Search

The knowledge of the Turonian stratotype, “from Saumur till Montrichard“, along the Loire and the Cher valleys waspublished in 2018 by Amédro et alii. Since then, the study of recent collecting of ammonites in southern Touraine provided significant informationto state more precisely the Turonian zonation. New outcrops are described at Bourgueil, Chinon, Loudun, Usseau, Sossay,Marigny-Marmande, Séligny and Ports-sur-Vienne where the following formations were recognized: the Amboise Chalk, the tuffeaux ofArdilliers, of Saumur, of Bourré and the Tuffeau Jaune de Touraine.In these southern countries, it is pointed out that: (1) more than the upper half of the Amboise Chalk appears like the Tuffeaude Saumur facies which at least develops till Châtellerault and contains the “Liron” marker level; (2) the upper part of the Tuffeau deBourré shows numerous firmgrounds; (3) the tempestites at the base of the Tuffeau Jaune de Touraine delivered an original ammoniteassociation where a new species, Romaniceras (R.) marigniacum, occurs with R. ornatissimum in the higher part of the R. ornatissimumzone (Tm 3); (4) consequently, the base of the Tuffeau Jaune de Touraine starts in the Middle Turonian and not in the Upper Turonian asit was traditionally admitted., Les connaissances relatives au Turonien stratotypique qui s’étend « depuis Saumur jusqu’à Montrichard » ont été publiées en2018 par Amédro et alii et concernent des localités réparties dans les vallées de la Loire et du Cher. L’étude de nouvelles récoltes d’ammonitesen Touraine méridionale apporte des compléments significatifs quant à la zonation de l’étage. De nouveaux affleurements sontdécrits à Bourgueil, Chinon, Loudun, Usseau, Sossay, Marigny-Marmande, Séligny et Ports-sur-Vienne où sont reconnues les formationsde la Craie d’Amboise, des Tuffeaux des Ardilliers, de Saumur, de Bourré et du Tuffeau Jaune de Touraine.Il est montré dans ces régions méridionales que : (1) plus de la moitié supérieure de la Craie d’Amboise se trouve sous le facièsdu Tuffeau de Saumur, ce dernier se développant au moins jusqu’à Châtellerault, avec le niveau repère « Liron » ; (2) la partie supérieuredu Tuffeau de Bourré comporte de nombreux arrêts de sédimentation avec firmgrounds ; (3) les tempestites de la base du Tuffeau Jaunede Touraine livrent une association d’ammonites inédite où une nouvelle espèce, Romaniceras (R.) marigniacum, coexiste avec R. ornatissimumau sommet de la zone du même nom (Tm 3) ; (4) ainsi, la base du Tuffeau Jaune de Touraine commence dans le Turonien moyenet non dans le Turonien supérieur comme il était traditionnellement admis.

The Geological Regional Natural Reserve (GRNR) of Pontlevoy, inaugurated in 2018, comprises two ancient quarries (theFour à Chaux quarry and the Hauts de la Plaine Saint-Gilles quarry). It shows the main Miocene formations, overlaying one on theother, which are characteristic of the area located between the Loire and the Cher valleys at the South of Blois: Aquitanian “Calcaire deBeauce”, Burdigalian “Sables et marnes du Blésois” and Langhian “Falun du Blésois”, the two last formations being fossiliferous. Aftera brief synthesis on the Miocene formations of this area, we present sedimentological data on the outcropping formation of the GRNRand results of new paleontological excavations in the “Sables et marnes du Blésois” of the reserve. The geophysical prospection usingelectrical conductivity method as well as borings and core drillings, performed before the preservation works in the area located betweenthe two quarries showed (1) a new fluvial formation filling a deep channel cut in the Langhian falun; this fluvial formation can be datedof the Serravalian or the Upper Miocene, and (2) a senestral strike-slip fault, also regarding to the east, which affects the whole Mioceneformations., La Réserve Naturelle Régionale Géologique (RNRG) de Pontlevoy inaugurée en 2018 comprend deux anciennes carrières (carrièredu Four à Chaux et carrière du Haut de la Plaine Saint-Gilles). On peut y observer en superposition stratigraphique les principalesformations miocènes du secteur situé entre Loire et Cher au sud de Blois : Calcaire de Beauce de l’Aquitanien, Sables et marnes duBlésois du Burdigalien et Faluns du Blésois du Langhien, les deux dernières étant fossilifères. Après une brève synthèse sur les formationsmiocènes de la région, sont présentées ici des données sédimentologiques sur les formations visibles dans la RNRG et les résultats denouvelles fouilles paléontologiques dans les Sables et marnes du Blésois de la réserve. La prospection géophysique par conductivité électrique,ainsi que les sondages et forages carottés effectués entre les deux carrières avant l’aménagement de la réserve, ont révélé (1) laprésence d’une nouvelle formation fluviatile comblant un profond chenal incisé dans le falun langhien ; cette formation peut être rapportéeau Serravallien ou au Miocène supérieur et (2) la présence d’une faille à regard est et décrochement sénestre affectant l’ensemble desformations miocènes.

The prehistoric site of La Roche-Cotard (LRC) is located on the right bank slope of the Loire Valley, a little upstream of Langeais in Indre-et-Loire. The site was made accessible by extensive material collection in 1846. The main cave, LRC I, was excavated in 1912: it contained a middle Paleolithic industry and digital traces were discovered in 1975 and validated in 2008. The resumption of excavations on the site since 2008 has highlighted a powerful 11 meter section with 22 distinct layers, the lower part of which fills a shelter: locus LRC IV, very close to LRC I. The stratigraphy combines from the bottom to the top, karstic inputs, fluvial and eolian sands from the Loire valley and slope deposits. Indices of anthropic occupation (lithic industry, burned bones) attest to the occupation of this space. Numerous radiocarbon and OSL ages make it possible to chronologically constrains this filling between the limit of the isotopic stages 7 and 6 (layer 22 - 169 ka) and the end of stage 3 (layer 2 - 25 ka). The locus has given rise to a multidisciplinary study as complete as possible (sedimentology and micromorphology, small and large vertebrate faunas, lithic industry...). These data provide new information on the palaeoenvironmental evolution of the region, which is poorly known in this time range. The geometry and the age of the deposits lead to the hypothesis that the main cave LRC I was impenetrable by Homo sapiens at least starting from the beginning of the isotopic stage 3 (60 ka) and thus that the parietal productions with symbolic character of the cave are most likely to be attributed to Neanderthal man.

7 pages; National audience

17 pages; National audience

Critical to the origin of life are the ingredients of life, of course, but also the physical and chemical conditions in which prebiotic chemical reactions can take place. These factors place constraints on the types of Hadean environment in which life could have emerged. Many locations, ranging from hydrothermal vents and pumice rafts, through volcanic-hosted splash pools to continental springs and rivers, have been proposed for the emergence of life on Earth, each with respective advantages and certain disadvantages. However, there is another, hitherto unrecognized environment that, on the Hadean Earth (4.5–4.0 Ga), would have been more important than any other in terms of spatial and temporal scale: the sedimentary layer between oceanic crust and seawater. Using as an example sediments from the 3.5–3.33 Ga Barberton Greenstone Belt, South Africa, analogous at least on a local scale to those of the Hadean eon, we document constant permeation of the porous, carbonaceous, and reactive sedimentary layer by hydrothermal fluids emanating from the crust. This partially UV-protected, subaqueous sedimentary environment, characterized by physical and chemical gradients, represented a widespread system of miniature chemical reactors in which the production and complexification of prebiotic molecules could have led to the origin of life. Key Words: Origin of life—Hadean environment—Mineral surface reactions—Hydrothermal fluids—Archean volcanic sediments. Astrobiology 18, 259–293.

International audience; Charles VIII (1483-1498) construction period in the castle at Amboise took place from 1492 to 1498. In 1495-1496, an account book was written mainly about the well-preserved Tour des Minimes, a tower one could climb up on horseback. A comparative study of the building, along with the account book, cut stones (petrography and statistics), mortars (grain size distribution and lime) and the whitewash jointing, requires a specific methodology and a constant dialogue between architectural historians, geologists, and archaeologists. The research enables to identify the name of the stones and the technical vocabulary used at the end of the middle ages. Moreover, it proves that achief stone dresser probably worked on the tower, and that the building site was likely to have been split into several centresand workshops; and it also reveals the rhythm of work to have been intense, since for the tower only, more than 15m of vaulted masonry had been created. All this have been allowed thanks to workers with an empirical knowledge of materials, the high quality of the chosen materials and the remarkable implementation they did. It resulted in an outstanding genuine edifice in which four revolutions and a half climb around an openwork newel.; Le chantier de Charles VIII (1483-1498) au château d’Amboise se déroula entre 1492 et 1498. L’année 1495-1496 est documentée par un livre de compte concernant notamment la tour cavalière des Minimes, aujourd’hui bien conservée. L’étude croisée du bâti, du livre de compte, des pierres de taille (pétrographie et statistique), des mortiers (granulométrie et analyses de la chaux) et du badigeon recouvrant les joints a nécessité la mise en place d’une méthodologie précise, demandant de continuels échanges entre historiens de l’architecture, géologues et archéologues. Ces investigations permettent d’identifier les dénominations des pierres et le vocabulaire technique en usage à la fin du Moyen Âge. Mais bien au-delà, elles démontrent l’intervention probable d’un appareilleur, l’organisation du chantier régi en plusieurs pôles et ateliers, ainsi que son rythme très soutenu puisque, pour la seule tour, plus de 15 m de maçonneries voûtées furent élevées. Ce fut possible grâce à la connaissance empirique des matériaux qu’avaient les hommes œuvrant à la construction, à la qualité des matériaux employés et à la remarquable mise en œuvre qui en fut faite. Il en résulte un ouvrage hors du commun, d’une rare audace où quatre révolutions et demie de voûtes d’ogives montent autour d’un noyau creux.

International audience; The search for traces of life is one of the principal objectives of Mars exploration. Central to this objective is theconcept of habitability, the set of conditions that allows the appearance of life and successful establishment ofmicroorganisms in any one location. While environmental conditions may have been conducive to the appearanceof life early in martian history, habitable conditions were always heterogeneous on a spatial scale andin a geological time frame. This ‘‘punctuated’’ scenario of habitability would have had important consequencesfor the evolution of martian life, as well as for the presence and preservation of traces of life at a specificlanding site. We hypothesize that, given the lack of long-term, continuous habitability, if martian life developed,it was (and may still be) chemotrophic and anaerobic. Obtaining nutrition from the same kinds of sourcesas early terrestrial chemotrophic life and living in the same kinds of environments, the fossilized traces of thelatter serve as useful proxies for understanding the potential distribution of martian chemotrophs and theirfossilized traces. Thus, comparison with analog, anaerobic, volcanic terrestrial environments (Early Archean>3.5–3.33 Ga) shows that the fossil remains of chemotrophs in such environments were common, althoughsparsely distributed, except in the vicinity of hydrothermal activity where nutrients were readily available.Moreover, the traces of these kinds of microorganisms can be well preserved, provided that they are rapidlymineralized and that the sediments in which they occur are rapidly cemented. We evaluate the biogenicity ofthese signatures by comparing them to possible abiotic features. Finally, we discuss the implications of differentscenarios for life on Mars for detection by in situ exploration, ranging from its non-appearance, throughpreserved traces of life, to the presence of living microorganisms. Key Words: Mars—Early Earth—Anaerobicchemotrophs—Biosignatures—Astrobiology missions to Mars. Astrobiology 15, 998–1029.

International audience; Riparian vegetation is a key factor of the morphological evolution of river. In Europe, riparian Salicaceae is declining following the loss of potential recruitment areas associated with river management. As an exception for lowland rivers, the Loire River (France) shows, in its middle reaches, an efficient sexual regeneration of Populus nigra and Salix alba on bare sediments deposited during flood events. In the literature, the influence of hydrological patterns as a key factor of the seedlings survival is well documented. Some studies focused on seedlings ability to withstand flood constraints and detailed the effect of duration and intensity of floods but few studies characterized precisely the processes applied on seedlings. As a working hypothesis, we consider that three types of flood stresses can induce mortality of seedlings: (i) uprooting by drag applied on the seedlings without sediment erosion, (ii) erosion of the recruited areas and (iii) burying. The distinction of these three processes allows identifying the importance of survival factors due to a strong sediment dynamics (e.g. erosion height > root height) or to the anchorage and resprouting ability. The main issues are: what are the governing processes (type and intensity) determining survival or death of seedlings and which factor (fluvial dynamics vs. own characteristics of seedlings) controls their survival? In-situ measurements were performed on a forced alluvial bar (20.000 m2) to detail the bar dynamics (bathymetry, topography, scour/fill processes, grain size surveys, flow velocity) and to survey the associated recruitment. On 48 plots (1.410 m2) the density, height and species (P. nigra and S. alba) were surveyed the year of recruitment (after dry period) and the next year after flood period. We highlight the following phases of processes during floods. The erosion of substrate dominates at the beginning of the rising limb. The erosion or uprooting processes depend of the balance between available bed shear stress and sediment size. Then the deposit occurs on the back of the bar before the peak discharge and protects them against uprooting by burying during the higher energy of flow. At the end of the falling limb, sediments are reworked, decreasing the burying height of seedlings and allowing possible uprooting (drag) or erosion of sediments.