Zechstein
Encyclopedia
The Zechstein is a unit of sedimentary rock
layers of Middle to Late Permian (Guadalupian to Lopingian) age located in the European Permian Basin
which stretches from the east coast of England to northern Poland. The name Zechstein was formerly also used as a unit of time in the geologic timescale, but nowadays it is only used for the corresponding sedimentary deposits in Europe.
The Zechstein lies on top of the Rotliegend
; on top of the Zechstein is the Buntsandstein or Bunter
.
that existed in the Guadalupian and Lopingian epochs of the Permian period. The Zechstein Sea occupied the region of what is now the North Sea
, plus lowland areas of Britain and the north European plain through Germany and Poland. At times the Zechstein Sea may have connected with the Paleotethys Ocean through southeastern Poland; the point is disputed by researchers.
Though situated at the time near the equator (where high temperatures and arid conditions facilitated evaporation), the sea's inception likely stemmed from a marine transgression rooted in a phase of de-glaciation; the southern portion of Pangaea
, the former (and future) Gondwanaland, supported ice sheet
s in the early Permian. The eventual disappearance of the Zechstein Sea was part of a general marine regression
that preceded and accompanied the Permian-Triassic extinction.
and as such encompasses a number of geologic formations.
The Zechstein consists of at least five depositional cycles of evaporite rocks, which are labelled Z1 to Z5 respectively. The lithologies
found are halite
("rock salt"), anhydrite
, dolostone
and shale
.
province. In the southern gas basin it forms the main cap rock to the gas fields with Rotliegend reservoirs. It also forms a reservoir in the Auk oilfield
in the central part of the North Sea. Further north the Zechstein salt becomes diapiric, forming salt domes which form the structure for several oil fields, such as Machar. Zechstein dolomites outcrop near the coast of County Durham
, England where they are known as the Magnesian Limestone
.
Just above the base of the Zechstein formation is a fairly thin layer of shale, or slate, where it has been metamorphized, known as the kupferschiefer for its high copper content. In its unmodified form, this layer is high in sulfur compounds that are typical of silt deposited in stagnant shallow marshland. Where faults have allowed mineral rich groundwater to circulate through this layer, the sulfur has oxidized metal ions to metallic sulfide ores. From Middle Ages into the modern era, this thin but widely dispersed constellation of ore bodies has been of immense importance as a source of copper across much of northern Europe.
The Zechstein salt layer is also utilised for underground gas storage in England, Germany and France.
Sedimentary rock
Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....
layers of Middle to Late Permian (Guadalupian to Lopingian) age located in the European Permian Basin
Permian Basin (Europe)
The European Permian Basin is a thick sequence of sedimentary rocks deposited in a large sedimentary basin during the Permian period in North Europe. The basin underlies northern Poland, northern Germany, Denmark, The Netherlands and under a significant portion of the North Sea to Scotland...
which stretches from the east coast of England to northern Poland. The name Zechstein was formerly also used as a unit of time in the geologic timescale, but nowadays it is only used for the corresponding sedimentary deposits in Europe.
The Zechstein lies on top of the Rotliegend
Rotliegend
The Rotliegend or Rotliegendes is a lithostratigraphic unit of Cisuralian age that is found in the subsurface of large areas in western and central Europe. The Rotliegend mainly consists of sandstone layers...
; on top of the Zechstein is the Buntsandstein or Bunter
Buntsandstein
The Buntsandstein or Bunter sandstone is a lithostratigraphic and allostratigraphic unit in the subsurface of large parts of west and central Europe...
.
Formation
The evaporite rocks of the Zechstein formation were laid down by the Zechstein Sea, an epicontinental or epeiric seaEpeiric Sea
An epeiric sea is a shallow sea that extends over part of a continent.Epeiric seas are usually associated with the marine transgressions of the geologic past, which have variously been due to either global eustatic sea level changes, local tectonic deformation, or both, and are occasionally...
that existed in the Guadalupian and Lopingian epochs of the Permian period. The Zechstein Sea occupied the region of what is now the North Sea
North Sea
In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...
, plus lowland areas of Britain and the north European plain through Germany and Poland. At times the Zechstein Sea may have connected with the Paleotethys Ocean through southeastern Poland; the point is disputed by researchers.
Though situated at the time near the equator (where high temperatures and arid conditions facilitated evaporation), the sea's inception likely stemmed from a marine transgression rooted in a phase of de-glaciation; the southern portion of Pangaea
Pangaea
Pangaea, Pangæa, or Pangea is hypothesized as a supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before the component continents were separated into their current configuration....
, the former (and future) Gondwanaland, supported ice sheet
Ice sheet
An ice sheet is a mass of glacier ice that covers surrounding terrain and is greater than 50,000 km² , thus also known as continental glacier...
s in the early Permian. The eventual disappearance of the Zechstein Sea was part of a general marine regression
Marine regression
Marine regression is a geological process occurring when areas of submerged seafloor are exposed above the sea level. The opposite event, marine transgression, occurs when flooding from the sea covers previously exposed land....
that preceded and accompanied the Permian-Triassic extinction.
Stratigraphy
The Zechstein is usually given the status of a lithostratigraphic groupGroup (stratigraphy)
A group in stratigraphy is a lithostratigraphic unit, a part of the geologic record or rock column that consists of defined rock strata. Groups are divided into formations and are sometimes themselves grouped into "supergroups"....
and as such encompasses a number of geologic formations.
The Zechstein consists of at least five depositional cycles of evaporite rocks, which are labelled Z1 to Z5 respectively. The lithologies
Lithology
The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples or with low magnification microscopy, such as colour, texture, grain size, or composition. It may be either a detailed description of these characteristics or be a summary of...
found are halite
Halite
Halite , commonly known as rock salt, is the mineral form of sodium chloride . Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, pink, red, orange, yellow or gray depending on the amount and type of impurities...
("rock salt"), anhydrite
Anhydrite
Anhydrite is a mineral – anhydrous calcium sulfate, CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the orthorhombic barium and strontium sulfates, as might be expected from the...
, dolostone
Dolostone
Dolostone or dolomite rock is a sedimentary carbonate rock that contains a high percentage of the mineral dolomite. In old U.S.G.S. publications it was referred to as magnesian limestone. Most dolostone formed as a magnesium replacement of limestone or lime mud prior to lithification. It is...
and shale
Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
.
Economic importance
The Zechstein has significant economic importance in the North Sea OilNorth Sea oil
North Sea oil is a mixture of hydrocarbons, comprising liquid oil and natural gas, produced from oil reservoirs beneath the North Sea.In the oil industry, the term "North Sea" often includes areas such as the Norwegian Sea and the area known as "West of Shetland", "the Atlantic Frontier" or "the...
province. In the southern gas basin it forms the main cap rock to the gas fields with Rotliegend reservoirs. It also forms a reservoir in the Auk oilfield
Auk oilfield
The Auk Oilfield is situated east, southeast of Aberdeen, Scotland, in block number 30/16. It was operated by Royal Dutch Shell until October 2006 when it was bought by Talisman Energy, and is now licensed by Talisman Energy. It was discovered in February 1971 in a water depth of 82 metres....
in the central part of the North Sea. Further north the Zechstein salt becomes diapiric, forming salt domes which form the structure for several oil fields, such as Machar. Zechstein dolomites outcrop near the coast of County Durham
County Durham
County Durham is a ceremonial county and unitary district in north east England. The county town is Durham. The largest settlement in the ceremonial county is the town of Darlington...
, England where they are known as the Magnesian Limestone
Dolostone
Dolostone or dolomite rock is a sedimentary carbonate rock that contains a high percentage of the mineral dolomite. In old U.S.G.S. publications it was referred to as magnesian limestone. Most dolostone formed as a magnesium replacement of limestone or lime mud prior to lithification. It is...
.
Just above the base of the Zechstein formation is a fairly thin layer of shale, or slate, where it has been metamorphized, known as the kupferschiefer for its high copper content. In its unmodified form, this layer is high in sulfur compounds that are typical of silt deposited in stagnant shallow marshland. Where faults have allowed mineral rich groundwater to circulate through this layer, the sulfur has oxidized metal ions to metallic sulfide ores. From Middle Ages into the modern era, this thin but widely dispersed constellation of ore bodies has been of immense importance as a source of copper across much of northern Europe.
The Zechstein salt layer is also utilised for underground gas storage in England, Germany and France.