Dating fluvial terraces with 10Be and 26Al profiles : application to the Wind River, Wyoming
Cosmogenic isotopes in geomorphology
Dating ; Fluvial terrace ; Fluvioglacial features ; Isotopedating ; Methodology ; Moraine ; Tephrochronology ; United States of America ; Wyoming
Dating depositional surfaces like terraces that are older than the range of 14C is difficult. The AA. employ a cosmogenic radionuclide (CRN) profile technique that addresses a major problem of CRN dating on such surfaces : nuclide inheritance
. By measuring 10Be and 26Al profiles, the AA. constrain the exposure age and the mean CRN inheritance for the deposit. Here they report their attempts to date terraces along the Wind River, which are inferred to reflect oscillation between glacial
and interglacial conditions in the headwaters, and compare the results with other dating methods.
Brunhes-Matuyama magnetic reversal dated at 790,000 yr B.P. by marine-astronomical correlations
is supported by a resulting consistent identification of principal isotope-ratio peaks with high-and low-latitude coincident insolation maxima. The Brunhes-Matuyama reversal is found in interglacial Stage 19, and is dated on the astronomical time scale
The presence of the Brunhes-Matuyama magnetic reversal in deep-sea core sediments makes possible an alternative to the usual K/Ar radioisotope method of dating the reversal as found in rocks. The alternative method uses correlations of Northern
Hemisphere summer insolation with oxygen-isotope ratios from tropical cores. The latitude-dependent insolation variations are calculated from planetary mechanics and thus provide a highly accurate astronomical time scale. The insolation variations strongly
influence glacial-ice volume fluctuations that dominate the oxygenisotope ratio changes recorded in core sediments. The summer half-year insolation variations are identified with corresponding isotope-ratio changes in cores from the present through glacial
Stage 20. During stages 1 to 10, major glacial extremes (strong isotope-ratio minima) coincide consistently with major insolation minima at times of low orbital eccentricity. In addition interstadials are directly associated with precessional insolation
peaks, and the envelope of isotope-ratio peaks resembles the envelope of precessionally dominated insolation peaks. The assumption that the glacial extremes depended similarly on insolation minima during Stages 10 to 20 permits minor age shifts of strong
Suggested terminology for Quaternary dating methods
The AA. recommend the use of the terms numerical-age, calibrated-age, relative-age, and correlated-age. They also classify dating methods by type into sideral, isotopic, radiogenic, chemical and biological, geomorphic and correlation methods
. The use of absolute is inappropriate for most dating methods, and should be replaced by numerical . The use of date should be minimized in favor of age or age estimate . They recommend use of the abbreviations ka and Ma for mostages| calender dates can
Climatic records from annual layers and stable isotopes of a stalagmite in Beijing over the last 2300 years
Beijing ; C 14 dating ; China ; Climatic variation ; Geochemistry ; Holocene ; Human impact ; Isotope analysis ; Monsoon ; Oxygen 18 ; Palaeoclimatology
with the thickness of annual layers the AA. reconstruct the climatic variation history of the last 2300 years in Beijing area. The oxygen isotopic composition preserves monsoon variations, which is matched in interpretation of the change in layer thickness. Carbon
isotopic composition reflects the changes in vegetation activity likewise the anthropogenic activity.
intervals and the chronology from thermoluminescence, infrared- and green-light-stimulated luminescence dates give a good opportunity to examine the isotopic data for paleoclimatic variability and relate this to other marine and terrestrial records.
In this paper, the AA. attempt to construct a detailed terrestrial late Pleistocene climatic record in India by studying oxygen and carbon stable isotopes in pedogenic calcrete from the Thar Desert. The nearly continuous calcrete record in eolian
Cosmogenic isotope analyses applied to river longitudinal profile evolution: problems and interpretations
Channel geometry ; Dating ; Erosion rate ; Geochemistry ; Hawaii ; Isotope analysis ; Longitudinal section ; River bed ; Stream
This paper presents an effort to link a field-based study with surface exposure dating techniques to understand river longitudinal profile evolution. The study was aimed at improving the understanding of the rates and processes governing bedrock
channel incision. Samples to be analysed for cosmogenic isotopes were collected along a river profile and both radionuclide and stable nuclide concentrations were measured in the rocks. Specifically the nuclides 10Be, 26Al,36Cl,21Ne and 3He allow direct
The object of this study is a 3029 m long deep ice core drilled in 1990-1992 by the European Greenland Ice-Core Project (GRIP). This core reaches nearly to bedrock and reaches back to 250,000 yr B.P., according to dating based partly
Présentation des résultats des mesures des delta O18 et delta C13 dans les échantillons de tuf datés par le carbone 14 et utilisation de ces résultats pour reconstituer les variations climatiques du sud de la Pologne. Les échantillons de tuf sont
Climate and sea level in isotope stage 5: an East Antarctic ice surge at 95,000 BP?
Six high-resolution records correlated with marine isotope stage 5 suggest that substage 5c was essentially interglacial, and was terminated by a catastrophic cooling. Over sixty Th dates indicate that the sea level in substage 5c rose to at least
This paper reports on the dating of some cores from the Gotland Deep, part of the Gotland Basin, and the Gdansk Basin. The focus is on the interpretation of Pb-210 data from the gamma-spectrometric method where the dating is verified
Carbon ; Cave ; Climatic cooling ; Isotope analysis ; Ocean atmosphere interaction ; Oregon ; Oxygen 18 ; Palaeoclimatology ; Quaternary ; Speleothem ; United States of America
The AA. develop a precisely datedisotope record (δO 18, δC 13) of the last deglaciation from a stalagmite recovered from the Klamath Mountains, southwestern Oregon. Since the climate of the region is strongly influenced by the Pacific Ocean
, this record is significant in providing one of the few precisely dated terrestrial record of Northeast Pacific climate variability during the last deglaciation.
The Holstein Interglaciation : time - stratigraphic position and correlation to stable-isotope stratigraphy of deep-sea sediments
Marine molluscan shells from para-type and other localities of the Holsteinian interglaciation were dated by Th/U and the election spin resonance method to more than 350,000 and 370,000 yr B.P., beyond the limit of Th/U dating. The high age estimate
Dating ; European part of Russia ; Isotopedating ; Methodology ; Radioactivity ; Russian Plain ; Soil erosion
Approches méthodologiques générales pour l'utilisation de l'isotope césium 137 dans les étude d'érosion et d'accumulation. Particularités de l'utilisation du césium radioactif dans l'étude de ces processus géomorphologiques. Exemple d'étude de la
A 30,000-yr isotope climatic record from Antarctic ice
Simple glaciological conditions at Dome C in East Antarctica have made possible a more detailed and accurate interpretation of an ice core to 950 m depth spanning some 32,000 yr than that obtained from earlier ice cores. Dated events in comparable
marine core has enabled the reduction of accumulation rate during the last ice age to be estimated. Climatic events recorded in the ice core indicate that the warmest Holocene period in the Southern Hemisphere occurred at an earlier date than
Late Quaternary vegetation dynamics in the southern Amazon Basin inferred from carbon isotopes in soil organic matter
Amazon Basin ; C 14 dating ; Carbon ; Climatic variation ; Forest ; Holocene ; Isotope analysis ; Palaeo-environment ; Quaternary ; Savanna ; South America ; Vegetation dynamics
Carbon isotopes of soil organic matter (SOM) were used to evaluate and establish the chronology of the vegetation dynamics of an ecosystem presently composed of savannas surrounded by forests. The study was carried out on a 200-km transect along
Isotope characterisation of ground ice in northern Canada
Special Issue : Stable isotopes and geochemistry of ground ice
Arctic Region ; C 14 dating ; Canada ; Cold area ; Geochemistry ; Ground ice ; Ice wedge ; Isotope analysis ; Oxygen 18 ; Permafrost ; Pingo ; Polar region
This paper reviews isotopic research on the characterisation and identification of various types of ground ice throughout the Canadian Arctic, including buried glacier ice, massive segregated ice, segregated ice lenses and offshore ice-rich
, when the region experienced widespread continental-scale glaciation. The ratios O 18/O 16 are analysed. Placing the ice bodies into a time frame can be accomplished either through age dating of the enclosing sediments and encased organics, or by direct
dating of the ice utilising tritium (3H) for relatively young ice and radiocarbon (14C) analysis of contained gas bubbles for older ice.
Australia ; Coastal environment ; Dating ; Inherited features ; Isotopedating ; Northern Territory ; Quaternary ; Shore platform ; Thermoluminescence
Using radiocarbon, thermoluminescence and uranium/thorium dating techniques, it can be shown that the present coastal morphology on the Cobourg Peninsula is partly inherited from features both deposited and eroded during the late Quaternary. Shore
platforms, in particular, are veneered with ferricretes, some of which can be U/Th dated.