The Konservat-Lagerstätte Menat (French pronunciation: [məna]) is a Konservat-Lagerstätte located in France dating to the mid-late Paleocene. Though the fossiliferous beds of the sites have been known for a long time, with the first large study being published in 1940, Menat has had much less study than other similar deposits. Since the 1980s, a number of excavations have been done by various museums. However, due to the loss of the original sites, most of this is a result of multiple excavations done in the area. The fauna of the lagerstätte is largely made up of insects, but various vertebrates such as mammals, reptiles, and birds have been described from the sites. These fossil were preserved in what was a volcanic maar lake surrounded by a forest with evidence of common forest fires.
History
Before the area was known for the Konservat-Lagerstätte Menat, the area nearby was known for its diatomite quarries which were mined until 1873. After this point, a factory was built outside of the town to avoid intoxication associated with the fumes produced. A number of things were produced using this sediment including abrasives and pigments, and later dynamite. In 1940, Piton published a study of the fossils that laid the groundwork for others in the future. However, similar to other specimens, a large amount of the fossils he described would be lost in World War II with holotypes being found in a number of different collections today. By the 1950s, mining at the quarries concluded with the factory later closing in 1964. Even before the mine closed, various people were collecting fossils from the mines associated with the factory. Around this time, the main quarry (known as “Les Grelins”) was turned into a pond with another quarry (known as “La Mer”) was filled and overlain with a road. Even though the main quarry was turned into a pond, a number of fossil collectors would travel to the site to collect specimens. This happened so often that in 1979, municipal council prohibited the collection of fossils to protect the site with a local museum being created soon after. During the 1980s, some excavations of the main site were done by the Muséum National d’Histoire Naturelle though this would not last very long. In 1988, the site became a Regional Natural Reserve with no excavations happening at “Les Grelins” since then. In the late 1990s and early 2000s, the paleontological association Rhinopolis began more work at the quarry. During this time, the group also opened a new site known as “Maison de retraite”. In 2009, the village worked with Paléovergne to preserve the paleontological heritage of the area. By 2010, “Maison de retraite” was closed to open a retirement home and a new site known as “Les Lavandes” was opened in 2011. In 2012, a test pit titled "Menat 1" was opened with the main purpose of studying the stratigraphy of the site with another test site known as "Menat 2" being opened in 2013. The most recent site to be excavated is the "Stream site" in 2014 which has much better preservation than the two test pits.
Geology The Konservat-Lagerstätte Menat is known from three more recently excavated sites which are the main source of more recent geological descriptions. The more well-known and oldest bed, referred to as "Menat 1", is located on the eastern region of the maar lake which was preserved at the site. Menat 1 has a total thickness of 5.82 metres (19.1 ft) and is made up of nine greyish to white silicified claystone beds which range in thickness from 3–20 centimetres (1.2–7.9 in). The upper clay beds are weathered at the top. Fossils are still present in these beds, but the preservation is worse than in the silicified beds. During excavations that took place in 2013 and 2014, a second site referred to as "Menat 2" was first worked on. This site is located near the eastern entrance to the village of Menat and has a thickness of 6 metres (20 ft). Similar to the first site, the upper clay beds were weathered, but the clay differs more throughout the site. Based on the differences in lithology under these weather beds, Menat 2 has been split into three intervals being A,B, and C.
The third site, known as the "Steam Site", was first referenced in the literature in 2018 and has been noted to have better preservation than the other two sites. The beds that make up the site consist of dark, organic clays and is suggested to be correlated to the “Les Grelins” and “La Mer” quarries. Both charcoal and soot have been found at every horizon of Menat. Fossils found at these sites are preserved on what has been labeled as spongo-diatomites. However, a more recent study that looked into the composition of these layers found no evidence of diatom sclerites or sponge spicules being present.
Dating The original dated of Menat was the mid to late Paleocene, with this being based on the presence of a fossil primate. Later palynological studies have suggested either a Thanetian or Selandian age. However, the more recent dating based on basalts and tuffs near Menat gave an "average age" of the Thanetian-Ypresian boundary. This age has been referenced as the age of the fossil maar lake itself though this has faced criticism due to the lack of correlation between the lake deposits and the sediments being dated. The most recent papers referencing the date of the site place the age as 59 mya based on pollen. In contrast to this however, macrofloral fossils suggest a slightly older age of 60-61 mya.
Paleoenvironment Konservat-Lagerstätte Menat represents a volcanic maar lake that has been estimated as measuring 1 kilometre (0.62 mi) in diameter. Based on the algae found at the sites, there would have been no inflow from rivers with there seemingly only being a few shallower areas on the coasts. Outside of these small areas around the margins, it is most likely the maar lake would have been relatively deep. This lake would have been surrounded by a largely deciduous forest, climate in the area would have been temperate to subtropical with cool winters being present. Though humid, the amount of charcoal and soot found at Menat suggests that forest fires would happen often in the surrounding forest. Based on the amount of insect trace fossils found on leaf fossils, the ecosystem was already healthy, even with it being only a few million years after the mass extinction event. This suggests that regions further away from the asteroid impact recovered faster than those in regions like North America.
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