Géoarchéologie alluviale du site antique de Molesme en plaine alluviale de Laigne (Bourgogne). Réunion des Sciences de la Terre (RST), Dijon.

International audience

The skeleton of the staghorn coral Acropora millepora: molecular and structural characterization.

15 pages; International audience; The scleractinian coral Acropora millepora is one of the most studied species from the Great Barrier Reef. This species has been used to understand evolutionary, immune and developmental processes in cnidarians. It has also been subject of several ecological studies in order to elucidate reef responses to environmental changes such as temperature rise and ocean acidification (OA). In these contexts, several nucleic acid resources were made available. When combined to a recent proteomic analysis of the coral skeletal organic matrix (SOM), they enabled the identification of several skeletal matrix proteins, making A. millepora into an emerging model for biomi…

Approche géoarchéologique de la vallée de la Laigne

The conclusions from the research project in the Laigne Valley show the relevance of the geoarchaeological approach conducted on two scales of investigation. The first, over the entire alluvial plain, allows general data to be collected which characterise the specific functions of each catchment basin during the Holocene period : determination of sedimentary sequences, evolution of specific functions of each catchment basin during the Holocene period : determination of sedimentary sequences, evolution of vegetation and phases of human occupation. The second is a geoarchaeological approach on the scale of a test site: it demonstrates and dates as precisely as possible, interactions between n…

Early–middle Jurassic lytoceratid ammonites with constrictions from Morocco: palaeobiogeographical and evolutionary implications.

13 pages; International audience; The ammonite genus Alocolytoceras Hyatt, 1900 is an uncommon lytoceratid with distinctive shell ornament. A set of 58 specimens, recently collected at Amellago in the central High Atlas (Morocco), has enabled us to trace a succession of three species over eight biozones from the Toarcian to the Aalenian. Two specimens from the Lusitanian Basin are added for comparison. Following a review of the genus, based on original specimens and data from the literature, seven species are considered valid. A palaeobiogeographical synthesis of 13 regions demonstrates irregular distribution patterns over time, with a constant presence in the south-west Tethys and an insta…

The karstic aquifer of Lake Antre (Jura Mountains - France): an anthropic control since the first century A.D.?

A Sulfuric Acid Speleogenesis in the Northern Pyrenees (France)?

The origin and timing of multiphase cementation in carbonates: Impact of regional scale geodynamic events on the Middle Jurassic Limestones diagenesis (Paris Basin, France)

The Middle Jurassic carbonates of the eastern part of the Paris Basin display surprisingly low values of porosity and permeability (Φ < 15‰ and K < 0.5 mD). The main objective of this study is to determine the causes and timing of the cementation that altered the petrophysical properties of these carbonates thereby destroying their potential as oil reservoirs; a fate that did not befall their equivalents in deeper, central parts of the Paris Basin. Using petrographic and geochemical analyses (stable O and C isotopes, Sr isotopes, major elements), we identify six calcitic spar stages, two dolomite stages, and several episodes of fracturing and stylolitization ordered in paragenetic sequence.…

Enregistrement du cycle du carbone au Pliensbachien (Jurassique inférieur) sur la marge sud téthysienne (Amellago, Haut-Atlas Central, Maroc)

International audience; Le Pliensbachien s’inscrit dans un contexte climatique greenhouse au Jurassique, en période de dislocation de la Pangée. De récentes études dans le domaine nord-ouest téthysien ont démontré une certaine variabilité climatique soutenue notamment par des variations isotopiques remarquables dans le cycle du carbone, comparables en amplitude et en durée à d’autres événements du Toarcien (e.g. T-OAE). Malgré la multiplication des travaux le long de la marge nord téthysienne avec la mise en évidence de changements géodynamiques importants, la marge sud n’a jamais été étudiée à haute résolution. Nous proposons, dans un cadre biostratigraphique extrêmement précis (ammonites …

Chupicuaro archaeological sites: from magnetic survey to excavation (Late pre-classic period, Middle Lerma Valley, Mexico)

Impact of basin burial and exhumation on Jurassic carbonates diagenesis on both sides of a thick clay barrier (Paris Basin, NE France).

27 pages; International audience; Several diagenetic models have been proposed for Middle and Upper Jurassic carbonates of the eastern Paris Basin. The paragenetic sequences are compared in both aquifers to propose a diagenetic model for the Middle and Late Jurassic deposits as a whole. Petrographic (optical and cathodoluminescence microscopy), structural (fracture orientations) and geochemical (δ18O, δ13C, REE) studies were conducted to characterize diagenetic cements, with a focus on blocky calcite cements, and their connection with fracturation events. Four generations of blocky calcite (Cal1-Cal4) are identified. Cal1 and Cal2 are widespread in the dominantly grain-supported facies of t…

The end of the Messinian Salinity Crisis in the western Mediterranean: insights from the carbonate platforms of south-eastern Spain.

International audience; How the Messinian Salinity Crisis (MSC) ended is still a matter of intense debate. The Terminal Carbonate Complex (TCC) is a late Messinian carbonate platform system that recorded western Mediterranean hydrological changes from the final stages of evaporite deposition till the advent of Lago-Mare fresh- to brackish water conditions at the very end of Messinian times. A multidisciplinary study has been carried out in three localities in south-eastern Spain to reconstruct the history of TCC platforms and elucidate their significance in the MSC. Overall, this study provides evidence that the TCC formed following a regional 4th order water level rise and fall concomitant…

Traces de pas de dinosaures du Jurassique moyen : bilan sur deux décennies de découvertes en Lozère.

8 pages; National audience; Depuis 1999, des découvertes fortuites ainsi que des campagnes de prospections menées en Lozère ont livré plusieurs sites à empreintes de pas de dinosaures d’âge jurassique moyen. Le nombre, la diversité et la remarquable préservation de ces traces constituent un patrimoine paléontologique exceptionnel. Les sites principaux sont localisés dans les Gorges du Tarn et de la Jonte. Leur récente étude a révélé (1) que ces empreintes ont été laissées par des dinosaures théropodes et sauropodes (2) que les écosystèmes parcourus par ces dinosaures correspondaient à des milieux tropicaux et littoraux tels que des marais côtiers, de vastes lagunes ou des baies bordées par …

Spatial and temporal distribution of ooids along a Jurassic carbonate ramp: Amellago outcrop transect, High-Atlas, Morocco

Carbonate ramp systems are widespread throughout the geological record, but very few areas have seismic-scale, continuous and structurally undeformed outcrops that allow reliable interpretation of facies distributions and stacking patterns. The Amellago outcrop shows the detailed depositional and stratigraphic relationships of an ooid-dominated ramp system that is almost completely exposed along a dip profile (37 km long and 1000 m thick) in the Lower to Middle Jurassic of the southern High Atlas, Morocco. Ammonite and brachiopod fauna provide excellent biostratigraphic control on small scale stacking patterns. At Amellago, the evolution of depositional environments is evident at different …

Early Jurassic normal faulting in a carbonate extensional basin: characterization of tectonically driven platform drowning (High Atlas rift, Morocco).

18 pages; International audience; This paper describes a tectonostratigraphic model of the synrift evolution of the Early Jurassic High Atlas rift of Morocco. The model is constrained by mapping of a set of inverted extensional blocks, by facies analysis of carbonate platform and turbiditic to hemipelagic synrift deposits, and by high-resolution (n 3 100 ka) biostratigraphy of the Early Jurassic succession. The chronostratigraphic packages of the High Atlas of Rich vary significantly in thickness, facies and architecture from one tectonic block to another. Our study shows how synrift strain varied in space and time over a long time interval (14 Ma) around the High Atlas rift. Initially, in …

A little walk between Early Jurassic sponges and corals: a confusing morphological convergence.

24 pages; International audience; Hispaniastraea Turnšek et Geyer, 1975 is a unique coral genus from the Early Jurassic Epoch (Liassic). Corals of this genus are characterised by a highly dominant major septum and a set of eleven minor septa that are very short or even abortive. Initially discovered in Spain, new samples of this genus were depicted from Morocco by Beauvais in 1980; however, this genus was interpreted as a synonym of Pseudoseptifer Fischer, 1970, a chaetetid sponge (i.e., a sponge with siliceous spicules embedded in a calcareous skeleton). The skeleton of Pseudoseptifer is composed of adjacent tubules that increase by fissiparity by means of a pseudoseptum. Based on the stud…

Magnetic survey on Chupicuaro's archaeological sites (late preclassic period, middle Lerma valley, Guanajuato - Mexico)

L’hydrosystème karstique du sanctuaire gallo-romain du lac d’Antre et des sources de l’Héria.

National audience

The Chupicuaro exploitation of hydrothermal resources, Mexico (600 B.C.- 300 A.D.): geochimical and mineralogical identification and archaeological inferences

International audience

Les environnements de dépôt du Sinémurien de la région stratotypique (faciès et microfaciès).

16 pages; National audience

Drowning of a carbonate platform as a precursor stage of the Early Toarcian global anoxic event (Southern Provence sub-Basin, South-east France)

The Toarcian Oceanic Anoxic Event is well-known as coinciding with a carbonate crisis, coupled with organic matter accumulation and perturbation of the carbon cycle expressed by carbon-isotope excursions. In this palaeoenvironmental setting, the present research attempts to better constrain the palaeoenvironmental conditions leading to the drowning of a carbonate platform during Late Pliensbachian to Early Toarcian times. This study is based on the integrated sedimentological, diagenetic and geochemical (stable isotopes and Rock-Eval pyrolysis) analysis of several stratigraphic successions located in the Southern Provence sub-Basin (South-east France). Eodiagenetic ferroan calcite cements b…

Acoustic properties of ancient shallow-marine carbonates: effects of depositional environments and diagenetic processes (Middle Jurassic, Paris Basin, France).

17 pages; International audience; Examination of petrophysical properties (acoustic velocity, porosity, permeability, and density) and petrographical characteristics (texture, facies composition, and diagenesis) of more than 250 core plugs from the Middle Jurassic carbonates of the eastern Paris Basin provides insights into the parameters controlling acoustic velocities in relatively low-porosity carbonate rocks ({Phi} < 20%). The pore-type observations reveal distinct acoustic velocities in samples with intergranular macropores and samples with micropores in subhedral micrite, such that velocities in microporous mudstone–wackestone (lagoonal) deposits are greater than in macroporous grains…

Structure and evolution of a Messinian mixed carbonate-siliciclastic platform: the role of evaporites (Sorbas Basin, South-east Spain).

36 pages; International audience; The Sorbas Member is a late Messinian complex sedimentary systemthat formed immediately following deposition of the Messinian evaporites in the Sorbas Basin (South-east Spain). This work describes the sequence architecture and facies organization of a continuous kilometre long, alluvial fan to open platform transect near the village of Cariatiz in the north-east of the basin. The postevaporitic Cariatiz platform was a mixed carbonate-siliciclastic system composed of four intermediate-frequency, fifth-order depositional sequences (Depositional Sequences 1 to 4) arranged in an overall prograding trend. The intense fracturing and brecciation of these deposits …

Reevaluation of the enigmatic Ordovician genus Bolboporites.

International audience

Les pistes d’archosauriens : Kayentapus ubacensis nov. isp. (théropodes) et crocodylomorphes du Bathonien des Grands-Causses (France). Conséquences paléo-biologiques, environnementales et géographiques

Resume Deux sites a traces de pas tridactyles II–IV de theropodes et de « probables » sauropodes des Grands Causses, sommairement decrits en 2006, sont ici reetudies. Il s’agit des sites du Capelan (commune de Meyrueis, Lozere) et de la Garene (commune de La Roque-Sainte-Marguerite, Aveyron), tous deux d’âge Bathonien. En 2012, l’un d’entre eux (Le Capelan) a fait l’objet d’une fouille et d’un agrandissement, permettant la decouverte de nombreuses traces. Dans le site du Capelan, 102 epireliefs concaves, compris entre 11 et 36 cm de longueur, appartiennent a, au moins, 21 pistes; la plus longue etant visible sur 37 metres. Dans l’ensemble, ces empreintes sont presque aussi longues que large…

The hydrothermal carbonated complexes in the Acambaro Valley: precolumbian and modern human impacts

Synthesis of recent stratigraphic data on bathonian to oxfordian deposits of the eastern Paris basin

International audience

Le gisement pléistocène moyen récent de Romain-la-Roche (Doubs, France) :synthèse biostratigraphique et paléoécologique

International audience; The Uppermost Middle Pleistocene site of Romain-la-Roche (Doubs, France) : synthesis of biostratigraphic and palaeoecological conclusions.- The site of Romain-la-Roche is a karstic swallowhole which acted as a natural trap where fall numerous large mammals, and where diverse small vertebrates were transported as preys of birds. The site was excavated between 1980 and 1991 by Patrick Paupe and his team. It yielded 52 species of mammals (more than 10 000 identifiable remains), more than 13 of species of birds, two of reptiles, one of amphibian, two of fishes and undetermined gastropods. Among the mammalian species 34.6 % are of rodents (3975 remains), 9.6 % insectivore…

Tectono-biosedimentary recordings at the Lias-Dogger transition: example of the Quercy carbonate platform (Aquitaine Basin, France).

AbstractOn the eastern edge of the Aquitaine Basin, the Lias-Dogger transition and the events, which occurred during this time interval are studied in the Quercy sedimentary basin. Stratigraphic correlations are proposed using a biochronological calibration based on the determination of numerous ammonites and brachiopods. Facies analyses using statistical processing integrate the presence of faults and tectonic compartments and lead to reconstruction of palaeoenvironments in space and time. The paper includes the description of system tracts following Haq et al. [1987] and Vail et al. [1991], and twelve palaeogeographic maps of the area studied. The objectives are to distinguish the various…

Characterization and origin of permeability-porosity heterogeneity in shallow-marine carbonates: from core scale to 3D reservoir dimension (Middle Jurassic, Paris Basin, France).

21 pages; International audience; Nuclear magnetic resonance (NMR), stable isotope geochemistry of micro-sampled cores, NMR well-logs and 3D modeling are used to investigate the carbonate permeability-porosity heterogeneity along 230 m-thick limestones of the Paris Basin. Despite the global low porosity and permeability of the limestones, two aquifers units with porosity greater than 15% were identified. These two aquifers are very different in terms of pore through radii and NMR signal. The first one (A1: Aquifer 1) is a 7 m-thick mudstone unit, dominated by extended microporosity with pore throat radii of 0.25 μm to 0.3 μm. The second one (A2: Aquifer 2) is a 15 m-thick oolitic grainstone…

The role of topography and erosion in the development and architecture of shallow-water coral bioherms (Tortonian-Messinian, Cabo de Gata, SE Spain).

23 pages; International audience; During the Miocene, Mediterranean shallow-water carbonates were rich in scleractinian corals, which thrive in various depositional settings. A Tortonian–Messinian bioherm belt developing in a heterozoan-dominated ramp was investigated along a 1.2 km continuous transect located in the Cabo de Gata region. The interval studied displays four depositional environments from mid-to-inner ramp, dominated by swell waves and storm energy, deposited as a single, large-scale depositional sequence during a 3rd to 4th order transgressive–regressive cycle. The bioherms grew in three phases, and were essentially composed of inplace primary frameworks. Three coral genera w…

Intra-skeletal variability in trace elemental content of Precolumbian Chupicuaro human bones: the record of post-mortem alteration and a tool for palaeodietary reconstruction.

14 pages; International audience; This study applies an intra-skeletal sampling strategy to examine post-mortem alteration of archaeological human bone from west Mexico, and to reconstruct ancient diet. Human bone from the Chupicuaro culture (Mexico, Preclassic period) constitutes an ideal material with which to examine subsistence strategies because the specific hydrothermal environment in which the population lived would have provided certain food components (hydrothermal waters and carbonates) with distinct signature in Ca, Mg, F, Li, Sr, Mn, V and U values. Four to ten samples were taken from the long bones of six skeletons. Bone trace element content (Ca, P, F, Mn, Mg, Na, Li, V, Zn, R…

Morphometry of micrite particles in cretaceous microporous limestones of the Middle East: influence on reservoir properties.

24 pages; International audience; Microporosity may account for a significant part of the total porosity of Cretaceous limestone reservoirs of the Middle East. In these microporous facies porosity is moderate to excellent (up to 35%) while permeability is poor to moderate (up to 190 mD). Micritic limestones also may form dense layers with very low porosity and permeability values. Micritic samples were collected from three fields of the Habshan and Mishrif Formations, to examine the spatial relationship with their porosity, permeability and pore throat radius distributions. Two key parameters of the micritic particles are studied using scanning electron microscopy: their morphology (shape a…

Skeletal organic matrices in molluscs: origin, evolution, diagenesis

8 pages; International audience; The mollusc shell comprises a small amount of organic macromolecules, mostly proteins and polysaccharides, which, all together, constitute the skeletal organic matrix (SOM). In the recent years, the study of the SOM of about two dozens of mollusc species via transcriptomics and/or proteomics has led to the identification of hundreds of shell-associated proteins. This rapidly growing set of data allows several comparisons, shedding light on similarities and differences at the primary structure level and on some peculiar evolutionary mechanisms that may have affected SOM proteins. In addition, it constitutes a prerequisite for investigating the SOM repertoires…

Modalites sequentielles de la transgression aaleno-bajocienne sur le sud-est du Bassin parisien

Abstract Sedimentologic, biostratigraphic and diagenetic studies made on Middle Aalenian to Lowermost Bathonian deposits in 25 outcrops of the Burgundy High (southeastern Paris basin) lead to a sequence stratigraphy subdivision of the early Dogger record into 7 third order depositional sequences. These sequences make up a second-order transgressive phase whose lower limit is a tectonically enhanced unconformity (the Mid-Cimmerian unconformity), associated with a large scale uplift during the Upper Toarcian and the Lower Aalenian. In the largest outcrops, where the geometry of sedimentary bodies is observable at the hectometre to kilometre scale, the combination of diagenetic, biostratigraph…

Lichen used to assess nickel atmospheric dispersion, an example of New Caledonia Asbestos and best practices View project Atmospheric signature in marine sediments View project Camille Pasquet Lichen used to assess nickel atmospheric dispersion, an example of New Caledonia

International audience; Fifteen epiphytic lichens, collected near an active nickel mine and along an East-West transect across New Caledonia island (South-West Pacific), were analyzed for their metal contents. The purpose is to evaluate atmospheric metal contamination and the impact of mining exploitation on the surroundings. The structure of the compositional dataset was explored using a covariance biplot. The score of the first principal component was used as a generic indicator to locally evaluate the degree of contamination. This study demonstrates that Ni, Co and Cr are highly concentrated in lichens near mining exploitation.

Découverte d’un nouveau site à traces de pas de Dinosaures dans le Bathonien des Causses (Le Gayrand, Gorges de la Jonte, Lozère, France).

7 pages; National audience

Tiempos de crisis y cambios socioculturales en Chupicuaro al final del Preclásico: evidencias paleoambientales e indicadores arqueológicos en el valle de Acámbaro, Guanajuato, México

International audience; "Los trabajos realizados en el valle de Acámbaro evidenciaron para finales del Preclásico (hacia 100 a.C.), una serie de cambios que denota un tiempo de crisis y de transición. El estudio revela una reducción drástica del número de sitios del Preclásico Terminal (fase Mixtlán: 1-250 d.C.), así como una nueva configuración espacial. Las excavaciones avalan las observaciones de superficie y comprueban que, a partir de 100 a.C., los asentamientos sufren una desocupación: en dos sitios excavados observamos estratos de abandono y luego de reocupación, y en los demás constatamos un abandono definitivo. Esta evolución parece coincidir con una baja demográfica. Los acontecim…

Climatic ups and downs in a disturbed Jurassic world.

4 pages; International audience; The tropical, warm, and equable climate of the Jurassic world is regularly challenged by geoscientists, especially since oxygen isotopes ( 18O) of fossil hardparts have been used to reconstruct the paleotemperature history of seawater. By applying the innovative “SiZer” (significant zero crossings of the derivatives) statistical approach to a newly compiled 18O database for the Jurassic, we demonstrate the occurrence of major and multiscale 18O changes mainly related to climate disturbances. For the first time, two long-term anomalies in 18O are identified during the Toarcian and the Late Jurassic, in conjunction with intensive volcanism in large igneous pro…

Les interfaces à traces de pas de théropodes du Plateau des Causses (Sud de la France) : déterminations palichnologiques et interprétations paléoenvironnementales

De nombreuses empreintes ont été découvertes depuis le début des années 2000 dans le Bathonien des Grands Causses, dans les vallées de la Jonte et de la Dourbie, autour de Meyrueis (48) et de Nant (12).Ces traces ont été identifiées par Sciau et al. (2006) comme étant des ichnites d’origine dinosaurienne. Les auteurs ont pu distinguer des traces tridactyles et d’autres de formes ovoïdes. Ils ont attribué la formation des premières à des théropodes et des autres à des sauropodes. Cependant, un doute subsistait quant à leur origine réelle, ainsi que leur détermination ichnologique qui restait à faire.Notre travail consiste en un relevé et des mesures des traces tridactyles et ovoïdes, supposé…

A Sulfuric Acid Speleogenesis in the northern Pyrenees ?

Intact seismic-scale platforms and ramps in the Lower to Middle Jurassic of Morocco: implications for stratal anatomy and lithofacies partitioning.

9 pages; International audience; The Jurassic carbonate platforms of the central High Atlas in Morocco are well known for several high-quality outcrops. In the central High Atlas, there are two complementary locations that offer critical lessons for our understanding of Jurassic carbonate system evolution in extensional basins: a Lower Jurassic high-relief, carbonate platform with steep slopes that developed on the footwall of a rotating fault block in an active half-graben (Djebel Bou Dahar [DBD]) and an upper Lower to Middle Jurassic low-angle prograding carbonate ramp rich in ooids (Amellago ramp [AR]). The DBD and AR outcrops provide superbly exposed, structurally intact, and fully acce…

&lt;p class="HeadingRunIn"&gt;&lt;strong&gt;Reinterpretation of the enigmatic Ordovician genus &lt;em&gt;Bolboporites &lt;/em&gt;(Echinodermata)&lt;/strong&gt;&lt;/p&gt;

Bolboporites is an enigmatic Ordovician cone-shaped fossil, the precise nature and systematic affinities of which have been controversial over almost two centuries. For the first time, a wide range of techniques (CT-scan, SEM, cathodoluminescence, XPL, UV epifluorescence, EBSD, FT-IR and XRF spectrometry) were applied to well-preserved specimens of Bolboporites from Norway and Russia. Our main finding confirms its echinoderm affinities, as shown by its stereomic microstructure and by the first definitive evidence of its monocrystalline nature. Each cone consists in a single, microporous calcitic crystal with a narrow longitudinal internal canal. These results are combined with all previous …

Une spéléogenèse à acide sulfurique dans le piémont nord-pyrénéen ?

Tout au long de l’histoire de structuration des Pyrénées, le jeu des grands accidents tectoniquesfont de la zone de piémont nord-pyrénéen une aire privilégiée de circulation de fluides. Parmiceux-ci, la présence de saumures profondes riches en CO2 et H2S a été attestée dans les réservoirspétroliers sud-aquitains d’âge Crétacé. Impliqués dans des processus de migration vers les margesde bassin, ces fluides sont susceptibles de former des cavités dans l’encaissant calcaire là où lesremontées d’H2S entrent en contact avec du dioxygène, produisant ainsi du H2SO4. C’est cettehypothèse de spéléogenèse à acide sulfurique (SAS) que la présente étude cherche à explorer dansles Pyrénées.Les premières…

Influence of a major exposure surface on the development of microporous micritic limestones - Example of the Upper Mishrif Formation (Cenomanian) of the Middle East.

18 pages; International audience; Microporous platform top limestones of the Cenomanian Mishrif Formation (offshore Qatar) were studied in order to investigate the diagenetic processes associated with the top-Mishrif subaerial unconformity and its influence on the development of microporosity in underlying carbonates. Petrographical and stable isotope results indicate that complex diagenetic changes occurred during subaerial exposure of the Mishrif Formation, including pervasive dissolution and meteoric cementation, as well as neomorphism of the micritic matrix. Micrites at the top of the Mishrif Formation are coarse (i.e. > 2 μm), sub-rounded and very dull luminescent under cathodoluminesc…

Burial dissolution of micrite in Middle East carbonate reservoirs (Jurassic–Cretaceous): keys for recognition and timing.

14 pages; International audience; This paper discusses burial diagenesis and especially a burial dissolution phase and its effects on micrite microtexture in reservoirs in the Middle East. Three microporous reservoirs were selected: the Cenomanian Mishrif Formation in Iraq; the Kimmeridgian–Tithonian Arab D and the Barremian Kharaib Formations, both in Abu Dhabi. Staining, cathodoluminescence and scanning electron microscopy were used for petrographic observations. In the selected reservoirs, three typical micrite microtextures are distinguished: micro-rhombic, compact anhedral, and rounded. The chronology of diagenesis, based on petrographic observations, shows that mineralogical stabilisa…

Magnetic survey on Chupicuaro archaeological sites (late pre-classic period, Middle Lerma Valley, Guanajuato, Mexico)

Mass mortality or exceptional fossilization ? The case of the early and middle Toarcian fossiliferous beds from the Digne-Les-Bains area (southeastern France)

Abstract The latest Domerian to late Toarcian sedimentary series (from −190 Ma up to −180 Ma) from the « Réserve Géologique de Haute-Provence » (southeastern France) yields two kinds of remarkable fossiliferous beds. The greatest interest of the early Toarcian type is the occurrence of ichtyosaur remains (at least in six sites) among many other fossils such as ammonites, belemnites, bivalves, wood. The middle Toarcian type is specifically rich in ammonites and nautiluses. Litho- and biostratigraphical, palaeontological, sedimentological and geochemical analyses allow us to determine whether these fossiliferous beds are the results of mass mortalities, linked or not to biological crisis, o…