This is Mazon Monday post #294.  What’s your favorite Mazon Creek fossil?  Tell us at email:esconi.info@gmail.com.

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Montceau-les-Mines is a commune located in the Saône-et-Loire department of the Bourgogne–Franche-Comté region in eastern France. It lies southwest of the city of Dijon and today has a population of just under 20,000 people. The town was officially established on June 24, 1856, from territory taken from several nearby villages — Blanzy, Saint-Vallier, Saint-Berain-sous-Sanvignes, and Sanvignes-les-Mines.

Like many communities with “-les-Mines” in their name, Montceau’s history is closely tied to coal. The first coal deposits were discovered in the area during the 16th century, leading to the formation of a small settlement known as “Le Montceau.” Coal mining brought growth and prosperity, especially in the 19th and early 20th centuries. At its peak during World War I, the mines produced nearly 2.8 million tons of coal each year. Production slowly declined through the 20th century. The last mines closed in 1992, marking the end of an era for this once-bustling industrial area. More information about the history of the area can be found on the Creusot Montceau tourism site.

Some 303-305 million years ago, during the Carboniferous Period, Central France was located near the equator. The landscape was hilly and covered with giant ferns and other familiar Carboniferous plants. The lowlands were shaped by rivers, lakes, and lagoons. These lowland areas were populated by millipedes, scorpions, spiders, and salamander amphibians and reptiles. The waterways were a place where ancestral sharks and fish swam, while the riverbanks were populated by worms, crustaceans, and mollusks. Eventually, these plants and animals died and were preserved as fossils.

Fossil plants and animals from Montceau-les-Mines were first discovered in the 19th century. But it wasn’t until the late 1970s, during modern strip-mining operations, that the true extent of the fossil deposit was revealed. The deposit is recognized as one of the richest localities of the late 20th century. Recognizing its scientific importance, local amateur collectors joined forces with professional paleontologists to rescue fossils before they were lost to mining.

Working with the Museum of Natural History in Paris and the Natural History Museum in Autun, they recovered thousands of shale slabs and more than 120,000 siderite nodules. As they collected them, they carefully documented each specimen’s location. This was one of the first times such precise modern collecting techniques were applied to deposits of this age. Although the mine has since been closed and recovered, researchers continue to study the enormous collection. Only a portion of the nodules have been opened so far, with nearly a quarter of those revealing beautifully preserved fossil. The fossils range from plant remains to delicate animal forms such as insect nymphs, soft-bodied worms, and early tetrapods.

To date, scientists have identified around 300 species of plants and pollen and 16 classes of animals representing about 30 genera. These fossils capture a critical transition in Earth’s history, from the humid, tropical world of the late Carboniferous to the drier, more temperate conditions of the early Permian, preserving a vivid record of life as climates and ecosystems changed.

Preservation is similar to the Mazon Creek fossil deposit with shale impressions and siderite nodules. Montceau-les-Mines is listed in the references of the 1985 paper “Mazon Creek-Type Fossil Assemblages in the U.S. Midcontinent Pennsylvanian: Their Recurrent Character and Palaeoenvironmental Significance [and Discussion]” by Gordon Baird, Steven Sroka, Charles Shabica, et al.

The September 1988 edition of the popular science magazine Scientific American had an article “The Fossils of Montceau-les-Mines” by Daniel Heyler and Cecile Poplin. They tell a good bit about the discovery, rescue and the importance of the fossils found there. Most of the story above came from that article.

A more recent (2013) survey of the site is a paper written by Vincent Perrier and Sylvain Carbonnier, “The Montceau-les-Mines Lagerstatte (Late Carboniferous, France)”.

“The Montceau-les-Mines Lagerstatte (Late Carboniferous, France)”

Abstract

The Montceau-les-Mines Lagerstätte (Late Stephanian, Late Carboniferous) is located northeast of the French Massif Central. Situated at equatorial latitudes during the Pennsylvanian, this Lagerstätte, probably a freshwater environment, preserves a rich and diverse flora (lycopsids, sphenopsids, ferns, pteridosperms, and cordaites) and fauna (bivalves, annelids, crustaceans, myriapods, insects, chelicerates, myxinoids, actinopterygians, sarcopterygians and tetrapods). These exceptionally preserved fossils can be found either flattened in shales or three- dimensionally preserved in sideritic nodules. The fossils from the nodules are exceptional for at least two reasons: the absence of major disarticulation of their body structure and the preservation of soft parts and extremely fragile cuticular structures. Such preservation was made possible by the combination of several factors: rapid burial in fine anoxic mud, early siderite precipitation (inducing the nodule formation) and phosphatization of cuticles and soft-bodied features.

The nodule-rich beds

The approximately 120,000 sideritic nodules that were collected during successive field seasons (Sotty, 1980) from three opencast mines (Saint-Louis, Saint-François, and Sainte-Hélène) come from clayey siltstones and silty claystones that occur a few meters above the First Seam of the Assise de Montceau (Fig. 1, Fig. 2). Nodule-bearing horizons are typically bounded by thin iron carbonate layers. The fossiliferous nodule-containing layers were numbered as they were discovered, from 0 to +5 and 0 to –12, layer 0 being the first layer discovered and the richest in nodules (Fig. 2). The majority of the nodules were collected from layer 0 and layer +2 of the Saint-Louis opencast mine (Chabard and Poplin, 1999, Pacaud and Sotty, 1994). The series of nodule-rich layers is demarcated at its base and top by thick sandstone units. Two fish-rich horizons also occur within the succession and allowed correlations between the three opencast mines (see Charbonnier et al., 2008, fig. 2). After mining operations closed down in the beginning of the 1990s, the opencast mines were banked up or flooded, making the nodule horizons inaccessible.

The Montceau Lagerstätte

The Montceau Lagerstätte was situated at equatorial latitudes during deposition (Cocks and Torsvik, 2011), allowing the development of a luxuriant vegetation, as demonstrated by abundant compression floras composed of lycopsids, sphenopsids, ferns, pteridosperms, and cordaites (see Section 4 and Fig. 3). Hygrophytic terrestrial plants flourished along the banks of water bodies, some of which being deep rooted in water, whereas more mesoxerophilic plants grew on the hills of the intermontane basin (Langiaux, 1994). A variety of freshwater habitats were occupied by a rich and diverse fauna. Major animal groups that have been identified include freshwater bivalves, annelids, crustaceans, myriapods, insects, spiders, merostomes, myxinoids, actinopterygian fishes, sarcopterygian fishes and tetrapods (see Section 5 and Fig. 4). The remarkable preservation of the fauna makes the Montceau-les-Mines Lagerstätte a major source of information for the reconstruction of Pennsylvanian freshwater biotas (Heyler, 1981, Heyler and Poplin, 1988, Poplin, 1994a, Rolfe et al., 1982).

Conclusion

The Montceau-les-Mines Lagerstätte (Late Stephanian, Late Carboniferous, France) was located at equatorial latitudes and probably represents freshwater environments.

The Lagerstätte displays a rich and diverse flora (lycopsids, sphenopsids, ferns, pteridosperms and cordaites) and fauna (bivalves, annelids, crustaceans, myriapods, insects, chelicerates, myxinoids, actinopterygians, sarcopterygians and tetrapods).

The exceptionally preserved fossils found in nodules exhibit a high degree of structural articulation and the 3D-preservation of soft parts, as well as extremely fragile cuticular structures.

This preservation was made possible by the combination of several factors: rapid burial in fine anoxic mud, early siderite precipitation inducing the nodule formation, and  phosphatization of cuticules and soft-bodied features.

The fossil plates from the paper show many familiar Mazon Creek fossils with similar names.

We’ll do a followup post about this location with some comparisons between it and the Mazon Creek deposit in the near future.