A new sediment core from the Bedoulian (Lower Aptian) stratotype at Roquefort-La Bédoule,SE France

New drill cores from the Lower Aptian historical stratotype at Roquefort-La Bédoule (SE France) provide continuous high-resolution geochemical and isotope records which closely track the onset of OAE 1a in a subtropical intra-shelf basin (South Provençal Basin). The drilling operation recovered a total of 180 m of undisturbed sediments in three holes. The lowermost 67 m correspond to the Bedoulian (core LB1) and are here analyzed in high-resolution using geochemical proxies (stable carbon isotopes, stable oxygen isotopes, and carbonate content) and foraminiferal biostratigraphy. Pervasive bioturbation through core LB1 suggests mostly oxygenated bottom water conditions with transient dysoxic episodes, as shown by higher pyrite and glauconite concentrations within the marlstones. Unprecedented resolution over the negative δ¹³C excursion preceding OAE 1a (segment C3) reveals a characteristic double trough extending over ∼5.5 m in core LB1. This long-lasting negative excursion was possibly linked to multiple pulses of enhanced CO₂ release to the atmosphere. Estimated sedimentation rates of 1.6–2 cm/kyr indicate that the negative δ¹³C excursion lasted >200 kyr, while the main positive carbon isotope shift (segment C4) had a duration of >300 kyr. Fluctuations in δ¹⁸O suggest transient episodes of climate warming and cooling at the northern margin of the Tethys or even on a more global scale prior to the onset of OAE 1a.     

New cranial remains of titanosaurian sauropod dinosaurs from the Late Cretaceous of Fox-Amphoux-Métisson (Var,SE France)

The Fox-Amphoux Syncline of the Aix Basin (SE France) has yielded a diverse Late Cretaceous vertebrate assemblage, including several taxa of dinosaurs. Here, we report on cranial material of titanosaurian sauropods, which consist of a partial braincase, two fragmentary skull roofs, and nine teeth, from the Métisson locality (Var Department). The braincase differs from those found previously in Europe (i.e., Ampelosaurus atacis, Lirainosaurus astibiae, and an unnamed juvenile skull from Romania) as well as from other titanosaurian braincases in having a groove that extends along the ventral surface of the occipital condyle neck (this feature may be autapomorphic). One of the fragmentary skull roofs may belong to the same taxon, whereas the other suggests the presence of a second titanosaur at Métisson very close to Ampelosaurus. Two dental morphologies are present in the sample; one of them includes teeth of different sizes. We suggest that this could be accounted for by age differences within a single taxon, or be due to different positions in the tooth row. The presence of a new, still unnamed titanosaurian taxon in the Ibero-Armorican Island supports previous works indicating a high titanosaurian diversity during the Campanian-Maastrichtian in southern Europe.     

High-resolution sequence stratigraphy of the Lower Triassic ‘Buntsandstein’ in the Netherlands and northwestern Germany

Detailed log correlations of the largely fluvio-lacustrine Lower Triassic Buntsandstein (Late Permian-Early Anisian), carried out on 80 wells in the Dutch onshore and offshore areas, can be linked to northwest-German high-resolution sequence stratigraphy. The correlations show that cyclic sedimentation occurred in large parts of the basin. Seven 1st-order sequences are recognised, namely the Main Claystone, Rogenstein, Volpriehausen, Detfurth, Hardegsen, Solling and Lower Röt Sequences. They are overlain by the lower part of the Upper Röt–Lower Muschelkalk Sequence. Distinct sequence boundaries have been identified at the bases of four sequences: Volpriehausen, Detfurth, Solling and Upper Röt. The higher-order sequences consist of fining-upwards cycles with a thickness of up to tens of metres. The sequences are laterally persistent and have a characteristic expression on gamma-ray and sonic logs. In the Lower Buntsandstein, they display a uniform character throughout most of the area, with only minor differences in thickness or lithology. NNE-oriented lows and swells were formed during deposition of the Volpriehausen, Detfurth and Hardegsen Sequences. Uplift prior to the deposition of the Solling Sequence caused deep erosion on the swells in the basin and minor erosion in the lows. The high-resolution sequences probably represent alternating, relatively wet and dry climatic periods, with a periodicity of about 100 000 years. An analysis of the sequences suggests that their reduced thickness on the swells is mainly the effect of erosion. This is supported by analyses of the accumulation patterns and rates.     

High-resolution cyclostratigraphic analysis from magnetic susceptibility in a Lower Kimmeridgian (Upper Jurassic) marl–limestone succession (La Méouge,Vocontian Basin,France)

High-resolution magnetic susceptibility (MS) analysis was carried out on a Lower Kimmeridgian alternating marl–limestone succession of pelagic origin that crops out at La Méouge (Vocontian Basin, southeastern France). The aim of the study was to characterize the strong, dm-scale sedimentary cyclicity of the succession at a very high resolution, and to analyze the cycles for evidence of astronomical forcing. From marl to limestone, MS varies progressively and closely tracks the highest frequency cyclicity corresponding to the basic marl–limestone couplets. Long-term wavelength cycling modulates the high-frequency cyclicity (couplets), and appears to be controlled by clay content. Spectral analysis of the MS record reveals the presence of the complete suite of orbital frequencies in the precession, obliquity, and eccentricity (95–128 ka and 405 ka) bands with very high amplitude of the precession index cycles originating from dm-scale couplets. 405 ka-eccentricity cycles are very pronounced in the MS maxima of the marl members of the couplets, suggesting eccentricity-driven detrital input to the basin. 405 ka-orbital tuning of the MS maxima further sharpens all of the orbital frequencies present in the succession. These results are similar to those of previous studies at La Méouge that used carbonate content observed in field. Our results are also in accordance with cyclostratigraphic studies in Spain and Canada that report dominant precession index forcing. By contrast, in the Kimmeridge Clay (Dorset, UK), obliquity forcing dominates cyclic sedimentation, with weaker influence from the precession index. Ammonite zone duration estimates are made by counting the interpreted precession cycles, and provide an ultra-high resolution assessment of geologic time. In sum, this study demonstrates the power of the MS as a proxy in characterizing the high-resolution cyclostratigraphy of Mesozoic sections, particularly in alternating marl–limestone successions, and for high-resolution correlation and astronomical calibration of the geologic time scale.     

Mobilization of Ag,heavy metals and Eu from the waste deposit of the Las Herrerias mine (Almería,SE Spain)

We studied the mobility of silver, heavy metals and europium in waste from the Las Herrerías mine in Almería (SE Spain). The most abundant primary mineral phases in the mine wastes are hematite, hydrohematite, barite, quartz, muscovite, anorthite, calcite and phillipsite. The minor phase consisted of primary minerals including ankerite, cinnabar, digenite, magnesite, stannite, siderite and jamesonite, and secondary minerals such as glauberite, szomolnokite, thenardite and uklonscovite. The soils show high concentrations of Ag (mean 21.6 mg kg^–1), Ba (mean 2.5%), Fe (mean 114,000 mg kg^–1), Sb (mean 342.5 mg kg^–1), Pb (mean 1,229.8 mg kg^–1), Zn (mean 493 mg kg^–1), Mn (mean 4,321.1 mg kg^–1), Cd (mean 1.2 mg kg^–1) and Eu (mean 4.0 mg kg^–1). The column experiments showed mobilization of Ag, Al, Ba, Cu, Cd, Eu, Fe, Mn, Ni, Sb, Pb and Zn, and the inverse modelling showed that the dissolution of hematite, hausmannite, pyrolusite and anglesite can largely account for the mobilization of Fe, Mn and Pb in the leaching experiment. The mobility of silver may be caused by the presence of kongsbergite and chlorargyrite in the waste, while the mobility of Eu seems to be determined by Eu(OH)₃, which controls the solubility of Eu in the pH–Eh conditions of the experiments. The mineralogy, pH, Eh and geochemical composition of the mine wastes may explain the possible mobilization of heavy metals and metalloids. However, the absence of contaminants in the groundwater may be caused by the carbonate-rich environment of “host-rocks” that limits their mobility.     

‘Filament’ marker beds in the Karababa-A Member (Turonian) of the Arabian platform,SE Turkey: Palaeo-environmental significance,stratigraphy and correlation potential

A ‘filament’ event bed/level corresponds to the occurrence of thin elongate calcitic, shells, or plates of pelagic, bivalve or crinoidal, origin, within pelagic, laminated and organic-matter rich limestones. These organic-rich limestones had been generally deposited under hypoxic/anoxic conditions in an outer-ramp environment. These thin elongate, bivalve shells, or crinoidal plates, are found broken in small pieces, disintegrated, or simply preserved parallel to bedding as almost complete specimens. Such ‘filament’ beds were spotted in SE Turkey in deposits, namely the Karababa-A Member, around the Cenomanian-Turonian boundary (C/TB) and above. On a global scale, these filament event beds illustrate sea-level rise related to eustacy and/or climatic change. The abundance of filaments close to the C/TB is a biological marker of high organic productivity resulting from a climatic change to warmer conditions. The prevailing higher sea-level conditions were then favourable to the accumulation and preservation of organic-rich facies, characteristic of the Oceanic Anoxic Event 2 (OAE2). Using both biostratigraphic and carbon isotopic data, those deposits were dated from the latest Cenomanian-Turonian age. ‘Filament’ event beds were recorded in the same order, except for some small differences. A good number of these bio-events are global. Consequently, on a global scale, they are susceptible to constrain the C/TB, especially the base of the Turonian stage, with a significant degree of confidence.     

Formal proposal for the Bathonian GSSP (Middle Jurassic) in the Ravin du Bès Section (Bas-Auran, SE France)

The Bathonian Global Stratotype Section and Point (GSSP) is proposed at the base of limestone bed RB071 (bed 23 in Sturani 1967) in the Ravin du Bès Section (43° 57′ 38′′ N, 6° 18′ 55′′ E), Bas-Auran area, “Alpes de Haute Provence” French department. The Ravin du Bès Section, as formal candidate GSSP for the base of the Bathonian Stage, satisfies most of the requirements recommended by the International Commission on Stratigraphy: 1) The exposure extends over 13 m in thickness. At the Bajocian-Bathonian transition, no vertical (bio-, ichno- or tapho-) facies changes, condensation, stratigraphic gaps or hiatuses have been recorded. Structural complexity, synsedimentary and tectonic disturbances, or important alterations by metamorphism are not relevant constraints. 2) There is a well-preserved, abundant and diverse fossil record across the boundary interval, with key markers (ammonites and nannofossils) for worldwide correlation. The base of the Bathonian Stage and Zigzag Zone in Bas-Auran corresponds to the first occurrence level of Gonolkites convergens Buckman, which coincides with the first occurrence of Morphoceras parvum Wetzel. Calcareous nannofossils, as secondary global marker, are present in all beds and allow characterizing the Bajocian-Bathonian transition. 3) Regional analyses of sequence stratigraphy and manganese chemostratigraphy are available. Spectral gamma-ray data corroborate an Early Bathonian deepening half-cycle of second order. 4) The criteria of accessibility, conservation and protection are assured by the “Réserve Naturelle Géologique de Haute Provence”. The Cabo Mondego Section (Portugal) is suggested as the Bathonian auxiliary section and point (ASSP) within this GSSP proposal.     

Petrogenesis of Fe–Ti oxides in amphibole-rich veins from the Lherz orogenic peridotite (Northeastern Pyrénées, France)

Accessory, homogeneous ilmenite and rutile are important oxide phases in amphibole-rich high-pressure cumulate veins which crosscut the Lherz orogenic lherzolite massif. Those veins crystallized from alkaline melts at P = 1.2–1.5 GPa within the uppermost lithospheric mantle. Transitional basalts contaminated by peridotitic wall-rocks and then uncontaminated alkali basalts (basanites) reused the same vein conduits. Petrographic observations give evidence that Fe–Ti oxide saturation depends on the silica contents of each parental melt. The water-poor silica-rich transitional melts that generated websterites and plagioclase-rich clinopyroxenites reached early Ti-oxide saturation (1,200°C; 1.5 GPa). Rutile is as abundant as ilmenite. It is enriched with Nb–Zr–Hf by a factor of 10–100 relative to either amphibole or ilmenite. The amphibole pyroxenites and hornblendites crystallized from basanites reached late Fe–Ti oxide saturation after precipitation of amphibole, with ilmenite crystallizing along with phlogopite in the latter. The Lherz ilmenites are devoid of exsolution and contain very little trivalent iron. This compositional feature indicates more reducing crystallization conditions than usually inferred for alkali lavas and their megacrysts (FMQ ± 1). The veins incompletely equilibrated for redox conditions with their wall-rock peridotites which record more oxidizing conditions (FMQ ± 1). The veins also exchanged magnesium and chromium, as suggested by Cr-bearing, Mg-rich ilmenite (up to 44 mol% MgTiO₃₎ in veins less than 3–4 cm thick. Mg-rich ilmenite megacrysts occurring in alkali basalts could be actually xenocrysts from veins similar in thickness to those occurring at the Lherz massif, although crystallized from more oxidized magmas.     

Arsenic and metal mobility from Au mine tailings in Rodalquilar (Almería,SE Spain)

In the old mining area of Rodalquilar, mine wastes, soil and sediments were characterized and the results revealed high concentration of Au, Ag, As, Bi, Cu, Fe, Mn, Pb, Se, Sb and Zn in tailings and sediments. The contaminant of greatest environmental concern is As. The mean concentration in the tailings was 679.9, and 345 mg/kg in the sediments of Playazo creek. The groundwater samples from the alluvial aquifer showed high concentration of Al, As, Cd, Fe, Hg, Mn, Ni, Pb, Se, Sb and Zn and very high concentration of chloride and sulfate, which were above the concentration defined in the European standards for drinking water. The presence of As in groundwater may be caused by the oxidation of arsenian pyrite, the possible As desorption from goethite and ferrihydrite and the jarosite dissolution. Groundwater concentrations of Cd, Fe, Mn, and possibly Cu, were associated with low values of Eh, indicating the possible dissolution of oxy-hydroxides of Fe and Mn. The mobility of metals in the column experiments show the release of Al, Fe, Mn, Cr, Cu, Ni, V and Zn in significant concentrations but below the detected values in groundwater. However, As, Cd, Sb, Se Pb and Au, are generally mobilized in concentrations above the detected values in groundwater. The possible mass transfer processes that could explain the presence of the contaminants in the aquifer and the leachates was simulated with the PHREEQC numerical code and revealed the possible dissolution of the following mineral phases: jarosite, natrojarosite, arsenian pyrite, alunite, chlorite, kaolinite and calcite.     

Early Aptian oceanic anoxic event (OAE 1a) in Northeastern Arabian Plate setting: an example from Dariyan Formation in Zagros fold–trust belt,SE Iran

The Dariyan Formation (southwestern Iran) records the characteristic features of an oceanic anoxic event with organic- and radiolarian-rich hemipelagic intervals. A biostratigraphic study based on benthic and planktonic foraminifers provides an early Aptian age for the organic-rich succession and an Aptian age for the entire Dariyan Formation in this area. In this study, we report the first stable carbon isotope curve for the Dariyan Formation which is characterized by a pronounced negative spike (reaching ?2?‰) at the base of the section followed by a subsequent positive excursion (4?‰) and a plateau with values fluctuating around 3?‰. The integration of the δ¹³C record with the previously published litho- and biostratigraphy provides the characteristic features of the oceanic anoxic events (OAE) 1a interval. This detailed curve improved the stratigraphic resolution in this area and allowed the establishment of a temporal framework which showed good correlations with other OAE 1a sections worldwide. High production of organic matter and abundance of radiolarians and planktonic foraminifers suggest high-nutrient fluxes and meso- to eutrophic conditions at the time of deposition of the organic-rich interval of the Dariyan Formation. This is in agreement with enhanced greenhouse conditions. The facies distribution (from shallow to deep water environments) and the paleogeography of Arabian Plate during the early Aptian suggest that increasing continental runoff was a primary trigger of high trophic level conditions. Redox conditions, estimated from manganese (Mn) behavior, indicate dysoxic to anoxic conditions within the basin during OAE 1a.     

Strain and deformation mechanisms in the Variscan nappes of Vendée,South Brittany,France

The Variscan nappes of Vendée (South Brittany, France) were displaced westward through a mechanism of regional subhorizontal ductile shear involving the entire body of the nappes. Ductile shear also affected the upper part of the Silurian footwall, including the rhyolite of Chapelle-Hermier, which was mylonitized and sheared with upward-increasing intensity, as well as the calcalkaline Vendée porphyroids of volcanic and volcanoclastic origin which form a mylonite sheet outlining the major basal thrust zone of the nappes. Nappe displacement was accompanied by a severe extensional strain, estimated at up to 300–400% in both the porphyroids and the rhyolite, and indicating that the deformational history may have involved a gravitational spreading component. Within the mylonitic rhyolite, accommodation of the bulk strain was mainly by solution-assisted mass-transfer, as shown by (1) growth of quartz fibres in low-pressure zones, (2) development of polycrystalline ribbons through continuous growth of quartz grains in pressure shadows and (3) crystallization of muscovite at the expense of the felsitic groundmass. A similar deformation process was probably active in the mylonitic porphyroids at the sole of the nappe, suggesting that pressure-solution flow was an important mechanism in nappe displacement.     

Retrograde formation of NaCl-scapolite in high pressure metaevaporites from the Cordilleras Béticas (Spain)

A Permo-Triassic pelite-carbonate rock series (with interacalated metabasitic rocks) in the Cordilleras Béticas, Spain, was metamorphosed during the Alpine metamorphism at high pressures (P _min near 18 kbar). The rocks show well preserved sedimentary features of evaporites such as pseudomorphs of talc, of kyanite-phengitetalc-biotite, and of quartz after sulfate minerals, and relicts of baryte, anhydrite, NaCl, and KCl, indicating a salt-clay mixture of illite, chlorite, talc, and halite as the original rock. The evaporitic metapelites have a whole rock composition characterized by high Mg/(Mg+Ca) ratios>0.7, variable alkaline and Sr, Ba, contents, but are mostly K₂O rich (<8.8 wt%). The F (<2600 ppm), Cl (<3600 ppm), and P₂O₅ (<0.24 wt%) contents are also high. The pelitic member of this series is a fine grained biotite rock. Kyanite-phengite-talc-biotite aggregates in pseudomorphs developed in the high pressure stage. Albite-rich plagioclase was formed when the rocks crossed the albite stability curve in the early stages of the uplift. Scapolite, rich in NaCl (Ca/(Ca+Na) mol% 24–40) and poor in SO₄, with Cl/(Cl+CO₃) ratios between 0.6 and 0.8, formed as porphyroblasts, sometimes replacing up to 60% of the rock in a late stage of metamorphism (between 10 and 5 kbar, near 600°C). No reaction with albite is observed, and the scapolite formed from biotite by: $$\begin{gathered} Al - biotite + CaCO_3 + NaCl + SiO_2 \hfill \\ = Al - poor biotite + scapolite + MgCO_3 + KCl \hfill \\ + MgCl_2 + H_2 O \hfill \\ \end{gathered}$$ Calculated fluid composition in equilibrium with scapolite indicates varying salt concentrations in the fluid. Distribution of Cl and F in biotite and apatite also indicates varying fluid compositions.     

Melt percolation and reaction atop a plume: evidence from the poikiloblastic peridotite xenoliths from Borée (Massif Central, France)

Poikiloblastic harzburgite xenoliths (P-type) from Borée, France are characterised by large (>1 cm), essentially unstrained olivines and high equilibrium temperatures (>1200 °C). Mineralogical data, trace element abundances and Sr-Nd-O isotopes of the constituent minerals are consistent with formation as a result of melt percolation-reactions in a lherzolite precursor during lithospheric erosion by an upwelling plume. This petrogenetic model contrasts with previous models involving isochemical recrystallisation from a granular lherzolite precursor (G-type) or derivation as metacumulates from tholeiitic magmas. Numerical simulation of percolation reactions at the lithosphere-plume boundary using the plate model of Vernières et al. (1997) indicates that the different textured xenoliths may represent mantle from different levels in a percolation-reaction column. If correct then the P-type harzburgites resulted from pyroxene-dissolving and olivine-producing reactions at increasing melt fraction (>3%) at the lower part of column (base of the lithosphere), whereas the G-type lherzolites were located within the low-porosity domain (<0.1%) above a permeability barrier, and are formed through a melt-rock reaction at decreasing melt mass. Given the very low melt fraction, the REE fractionation in this zone is controlled by chromatographic effects coupled with source effects of reaction. The variations in porosity, melt/rock ratio and melt-rock reaction mechanism are believed to be responsible for the diversity of REE patterns and striking correlation between REE abundance and texture in Borée xenoliths. Received: 15 June 1997 / Accepted: 7 January 1998     

Effects of the October 25, 2010, Mentawai tsunami in La Réunion Island (France): observations and crisis management

On October 25, 2010, a Mw = 7.7 magnitude earthquake was recorded in the Kepulauan Mentawai archipelago, in Indonesia. Following the earthquake, the Pacific Tsunami Warning Center issued a tsunami bulletin to the countries of the Indian Ocean informing them that a local tsunami watch was in effect for Indonesia. La Réunion Island, a French territory located 5,000 km southwest of the seismic source, did not trigger its tsunami early warning protocol, but did suffer the impact of this tsunami 7h20 post-earthquake. This paper presents the post-tsunami survey conducted in La Réunion Island a few days after the event, providing run-up measurements that reach 1.72 m locally as well as information about the material losses and the crisis management. It provides a time sequence of the observations along the coast and the reactions of the population and authorities in dealing with this crisis. This paper also shows the local authorities’ lack of action in managing this event—thus increasing human and material vulnerabilities—the consequences for victims and the impact on the credibility of the local early warning system. These results provide geophysicists with information to better describe the source of this tsunami through far-field inversion and provide local decision makers with a comprehensive assessment of the weaknesses of the local early warning system and protocols.     

U–Pb geochronology and palynology from Lopingian (upper Permian) coal measure strata of the Galilee Basin,Queensland, Australia

This study presents the first chemical abrasion-isotope dilution thermal ionisation mass spectrometry (CA-IDTIMS) U–Pb zircon ages from tuffs in Lopingian (upper Permian) strata of the Galilee Basin, Queensland and reassigns the B coal-seam to the ‘Burngrove Formation equivalent.’ Five Lopingian tuffs were dated: four from the CRD Montani-1 drill hole including three from the ‘Fair Hill Formation equivalent’ (255.13 ± 0.09, 254.41 ± 0.07 and 254.32 ± 0.10 Ma) and one from the ‘Burngrove Formation equivalent’ (252.81 ± 0.07 Ma, approximately the age of the Yarrabee Tuff in the adjacent Bowen Basin); and a single tuff from the Black Alley Shale in the GSQ Tambo-1-1A drill hole (254.09 ± 0.06 Ma). In the Galilee Basin, all three units are constituents of the Betts Creek Group, here formally elevated in nomenclatural status from the Betts Creek beds. On the western margin of the basin, the group thins, and the ‘J and K’ seams (formerly known as the Crossmore and Glenaras sequences, respectively) in the GSQ Muttaburra-1 drill hole have been interpreted through palynology as Cisuralian–early Guadalupian (spore-pollen assemblage APP3.2). This corroborates the exclusion of the ‘J and K’ seams from the overlying Lopingian Betts Creek Group (spore-pollen assemblage APP5), and the underlying lower to mid-Cisuralian Aramac Coal Measures (spore-pollen assemblage APP2.2), which represent the uppermost unit of the Joe Joe Group. It is proposed that the ‘J and K’ seams are restricted to a depocentre in the Hulton–Rand structure. The recognition of these strata containing APP3.2 spore-pollen assemblages suggests that the mid-Permian hiatus is locally reduced to 12–13 My from 30 Ma (where the ‘J and K’ seams are absent). The results of the radiometric dating and palynological analysis in the Galilee Basin support the proposed, albeit informal stratigraphy, that is given in terms of equivalents of formational units in the Bowen Basin and on the intervening Springsure Shelf.     

Reassessment of the ‘Abbevillien’ in the perspective of new discoveries from the Lower Palaeolithic and Quaternary sites of Abbeville (Somme,northern France)

North-West Europe yields few traces of early human occupation, in particular for the Acheulean. In this context, the Somme Valley in northern France offers a route to Britain during various Pleistocene low sea levels, and has provided numerous evidence of Lower Palaeolithic human occupation through fieldwork initiated during the 19th century. These localities are associated with the original definition in the 1930s by the French prehistorian Abbé Henri Breuil of the ‘Abbevillien’ (Abbevillian facies), based on lithic pieces including crudely made bifaces recovered in particular in some famous key localities of Abbeville, Carpentier, Léon and Moulin Quignon quarries. The history of the term and its definition subsequently gave rise to debates concerning the chronocultural framework of Palaeolithic assemblages among the scientific community of prehistorians over time, from Jacques Boucher de Perthes, Gabriel de Mortillet, Geoffroy d'Ault du Mesnil, Victor Commont, Henri Breuil and François Bordes. New investigations at these three localities, all associated with the High Terrace of the Somme system, pushed back the age of the expansion of the Acheulean both in northern France and in Western Europe to c. 670–650 000 years. They imply that early hominins were able to settle in North-West Europe during both climatic temperate and cold phases. Our work, including new excavations and associated field observations of the three Abbeville localities involved at the onset of the controversy, allows a re-examination of the Abbevillian and contributes to the discussion of the history of Prehistoric Science and the Earliest ‘Acheuleans’ in North-West Europe.     

The origin of zircon and the significance of U–Pb ages in high-grade metamorphic rocks: a case study from the Variscan orogenic root (Vosges Mountains, NE France)

U–Pb zircon dating is combined with petrology, Zr-in-rutile thermometry and mineral equilibria modelling to discuss zircon petrogenesis and the age of metamorphism in three units of the Variscan Vosges Mountains (NE France). The monotonous gneiss unit shows results at 700–500?Ma, but no Variscan ages. The varied gneiss unit preserves ages between 600 and 460?Ma and a Variscan group at 340–335?Ma. Zircon analyses from the felsic granulite unit define a continuous array of ages between 500 and 340?Ma. In varied gneiss samples, zoned garnet includes kyanite and rutile and is surrounded by matrix sillimanite and cordierite. In a pseudosection, it points to peak conditions of?~16 kbar/850?°C followed by isothermal decompression to 8–10 kbar/820–860?°C. In felsic granulite samples, the assemblage K-feldspar–garnet–kyanite–Zr-rich rutile is replaced by sillimanite and Zr-poor rutile. Modelling these assemblages supports minimum conditions of?~13 kbar/925?°C, and a subsequent P–T decrease to 6.5–8.5 kbar/800–820?°C. The internal structure and chemistry of zircons, and modelling of zircon dissolution/growth along the inferred P–T paths are used to discuss the significance of the U–Pb ages. In the monotonous unit, inherited zircon ages of 700–500?Ma point to sedimentation during the Late Cambrian, while medium-grade metamorphism did not allow the formation of Variscan zircon domains. In both the varied gneiss and felsic granulite units, zircons with a blurred oscillatory-zoned pattern could reflect solid-state recrystallization of older grains during HT metamorphism, whereas zircons with a dark cathodoluminescence pattern are thought to derive from crystallization of an anatectic melt during cooling at middle pressure conditions. The present work proposes that U–Pb zircon ages of ca. 340?Ma probably reflect the end of a widespread HT metamorphic event at middle crustal level.