Between Saalfeld and Neustadt/ Orla unique reefs of the Werra sequence of the Zechstein sea occur for Europe, which were essentially formed by microorganisms (presumably calcifying cyanobacteria) and reach up to 70 m thickness. They are excellently preserved, often rich in fossils and developed by numerous quarries. Located near Oelsen, about 3 km southwest of Krölpa at the southern edge of the Orlasenke, Clydenberg is part of an elongated barrier reef that grew in the shallow water near the southeastern shore of the Zechstein Sea. the partly deposited at the same time in the deeper water to the north (werra carbonate, gypsum, mudstone) is much easier to erode, therefore the weathering has often impressively modeled the former shapes of the reefs. Accordingly, on the Clydenberg the steep northern slope consists of reef slope sediments and the flat hilltop of reef platform deposits.