Peering out from this vantage point, imagine a sea. Not the Elbe. Think back millions of years. I’m talking about the Zechstein Sea.
We are standing near the Zechstein. It is more than just a place. It is a window into a very distant past.
The Zechstein refers to a fascinating geological formation. It is a group of sedimentary rock layers. These rocks formed in the Late Permian period. That was between 257.3 and 251.0 million years ago.
The name “Zechstein” comes from German. It means either “mine stone” or “tough stone.” The Zechstein was once used as a unit of time. Now, it only describes the sedimentary deposits in Europe.
The Zechstein sits atop the Rotliegend. Above the Zechstein is the Buntsandstein or Bunter. The Zechstein is known for its large amounts of salt rock.
These evaporite rocks came from the Zechstein Sea. This was a shallow sea that existed during the Permian period. It covered what is now the North Sea. It also included areas of Britain and the north European plain. This stretched through Germany and Poland.
The Zechstein Sea was in the rain shadow. The Central Pangean Mountains blocked rainfall to the south. Some researchers believe the Zechstein Sea connected to the Paleotethys Ocean. This connection may have been through southeastern Poland. This point is still debated.
At that time, the sea was near the equator. High temperatures and dry conditions caused evaporation. However, the sea’s beginning may have come from a marine transgression. This was due to a period of de-glaciation. The southern part of Pangaea had ice sheets in the early Permian.
The Zechstein includes several layers. These are labeled Z1 to Z5. The rocks found here include halite “rock salt”, anhydrite, dolomite, and shale.
The Zechstein plays a crucial role. It forms the cap rock for gas fields. These fields have Rotliegend reservoirs. The Zechstein also acts as a reservoir itself. This is seen in the Auk oilfield in the North Sea’s central part. Further north, the Zechstein salt creates salt domes. These domes create the structure for several oil fields.
Near the coast of County Durham, England, Zechstein dolomites appear. There they are known as the Magnesian Limestone.
Just above the base of the Zechstein formation is a thin layer. This is shale or slate. It is known as the kupferschiefer. This is because of its high copper content. This layer contains sulfur compounds. These compounds are typical of silt. Silt was deposited in stagnant shallow marshland. Groundwater circulated through this layer via faults. The sulfur oxidized metal ions into metallic sulfide ores. This thin layer was a vital copper source. It was important across much of northern Europe. This lasted from the Middle Ages into the modern era.
The Zechstein salt layer is also useful today. It is used for underground gas storage. This occurs in England, Germany, and France.
As we stand here, remember the vastness of time. The Zechstein reminds us of the Earth’s ever-changing nature. From ancient seas to modern energy storage, it is a story etched in stone.