Zechstein north sea
Hem / Natur, Miljö & Klimat / Zechstein north sea
The identification of these platform facies from the less prospective basinal facies, requires regional high quality 3D seismic to fully constrain the distribution. With seismic quality unable to easily resolve reservoir variability, it was not the primary target for exploration, also meaning that wells through the Zechstein unit were neither aimed at the most prospective parts, nor significantly investigated.
However, there are several hints toward the potential of this unit.
Repeated cycles of marine flooding and evaporation led to deposition cycles of sediments followed by evaporite salts. Reefs developed just off the shores of this ancient sea which was a vast evaporating basin – a so-called saline giant. Its importance extends beyond geological curiosity, as the minerals formed within its basin continue to be economically relevant today.
The Ancient Zechstein Sea
The Zechstein Sea was a vast epicontinental sea that existed during the Late Permian period, approximately 257.3 to 251.0 million years ago.
IONs MNSH PRIME 3D survey enables the explorer to do just this.
Spectacular initial results
Imaging of the first phase of the MNSH PRIME 3D is in progress, using a full range of modern processing and imaging techniques. The Zechstein Sea’s unique geographical position contributed to the eventual deposition of its extensive mineral wealth.
Geological Formation and Evaporation
The formation and subsequent evaporation of the Zechstein Sea were driven by a unique combination of geological and climatic factors.
In the case of the Zechstein reefs, the sedimentary rocks that were bulged upwards by the formation salt domes created important traps for hydrocarbon in the South North Sea but the big prizes were hosted in the strata below the salt, sealed in by the impermeable salt deposits (e.g. Where the platformal zones dominate, and the overall Zechstein is thinner in the east, the Plattendolomit is characterized by karstification and the presence of sinkhole-type features.
This prehistoric body of water provides a window into understanding profound environmental changes and the processes that shaped our planet’s crust. From the 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 used for underground gas storage in England, Germany and France.
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The Zechstein is usually given the status of a lithostratigraphic group and as such encompasses a number of geologic formations.
In the west of the survey, the platform edge is well picked out seismically defining potential targets; in the east we see more erosion and collapse in this unit, giving the potential for karstified secondary porosity development.
Overall, our initial results from this exciting new dataset show how high quality data can illuminate and unlock the potential of this previously largely overlooked play in the UKCS.
Modern day position of the ancient Zechstein Sea: © San Jose, Drdoht
Hidden beneath the waters of the North Sea between the UK and Norway are the Zechstein reefs.
Where faults have allowed mineral-rich groundwater to circulate through this layer, the sulfur has oxidized metal ions to metallic sulfide ores. One of the earliest discoveries offshore in the SNS was Resolution (1966) which found oil in the Z2 Hauptdolomit just offshore Yorkshire. The eventual disappearance of the Zechstein Sea was part of a general marine regression that occurred before and during the Permian–Triassic extinction event.
Precious Mineral Deposits
The repeated cycles of evaporation within the Zechstein Sea left behind extensive and remarkably pure layers of various valuable minerals.
It consists of at least five depositional cycles of evaporite rocks, which are labelled Z1 to Z5, respectively. Figures 3–5 show sections and horizon maps of the Top Zechstein, Plattendolomit (Z3) and Hauptdolomit (Z2) respectively.
The Top Zechstein (Figure 3) shows varying amounts of halokinesis causing collapse and thickening of the overlying Bacton group Triassic strata, itself a potential target.
In the southern gas basin, it forms the main cap rock to the gas fields with Rotliegend reservoirs.
Salt has a habit of flowing in the subsurface and rises up into domes called diapirs.