Jotnian
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In north European
geology Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ear ...
, Jotnian
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...
s are a group of
Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...
rocks more specifically assigned to the Mesoproterozoic Era ( Riphean), albeit some might be younger. Jotnian sediments include the oldest known sediments in the Baltic area that have not been subject to
metamorphism Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of chem ...
. Stratigraphically, Jotnian sediments overlie the
rapakivi granite Rapakivi granite is a hornblende-biotite granite containing large round crystals of orthoclase each with a rim of oligoclase (a variety of plagioclase). The name has come to be used most frequently as a textural term where it implies plagioclase r ...
s and other
igneous Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...
and
metamorphic rock Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causin ...
s and are often
intruded Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form '' intrusions'', such as batholiths, dikes, sills, laccoliths, and volcanic necks.Intrusive RocksIntrusive rocks accessdate: March ...
by younger
diabase Diabase (), also called dolerite () or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-graine ...
s.


Overview

Jotnian sediments include
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...
-rich
sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...
s,
siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...
s, arkose,
shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...
and conglomerates. The characteristic red colour of Jotnian sediments is due to their deposition in subaerial (e.g. non-marine) conditions. Jotnian sediments are the oldest known sediments in the Baltic area that have not been subject to
metamorphism Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of chem ...
. Their age is poorly constrained, but generally they are younger than the rapakivi granites and older than ''Postjotnian''
diabase Diabase (), also called dolerite () or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-graine ...
s that intrude the sediments. This means that Jotnian sediments were deposited approximately 1600–1260 million years ago. Some Jotnian sediments are, however, younger than the diabases, meaning they can be younger than 1260 million years. Jotnian sediments are usually assigned to the
Riphean Stage The Riphean is a stage or age of the geologic timescale from . The name Riphean is used in the Proterozoic stratigraphy of Russia and the Fennoscandian Shield in Finland. It was also used in a number of older international geologic timescales ...
of the Mesoproterozoic Era. Jotnian sediments rests on what is known as ''Subjotnian'' rocks which include
weathered ''Weathered'' is the third studio album by American rock band Creed, released on November 20, 2001. It was the last Creed album to be released until '' Full Circle'' came out in October 2009, with Creed disbanding in June 2004. It is the only Cr ...
rapakivi granites and the
Hogland Series The Hogland Series are a series of Subjotnian sedimentary rocks exposed in the island of Gogland ( sv, Hogland), the Sommer Islands and the nearby sea bottom in the Gulf of Finland. The series encompass quartz-rich conglomerates and breccias pl ...
. Amantov and co-workers comments about the terms Jotnian and Postjotnian that: At large scale, Jotnian sediments are classified as being part of a "quasiplatform" group of sediments of the
East European Platform East European Platform or Russian Platform is a large and flat area covered by sediments in Eastern Europe spanning from the Ural Mountains to the Tornquist Zone and from the Caspian Depression, Peri-Caspian Basin to the Barents Sea. Over geologic ...
not being metamorphosed enough to be part of the "protoplatform" and not being undeformed enough to be part of the "cataplatform" category. By analogy to the established Sub-Cambrian peneplain that extends across much of
Fennoscandia __NOTOC__ Fennoscandia (Finnish language, Finnish, Swedish language, Swedish and no, Fennoskandia, nocat=1; russian: Фенноскандия, Fennoskandiya) or the Fennoscandian Peninsula is the geographical peninsula in Europe, which includes ...
there have been suggestions of the existence of an exhumed Subjotnian
peneplain 390px, Sketch of a hypothetical peneplain formation after an orogeny. In geomorphology and geology, a peneplain is a low-relief plain formed by protracted erosion. This is the definition in the broadest of terms, albeit with frequency the usage ...
. This surface actually exists but its extent is very limited, represented as small valley plains at Sveg and along the Västerdalälven-
Dalälven The Dal River ( sv, Dalälven, Elfdalian: ''Dalövę'') is a river in central Sweden that flows from the north of Dalarna and runs into the sea in northern Uppland; it is commonly considered to be the southern border of Norrland, however only th ...
system.


Distribution

There is evidence suggesting that Jotnian cover rocks or a Jotnian
platform Platform may refer to: Technology * Computing platform, a framework on which applications may be run * Platform game, a genre of video games * Car platform, a set of components shared by several vehicle models * Weapons platform, a system or ...
once covered much of
Fennoscandia __NOTOC__ Fennoscandia (Finnish language, Finnish, Swedish language, Swedish and no, Fennoskandia, nocat=1; russian: Фенноскандия, Fennoskandiya) or the Fennoscandian Peninsula is the geographical peninsula in Europe, which includes ...
and were not restricted to a few localities like today. The limited geographical extent of Jotnian sediments at present is indebted to their
erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...
over
geological time The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochron ...
. Sedimentary rocks as old as the Jotnian sediments age have a low preservation potential. The distribution of some Jotnian sediments is spatially associated with the occurrence of rapakivi granite. Korja and co-workers (1993) claim the Jotnian sediment–rapakivi granite coincidence at the Gulf of Finland and the Gulf of Bothnia is associated with the existence of thin crust at these locations. At present Jotnian sedimentary rocks are commonly found in half-grabens, narrow
graben In geology, a graben () is a depressed block of the crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German, meaning 'ditch' or 'trench'. The word was first used in the geologic contex ...
s, in slightly downfolded (syncline) positions or in mixed graben-synclines. Most of the grabens hosting Jotnian sediments are northwest-southeast oriented. The largest occurrence of Jotnian sediments appear however to occur neither in a rift or a graben and lie in
Dalarna Dalarna () is a '' landskap'' (historical province) in central Sweden. English exonyms for it are Dalecarlia () and the Dales. Dalarna adjoins Härjedalen, Hälsingland, Gästrikland, Västmanland and Värmland Värmland () also known a ...
, Sweden. It has been suggested that the sedimentary basins hosting Jotnian sediments at Dalarna, Gävle, the
Bothnian Sea The Bothnian Sea ( sv, Bottenhavet; fi, Selkämeri) links the Bothnian Bay (also called the Bay of Bothnia) with the Baltic proper. Kvarken is situated between the two. Together, the Bothnian Sea and Bay make up a larger geographical entity, t ...
,
Satakunta Satakunta (in both Finnish and Swedish, ) is a region ( / ) of Finland, part of the former Western Finland Province. It borders the regions of Southwest Finland, Pirkanmaa, South Ostrobothnia and Ostrobothnia. The capital city of the region is ...
and Lake Ladoga form an alignment of
subsidence Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope move ...
parallel to the area of inferred Hallandian-Danopolonian
subduction Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...
, possibly corresponding to an ancient back-arc basin.


Baltic Sea

Between Finland and Sweden Jotnian sediments are common in the
Gulf of Bothnia The Gulf of Bothnia (; fi, Pohjanlahti; sv, Bottniska viken) is divided into the Bothnian Bay and Bothnian Sea, and it is the northernmost arm of the Baltic Sea, between Finland's west coast ( East Bothnia) and the Sweden's east coast (West ...
, the
Bothnian Sea The Bothnian Sea ( sv, Bottenhavet; fi, Selkämeri) links the Bothnian Bay (also called the Bay of Bothnia) with the Baltic proper. Kvarken is situated between the two. Together, the Bothnian Sea and Bay make up a larger geographical entity, t ...
and the
Åland Sea Åland ( fi, Ahvenanmaa: ; ; ) is an autonomous and demilitarised region of Finland since 1920 by a decision of the League of Nations. It is the smallest region of Finland by area and population, with a size of 1,580 km2, and a populati ...
including
South Kvarken South Kvarken ( fi, Ahvenanrauma, sv, Södra Kvarken) is the narrowest stretch of sea between Finnish Åland and Sweden, forming a strait connecting the Sea of Åland and the Bothnian Sea The Bothnian Sea ( sv, Bottenhavet; fi, Selkämeri) ...
. Known Jotnian rocks at the Åland Sea are sandstones and belong to the Söderarm Formation (informal). Above these there are Upper riphean and Vendian sandstones and shales. Fully within Swedish waters there is a Jotnian sediment occurrence at the Landsort Basin between
Gotland Gotland (, ; ''Gutland'' in Gutnish), also historically spelled Gottland or Gothland (), is Sweden's largest island. It is also a province, county, municipality, and diocese. The province includes the islands of Fårö and Gotska Sandön to the ...
and Stockholm archipelago. Jotnian rocks found in the Landsort Basin are red sandstones. In the Bothnian Sea offshore
Pori ) , website www.pori.fi Pori (; sv, Björneborg ) is a city and municipality on the west coast of Finland. The city is located some from the Gulf of Bothnia, on the estuary of the Kokemäki River, west of Tampere, north of Turku and north-w ...
in Satakunta Jotnian sediments reaches a thickness of thousand metres, in other locations thickness is much less, for example 100 m at the Sylen shoal and yet in other places of the Bothnian Sea Jotnian sediments are absent. The Sub-Cambrian peneplain cuts across Jotnian rocks in the Bothnian Sea.


Finland


Muhos

Muhos Muhos is a municipality of Finland. It is located in the province of Oulu half an hour's drive (35 km) on route 22 from the city of Oulu, the capital of Northern Finland, and is part of the Northern Ostrobothnia region. The municipality has a ...
in the northeastern
Gulf of Bothnia The Gulf of Bothnia (; fi, Pohjanlahti; sv, Bottniska viken) is divided into the Bothnian Bay and Bothnian Sea, and it is the northernmost arm of the Baltic Sea, between Finland's west coast ( East Bothnia) and the Sweden's east coast (West ...
is a site of Jotnian sediment occurrence. At this location Jotnian sediments can be found within the
Muhos Graben Muhos is a municipality of Finland. It is located in the province of Oulu half an hour's drive (35 km) on route 22 from the city of Oulu, the capital of Northern Finland, and is part of the Northern Ostrobothnia region. The municipality has ...
that has had a downward displacement of about one kilometre. The sediments in the Muhos Graben at the bottom are conglomerates and arkoses whose contact with the underlying metamorphic rocks constitute an
unconformity An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval o ...
. The pebbles of the conglomerate are made of
schist Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes o ...
and granite while the
matrix Matrix most commonly refers to: * ''The Matrix'' (franchise), an American media franchise ** ''The Matrix'', a 1999 science-fiction action film ** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchis ...
is made of arkose. The bulk (90–80%) of the sequence of sediments is made up of
siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...
s and
shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...
s. The colour of the siltstones and shales vary from red and brown to grey to green. The siltstones and shales are intercalated with arkosic sandstone. The red arkosic sandstones of Muhos Graben are comparable to the ones of Satakunta. These sediments are of fluvial origin.


Satakunta

Southern Satakunta near the shores of the
Bothnian Sea The Bothnian Sea ( sv, Bottenhavet; fi, Selkämeri) links the Bothnian Bay (also called the Bay of Bothnia) with the Baltic proper. Kvarken is situated between the two. Together, the Bothnian Sea and Bay make up a larger geographical entity, t ...
hosts some Jotnian sediments known as Satakunta sandstone. This sediments are
arkosic Arkose () or arkosic sandstone is a detrital sedimentary rock, specifically a type of sandstone containing at least 25% feldspar. Arkosic sand is sand that is similarly rich in feldspar, and thus the potential precursor of arkose. Quartz is c ...
sandstones of red colour and clear
stratification Stratification may refer to: Mathematics * Stratification (mathematics), any consistent assignment of numbers to predicate symbols * Data stratification in statistics Earth sciences * Stable and unstable stratification * Stratification, or st ...
that are intercalated with lesser amounts of red or black shale. According to the sediments mineralogical as well as geochemical characteristics they are classified as
immature Mature is the adjectival form of maturity, as immature is the adjectival form of immaturity, which have several meanings. Mature or immature may also refer to: * Mature, a character from ''The King of Fighters'' series *"Mature 17+", a rating in ...
. The Satakunda sandstones is a fluvial sediment
formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...
. Based on the finding of
glauconite Glauconite is an iron potassium phyllosilicate ( mica group) mineral of characteristic green color which is very friable and has very low weathering resistance. It crystallizes with a monoclinic geometry. Its name is derived from the Greek () m ...
in the Jotnian rocks of the northwestern part of the
outcrop An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. Features Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial ...
, it has been suggested that at least in that place the
diagenesis Diagenesis () is the process that describes physical and chemical changes in sediments first caused by water-rock interactions, microbial activity, and compaction after their deposition. Increased pressure and temperature only start to play a ...
occurred under water. It is found in a northwest-southeast trending graben structure that has helped to preserve the sediments. This graben has seen a downward displacement of about 650 metres. The Satakunta sandstone is not younger than 1400–1300 million years. The Satakunta sedimentary pile is at least 600 metres thick but might likely be as thick as much as 1800 metres. 1270–1250 million years old Postjotnian
olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...
-bearing
diabase Diabase (), also called dolerite () or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-graine ...
dykes cuts through the Satakunta Sandstones.


Russia


Lake Ladoga

Sedimentary and volcanic rocks crop out on the eastern shores of the Lake Ladoga in Russia. Among these are the "Salmi series" or "Salma suite" and the "Priosersk suite", which are Jotnian units. These rocks overlie the Salma rapakivi granite and
igneous Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...
and
metamorphic rock Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causin ...
s of
Paleoproterozoic The Paleoproterozoic Era (;, also spelled Palaeoproterozoic), spanning the time period from (2.5–1.6  Ga), is the first of the three sub-divisions (eras) of the Proterozoic Eon. The Paleoproterozoic is also the longest era of the Earth's ...
age.
Gritstone Gritstone or grit is a hard, coarse-grained, siliceous sandstone. This term is especially applied to such sandstones that are quarried for building material. British gritstone was used for millstones to mill flour, to grind wood into pulp for pa ...
, sandstone and conglomerate are the sedimentary components of the Salmi suite which further includes
mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...
volcanic rock Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic r ...
s. As with Satakunta and Muhos in Finland, the sediments at Lake Ladoga are located in a graben of Late Proterozoic age. The graben structure that hosts the sediments is known as the "Pasha–Ladoga structure", which is also in part a syncline, thus being referred to as graben-syncline. The maximum thickness of the pile of sediments is no less than 800 metres. Jotnian sediments are exposed only as small outcrops on land but exposures are larger at the lake bottom.


Rybachy Peninsula

The
Rybachy Peninsula Rybachy Peninsula (russian: полуо́стров Рыба́чий, ''poluostrov Rybachiy''; se, Giehkirnjárga; no, Fiskerhalvøya; fi, Kalastajasaarento) is the northernmost part of continental European Russia. Its name is translated as " ...
in northern
Murmansk Oblast Murmansk Oblast (russian: Му́рманская о́бласть, p=ˈmurmənskəjə ˈobləsʲtʲ, r=Murmanskaya oblast, ''Murmanskaya oblast''; Kildin Sami: Мурман е̄ммьне, ''Murman jemm'ne'') is a federal subject (an oblast) of ...
hosts Jotnian sedimentary rocks dated to have sedimented 1126±50 million years ago. These rocks are thrusted over by younger
Vendian The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and the ...
and Upper Riphean rocks.


White Sea area

The Jotnian Tersky Formation crops out along the Tersky Coast at the southern shores of the
Kola Peninsula sjd, Куэлнэгк нёа̄ррк , image_name= Kola peninsula.png , image_caption= Kola Peninsula as a part of Murmansk Oblast , image_size= 300px , image_alt= , map_image= Murmansk in Russia.svg , map_caption = Location of Murmansk Oblas ...
. These outcrops are an overfill of the neighbouring Kandalaksha Graben, which is also filled with these sediments. The formation has
silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel when ...
y
bed A bed is an item of furniture that is used as a place to sleep, rest, and relax. Most modern beds consist of a soft, cushioned mattress on a bed frame. The mattress rests either on a solid base, often wood slats, or a sprung base. Many beds ...
s within a matrix of
mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...
and
clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...
. The Tersky Formation was deposited in the timespan between 1263 and 1080 million years ago (±40 million years of error). The neighboring Kerets Graben in the White Sea is filled with 2000–1500 metres of Jotnian sediments.


Sweden

In Sweden Jotnian rocks can be found in
Dalarna Dalarna () is a '' landskap'' (historical province) in central Sweden. English exonyms for it are Dalecarlia () and the Dales. Dalarna adjoins Härjedalen, Hälsingland, Gästrikland, Västmanland and Värmland Värmland () also known a ...
, Gävle,
Nordingrå Nordingrå () is a locality situated in Kramfors Municipality, Västernorrland County, Sweden, with 306 inhabitants in 2010. It is also a parish of some 50 villages, with a population of about 1500. Nordingrå is a part of the ''Höga Kusten'' (Hi ...
, Svartälven,
Lake Mälaren A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...
and Almesåkra (Almesåkra Group).


Almesåkra

The Jotnian Almesåkra Group of sediments lie in northern
Småland Småland () is a historical province () in southern Sweden. Småland borders Blekinge, Scania, Halland, Västergötland, Östergötland and the island Öland in the Baltic Sea. The name Småland literally means ''Small Lands''. The Latinized fo ...
in a triangle-shaped area centered around
Nässjö Nässjö () is a locality and the seat of Nässjö Municipality, Jönköping County, Sweden with 16,678 inhabitants in 2010. History For many years, Nässjö was a rural village with agriculture as the dominant occupation. The turning point was t ...
, in addition to this there is a small strip of these sediments running north from the main area. The Almesåkra Group extends over a ca. 380 km2 wide area. The Almesåkra Group consists of
feldspar Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) feldsp ...
-rich sandstones,
argillite :''"Argillite" may also refer to Argillite, Kentucky.'' Argillite () is a fine-grained sedimentary rock composed predominantly of indurated clay particles. Argillaceous rocks are basically lithified muds and oozes. They contain variable amounts ...
s and minor amounts of conglomerate. The deposits are believed to be of fluvial origin. Argillites constitute about 10% of the outcrops while the sandstones and conglomerates make up the remaining 90% of outcrops. The sedimentary pile is at most not more than 1200 metres thick. The Almesåkra Group is tectonically disturbed, shows considerable
folding Fold, folding or foldable may refer to: Arts, entertainment, and media * ''Fold'' (album), the debut release by Australian rock band Epicure * Fold (poker), in the game of poker, to discard one's hand and forfeit interest in the current pot *Abov ...
and is
intruded Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form '' intrusions'', such as batholiths, dikes, sills, laccoliths, and volcanic necks.Intrusive RocksIntrusive rocks accessdate: March ...
by diabase. Almesåkra Group overlies the
pluton In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...
s of the Transscandinavian Igneous Belt. At least in some outcrops the lowermost sediments are arkoses, presumably of local origin as grus. Geologists Eva-Lena Tullborg and co-workers consider the Almesåkra Group as originating from first phases of erosion of the uplifted Sveconorwegian region to the west. Near Brevik and Röjda there are diabases dykes hosting numerous rounded clasts of red Jotnian
sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...
including both
quartz arenite A quartz arenite or quartzarenite is a sandstone composed of greater than 90% detrital quartz. Quartz arenites are the most mature sedimentary rocks possible, and are often referred to as ultra- or super-mature, and are usually cemented by sili ...
and arkose. These Jotnian
xenolith A xenolith ("foreign rock") is a rock fragment ( country rock) that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term ''xenolith'' is almost exclusively used to describe inclusions in ig ...
s are interpreted as having been part of a conglomerate that was disintegrated by the diabase magma. The conglomerate which contained the rounded Jotnian sedimentary rock clasts has only been deduced to exist and has not found in the proximity of the diabases in question.


Dalarna

The occurrence at Dalarna (Dala sandstone), with its 50 km x 150 km area, constitutes the largest region known to be covered at present with Jotnian sediments. The sandstone extends beyond Sweden's border into
Hedmark Hedmark () was a county in Norway before 1 January 2020, bordering Trøndelag to the north, Oppland to the west, Akershus to the south, and Sweden to the east. The county administration is in Hamar. Hedmark and Oppland counties were merged int ...
in
Norway Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and t ...
where it is known as the "Trysil sandstone". At
Idre Idre ( sma, Eajra, Elfdalian: ''Iðer'') is a locality and ski resort situated in Älvdalen Municipality, Dalarna County, Sweden with 794 inhabitants in 2010. It was also a historical parish and former municipality. History The two parishes ''Sä ...
drilling has revealed that the Dala sandstone extends beneath the Caledonian
nappe In geology, a nappe or thrust sheet is a large sheetlike body of rock (geology), rock that has been moved more than or above a thrust fault from its original position. Nappes form in compressional tectonic settings like continental collision z ...
s. The Dala sandstone
unconformably An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...
overlies the Transscandinavian Igneous Belt basement. The unconformity, believed to have been formed by subaerial erosion, was the surface of a
peneplain 390px, Sketch of a hypothetical peneplain formation after an orogeny. In geomorphology and geology, a peneplain is a low-relief plain formed by protracted erosion. This is the definition in the broadest of terms, albeit with frequency the usage ...
at the time of deposition of the Dala sandstone. The peneplain landscape formed after protracted periods of erosion. Sedimentation of the Dala sandstone happened between 1650 and 1200 million years ago. The maximum thickness of the sediments at Dalarna is 800 m. The lowermost sediments are conglomerates and
breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of di ...
s. Above this basal layer, sediments are mainly stratified red sandstone intercalated with shale and conglomerate. Among the sandstones there are
greywacke Greywacke or graywacke (German ''grauwacke'', signifying a grey, earthy rock) is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lit ...
sandstones and quartz-rich sandstones. A remarkable feature on the Dala sandstones is that delicate features like
ripple mark In geology, ripple marks are sedimentary structures (i.e., bedforms of the lower flow regime) and indicate agitation by water (current or waves) or wind. Defining ripple cross-laminae and asymmetric ripples * ''Current ripple marks'', ''unidi ...
s,
rain drop A drop or droplet is a small column of liquid, bounded completely or almost completely by free surfaces. A drop may form when liquid accumulates at the lower end of a tube or other surface boundary, producing a hanging drop called a pendant d ...
marks and
mudcrack Mudcracks (also known as mud cracks, desiccation cracks or cracked mud) are sedimentary structures formed as muddy sediment dries and contracts.Jackson, J.A., 1997, ''Glossary of Geology'' (4th ed.), American Geological Institute, Alexandria, VA, ...
s have survived in the sediments. The sandstones in Dalarna are of aeolian origin and represent ancient
dune A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, f ...
s and interdune sediments. The Dala sandstone has an imprint of low grade burial metamorphism of the pumpellyite type, meaning they must once have been buried beneath several kilometres of sediments. It is possible that the Dala sandstone was once connected to the Gulf of Bothnia by an
epicontinental sea An inland sea (also known as an epeiric sea or an epicontinental sea) is a continental body of water which is very large and is either completely surrounded by dry land or connected to an ocean by a river, strait, or "arm of the sea". An inland s ...
. The Dala sandstone constitute a part of broad north-south aligned
syncline In structural geology, a syncline is a fold with younger layers closer to the center of the structure, whereas an anticline is the inverse of a syncline. A synclinorium (plural synclinoriums or synclinoria) is a large syncline with superimpose ...
. Sedimentation at Dalarna happened apparently not in a graben or rift as is the case for most other Jotnian sediments.


Gävle

Onshore Jotnian sediments at Gävle (Gävle sandstone) have an estimated maximum thickness of 900 metres. Along with the Dala sandstone the Gävle sandstone has been subject to low grade burial metamorphism of the pumpellyite type, meaning they must once have been buried beneath several kilometres of sediments. Together with the Jotnian sediments of
Nordingrå Nordingrå () is a locality situated in Kramfors Municipality, Västernorrland County, Sweden, with 306 inhabitants in 2010. It is also a parish of some 50 villages, with a population of about 1500. Nordingrå is a part of the ''Höga Kusten'' (Hi ...
the Gävle sandstone share links with the Satakunta Jotnian rocks. Archaeological finds show that Gävle sandstone has been used as
millstone Millstones or mill stones are stones used in gristmills, for grinding wheat or other grains. They are sometimes referred to as grindstones or grinding stones. Millstones come in pairs: a convex stationary base known as the ''bedstone'' and ...
in Lejstaån near
Uppsala Uppsala (, or all ending in , ; archaically spelled ''Upsala'') is the county seat of Uppsala County and the List of urban areas in Sweden by population, fourth-largest city in Sweden, after Stockholm, Gothenburg, and Malmö. It had 177,074 inha ...
.


Lake Mälaren

Jotnian sandstone crops out around Södra Björkfjärden in
Lake Mälaren A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...
. Visible outcrops can be found in the locality of Rasta in western Ekerön island and several small islands and islets: Midsommar, Pingst, Gåsholmen, Gåsholmsskäret and Gåsholmshatten, the last three being part of a nature reserve. Jotnian sandstone also occurs at the bottom of Björkjärden and studies of
glacial erratic A glacial erratic is glacially deposited rock differing from the type of rock native to the area in which it rests. Erratics, which take their name from the Latin word ' ("to wander"), are carried by glacial ice, often over distances of hundred ...
s suggest there is unexposed Jotnian sandstone to north of the Björkfjärden area, where the outcrops are vestiges of an eroded Precambrian
meteorite crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters ...
, filled with Jotnian sediments. At Rasta, the basement below the sediments is made of
granite Granite () is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies undergro ...
s and
pegmatite A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic com ...
s of the Svecofennian orogeny.


Nordingrå

In the Nordingrå area, spanning from Malmön to Hernön, Jotnian sediments rest on a complex of
gabbro Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is che ...
s,
monzogranite Monzogranites are biotite granite rocks that are considered to be the final fractionation product of magma. Monzogranites are characteristically felsic (SiO2 > 73%, and FeO + MgO + TiO2 < 2.4), weakly
granite Granite () is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies undergro ...
s and
anorthosite Anorthosite () is a phaneritic, intrusive igneous rock characterized by its composition: mostly plagioclase feldspar (90–100%), with a minimal mafic component (0–10%). Pyroxene, ilmenite, magnetite, and olivine are the mafic minerals most ...
s. Jotnian sediments consist of quartz-rich
sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...
, arkose and conglomerate. The sandstone and arkose have black and violet coloured
siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...
and
shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...
lenses and beds. Siltstone beds are commonly 5 to 10 centimetres thick. Jotnian sediments in the Nordingrå area display often
cross-bedding In geology, cross-bedding, also known as cross-stratification, is layering within a stratum and at an angle to the main bedding plane. The sedimentary structures which result are roughly horizontal units composed of inclined layers. The origina ...
and
ripple mark In geology, ripple marks are sedimentary structures (i.e., bedforms of the lower flow regime) and indicate agitation by water (current or waves) or wind. Defining ripple cross-laminae and asymmetric ripples * ''Current ripple marks'', ''unidi ...
s. There are also fossil
dune A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, f ...
s. At Ringkallen the pile of Jotnian sediments is of 65 metres. Exposed sediment profiles show considerable variation in
sedimentary facies In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with specified characteristics, which can be any observable attribute of rocks (such as their overall appearance, composition, or condition of formatio ...
. The deposition environment for sandstones including the arkose was one of an embankment or a channel with little current. The environment was likely one of a river as
paleocurrent A paleocurrent or paleocurrent indicator is a geological feature (typically a sedimentary structure) that helps one determine the direction of flowing water in the geologic past. This is an invaluable tool in the reconstruction of ancient deposit ...
s are somewhat uniform. It is also possible that some beds were deposited in
tidal flat Mudflats or mud flats, also known as tidal flats or, in Ireland, slob or slobs, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A global analysis published in 2019 suggested that tidal fl ...
s or as
aeolianite Eolianite or aeolianite is any rock formed by the lithification of sediment deposited by aeolian processes; that is, the wind. In common use, however, the term refers specifically to the most common form of eolianite: coastal limestone consisting ...
s. Similarly to the Gävle sandstones, the outcrops at Nordingrå are linked to the Satakunta outcrops in Finland. The sediments are both
intruded Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form '' intrusions'', such as batholiths, dikes, sills, laccoliths, and volcanic necks.Intrusive RocksIntrusive rocks accessdate: March ...
and covered by
diabase Diabase (), also called dolerite () or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-graine ...
.


Tärnö

In the island of
Tärnö Tärnö is an island in the Blekinge archipelago, the largest and southernmost island in Hällaryd archipelago, in Karlshamn municipality, Blekinge County. Geography The island measures 115.7 ha (285.9 acres) in surface. The island boasts forty ...
Jotnian sandstone
xenolith A xenolith ("foreign rock") is a rock fragment ( country rock) that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term ''xenolith'' is almost exclusively used to describe inclusions in ig ...
s have been found in a
diabase Diabase (), also called dolerite () or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-graine ...
dyke. These xenoliths have been interpreted as originating from Jotnian cover rocks lying above the dyke that have since been eroded. Once the dyke intruded, Jotnian rock fragments would have been incorporated into the dyke and then went down during a "reversal of magma ascent". The relationships of the dyke with Jotnian sediments suggest that magma intruded wet sediments as a sort of
peperite A peperite is a type of volcaniclastic rock consisting of sedimentary rock that contains fragments of younger igneous material and is formed when magma comes into contact with wet sediments. The term was originally used to describe rocks from th ...
.


Other occurrences

Jotnian sediments (mostly quartz sandstone and siltstone) exist at some locations beneath the Phanerozoic platform sediments of western
Latvia Latvia ( or ; lv, Latvija ; ltg, Latveja; liv, Leţmō), officially the Republic of Latvia ( lv, Latvijas Republika, links=no, ltg, Latvejas Republika, links=no, liv, Leţmō Vabāmō, links=no), is a country in the Baltic region of ...
and western
Lithuania Lithuania (; lt, Lietuva ), officially the Republic of Lithuania ( lt, Lietuvos Respublika, links=no ), is a country in the Baltic region of Europe. It is one of three Baltic states and lies on the eastern shore of the Baltic Sea. Lithuania ...
within the Baltic Syneclise.


Notes


References

{{Geology of Fennoscandia Geology of Finland Geology of Norway Geology of Sweden Geology of European Russia Mesoproterozoic Stratigraphy of Europe