Inversion du champ magnétique terrestre

I study how landscapes are shaped by climate and tectonics over geological timescales. Much of this work applies cosmogenic radionuclides and computational modelling to sedimentary environments with the aim to gauge rates of erosion, transport and deposition. Inspiring to the end, Leah and I visited him in July to work on some cosmo data from central Oz — and for a final salute. At his election to the Australian Academy of Sciences in While discussing my work on the Eulerian-Lagrangian reference frame for quantifying erosion, John offered this characteristic flourish: It is at the top floor. M Lagrange enters, notes the exact time and presses the down-button. The lift accelerates then acceleration ceases, with no sensation of motion. A little later, deceleration commences, and shortly the lift stops. Lagrange has noted the exact moments of each change.

Emeritus Professor Leslie Fifield

Similarly, the extent of past glaciers gives valuable insights into paleoclimatic changes. For this purpose, we reviewed the paleo-glaciated mountains where cosmogenic surface exposure dating was applied in Turkey. We also evaluated the paleoclimatic results obtained from these studies to provide a regional overview.

A geomagnetic reversal is a change in a planet’s magnetic field such that the positions of magnetic north and magnetic south are interchanged (not to be confused with geographic north and geographic south).The Earth’s field has alternated between periods of normal polarity, in which the predominant direction of the field was the same as the present direction, and reverse polarity, in which it.

High-energy cosmic ray particles collide with atoms in the earth’s atmosphere producing protons and neutrons. After the emission of other particles to lower the energy state, the final result is either a stable element or a long-lived radioactive isotope. Roughly two thirds of atmospheric 36Cl is produced by the following spallation reaction: These reactions result in an average atmospheric deposition rate of 12 to 20 atoms 36Cl per second per square meter.

Spallation reactions also occur when gamma rays interact with minerals in the top several meters of the earth’s surface. The following reactions can result: Chlorine can also be produced through muon reactions. Muons are negatively charged, short-lived particles that are produced by high-energy cosmic ray reactions. When produced at the earth’s surface, a muon can react with the nucleus of an atom.

When a muon interacts with a calcium or potassium atom both are commonly found in minerals at the earth’s surface , 36Cl can be produced through the following reactions: Finally, 36Cl is produced through thermal neutron absorption. The 35Cl isotope has a large neutron absorption cross-section, making a relatively large target for collisions with thermal neutrons.

The Cosmogenic Isotope Record and the Role of The Sun in Shaping Earth’s Climate

Reply kB Desilets, D. Prabu, , Extended scaling factors for in situ cosmogenic nuclides: New measurements at low latitude, Earth and Planetary Science Letters , Metoda datowania kosmogenicznym izotopem 36Cl – nowe dane do chronologii glacjalnej Tatr Wysokich [The method of dating by cosmogenic 36Cl – new data in glacial chronology of the High Tatra Mts. Todero, , Image processing and roughness analysis of exposed bedrock fault planes as a tool for paleoseismological analysis: Zreda, , Late Wisconsinan glaciation of southern Eureka Sound:

Pizarro D., Divakar P.K., Grewe F., Leavitt S.D., Huang J.-P., Dal Grande F., Schmitt I., Wedin M., Crespo A. & Lumbsch H.T. (): Phylogenomic analysis of.

As expected for such a microinterface, the regime for mass transport depends on the scan rate of voltammetry, low scan rates being characterized by steady-state currents corresponding to radial diffusion; faster sweeps give rise to conventional cyclic voltammograms, from linear diffusion. This has been used as an electrochemical method for the study of tetraalkylammonium picrates at interfaces between water and immiscible solvents nitrobenzene, 1,2-dichloroethane.

When the organic solvent is DCE, the estimation of ionic interactions is risky in such a poorly dissociating medium; the microhole interface works well however, showing the influence of the medium on solvation of the cations and on the extraction of the picrates. Regression of the Lake Pannon from the southernmost part of the study area is evidenced after 8. Alluvial deposition of meandering rivers lasting until 6. The canyon has cut into a Middle Miocene pediment system—now forming a raised plateau at — m—and displays nine cave levels over a vertical height of 1 km.

It is concluded that: It follows that the elevated erosion surfaces of the Pyrenees, such as the Miocene pediment directly situated above the canyon edge, were not shaped at high elevations, e. The study emphasizes the more general proposition that tectonic signals as opposed to climatic or eustatic in valley-incision chronologies are best singled out at locations situated among the outer ranges of mountain belts, i.

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Geology 10Be terrestrial cosmogenic nuclide dating of alluvial surfaces in the Coachella Valley, southern California, shows two alluvial fan surfaces with ages of When combined with additional fan dates from the Mojave and Sonoran Desert climatic regimes, statistically relevant episodes of fan production in southern California and Baja California were identified by mean standard weighted deviance analysis. Three major episodes have been identified at These correlate well with the first 2 ka of glacial advance with the Sierra Nevada as established by dating of moraines and rock flour analysis of lake cores from Owens Lake.

These data suggest that regional climate rather than global climate or local tectonics influences the production, transport, and deposition of sediment onto fan surfaces in the Sonoran and Colorado Deserts. Regional data on the ages of fan surfaces highlights a temporal link between the initiation of glacial advance and fan production.

Selon la théorie en vigueur, le noyau de la Terre, comme celui d’autres planètes, est une gigantesque dynamo magnétohydrodynamique qui génère le champ magnétique phénomène serait dû aux mouvements du noyau externe, composé d’alliages de fer et de nickel en fusion, et aux courants électriques induits par rapport au noyau interne (solide).

Atmospheric nuclear weapon tests almost doubled the concentration of 14C in the Northern Hemisphere. One side-effect of the change in atmospheric carbon is that this has enabled some options e. The gas mixes rapidly and becomes evenly distributed throughout the atmosphere the mixing timescale in the order of weeks. Carbon dioxide also dissolves in water and thus permeates the oceans , but at a slower rate.

The transfer between the ocean shallow layer and the large reservoir of bicarbonates in the ocean depths occurs at a limited rate. Suess effect Many man-made chemicals are derived from fossil fuels such as petroleum or coal in which 14C is greatly depleted. Such deposits often contain trace amounts of carbon


Cosmogenic exposure dating constraints for coastal landslide evolution on the Island of Malta Mediterranean Sea. Journal of Coastal Conservation, Online First Abstract Landslides affecting the north-western coast of the Island of Malta have been investigated and monitored for 10 years.

Carbon, (14 C), or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues () to date archaeological, geological and hydrogeological samples. Carbon was discovered on February 27, , by Martin Kamen and Sam.

Some cosmic ray particles reach the surface of the earth and contribute to the natural background radiation environment. It was discovered about a decade ago that cosmic ray interaction with silica and oxygen in quartz produced measurable amounts of the isotopes Beryllium and Aluminium Researchers suggested that the accumulation of these isotopes within a rock surface could be used to establish how long that surface was exposed to the atmosphere.

Assuming a constant rate of production, the number of atoms of Be and Al that accumulate in a rock surface will be proportional to the length of time the rocks were exposed to cosmic ray bombardment and the respective rates of radioactive decay for each isotope. An age determined by measurement of the amount of each nuclide would be an estimate of the minimum time that the particular surface had been exposed, but would not date the maximum age of the surface exposure, that is, the surface could have been exposed for much longer than the minimum calculated age.

Theoretically, exposures of surfaces from between a few thousand to about 10 million years old can be dated by the measurement of the Be and Al isotopes.


This basin has been reinvestigated and new stratigraphic and sedimentological data are now presented. The lowest debris flows derive from the local carbonate platforms of Cretaceous and Palaeogene age. The origin of these ophiolitic detritus is a matter of debate. The new data obtained in this study favour a northern origin. The Kartal, Cevizlik, and Lorut Faults are normal faults that have evident surface expression within the strip.

Terrestrial cosmogenic nuclide geochronology revealed that the Kartal Fault deformed the

Five limestone boulders from an end moraine in the Galicica Mountains The 36Cl concentrations from the five boulders are identical within their measurement uncertainties ruling out major effects of inheritance, erosion, or snow cover. The calculated ages are very consistent ranging from The applied corrections for weathering and snow shielding cause a shift to older ages in the order of magnitude of ca. The ages point to a moraine formation during the Younger Dryas period, consistent with the timing of the last deglaciation in the Galicica Mountains derived from previous geomorphological studies in the area.

The formation of a glacier was likely favoured by several topoclimatic factors, accounting for additional snow input.

Dr Angel Rodes

PowerPoint PPT presentation free to download 1. These radionuclides are produced by nuclear reactions between cosmic rays and PowerPoint PPT presentation free to download New directions in limnology and oceangraphy using cosmogenic radionuclides.

The Dating Process Cosmogenic Burial Dating Over the last decade in-situ-produced cosmogenic nuclides such as 26Al, 10Be and 36Cl have been increasingly used to date glacial landforms. This method has been checked by other dating techniques Grainger and and has been proven to be effective. There are two main requirements for this technique to be useful. First there must be quartz present in the sediment for the nuclides to be created by the neutron spallation of quartz and second the quartz must be buried deep enough for neutron spallation to stop.

Normally sediment above 5 meters in depth encounters is not acceptable for this type of technique. By measuring the different decay rates of 10 Be with a half life of 1. This constant decay rate is also matched by a constant production ratio. The 26Al nuclide produces six times faster than 10Be nuclide which makes calculating decay rates less tenuous.

The results of the cosmogenic testing resulted in a sequential set of dates. The field and laboratory preparation was performed by David Gaunt in association with Dr. Rovey at Southwest Missouri State University. The isotope dating was conducted by Dr. Balco at the University of Washington.

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Cosmogenic Exposure Dating and the Age of the Earth Cosmogenic nuclides are nuclides formed by the interaction of ‘target’ atoms with cosmic radiation. Such nuclides are formed in space, in the atmosphere e. The accumulation of cosmogenic nuclides in minerals at or near the earth’s surface provides a basis for exposure ‘dating‘ of landforms, the quantification of erosion rates, and other geologic applications Bierman, ; Cerling and Craig, ; Gosse and Phillips,

Cave and Karst Science, Vol. Transactions of the British Cave Research Asso Transactions of the British Cave Research Association. Terrestrial cosmogenic nuclide 10 Be surface-exposure ages are reported for three glacially-transported gritstone boulders and one glacially-scoured exposure of gritstone bedrock in the vicinity of Stump Cross Caverns, North Yorkshire.

Although the ages do not form a statistically consistent cluster, three of them nevertheless indicate that the transport and deposition of boulders was by ice of the last Late Devensian glaciation. The ages provide evidence for glacier ice at the Wharfe—Nidd interfluve, in contrast to previously held views that these uplands had remained above the level of the last ice sheet. This is consistent both with surface-exposure ages from sites elsewhere around the southern margin of the Yorkshire Dales and with uranium-series dated speleothems in Stump Cross Caverns.

Cave shaft sediments in northwest England associated with the 9. Both the opening of the cave shaft to the surface and its infilling by clastic sediments are attributable to accelerated landscape erosion associated with the 9. Evidence that wild boar had died in winter or spring suggests that their deaths relate to the prolonged periods of annual snow cover experienced by the uplands of northwest England during the 9.

The dominance of wild boar in the pit fall assemblage is explained by the snow pack concealing the open shaft and turning it into a baited trap for wild boar whenever it contained carrion.

RKVV Volharding