The Cabrières Biota () is in part a Konservat-Lagerstätte (a fossil site noted for its exceptional preservation of fossils) located near Cabrières village in Hérault, southern France. It preserves a diverse biota dating back to the Floian stage of the early Ordovician. It is part of the Landeyran Formation. Exceptional soft-tissue preservation is known from this Lagerstätte. The biota inhabited a wave-influenced delta environment. Exceptional preservation occurs in the deeper prodeltaic (the offshore zone in front of the delta) waters.
History The area around Cabrières was recognized as an important region for its Paleozoic geologic interest in France by the Société Géologique de France after a field excursion in Hérault in 1868. The participants of this excursion discovered abundant trilobite fossils and noted the large number of horizons accumulated within a narrow space in the Pic de Vissou. The area around Cabrières became a reference for the Paleozoic in France. Furthermore, the presence of Armorican sandstones was also reported near Cabrières. By the end of the nineteenth century, debates arose about the stratigraphy of the area. Some authors suggested that the Armorican beds represented the transition between the Cambrian and the "Silurian" (strata now placed within the Ordovician were formerly categorized as being Silurian). However, other works contested this. They argued that the beds lay above strata accepted as belonging to the Arenig (equivalent to the Floian) and so, that they had to be younger. Later authors realized why the stratigraphy of Cabrières was so complex. They found the strata within the Pic de Vissou were overturned and deformed by tectonic activity. Upon realization, a more accurate stratigraphic series could be established, and strata from the Cabrières region were assigned to the Arenig.
From the 1930s to the mid-20th century, the natural sciences teacher Marcel Thoral published several works on the geology and paleontology of the Montagne Noire, including Cabrières. In the second half of the 20th century and the beginning of the 21st century, detailed studies of the fossils of the Landeyran Formation were published, including those of Dean (1966), Courtessole et al. (1981 and 1991),Courtessole, R., Pillet, J., & Vizcaïno, D. (1981). Nouvelles données sur la biostratigraphie de l'ordovicien inférieur de la Montagne Noire: révision des Taihungshaniidae, de Megistaspis (Ekeraspis) et d'Asaphopsoides (Trilobites). Société des Etudes Scientifiques de l'Aude. Babin et al. (1982),Babin, C. (1982). Brachiopodes (articules) et mollusques (bivalves, rostroconches, monoplacophores, gastropodes) de l'ordovicien inferieur (tremadocien-Arenigien) de la Montagne Noire (France Meridionale). na. Vizcaïno & Lefebvre (1999) and Vizcaïno et al. (2001).
The site that would become known as the Cabrières Biota was discovered by Eric and Sylvie Monceret in 2018, after fieldwork in the area. Farid Saleh and Betrand Lefebvre were subsequently invited to the site to assist in specimen collection and identification. Over the next 3 years the team continued to do fieldwork on the site. Saleh et al., published the initial description of the biota in 2024. A reply paper by Muir & Botting later that year cast doubt on the identification of the biota as a Konservat-Lagerstätte, instead stating that the proposed non-arthropods represented trace fossils filled with fecal material. An additional reply to Muir & Bottling from the original authors refuted their claim and reaffirmed that the fossils preserved represented a soft-tissue Lagerstätte. In the same year, in his revision of the evolutionary origins of hemichordates, Jörg Maletz considered that the supposed specimen of the enteropneust tube Margaretia and some remains attributed to sponges from Cabrières were actually trace fossils. In 2026, further fossils were described which provided additional information on the diversity and environment of the site, while acknowledging that some of the specimens in the original paper were misidentified. Saleh and colleagues also argued that the term "Cabrières Biota" be expanded from that found in Saleh et al., (2024) to not only include the Lagerstätte site, but also other sites that are stratigraphically equivalent within the lower Landeyran Formation. Three other major sites beyond the Lagerstätte were attributed to the biota: The Landeyran River, Abandoned Vineyard, and Road Cut sites, all of which are near the Landeyran River between the towns of Causses-et-Veyran and St-Nazaire-de-Ladarez within the Mont Peyroux unit.
Geology The soft tissue preservation of the Cabrières Biota occurs within a interval above the base of the Landeyran Formation, which overlies the older Foulon Formation. The Landeyran Formation is the uppermost geological formation of the early Ordovician sequence of southern Montagne Noire. It is a thick formation composed mainly of mudstone with siliceous nodules. The Cabrières Biota can be assigned to the Apatokephalus incisus trilobite biozone and the Baltograptus minutus graptolite biozone, which indicate an early late Floian age for the site.
Fossil preservation
The fossils are brown, red, or orange, and are embedded within mudstone and siltstone. Scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analyses have shown that the fossils are composed of dense iron oxide crystals. Synchrotron-based investigations of the chemical speciation of iron further found that the iron was in the form of Fe(III). Furthermore, carbonized black films were also reported. Subsequent research on the sponge, algal, and vermiform organisms has shown a variety of different preservational modes within the Lagerstätte. Fossilized organisms all contain iron oxide minerals, which is similar to what Saleh et al. (2024) found. Additionally, a limited number of fossils also showed partial carbonization and silicification (replacement of soft tissues with carbon and silicon respectively). The morphology of some minerals suggests that the iron oxides might have been a result of early diagenetic pyrite precipitation, where organic matter was replaced by pyrite crystals. Pyritization of soft tissue fossils occurs with the reaction of sulfide and iron. During the decay of the soft tissues, before burial, hydrogen sulfide is produced by sulfate-reducing bacteria, which combines with Fe(II) ions made by iron-reducing bacteria to form monosulfides, which eventually crystalize into pyrite. The pyritization is incomplete in some fossils, which may be due to an insufficient supply of iron within the depositional environment. Pyritization is the principal mode of preservation in several Lagerstätten, such as Chengjiang, the Fezouata Formation and the Beecher's Trilobite Bed. The presence of partially silicified an carbonized fossils in addition to pyritized ones suggests a complex diagenetic process, where different material replaced the soft tissue due to changing conditions within the environment, such as a change in redox conditions.
Paleoenvironment
Paleolatitude During the Floian, the Montagne Noire was located near the south pole. Of the other Early Ordovician polar biotas, such as the Fezouata Formation in Morocco, and the Klabava Formation from the Czech Republic, the Cabrières Biota was possibly the closest to the south pole during deposition. Saleh et al., (2024) hypothesized that during the Early Ordovician, polar sites represented a refuge from higher sea temperatures found within the lower latitudes. Furthermore, due to the diversity of fauna found within the Cabrières Biota that favorable oceanic currents could have influenced groups of organisms to migrate pole-ward.
The Cabrières Biota is dominated by algae and sponges, which is very similar to the make up of some modern polar ecosystems. The sponges in the biota specifically were noted as being able to grow to large sizes, which is similar to sponges in modern polar ecosystems. Saleh and colleagues said that while sponges also thrive in hypoxic environments, the diversity of other organisms preserved indicates that hypoxic conditions for the biota is unlikely. The diversity of arthropod remains at the site, however, is more comparable with that of more temperate environments, specifically being compared to the subarctic and low-arctic. The echinoderms present at the site is harder to interpret. Saleh and others said that while echinoderm diversity is lower in polar regions in modern ecosystems, places within polar settings can still show large numbers of them. So the relative low proportion of echinoderms is consistent with polar regions, however other factors, such as the relatively high diversity of echinoderms found elsewhere within the Montagne Noire. They hypothesize that due to the higher diversity of animals present within the biota, echinoderms faced more competition and were less likely to dominate the ecosystem, while other sites within the region were less diverse and therefore allowed for echinoderms to colonize in large numbers. Similar evidence was reported from the Fezouata formation, where echinoderms can be found regularly within certain layers where other animals were less diverse. Finally, the Cabrières Biota was noted as containing no bryozoans; notably, bryozoans are more commonly found within tropical and temperate waters. This lack of bryozoans does distinguish the biota from the nearby Klabava Formation, which while also being a high latitude environment, does contain bryozoans.
Depositional environment
In 2026, Vaucher and colleagues further investigated the depositional environment of the larger sequence within the Mont Peyroux unit, since the Pic de Vissou unit, which contains the Cabrières Biota, was harder to collect data from due to extensive foliage cover. The studied section contains the Cluse de l'Orb, Foulon, and Landeyran Formations, which allowed for a broader understanding of the environmental context of the biota itself. They found 8 distinct sedimentary facies in the site (F1-F8), which were grouped into two broad assemblages, distal shallow marine facies (F1-F5), and proximal shallow marine facies (F6-F8). They defined distal facies as occurring below the mean storm wave base, while proximal, or "coastal" facies occurred above the mean storm wave base.
Distal shallow marine facies F1 and F2 consist primarily of mudstones, indicating settling of mud and silt from suspension. F2 shows lenticular bedding, which indicates that the section was impacted by low density turbidity currents. Due to these factors, the authors hypothesized that F1 was a shallow shelf environment not affected by the delta, while F2 represented the edge of the prodelta, where storms would rarely transport sand into the deposit. F3 and F4 contain more siltstones, but also have a higher concentration of sandstone. For F3, the authors noted that the amount was consisting with the edges of areas impacted by river deposition, or possibly storm conditions. F4, indicated an environment closer to the source of the delta, with a lower amount of density currents. F5 alternates between siltstone and sandstone. Unlike F4, which was dominated by river deposition, F5 was more indicative of a deposit influenced by storms near shore without deltaic influence, containing finely laminated siltstones and sandstones with evidence of scouring. The authors note that F3-F5 were deposited at roughly the same elevation, with the differences shown being more indicative of the relation to the prodelta rather than depth.
Proximal shallow marine facies