Montagne Noire Research Articles

Plastic deformation and trace element mobility in sphalerite

Abstract Sphalerite (ZnS) is a sulfide found in a large variety of ore deposits and is frequently hosted in meta-morphic terranes that have undergone deformation and related recrystallization. However, the deformation mechanisms of sphalerite are still poorly understood because recrystallization evidence is barely visible under an optical microscope and may reflect complex and frequently multistage mechanisms. Furthermore, sphalerite may host up to a few thousands of parts per million of critical metals such as gallium (Ga), germanium (Ge), and indium (In). Metamorphic conditions and dynamic recrystallization may have induced local or total redistribution of these elements. Modern techniques such as electron backscattered diffraction analyses (EBSD) and laser-induced breakdown spectroscopy (LIBS) applied on sphalerite allow for the examination of grain boundaries, crystal-plastic deformation, and internal chemical diffusion, which classically reflect active deformation mechanisms. In this study, a microstructural and in situ chemical comparison between four sphalerite types (types 1, 2, 3, and 4) has been made for the first time. The four sphalerite types present different deformation imprints, although they are hosted in a similar geological setting: the Pyrenean Axial Zone and the Montagne Noire Variscan massifs (France). Based on EBSD and LIBS mapping, we describe two regional sphalerite growth stages composed of dark red crystals with polygonal shape (type 1, Bentaillou-Liat deposit) and light- to dark-brown euhedral crystals (type 3, Saint Salvy deposit). New investigation at microscale on sphalerite grains from the Saint-Salvy deposit shows late Cu-Ge-Ga enrichment not only in specific sector zonings but also along grain boundaries, growing crystal edges, and in low-angle misorientations or twin boundaries. Following a deformation event that probably occurred during the Pyrenean-Alpine orogeny, these two sphalerite mineralizations have both endured plastic deformation in a dislocation creep regime and dynamically recovered by subgrain rotation (SGR) mechanism. Two mechanisms of Cu-Ga-Ge spatial redistribution are observed and are key processes for the crystallization of Cu-Ga-Ge-rich minerals in sphalerite veins. The first mechanism involved the in situ redistribution of Cu-Ga-Ge contents from a pre-existing concentration in the sphalerite lattice (type 3, Arre deposit), creating Ge-sulfides (briartite), probably during Pyrenean-Alpine orogeny. Formation of this type of Ge-mineral may be related to solid-state diffusion processes. The second mechanism is associated with the circulation of a Cu-Ga-Ge-rich fluid in surrounding rocks. In the pre-existing polygonal sphalerite from Late-Variscan veins (type 2, Pale Bidau deposit), millimeter-size bands of small (<50 µm), recrystallized sphalerite grains are locally observed. Those domains contain inclusions of Cu (chalcopyrite) and Ga and Ge minerals (brunogeierite, carboirite). Fluid-induced diffusion in the polygonal sphalerite aggregates may occur with superimposed dynamic recrystallization, such as the Late-Variscan veins (type 2, Pale Bidau-type). During post-Variscan time, this fluid enriched in Cu-Ga-Ge largely circulated in the upper-crust of this Variscan terrane. This study highlights the key importance of coupled textural (EBSD) and in situ chemical analyses (LIBS) of diverse sphalerite types at a regional scale to indirectly unravel the origin of vein mineralization, and their related critical metal distribution.

The brachiopod faunas from the Fezouata Shale (Lower Ordovician; Tremadocian–Floian) of the Zagora area, Anti‐Atlas, Morocco: evidence for a biodiversity hub in Gondwana

AbstractSince the early 2000s, the discovery of fossils and their collection from the Fezouata Shale has accelerated; enabling us to understand the faunas more thoroughly. The brachiopod fauna has not been investigated for the past 50 years, and we present here the results of our recent studies. From the material (c. 350 samples), 30 species were identified and assigned to 23 genera. Among these, one new genus (Tinzoulinorthis) and four new species (Wosekella maghribi, Rafanoglossa inversa, Orbithele tazagurta, Lacunites punctum) are erected; one taxon is recognized at the family level. The fauna described from the upper Tremadocian horizons is more diverse than those in the Floian. The former is characterized by a high γ‐diversity, although at the horizon level the α‐diversity is low to medium. This fauna is typical of high‐energy, shallow‐water, unstable environmental conditions, in which long‐lived communities were prevented from developing into climax communities, and the succession of opportunists were regularly smothered in situ and killed by storm deposits. Multivariate analyses of the faunas indicate that the Tremadocian fauna, characterized by many endemic taxa, has closer affinities with faunas from peri‐Gondwanan terranes, in particular Bohemia. The Tremadocian Fezouata fauna is very rich in taxon first occurrences, which, coupled with a high γ‐diversity, suggest that it may have been a diversity hub. In contrast, the Floian Fezouata fauna not only shows stronger connections with Bohemia and the Montagne Noire, it also has links with the South Urals and Baltica, reflecting the changing Early Ordovician palaeogeography.

The Cabrières Biota (France) provides insights into Ordovician polar ecosystems

Early Palaeozoic sites with soft-tissue preservation are predominantly found in Cambrian rocks and tend to capture past tropical and temperate ecosystems. In this study, we describe the diversity and preservation of the Cabrières Biota, a newly discovered Early Ordovician Lagerstätte from Montagne Noire, southern France. The Cabrières Biota showcases a diverse polar assemblage of both biomineralized and soft-bodied organisms predominantly preserved in iron oxides. Echinoderms are extremely scarce, while sponges and algae are abundantly represented. Non-biomineralized arthropod fragments are also preserved, along with faunal elements reminiscent of Cambrian Burgess Shale-type ecosystems, such as armoured lobopodians. The taxonomic diversity observed in the Cabrières Biota mixes Early Ordovician Lagerstätten taxa with Cambrian forms. By potentially being the closest Lagerstätte to the South Pole, the Cabrières Biota probably served as a biotic refuge amid the high-water temperatures of the Early Ordovician, and shows comparable ecological structuring to modern polar communities.

Terreneuvian skeletonized microfossils from the Central Iberian Zone (Spain) and correlation of the Fortunian Stage throughout southwestern Europe

During the Ediacaran–Cambrian boundary interval, the Iberian margin of West Gondwana recorded oceanic upwelling and phosphogenesis favouring the preservation of originally phosphatic and diagenetically phosphatized shells. In the Abenójar Dome and the Alcudia Anticline of the Central Iberian Zone, the Fuentepizarra Formation comprises several phosphorite and phosphatic limestone interbeds that yield a microfossil assemblage rich in the helcionellid Anabarella plana, the halkieriid Halkieria sacciformis, the hyolith Conotheca subcurvata and chancelloriid debris. The assemblage is correlatable with the Purella antiqua Zone of the Aldan-Lena region and the Purella cristata Zone of the Anabar Uplift (Siberian Platform), slightly predating the Watsonella Zone of the Siberian Platform and the Watsonella crosbyi–Oelandiella korobkovi Zone of the northern Montagne Noire (France), both close to the (not yet globally defined) base of Cambrian Age 2. Despite the intra-Terreneuvian collapse of the Cadomian Orogen, stratigraphically associated with the onset of diachronous gaps, the base and top of the Fortunian Stage is well constrained throughout southwestern Europe based on radiometric ages and the micro- and ichnofossil record.

Shape diversity in conodont elements, a quantitative study using 3D topography

The flourishment of conodont diversity through the Paleozoic is evidenced by the strong diversification of the shape of the elements composing their feeding apparatus. Among the different elements that compose the feeding apparatus, the platform elements (P1) are the most robust. However, the P1 elements also represent the most posterior dental elements of the apparatus, performing therefore the ultimate stage of food processing before ingestion of the food bowl. Thus, characterizing the shape of these elements across various species of conodonts could be relevant to decipher the diversity of feeding behavior among this group. Here we use topographic indices initially developed for the description of teeth relief (RFI, Slope), orientation (OPCr) and sharpness (ARC, DNE) to discriminate quantitatively P1 element shapes among conodont communities of the Late Famennian from the Montagne Noire Area (south France). We evidence methodological considerations such as voxel size impact on topographic indices that should be imperatively considered before conducing these methods on conodonts. Under several homogeneous conditions, this quantification of shape diversity, even on poorly damaged specimens, could bring new clues for the understanding of P1 elements kinematics and feeding strategies among conodonts.

Lower Ordovician Trilobites from SE Sardinia (Italy): A new record of the “Taihungshania bioprovince”

A systematic description of the so far unique trilobite fauna and the associated biota from the Arenarie di San Vito Formation, in the outcrops close to the abandoned Tacconis mine (allochthonous nappe zone, Sarrabus, SE Sardinia, Italy), proves the occurrence of Taihungshania shui landayranensis, Ampyx priscus, Asaphellus sp., Merlinia sp., Niobe fourneti?, Geragnostus sp. and Symphysurus sp., accompanied by several taxa of graptolites, ichnofossils and less common bivalves, gastropods, cephalopods and hyolithids. The taphonomical signature, sedimentary structures and “Raphiophorid biofacies” clearly argue for an early Floian age and a median platform (i.e., offshore to shoreface) depositional environment. The occurrence of T. shui landayranensis in Sardinia allows us to determine the age of the Arenarie di San Vito Formation (just below the Sarrabese unconformity) and to discuss the palaeobiogeographical affinities highlighting the value of the “Taihungshania bioprovince”. The Tacconis trilobite fauna displays close affinities with Montagne Noire in France, Taurides in Turkey, Alborz in Iran, and south China, placing the SE Sardinia allochthonous area in a global Ordovician palaeogeographic sketch. A brief discussion on relationships and palaeobiogeographical affinities between the Sardinian nappe zone and the autochthonous “foreland” Sulcis-Iglesiente, which are adjacent today, strongly suggests a separation during the Ordovician, although both areas pertain to the Gondwana margin.

Weak and intermittent anoxia during the mid-Tournaisian (Mississippian) anoxic event in the Montagne Noire, France

AbstractThe mid-Tournaisian black radiolarian cherts of the Lydiennes Formation are exposed in deep-shelf successions of the Puech de la Suque and Col des Tribes sections of the Mont Peyroux Nappe area in the Montagne Noire, southern France. This interval represents the mid-Tournaisian anoxic event that is also termed the Lower Alum Shale Event. This event is associated with a global marine transgression that was characterized by increased productivity and drastic facies changes from pelagic carbonate sedimentation to the widespread deposition of black organic-rich siliceous shales and radiolarites in many parts of the world. In the present study, high-resolution inorganic geochemistry and framboidal pyrite analyses were employed to decipher changes in depositional conditions during the mid-Tournaisian anoxic event in the Montagne Noire. The results show that the total organic carbon contents of sediments associated with the Lower Alum Shale Event vary from 0.09 to 1.9 wt %. These low to moderate total organic carbon contents, high U/Th, low Corg/P and intermediate V/Cr ratios, enrichment in redox-sensitive trace elements, such as U, Mo and V, as well as varying sizes of pyrite framboids, indicate periodic dysoxic to anoxic bottom-water conditions during deposition of the studied sediments. Anomalous Hg spikes (>500 ppb) are also reported in the mid-Tournaisian deep-water marine succession of the Montagne Noire in the present study, which confirm a possible influence of increased regional volcanic activity during this environmental turnover.

The Ordovician of France and neighbouring areas of Belgium and Germany

Abstract The Ordovician successions of France and neighbouring areas of Belgium and Germany are reviewed and correlated based on international chronostratigraphic and regional biostratigraphic charts. The same three megasequences related to the rift, drift and docking of Avalonia with Baltica can be tracked in Belgium and neighbouring areas (Brabant Massif and Ardenne inliers), western (Rhenish Massif) and northeastern Germany (Rügen). The remaining investigated areas were part of Gondwana in the Ordovician. The Armorican Massif shares with the Iberian Peninsula a Furongian–Early Ordovician gap (Toledanian or Norman gap), and a continuous Mid–Late Ordovician shelf sedimentation. The Occitan Domain (Montagne Noire and Mouthoumet massifs), eastern Pyrenees and northwestern Corsica share with southwestern Sardinia continuous shelf sedimentation in the Early Ordovician, and a Mid Ordovician ‘Sardic gap’. In the Ordovician, the Maures Massif probably belonged to the same Sardo-Occitan domain. The Vosges and Schwarzwald massifs display comparable, poorly preserved Ordovician successions, suggesting affinities with the Teplá-Barrandian and/or Moldanubian zones of Central Europe.

Le Sor en Montagne noire, histoire d’une source d’énergie hydraulique

Un débit raisonnable et un des plus réguliers du piémont de la Montagne noire sont à l’origine de l’installation de moulins hydrauliques sur la rivière Sor, plus précisément dans la vallée de Durfort, dans le Tarn. On trouve les premières mentions de moulins à grains ou bladiers et de moulins foulons ou drapiers au XIIIe siècle. Apparaissent au XVe siècle les premières moulines à métal ou martinets qui, aux XVIe et XVIIe siècles, remplacent et supplantent progressivement les moulins foulons. Ce n’est qu’à partir du début du XVIIe siècle que ces martinets se spécialisent dans le travail du cuivre, faisant la renommée de Durfort jusqu’à la fin du XXe siècle. Il faut ajouter à tout cela quelques scies hydrauliques ou ressègues et de rares clouteries. Cette industrie hydraulique constitue un cas particulier dans l’histoire économique du Lauragais par l’exceptionnelle densité de ses usines.La documentation historique, vérifiée et complétée par des prospections sur le terrain, a permis de dresser une carte exhaustive de toutes ces usines, dans les limites de la vallée du Sor, et d’en établir un inventaire chronologique du XIIIe siècle à nos jours.

Solutan echinoderms from the Lower Ordovician of the Montagne Noire (France): new data and palaeobiogeographic implications

Solutan echinoderms from the Lower Ordovician of the Montagne Noire (France): new data and palaeobiogeographic implications

Orogenic eclogites record relative magnitude of deep crustal flow and extent of migmatite-eclogite interaction

In exhumed orogens, refractory mafic rocks have the potential to preserve a record of petrogenesis and high-pressure (H P ) metamorphism that is commonly obliterated in quartzofeldspathic rocks owing to re-equilibration at high-temperature, low-pressure (L P –H T ) conditions. In the Montagne Noire (France) migmatite dome, located in the foreland of the Variscan orogen, eclogite is exposed in both the core and margin of the dome. In this study, we combine in situ U Pb petrochronology and oxygen-isotope analyses of key eclogite phases to demonstrate that eclogites from the two distinct domains had different protoliths and source regions, traveled relatively variable distances in the deep crust, and differentially interacted with surrounding migmatite prior to exhumation. Dome-margin eclogite zircons are small (~40 μm) with well-preserved inherited cores and thin (<15 μm) rims, compared to larger (40–120 μm) neo- and recrystallized dome-core zircons with small relict cores and wide (15–30 μm) recrystallized rims. Protolith and H P metamorphism ages were determined using in situ zircon and rutile petrochronology (LASS-ICP-MS). Both eclogites formed in a continental setting; dome margin protolith zircon cores formed at 442.5 ± 3.4 Ma (steep HREE slope, no Eu-anomaly) whereas zircon cores of the dome-core eclogites yielded scattered dates suggesting protolith crystallization between ~500–400 Ma (steep HREE slope, pronounced Eu-anomaly). Both eclogites experienced H P metamorphism at c. 320–310 Ma in garnet-stable, plagioclase-absent conditions. Most analyzed rutile yielded dates of 307–304 Ma associated with cooling. The record of H P fluid conditions was determined by O-isotope (SIMS) analyses of garnet and zircon. Dome-margin zircon cores and rims have δ 18 O of ~8.2–8.5 ‰, indistinguishable within uncertainty, in isotopic equilibrium with isotopically unzoned garnet (δ 18 O ~ 8.0–8.2 ‰). In contrast, zircons in dome-core eclogites have systematically lower zircon-core δ 18 O values compared to their rims and neocrystallized grains, and zircon cores were in equilibrium with major-cation zoned garnet with respect to oxygen. The two dome-core eclogite samples yielded zircon and garnet δ 18 O values of ~8.6–9.5 ‰ and ~ 9.7–10.5 ‰. Based on these results and existing H P fabric data for these eclogites, we propose that (1) gabbro protoliths for the two eclogites were emplaced at different depths in a Cambro-Ordovician continental crustal package; and (2) dome-core eclogites interacted extensively with surrounding gneiss during burial and foreland-vergent crustal flow, whereas the dome-margin eclogite was sourced proximally to the dome-emplacement location and had minimal chemical interaction with surrounding gneiss. At least parts of the Montagne Noire migmatite dome were deeply sourced, but rocks exhumed in the core had a more extensive and protracted history of deep-crustal flow than deep-crustal rocks exhumed at the margin. • Eclogites in migmatite dome retain memory of deep crust history. • Zircon (re)crystallization extent reveals distinct eclogite source, flow paths. • Petrochronology and O-isotopes record migmatite-eclogite interaction at depth. • Integrated garnet, zircon datasets reveal protolith, peak, exhumation histories. • Domes may exhume crust laterally-sourced >100 s of km from emplacement location.

Shifts in the Ediacaran to Lower Ordovician sedimentary zircon provenances of Northwest Gondwana: the Pyrenean files

Detrital zircon grains from Cambrian–Lower Ordovician sandstones and quartzites sampled in the Pyrenees were dated by LA-ICPMS in order to assess their provenance sources. Resulting age distributions are compared to other available datasets from neighbouring margins, such as Morocco, the Iberian Peninsula, southern France and Sardinia. Kolmogorov-Smirnov (K-S) test and Crystallization Age-Depositional Age (CA-DA) diagrams were used to compare zircon populations estimating their possible correlation with the arc/rift/drift geodynamic evolution of the northwestern Gondwana margin. During Terreneuvian times, zircon populations allowed the distinction of i) a southwesternmost edge (Anti-Atlas-Ossa-Morena Rift) mostly influenced by Panafrican and Anti-Atlasian sources (ca. 0.63–0.54), ii) a northeasternmost edge (Sardinia) recording the influence of the Saharan Metacraton and the Arabian Nubian Shield, with an distinct Stenian–Tonian shift (ca. 1.25–0.85Ga) and iii) an intermediate palaeogeographic transect, where lies the Central-Iberian, West Asturian-Leonese and Cantabrian Zones, the Montagne Noire and the Pyrenees sharing similar populations and a chronologically progressive influence from Anti-Atlasian/Panafrican to Saharan Metacraton/Arabian Nubian Shield sources. This gradual modification in zircon percentage populations supports similar trends based on climatically sensitive indicators, biogeographic patterns of Cambrian Epoch 2 archaeocyathan and microfossil assemblages, and laterally correlatable episodes of carbonate production, all of them pointing to a Cambrian setting for the Pyrenean Basin between the Montagne Noire (Occitan Domain) and the Sardinian margins of NW Gondwana. The Terreneuvian zircon patterns recorded in the Pyrenees gradually evolved from Cambrian Epoch 2 to Early Ordovician times, reflecting the geodynamic evolution from Panafrican and Cadomian arc-related to rift-dominant conditions. During Furongian and Ordovician times, the relative percentage of zircon populations led to a more spread age curve, characteristic of extensional settings and pointing to rift (passive margin) conditions.

Gigantoproductid shell spiral and microstructure of tertiary layer: evaluation as taxonomical characters

ABSTRACTBrachiopod taxonomy is based on descriptions of shell morphology and key characters, but diagenesis generally modifies or erases some of them, hindering brachiopod identification. Brachiopods that are taxonomically related usually present shells with similar appearance but can differ in size (i.e., Rhynchonellata). Some aspects of morphology – for example the angular measurement of the curvature of the shell or details of shell microstructure – could aid taxonomic identification. Gigantoproductids, which lack a robust taxonomy, have the largest shells among brachiopods and are ideal for this kind of study because of their gigantic size and morphological variability. Furthermore, they have a great abundance and worldwide distribution during the mid-Carboniferous. More than 700 samples have been collected from Sierra Morena (Spain), Montagne Noire (France) and Adarouch (Morocco) identifying up to six gigantoproductid genera:Globosoproductus,Semiplanus, Kansuella?,Latiproductus,GigantoproductusandDatangia. Microstructural features from 170 thin sections belonging to gigantoproductid ventral valves have been studied, and six crystal morphologies have been distinguished within the tertiary layer: subhorizontal, imbricated, crenulated, acicular, short and long columnar morphologies. Moreover, 23 complete shells from all genera have been selected to investigate shell size and curvature. Results from this study emphasise that shell size, curvature and crystal shape are taxa-related. Finally, a remarkable morphological change in the gigantoproductid populations from the western Palaeo-Tethys occurred during the Viséan–Serpukhovian, from thin-shelled genera with subhorizontal morphology (Viséan) to thick-shelled genera with a tertiary layer consisting of long columnar crystals (Serpukhovian). This study proves that microstructure, maximum thickness and shell spiral characterisation are robust characters when applied to gigantoproductid taxonomy, but also have great potential in other brachiopod groups.

Improvement of growth performance through crossbreeding in the Pyrenean suckling lamb protected geographical indication

The production of Pyrenean suckling lambs is a way to contribute to the economic activity of the Pyrenees, the maintenance of sheep farmers, the preservation of the environment and the life of the region. In order to defend this product, it is necessary to re-evaluate precisely the interest of crossbreeding between local dairy breeds and local Pyrenean meat breeds, in terms of growth gain and weight at slaughter, but also of conformation and adaptation to the market. The trial compared purebred lambs (PB) and lambs crossed with beef breeds (SBCB) or with the Montagne Noire breed (MNCB).In accordance with feedback from the field, purebred lambs (PB) had lower growth performance (192.7 g/day vs 240 and 241 g/day in average) but also lighter slaughter weight (11.31 vs 12.43 and 13.5 kg) and carcass weight (6.42 vs 7.42 and 8.10 kg) than crossbred lambs (MNCB and SBCB respectively).Crossbreeding seems to affect fat color and especially the yellow index (b*): purebred lambs' fat is significantly less yellow than crossbred animals (p < 0.01). Crossbreeding also affects the color of muscles, the lambs crossed with Montagne Noire and purebred having lighter meat than lambs crossed with other breeds (p < 0.001).In our work, we found that purebred lambs were slightly tougher than Black Mountain crossbred lambs and significantly tougher than lambs from other crossbreeds (p < 0.05). This exploratory work thus provides the first characterizing elements of breeds and crosses that have been, until now, little treated in the literature.

Flow of the partially molten crust in the Variscan foreland revealed by U–Th–Pb dating of metamorphism, magmatism and deformation (Agly Massif, Eastern Pyrenees)

In this contribution, we investigate the spatial and temporal evolution of mid-crustal flow in the Agly Massif (North Pyrenean Zone) that represents the southern foreland of the Variscan orogenic plateau. In the Agly Massif, the middle crust is represented by an Ediacarian–Devonian series of metasedimentary rocks that recorded high-grade metamorphism synchronously with crustal thinning (D2) and dextral wrenching (D3) during Carboniferous. D2 crustal thinning formed a penetrative S2 flat-lying foliation and localized C2 extensional shear zones with a top-to-the-North kinematics. D2 planar fabrics are deformed by a D3 dextral transpression localized into a two-kilometer wide high-strain zone. We performed LA-ICPMS U–Th–Pb dating on zircon and monazite from small magmatic bodies and from metamorphic rocks showing strain features relative to D2 and/or D3. Our results, compiled with published data, argue that the middle crust of the Agly Massif reached high-temperature and suprasolidus conditions at ca. 325–320 Ma and was partially molten until ca. 300 Ma. They also indicate that the D2 thinning and top-to-the north shearing was active from ca. 325–290 Ma. D2 extension and D3 transpression were synchronous from ca. 308–290 Ma. Making a comparison with the Pyrenean Axial Zone, the Montagne Noire and the French Central Massif, we propose a two-step tectonic model for the mid-crustal flow with a horizontal flow towards South in both the orogenic plateau and the southern forelands between ca. 325 and 310 Ma and locally reoriented into an E–W longitudinal flow between 310 and 300 Ma in high-strain dextral strike-slip shearing domains.

Vice-versa: The iron trade in the western Roman Empire between Gaul and the Mediterranean.

Starting from the second century BC, with the fast expansion of the Roman Empire, iron production and consumption developed exponentially in north-western Europe. This rapid growth naturally led to an increase in trade, that still remains to be studied encompassing a broad scope, so as to not neglect long-distance exchanges. This is today possible by taking advantage of the progress made in the past 40 years in archaeology and archaeometallurgy. Cargoes of iron bars recovered from a group of 23 wrecks located off the coast of Saintes-Maries-de-la-Mer (Bouches-du-Rhône, France), opposite an old branch of the Rhône River, constitute a rich opportunity to examine this trade, by comparing the slag inclusions trapped in iron bars to primary slag from the six main ironmaking areas in Gaul. Based on a trace element analysis of these inclusions and this slag, we suggest that ships travelled down the Rhône carrying iron produced in Wallonia (Belgium), while others sailed up the Rhône transporting iron produced in Montagne Noire (Aude, France).

Contrasting Early Ordovician assembly patterns highlight the complex initial stages of the Ordovician Radiation

The Early Ordovician is a key interval for our understanding of the evolution of life on Earth as it lays at the transition between the Cambrian Explosion and the Ordovician Radiation and because the fossil record of the late Cambrian is scarce. In this study, assembly processes of Early Ordovician trilobite and echinoderm communities from the Central Anti-Atlas (Morocco), the Montagne Noire (France), and the Cordillera Oriental (Argentina) are explored. The results show that dispersal increased diachronically in trilobite communities during the Early Ordovician. Dispersal did not increase for echinoderms. Dispersal was most probably proximally triggered by the planktic revolution, the fall in seawater temperatures, changes in oceanic circulation, with an overall control by tectonic frameworks and phylogenetic constraints. The diachronous increase in dispersal within trilobite communities in the Early Ordovician highlights the complexity of ecosystem structuring during the early stages of the Ordovician Radiation. As Early Ordovician regional dispersal was followed by well-documented continental dispersal in the Middle/Late Ordovician, it is possible to consider that alongside a global increase in taxonomic richness, the Ordovician Radiation is also characterized by a gradual increase in dispersal.

Cambrian Age 3 small shelly fossils from the Terrades inlier, southern Pyrenees, Spain: Biostratigraphic and paleobiogeographic implications

AbstractThe Cambrian stratigraphic succession of the Pyrenees (SW Europe) has undergone a complex Variscan and Alpine tectonothermal history leading to marked metamorphism and development of cleavage networks, which might partly explain the lack of Cambrian fossiliferous beds. This gap has traditionally precluded its paleobiogeographic and biostratigraphic relationships with other neighboring peri-Gondwanan units. Correlations are only based on lithostratigraphic comparisons and radiometric constraints. In this general scheme, the Terrades inlier (Gerona Province, Spain) provides the only significant and indisputable ‘early Cambrian’ fossil record of the Pyrenees. This predominantly siliciclastic outcrop consists of multiple patch reefs and bioherms having yielded archeocyaths dated at Cambrian Epoch 2, Age 3. This paper describes, for the first time, the microfossil assemblage included in the archeocyathan-microbial reefal complex that crops out in the Terrades inlier to clarify its age and affinities with surrounding tectonostratigraphic units. Reefal flanks of patch reefs have yielded bradoriids, brachiopods, molluscs, tommotiids, chancelloriids, hyoliths, and the problematic fossil (and chronostratigraphically significant)Rhombocorniculum cancellatumCobbold, 1921. In addition to confirming the previously assigned age of the succession, the recovered fauna emphasizes strong affinities with the surrounding Occitan Domain (Montagne Noire, southern Massif Central, France) and Sardinia (Italy). Along with lithostratigraphic comparison and tectonic considerations, this further supports the recent reconstructions positioning the Pyrenean domain between the Montagne Noire (to the southwest) and Sardinia (further to the northeast) on the Gondwana margin during Cambrian times.

Vertebrate diversity reveals perturbations in faunal communities prior to the Hangenberg event in the Montagne Noire (France)

Vertebrate diversity reveals perturbations in faunal communities prior to the Hangenberg event in the Montagne Noire (France)

Phacopid trilobites in post-Taghanic Givetian through Frasnian cephalopod limestones, Montagne Noire (France) and related areas (Thuringia, Morocco)

Phacopid trilobites in post-Taghanic Givetian through Frasnian cephalopod limestones, Montagne Noire (France) and related areas (Thuringia, Morocco)