Alien Registration- De Beaulieu, Katherine F. (Portland, Cumberland County)

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The Pollen Sequence of Les Échets (France): A New Element for the Chronology of the Upper Pleistocene

Les Échets mire (near Lyon, France) is one of the very few European sites showing an almost continuous record from the glaciation that preceded the Eemian up to now. The pollen diagram can easily be correlated with those from Grande Pile (Vosges). On the basis of a comparison between the two sequences, the age of three clearly temperate post-Eemian episodes (Saint-Germain Ia, Ic and Il at Grande Pile) is discussed. The authors correlate these episodes with the Early Würm Interstadials of Amersfoort, Brorup and Odderade described in Northern Europe and accept the chronology of Grande Pile that dates Saint-Germain I and Saint-Germain Il between ca 115 000 and 70 000 BP, thus making them equivalents of deep sea isotopic stages 5c and 5a. This leads to refute the 14C chronology admitted up to now that places the Early Würm between 75 000 and 55 000 BP. Considering the predominant temperate episodes during this period, the authors propose to use the term "Pre-Würm" instead of "Early Würm". During the Middle Würm, three not well-marked interstadials can be recognized. No interstadial is found during the late Pleni-Würm.Le marais des Échets (près de Lyon, France) constitue l'un des rares sites européens qui présente un remplissage à peu près continu depuis la glaciation qui a précédé l'Éémien jusqu'à nos jours. Le diagramme pollinique peut aisément être mis en corrélation avec ceux de La Grande Pile (Vosges). À partir de comparaisons entre ces deux séquences, la position chronostratigraphique des trois épisodes très nettement tempérés post-éémiens (Saint-Germain la, Ic et II à La Grande Pile) est discutée. Les auteurs mettent en corrélation ces épisodes avec les interstades du Würm ancien, Amersfoort, Brorup et Odderade, décrits en Europe du Nord et acceptent la chronologie de La Grande Pile qui situe Saint-Germain I et II entre environ 115 000 et 70 000 BP et qui en font les équivalents des étages isotopiques océaniques 5c et 5a. Ceci implique que la chronologie 14C admise jusqu'ici et plaçant le Würm ancien entre environ 75 000 et 55 000 BP est totalement erronée. Compte tenu de la prépondérance des épisodes tempérés durant cette période, les auteurs proposent le remplacement de la dénomination "Würm ancien" par celle de "Pré-Würm ". Durant le Würm moyen, trois interstades de faible amplitude ont été reconnus aux Échets, alors qu'aucune variation climatique positive n'est décelable durant le Pléni-Würm final.Das Moor von Les Échets (in der Nàhe von Lyon, Frankreich) ist eines der wenigen europàischen Gelànde, das ein fast kontinuierliches Zeugnis ablegt von der dem Eemian vorausgehenden Eiszeit bis heute. Das Pollendiagramm kann sehr leicht mit denen von Grande Pile (Vogesen) in Zusammenhang gebracht werden. Ausgehend von dem Vergleich zwischen diesen zwei Sequenzen wird das Alter von drei auf das Eemian folgenden und eindeutig gemàpigten Stadien diskutiert (Saint-Germain la, Ic und Il in Grande Pile). Die Autoren setzen dièse Episoden in Beziehung zu den Interstadialen von Amersfoort, Brerup und Odderade, die in Nord Europa beschrieben werden und akzeptieren die Chronologie von Grande Pile, die Saint-Germain I und Saint-Germain II zwischen etwa 115 000 und 70 000 v.u.Z. datiert, und sie so zu Àquivalenten der iso-topischen Tiefsee-Stadien 5c und 5a macht. Das fùhrt zu einer Ablehnung der 14C Chronologie, die bisher galt, und das frühe Würm zwischen 75 000 und 55 000 v.u.Z. ansetzte. Unter Beachtung der dominierenden gemàssigten Episoden wàhrend dieser Zeit schlagen die Autoren vor, den Terminus "Prâ-Würm" an Stelle von "Frùhes Würm" zu benutzen. Wàhrend des Mittel-Würms kônnen drei nicht gut voneinander abgegrenzte Interstadiaie erkannt werden. Während des spàteren Pleni-Würms kann kein Interstadial festgestellt werden

An oxygen isotope record of lacustrine opal from a European Maar indicates climatic stability during the Last Interglacial

The penultimate temperate period, 127–110 ka before present (BP), bracketed by abrupt shifts of the global climate system initiating and terminating it, is considered as an analogue of the Holocene because of a similar low global ice‐volume. Ice core records as well as continental and marine records exhibit conflicting evidence concerning the climate variability within this period, the Last Interglacial. We present, for the first time, a high‐resolution record of oxygen isotopes in diatom opal of the Last Interglacial obtained from the Ribains Maar in France (44°50′09″N 3°49′16″E). Our results indicate that the Last Interglacial in southwestern Europe was generally a period of climatic stability. The record shows that the temperate period was initiated by an abrupt warm event followed midway by a minor climatic transition to a colder climate. An abrupt isotopic depletion that occurs simultaneously with abrupt changes in pollen and diatom assemblages marks the end of the temperate period, and is correlative with the Melisey I stadial. Variations in the isotopic composition of lake‐water related to the isotopic composition of precipitation and evaporation dominate the biogenic opal oxygen isotope record

Counterexamples to the classical central limit theorem for triplewise independent random variables having a common arbitrary margin

We present a general methodology to construct triplewise independent sequences of random variables having a common but arbitrary marginal distribution $F$ (satisfying very mild conditions). For two specific sequences, we obtain in closed form the asymptotic distribution of the sample mean. It is non-Gaussian (and depends on the specific choice of $F$). This allows us to illustrate the extent of the 'failure' of the classical central limit theorem (CLT) under triplewise independence. Our methodology is simple and can also be used to create, for any integer $K$, new $K$-tuplewise independent sequences that are not mutually independent. For $K \geq 4$, it appears that the sequences created using our methodology do verify a CLT, and we explain heuristically why this is the case.Comment: 15 pages, 5 figures, 1 tabl

Fragmentation Experiment and Model for Falling Mercury Drops

The experiment consists of counting and measuring the size of the many fragments observed after the fall of a mercury drop on the floor. The size distribution follows a power-law for large enough fragments. We address the question of a possible crossover to a second, different power-law for small enough fragments. Two series of experiments were performed. The first uses a traditional film photographic camera, and the picture is later treated on a computer in order to count the fragments and classify them according to their sizes. The second uses a modern digital camera. The first approach has the advantage of a better resolution for small fragment sizes. The second, although with a poorer size resolution, is more reliable concerning the counting of all fragments up to its resolution limit. Both together clearly indicate the real existence of the quoted crossover. The model treats the system microscopically during the tiny time interval when the initial drop collides with the floor. The drop is modelled by a connected cluster of Ising spins pointing up (mercury) surrounded by Ising spins pointing down (air). The Ising coupling which tends to keep the spins segregated represents the surface tension. Initially the cluster carries an extra energy equally shared among all its spins, corresponding to the coherent kinetic energy due to the fall. Each spin which touches the floor loses its extra energy transformed into a thermal, incoherent energy represented by a temperature used then to follow the dynamics through Monte Carlo simulations. Whenever a small piece becomes disconnected from the big cluster, it is considered a fragment, and counted. The results also indicate the existence of the quoted crossover in the fragment-size distribution.Comment: 6 pages, 3 figure

Prospectives

Tiré de: Prospectives, vol. 11, no 2-3, avril/juin 1975Titre de l'écran-titre (visionné le 24 janv. 2013