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> Forsiden > Publikationer > Geology of Greenland Survey Bulletin > Vol. 191 Geol. Greenl. Surv. Bull. > Review of Greenland Activities 2001, pp 126-132

GEOLOGY OF GREENLAND SURVEY BULLETIN 191

 
Late Permian carbonate concretions in the marine siliciclastic sediments of the Ravnefjeld Formation, East Greenland

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This investigation of carbonate concretions from the
Late Permian Ravnefjeld Formation in East Greenland
forms part of the multi-disciplinary research project
Resources of the sedimentary basins of North and East
Greenland (TUPOLAR; Stemmerik et al. 1996, 1999).
The TUPOLAR project focuses on investigations and
evaluation of potential hydrocarbon and mineral
resources of the Upper Permian ­ Mesozoic sedimen-
tary basins. In this context, the Upper Permian Ravnefjeld
Formation occupies a pivotal position because it con-
tains local mineralisations and has source rock poten-
tial for hydrocarbons adjacent to potential carbonate
reservoir rocks of the partly time-equivalent Wegener
Halvø Formation (Harpøth et al. 1986; Surlyk et al. 1986;
Stemmerik et al. 1998; Pedersen & Stendal 2000). A bet-
ter understanding of the sedimentary facies and diage-
nesis of the Ravnefjeld Formation is therefore crucial
for an evaluation of the economic potential of East
Greenland.
The original field work was carried out in 1998, when
sampling was undertaken of representative carbonate
concretions and surrounding beds from a limited num-
ber of well-exposed sections in the Ravnefjeld Formation.
The sampled material was subsequently investigated
by a combination of petrography and stable isotope
chemistry to decipher the relationships between the
diagenetic development of the carbonate concretions
and the mineralisation in the sequence. The sequential
precipitation of the cement generations was analysed
in cement-filled primary voids in gastropods because
these showed the most complete development of the
different cement generations. The geochemistry of sta-
ble isotopes (
13
C,
18
O and
34
S) was also studied
(Nielsen 2001). During the petrographic work, we
became aware of a hitherto unrecognised biota domi-
nated by calcispheres. The well-developed cement gen-
erations in primary cavities in skeletal material were used
to elucidate the diagenesis.
Geology and carbonate concretions
The East Greenland Basin was formed through a com-
bination of Late Carboniferous rifting and Early Permian
subsidence related to thermal contraction of the crust
(Surlyk et al. 1986). A major transgression in the Upper
Permian brought a change from continental to marginal
marine deposition characterised by the formation of
fluvio-marine conglomerates, hypersaline algae-lami-
nated carbonates and evaporites. After a new regressive
phase with the development of karstified palaeosurfaces
(Surlyk et al. 1984, 1986), a eustatic sea-level rise led
to the establishment of marine conditions under which
the muddy sediments of the Ravnefjeld Formation were
deposited in a partially restricted basin with euxinic
(super-anoxic) bottom water (Fig. 1; Piasecki & Stem-
merik 1991; Nielsen 2001). Contemporaneously, the
open marine carbonate platforms and bryozoan buildups
of the Wegener Halvø Formation were formed along
the basin margins and on submarine structural highs,
leading to a partially closed basin which was at least
400 km long and 80 km wide (Surlyk et al. 1986).
In the Kap Stosch area (Fig. 1), the Ravnefjeld
Formation comprises calcareous and micaceous shales
and bioturbated siltstones subdivided into two lami-
nated (L1 and L2) and three bioturbated (B1, B2 and
B3) intervals (Figs 2, 3). This subdivision is similar to
that described elsewhere in the basin (Piasecki 1990;
Piasecki & Stemmerik 1991). The thickness of the lam-
inated intervals, including the intercalated bioturbated
interval (B2), is remarkably uniform in the exposed
parts of the basin and usually amounts to 12 to 15 m,
whereas the lower and upper bioturbated intervals (B1
and B3) vary significantly in thickness due to the
palaeotopography of the underlying karstified palaeo-
surfaces and structural elements (Piasecki & Stemmerik
1991).
126
Late Permian carbonate concretions in the marine
siliciclastic sediments of the Ravnefjeld Formation,
East Greenland
Jesper Kresten Nielsen and Nils-Martin Hanken
Geology of Greenland Survey Bulletin 191, 126­132 (2002) © GEUS, 2002
GSB191-Indhold 13/12/02 11:33 Side 126
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Compilation and lithostratigraphic correlation of
profiles along the coastline of Kap Stosch indicate a sub-
basin about 25­30 km wide in an east­west direction,
connected by a seaway with the southern part of the
East Greenland Basin (Piasecki 1990; Piasecki &
Stemmerik 1991). Deposition of the basinal, shale-
dominated Ravnefjeld Formation was confined to the
sub-basin centre, enclosed by partly time-equivalent
carbonate buildups of the Wegener Halvø Formation to
the west along the post-Devonian main fault, the
Stauning Alper fault, and at the Clavering Ø high north-
east of Kap Stosch (Fig. 1; Christiansen et al. 1993).
Carbonate concretions occur in the laminated inter-
vals (L1 and L2) of the Ravnefjeld Formation at Kap
Stosch and in the similarly developed sequence at
Triaselv to the south (Fig. 1). These concretions are
typically distributed in distinct horizons that are trace-
able throughout the outcrops in the Kap Stosch and
Triaselv areas. Carbonate concretions are more frequent
in the bioturbated intervals (B1 and B3) at Kap Stosch
than in other parts of the basin. The concretions are
127
50 km
Kap
Stosch
Carbonates
Shales
Sandstones
Fault
Triaselv
Hold
with
Hope
Traill Ø
Post-De
vonian main fault
Clavering
Ø
Liverpool Land
Jameson
Land
Scoresby
Land
Wegener Halvø
Sta
un
ing
Alp
er
fau
l
t
?
?
?
?
28
26
°
24
°
22
°
Greenland
73
°
74
°
72
°
71
°
24
°
22
°
74
°
73
°
72
°
71
°
Outcrop
Fig. 1. Map of central East Greenland showing the distribution
and extent of the Upper Permian outcrops, the shale, sandstone
and carbonate facies of the East Greenland Basin and structural
lineaments. Modified from Christiansen et al. (1993).
Fig. 2. The Upper Permian ­ Lower Triassic succession on the
Kap Stosch peninsula on Hold with Hope. The Ravnefjeld
Formation (c. 25 m shown) in the lower part of the photograph
is unconformably overlain by the lowermost Triassic sediments
of the Wordie Creek Formation. Dark screes are Palaeogene
basalt blocks derived from about 1300 m above sea level.
GSB191-Indhold 13/12/02 11:33 Side 127
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slightly elliptical and range from a few centimetres to
more than three metres in diameter. Their long axes are
parallel to the bedding, but they show no sign of par-
allel orientation. Although fish remains have been found
both in the concretions and in the surrounding sedi-
ments since the late 1920s (e.g. Bendix-Almgreen 1993),
knowledge of the nature of concretion formation was
very limited prior to initiation of the present project.
The Ravnefjeld Formation comprises most of the for-
mer Posidonia (originally Posidonomya) Shale (Newell
1955; Maync 1961) considered to be of Kazanian age,
which is roughly equivalent to the European Zechstein
cycle 1 (Piasecki 1984; Rasmussen et al. 1990; Utting &
Piasecki 1995); it is of latest Wuchiapingian age, based
on the conodont fauna (Stemmerik et al. 2001).
Biological constituents of the carbonate
concretions
Both pellets and trace fossils are very common in the
carbonate concretions. The pellets show signs of bed-
ding-parallel, compactional deformation, indicating
loading due to overburden before cementation.
Some carbonate concretions contain a rich skeletal
fauna consisting mostly of small fragments due to
mechanical breakage before final deposition. No sys-
tematic investigation of the skeletal fauna has been
undertaken, but some aspects that are important for
the facies analysis and diagenesis of the Ravnefjeld
Formation are pointed out.
Calcispheres (calcareous, hollow, spherical bodies
about 75­200 microns in diameter) are very abundant
in the laminated concretions from the L1 and L2 inter-
vals (Fig. 4A, B). The origin of calcispheres has been a
matter of debate, but most are believed to represent
reproductive cysts of green algae belonging to the fam-
ily Dasycladaceae (Wray 1977). Upper Palaeozoic cal-
cispheres are often encountered in shallow-water
deposits (especially in restricted or back-reef environ-
ments), and as such they provide a useful palaeoenvi-
ronmental indicator. This interpretation is in good
agreement with Piasecki & Stemmerik (1991) and Nielsen
128
B3
B2
L2
L1
B1
0
15
10
20
25
m
5
Calcareous,
micaceous mudstone
Bioturbated siltstone
Carbonate concretions
Carbonate beds
Fish remains
Fig. 3. Simplified sedimentolo-
gical log showing the typical
five-fold division of the
Ravnefjeld Formation. L1 and
L2 are laminated intervals, and
B1, B2 and B3 are bioturbated
intervals. The compilation is
based on lithological features
observed at Kap Stosch and
Triaselv, and elsewhere in the
region (Piasecki 1990; Piasecki
& Stemmerik 1991; Nielsen
2001).
A
B
0.50 mm
0.50 mm
Py
Py
Fig. 4. Micrographs of the abundant calcispheres, partially replaced
by euhedral pyrite (Py) as viewed in transmitted light (A) and
ultraviolet fluorescence (B) (sample GGU 446352). The pyrite con-
tains fluorescent calcite inclusions.
GSB191-Indhold 13/12/02 11:33 Side 128
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129
Fig. 5. Micrographs of the millimetre-sized gastropods containing authigenic calcite and baryte (Ba) viewed in transmitted
light (A) and cathodoluminescence (B); compaction has not affected these shells. Bivalve shell in transmitted light (C) and
cathodoluminescence view (D) is affected by micritisation and authigenic calcite crystals. The youngest calcite generation
(E) is confined to veins and displays orange luminescence. Weak disintegration and displacement of the prismatic crystals of
a thin-shelled fossil (F, G) followed by calcite cementation of the cavity (sample GGU 446370-2).
0.5 mm
0.5 mm
0.5 mm
0.5 mm
A
B
C
E
0.5 mm
0.5 mm
F
G
Ba
Ba
C
D
0.5 mm
GSB191-Indhold 13/12/02 11:34 Side 129
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(2001), who pointed out the restricted nature of the
basin during deposition of the sediments in the Ravne-
fjeld Formation.
Disarticulated bivalves of Posidonia permica are
common in carbonate concretions from intervals L1
and L2. The bivalves have two distinct shell layers: an
outer layer that has retained the original, normal pris-
matic microstructure, and an inner layer preserved as
drusy sparite, indicating that this part of the shell was
originally composed of aragonite which dissolved dur-
ing early diagenesis leaving a void that was later filled
with sparry calcite. The outline of the aragonitic layer
has often been preserved as a dark micritic envelope
(Fig. 5C, D). Such envelopes are usually produced by
endolithic cyanobacteria which bore into the skeletal
debris. Micritic envelopes due to endolithic cyanobacte-
ria can be used as a depth criterion, indicating deposi-
tion within the photic zone (less than 100­200 m); this is
in good agreement with the facies analysis of the Ravne-
fjeld Formation carried out by Christiansen et al. (1993).
Small gastropods occasionally occur in the carbon-
ate concretions of the L1 and L2 intervals. Their origi-
nal wall structure is preserved as drusy sparite, indicating
that the shell was originally composed of aragonite that
dissolved leaving a void filled with sparry calcite at a
later diagenetic stage. Many specimens have a muddy
geopetal fill in the lower part of the cavity, with sparry
calcite filling the upper part (Fig. 5A, B).
Diagenesis of the carbonate concretions
An investigation of the cement generations in the primary
cavities of gastropods has been undertaken. Since these
cavities are the largest encountered in the carbonate con-
cretions, the various cement generations are best devel-
oped here. A cathodoluminescence study of these cavities
has shown a distinct pattern of zoning, representing a
series of cement generations or phases of crystal growth.
Each zone represents the precipitation of calcite from pore
waters with different chemical compositions (Meyers
1991; Machel 2000). Four distinct calcite generations have
been detected (Fig. 5B, E, G). The initial carbonate cement
shows dark brown luminescence and the second gen-
eration bright yellow; both these generations are volu-
metrically small. The third calcite generation displays
brownish luminescence and is volumetrically dominant,
while the fourth and youngest calcite generation shows
orange luminescence and is limited to veins cutting
through all the other cement generations.
The cathodoluminescence colours in calcite cements
depend upon the concentration of Mn
2+
and/or Fe
2+
ions
(e.g. Smith & Dorobek 1993), and normally the earli-
est is black, precipitated from shallow oxic water, fol-
lowed by yellow and brownish generations that reflect
gradually more reducing conditions due to increased
burial. The lack of non-luminescent carbonate cement
in the concretions implies that all the carbonate cement
was precipitated from reducing pore water. Prior to cal-
cite cementation, there had also been sufficient over-
burden to cause incipient compaction of both pellets
and thin-shelled fossils (Fig. 5F, G).
Authigenic baryte crystals are present in primary
voids in some gastropods (Fig. 5A, B). Petrographic
investigations show that the baryte crystals were pre-
cipitated on the yellow luminescent calcite generation,
and overgrown by the brownish, indicating an early dia-
genetic precipitation of baryte. Baryte seems to be lim-
ited to concretions which contain a high concentration
of originally aragonitic skeletal material. As shown by
Turekian & Armstrong (1960) the concentration of bar-
ium in recent aragonitic gastropods and bivalves can
be fairly high. If this was also the case in Upper Palaeo-
zoic time, the early diagenetic dissolution of aragonite
may have provided a local barium source for precipi-
tation of baryte.
Both pyrite framboids and euhedral pyrite crystals
are common. A combination of stable isotope analyses
and a study of the size distributions of small pyrite
framboids indicates that these formed within the euxinic
parts of the water column while the laminated sediments
were being deposited (Nielsen 2001). When they reached
130
0.05 mm
Fig. 6. Micrograph of a pyrite framboid in the bioturbated sedi-
ments (B3 interval) of the Ravnefjeld Formation (sample GGU
446358).
GSB191-Indhold 13/12/02 11:34 Side 130
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a maximum size of about 10 microns, they became
hydrodynamically unstable and sank to the sea floor
where they were incorporated in the bottom sediments
(Wilkin & Barnes 1997; Cutter & Kluckholm 1999).
Larger authigenic pyrite framboids are commonly found
within and around burrows (Fig. 6). This association is
well known from recent deposits where it results from
the sharp redox transition between the burrow and the
surrounding sediments arising from the decay of organic
matter in the burrows during bacterial sulphate reduc-
tion (Berner & Westrich 1985). In addition to these early
diagenetic pyrite framboids, later diagenetic euhedral
pyrite partly replaces both the calcareous matrix and
calcite cements, leaving calcareous inclusions in the
euhedral pyrite (Fig. 4B; Nielsen 2001).
Chalcedonic quartz, with its characteristic bundles of
thin fibres, is only known as sporadic infill in calci-
spheres and articulated ostracods. The silica most likely
originated from the dissolution of opaline sponge
spicules, which have been identified in thin sections.
There is no sign of calcite cement together with chal-
cedonic quartz which indicates that precipitation of
quartz was prior to calcite precipitation.
Rhombohedral microdolomite crystals (< 20 microns)
are disseminated throughout the calcareous matrix,
often associated with fecal pellets. Mesodolomite crys-
tals (> 20 microns) occur only sparsely. As shown by
Nielsen (2001), the dolomite is characterised by a deple-
tion in
18
O, which indicates that the partial dolomitisa-
tion might be due to meteoric water invasion at a
shallow burial depth.
Timing of the carbonate concretion
formation
The investigations in the Kap Stosch area have revealed
a succession of five laminated and bioturbated intervals,
with several distinct horizons of carbonate concretions.
The concretions studied from the bioturbated intervals
B1 and B3 show well-preserved bioturbation, and this
indicates that concretion formation was initiated sub-
sequent to the infaunal activity. Compactional defor-
mation such as deflected laminae and very thin beds
at the outermost rims of the studied concretions, which
are distinctive for the concretions in the L1 and L2 inter-
vals, points to formation after some compaction. This view
is also supported by the finds of slightly deformed pel-
lets and thin-shelled fossils, which clearly indicate that
some compaction of the soft, fine-grained sediment had
occurred before carbonate precipitation took place.
Acknowledgements
B.M. Nielsen, M. Pedersen, S. Piasecki and H. Stendal (GEUS)
are thanked for many helpful discussions during the 1998 field
season. R. Binns kindly improved the English of the manuscript.
J.K.N. gratefully acknowledges the financial support of a Ph.D.
studentship at the Geological Institute, University of Copenhagen.
H. Stendal (GEUS) and B. Buchardt (Geological Institute) are
thanked for help and advice during the Ph.D. studentship com-
pleted in 2001. This paper is a contribution to the project Resources
of the sedimentary basins of North and East Greenland, sup-
ported by the Danish Research Councils.
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Authors' addresses
J.K.N., Geological Institute, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. Present address: Department
of Geology, University of Tromsø, Dramsveien 201, N-9037 Tromsø, Norway. E-mail: jesper.kresten.nielsen@ibg.uit.no
N.-M.H., Department of Geology, University of Tromsø, Dramsveien 201, N-9037 Tromsø, Norway
.
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Review of Greenland Activities 2001, pp 126-132