F. Melieres

Bio: F. Melieres is an academic researcher from University of Paris. The author has contributed to research in topics: Holocene & Total organic carbon. The author has an hindex of 6, co-authored 11 publications receiving 1869 citations. Previous affiliations of F. Melieres include Centre national de la recherche scientifique.

History of the Mediterranean salinity crisis

Abstract: A history of geodynamic evolution of the Mediterranean leading to the salinity crisis is outlined, based on the ‘desiccated deep-basin model’. An accurate portrayal of the crisis is presented, based on data from new drilling and studies of on-land geology.

A 13,000-year climate record from western tibet

Abstract: ALTHOUGH the Tibetan plateau is important in influencing the atmospheric circulation of the Northern Hemisphere1–3, there are only a few continuous palaeoclimate records available, and these are limited to the plateau's northeastern margin4–6. Here we present a 13,000-yr record from Sumxi Co (western Tibet), constructed from both lake-core and shoreline studies, which shows that conditions in the early–middle Holocene were warmer and wetter than at present. These results confirm model predictions of an intensified monsoon over the region at ∼9,000 yr BP, owing to an orbitally induced increase in summer insolation7,8. We also find evidence for warm, humid pulses at ∼12,500 and ∼10,000 yr BP, in phase with the steps of the last deglaciation, and for a return to cold, dry conditions at ∼11-10,000 yr BP, none of which can be explained by orbital variations. The existence of the cold episode confirms that the cooling associated with the Younger Dry as event occurred in continental China6,9, and provides further evidence of the global nature of this event10

Variation of the Distribution of Organic Matter Within a Transgressive System Tract: Kimmeridge Clay (Jurassic), England: Chapter 6

Abstract: The Kimmeridge Clay of northern England is part of a highstand system tract, rich in organic material, whose offshore correlatives sourced much of the North Sea oil province. Spatial and temporal variation over a 35-km-long transect (extended to 100 km by correlation offshore), some 200 m thick ranging from the Cymodoce to the Pallassioides zones, and representing some 6.5 m.y. of marine sedimentation, was evaluated by study of four continuously cored boreholes sited to sample both basin and shelf facies. Thin-bed stratigraphy, established by geophysical log signatures calibrated by the ammonite succession, enables organic-rich beds to be traced throughout the transect and into other English basins. These results show that total organic carbon may be computed reliably from a combination of resistivity, density, and sonic logs and increases by over 50% as each level is traced from shelf to basin where deeper waters are thought to have favored its entrapment and preservation in an environment more depleted in dissolved oxygen and with a more rapid burial. Associated, coccolith-rich, marker bands of the shelf pass into dolomites in the basin owing to the precipitation of early dolomite through bacterial decay of the organic-rich material. Vertical distribution of the organic content of each section identifies a hierarchy of sedimentary cycles with periodicities of about 25,000 and 280,000 End_Page 67------------------------- years. The short period cycles, less than 1 m thick, comprise alternations of more or less organic-rich beds. The analysis of the extracts suggests unity of origin of the organic matter of type II origin (zoo- and phytoplankton) throughout the period of sedimentation. The differences observed in the kerogens can be interpreted in terms of a fluctuation of oxygen deficiency whose variations (dysaerobic, anaerobic, or anoxic) are recorded in time and in space. Some of the variation, near coccolith-rich beds, can be related to a very high organic productivity (up to 40 wt.% total organic carbon). The second order cycles show maximum kerogen enrichment in the middle of the transgressive tract intervals, or at the base of high level, or platform edge prisms. These relationships allow the d stribution of the organic matter to be deduced from sequence stratigraphic studies.

Hétérogenéité quantitative et qualitative de la matière organique dans les argiles du Kimmeridgien du val de Pickering (Yorkshire, UK). Cadre sédimentologique et stratigraphique

Abstract: Les argiles du Kimmeridgien contribuent a l'alimentation de nombreux gisements en mer du Nord. L'etude de quatre puits localises sur une coupe Est-Ouest dans le Val de Pickering (Bassin de Cleveland) permet d'illustrer dans cette formation l'heterogeneite de distribution verticale et laterale de la matiere organique en terme de quantite et de qualite. La coupe etudiee (35 km de long, 200 m de haut) represente environ 6,5 millions d'annees d'histoire geologique. Les analyses mineralogiques montrent que la formation est caracterisee par une grande homogeneite des apports sedimentaires, ce qui suppose des conditions de sedimentation stables dans le temps et dans l'espace. Le materiel sedimentaire, depose dans un environnement calme, est compose de mineraux argileux (kaolinite, illite, et interstratifies irreguliers illite/smectite) avec des niveaux carbonates resultant d'une production biogenique. Ces niveaux carbonates intercales au sein des argiles peuvent etre correles entre les puits. Pour la plupart dolomitises, ils resultent d'une transformation plus importante al'ouest (Marton) qu'a l'est (Reighton) de couches presque exclusivement formees de coccolithes. L'extension horizontale de ces niveaux indique qu'ils correspondent a des evenements geodynamiques regionaux. L'etude des ammonites permet de reconnaitre, dans le Yorkshire, la succession de 10 zones du Kimmeridgien (sensu anglico) et d'identifier 8 sous-zones depuis la zone a Cymodoce (- 144 m. a. ) jusqu'a celle a Pectinatus (- 137,5 m. a. ). Les zonations reconnues permettent de correler ces quatre puits avec les autres regions d'Angleterre. L'existence de reperes stratigraphiques et de reperes diagraphiques caracteristiques au sein des zones d'ammonites permet d'etablir des zones de correlation entre une partie bassin (puits de Marton 87, Ebberston 87, Flixton 87) et une zone haute appartenant a la plate-forme Est de l'Angleterre (puits de Reighton 87). L'etude de l'heterogeneite quantitative de la matiere organique des sediments du Kimmeridgien du Yorkshire montre le caractere ordonne (non aleatoire) de la distribution du COT dans l'espace et dans le temps. L'heterogeneite dans l'espace montre un gradient de preservation d'est en ouest : minimum sur la zone haute, maximum vers le centre du bassin ou les depots sont les plus epais. L'existence de niveaux riches dans la zone presentant le plus fort taux d'accumulation sedimentaire (depot centre) peut s'expliquer d'une part par un environnement plus favorable a la preservation de la matiere organique dans une zone bathymetrique plus profonde (et un milieu de plus faible energie que la plate-forme) et d'autre part par une meilleure preservation liee a un enfouissement plus rapide. L'heterogeneite dans le temps se caracterise - quels que soient les puits - par une sedimentologie presentant des alternances de niveaux plus ou moins riches en matiere organique. Le debut de la preservation de la matiere organique apparait dans le Kimmeridgien inferieur (zone a Cymodoce) pour atteindre un premier paroxysme au sommet de la zone a Eudoxus, un second a la base de la zone a Hudlestoni, un troisieme a la base de la zone a Pectinatus. Pour les deux derniers, cette accumulation pourrait correspondre avec le maximum de transgression. Bien que tres variable dans le temps et dans l'espace, la distribution de la matiere organique montre par consequent une logique, interpretable a l'echelle horizontale (fluctuations liees a l'epaisseur de la tranche d'eau par exemple donc aux cycles transgressifs et regressifs), plus hypothetique en l'etat des connaissances a l'echelle verticale (cycle climatique). Dans les cycles, l'heterogeneite de distribution quantitative en terme sequentiel ( haut de sequencecorrespondant aux fortes teneurs en COT et bas de sequenceaux faibles teneurs en COT) est confirmee par l'etude qualitative des residus stables (analyses elementaires : H/C-O/C) ou de la roche brute (index d'hydrogene/index d'oxygene, IH/10). La matiere organique associee aux niveaux de haut de sequence sont tres proches de la lignee Il alors que les bas de sequences voient leur rapport atomique H/C decroitre en meme temps que le rapport atomique O/C augmenter. L'etude des extraits suggere au contraire qu'il existe une unite dans l'origine du materiel organique tout au long de la sedimentation quels que soient les termes de la cyclicite et le niveau lithologique. Les differences observees au niveau des residus stables refleteraient par consequent une difference dans les etats de preservation d'une meme matiere organique (coccolithes, dinoflagelles) avec des variations affectant tant la quantite ( % COT) que la qualite (H/C-O/C, IH-10). L'heterogeneite de la matiere organique dans les cyclicites elementaires peut etre interpretee en terme de fluctuation du milieu : plus ou moins anaerobique, dont on enregistre les variations dans le temps et dans l'espace. Les tres fortes concentrations de matiere organique (20-40 %) correspondant aux anomalies organiquesse superposent a ces fluctuations. Localisees a proximite des niveaux carbonates (niveaux equivalents aux Rope Lake Head Stone Bandet White Stone Banddu Dorset), elles semblent conjuguer a la fois des phenomenes de preservation et de productivite comme le suggere l'abondance exceptionnelle des coccolithes.

Tropical Climate Instability: The Last Glacial Cycle from a Qinghai-Tibetan Ice Core

Abstract: An ice core record from the Guliya ice cap on the Qinghai-Tibetan Plateau provides evidence of regional climatic conditions over the last glacial cycle. 36 Cl data suggest that the deepest 20 meters of the core may be more than 500,000 years old. The δ 18 O change across Termination I is ∼5.4 per mil, similar to that in the Huascaran (Peru) and polar ice cores. Three Guliya interstadials (Stages 3, 5a, and 5c) are marked by increases in δ 18 O values similar to that of the Holocene and Eemian (∼124,000 years ago). The similarity of this pattern to that of CH 4 records from polar ice cores indicates that global CH 4 levels and the tropical hydrological cycle are linked. The Late Glacial Stage record contains numerous 200-year oscillations in δ 18 O values and in dust, NH 4 + , and NO 3 − levels.

Toward a complete Himalayan hydrological budget: Spatiotemporal distribution of snowmelt and rainfall and their impact on river discharge

Abstract: [1] The hydrological budget of Himalayan rivers is dominated by monsoonal rainfall and snowmelt, but their relative impact is not well established because this remote region lacks a dense gauge network. Here, we use a combination of validated remotely-sensed climate parameters to characterize the spatiotemporal distribution of rainfall, snowfall, and evapotranspiration in order to quantify their relative contribution to mean river discharge. Rainfall amounts are calculated from calibrated, orbital, high-resolution Tropical Rainfall Measurement Mission data, and snow-water equivalents are computed from a snowmelt model based on satellite-derived snow cover, surface temperature, and solar radiation. Our data allow us to identify three key aspects of the spatiotemporal precipitation pattern. First, we observe a strong decoupling between the rainfall on the Himalayan foreland versus that in the mountains: a pronounced sixfold, east-west rainfall gradient in the Ganges plains exists only at elevations <500 m asl. Mountainous regions (500 to 5000 m asl) receive nearly equal rainfall amounts along strike. Second, whereas the Indian summer monsoon is responsible for more than 80% of annual rainfall in the central Himalaya and Tibetan Plateau, the eastern and western syntaxes receive only ∼50% of their annual rainfall during the summer season. Third, snowmelt contributions to discharge differ widely along the range. As a fraction of the total annual discharge, snowmelt constitutes up to 50% in the far western (Indus area) catchments, ∼25% in far eastern (Tsangpo) catchments, and <20% elsewhere. Despite these along-strike variations, snowmelt in the pre- and early-monsoon season (April to June) is significant and important in all catchments, although most pronounced in the western catchments. Thus, changes in the timing or amount of snowmelt due to increasing temperatures or decreasing winter precipitation may have far-reaching societal consequences. These new data on precipitation and runoff set the stage for far more detailed investigations than have previously been possible of climate-erosion interactions in the Himalaya.

Kinematic model of active deformation in central Asia

Abstract: The velocity field of present‐day deformation in Central Asia is modelled using a set of four rotating blocks (Siberia, Tarim, Tibet, India) on a spherical earth. A best‐fit is inverted on the basis of estimated shortening‐rates across the main thrust zones (Himalayas, Tien Shan) and measured slip‐rates along the principal strike‐slip faults (Altyn Tagh and Karakorum) separating those blocks. The fit to the data implies that nearly all the present convergence between India and Asia can be accounted for by slip‐partitioning on these four zones, with as much as 50% absorbed by northeastwards extrusion of Tibet. This suggests that localised deformation governs the present mechanical behaviour of the Central Asian lithosphere.

Molecular biogeography of Europe: Pleistocene cycles and postglacial trends

Abstract: The climatic cycles with subsequent glacial and intergalcial periods have had a great impact on the distribution and evolution of species. Using genetic analytical tools considerably increased our understanding of these processes. In this review I therefore give an overview of the molecular biogeography of Europe. For means of simplification, I distinguish between three major biogeographical entities: (i) "Mediterranean" with Mediterranean differentiation and dispersal centres, (ii) "Continental" with extra-Mediterranean centres and (iii) "Alpine" and/or "Arctic" with recent alpine and/or arctic distribution patterns. These different molecular biogeographical patterns are presented using actual examples. Many "Mediterranean" species are differentiated into three major European genetic lineages, which are due to glacial isolation in the three major Mediterranean peninsulas. Postglacial expansion in this group of species is mostly influenced by the barriers of the Pyrenees and the Alps with four resulting main patterns of postglacial range expansions. However, some cases are known with less than one genetic lineage per Mediterranean peninsula on the one hand, and others with a considerable genetic substructure within each of the Mediterranean peninsulas, Asia Minor and the Maghreb. These structures within the Mediterranean sub-centres are often rather strong and in several cases even predate the Pleistocene. For the "Continental" species, it could be shown that the formerly supposed postglacial spread from eastern Palearctic expansion centres is mostly not applicable. Quite the contrary, most of these species apparently had extra-Mediterranean centres of survival in Europe with special importance of the perialpine regions, the Carpathian Basin and parts of the Balkan Peninsula. In the group of "Alpine" and/or "Arctic" species, several molecular biogeographical patterns have been found, which support and improve the postulates based on distribution patterns and pollen records. Thus, genetic studies support the strong linkage between southwestern Alps and Pyrenees, northeastern Alps and Carpathians as well as southeastern Alps and the Dinaric mountain systems, hereby allowing conclusions on the glacial distribution patterns of these species. Furthermore, genetic analyses of arctic-alpine disjunct species support their broad distribution in the periglacial areas at least during the last glacial period. The detailed understanding of the different phylogeographical structures is essential for the management of the different evolutionary significant units of species and the conservation of their entire genetic diversity. Furthermore, the distribution of genetic diversity due to biogeographical reasons helps understanding the differing regional vulnerabilities of extant populations.