesser extent calcite[ Microlithic plagioclase nee!
dles are only present in some of the grains[
3[1[1[ Secondary volcaniclastic layers
These rocks represent resedimented volcaniclastic
deposits[ The criteria used to distinguish between epicl!
astic and pyroclastic layers is the presence of erosive bases
and ~oating mudclasts of the former\ as well as the grain
composition[ The epiclastic layers are normally graded
and massive\ without any sign of lamination[
The bases of the secondary volcaniclastic layers are
markedly di}erent from the primary pyroclastic deposits
as their contacts to underlying mud layers are erosive[ In
contrast to the knife!sharp base of the primary vol!
caniclastic layers\ the secondary volcaniclastics have an
irregular base[ There is no sign of load features like lam!
inae forced into the underlying sediments[ In two of the
thin sections mudclasts {~oating| in the layers have been
observed[ The di}erent grains in the layers range from
purely pyroclastics to mixed pyroclastic and lithics\ with
pyroclastic fragments consisting of Surtseyan!type shards
and vitric\ non!vesicular shards[ The lithic fragments con!
sist of plagioclase\ biotite\ muscovite and mud clasts[
The epiclastics can be further subdivided into two
types[ Those of pure pyroclastic origin are found in the
Balder and Sele Formations whereas those with mixed
pyroclastic and lithic grains only are found in the Lista!
and Sele Formations[ "i# Epiclastics of pure pyroclastic
origin consist of the same fragments as those described
H[J[ Haaland et al[ : Marine and Petroleum Geolo`y 06 "1999# 090Ð007
096
Fig[ 4[ "a# Weathered aphyric vitreous\ vesicular shard[ "b# Strongly weathered dark ash granule with small microlithic plagioclases "white#[ "c# Dark
microlithic vesicular granule\ well 14:00!06\ depth 0520[79 m[ "d# Platy vitric shards\ well 14:00!06\ depth 0520[61 m[
097
H[J[ Haaland et al[ : Marine and Petroleum Geolo`y 06 "1999# 090Ð007
in the primary volcaniclastic deposits\ consisting of ves!
icular pyroclasts or dark microlithic granules[ "ii# Epicla!
stics with mixed pyroclastics and lithics consist of vitric
chards\ biotite and mud clasts in a clayey matrix in
addition to Surtseyan!type shards[
Vitric shards] These shards are brown to transparent
and have a grain size distribution from 9[91Ð9[1 mm[
Their shapes are either platy concave or vesicular "Fig[
4"d##[ The platy fragments are more angular and de_ne
inward curving walls re~ecting the breakage of vesicle
walls[
Plagioclase] Plagioclase grains have only been found in
dark microlithic\ vesicular granules of which plagioclase
crystals are the only fresh remnants[ The size of the
plagioclase needles vary from 9[92Ð9[1 mm[
Biotite] Biotite has only been found within one of the
epiclastic layers[ The platy crystals\ varying in size from
9[0Ð9[1 mm\ are brown and pleochroic[
Mud clasts] The mud clasts vary in size from 9[1Ð
0[9 mm and are situated immediately above the base of
the layers aligned in the direction of ~ow[ These clasts
consist of resedimented\ consolidated mud or fragments
of consolidated epiclastic layers[
3[1[2[ Volcaniclastic shale
The volcaniclastic shale is con_ned to the laminated
intervals immediately above the normally graded tu} lay!
ers in the Balder and Sele Formations[ These layers con!
sist of shaly mud with undulating\ allochtonous\ coaly
laminae[ The coaly laminae are discontinuous and consist
of fragments with a length from 9[94Ð9[1 mm and a width
of ca 9[91 mm[ Small concretions\ 9[0Ð9[1 mm\ are ran!
domly scattered within the layers[ Semiquantitative SEM
analyses show that these concretions predominantly con!
sist of iron\ manganese and magnesium[
The depositional origin of the volcaniclastic shales is
similar to that of the primary volcaniclastic layers[ There
is no indication of transportation other than passive set!
tling from water[ Occasionally 9[94Ð9[1 mm sized pyro!
clastic fragments are present[
3[1[3[ Volcaniclastic mud
The muddy microfacies consists of a matrix of clay
minerals in addition to fragments of plagioclase\ coal and
biogenic material[ The minerals are dominantly chloriteÐ
smectite mixed layer clays with subordinate illite and
smectite "N[ Gjelsvik\ pers[ comm[#[ Plagioclase\ ranging
in size from 9[90Ð9[94 mm\ is present as microliths ident!
ical to those described in the Surtseyan!type shards[
The coal fragments\ constituting 0Ð09) of the rock\
are of the same size as the plagioclase microliths[ Neither
of these seem to be con_ned to speci_c levels\ they are
both randomly distributed[ Minor occurrences of fora!
minifers are found[
Macroscopically the rock has a massive appearance\
but the plagioclase grains coal fragments are aligned\
de_ning thin laminae in the majority of the samples[
4[ Geochemistry
Geochemical analysis have been performed on rocks
from all four wells investigated[ Special emphasis is\ how!
ever\ put on well 14:00!06\ which was petrographically
studied in detail[ A total of 041 samples of the identi_ed
tu} layers\ rocks supposed to represent tu}s\ mudstones
and sandstones throughout the cores\ have been exam!
ined "05 from well 14:00!04\ 16 from well 14:00!05\ 55
from well 14:00!06 and 32 from well 14:7!3#[ Due to the
pervasive alteration of the pyroclastic layers\ the appli!
cation of major elements\ was not considered useful for
this study[ The geochemical study is therefore based on
immobile trace elements of bulk!rock analyses[
4[0[ Analytical methods
The trace element analyses were carried out in the
Geological Institute\ University of Bergen[ The analyses
were performed on a Philips PW 0393 X!ray ~uorescence
"XRF#\ using pressed powder!pellets[ The method is
described by Norrish and Hutton "0858#\ and inter!
national standards with recommended values after Gov!
indaraju "0873# were used for calibration[
4[1[ Element mobility
All the tu}aceous sediments have su}ered severe alter!
ation as evidenced by thin section and SEM studies[ The
initial vitric material is entirely altered to smectite "Mor!
ton + Knox\ 0889#[ The trace elements Zr\ Nb\ Y and Ti
are recognised to be stable during alteration and weath!
ering "Pearce\ 0864^ Winchester + Floyd\ 0866^ Pearce +
Norry\ 0868^ Malm et al[\ 0873#[ Cr is also found to be
fairly stable during alteration "Hu}\ 0872#\ and in the
absence of major elements\ it may be used to indicate the
degree of di}erentiation of the rock[
During weathering\ pyroclastic material will undergo
di}erent chemical changes depending on whether it con!
sists of basaltic or silicic glass "Fisher + Schmincke\
0873#[ Such di}erences are most pronounced when alter!
ation occurs at low temperature[ Basaltic glass changes
its nature from palagonite\ commonly a non!crystalline
or poorly crystalline material\ and further to smectite
"Thorseth\ Furnes + Tumyr\ 0880#[ Ti is the only above!
mentioned element which may be a}ected by this alter!
ation "Cas + Wright\ 0877#\ but is found to be stable by
most authors "e[g[ Pearce\ 0864^ Winchester + Floyd\
0866^ Pearce + Norry\ 0868#[
Silicic glass is not so easily altered as basaltic glass due
to the rigid framework of Si and Al[ Y and Zr tend to
increase and Cr decreases during alteration "Fisher +
H[J[ Haaland et al[ : Marine and Petroleum Geolo`y 06 "1999# 090Ð007
Schmincke\ 0873#[ Zr\ however\ has to be used with care
as zircon may be present locally and thus bias the chemi!
cal data "Schmincke\ Viereck\ Gri.n + Pritchard\
0871#[
4[2[ Classi_cation of the samples
During core!investigation\ the samples were grouped
into sandstone\ mudstone and layers of probable pyro!
clastic origin[ For petrographic evaluation the samples
were investigated microscopically[ These studies made it
possible to isolate the end members\ i[e[ sandstone\ clean
mudstone and clean tu}[ The end members were plotted
in all possible combinations of the elements Cr\ Nb\ Zr\
Ti and Y[ The YÐNb and ZrÐTiO1 diagrams "Fig[ 5"a#
and "c## were found most suitable to separate the pyro!
clastics from mudstones and sandstones\ thus de_ning a
pyroclastic origin[
The YÐNb and ZrÐTiO1 diagrams were subsequently
used to identify the nature of the {unknown| "not micro!
scopically investigated# samples further down in the Lis!
ta! and Vale Formations[ The samples which plot in the
_eld de_ned by pure pyroclastic material "Fig[ 5"b# and
"d## are on this basis {de_ned| to represent pyroclastic
rocks[
4[3[ Bulk rock chemistry
Of all the analysed samples\ approximately 0:2 have
been identi_ed as tu}s based on macroscopic textures
and the YÐNb and ZrÐTiO1 relationships "Fig[ 5"a#Ð"d##[
The selected elements show a wide range of values[ Cr
varies from 7Ð547 ppm\ Nb from 02Ð192 ppm\ Zr from
028Ð1744 ppm\ Y from 14Ð506 ppm\ and TiO1 from 9[38Ð
4[47 wt)[ These values re~ect the highly variable com!
position of the di}erent tu}s[
4[3[0[ Classi_cation of the individual rock!types
The tu}s can be classi_ed into di}erent rock series by
using the Zr:TiO1ÐNb:Y diagram Winchester and Floyd
"0866#[ Based on the Nb:Y ratio\ the volcanic rocks may
be divided into subalkaline and alkaline suites[ Pearce
and Cann "0862# and Floyd and Winchester "0864# found
the Y:Nb ratios suitable for separating tholeiitic and
alkaline rocks\ for which purpose Winchester and Floyd
"0866# suggested a value of 9[56[ This applies to all rocks
except the most siliceous ones\ as the Nb:Y ratio increases
slightly with increased di}erentiation[
The Zr:TiO1 ratio may be used as an index of frac!
tionation and since these elements are stable during alter!
ation\ they can be applied to classify altered rocks\ plotted
against Nb:Y[ With di}erentiation from basic to acid
rocks\ the Zr:TiO1 ratio increases[
In the four wells\ 46 tu} layers have been recognised
"Table 0#[ Fig[ 6"a# classi_es the identi_ed pyroclastics
"based on textural interpretation#\ and Fig[ 6"b# classi_es
098
the assumed pyroclastics "based on a geochemical
interpretation#[ The majority of the identi_ed pyroclastic
samples plot in the sub!alkaline suite of basalts and the
transition andesites:basalts[ Only one is a rhyolite[ One
sample is an alkali basalt and two are trachyandesites[
The majority of the assumed pyroclastics "29 samples#
plot as sub!alkaline basalts and andesite:basalts[ Four
samples plot as andesites\ one rhyolite and one is a per!
alkaline comendite:pantellerite[ Only a minority of the
samples plots in the alkaline _eld\ with two alkali basalts
and two trachyandesites[
Thus\ the majority of assumed and identi_ed tu}s are
sub!alkaline basalts\ transitional andesites:basalts and
andesites "Fig[ 6"a# and "b##[
4[4[ Geochemical variations with depth
In Fig[ 7 the geochemical data from well 14:00!06 are
shown in relation to stratigraphic depth[ In the Balder
Formation the tu}s are dominantly sub!alkaline basalts
and minor andesites:basalts characterised by low Nb:Y!
and Zr:TiO1!ratios "Figs[ 7\ 6"a# and "b##[ Samples 2[510
and 2[520 have anomalously high Cr values\ and are
correspondingly low in the incompatible elements\
especially Y and Nb "Table 0#\ indicative of a {primitive|
composition of the magma[ The andesitic:basaltic rocks
have slightly lower Nb:Y!ratios[ Their Y values have a
profoundly higher average value "195 ppm# than that of
the average the sub!alkaline basalts "56 ppm#\ consistent
with a more di}erentiated magma[
Only two sub!alkaline basalt samples are represented
from the Sele Formation "Fig[ 7#[ The Nb:Y!ratios are
similar to those of the tu}s in the Balder Formation\ but
their Y and Nb values are slightly higher[
The Lista Formation shows a much wider range in the
composition of the tu}s compared to those of the Balder
and Sele Formations "Fig[ 7#[ The majority of the tu}s
range from sub!alkaline basalts\ andesite:basalts\ andes!
ite to rhyolites[ There are minor occurrences of alkali
basalts and trachyandesites[ In general\ the Cr content of
the tu}s decreases upwards\ indicating that the magmas
become more fractionated with time[
Of the tu} layers sampled in the Vale Formation\ three
are sub!alkaline basalts\ one is an alkaline basalt and two
are samples of andesitic:basaltic composition "Fig[ 7#[
4[5[ Geochemical character and tectonic setting
For the purpose of viewing the geochemistry of the
tu}s in relation to the tectonic setting\ two discriminant
diagrams have been applied[ The TiÐZrÐY diagram of
Pearce and Cann "0862# separates within!plate basalts\
volcanic!arc basalts\ and mid!ocean ridge basalts\ and
the NbÐZrÐY diagram of Meschede "0875# which dis!
tinguishes between di}erent types of mid!ocean!ridge
009
H[J[ Haaland et al[ : Marine and Petroleum Geolo`y 06 "1999# 090Ð007
Fig[ 5[ NbÐY and ZrÐTiO1 diagrams showing the range of values for pure sandstone\ mudstone and tu}aceous layers of the Balder!\ Sele!\ Lista! and
Vale Formations in well 14:00!06[ "a# Shows the de_ned areas in which the sandstones and the microscopically identi_ed mudstones and pyroclastics
plot[ "b# De_nes the assumed pyroclastics by the Nb and Y range found in "a#[ "c and d# Zr vs TiO1 data of sandstone\ mudstone and tu}aceous
layers[ "c# Shows the de_ned areas in which the sandstones and the microscopically identi_ed mudstones and pyroclastics plot[ "d# De_nes the
assumed pyroclastics by the Zr:TiO1!range found in "c#[
basalts\ within!plate tholeiites and within!plate alkali
basalts[
Of the samples classi_ed as tu}s "based on thin section
studies#\ only those of primary origin " _ve samples# have
been considered[ In the TiÐZrÐY diagram "Fig 8"a##\ four
of the analyses plot in the area between volcanic!arc and
ocean!~oor basalts\ close to _eld of within!plate basalt[
In the NbÐZrÐY diagram\ the analyses plot in _elds of
N! and E!type MORB\ volcanic!arc basalts "Fig[ 8"b##[ In
the TiÐZr diagram of Pearce "0871# which distinguishes
between within!plate lavas\ and volcanic!arc lavas and
MORB\ all analyses plot in the _eld of within!plate
basalts "Fig[ 8"c##[
In Fig[ 09"a# and "b#\ the assumed tu}s are plotted in
the TiÐZrÐY and NbÐZrÐY diagrams[ A large number
of the samples show high Y\ and some have high Zr
concentrations[ This is probably an e}ect of the sec!
ondary reworking and sorting resulting in enrichment of
zircon and apatite\ resulting in abnormally high contents
of Zr and Y\ respectively[ The majority of the samples\
however\ cluster in the area between volcanic!arc and
ocean!~oor basalts\ close to _eld of within!plate basalt[
Mobility of Y of the North Sea tu}s is a feature also
noted by Morton and Evans "0877# and Morton and
Knox "0889#\ and Winchester and Floyd "0866# found
the Y values of the altered North Sea samples to be
H[J[ Haaland et al[ : Marine and Petroleum Geolo`y 06 "1999# 090Ð007
Table 0
Selected major "TiO1# and trace elements "Cr\ Zr\ Y\ Nb# of the various
tu} layers[ Sample pre_xes 0\ 1\ 2\ 3 refer to wells 14:00!04\ 14:00!05\
14:00!06 and 14:7!3\ respectively
Sample
Depth "m#
Cr
TiO1
Zr
Y
Nb
Subalkaline basalt
0[009
0607[649
0[049
0617[369
1[249
0764[449
1[259
0765[179
1[289
0771[019
2[911
0529[054
2[913
0529[109
5[439
0529[689
4[659
0521[299
4[239
0522[979
2[939
0522[069
2[930
0522[079
2[950
0539[704
2[980
0536[719
2[989
0536[729
2[199
0692[719
2[129
0609[789
2[510
0612[799
2[520
0612[704
3[930
0583[249
3[949
0586[904
3[969
0690[024
3[961
0690[089
3[963
0690[129
3[089
0650[739
192
132
087
024
087
005
093
007
74
028
76
64
88
74
71
88
129
301
547
15
063
65
64
006
121
1[96
2[04
4[96
1[26
1[20
3[44
3[78
3[53
4[45
2[56
2[09
1[21
2[49
3[97
1[80
4[47
4[23
0[25
1[72
2[42
2[09
2[97
2[07
2[12
1[82
107
146
213
136
172
274
276
271
214
277
240
108
259
263
297
310
244
078
138
028
144
290
165
184
118
28
22
60
41
39
85
78
51
75
78
52
56
70
82
091
095
69
23
39
38
64
40
50
44
32
07
05
16
19
08
22
20
20
17
18
29
10
23
49
33
25
14
04
08
08
10
10
08
11
03
Andesite:Basalt
0[969
0602[509
0[099
0605[239
1[034
0627[239
1[204
0748[729
5[929
0520[839
7[059
0520[799
6[969
0532[054
2[079
0587[009
2[074
0699[599
2[169
0629[539
2[179
0622[069
3[951
0587[659
3[109
0664[059
60
012
230
050
77
84
63
126
115
13
66
37
35
1[56
0[57
3[15
3[08
1[63
1[97
2[60
1[31
0[74
2[80
3[08
1[41
1[68
060
006
164
321
192
052
279
066
198
152
215
165
177
506
393
010
68
60
65
026
350
056
024
217
86
096
28
12
15
10
03
02
17
29
05
13
33
14
10
Andesite
0[019
0[039
1[209
3[909
0608[639
0615[789
0748[659
0551[074
073
050
049
62
0[58
0[18
1[49
1[18
107
118
210
335
70
26
42
52
03
04
04
11
Rhyolitt
2[039
3[069
0559[269
0645[769
05
7
9[59
9[35
801
611
69
63
29
07
Comendite:Pantellerite
0[959
0698[389
01
9[38
1744
256
192
Alkali!basalt
1[039
0627[179
1[109
0674[439
2[159
0612[499
171
029
143
2[70
1[20
2[81
134
123
213
16
26
14
10
39
13
000
Table 0 "continued#
Trachyandesite
1[239
0762[819
1[279
0768[689
2[019
0545[879
2[130
0604[089
32
79
16
59
0[24
0[48
9[84
0[42
0106
623
178
894
037
004
17
024
079
007
31
052
Fig[ 6[ "a# Samples petrographically identi_ed as pyroclastic by the use
of thin sections\ plotted in the Zr:TiO1ÐNb:Y diagram of Winchester
and Floyd "0866#[ "b# The rocks de_ned as pyroclastic material based
on the YÐNb and ZrÐTiO1 diagrams "Fig[ 5"a#Ð"d##\ plotted in the
Zr:TiO1ÐNb:Y diagram of Winchester and Floyd "0866#[
001
H[J[ Haaland et al[ : Marine and Petroleum Geolo`y 06 "1999# 090Ð007
Fig[ 7[ Cr\ Nb\ Zr\ TiO1\ Y and Nb:Y plotted against the core log in well 14:00!06[ The tu}s are marked with symbols showing the rock types[ Open
square subalkaline basalt^ open diamonds] andesite:basalt^ open triangle] rhyolite^ _lled circle] trachyandesite[ The arrows indicate levels from which
thin sections of the tu}s have been studied[
slightly higher than the contemporaneous\ fresh Danish
tephra[ On this basis\ it is thus reasonable to suggest that
the samples re~ect within!plate character[
5[ Discussion and conclusions
5[0[ Magmatic setting
The theory of an Icelandic hot spot has prevailed in
the literature since Holmes "0807# described the Thulean
Volcanic Province[ The _rst indications of volcanism
related to plume activity are from 53 Ma in the British
Tertiary Province and from 51Ð50 Ma in East Greenland
"White + McKenzie\ 0878#[ The timing suggests that the
volcanism in these two areas were linked to the same
plume activity "White 0878^ Ritchie + Hitchen\ 0885#[
The plume was supposedly generated by rising jets of
buoyant mantle which created vertical and horizontal
~ow within the mantle\ thus causing uplift of the litho!
sphere above "Nadin\ Kusznir + Cheadle\ 0886#[ The
plume a}ected an area of ×1999 km in diameter "White\
0878#[ After the plume impinged on the lithosphere\ the
North Atlantic rift responded isostatically by uplift and
subsequent spreading "White + McKenzie\ 0878#[ The
magmatic activity increased in magnitude until its
maximum at around 51Ð47 Ma "Ritchie + Hitchen\
0885#[ The volcanism was active from 50Ð44 Ma "Dewey
+ Windley\ 0877# and terminated at the time of the
initiation of the North Atlantic Ocean "Ritchie +
Hitchen\ 0885#[
5[1[ The deposition and origin of the tuff layers
The tu} layers are related to the opening of the North
Atlantic Ocean\ an interpretation based on geochemical
correlations "as discussed below#[ The tu}s were trans!
ported by prevailing winds from the northwest into the
North Sea Basin "Knox + Morton\ 0877#[ Based on sedi!
H[J[ Haaland et al[ : Marine and Petroleum Geolo`y 06 "1999# 090Ð007
002
mentary facies interpretation and petrography\ the tu}s
are classi_ed as "0# normally graded tu} beds or "1#
isolated tu}s[ This division is evident in the stratigraphic
distribution of the layers[ There is an upward increase
in the occurrence of the tu} beds throughout the Vale
Formation and the lower part of the Lista Formation[
The majority of these single tu} beds are reworked or
resedimented[ There is a period of quiescence in the upper
part of the Lista Formation\ before amalgamated tu}
beds are deposited in the upper Sele Formation and the
lower part of the Balder Formation[ These amalgamated
tu}s probably re~ect more continuous\ explosive volcan!
ism[ In the Sele and Balder Formations the amalgamation
e}ectively protected the ones previously deposited[ This
is due to repeated rapid sedimentation as primary water!
lain tu}s as opposed to single events[ From thin section
studies it seems that the Balder and Sele were rarely
exposed long enough to be a}ected by resedimentation
or reworking by bottom currents[ Therefore the amal!
gamated tu}s are better preserved than the single layers
in the Lista and Vale Formations[
5[2[ Regional correlation of the volcanic activity
Fig[ 8[ "a# The petrographically determined primary tu}s plotted in the
TiÐZrÐY diagram of Pearce and Cann "0862#[ The samples plot in _elds
B and C\ denoting calc!alkali basalts "B and C# and ocean!~oor basalts
"B#[ Field A and B represents low!potassium tholeiites and D within!
plate basalt[ "b# The same samples plotted in the NbÐZrÐY diagram of
Meschede "0875#[ The samples plot in _eld B and C in addition to one
in _eld D[ The representative setting for Ai\ Aii and C are within!plate
basalt\ E!type MORB in B\ N!type MORB in D and volcanic!arc
basalts in C and D[ "c# The samples plotted in the TiÐZr diagram of
Pearce "0871#[
The reworked tu}s of the Vale and Lista Formations
are not suitable for geochemical correlation\ leaving their
stratigraphic position as the only useful tool for corre!
lation[ Knox and Morton "0877# attribute these layers to
the volcaniclastic phase 0\ the timing of which is con!
sistent with the doming related to the Icelandic hot!spot
"½47Ð64 Ma#[ The proposed source areas\ the FaroeÐ
Greenland Province and the British Province "Knox +
Morton\ 0877#\ are also comparable by being time!equi!
valents[
Geochemical data from di}erent areas of the North
Atlantic Igneous Province "NAIP# are compared with the
contemporaneous phase 1 tu}s[ The areas of extrusive
activity in the North Atlantic Igneous Province at the
given time are East Greenland\ the Vo
ring Plateau
"Upper Series#\ Hatton Bank\ Faroe Plateau "the Middle
and Upper Series of Faroe Lava Group# and the North
Rockall Trough!Hebrides "the North Rockall Trough!
Hebrides Lava Group# "Fig[ 00#[
In the TiÐZrÐY diagram\ the Flado
dykes and basalts
from the Lower Lavas from East Greenland plot in the
_eld of within!plate basalts "WPB# extending into the
_eld of mid!ocean ridge basalts "MORB# "Fig[ 01"a##[ In
the NbÐZrÐY diagram "Fig[ 01"b## and the Flado
dykes
straddle the boundaries between WPA "within!plate alk!
ali basalt#\ WPB:VAB and P!type MORB "plume in~u!
enced mid!ocean ridge basalt#\ whereas the Lower Lavas
plot between WPB and VAB "volcanic!arc basalts#[ The
Upper Series on the Vo
ring Plateau show WPB to
MORB:VAB a.nity by applying the TiÐZrÐY diagram
"Fig[ 01"a## and N!type MORB "normal mid!ocean
basalt#:VAB to WPB:VAB in the NbÐZrÐY diagram
003
H[J[ Haaland et al[ : Marine and Petroleum Geolo`y 06 "1999# 090Ð007
Fig[ 09[ "a# The assumed tu}s plotted in the TiÐZrÐY diagram of Pearce and Cann "0862#\ and "b# the NbÐZrÐY diagram of Meschede "0875#[
Explanation to diagrams as in Fig[ 8[
"Fig[ 01"b##[ This series is partly time!equivalent with the
Middle Series on Faroes "Hitchen + Ritchie\ 0885#[ Data
from the Middle Series "Gariepy\ Ludden + Brooks\
0872# are only plotted in the NbÐZrÐY diagram in Fig[
01"b#\ due to the lack of TiO1 data[ Here they plot entirely
in the joint _eld of WPB:VAB[ Data from well 052:5!0A
from the Rockall Trough "Morton et al[\ 0877# show a
WPB origin "Fig[ 01"b# and "b##[ A majority of the sam!
ples tend to plot in the _eld of within!plate basalts[ The
TiÐZrÐY diagram does not\ however\ separate con!
tinental tholeiites "WPB# from mid!ocean ridge or con!
tinental!arc basalts "Meschede\ 0875#[ The NbÐZrÐY
H[J[ Haaland et al[ : Marine and Petroleum Geolo`y 06 "1999# 090Ð007
004
Fig[ 00[ Correlation diagram of early Tertiary volcanic events in the North Atlantic Igneous Province[ The correlation is based on the data of the
authors mentioned in the _gure\ in addition to data of Eldholm et al[ "0878#^ Hitchen and Ritchie "0882# and Ritchie and Hitchen "0885#[ The
geomagnetic polarity time scale is that of Cande and Kent "0884#[ The phase 1 tu}s in the Grane Field comprise phase 1b and 1c of Knox "0873#[
diagram separates these di}erent types "Fig[ 01"b##[ By
applying the TiÐZr!diagram of Pearce "0871# the above!
mentioned basalt provinces plot in the _elds of within!
plate basalts MORB "Fig[ 01"c##[
The basalts from the Vo
ring Plateau "Vierick et al[\
0877# are most comparable to N!type MORB\ whereas
the Flado
dykes from East Greenland "Gill\ Nielsen\
Brooks + Ingram\ 0877# range from WPA:WPB to P!
type MORB[ The Lower Basalts in East Greenland\ the
Rockall Trough and the Middle Series on Faroes "Gill et
al[\ 0877^ Morton et al[\ 0877^ Gariepy et al[\ 0872# all
plot in the within!plate basaltic _eld[ It is apparent that
the phase 1 data from the Grane Field are compatible
with all the samples that plot in the P!type MORB and
the WPB _elds " _lled circles in Fig[ 01"b##[ They are time!
equivalent\ have a similar geochemistry and hence most
probably can be linked to the same source area[
5[2[0[ Textural and paleogeographic considerations
The volcaniclastic fragments in the Sele and Balder
Formations are de_ned as Surtseyan!type shards[ Their
formation requires eruption in a shallow!marine setting\
thus providing a criterion to be used to limit possible
source areas in the NAIP[
Due to the lack of pillow structures in the Lower
Basalts of the Rockall Trough\ they are considered to
have erupted subaerially "Morton et al[\ 0877^ Upton\
0877#[ Also the basalts on the Faroes are of subaerial
origin "Gariepy et al[\ 0872#[ The basalts of the Vo
ring
Upper Series have reddened tops due to subaerial erup!
tion and weathering "Vierick et al[\ 0877#[ The Lower
Basalts in East Greenland\ however\ may have erupted
in a submarine setting due to the presence of interbedded
hyaloclastites and pyroclastics\ indicating explosive vol!
canism in an aqueous environment "Gill et al[\ 0877#[
On the Faroes\ basaltic tu}s are deposited subaerially
on top of the Upper Series[ Based on the occurrence of
palagonitized sideromelane fragments\ variable ves!
icularity and the abundance of small blocky and vitric
clasts\ Waagstein and Heilmann!Clausen "0884# inter!
preted these basaltic tu}s as having originated from a
phreatomagmatic eruption[ On the Vo
ring Plateau sec!
ondary tu} beds are interlayered in the Upper Series[
These have characteristics of submarine origin and may
on this basis\ in addition to their chemical composition\
be correlated with the Balder Formation "Vierick et al[\
0877#[
The data above indicate an aerially extensive carpet of
tu}s of similar origin as the phase 1 tephras of the Grane
Field[ Regarding possible source areas\ the basalts having
erupted subaerially are unlikely candidates[ That leaves
a source near East Greenland as the most plausible\ a
connection which is also geochemically consistent[
5[2[1[ Other suggested volcanics to be equal to phase 1
A temporal correlation "based on biostratigraphy#
between the Balder Formation and the coal!bearing tu}!
agglomerate zone of the Faroe Islands "between the
Lower Series and the Middle Series# has been proposed
"Smythe\ Chalmers\ Skuce\ Dobinson + Mould\ 0872#[
This correlation was later regarded as speculative due
to the local distribution of the tu}s and their di}erent
chemistry and hence dismissed "Waagstein\ 0877#[
Morton and Knox "0889# indicated a relationship
005
H[J[ Haaland et al[ : Marine and Petroleum Geolo`y 06 "1999# 090Ð007
between the only known volcanic centre in the North
Atlantic Igneous Province\ the Erlend Volcano "Ridd\
0872# as a possible source for the Balder Formation
tephras[ However\ seismic!re~ection mapping show that
the Balder Formation "phase 1b of Knox and Morton
"0877## onlaps the volcanic succession of the Erlend Vol!
cano and thus postdates these deposits "Hitchen +
Ritchie\ 0882#[
5[3[ Concluding remarks
A thorough investigation of the stratigraphic occur!
rence\ the texture and geochemistry of tu}aceous layers
in the wells 14600!04\ 14:00!05\ 14:00!06 and 14:7!3 on
the Grane Field allow the following conclusions to be
drawn]
The tu} layers consist of two types of deposits\ primary
water!lain tu}s and tu} layers redeposited as thin bedded
turbidites[
Two types of pyroclastic fragments can be recognized]
"0# Surtseyan!type fragments which originated from shal!
low submarine explosive eruptions and "1# vitric shards
which originated by quenching granulation during suba!
queous eruptions[
The tu}s in the Lista and Vale Formations "phase 0#
become more fractionated with time\ from basic to acid
composition[ The Balder and Sele Formations "phase
1# consist of tu}s of the sub!alkaline group exclusively\
indicating a rather uniform magmatic composition[
The majority of the samples are of a within!plate origin
inferred from the TiÐZrÐY and NbÐZrÐY diagrams[
Phase 1 tu}s have a similar geochemistry as the Lower
basalts in East Greenland\ the Rockall Trough and the
Middle Series on Faroes\ all of which are extruded at an
incipient stage of the North Atlantic spreading ridge[
Acknowledgements
Fig[ 01[ "a\ b\ c#[ The phase 1 petrographically identi_ed tu}s " _lled
circles# compared with various basalt lavas\ pyroclastics and dykes of
the North Atlantic Igneous Province plotted in ZrÐYÐTi\ ZrÐYÐNb
and ZrÐTi diagrams[ Explanation to diagrams in Fig[ 8[ Explanation
to letters in diagram "a#] a# Flado
dykes "Gill et al[\ 0877#\ b# Lower
Basalts on East Greenland "Gill et al[\ 0877^ Holm 0877#\ c# Vo
ring
Upper Series "ODP site 531E\ Vierick et al[\ 0877#\ d# Rockall Middle
Series "well 052:5!0A\ Morton et al[\ 0877# and e# the Faroe tu}
"Waagstein + Heilmann!Clausen\ 0884#[ Explanation to letters in diag!
ram "b#] a# Flado
dykes "Gill et al[\ 0877#\ b# Lower Basalts on East
Greenland "shaded area\ Gill et al[\ 0877#\ c# Lower Basalts on East
Greenland "Holm\ 0877#\ d# Vo
ring Upper Series "ODP site 531E\
Vierick et al[\ 0877#\ e# Rockall Middle Series "well 052:5!0A\ Morton
et al[\ 0877# and f# the Faroe tu} "Waagstein + Heilmann!Clausen\
0884#[ "c# Basalt dykes\ lavas and tu}s of the North Atlantic Igneous
Province plotted in a ZrÐTi diagram[ References to sources are given
in the text[
This work represents the main parts of the lead
author|s Cand[ Scient[ thesis at the University of Bergen\
Norway[ Prof[ R[ J[ Steel is acknowledged for his e}orts
in the initial planning of the study\ and the formal organ!
ising with Norsk Hydro for sample collection[ We further
thank Dr J[ P[ Nystuen for useful discussions\ and Dr J[
Tveranger for critical comments on an early version of
the manuscript[ The thin sections and illustrations were
kindly prepared by G[ Torkildsen and J[ Ellingsen\
respectively[ We thank Norsk Hydro for _nancial
support\ and for making the cores available for this study[
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