Siljan, in Dalarna

Dalarna

', English exonym: Dalecarlia, is a historical province or landskap in central Sweden. Another English language form established in literature is the Dales. Places involving the element Dalecarlia exist in the United States....

 in central Sweden

Sweden

Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....

, is Sweden's sixth largest lake

Lake

A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...

. The cumulative area of Siljan and the adjacent, smaller lakes Orsasjön and Insjön is 354 km² (136.7 sq mi). Siljan reaches a maximum depth of 120 m (393.7 ft), and its surface is situated 161 m (528.2 ft) above sea level. The largest town bordered by its shore is Mora.

Impact crater

The lake is located around the southwestern perimeter of the Siljansringen (Siljan Ring), a circular geological formation which was formed 377 million years ago in the Devonian

Devonian

The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

 by a major meteorite

Meteorite

A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...

 impact. The original crater, now mostly eroded, is estimated to have been about 52 km (32 mi) in diameter and is the largest known impact crater in Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

 (excluding Russia

Russia

Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

). The Cambrian

Cambrian

The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...

, Ordovician

Ordovician

The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...

 and Silurian

Silurian

The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...

 sediment

Sediment

Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

ary rocks deformed by the impact are rich in fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s.

Some people suspect that there might be oil

Petroleum

Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...

 in the area, but drilling has been unsuccessful so far. There are large deposits of lead

Lead

Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

 and zinc

Zinc

Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

 in the Boda

Boda, Sweden

Boda is a locality situated in Rättvik Municipality, Dalarna County, Sweden with 576 inhabitants in 2005....

 area.

Deep drilling project

Vattenfall

Vattenfall

Vattenfall is a Swedish power company. The name Vattenfall is Swedish for waterfall, and is an abbreviation of its original name, Royal Waterfall Board...

 (Swedish State Power Board) drilled a deep well in search of natural gas. Sweden was searching for energy sources, but recent ice age cycles removed sediment which usually would be searched for oil and natural gas. The project began as a deep commercial wildcat well, and its unusual location in fractured granite

Granite

Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...

 attracted scientific attention.
The Gravberg-1 well location, in the north-northeast section of the ring, was chosen because a gravity anomaly indicates less dense rock below, and four seismic reflectors may represent cap rock above a natural gas reservoir. Electrical resistance is lower in the ring than outside it, suggesting the rocks contain fluid. Soil in the area showed clear traces of methane

Methane

Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

 and heavy hydrocarbons, with a halo around the ring coincident with vanadium

Vanadium

Vanadium is a chemical element with the symbol V and atomic number 23. It is a hard, silvery gray, ductile and malleable transition metal. The formation of an oxide layer stabilizes the metal against oxidation. The element is found only in chemically combined form in nature...

 and nickel

Nickel

Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

 trace elements; the sediment was shown to not be the source of the hydrocarbons due to their location, ice movement pattern, and low level of maturity. Although the greatest gas leakage was in the north-northwestern corner, the lack of leakage in the central area suggested an underlying cap.

Drilling began on 1 July 1986. By September 1987 it reached 6700 m (21,981.6 ft) in depth.

Four seismic reflectors were detected at 1440 m (4,724.4 ft), 2800 m (9,186.4 ft), 4740 m (15,551.2 ft) and 7400 m (24,278.2 ft). The first three were penetrated and found to be dolerite sills, but the fourth had been identified before drilling as having the best potential for gas production. The dolerite is believed to have existed as much as 1/2 billion years before the meteorite impact. The granite is extensively fractured, with calcite

Calcite

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...

 as the principal cement down to the 3200 m (10,498.7 ft) depth, with lesser amounts to 5000 m (16,404.2 ft).

Traces of methane were found at all depths, with higher levels in dolerite. Although they appear to be of abiogenic origin, only that near the dolerite sills points to a probable mantle origin. Hydrogen

Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 was found in most sections of the hole, correlated with helium

Helium

Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

. The helium isotopic pattern was consistent with a radiogenic, crustal origin.

A black sticky substance was found to be blocking the drill pipe when circulation was stopped for several days at a depth of 5520 m (18,110.2 ft). The substance was black, sticky when wet, powdery when dry, showed no fluorescence, and was strongly magnetic. None of the drilling materials showed gas chromatographic patterns which corresponded with the black substance. It contained no ordinary rock minerals, none of the granite fines expected in the drilling fluid, but is made up of microscopic magnetite

Magnetite

Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. The chemical IUPAC name is iron oxide and the common chemical name is ferrous-ferric oxide. The formula for magnetite may also be written as FeO·Fe2O3, which is one part...

 held together by oils.

The well did not penetrate the fourth seismic reflector, did not produce large quantities of fuel and never entered commercial production. Only 84 barrels (13,354.9 l) of oil were produced, which later was shown to derive from organic additives, lubricants and mud used in the drilling process.

A second hole, Stenberg-1, was drilled in the center of the ring, 12 km (7.5 mi) distant from the ring sediments and from Gravberg-1. This well went to a depth of 6500 m (21,325.5 ft). The hole produced gases and oily magnetite sludge similar to those found in Gravberg-1. http://web.archive.org/web/20021015163818/www.people.cornell.edu/pages/tg21/usgs.html

Localities in the Siljan Ring

• Leksand
  Leksand
  Leksand is a locality and the seat of Leksand Municipality in Dalarna County, Sweden, with 5,861 inhabitants in 2005.- Sport :Leksand is famous for the Leksands IF ice hockey team. Leksand is also home to the Leksands Baseball and Softball Club, one of the oldest and more successful baseball clubs...
  
  
• Mora
• Orsa
  Orsa
  Orsa is a locality and the seat of Orsa Municipality, Dalarna County, Sweden, with 5,278 inhabitants in 2005. It is located in the northern part of lake Siljan, about 15 kilometers north of the town Mora...
  
  
• Rättvik
  Rättvik
  Rättvik is a locality and the seat of Rättvik Municipality, Dalarna County, Sweden, with 4,588 inhabitants in 2005. It's bandy club IFK Rättvik wants to reach the highest division Elitserien and has built an indoor arena.- References :...
  
  
• Boda
  Boda, Sweden
  Boda is a locality situated in Rättvik Municipality, Dalarna County, Sweden with 576 inhabitants in 2005....