The Geiseltal fossil deposit is located in the former lignite district of the Geiseltal south of the city of Halle in Saxony-Anhalt, Germany. It is an important site of now extinct plants and animals from the Middle Eocene period 48 to 41 million years ago. There is evidence that coal was first mined in the Geiseltal in 1698, but the first fossils only came to light by chance at the beginning of the 20th century. Scheduled scientific excavations began in 1925 by the Martin Luther University Halle-Wittenberg. Interrupted by World War II, the investigations can be divided into two research phases. Due to the increasing depletion of the raw material deposits, the excavations gradually came to a standstill in the mid-1980s and finally ended at the beginning of the third millennium.
The lignite of the Geiseltal is subdivided into four main seams, the three lower ones were mainly fossil-bearing. The focus of the fossil distribution is in the southern and central Geiseltal. The finds include remains of plants and animals. A special feature are almost complete finds with leaves, fruits and stems, but also skeletons of vertebrates and remains of insects. One of the most famous finds is that of a complete skeleton of the prehistoric horse Propalaeotherium from 1933. Other vertebrates include even-toed ungulates, small mammals such as insectivores and bats as well as birds, crocodiles, turtles, snakes, amphibians and fish. Remains of soft tissue were also found in numerous vertebrates. In total, more than 80 individual sites with more than 50,000 finds are known, including 36 with a significant number of vertebrates. Due to the good and extensive preservation of fossils, the Geiseltal is considered a conserve and concentrate deposit.
The special feature of the Geiseltal fossils, above all the vertebrates and especially the mammals, lies in their unique preservation in lignite, which is not found anywhere else in Central Europe. The Geiseltal is an important site for the development of mammals, as the development of individual groups can be observed there over a period of several million years. This makes the mammal fauna a reference for the Geiseltalium, a section of the stratigraphy of European land mammals from 47 to 43 million years ago. The extensive finds from the animal and plant world, as well as the numerous geological data, make it possible to reconstruct the landscape quite accurately. According to this, at the time of lignite formation there was a multi-storey lowland forest near the coast, which was interspersed with streams, ponds and bogs. The forest was subject to the influence of subtropical climate and was home to a species-rich fauna. The entire fossil record of the Geiseltal is under national protection.
Geographical location
The Geiseltal, a peripheral area of the Central German Lignite Mining Area, is located about 20 km south of Halle (Saale) and about 10 km southwest of Merseburg in Saxony-Anhalt. It extends over a length of 15 km from west-northwest to east-southeast and over a width of 0.5 to 5 km. In the north it borders on the flat Merseburg red sandstone plateau, in the south on the Müchelner shell limestone plateau of the Querfurt-Freyburger Mulde. The River Geisel, which gives the valley its name, flows through the Geiseltal. It rises in St. Micheln near Mücheln from one of the largest springs in central Germany and drains after 19 km in Merseburgd via the Gotthardtsteiche into the Saale. Its catchment area is about 35 km2.
Originally, the area of the Geiseltal was relatively flat, which can be explained by the Buntsandsteins spreading west of the Saale. In general, the heights in the eastern Geiseltal were around 100 meters above sea level, rising to 150 meters and more towards the west. However, the intensive activity of open-cast lignite minings has seriously altered the landscape, especially in the last 150 years, and in addition to the destruction of several villages, has also led to the shaping of an area of around 90 km2 with the course of the Geisel river being shifted several times to the south. As a result of the renaturation of the later abandoned open-cast mines, larger lakes were created, which currently dominate the entire Geisel valley. The Südfeldsee and Runstedter See were created in the eastern and south-eastern Geiseltal as early as the second half of the 20th century, while in the western part the Geiseltalsee, one of the largest artificial lakes in Central Europe, was only completed in 2011. Today, the western and eastern Geiseltal valleys are separated by a tipping dam up to 140 m high, which, in addition to the current course of the Geisel River, also carries important transportation routes such as roads and railways.
Geology Geological subsoil
The geology of the Geiseltal has been well investigated since the beginning of the 20th century during preliminary investigations to determine lignite storage conditions with deep boreholes. These were only 100 m apart in individual sections. The geological subsurface consists largely of Rotliegengendes and Zechstein deposits from the Permian geological period, around 300 to 240 million years ago. These deposits are overlain by sediments from the Buntsandstein (251 to 243 million years ago), where the lower and middle Buntsandstein predominate. In the southern part of the Geiseltal, towards the Mücheln shell limestone plateau, however, there are also remnants of the Upper Buntsandstein, in which the shell limestone deposits are found at the edges of the valley. The following Hiatus comprises the Keuper and Cretaceous of a period of around 140 million years.
The Geiseltal heutige is increasingly present in its geography. The Neumark main threshold, a rise of the Buntsandstein, divides it into two roughly equal-sized areas, the western and eastern Geiseltal. Secondary and subordinate basins are the Elise basin, the Elisabeth basin, the Wernsdorf basin and others; pre-Tertiary thresholds are the Kayna threshold and the eastern threshold. Geologically, the Geiseltal represents a subsidence structure whose formation has not yet been fully clarified, but which was controlled by several processes. It is possible that in the Palaeogene the leaching of the Zechstein salt combined with the chemical weathering of the shell limestone (subrosion) led to mass loss in the subsoil, which resulted in the subsidence of the overlying layers and the formation of the basin. The salt movement (halokinesis) in particular was associated with tectonic forces in the subsurface, resulting from plate tectonics, which also caused the folding of the Alps during the Cretaceous/Tertiary turn about 65 million years ago. This led to an increase in pressure on the originally flat Zechstein Sea, which then flowed sideways. In the northern area of the Geiseltal, seismic measurements have identified tectonic faults, the so-called Geiseltal-Nordrand-Störung (Geiseltal northern edge fault), which in some places reaches a jump height of up to 200 m in the upper layers (red sandstone).
Paleogene deposits The entire deposits of the Palaeogene reach a thickness of up to around 200 m in the Geiseltal, but are largely limited to the Eocene (56 to 34 million years ago). These Tertiary sediments are initiated by clays and silts as well as partly gröberclastic material. The thickness of the predominantly finely layered to flaky lignite is around 30 to 80 m, but can reach over 120 m in places. In general, the Geiseltal lignite is divided into four main seams, the Lower Coal, Middle Coal (differentiated into Lower and Upper Middle Coal) and Upper Coal, but also has a local Basiskohle in the northern Geiseltal. With the exception of the base coal, all seams are subdivided into further seam sections. The individual seams reach a thickness of 10 to partly 60 m. They are interrupted by sand-silty sedimentary sections (the so-called main middle), which represent guiding horizons and serve to differentiate the seams. In the southern Geiseltal in the open-cast mine Cecilie, however, there was a partially unbroken transition from the middle coal to the upper coal. The extent of the individual coal seams varies from north to south and is linked to the halokinetic and subrosive subsidence of the subsoil. subsidence of the subsurface, but it generally continues further south with the increasing stratigraphic altitude of the seams. Only the Upper Coal is formed throughout the Geiseltal. The very rich Eocene fossil community originates mainly from the Lower Coal and Middle Coal.
Supporting layers The overburden in the Geiseltal consists of up to 50 m thick deposits of the Middle Pleistocene and Late Pleistocene (0.78 to 0.012 million years ago). The oldest layers, spared from erosion, were formed as ground moraine by the inland ice of the Elster glacial period (400,000 to 335,000 years ago). In the Holstein Warm Period (335,000 to 320,000 years ago), the Unstrut river shifted its course as far as the Geiseltal and created the so-called Körbisdorf Terrace. The inland ice of the Saale Cold Period (320,000 to 128,000 years ago) only passed over the Geiseltal during the first advance, known in Central Germany as the "Zeitz Phase" and in Northern Germany as the "Drenthe I Phase" or "Main Drenthe".
The retreat of the inland glacier of the Saale glacial period led to the formation of drainless and mostly water-filled depressions, particularly in the north-eastern part of the Geiseltal, in the former open-cast mining field Neumark-Nord, through mollisol diapirism, in which predominantly limnic sediments were deposited. Between 1986 and 2008, the individual lake basins were the focus of interdisciplinary scientific research, the results of which were published in numerous publications. The largest, around 600 m long and 400 m wide Neumark-Nord 1 basin contained the remains of a rich large mammal fauna, including complete skeletons of the European forest elephant, aurochs, bison, fallow deer and various rhinoceross (forest rhinoceros, steppe rhinoceros), but also cave lions and spotted hyenas. The large mammal fauna of the smaller Neumark-Nord 2 basin was similar in principle to that of the larger basin, but with a few exceptions it was small and disarticulated. A large number of flint artifacts of Middle Palaeolithic humans were discovered in the shore areas of both basins. humans have been discovered. There is still no agreement on the age position. According to various pollen analyses, the Warm Period sediments of the two basins show a succession typical of the Eemian Warm Period (128,000 to 115,000 years ago) typical succession. For the Neumark-Nord 2 basin, an Eemian classification is supported by further analyses, such as paleomagnetics and radiometric age dating. In contrast, the interglacial sediments of the Neumark-Nord 1 basin could also have been deposited during an "intrasaalean" interglacial period. This is indicated by the botanical remains, such as the macroflora with the extremely rich relicts of a steppe-oak-mixed forest characterized by the Tatar maple, or individual fossils of small mammals, including the dwarf forest mouse Apodemus maastrichtensis. The ostracod fauna as well as other findings do not suggest an Eneolithic age.