Zechstein

From Wikipedia, the free encyclopedia

Zechstein (German either from mine stone or tough stone) is a geological formation of Late Permian (Guadalupian and Lopingian) age located in the European Permian Basin which stretches from the East Coast of England to Northern Poland. It was formerly referred to as the Zechstein epoch of the Permian Age, although this is now obsolete.

The Zechstein consists of five cycles of evaporite rocks, (Halite, Anhydrite, Dolomite and shales) labelled Z1 to Z5 respectively. The zechstein has significant economic importance in the North Sea Oil 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 North Sea. Further North the Zechstein salt becomes diapric, becoming 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.

The evaporite rocks of the Zechstein formation were laid down by the Zechstein Sea, an epicontinental or epeiric sea that existed for the last five to seven million years 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 Tethys Ocean through southeastern Poland; the point is disputed by researchers. Though located, in its own era, near the Earth's 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 sheets in the Permian. The eventual disappearance of the Zechstein Sea was part of a general marine regression that preceded and accompanied the Permian-Triassic extinction.^[1][2]

[edit] References

1. ^ Glennie, Kenneth William, ed. Petroleum Geology of the North Sea: Basic Concepts and Recent Advances. London, Blackwell, 1998; pp. 160-75.
2. ^ Moores, Eldridge M., and Rhodes Whitmore Fairbridge, eds. Encyclopedia of European and Asian Regional Geology. London, Chapman & Hall, 1997; pp. 97, 263.