User:Geopark official/Geopark Thuringia Inselberg – Drei Gleichen

The Geopark Thuringia Inselsberg - Drei Gleichen is a geopark in Thuringia. It covers an area of around 725 km² and includes parts of the Thuringian Forest and the southern foothills of the Thuringian Basin. It touches the territory of 18 municipalities (7 of which are towns). On February 15, 2008, the Geopark Inselsberg - Drei Gleichen was awarded the title "National GeoPark in Germany"; on April 21, 2021, UNESCO designated the Geopark as a UNESCO Global Geopark.

Location and Description
The UNESCO Global Geopark Thuringia Inselsberg - Drei Gleichen covers the western part of the Thuringian Forest with its northern foreland as a transition area from the low mountain range to the undulating arable plains of the Thuringian Basin. It is bordered by several cities, in the east by Erfurt and Arnstadt, in the north by Gotha, in the south by Oberhof and Schmalkalden and in the west by Eisenach and Bad Salzungen. Main hiking and cycling routes such as the Rennsteig, the former Thüringenweg and the Thuringian city chain (part of an European cycle route) lead through the Geopark area.

The Geopark got its name from the Großer Inselsberg (916 m above sea level) in the Thuringian Forest and the castle ensemble of the “Drei Gleichen” (“Three Equals”), formed from the medieval castles Mühlburg, Wachsenburg and Gleichen, which are in close proximity to each other.

The area of ​​the Geopark includes most of the Ohrdruf military training area in its eastern area, an area that the public is not allowed to enter.

Geology
The Geopark is divided into three natural units: the western Thuringian Forest (Inselsberg region), a representative part of the southwestern Thuringian Basin (Drei Gleichen region) and a small part of the southwestern Thuringian Triassic landscape. In the Inselsberg region, all of the rocks found throughout the Thuringian Forest are represented, from the Ruhlaer Kristallin to the Rotliegend. The landscape is dominated by the more weather-resistant rhyolite peaks, which are bordered by deep valleys in softer rock types. The metamorphic and igneous rocks build up the basement, which was formed during the Variscan Orogeny.

This is followed by the rocks of the transitional floor from the Rotliegend period. These predominantly reddish sedimentary rocks are the solidified debris from the Variscan Orogen. The important early tetrapod site Bromacker can be found in these sediments. Here, for the first time, footprints and the skeletons of their creators were discovered in the same site, which is unique in the world. During the Lower Rotliegend period, intense volcanic activity occurred in what is now the Geopark area. For example the Großer Inselsberg consists of these rocks. During the Zechstein time, the region was flooded several times by the advancing sea. This is evidenced by the Zechstein unconformity in Auwallenburg, where slab dolomite was deposited on older mica schist. The Zechstein encloses the Thuringian Forest like a band in the northeast and southwest.

The Drei Gleichen area forms part of the Eichenberg–Gotha–Saalfeld fault zone, which runs from northwest to southeast. Part of this is the Wachsenburg Graben. Here, the stratigraphy from the Muschelkalk to the Early Jurassic is completely exposed in a very limited space. In valley areas they are covered by the Pleistocene deposits of the Apfelstädt River. Sinkholes and local subsidence areas caused by subrosion also form the relief in this region. In the area of ​​the Wachsenburg Graben there are several artesian springs, from which karst groundwater emerges. These include the Mühlberger Spring, the Gräfenbrunnen and the salt spring near Sülzenbrücken.

The Gottlob mountain near Friedrichroda is considered a type locality for four minerals (as of 2024): Crednerite, Vésigniéite, Wakefieldite-(La) and the Gottlobite, which is named after the type locality.

The latter mineral has only ever been discovered at this site.

Geopark theme
The UNESCO Global Geopark Thuringia Inselsberg – Drei Gleichen has the motto “In the footsteps of Pangaea”. The rocks and geological outcrops in the Geopark testify to the formation of the supercontinent Pangaea and its development from its beginnings to its disintegration.

340 million years ago, the northern large continent Old Red Continent, and the southern continent Gondwana joined to form the giant global continent of Pangaea. The huge geological suture of this connection is formed by the Ruhlaer Kristallin. It is the oldest rock in the Geopark and provides impressive evidence of the formation of Pangaea. The younger rock layers were formed in the center of the giant continent. Every layer from the Upper Carboniferous (310 million years ago) to the youngest sections, the approximately 190 million year old layers of the Lower Jurassic, represents the imprint of the surface of Pangaea. Fossils tell us about the life on Pangaea. This applies to a tree-high fern plant from the Rotliegend period as well as to a ceratite (marine cephalopod) from the sea in the Upper Muschelkalk. About 150 million years ago, Europe and North America split up and the final disintegration of Pangaea began. In the Keuper there is a striking unconformity that shows this breakup.

The many geological objects in the Geopark Thuringia Inselsberg – Drei Gleichen have one thing in common: they all represent the imprint of a land surface “in the middle of Pangaea”.

Research projects
As part of the Bromacker project, excavations will take place annually from 2021 to 2025 in the famous Bromacker tetrapod site between Georgenthal and Tambach-Dietharz. This reveals the living environment from around 290 million years ago from the Permian period, and several animal species have been identified so far. They belong to different taxonomic groups, but are grouped together as “early tetrapods”. The project is funded by the German Federal Ministry of Education and Research and dedicated to science communication. The Geopark's project partners are the Natural History Museum Berlin, the Friedrich Schiller University Jena and the Schloss Friedenstein Foundation in Gotha.

A cooperation with the Greek Chelmos-Vouraikos UNESCO Global Geopark and the University of Patras exist since 2021. It aims to explore and research of ostracods living in caves in the two geoparks. For this purpose, sediment samples were taken in various caves, examined microscopically and evaluated. The project is supported by the German Academic Exchange Service (DAAD) and the Greek State Scholarship Foundation I.K.Y. Ίδρυμα Κρατικών Υποτροφιών.

Important geotopes
The most important inventory of the Geopark are the geotopes. They provide insights into the internal structure and history of the earth. Some geotopes from the Geopark Thuringia Inselsberg – Drei Gleichen are listed here:


 * Bromacker tetrapod fossil site near Tambach-Dietharz

The quarries at the Bromacker near Tambach-Dietharz are among the world's most important sites of early land-dwelling tetrapods; the site is unique in Europe. Around 30 years ago, the first bones of these early tetrapods were found, which represent a transitional form from amphibians to reptiles.


 * Mühlberger Spring

The Mühlberger Spring is one of the most important karst springs in the central part of the Thuringian Basin. It feeds the Weidbach creek, which used to power up to six mills. This has been the basis of the water supply in the area for centuries and also formed the basis for the settlement of the region.


 * Haarhausen gravel pit

The disused quarry on the southern edge of the town of Haarhausen shows a section of the Wachsenburg Graben, which is part of the Eichenberg-Gotha-Arnstadt-Saalfeld fault zone. Here you can impressively see how the originally horizontal rock layers are folded during mountain formation.


 * Trusetal waterfall and Trusetal main vein

The artificial Trusetal waterfall served to drain the Trusetal mining area. It has a fall height of 58 m. The rocks around the Trusetal waterfall are an excellent example of the so-called spheroidal weathering of granite rock. The granite in this area is cut by a mixed vein of syenite porphyry and kersantite. Since the vein was mined, it can now only be seen as an open crack.


 * Oven holes

The oven holes near Bad Tabarz are three parallel caves in volcanic rock (rhyolite), the origins of which are still unclear. On the one hand, they could be lava tunnels, which have so far only been known in young basalt rock. On the other hand, the tubes could have been formed by water erosion; however, the shape would be very unusual for such a pseudokarst. If either theory comes true, it would be unique in the world.


 * Marienglashöhle Friedrichroda

The Marienglashöhle is a show cave with a natural crystal grotto that was fortuitously discovered by miners in 1778. Selenite (German: Marienglas) was mined here and used to decorate altars, chandeliers and images of the Virgin Mary, which also gave the mineral its German name. It is a variety of gypsum. The grotto is a natural monument that is unique in Germany.


 * Outcrop on the hollow path near Schmerbach

The outcrop on the Hohlweg near Schmerbach (belongs to Waltershausen) shows a basal Zechstein deposit with a very unusual fossil content. This fauna in Kupferschiefer, for example, includes many soil organisms that normally do not exist in this oxygen-poor environment. They are evidence of reef formation and thus of an earlier formation of the Kupferschiefer.


 * Catterfeld mining settlement

In the northern part of Catterfeld (Georgenthal) there are still four one-story houses from a former mining settlement. The plots of land are hardly larger than the size of the house. The houses date from the cobalt mining era in the 18th century. At the time, this raw material was mined for the “Blaufarbenwerke” on the nearby Ziegelberg.


 * Großer Inselsberg

At 916.5 m above sea level, the Große Inselsberg is the fourth highest mountain in Thuringia, but it is also the most famous peak. It towers over its foreland by 100 m and is visible from afar. The Inselsberg is a lava dome with very viscous lava that never ran beyond the edge of the vent.


 * Mountain lake at the Ebertswiese

The mountain lake at the Ebertswiese is a former quarry, the bottom of which is now filled with water. Between 1900 and 1942, Hühnberg dolerite was mined here, a high-quality raw material from which gravel, paving stones and building stones were obtained. The remaining opencast mine has been used as a swimming lake for a very long time.


 * Kammerbruch

For centuries, the Rätsandstein from the Seeberg represented an important raw material for construction work. The yellow-brown sandstone from the Seeberg was used primarily in representative buildings in Gotha, Eisenach and Erfurt. The quarry is still active today. The Kammerbruch offers the most comprehensive geological profiles of the Upper Keuper and the Lias in the Thuringian Basin.


 * Maternbrunnen near Grabsleben

The Maternbrunnen near Grabsleben is a layered spring that arises when groundwater-conducting and groundwater-retaining rocks in the subsoil frequently change. The spring served to supply drinking water to the town of Grabsleben until the 1980s. The Way of St. James also leads past the fountain.


 * Badlands in the Drei Gleichen area

On the southern slopes of the Wachsenburg, the Mühlburg and the Gleichen Castle, what catches the eye of every visitor is the area with little vegetation and its strong reddish-brown to grey-green coloring: the so-called badlands. Because of the underlying geological rocks, soil has difficulty forming here and therefore the area cannot be used for agriculture – hence the name. Claystone and stone marl banks are exposed here on the surface.


 * Kittelsthal dripstone cave

The Kittelsthal dripstone cave is a karst cave that is created by chemically dissolving limestone (here from Zechstein reefs). The cave is much younger than the surrounding rock; it was created when the reef limestone was exposed 1.7 million years ago. The cave was probably discovered in 1888 and has been used as a show cave on and off since 1919.


 * Hainfelsen

The Hainfelsen is a natural rock formation on the eastern steep slope of the Kleine Leina. It consists of Tambach sandstone and the so-called “Finsterberg conglomerate”, which is made up of various rock debris (granite, slate, porphyry). The rock has been protected as a natural monument since 1938.


 * Hohenkirchen gravel pit

During the Ice Age, the Apfelstädt river deposited gravel sand from the Thuringian Forest here. Back then, the course of the river changed frequently and the Apfelstädt did not yet have ist current riverbed. The gravels consist primarily of volcanic rocks: rhyolite and dacite. The Hohenkirchen gravel pit is still active.


 * Gerberstein

The Gerberstein was mentioned in a document as “Gervuenstein” as early as 933 and is therefore considered the earliest peak in the Thuringian Forest mentioned by name – although it only measures 728 m above sea level. The rock consists of Ruhla granite and is especially resistant to erosion. From the Gerberstein, which has been under protection since 1940 for biological and local historical reasons, you can see as far as the Rhön Mountains when the weather is good.