The Tambach Formation is an Early Permian-age geologic formation in central Germany. It consists of red to brown-colored sedimentary rocks (red beds) such as conglomerate, sandstone, and mudstone, and is the oldest portion of the Upper Rotliegend within the Thuringian Forest Basin. The overall geology records a history with three distinct stages of sedimentation within a mountainous environment. First, tectonic activity forms a basin (the Tambach Basin) dominated by high-energy debris flows, sheetfloods, and braided rivers. These incise underlying rhyolitic rock, depositing a coarse conglomerate known as the Bielstein Conglomerate. Second, calmer conditions allow the basin to widen, and the conglomerate is marginalized by finer sediments which were previously only common at the center of the basin, such as the characteristic Tambach Sandstone. These finer sediments were deposited through repeated sequences of flooding, followed by calm water, followed by exposure to air. The overall climate would have been similar to modern tropical savannas, with hot and dry periods broken up by heavy rainfall, likely multiple times in a year. The third stage involves a return of tectonic conditions, this time inducing wide deposits of polymictic (heterogenous) conglomerate known as the Finsterbergen conglomerate. The Tambach Formation also includes one of the most important Permian fossil localities in Europe: the Bromacker locality. This former sandstone quarry and surrounding sites preserves several different facies types, with different fossil components. Thick sandstone channel fills in the lower section at Bromacker are overlain with mudstone from ephemeral lakes. A diverse assemblage of trace fossils such as footprints are imprinted onto the mudstone drapings. The upper section of Bromacker contains siltstone deposited through sheetfloods, in which well-preserved articulated skeletons of terrestrial tetrapods have been discovered. These include early amphibians like Rotaryus and Tambaroter, and early reptiles like Eudibamus and Thuringothyris. Unlike most fossil-preserving Permian red beds, aquatic vertebrates are absent at Bromacker while carnivorous synapsids (like Dimetrodon) are rare and herbivorous diadectids are abundant. Plant and arthropod fossils have also been found in shales at Bromacker.
History
Starting in the 1840s, five-toed footprints had been described from various sandstone quarries and roadcuts in the Gotha district of Germany. The stratigraphy of rocks near Tambach-Dietharz was mapped out in 1876, and named as the "Tambacher Schichten" (Tambach strata) in 1895, although at the time it was believed to include several additional rock layers (now termed the Elgersberg and Eisenach Formations) which have since then been separated from it. in 1887 the first fossilized footprints from Bromacker were discovered by a local fossil collector named Heinrich Friedrich Schäfer. The find was donated to the Ducal Museum in the city of Gotha, after which it was independently reported on by various German paleontologists who had received photographic evidence. Wilhelm Pabst, the curator of the Ducal Museum's natural history department, collected and described 140 sandstone slabs from the Tambach Formation from 1890 until his death in 1908. The collection was rediscovered in the 1950s, and subsequently restudied by GDR paleontologists such as Hermann Schmidt, Arno Hermann Müller, and Hartmut Haubold. Fossilized tetrapod bones were discovered in the upper beds of Bromacker by Thomas Martens in 1974, prompting further attention from Gotha paleontologists. These include Harald Lutzner, who formally delineated the Tambach Formation as a sequence including two conglomerate layers separated by a sandstone layer. In the coming years, research contacts were made with Western paleontologists such as Jürgen Boy (University of Mainz) and David Berman (Carnegie Museum of Natural History). This allowed excavation to ramp up and the Tambach Formation to achieve worldwide fame. A 1993 German-American joint expedition recovered articulated tetrapod fossils, and trace fossil collecting was resumed after more than 80 years thanks to the excavation of a new sandstone quarry at Bromacker in 1995. The first Tambach body fossils outside of Bromacker were discovered in 2008, in a construction site in downtown Tambach-Dietharz. In 2010, the exhibits comprising Gotha's Museum of Nature began the process of being moved from the Ducal Museum (which was being converted to an art museum) to the Friedenstein Castle. Due to funding issues, collecting from Bromacker has been limited and the Tambach collection is being archived at the historic Perthesforum complex prior to the construction of a new Permian exhibit.
Geology
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