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Jotnian and Postjotnian: Sandstones and diabases in the surroundings of the Gulf of Finland

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Abstract

The Jotnian sandstones and Postjotnian diabases in the Satakunta and Bothnian Sea, Åland Sea and Lake Ladoga areas appear to belong together. The Jotnian sandstones are stratified and contain many types of primary structures, e.g. conglomerate interbeds and siltstone inclusions. Stratified structures in all the areas indicate quite a long period of sedimentation and, at least in the Satakunta area, quite clear evidence of delta formation. At Harjavalta and a couple of other areas e.g. trough cross bedding has been described. The sandstone beds dip quite steeply indicating a shear zone along the northeastern contact of the present sandstone area. In the Ladoga - Pasha graben the sandstone covers practically all of Lake Ladoga. In this area, aeromagnetic surveys have detected the "Prejotnian" form of the old graben. Drilling and aeromagnetic studies reveal that the depth of the sandstone deposits seldom reaches more than 2 000 m below sea level. In Satakunta and in the coastal area of the Bothnian Sea, the diabase forms mostly sills. However, in recent years, much younger crosscutting diabases have been found e.g. on the Yläne and Kokemäki map sheet areas. The older diabases are usually at least 100 m in width and the younger seldom more than 2 m in width. The older diabases in Satakunta are 1258-1265 Ma old (U-Pb, zircon). Most of the age determinations are from diabase pegmatoids, pegmatitic diabases or pegmatites in diabase. In the Lake Ladoga area, the so-called Valaam diabases are at least 250 km long and mostly less than 300 m wide. In Valaam, at least, the diabases also include rheomorphic rocks and volcanic rocks. The latter do not show any evidence of younging against the sandstone. North of Lake Ladoga two diabase dykes, for which there are no isotopic ages, cut the Salmi rapakivi.
Explanation to the Map of Precambrian basement
of the Gulf of Finland and surrounding area 1 : 1 mill
Edited by Tapio Koistinen
Geological Survey of Finland, Special Paper 21, 99-113, 1996
JOTNIAN AND POSTJOTNIAN: SANDSTONES AND DIABASES IN THE
SURROUNDINGS OF THE GULF OF FINLAND
by
Amantov, A., Laitakari, I. and Poroshin, Ye.
Amantov, A., Laitakari, I. and Poroshin, Ye., 1996. Jotnian and Postjotnian:
Sandstones and diabases in the surroundings of the Gulf of Finland. Geological
Survey of Finland, Special Paper 21, 99-113, 4 figures.
The Jotnian sandstones and Postjotnian diabases in the Satakunta and Bothnian
Sea, Aland Sea and Lake Ladoga areas appear to belong together.
The Jotnian sandstones are stratified and contain many types of primary struc
tures, e.g. conglomerate interbeds and siltstone inclusions. Stratified structures in all
the areas indicate quite a long period of sedimentation and, at least in the Satakunta
area, quite clear evidence of delta formation. At Harjavalta and a couple of other
areas e.g. trough cross bedding has been described. The sandstone beds dip quite
steeply indicating a shear zone along the northeastern contact of the present sand
stone area. In the Ladoga—Pasha graben the sandstone covers practically all of Lake
Ladoga. In this area, aeromagnetic surveys have detected the "Prejotnian" form of
the old graben. Drilling and aeromagnetic studies reveal that the depth of the
sandstone deposits seldom reaches more than 2 000 m below sea level.
In Satakunta and in the coastal area of the Bothnian Sea, the diabase forms
mostly sills. However, in recent years, much younger crosscutting diabases have
been found e.g. on the Ylane and Kokemaki map sheet areas. The older diabases are
usually at least 100 m in width and the younger seldom more than 2 m in width.
The older diabases in Satakunta are 1258-1265 Ma old (U-Pb, zircon). Most of the
age determinations are from diabase pegmatoids, pegmatitic diabases or pegmatites
in diabase.
In the Lake Ladoga area, the so-called Valaam diabases are at least 250 km long
and mostly less than 300 m wide. In Valaam, at least, the diabases also include
rheomorphic rocks and volcanic rocks. The latter do not show any evidence of
younging against the sandstone. North of Lake Ladoga two diabase dykes, for which
there are no isotopic ages, cut the Salmi rapakivi.
Key words (GeoRef Thesaurus, AGI): areal geology, explanatory text, sandstone,
dikes, diabase, volcanic rocks, Mesoproterozoic, Jotnian, Riphean, Southwestern
Finland, Russian Federation, Republic of Karelia, Lake Ladoga
Aleksey Amantov and Yevgeniy Poroshin, All-Russian Geological Research Institute
(VSEGEI), Sredniy Prospekt 74, 199026 St. Petersburg, Russia
Geological Survey of Finland, Special Paper 21
A. Amantov, I. Laitakari & Ye. Poroshin
CONTENTS
O vervie w............................................................................................................................................... 101
Satakunta, Gulf of Bothnia and Aland Sea areas .
.......................................................................... 102
Jotnian sediments...............................................................................................................................102
Postjotnian diabases..........................................................................................................................104
Conclusions on the Jotnian Postjotnian development in southwestern Finland
.........................
104
Lake Ladoga a rea ..................................................................................................................................105
Jotnian (Riphean) sediments in the Lake Ladoga area
.................................................................. 105
Postjotnian diabases and associated mafic volcanic rocks in the Lake Ladoga area
....................
108
Conclusions on the Riphean evolution in the Lake Ladoga a re a ....................................................Il l
References .............................................................................................................................................Il l
100
Geological Survey of Finland, Special Paper 21
Jotnian and Postjotnian: Sandstones and diabases in the surroundings...
OVERVIEW
The term "Jotnian" was first used by Sederholm
(1897) and the term "Postjotnian" by Ramsay
(1909). The history of these terms is more thor
oughly described in the chapter "Subdivision of
rocks and structures".
The principal localities of Jotnian sediments and
Postjotnian diabases, in the map area, are the
Satakunta—Gulf of Bothnia area, the Aland Sea
area and the Lake Ladoga area. At all localities
the sandstone is (with few exceptions) older than
diabase and the terms Jotnian and Postjotnian
apply within each investigated area. However,
there is little evidence, that this (age order) pre
vails from one area to an other. Therefore, the
terms should be interpreted as more descriptive
(i.e. the diabase usually cuts the sandstone) than
temporal (all the Jotnian sandstones not necessarily
older than all the Postjotnian diabases).
The Jotnian sediments, within all these areas,
occur in large grabens, which, in addition to sedi
ments, are characterized by extensive dykes and
sills of diabase and, in places, by coeval volcanic
rocks. The sinking of the grabens probably oc
curred over a very long period and the present
form of the depressions appear to represent either
the end of the Jotnian sedimentation, or possibly a
still later time. According to geological data, the
age of the Jotnian sediments is (mostly) between
rapakivi granites (ca. 1600 Ma) and Postjotnian
diabases (ca. 1260 Ma).
When discussing the origin of the sandstone
grabens, the presence of rapakivi plutons near all
of them appears to be of importance. Korja et al.
(1993) have suggested that the grabens and rapa
kivi emplacement are causally related.
[IL]
The terms "Jotnian" and "Riphean" are used for
comparable Mesoproterozoic sedimentary sequenc
es. The Riphean stratotype has been defined in the
Urals region (the previous name of this mountain
chain was Ripheus).
Some Jotnian / Riphean basins are shown on the
appended map, on the Inset map of the Fenno-
scandian Shield. These structures are filled by
mainly sandstones and other sedimentary rocks.
These can be subdivided (Amantov, 1992a, b)
into: Marginal pericratons, such as the Mezenck
Barents Sea basin that frames the shield in the
northeast; so-called aulacogens or elongated rift
like grabens on reworked blocks of Archean crust,
e.g. the basin of the Kandalaksha and Dvina Bays
of the White Sea, where the thickness of sand
stones and siltstones reaches several kilometers;
more isometric graben-synclines or half-grabens,
e.g. the Ladoga—Pasha structure of Lake Ladoga
and the Aland Sea basin (Soderberg 1993), which
is partly on the appended geological map, south
west of Aland. The Lake Ladoga graben and its
contents will be described in detail below.
The map shows that Jotnian basins are spatially
associated with younger large rapakivi intrusions.
The master faults, which determine basin shape,
have formed parallel to the deep unexposed boun
dary of the granite bodies. The rapakivi granite of
Salmi outcrops along the northeastern margin of
the Ladoga basin. The development of Jotnian
basins was presumably triggered by intrusive
injections that accompanied radial faulting; land
scape development and isostatic rebound at the
uppermost level shaped the subsequently formed
basins (Amantov 1993). Soderberg (1993) dis
cusses comparable mechanisms. [AA]
101
Geological Survey of Finland, Special Paper 21
A. Amantov, I. Laitakari & Ye. Poroshin
THE SATAKUNTA, GULF OF BOTHNIA AND ALAND SEA AREAS
Jotnian sediments
The Satakunta sandstone has been known for
over 200 years. The first maps to show its distri
bution (Wiik 1877, Moberg 1880) were made in
the 1870’s and the first scientific publication on
this (that time still called Cambrian) sandstone was
by Gylling (1887). The Satakunta sandstone is
almost completely covered by Quaternary sedi
ments and most of the outcrops within the sand
stone area consist of younger diabase dykes and
sills. The cover caused difficulties in the com
pilation of a realistic bedrock map for the area;
e.g. Sederholm (1893, 1903), only two decades
after Gylling, mapped most of the sandstone area
as diabase.
The first detailed mapping of the Jotnian area of
Satakunta was made by A. Laitakari (1925). He
also extended the sandstone to the bottom of the
Bothnian Sea, but, unfortunately, the offshore part
of his map only covers a very limited area. Scat
tered observations of sandstone erratics, which
clearly originate from the sea bottom, had been
made in many places (e.g. Hausen 1911, Sauramo
1924), but the first attempt to compile a realistic
map of the bedrock of the bottom of the Bothnian
Sea, was made by Backlund (1937). This map,
which in general is still applicable, shows that the
Satakunta sandstone graben is only an appendage
to the main part of the Jotnian sandstone, which
forms the Bothnian sea-floor.
Later the distribution of sandstone has been
studied in greater detail on the sea-floor and on
land (e.g. Veltheim 1962). The map of the Pre-
Quaternary geology of the northern part of the
Baltic Sea (Winterhalter et al. 1981) shows that
the bottom of the Bothnian sea almost completely
consists of Jotnian sandstone. More recent maps of
the sandstone onshore have been compiled by
Hamalainen (1985) and Kohonen et al. (1993). In
detail, new 1 : 100 000 scale maps of Pre-Quater
nary geology (Pihlaja 1994a, b and iii prep., Ha
malainen 1994, Vorma & Niemela 1994) give still
more information. Kohonen et al. (1993) have also
listed all the known outcrops and drilling sites in
the Satakunta sandstone area.
The provenance of the sandstone material has
been a question of debate since the time of Gylling
(1887) and Sederholm 1897. According to the
thorough mineralogical investigations of Marttila
(1969), it appears clear that the Svecokarelian
orogenic bedrock was the only source of material
for the sandstone and, apparently, the rapakivi
plutons were not exposed at the time of sedimenta
tion.
.Analyses of sedimentary structures (e.g. Ko
honen et al. 1993) have revealed that the main
medium for material transport was running water.
It should, however, be considered that the avail
able observations are almost exclusively from the
uppermost part of the Jotnian sedimentary forma
tion. In drill holes very few primary sedimentary
structures have been recognized. From a 600 m
hole, south of Pori (the deepest in the Satakunta
sandstone), the most important observation is that
most of the drill core is more fine-grained than
most sandstones in outcrop. This fact infers that
the bulk of the sandstone formation is more fine
grained than is usual in the few outcrops available.
Further, the glacial boulders that originate from
the bottom of the Bothnian sea are mostly of fine
grained sandstone. However, this does not neces
sarily infer deep-water deposition since many
boulders contain ripple marks and raindrop im
prints. It is concluded that sedimentation and the
deepening of the grabens were simultaneous and
only the water in the younger part of the basin
was very deep.
The 600 m drill hole mentioned above did not
reach the Svecokarelian bedrock and the few
bedrock windows within the sandstone area have
proved to be huge glacial boulders (Hamalainen
1985). Thus, no direct observations of the thick
ness of the sandstone are available. From geo
physics, the maximum thickness of sandstone has
been estimated to be 800+400 meters and the
mean thickness 1300 + 300 meters (Elo 1976). In
Sakyla, near the eastern contact of the sandstone
area, the thickness has been estimated at
180-195 m (Elo et al. 1993).
The coarse-grained sandstones in the uppermost
part of the formation show that the flow velocity
102
during river tranisxr. » is fairly high and, conse
quently. the topography was quite rough during
the late phase of the sedimentation. Apparently,
there was still vertical faulting of the crust at this
time.
In the channel of the Lammaistenkoski hydro
electric power plant, Harjavalta, the sandstone
layers have tilted about 35° SW, which indicates
marked sinking (causing tilting) of the graben after
sedimentation. The present northeastern contact of
the sandstone is also controlled by a NW—SE-
trending fault line, not far from Lammaistenkoski.
Axberg (1980) has described an offshore continua
tion of this fault up to the Swedish coast. It is
possible that at least the last tectonic activity was
connected to the Postjotnian diabase intrusions.
This relationship is also indicated by the fact that,
in places (e.g. to the northwest of Pori) extensive
diabase intrusions follow the contacts of the Jot
nian sandstone area.
The original extent of the sedimentation basins
is hard to estimate, but at least the onshore part of
the Satakunta sandstone graben, at present fault
controlled, is clearly only a fraction of the original
area of Jotnian sediments on the eastern shore of
the Bothnian Sea. Further, the sandstone area at
the bottom of the Bothnian Sea is, at least in the
west (Axberg 1980), controlled by faults and may
have been more extensive at the end of the Jotnian
period.
The sandstone at the bottom of the Bothnian Sea
is a direct continuation of the Satakunta sandstone
and apparently of similar type. Older publications
on it are based on glacial erratics around the
Bothnian Sea (e.g. Hausen 1911; Sauramo 1924)
and later papers on bottom samples taken with
different types of equipment by research vessels
(e.g. Veltheim 1962, Winterhalter 1972). These
studies show no essential differences between the
sandstone of the Bothnian Sea and that of Sata
kunta. The sandstones of the bottom of the Both
nian Sea are often called "quartzitic" by Swedish
geologists (e.g. Axberg 1980), but this term does
not infer any state of metamorphism, but only the
mineral composition of the main rock type. The
maximum thickness estimations of the Jotnian
sandstone at the bottom of the Bothnian Sea, near
the town of Pori, is about 1000 meters (Winter
halter (1972) and about 900 meters in the Aranda
Rift, slightly to the north of the map sheet border
(Axberg (1980). A thickness estimation of 700
meters for the Jotnian sandstone of the Aland Sea
is given by Winterhalter et al. (1981).
Quite few direct observations are available on
the fault zones bordering the sandstone graben.
The Oripaa breccia is interesting. It has not been
observed directly in contact with the sandstone,
but occurs on the southeastern continuation of the
same fault system. The breccia has only been
found as glacial boulders; so numerous that the
rock type is quite well established. The fragments
of the breccia consist of intensively mylonitized
granitic rock brecciated by numerous generations
of small quartz dykes.
The last phase in the development of the Both
nian Bay - Satakunta sandstone was peneplanation.
This phase is described in detail in later sections,
but problems directly connected with the sandstone
are briefly discussed here.
The Satakunta sandstone is clearly on the north
eastern side of the basin bordered by a fault zone.
The faults are usually parallel to the present gra
ben and also apparently with the paleobasin, but
there is no reason to think that the distribution of
the sandstone in Jotnian time was limited to the
present graben. Postsedimentary subsidence pro
tected the central part of the sandstone against
erosion, when most of it outside the graben was
eroded away. The small area / areas of sandstone
in many parts of southwestern Finland indicate an
originally wider distribution for the Jotnian sand
stone.
The harder diabase was more resistant to ero
sion and formed hills while the softer sandstone
was eroded deeper and formed wide valleys.
Erosion also exposed the uppermost parts of the
rapakivi plutons, which, during the sedimentation
of the sandstone, were still covered by Svecoka
relian orogenic rocks.
The Aland Sea sandstone is known from marine
geological and geophysical studies only. Recently
these studies, mostly carried out by the Depart
ment of Geology and Geochemistry of the Univer
sity of Stockholm, have been summarized by
Soderberg (1993). PL]
103
Jotnian and Posgotman: Sands:ones and diabases
Mo st o f the Svecokarelian orogenic belt formed
1900-1850 Ma ago and underwent simultaneous
uplift and erosion, fluvial and aeolian. When the
rapakivi plutons of Laitila, Vehmaa and Aland
were intruded, the Svecokarelian mountains were
ready quite deeply eroded. Rapakivi is lighter
тЬяп most surrounding rocks and rises gravitation-
ally in the earths crust. This large scale uplift
caused depression of some other areas. In south
western Finland, the grabens of Satakunta - Both
nian Sea and that of Aland started to form. It is
quite possible that the sinking already began be
fore crystallization of the rapakivi magma, because
the gravitational rise of granitic material does not
depend on its state, but on its density.
When crystallizing 1540-1590 Ma ago (Suo
minen 1991), the rapakivi plutons were at a depth
of several kilometers. Their heating effect in the
earths crust lasted for tens of millions of years and
was possibly enhanced by the probable thick bed
of volcanic deposits on top of the bedrock.
At that time Fennoscandia was in the tropics
(Bylund 1994). Disintegration of rocks was rapid
and the climate was rainy. The lack of land vege
tation supported erosion and transport of material
to the valleys. This sedimentation was simulta
neous with the sinking of the grabens and appar
ently lasted for hundreds of millions of years. The
sandstone is not suitable for radiometric age deter
minations, but intercalated shales yield a K-Ar age
of 1278-1097 Ma (Suominen 1991). According to
paleomagnetic studies, the Jotnian sandstone of
Satakunta is only a little older than the Postjotnian
diabase. However, both the age determinations
and the paleomagnetic measurements were appar
ently made from the uppermost (youngest) part of
the Jotnian formation.
The grabens were already filled with sand, and
the sand apparently cemented as sandstone, when
large masses of basaltic magma intruded in the
bedrock. Within the sandstone area, it formed
extensive sills and dykes that are now exposed by
erosion. However, it is very probable that it also
erupted at the surface forming volcanic deposits
and that these eruptions are linked with the last
subsidence of the Satakunta graben, apparently
after the sedimentation and cementation of the
sandstone.
The typical Jotnian diabase of Satakunta shows
no or very few phenocrysts indicative of crystalli
zation in some kind of magma chamber. There
fore, it is likely that it intruded directly from the
upper mantle where the magma had formed by
partial melting (Ramo 1990). Thus, the magma
was very hot when it reached the present erosion
level and consequently melted walls of the host
rock (Kahma 1951).
The last phase of diabase intrusion was the
injection of small, almost N—S-trending dykes,
which sharply cut the normal Postjotnian diabases.
After the Jotnian sedimentary and Postjotnian
magmatic events, erosion continued. This process
destroyed all the volcanic rocks, associated with
diabase intrusions and exposed the diabase sills
and tops of the rapakivi plutons. In the Vendian,
the erosion level was practically the same as the
present one. That can be seen at Lauhanvuori (on
the northern margin of the bedrock map), where
the Pre-Vendian peneplain under the Vendian
sandstone is exactly on the same level as the pres
ent land surface in surrounding areas (see Puura et
al. this volume). [IL]
THE LAKE LADOGA AREA
Jotnian (Riphean) sediments in the Lake Ladoga area
Jotnian sedimentary and volcanic layers un-
conformaby overlie older Proterozoic rocks in the
Lake Ladoga area.
Jotnian sediments are more similar in mechani
cal properties to the overlaying platform cover
than to the underlaying crystalline basement. As a
result, exposed parts of the Jotnian sediments have
been subjected to particularly strong selective
denudation, resulting in considerable erosion
forms. Lake Ladoga basin is an example, especial
ly in its northern deepest part. Its origin is con
nected with Tertiary erosion and Pleistocene
105
Geological Survey of Finland, Special Paper 21
A. Amantov, I. Laitakari & Ye. Poroshin
Pitkaranta
Mantsinsaari
:ern Archipelago :ulansaari
ozersk LAKE LADOGA
,4Conevets
Moryin Nos Ca
St. Petersburg 50 Km
Fig. 1. Localities mentioned in the text.
glacial overdeepening of that part of the Jotnian
Ladoga—Pasha structure (Fig. 1). The distribution
of the Jotnian sediments is restricted mainly to the
sub-bottom area of Lake Ladoga with only minor
extensions on the land areas. In the northwest the
Jotnian rocks extend close to the coastal skerries
(small rocky islands) of Lake Ladoga (Amantov &
Spiridonov 1989, Amantov et al. 1989, Amantov
1991).
The Ladoga—Pasha graben-syncline comprises
a complicated section of sedimentary and extrusive
rocks with a supposed total thickness of over 2000
m. At least two generations of mafic intrusions
have been injected into this sequence. Red-gray or
white-gray sandstones with siltstone layers pre
dominate.
The basin morphology under the Jotnian sedi
ments is not known in detail, but the geophysical
data allow its preliminary reconstruction (Figs. 2
and 3). The collapse structure at Ladoga has a
radial framework of master fault zones with three
narrow grabens that intersect approximately in the
center of the main circular structure, slightly
southeast of 61° N 32° E. The NW-trending
Pasha graben is the deepest (Fig. 3). The Ladoga
—Pasha graben-syncline extends southeastwards
from Lake Ladoga, out of the map area. The
Pasha graben has some asymmetric features; the
Fig. 2. The present morphology of the sub-Jotnian nonconfor
mity surface.
Fig. 3. The morphology of the sub-Jotnian nonconformity seen
in three dimensions, looking southeast, along the Pasha graben.
The Pasha graben continues out of the diagram.
master fault bounds the southwestern side, running
in the coastal zone between Voltshy Nos and the
Storozhensky capes. The South Konevets graben
was generated by an approximately E—W-trending
running fault zone. In the upper part of the sedi
mentary sequence it mirrors the trend of the fault
fold.
Dissimilar Jotnian sections are known around
106
Geological Survey of Finland, Special Paper 21
Jotnian and Postjotnian: Sandstones and diabases in the surroundings...
Priozersk (so-called Priozersk suite), in the Salmi
region (Salmi suite with volcanic rocks) and in the
southern coastal area. They have been investigated
in detail by SEVZAPGEOLOGIA (A. Yanovskiy
and others). Continuous reflection profiling was
done in 1989-1992 by VSEGEI with support of
SEVZAPGEOLOGIA. Accordingly, the general
seismic stratigraphy of the sub-bottom area has
been established (Amantov 1992, 1993). Seismic
units have been correlated with the geology of the
adjacent shore areas and bottom outcrops and
some lithological varieties are known from the
boulder material. Investigations have established a
more complex Jotnian succession than established
previously.
The whole Jotnian / Riphean sequence may be
divided into four main units (Fig. 4). Their proper
age is tentative, due to limited chronostratigraph-
ical data. The lowermost unit is referred to as
partly Lower and partly Middle Riphean; the two
following subdivisions are referred to as mainly
Middle Riphean while the youngest is referred to
as Upper Riphean or even Lower Vendian (Aman
tov 1992a; 1993).
Fig. 4. Sketch cross section of the Ladoga - Pasha basin.
Unit 1.
The basal unit covers the crystalline basement
with saprolites, also known on rapakivi granites of
the Salmi pluton.
Conglomerates occur in the basal part of the
section. The layers of fine sandstones and silt-
stones are subordinate. The total thickness of the
unit is about 1000 m.
A laterally variable seismic signature is typical
and indicates lateral lithological variation. Distinct
reflectors on seismic diagrams are more rare along
the northeastern and southwestern slopes of the
basin where there is a more homogeneous sandy
succession. Along the northwestern axis of the
basin, in the Western Archipelago area, strong
parallel tilted reflectors are typical. These are
caused by an increasing amount of siltstone layers,
which are blue gray and dark red micaceous silt-
stones intercalated by fine grained gray, pink or
red siltslone. They occur mostly along the north
ern coast, particularly west of the Kilpisaaret
islands (between 30° and 30.5° of longitude).
The prominent parallelism of seismic layers
supports the idea of widespread Riphean sedimen
tation.
In the eastern and central parts of the basin, as
well as along the Pasha graben, sheets of basaltic
magma complicate the succession, together with a
swarm of sills and dykes. Volcanic layers are
exposed along the northern and northeastern bor
ders of the structure beneath thin Quaternary cover
and in bottom outcrops. Characteristically, the
resistant igneous units form several skerries in
northern Lake Ladoga (cf. profile e—f of the
appended geological map). The thickness of igne
ous layers may reach hundreds of meters in the
central part of the basin. Their composition will
be described in a later section.
Unit 2.
The next main subdivision has been traced
everywhere to overlay the lower subdivision with
out evident unconformity but with distinct seismic
boundary. The unit is characterized by dark col
ored (from gray to nearly black) laminated varved
siltstones. They are interdigitated with relatively
light siltstone layers. The layer thickness increases
downwards, where also sandstone layers appear.
The total thickness of the unit is about 500 m,
with 350-400 m (mean values range between
250-300 m) of mainly varved dark siltstones.
The dark fine-grained sequence mentioned may
be used as a reference horizon between different
Riphean grabens and probably illustrates either a
regional tectonic event, or deposition in single or
intermutual basin(s).
The dark varved siltstones and siltstones of the
Muhos formation in Western Finland are possibly
equivalents to those in the Fennoscandian area;
their age, based on biotype, is about 1200 Ma
107
(Tynni & Uutela, 1984). The age fits well with the
position of the Lake Ladoga unit because the dark
siltstones are cut by the Valaam layered intrusive,
which presumably formed around 1280 Ma ago
(A. Savitskiy pers. comm). Erratics of similar
black shales occur also in the Aland basin (Hagen-
feldt & Soderberg, 1985), but their stratigraphic
level is still uncertain (Soderberg 1993, Amantov,
Soderberg, Hagenfeldt 1993).
Unit 3.
This seismic unit, ca. 400 m thick, overlies
Unit 2, and possesses a very specific seismic
signature, a strong reflector. Acoustically non-
penetrative sediments mask the form of the foot
boundary of the unit. North of Konevets island the
subdivision may cover not only an older varved
part of the Riphean succession, but also an even
older lower unit, thus indicating a minor uncon
formity. However, fault displacements prevent
easy interpretation and the varved unit appears to
be connected to the lower unit, indicating the same
paleoenvironmental evolution.
The northern boundary of the unit is related to
an erosion scarp or slope exceeding 40-50m.
Lithological composition is as yet unsatisfactori
ly known. Massive, often crosslaminated sand
stones prevail among erratic blocks in the washout
debris of the moraine line slightly to the southeast
from the slope mentioned. Reddish sandstone with
light and brown bands and (or) spots is mainly
medium- or fine-grained; compact yellow white,
white gray or pink quartzitic sandstones are the
hardest rocks. These varieties satisfactorily explain
the origin of the acoustically hard seismic signa
ture.
The subdivision appears similar to the upper
units of the Aland basin from its position above
dark shales as well as from its seismic signature.
Geological Survey of Finland, Special Paper 21
A. Amantov, I. Laitakari & Ye. Poroshin
Unit 4
The deposition of the unit is connected with г
new phase of tectonic activity, starting, probably,
with the emplacement of magma of the same age
as the Valaam sill. New faulting, with the uncom
mon major trend of 100-110°, is associated. Such
fault zones caused the development of deep and
narrow composite synclinal fold-faults. Two minor
structures belonging to this group occur north of
Konevets island, but the main structure is the
South Konevets composite syncline.
The associated sequence overlies older Riphean
sequences with obvious unconformity. There is
also a minor inner unconformity that separates the
unit into two secondary subdivisions, indicated by
seismic studies. Direct data are lacking. The unit
is characterised by deep seismic penetration.
Two or three reflectors occur in the eastern pan
of the composite syncline each with an approxi
mate thickness of 110-190 m.
The upper part of the unit with probable Upper
Riphean - Lower Vendian age comprises the fold
bend of the South Konevets syncline. The proba
ble Lower Vendian age suggests the conservation
of Volygian glacial tillites and associated sedi
ments as the youngest sequence before the region
al planation. Such position in the upper part of
Riphean graben-like structures is well known on
the Russian platform.
Unit 4 represents the youngest known infilling
of the Ladoga—Pasha graben-syncline, totalling
about 600-700 m. After peneplanation, the mature
tableland was covered by Upper Vendian sedi
ments of the Valdai series, starting with the Red-
kino Horizon. The thickness of the whole series
(both Redkino and Kotlin Horizons) reaches
250-270 m near the southern coast. Sedimentation
of the overlying Paleozoic sediments starts from
the Lower Cambrian in this area (Amantov et al.
1993). [AA]
Postjotnian diabases and associated mafic volcanic rocks in the Lake Ladoga area
Main features
The main areas of Middle Riphean mafic mag- coast of Lake Ladoga and in the Valaam ridge,
matic rocks lie in Karelia and in southwestern Analysis of the published sources (Kairyak &
Finland in Satakunta (Kahma 1951). In Karelia, Khazov 1967, Tikhomirov & Yanovskiy 1970,
they outcrop along the northeastern and eastern Khazov & Popov 1984, Golubev & Svetov 1983)
10 8
Geological Survey of Finland, Special Paper 21
Jotnian and Postjotnian: Sandstones and diabases in the surroundings...
and the results of the thematic works by VSEGEI
(A. V. Savitskiy, A. V. Amantov) and SZGTU
(A. S. Yanovskiy) reveals three phases of mag-
matic activity in the Riphean of the North Ladoga
region. During the first two phases, basaltic lavas
were erupted. They comprised two sheets intruded
by several subvolcanic bodies (dykes and sills).
The thickness of the lower sheet is 130 to 140 m
and that of the upper sheet 80 to 90 m. The sheets
are separated by a layer of terrigenous sedimen
tary rocks (0 to 30 m in thickness), which indi
cates a break in volcanic activity. In the later
phase of magmatic activity, the differentiated
gabbro-monzonitic-granosyenitic Valaam sill was
intruded. Its estimated thickness is 130 to 150 m.
The isotope age of formation of the magmatic
rocks varies from 1500 Ma to 1100 Ma. Accord
ing to K-Ar data (bulk rock samples), emplace
ment of the basalt sheets took place in the time
interval 1500-1350 Ma and the intrusion of the
Valaam sill at 1300-1100 Ma (Kairyak & Khazov
1967, Zhdanov 1972, Tikhomirov & Yanovski
1970, Shcheglov 1993, etc.). U-Pb dating of zir
cons separated from gabbro-monzonites gives a
more precise date for the formation of the sill as
1150+30 Ma. Results of the Rb-Sr method (A. V.
Savitskiy and E. S. Sobotovich, unpublished data)
show subcontemporary formation of all magmatic
rocks in the North Ladoga region at 1260-1280
Ma.
The basalt sheets are located between the sandy
and clayey deposits of the Priozersk suite (the
lower sheet) and the Salmi suite (the upper sheet).
The Valaam sill is intruded along the bedding
surface of the dark-colored argillites of the Pasha
suite. Nearly contemporaneous formation of the
basalt sheets and their host sediments is proved by
remnants of disintegrated sandstone found in the
contact zones of the lava flows, as well as by the
limited evidence for intrusion of basaltic melts into
unconsolidated sandstones. Traces of erosion and
resedimentation of volcanic rocks can only be seen
in the immediate vicinity of the lava flows. These
observations show that there were short and local
phases of erosion of the volcanic rocks at the same
time as the dominant process of sedimentation of
terrigenous material.
The volcanic sheets are composed of a series of
lava flows, some brecciated (lava breccias) and
some massive (with brecciated roof). The flows
have been deposited immediately one on top of
another. The thickness of individual flows varies
between 5 m and 15 m. Scarce, thin (not more
than 10 cm) interlayers of terrigenous material that
occur between the flows indicate short interrup
tions in volcanic activity. The high degree of
oxidation (red alteration), great abundance of
amygdales in rocks and the presence of "slag and
foam" structures suggest subaerial solidification of
the lavas.
Composition
The lower part of the Valaam sill is composed
mainly of gabbroic rocks and the upper part of
monzonites to quartz syenites. This stratification is
also seen along the strike of the sill: gabbroic
rocks occur in the east (Lukkulansaari island) and
turn into intermediate rocks to the west (Valaam
and Verkonsaari islands).
The volcanic rocks are aphyric and micropor-
phyritic with a hyaline to holocrystalline (in the
subvolcanic bodies) groundmass texture. The
amygdaloids are filled with chlorite, quartz, car
bonate and in places iron hydroxides. The most
prominent types are olivine-plagioclase-clinopyro-
xene basalts (distinctly dominant) and (rare) pla-
gioclase-clinopyroxene basalt with quartz in the
groundmass.
The diagnostic features of the olivine basalts are
high apatite contents (up to 1 vol. %), Fe-Ti-
oxides (3 to 7 %) such as ilmenite (48-51 %
Ti02) and titanomagnetite (15-17 % T i02), iron
hydroxides (in the roof parts of the flows) and
ferroan olivine (F o^^). Clinopyroxene is repre
sented by a sequence of titanaugite - ferroan titan-
augite (En42_34 Wo41_38Hd19_28) with a titanium con
tent Ti02 = 1-2 %. In the late stages of crystalli
zation, ferroan orthopyroxene (En42Fs58) appears.
The plagioclase is orthoclase.
The plagioclase-clinopyroxene basalts differ
from the olivine basalts by having a low content of
apatite, magnetite (23-24 % TiO^ and ilmenite
(51-53 % Ti02), by absence of the orthoclase
compound in the plagioclases (An^^,) and by the
presence of quartz in the groundmass. Clinopyro-
xenes are represented by a sequence of diopside -
ferroan augite (En54_37Wo31_26Hd 15_37) with a titani
um content ТЮ2 = 0.3-0.6 %. The late phases
are metastable and have disintegrated into ferroan
orthopyroxene (En^FSjg) and titanoaugite (En36.
109
Geological Survey of Finland, Special Paper 21
A. Amantov, I. Laitakari & Ye. Poroshin
Wo31Hd33), which contains up to 1.8 % ТЮ2.
Orthopyroxene lamellae in the clinopyroxene ma
trix make up 1-3 % of the grain area. During the
final stages of crystallization, ilmenite-biotite in
tergrowths have formed.
The holocrystalline rocks of the differentiated
Valaam sill are characterised by high variations in
the mineral content. The rock minerals in the
gabbros and gabbro-monzonites are: clinopyroxene
of the diopside - augite sequence (En41_37Wo39_41-
Hd20_2i) that has partly altered to titanaugite with
up to 1.2 % Ti02; plagioclase (An46_23Ab51_71-
Or2_6), which at the latest crystallization stages-
turns over to a K-Na feldspar (Ab^Or^An^;
ilmenite (ТЮ2 = 49-51 %, MgO = 2.5-1 %,
MnO = 0.4-0.8 %) and titanomagnetite (ТЮ2 =
18-19 %, MgO = 0.6-0 %, MnO = 0-1.5 %).
Apatite is abundant.
In the intermediate rocks (syenites - monzosye-
nites) there are ferroan orthopyroxene (En19Fs81),
clinopyroxene and some biotite. The plagioclase
(A n^gA b^g Or^ undergoes during the crystalli
zation an evolution towards increase of the albite
compound, and eventually changes into K-Na feld
spar (Ab67_46Or22_54An11_0). In the final stages sym-
plectitic decomposition textures (quartz inter
growths in orthoclase matrix) appear in the feld
spars, which indicates metastable conditions dur
ing crystallization.
In the granosyenites the end products of
differentiation there are no Fe-Mg silicates and
plagioclases among the rock-forming minerals.
The crystallization of the melt starts with precipi
tation of ilmenite (Ti02 = 50-53 %) and titano
magnetite (Ti02 = 16 %) with rather high manga
nese contents (0.7-2.5 %, seldom up to 7 %). The
feldspars consist of K-Na feldspar (Ab590 r41) with
high Fe contents (up to 2.2 %), pure albite and
orthoclase. Symplectitic textures are abundant.
For reference, we analyzed the compositions of
some minerals from the diabase in the Satakunta
complex (samples kindly provided by GSF). The
Fe-Mg minerals, such as olivine (Fo52_54) and cli
nopyroxene, of the diopside-augite sequence have
higher Mg concentrations and lower Ti contents
than the olivine basalts in the North Ladoga Re
gion. The plagioclases (An^gAb^goOro^) have a
rather low content of the orthoclase compound; K-
Na feldspar is practically absent. Biotite is always
present.
According to petrochemical characteristics the
Riphean magmatic rocks in the North Ladoga
Region fall into three groups. Two of these repre
sent the volcanic rocks and the third one the rocks
of the Valaam sill and the sortavalite dykes. On a
(K20 + Na20) - S i02 diagram, the main part of the
volcanic rocks is concentrated in the subalkaline
basalt field. The compositions of the basalts of the
two sheets overlap; however, the volcanic rocks of
the Priozersk suite are more differentiated with
respect to Si02 (40 to 54 %) and to the alkalis (3
to 6 %). A few assays of the low-titanium sodium
volcanic rocks are located in the normal basalt
field.
The compositions of the rocks of the Valaam
sill consitute two independent fields, which range
from subalkaline gabbroic rocks through monzo-
nites to granosyenites and from alkaline granites to
alkaline leucogranites. The whole multiplicity of
the rocks of the sill is interpreted via differenti
ation, complicated by their pneumatolytic to hy
drothermal alteration at the late-magmatic stage.
The Jotnian basalts and gabbroic rocks of the
Satakunta complex fall into the subalkaline basalt-
oid field. They differ from those of the Northern
Ladoga region by lower contents of alkalis and
titanium and by higher values of magnesium and
calcium; the alkali ratios are quite similar.
A clearer difference between the rocks investi
gated is seen in the T i02 - K20 diagram. Practical
ly all basic rocks are concentrated in the field of
composition for basalts of intraplatal formations
and island arcs. In respect to potassium content,
the basalts of the North Ladoga region consitute
an uninterrupted rocks series ranging from sub
stantially sodic varieties (K20 < 0.7 %) to potas-
sic ones (K20 = 2.8-5.9 %). An overwhelming
majority of assays of the volcanic rocks plot as
potassic-sodic subalkaline basalts. Due to the
similarity in mineralogical and petrochemical
parameters, all subalkaline basalts in the North
Ladoga region can be regarded as members of a
single petrogenetic series. The origin of sodic
subalkaline basalts is ascribed to processes of
albitization and the origin of the most potassic and
titanium-rich (Ti02 = 3.5-5.5 %) varieties to the
enrichment of the basalts in these elements in
subvolcanic bodies. In respect to titanium content
the basaltic rocks of the upper sheet (Ti02 =
3.8-4.8 %) differ from those of the lower sheet
11 0
Geological Survey of Finland, Special Paper 21
Jotnian and Postjotnian: Sandstones and diabases in the surroundings...
(Ti02 = 2.6-4 %). A similarity in the titanium
and potassium content is seen between the subalka-
line basalts and gabbroic rocks of the Valaam sill
and the sortavalite dykes. The subalkaline basalts
and gabbroic rocks of the Satakunta complex
differ from the basic rocks in North Ladoga re
gion in respect of their lower titanium contents.
The similarity of the petrochemical (K20, Ti02,
high Fe/Mg, uniform values of K20/Na20) and
geochemical (high contents of P2Os, Zr, Nb, Rb)
parameters between the subalkaline basalts and
gabbroic rocks of the Valaam sill and the sorta
valite dykes is the reason for the assumption of a
single mantle source for them. In this respect at
tention should be paid to the Rb-Sr dating results,
which prove a nearly contemporaneous origin of
these rocks. The large dispersion of the K-Ar data
may be connected to the high mobility of potassi
um in the magmatic and postmagmatic processes.
In the contrast to the North Ladoga region, the
origin of the Jotnian basaltic rocks of Satakunta
can be explained by either melting of basalt mag
mas derived from a less deep-seated mantle
source, or by a selective melting of more depleted
magma. [YeP+AA]
Conclusions on the Riphean evolution of Lake Ladoga region
1. In the Middle Riphean, three phases of mag
matic activity are distinguished in the North La
doga region, represented by two lava sheets of
subalkaline K-Na basalts and the differentiated
gabbro-granosyenitic Valaam sill.
2. The emplacement of the basalt sheets was near
ly contemporaneously with the sedimentation of
the Middle Riphean terrigenous deposits, com
plicated by transient breaks representing erosion
and sedimentation of the volcanic rocks.
3. Basaltic rocks in dredge samples from the
bottom of Lake Ladoga are identical with those,
that are widespread on the eastern coast.
4. The high phosphorus contents and the high
Fe/Mg ratio of the femic silicate minerals are
distinctive features of the Riphean magmatic rocks
and make it possible to distinguish them from the
older magmatic formations in Karelia.
[YeP+AA]
REFERENCES
A man to v, A. 1991. Bedrock basin of the Gulf of Finland as a
part of Baltic-White Sea formed at the boundary of Fenno-
scandian shield. - Abstracts of the 2nd Marine Geological
Conference "The Baltic", Rostock-Warnemiinde, 2 p.
[Amantov, A. V.] Амантов, А. В. 1992a. Геологичес
кое строение осадочного чехла бассейнов Севе
ро-Запада России. In: Спиридонов, М. А & Ры
балко, А. Е. (рэд.), Осадочный покров гляци-
ального шельфа северо-западных морей Рос
сии. 25-47. Санкт Петербург.
[A m an tov , A . V.] Амантов, А. В. 1992b. Изучение
структуры и оценка возможной металлогени-
ческой специалиации окраины Балтийского
шита в пределах акваторий. In: Щеглов, А. Д.
(рэд. . Тектонические основы прогнозно-метал-
логенических исследований, 92-102. Санкт Пе
тербург.
[A m anto v, А. V.] Амантов, А. В. 1993. Этапы геоло
гического развития Ладожского озера. Россий
ская Академия Наук, Российская Геологичес
кая Общество, 5-13. Санкт Петербург.
Amantov, A., Soderberg, Р. & Hagenfeldt, S. 1995. The
Meso-Neoproterozoic and Lower Paleozoic sedimentary
bedrock sequence in the northern Baltic Proper, Aland
Sea Basin, Gulf of Finland and Lake Ladoga. Abstracts
of The Third Marine Geological Conference — The
Baltic. Sopot, Poland.
Amantov, A., Spiridonov, М., Rybalko, A. & Davydova,
N. 1989. New data on geology of the Lake Ladoga in con
nection with the problem of study of Littoral Zones. Issue
of International Symposium: Protection and Development of
Shores, 32-33. Tallinn.
[Amantov, A. V. & Spiridonov, М. А.] Амантов, A . B.
& Спиридонов, M. A . 1989. Геология Ладожско
го озера. Советская геология, Н4, 83-89.
Аго, К. 1987. Vaasan saariston ja Petolahden diabaasit. Ab
stract: Diabases of the Vaasa archipelago and Petolahti. In:
111
Geological Survey of Finland, Special Paper 21
A. Amantov, I. Laitakari & Ye. Poroshin
Aro, K. & Laitakari, I. (eds.), Suomen diabaasit ja muut
mafiset juonikivilajit. Abstract: Diabases and other mafic
dyke rocks in Finland. Geological Survey of Finland, Re
port of Investigation 76, 179-184.
Aro, K. & Laitakari, I. (Eds.) 1987. Suomen diabaasit ja
muut mafiset juonikivilajit. Abstract: Diabases and other
mafic dyke rocks in Finland. Geological Survey of Finland,
Report of Investigation 76, 254 p.
Axberg, S. 1980. Seismic stratigraphy and bedrock geology of
the Bothnian Sea, Northern Baltic. Stockholm Contributions
in Geology, XXXVI, 3, 153-213.
Backlund, H. G. 1937. Die Umgrenzung der Svekofenniden.
Bulletin of the Geological Institution of the University of
Uppsala 27, 219-269.
Berghell, H. 1909. Berggrundsbeskrifning till kartbladet Ny-
slott. Manuscript in Geological Survey of Finland.
Bylund, G. 1994. Magnetismen som ett geologiskt verktyg.
Geologiskt forum 2, 3-7.
Eklund, O. 1990. Postjotniska olivindiabaser i pyterlit, Eck-
ero, Aland. Summary: Postjotnian olivine diabases in pyter-
litic rapakivi granite Eckero, Aland. Geologi 42, 124-125
EIo, S. 1976. An interpretation of a recently measured gravity
profile across the Jotnian Sandstone Formation in south
western Finland. Unpublished report Q20/21/1976/1, Geo
logical Survey of Finland, 11 p.
Elo, S ., Mattson, A. & Kurimo, M. 1993. Kauttua — Virt-
taankangas tunnelilinjauksen geofysikaaliset jatkotutkimukset
v. 1992. Unpublished report, Geological Survey of Finland,
16 p.
Eskola, P. 1907. Satakunnan hiekkakiven geologiasta. Sata
kunta, Kotiseutututkimuksia I, 39-45.
Eskola, P. 1925. Ala-Satakunnan kallioperusta. Satakunta,
Kotiseutututkimuksia V, 297-334.
[Golubev, A. I. & Svetov, A. P.] Голубев, А. И . & Све-
тов, А. П. 1983. Геохимия базальтов платфор
менного вулканизма Карелии. "Карелия", Пет
розаводск. 193 с.
Gorbatschev, R ., Lindh, A., Solyom, Z., Laitakari, I.,
Aro, K ., Lobach-Zuchenko, S. B., Markov, M. S., Iv-
liev, A. I. & Bryhni, I. 1987. Mafic dyke swarms of the
Baltic Shield. Geological Association of Canada, Special
Paper 34, 361-372.
Gylling, Hj. 1887. Zur Geologie der cambrischen Arkosen-
Ablagerung des westlichen Finnland. Zeistchrift der deut-
schen geologischen Gesellschaft 39, 1, 770-792.
Hackman. V. 1931. Beskrivning till bergartskartan, Sektionen
D 2, Nyslott, Resume en Frangais. Geologisk oversiktskarta
over Finland, 187 p.
Hackman, V. 1933. Kivilajikartan selitys, Lehti D 2, Savon-
linna. Suomen geologinen yleiskartta, 175 p.
Hagenfeldt, S. E. & Soderberg, P. 1985. Excursionsguide till
de sedimentara bergartema i Uppland. Geologklubben vid
Stockholms Universitet, 34 p.
Hamalainen, A . 1985. Satakunnan jotunialueen geologisen
karttakuvan historiallinen kehitys seka uuteen tutkimusai-
neistoon perustuva kallioperakarttaluonnos. Unpublished
M.Sc. thesis, University of Helsinki, Department of Geolo
gy, 104 p.
Hamalainen, A. 1987. Satakunnan postjotuniset diabaasit.
Abstract: The Postjotnian diabases of Satakunta. In: Aro, K.
& Laitakari, I. (Eds.), Suomen diabaasit ja muut mafiset
juonikivilajit. Abstract: Diabases and other mafic dyke
rocks in Finland. Geological Survey of Finland, Report of
Investigation 76, 173-178.
Hamalainen, A. 1994. Pre-Quaternary rocks, Sheet 1134
Kokemaki. Geological map of Finland 1 : 100 000.
Harme, M. 1958. General geological map of Finland, Pre-
Quaternary rocks, Sheet В 1 Turku.
Harme, M. 1960. Kivilajikartan selitys. Summary: [Explana
tion to the map of Pre-Quaternary rocks]. The general geo
logical map of Finland, В 1 Turku, 78 p.
Hausen, H. 1911. Stenrakningar pa A land. Geologiska Foren-
ingens i Stockholm Forhandlingar 33, 495-502.
Hausen, H. 1964. Geologisk beskrivning over landskapet
Aland. Skrifter utgivna av Alands Kulturstiftelse IV, 196 p.
Hjelmqvist, S. 1966. Beskrivning till berggrundskarta over
Kopparbergs lan. Summary: Description to map of the Pre-
Quaternary rocks of the Kopparberg County, Central Swe
den. Sveriges Geologiska Undersokning, Ser. Ca. 40, 217
P-
Inha, I. K. 1896. Finland i bilder — Suomi kuvissa — La Fin-
lande pittoresque Живописная Финляндия
Finnland in Bildern Pictorial Finland. Wenzel Hagestam,
Uno Wasastjema, Helsingfors [363] p.
Kahma, A. 1951. On the contact phenomena of the Satakunta
diabase. Bulletin de la Commission geologique de Finlande
152, 84 p.
[Kairyak, A. N. & Khazov, R. А.] КаЙрЯК, A. H. и
Хазов, P. A. 1967. Йотнийские образования
северно-восточного Приладожья. Вестн, Ленин
градский Государственный Университет, No 12,
стр. 62-72.
[Khazov, R. А. & Popov, М. G.] Хазов, Р. А. & Попов,
М. Г. 1984. Рифейские вулкано-плутонические
формации Приладожья. In: Интрузивные
базкты и гипербазиты Карелии. Петрозаводск.
20-30.
Kohonen, J., Pihlaja, P., Kujala, H. & Marmo, J. 1993.
Sedimentation of the Jotnian Satakunta sandstone, western
Finland. Geological Survey of Finland Bulletin 369, 35 p.
Korja, A. Korja, Т ., Luosto, U. & Heikkinen P. 1993.
Seismic and geoelectric evidence for collisional and exten-
sional events in the Fennoscandian Shield — implications of
Precambrian crustal evolution. Precambrian Research 219,
129-152.
Kukkonen, E. & Tynni, R. 1968. Biogeenisia rakenteita
Satakunnan hiekkakivessa? Geologi 20, 12-14.
Laitakari, A. 1925. Uber das Jotnische Gebiet von Satakunta.
Bulletin de la Commission geologique de Finlande 73, 43 p.
Laitakari, A. 1928. Palingenese am Kontakt des postjotnischen
Olivindiabases. Fennia 50, 35, 25 p.
Laitakari, I. 1983. The Jotnian (Upper Proterozoic) sandstone
of Satakunta. Geological Survey of Finland, Guide 12, 135-
138.
Laitakari, I. & Aro, K. 1990. Mafic dykes. Atlas of Finland
123-126, Geology (Appendix), 123/3-123/4.
Lauren, L. 1970. An interpretation of the negative gravity
anomalies associated with the rapakivi granites and the Jot
nian sandstone in southern Finland. Geologiska Foreningens
11 2 7
Geological Survey of Finland, Special Paper 21
Jotnian and Postjotnian: Sandstones and diabases in the surroundings...
i Stockholm Forhandlingar 92, 21-34.
Marttila, E. 1969. Satakunnan hiekkakiven sedimentaatio-olo-
suhteista. Unpublished Ph.Lie. thesis, University of Turku,
Department of geology, 157 p.
Moberg, K. A. 1890. Geologillinen yleiskartta Suomenmaasta.
Neuvonen, K. J. 1965. Paleomagnetism of the dike systems in
Finland, 1. Remanent magnetization of the Jotnian olivine
dolerites in southwestern Finland. Bulletin de la Commis
sion geologique de Finlande 218, 153-168.
Neuvonen, K. J. 1973. Remanent magnetization of the Jotnian
sandstone in Satakunta, SW-Finland. Bulletin of the Geolog
ical Society of Finland 45, 23-27.
Pihlaja, P. 1994. Pre-Quaternary rocks, Sheet 1143 Pori.
Geological map of Finland 1 : 100 000.
Pihlaja, P. & Kujala, H. 1994. Pre-Quaternary rocks, Sheet
1141 Luvia. Geological map of Finland 1 : 100 000.
Pihlaja, P. in prep. Pre-Quaternary rocks, Sheet 1142 Manty-
luoto. Geological map of Finland 1 : 100 000.
Ramo, О. T. 1990. Diabase dyke swarms and silicic mag-
matism — Evidence from the Proterozoic of Finland. In: A.
J. Parker, P. C. Rickwood & D. H. Tucker (Eds.), Mafic
Dykes and Emplacement Mechanism. Publication Number
23, International Geological Correlation Program, Project
257, A. A. Balkema, Rotterdam, Brookfield. 185-199.
Ramsay, W. 1909. Geologins grunder. G. W. Edlunds For-
lagsaktiebolag, Helsingfors, 486 p.
Sauramo, M. 1916a. Jotunisen ajan Satakunta. Satakunta,
Kotiseutututkimuksia IV, 192-199.
Sauramo, M. 1916b. Uber das Vorkommen von Sandstein in
Karstula in Finland. Fennia 39, 7, 13 p.
Sauramo, M. 1924. Maalajikartan selitys В 2 Tampere. Gen
eral geological map of Finland, 76 p.
Sederholm, J. J. 1893. Om berggrunden i sodra Finland.
Referat: Uber den Berggrund des sudlichen Finnlands.
Fennia 8, 3, 166 p.
Sederholm, J. J. 1897. Om inledningen af prekambriska
formationerna i Sverige och Finland och om nomenklaturen
for dessa aldsta bildningar. Geologiska Foreningens i Stock
holm Forhandlingar 19, 20-53.
Sederholm, J. J. 1903. Suomen geologinen yleiskartta (Vuori-
lajikartta) Geologisk ofersiktskarta ofver Finland (Berg-
artskarta) — [The general geological map of Finland (Pre-
Quaternary rocks)] В 2, Tampere — Tammerfors.
Sederholm, J. J. 1911. Beskrifning till bergartskartan В 2,
Tammerfors. Resume [en franyais]. Geologisk ofversikts-
karta ofver Finland, 120 p.
Sederholm, J. J. 1913. Vuorilajikartan selitys В 2, Tampere.
Suomen geologinen yleiskartta, 122 p.
Sederholm, J. J. 1927. Om de jotniska och sk. subjotniska
bergartema. Geologiska Foreningens i Stockholm Forhand
lingar 49, 397-426.
[Shcheglov, A. D. (Ed.)] Щеглов, А . Д. (ред.) 1993.
Магматизм и металлогения Балтийского щита.
"Недра", С-Петербург. 244 с.
Simonen, А. & Kouvo, О. 1955. Sandstones in Finland.
Bulletin de la Commission geologique de Finlande 168, 57-
87.
Simonen, A. 1980. The Precambrian of Finland. Geological
Survey of Finland Bulletin 304, 58 p.
Soderberg, P. 1993. Seismic stratigraphy, tectonics and gas
migration in the Aland Sea, northern Baltic Proper. Stock
holm Contributions in Geology 43, 1, 67 p.
Suominen, V. 1991. The chronostratigraphy of Southwestern
Finland, with special reference to Postjotnian and Subjot-
nian diabases. Geological Survey of Finland Bulletin 356,
100 p.
[Tikhomirov, S. N. & Yanovskiy, A. S.] Тихомиров, С.
H. & Яновский, А. С. 1970. Новые данные о до
кембрии юго-восточного Приладожья. Докла
ды Академии Наук СССР XXX, No 3, 660-663.
Tynni, R. & Uutela, A. 1984. Microfossils from the Pre
cambrian Muhos formation in Western Finland. Geological
Survey of Finland Bulletin 330, 38 p.
Vaasjoki, M. & Sakko, M. 1987. Zirkoni-indikaatio Sata
kunnan hiekkakiven alkuperasta. Summary: A zircon indica
tion on the provenance of the middle Proterozoic Satakunta
sandstone, Finland. Geologi 39, 184-187.
Vorma, A. & Niemela, R. 1994. Pre-Quaternary rocks, Sheet
1133 Ylane. Geological map of Finland 1 : 100 000.
Veltheim, V. 1962. On the Pre-Quaternary geology o f the
bottom of the Bothnian Sea. Bulletin de la Commission
geologique de Finlande 200, 166 p.
Wahl, W. 1908. Beitrage zur Geologie der prakambrischen
Bildungen im Gouvernement Olonez, II, 3. Die Gesteine
der Westkiiste des One'ga-Sees. Fennia 24, 3, 94 p.
Wahl, W. [1904?] Bergartema pa holmarna i norra delen av
Ladoga. Manuscript, Geological Survey of Finland, Espoo,
15 p.
Wannas, K. O. 1989. Seismic stratigraphy and tectonic devel
opment of the Upper Proterozoic of the Bothnian Bay,
Baltic Sea. Stockholm Contributions in Geology 40, 3, 83-
168.
Wiik, F. J. 1877. Ofversigt af Finlands geognostiska forhal-
landen II. Orografi och geogeni. Bidrag till kannedom af
Finlands natur och folk 26, 89 p.
Winterhalter, B. 1972. On the geology of the Bothnian Sea,
an epeirogenic sea that has undergone Pleistocene gla
ciation. Geological Survey of Finland Bulletin 258, 66 p.
Winterhalter, B., Floden, Т., Ignatius, H ., Axberg, S. &
Niemisto, L. 1981. Geology of the Baltic Sea. In: Voipio,
A. (ed.), The Baltic Sea. Elsevier Oceanographic Serie 30,
1-121.
[Zhdanov, V. V.] Жданов, В. В. 1972. О СВЯЗИ ОСНОВ
НОГО и кислого магматизма Ладожского проги
ба. Бюллетин МОИП, Отделение геологии
47(4), 48-24.
113
A. Amantov, I. Laitakari &Ye. Poroshin
Jotnian and postjotnian: Sandstones and Diabases in the surroundings of Gulf of Finland
(Remarks AA: Early Riphean is correct to use instead of Middle Riphean now due to redatings
of the Valaam sill and volcanic rocks.)
... The Mesoproterozoic Pasha-Ladoga Basin is located at the margin of the Archean Karelian Craton and Paleoproterozoic Svekofennian Belt in northwest Russia (Fig. 1). The basin is poorly exposed, and available information on the basin stratigraphic framework and structure is largely derived from seismic profiling records and drilled boreholes (Amantov et al. 1996). The Pasha-Ladoga Basin occupies a northwest-elongated graben, covering approximately 70,000km 2 , that formed during the Early Riphean (Russian/chronostratigraphic scale) which equates to Early Mesoproterozoic (International Chronostratigraphic scale). ...
... The Pasha-Ladoga Basin is bounded by a complex system of northwest-striking faults that form a series of elongated horst and graben blocks. Seismic studies recognized a deep graben structure in the southeast part of the basin, referred to as the Pasha Graben (column 3, Fig. 2) and two smaller grabens in the western part of the basin (Amantov et al. 1996). ...
... Based on seismic reflection data (Amantov et al. 1996), the Pasha-Ladoga Basin can be divided into five stratigraphic units, comprising flat-lying unmetamorphosed sedimentary sequences which locally host minor volcanic rocks and intrusive mafic sills (Fig. 2). A major sill-like mafic intrusion referred to as the Valaam Sill is emplaced in the upper part of the basin stratigraphy. ...
Article
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The Mesoproterozoic Pasha-Ladoga Basin is located at the margin of the Karelian Craton and Svecofennian Belt in northwest Russia. It is the only basin in Russia that is currently recognized to host unconformity-type uranium mineralization (e.g., Karku deposit). Mineralization is associated with the Priozersk Formation which comprises a basal sequence of immature arkosic sandstones and conglomerates interpreted as high-energy braided stream channel and channel bar facies within an alluvial fan depositional environment. Diagenetic and hydrothermal alteration of the Priozersk sandstones is similar to that observed in unconformity-related uranium deposits of the Athabasca Basin (Canada) and includes three main stages: (1) an early diagenetic assemblage comprising illite-smectite (K-rectorite), calcite, minor chlorite, and kaolinite precipitated at 100–150 °C; (2) a peak diagenetic-hydrothermal assemblage composed of kaolinite-dickite, Fe- and Fe-Mg chlorite, calcite, and sulfides formed at 150–250 °C; (3) late diagenetic-hydrothermal event involving fracture-controlled kaolinite and late hematite. Similar to the Athabasca Basin type uranium mineralization, the Karku deposit exhibits anomalous concentrations of LREE, Nb, Pb, and positive correlations between U and Cu, Zn, Ag, and Pb that is a geochemical signature of unconformity-type uranium mineralization. Based on oxygen and hydrogen stable isotope study, it was found that fluids in equilibrium with early and peak diagenetic clays were consistent with oxidized basinal brines and reduced basement fluids. In contrast to the Athabasca Basin, mineralizing fluids at the Karku area were more reduced and potassic. A new geological model for the Karku deposit is proposed based on petrographic observations and sandstones geochemistry. The proposed model envisages the permeable rocks of paleoregolith and the coarse-grained basal part of the Priozersk Formation as the main pathway for migration of uraniferous fluids responsible for the formation of Karku uranium deposit. From the perspective of the geological setting, the Karku deposit differs from deposits of the Athabasca Basin in that it occurs in a rapidly deposited rift-related basin with associated mafic magmatism, the host sandstone sequence is relatively thin (e.g., Priozersk Formation) and exhibits abrupt lateral facies variations, and the widespread presence of early diagenetic interstitial swelling clays. Based on these sedimentological characteristics, it is considered that the Karku deposit setting precludes optimum conditions to create high tonnage high-grade unconformity-type U deposits as found in the Athabasca basin.
... Coarse-grained inequigranular sandstone of the Pasha suite (sample DDH- 11-237 m, Pasha area), parallel nicols, photomicrograph scale 0.5 mm.................. 177 Fig. 3.12. Cross section of the Lake Ladoga basin based on seismic reflection studies as reported by Amantov et al (1996)........................................................... 179 Fig. 3.13. Process of the partial dissolution of K feldspar in the Priozersk sandstones. ...
... Lithology and stratigraphy of the Mesoproterozoic (Riphean) Formations below the Ladoga Lake has been described in Amantov et al, (1989Amantov et al, ( , 1990Amantov et al, ( , 1991Amantov et al, ( , 1992Amantov et al, ( , 1993Amantov et al, ( , 1996. The rock units have been defined from their seismic properties and correlated with the geology of the adjacent shore areas and outcrops from the bottom of the lake. ...
... Chapter IV Mesoproterozoic basaltic magmatism of the Pasha -Ladoga basin and siltstones successions within rift complex zones and faulted-bounded basins (Kohonen & Ramo, 2004). lt corresponds to crosscutting (occasionally also concordant) tholeitic dikes in southwestern Finland and adjacent Sweden (Patchett et al, 1994;Amantov et al, 1996), and as extensive alkali basaltic sills in Russian Karelia -Ladoga Lake region ( Amantov et al, 1996;Golubev & Svetov, 1983;Kayryak & Khazov, 1967;Khazov & Popov, 1984;Ramo et al., 2004;Tikhomirov & Yanovsky, 1970;Upton et al, 1998). ...
Thesis
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Une étude minéralogique et géochimique du bassin volcano-sédimentaire clastique intracontinental mésoprotérozoique (Riphéen) de Pasha Ladoga (Carélie, Russie) ainsi que des minéralisations uranifères associées et des lithologies du socle sous-jacent a été réalisée. Une comparaison avec d'autres districts fortement minéralisés d'âge et de lithologie comparables indique qui les sédiments clastiques du bassin de Pasha Ladoga sont nettement moins matures que ceux des bassins fortement minéralisés de l'Athabasca (Canada) et de Kombolgie (Australie). Toutefois, des circulations importantes de fluides ont été mises en evidence dans les roches métamorphiques de l'Archéen et du Paléoprotérozoique et les granites rapakivi du socle, ainsi que dans les sediments clastiques sus-jacent dans la région de Pasha Ladoga, où les gisements d'uranium de type discordance de la zone de Karkou ont été découverts. Ces circulations de fluides ont conduit à une altération a l'échelle régionale du zircon et, dans une moindre de mesure, de la monazite, ainsi qu'à la formation de chlorites ferrifères et de carbonates dans les zones minéralisées.
... Ahl et al. 1997), graben formation and deposition of clastic sediments such as the so-called Jotnian sedimentary rocks in these grabens (e.g. Sederholm 1897, Gorbatschev 1967, Amantov et al. 1996, Lidmar-Bergström 1996, Stephens et al. 2015 and references therein). The Jotnian sedimentary rocks are dominantly fluvial and subaerial deposits and are estimated to have been deposited between 1.6 and 1.26 Ga onto a sub-Jotnian denudation surface (Amantov et al. 1996, Lidmar-Bergström 1996. ...
... Sederholm 1897, Gorbatschev 1967, Amantov et al. 1996, Lidmar-Bergström 1996, Stephens et al. 2015 and references therein). The Jotnian sedimentary rocks are dominantly fluvial and subaerial deposits and are estimated to have been deposited between 1.6 and 1.26 Ga onto a sub-Jotnian denudation surface (Amantov et al. 1996, Lidmar-Bergström 1996. In the study area, the Jotnian sedimentary units are partially bound by faults forming the Gävle graben ( Figure 2-3), which strike WSW-ENE under the Bothnian Sea ( Figure 2-3, see also Ahlberg 1986, Lidmar-Bergström 1996. ...
Technical Report
The aim of this study is to detect and characterise Phanerozoic faulting of the Precambrian basement for a 112×112 km large study area in parts of Uppland and Gästrikland. Bedrock block models are presented based on an updated digital elevation model and an updated model for the depth to bedrock. The area covers both on-shore and off-shore parts. Maximum values for rock block elevation are calculated for each model and relative movement across rock block boundaries, i.e. faults, is detected and characterised. Even though determining the relative timing of fault movement is not possible using the rock block models alone, vertical block displacement is detected mainly across three fault orientations: WNW-ESE and NNE-SSW striking faults with dip slip on the order of tens of meters, and along ENE-WSW striking graben faults around Gävle with a minimum of circa 80 m cumulative slip.
... Ga (Fig. 2). Most of the regional studies in central Fennoscandia show, that distribution of Jotnian sediments (Fig. 1) has to be spatially associated with the occurrence of Mesoproterozoic rapakivi granite and their deposition has been continued (Amantov et al., 1996;Pokki et al., 2013;Lundmark, Lamminen, 2016). The K-Ar datings of the Jotnian sandstone in Finland documented a diagenesis time at approximately 1300 Ma (Kohonen et al., 1993). ...
... The terms "Jotnian" (Finland, Sweden) or "Riphean" (Russia) are used for Mesoproterozoic low-grade metasedimentary rocks spatially associated with large rapakivi intrusions and/or AMCG suites. Extensive rapakivi plutonism with gravitational rise and heating effects was a major tectonic factor that marked the start of grabens development, which were then filled with terrigenous Jotnian sandstones (Amantov et al., 1996;Pokki et al., 2013;Lundmark, Lamminen, 2016). The principal localities of Jotnian sediments are the Satakunta in southwest Finland, Gulf of Bothnia, the Åland Sea, the Lake Ladoga, and also Dala basin in central Sweden. ...
Article
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Drilling at Mońki IG-2 and Zabiele IG-1 in the Mazowsze domain has intersected mature quartz-rich metasedimentary rocks belonging to the basement of NE Poland, described so far as a Biebrza complex. The geochemical composition of these rocks is characteristic of a passive margin. The subarkose–quartz arenite underwent low-T metamorphism, but preserved textures typical for the fluvial sediments. The detrital material in range 1.68–2.11 Ga was provided from surrounding late Paleoproterozoic margins of the Fennoscandia and Sarmatia. The maximum depositional age probably did not exceed 1.6 Ga. A previously suggested correlation with Mesoproterozoic molasse-type deposits of the Jotnian formation has not been confirmed. It seems more likely that the sediments formed after Fennoscandia-Sarmatia collision (i.e. termination of Svecofennian orogeny) but before denudation of the Mesoproterozoic Mazury AMCG intrusions.
... The wellknown post-rapakivi faulting event created a number of Mesoproterozoic graben-like structures, filled with 1.4-1.3 Ga Jotnian sandstones, around the present Baltic Shield-EEP contact and along the Gulf of Bothnia (Flodén 1980;Winterhalter et al. 1981;Wannäs 1989;Söderberg 1993;Amantov et al. 1995Amantov et al. , 1996. Many of these structures reveal signs of the 1.27-1.25-Ga-post-Jotnian ...
Article
Full-text available
Analysis of data published on basement faulting in the Baltic region makes it possible to distinguish the >700 km long East European Craton (EEC) interior fault zone extending from the Leba Ridge in the southern Baltic Sea across the Latvian cities of Liepaja and Riga to Pskov in Russia (LeRPFZ). The complex geometry and pattern of its faults, with different styles and flower structures, suggests that the LeRPFZ includes a significant horizontal component. Exceptionally high fault amplitudes with signs of pulsative activities reveal that the LeRPFZ has been acting as an early Palaeozoic tectonic hinge-line, accommodating bulk of the far-field stresses and dividing thus the NW EEC interior into NW and SW halves. The LeRPFZ has been playing a vital role in the evolution of the Baltic Ordovician-Silurian Basin, as a deep-facies protrusion of this basin (Livonian Tongue) extending into the remote NW EEC interior adheres to this fault zone. The Avalonia-Baltica collision record suggests that transpression with high shear stress, forcing the SE blocks in the LeRPFZ to move obliquely to the NE, reigned in the Ordovician. In the Silurian, the LeRPFZ with surrounding areas became increasingly affected by Laurentia-Baltica interaction and compression from the NW, while the orogenic load by Avalonia-Baltica collision flexed the foreland basin along the NW margin of the EEC. As a highly mobile basement flaw liable to differentiated tectonic movements, the LeRPFZ has experienced tectonic inversion in accordance with the stress-field changes induced by Avalonia-Baltica-Laurentia interaction. Being an axial area of the Livonian Tongue in Ordovician-early Silurian time, by the Devonian, due to the progressing Caledonian Orogeny and growing compression from the NW, the LeRPFZ became the most uplifted and intensively eroded zone in the NW EEC interior.
... In places, these units are overlain by Neoproterozoic, possibly Ediacaran, to Lower Palaeozoic sedimentary rocks (Fig. 1b). These platformal sedimentary rocks exceeds 1000 m in thicknesses while their development is attributed to a combination of syn-depositional subsidence and faulting 16,17 ; the present-day distribution is related to post-depositional tectonic events. In addition to the Bothnian Sea, the Mesoproterozoic sedimentary rocks are preserved in fault-controlled basins in the Åland Sea, in the Landsort trench in the Baltic Sea and in down-faulted blocks or half-grabens on land in Sweden, Finland and western Russia, like Lake Ladoga 18 . ...
Article
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Saucer-shaped intrusions of tens of meters to tens of kilometres across have been observed both from surface geological mapping and geophysical observations. However, there is only one location where they have been reported to extend c. 100 km laterally, and emplaced both in a sedimentary basin and the crystalline basement down to 12 km depth. The legacy BABEL offshore seismic data, acquired over the central Fennoscandian Shield in 1989, have been recovered and reprocessed with the main goal of focusing on this series of globally unique crustal-scale saucer-shaped intrusions present onshore and offshore below the Bothnian Sea. The intrusions (c. 1.25 Ga), emplaced in an extensional setting, are observed within both sedimentary rocks (<1.5 Ga) and in the crystalline basement (>1.5 Ga). They have oval shapes with diameters ranging 30–100 km. The reprocessed seismic data provide evidence of up-doming of the lower crust (representing the melt reservoir) below the intrusions that, in turn, are observed at different depths in addition to a steep seismically transparent zone interpreted to be a discordant feeder dyke system. Relative age constraints and correlation with onshore saucer-shaped intrusions of different size suggest that they are internally connected and fed by each other from deeper to shallower levels. We argue for a nested emplacement mechanism and against a controlling role by the overlying sedimentary basin as the saucer-shaped intrusions are emplaced in both the sedimentary rocks as well as in the underlying crystalline basement. The interplay between magma pressure and overburden pressure, as well as the, at the time, ambient stress regime, are responsible for their extensive extent and rather constant thicknesses (c. 100–300 m). Saucer-shaped intrusions may therefore be present elsewhere in the crystalline basement to the same extent as observed in this study some of which are a significant source of raw materials.
... Раннерифейские осадочные и по крайней мере двухфазные магматические образования [1,2,6,11,12,13,14,15] ЛПГ доминируют на дочетвертичном срезе в северной части Ладожского озера [1,2,4], где более молодые несогласно залегающие позднерифейско-ранневендские комплексы сохранились фрагментарно в осевых частях отрицательных структур. Последние распространены южнее Коневецкого порога, например, в пределах Вуоксинской рубцовой синклинали простирания 100-110º, смыкающейся с северо-западным Пашским грабеном [1,2]. ...
Conference Paper
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Lake Ladoga’s basin was formed within the fragment of the slope of the Baltic Shield, complicated by the Riphean (Jotnian) Ladoga-Pasha graben-syncline. It belongs to the family of Jotnian structures spatially located around large Gothian intrusive bodies in contrast with linear extended aulacogens. Platform strata thin out with erosional truncation. They dip southeast, defining the monocline that reflects the subsiding of the epi-Late Vendian peneplain. Low-amplitude tectonic dislocations of the cover usually inherit the most pronounced Jotnian structural elements. Clinoforms are common in lower Kotlin Ediacaran unit. Disturbance of subjacent strata by glacial action is common. Glacial and fluvio glacial erosion was a dominate factor in the Pleistocene shaping of structural-denudational geomorphological elements of different order. Keywords: Riphean, Ediacaran, Lake Ladoga, geology, geomorphology, tectonics, neotectonics.
... Dolerites and basaltic intercalations that belong to Jotnian formations are scattered over large areas in the Fennoscandian Shield (Nystro¨m 2004;Ra¨mo¨et al. 2004). In the Nordingra˚and Satakunta areas Jotnian sediments rest partly on c. 1.58 Ga rapakivi intrusions, in the Lake Ladoga area on 1.53 Ga rapakivi granite and in the Ga¨vle area on 1.50 Ga rapakivi intrusions (Amantov et al. 1996;Andersson 1997a). In the Dala area of south central Sweden, in addition to the Bunkris dike, the NE-trending swarm of Tuna dolerites are associated and partly mingled with c. 1.47 Ga quartz-feldspar porphyries and the small alkaline Noran intrusion (Claesson and Kresten 1997). ...
... Dolerites and basaltic intercalations that belong to Jotnian formations are scattered over large areas in the Fennoscandian Shield (Nystro¨m 2004;Ra¨mo¨et al. 2004). In the Nordingra˚and Satakunta areas Jotnian sediments rest partly on c. 1.58 Ga rapakivi intrusions, in the Lake Ladoga area on 1.53 Ga rapakivi granite and in the Ga¨vle area on 1.50 Ga rapakivi intrusions (Amantov et al. 1996;Andersson 1997a). In the Dala area of south central Sweden, in addition to the Bunkris dike, the NE-trending swarm of Tuna dolerites are associated and partly mingled with c. 1.47 Ga quartz-feldspar porphyries and the small alkaline Noran intrusion (Claesson and Kresten 1997). ...
Article
The Mesoproterozoic (Jotnian) Dala Sandstone, western Sweden, is investigated using zircon U-Pb SIMS. The Dala Sandstone was deposited in a gentle sag basin and underwent post-depositional downfaulting and local deformation along the Sveconorwegian Frontal Deformation Zone. The maximum depositional age is lowered to 1.58 Ga, lending support to a suggested 1.5 Ga maximum age from regional basement age considerations. Associated 1.46 Ga volcanism (Öje basalt) indicates that the 1.5-1.4 Ga Hallandian-Danopolonian event triggered basin formation; in addition, repeated local magmatism and deformation over several 100 m.y. hint at the presence of a crustal weak zone. Provenance data indicate sediment sources in surrounding Svecofennian, Transscandinavian Igneous Belt and Gothian domains; age peaks coinciding with early Gothian phases suggest that older inboard parts of the orogen shielded the Dala region from the younger outboard parts. Decreasing input from the Gothian orogen after 1.46 Ga suggests changing regional drainage patterns. Archaean/Paleoproterozoic zircon in pre-Sveconorwegian sediments in southern Norway is proposed to reflect sediment routing from the north, or significant sinistral Sveconorwegian displacement of southern Norway along the Fennoscandian margin. The latter would potentially juxtapose the Dala basin and the Rjukan rift in southern Norway, however, these formed two distinct and separate basins.
Article
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Direction and intensity of remanent magnetization were measured on samples from a flat-laying Precambrian sandstone before and after heating at 400°C. The direction revealed and the calculated pole position agree with those observed for dike rocks in SW-Finland. The origin of the magnetization is discussed.
Article
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Investigations by marine seismic and frequency counts of erratic boulders in and around the Aland Sea Basin and the Stockholm Archipelago indicate the presence of a thick sedimentary bedrock sequence in the Aland Sea Basin, с. 1,600 m in thickness. In the archipelago area, parts of this sedimentary bedrock sequence are assumed to be preserved in downfaulted protected positions. A subdivision of the sedimentary bedrock sequence in the Aland Sea Basin is set up into 3 informal units. These are, in ascending order from the base: Unit 1 — Middle Riphean (“Jotnian”) sandstones, up to 1,200 m in thickness; Unit 2 — Upper Riphean to Vendian sandstones and shales, up to 400 m in thickness; Unit 3 — Lower Cambrian sandstones, possibly Middle Cambrian shales, and Lower to Upper Ordovician limestones, up to 360 m in thickness. Units 1 and 2 are referred to the informal Soderarm formation. The sedimentary bedrock sequence is disturbed by two phases of dolerite intrusions, i.e. Middle Riphean and post Upper Riphean to Vendian. The latter phase might be of considerably younger age, however, possibly Early Palaeozoic. The development of the Aland Sea sedimentary bedrock sequence reflects influence from several orogenic events, viz., the Gothian, the Sveconorwegian, and the Caledonian. The occurrences of the sedimentary bedrock sequences in the northern Baltic Proper, Aland Sea Basin, Gulf of Finland, and Lake Ladoga show development under similar conditions.