175 research outputs found
La capture du Grand-Morin par la Marne (Bassin parisien, France) : ùge et mécanisme
Des sondages, réalisés dans la vallée aval abandonnée du Grand-Morin, à l'ouest d'EsbIy, permettent de dater son abandon du Tardiglaciaire (Dryas ancien probable). La capture qui en est la cause est attribuée à un chenal de la Marne qui divaguait sur un lit exhaussé par les alluvions pléniglaciaires et tardiglaciaires. Elle a toutefois été préparée par un travail des deux riviÚres, dont les méandres s'étaient progressivement rapprochés durant le Pleistocene moyen.Drillings were undertaken in the fossil lower valley of the Grand-Morin river near Esbly. They date its piracy by the Marne river from the Late Glacial (Early Dryas probably). This capture is related to a braided channel flowing on the raised bed of Pleniglacial and Late Glacial alluvium. However, this piracy was prepared by the migration of the meanders of the two rivers during the Middle Pleistocene
Vegetation dynamics, human impact and exploitation patterns in the Paris Basin through the Holocene: palynology vs. anthracology.
Arlette Leroi-Gourhan (1913-2005) : lâinitiatrice de la palynologie appliquĂ©e Ă lâarchĂ©ologie prĂ©historique
Arlette Leroi-Gourhan est dĂ©cĂ©dĂ©e le 25âŻavril 2005 en son domicile familial de Vermenton. NĂ©e Royer le 9âŻjanvier 1913 Ă Paris, elle est issue dâune famille dâindustriels. Son appartenance Ă une bourgeoisie aisĂ©e lui ouvre les portes des milieux intellectuels et artistiques. Elle pratique ainsi danse, musique et diffĂ©rents sports (natation, Ă©quitation, skiâŠ) tandis quâelle voyage beaucoup en Europe et en Afrique du Nord. DiplĂŽmĂ©e de lâĂcole du Louvre, elle suit en 1934 les cours que lâethnolog..
Les transformations de la végétation du bassin parisien par la modélisation des données polliniques holocÚnes
International audienceLa synthĂšse palynologique du Bassin parisien repose sur un corpus de 91 sĂ©quences de fonds de vallĂ©es qui rĂ©sume lâhistoire de la vĂ©gĂ©tation holocĂšne rĂ©gionale. Parmi elles, 22 ont Ă©tĂ© utilisĂ©es pour reconstruire quantitativement le couvert vĂ©gĂ©tal, en utilisant un nouveau modĂšle de reconstitution des paysages, REVEALS. Il corrige la relation non linĂ©aire entre pollen et vĂ©gĂ©tation et permet ainsi de convertir les assemblages polliniques en surfaces de couverture relatives aux diffĂ©rents taxons vĂ©gĂ©taux. Les dynamiques de ces plantes, ou groupes de plantes, reconstituent alors lâĂ©volution de la structure des paysages du Bassin parisien durant lâHolocĂšne
Mid Holocene vegetation reconstruction from Vanevan peat (south-eastern shore of Lake Sevan, Armenia)
International audienceA sediment core has been retrieved from Vanevan peat (south-eastern shore of Lake Sevan, Armenia), which is today disconnected from Lake Sevan thanks to an artificial shallowing of the lake. Based on 5 radiocarbon dates, Vanevan record covers the Mid Holocene (from ca. 7800 to ca. 5100 cal. BP). The Late Holocene is today absent in the peat stratigraphy due to modern peat exploitation by surface mining. This study focuses on a multi-proxy approach including pollen, charcoals, and pollen-inferred climate reconstruction. An open-land, steppic vegetation is recorded up to ca. 7700 cal. BP, followed by a more forested landscape during the Mid Holocene (up to ca. 5700 cal. BP), and ending again with an open-land vegetation (to the end of record, 5100 cal. BP). This vegetation dynamics responds to general climate changes documented in the Near East. Whether human activities are documented since ca. 7500 cal. BP (Late Neolithic) in Vanevan, they remain marginal and probably did not affect the area. Early Holocene dry climate, which caused the steppic environment to be widespread through the Near East, is strongly related to low late spring precipitation (PMayâJun = 180 mm). Mid Holocene forested landscape and increasing lake-level seem related to late spring precipitation (+28%), which is the main change in estimated climate parameters. This has to be linked with reinforcement of the Westerlies and less active Siberian High, which are inversely involved in the following, dry phase starting at ca. 5700 cal. B
CONTEXTE GĂOMORPHOLOGIQUE, CHRONOSTRATIGRAPHIQUE ET PALĂOENVIRONNEMENTAL DES SITES MĂSOLITHIQUES ET PALĂOLITHIQUES DE WARLUIS DANS LA VALLĂE DU THĂRAIN (OISE, FRANCE)
International audienceWarluis Mesolithic sites were discovered during rescue archaeological excavations in a quarry spread over 40 hectares, located in the Therain alluvial plain (Northern France). Several palaeochannels of Lateglacial and Holocene age are present. The Lateglacial sequence contains organic and silty deposits. Holocene infillings are mainly peaty, except one tufaceous channel. Some 30 concentrations of lithic artefacts and faunal remains have been handdigged over 2 400 mÂČ. The most frequent sedimentary sequence is composed of (from bottom to top): weichselian gravel, white silty sands, organic sandy silts, peat, clayey silts. Organic sandy silts are divided into a basal greyish bed and an upper brown horizon. Stratigraphical, archaeological, malacological and palynological arguments together with radiocarbon datings allow to establish an AllerĂžd age for the basal greyish sediment that contains Final Palaeolithic industry. Above the AllerĂžd bed are deposited Preboreal and Boreal brown sediments. Boreal deposits are marked by the development of the gastropod Discus rotundatus. These intensively bioturbated sediments contain Mesolithic artefacts and faunal remains. Peat spreads on almost the whole valley bottom, overlaying all mesolithic settlements. Peat thickness varies from a few meters within channels down to a few centimetres (even absent) on higher places. It is dated from the Boreal to the Early Atlantic. Mesolithic settlements are located on channel banks or on the hummocks in the valley bottom. Radiocarbon datings indicate that many occupations occurred since the Early Holocene (ca 9900 BP) to the Early Boreal (ca 8800 BP). First results of archaeozoological studies show a predation on red deer, roe deer and aurochs on the earliest sites and on wild boar at the beginning of the Boreal. This fits with a gradual afforestation of the area as showed by both malacological and palynological records.Le gisement mĂ©solithique de Warluis (Oise) a Ă©tĂ© mis au jour dans une graviĂšre couvrant une quarantaine d'hectares de la plaine alluviale du ThĂ©rain, un affluent de l'Oise. Plusieurs palĂ©ochenaux ont Ă©tĂ© repĂ©rĂ©s : un chenal tardiglaciaire Ă comblement organique et limoneux, des chenaux tourbeux et un chenal de tuf holocĂšne. Une trentaine de concentrations de vestiges lithiques et fauniques ont Ă©tĂ© fouillĂ©es manuellement sur 2 400 mÂČ. La sĂ©quence sĂ©dimentaire la plus reprĂ©sentĂ©e sur les sites est une succession : grave de fond weichselienne â sables limoneux blancs â limons sableux organiques â tourbe â limons plastiques peu Ă©pais. Deux couches se distinguent gĂ©nĂ©ralement dans les limons sableux organiques, l'une plus grise Ă la base, l'autre plus brune. Des arguments stratigraphiques, archĂ©ologiques, malacologiques, palynologiques et des datations radiocarbone permettent d'attribuer un Ăąge AllerĂžd aux limons gris, qui contiennent des industries du PalĂ©olithique final Ă Federmesser. Sur l'AllerĂžd se superposent directement des apports dĂ©tritiques plus organiques bruns trĂšs bioturbĂ©s qui correspondent au PrĂ©borĂ©al et au dĂ©but du BorĂ©al (ce dernier marquĂ© par le dĂ©veloppement du gastĂ©ropode Discus rotundatus). Ces sĂ©diments contiennent les vestiges mĂ©solithiques. Les tourbes sont prĂ©sentes sur quasiment toute la carriĂšre sur une Ă©paisseur variable (plusieurs mĂštres dans les chenaux, quelques centimĂštres ou absentes sur les points les plus hauts). Les datations obtenues jusqu'Ă prĂ©sent convergent pour attribuer un Ăąge borĂ©al et atlantique ancien Ă cette tourbe qui recouvre l'ensemble des niveaux archĂ©ologiques. Les populations mĂ©solithiques se sont installĂ©es Ă proximitĂ© de palĂ©ochenaux ou sur de petites Ă©minences du fond de vallĂ©e. Les premiĂšres datations radiocarbone indiquent une succession d'occupations depuis le dĂ©but de l'HolocĂšne, vers 9900 BP, jusqu'au dĂ©but du BorĂ©al vers 8800 BP. Les premiers rĂ©sultats de l'Ă©tude archĂ©ozoologique tĂ©moignent d'une prĂ©dation du cerf, du chevreuil et de l'aurochs sur les sites les plus anciens et d'une exploitation qui se rĂ©oriente sur le sanglier au dĂ©but du BorĂ©al. Ceci coĂŻncide avec la densification du couvert vĂ©gĂ©tal et le boisement progressif rĂ©vĂ©lĂ©s par l'analyse palynologique et les cortĂšges malacologiques
Paléoenvironnements tardiglaciaires en Aquitaine : la séquence alluviale de la BrunetiÚre (Bergerac, France)
Des dĂ©pĂŽts alluviaux datant du Tardiglaciaire et du dĂ©but de lâHolocĂšne ont Ă©tĂ© dĂ©couverts dans la plaine du Caudeau, petit affluent de la Dordogne, Ă La BrunetiĂšre sur la commune de Pombonne (Dordogne) Ă lâoccasion de travaux dâarchĂ©ologie prĂ©ventive. Leur analyse permet de renouveler nos connaissances sur lâĂ©volution des cours dâeau en Aquitaine pendant cette pĂ©riode charniĂšre. Ils montrent en particulier que les principales phases de mĂ©tamorphose alluviale dĂ©crites dans le nord de lâEurope se sont Ă©galement produites dans cette rĂ©gion de maniĂšre Ă peu prĂšs synchrone, pour autant que lâon puisse en juger dâaprĂšs les dates disponibles. Deux phases majeures dâincision aux dĂ©pens de la nappe alluviale Ă galets plĂ©niglaciaire sont identifiables. La premiĂšre intervient pendant une phase trĂšs prĂ©coce du BĂžlling, soit avant 12 700 ± 45 BP, dans un environnement steppique. Lâabandon rapide du chenal, associĂ© Ă du soutirage karstique, permet ensuite lâinstallation dâun petit lac colmatĂ© par des argiles avec quelques intercalations tourbeuses riches en macrorestes vĂ©gĂ©taux (bouleau nain, saule). Lâimage de la vĂ©gĂ©tation donnĂ©e aussi bien par les pollens que par la faune de mollusques et dâinsectes est celle dâune steppe encore trĂšs ouverte Ă armoise et genĂ©vriers, alors que les palĂ©otempĂ©ratures estivales indiquĂ©es par les insectes sont dĂ©jĂ proches de celles connues actuellement dans la rĂ©gion. Des palĂ©otempĂ©ratures hivernales sensiblement plus froides que les actuelles (-20 Ă 5 °C) renvoient cependant lâimage dâun climat Ă caractĂšre plus continental. Les dĂ©pĂŽts lacustres sont ensuite recouverts par une couche de sables dâinondation attribuĂ©s au Dryas moyen et/ou rĂ©cent. LâassĂšchement du chenal et le dĂ©veloppement dâun sol hydromorphe pourrait correspondre respectivement soit Ă lâAllerĂžd, soit au tout dĂ©but de lâHolocĂšne. La seconde phase dâincision est attribuĂ©e au PrĂ©borĂ©al et tronque la sĂ©quence tardiglaciaire; elle est associĂ©e Ă un style alluvial Ă chenaux anastomosĂ©s. Lâabandon de la majoritĂ© des chenaux pendant le BorĂ©al marque la rĂ©duction du lit Ă un chenal unique sinueux, comparable Ă celui qui caractĂ©rise le Caudeau actuel. Une industrie lithique de type MagdalĂ©nien supĂ©rieur a Ă©galement Ă©tĂ© dĂ©couverte sur la berge du chenal tardiglaciaire. Lâindustrie recueillie est exclusivement taillĂ©e dans le silex local maestrichtien. Elle comprend environ 200 Ă©clats et 800 petits restes de taille, pour seulement 15 lames de plein dĂ©bitage et 6 outils (sans aucun microlithe). Lâutilisation exclusive dâun percuteur minĂ©ral tendre, la morphologie du nuclĂ©us laminaire, la rectitude des petites lames, les 2 lames appointĂ©es sont autant de caractĂšres qui Ă©voquent le stade ultime du MagdalĂ©nien supĂ©rieur, tel quâil est connu plus en amont le long de la Dordogne sur les sites de la Gare de Couze et du Moulin du Roc.Late-glacial to Holocene alluvial deposits have been discovered along a small tributary of the Dordogne river at âLa BrunetiĂšreâ near Bergerac (Dordogne, southwestern France) and yield novel information on the evolution of rivers at the end of the Weichselian. The deposits show that the main alluvial changes described in Northern Europe occurred simultaneously at âLa BrunetiĂšreâ. Two major phases of channel incision in the basal Pleniglacial gravel body have been identified. The first channels developed at the very onset of the BĂžlling, i.e. before 12,700 ± 45 BP, in a steppic landscape. Rapid channel abandonment allowed development of a small lake, filled in with alternating peat and clay layers rich in vegetal debris. Pollen data as well as molluscs and insects point to an open Artemisia steppe with juniper trees, together with a local component of riparian shrubs (willow and dwarf birch). Palaeotemperatures reconstructed from coleopteran assemblages indicate larger-than-today yearly thermal amplitude with cold winters and warm summers. The lacustrine clays and peats are buried by sandy overbank deposits that are attributed to the Older and/or the Upper Dryas. Channel drying and subsequent hydromorphic soil development relate respectively to the AllerĂžd or the early Holocene. The second phase of incision corresponds to the Preboreal and is typified by stable anastomosed channel formation. Most of these were abandoned during the Boreal and filled by organicclay. An Upper Magdalenian lithic industry has been discovered in a paleosol on the bank of the Late-glacial channel. It includes ca. 200 flakes and 800 small debris of local Maestrichtian flint, and only 15 full-debitage blades and 6 tools. Exclusive use of soft hammer, laminar core morphology, straightness of the small blades, and the 2 pointed blades indicate an ultimate stage of the Upper Magdalenian
Neuilly-sur-Marne â La Haute Ăle
Le lieu-dit « la Haute Ăle », Ă Neuilly-sur-Marne, occupe, sur 70 ha, lâune des derniĂšres grandes boucles de la Marne avant sa confluence avec la Seine. Il sâagit dâune trĂšs basse terrasse de la riviĂšre constituĂ©e de sĂ©diments sabla-graveleux et culminant Ă 38 m NGF (3,5 m au-dessus du niveau moyen de la Marne). Ces terrains servaient de domaine agricole Ă la ferme thĂ©rapeutique dĂ©pendant de lâhĂŽpital psychiatrique de Ville-Evrard. Le dĂ©partement de Seine-Saint-Denis les a acquis il y a une q..
Neurotrophin p75 receptor (p75NTR) promotes endothelial cell apoptosis and inhibits angiogenesis:implications for diabetes-induced impaired neovascularization in ischemic limb muscles
Diabetes impairs endothelial function and reparative neovascularization. The p75 receptor of neurotrophins (p75<sup>NTR</sup>), which is scarcely present in healthy endothelial cells (ECs), becomes strongly expressed by capillary ECs after induction of peripheral ischemia in type-1 diabetic mice. Here, we show that gene transfer-induced p75<sup>NTR</sup> expression impairs the survival, proliferation, migration, and adhesion capacities of cultured ECs and endothelial progenitor cells (EPCs) and inhibits angiogenesis in vitro. Moreover, intramuscular p75<sup>NTR</sup> gene delivery impairs neovascularization and blood flow recovery in a mouse model of limb ischemia. These disturbed functions are associated with suppression of signaling mechanisms implicated in EC survival and angiogenesis. In fact, p75<sup>NTR</sup> depresses the VEGF-A/Akt/eNOS/NO pathway and additionally reduces the mRNA levels ofITGB1 [beta (1) integrin], BIRC5 (survivin), PTTG1 (securin) and VEZF1. Diabetic mice, which typically show impaired postischemic muscular neovascularization and blood perfusion recovery, have these defects corrected by intramuscular gene transfer of a dominant negative mutant form of p75<sup>NTR</sup>. Collectively, our data newly demonstrate the antiangiogenic action of p75<sup>NTR</sup> and open new avenues for the therapeutic use of p75<sup>NTR</sup> inhibition to combat diabetes-induced microvascular liabilities
European pollen-based REVEALS land-cover reconstructions for the Holocene: methodology, mapping and potentials
Abstract. Quantitative reconstructions of past land cover are necessary to determine the processes involved in climateâhumanâland-cover interactions. We present the first temporally continuous and most spatially extensive pollen-based land-cover reconstruction for Europe over the Holocene (last 11â700âcalâyrâBP). We describe how vegetation cover has been quantified from pollen records at a 1ââĂâ1â spatial scale using the âRegional Estimates of VEgetation Abundance from Large Sitesâ (REVEALS) model. REVEALS calculates estimates of past regional vegetation cover in proportions or percentages. REVEALS has been applied to 1128 pollen records across Europe and part of the eastern MediterraneanâBlack SeaâCaspian corridor (30â75ââN, 25ââWâ50ââE) to reconstruct the percentage cover of 31 plant taxa assigned to 12 plant functional types (PFTs) and 3 land-cover types (LCTs). A new synthesis of relative pollen productivities (RPPs) for European plant taxa was performed for this reconstruction. It includes multiple RPP values (â„2 values) for 39 taxa and single values for 15 taxa (total of 54 taxa). To illustrate this, we present distribution maps for five taxa (Calluna vulgaris, Cerealia type (t)., Picea abies, deciduous Quercus t. and evergreen Quercus t.) and three land-cover types (open land, OL; evergreen trees, ETs; and summer-green trees, STs) for eight selected time windows. The reliability of the REVEALS reconstructions and issues related to the interpretation of the results in terms of landscape openness and human-induced vegetation change are discussed. This is followed by a review of the current use of this reconstruction and its future potential utility and development. REVEALS data quality are primarily determined by pollen count data (pollen count and sample, pollen identification, and chronology) and site type and number (lake or bog, large or small, one site vs. multiple sites) used for REVEALS analysis (for each grid cell). A large number of sites with high-quality pollen count data will produce more reliable land-cover estimates with lower standard errors compared to a low number of sites with lower-quality pollen count data. The REVEALS data presented here can be downloaded from https://doi.org/10.1594/PANGAEA.937075 (Fyfe et al., 2022). </jats:p
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