Uranium series disequilibrium in river sediments and waters: the significance of anomalous activity ratios

1992 ◽  
Vol 7 (2) ◽  
pp. 101-110 ◽  
Author(s):  
A.J. Plater ◽  
M. Ivanovich ◽  
R.E. Dugdale
Geology ◽  
2021 ◽  
Author(s):  
Simon Turner ◽  
Heather Handley ◽  
Paul Hesse ◽  
Bruce Schaefer ◽  
Anthony Dosseto

Dust plays important roles in the environment, and there has been much interest in the formation, provenance, and age of the world’s dust deposits. Ongoing debates are concerned with the importance of glacial grinding versus eolian abrasion and fluvial transport in the formation of silt-sized particles. Short-lived uranium-series isotopes afford new insights because they can be used both for provenance fingerprinting and for constraining the integrated age of chemical and physical weathering and subsequent transport and storage of sediments. Here we present trace element and Sr, Nd, and U-series isotope analyses from a number of Australian dusts and suspended river sediments remobilized during floods a year later. The inferred ages of the Australian dust appear to be linked to aridification and the loss of inland megalakes ~30–120 k.y. ago. This provides preliminary evidence that the age of dust may provide a new hydrological indicator in arid environments.


1984 ◽  
Vol 21 (5) ◽  
pp. 559-566 ◽  
Author(s):  
A. A. Levinson ◽  
C. J. Bland ◽  
J. R. Dean

Disequilibrium studies involving the determination of total U and the activity ratios of 234U/238U and 234U/230Th or activities of 230Th, 226Ra, and 210Pb were carried out on samples from three surficial (generally within 5 m of the surface) uranium deposits in south-central British Columbia that give apparent 234U/230Th ages of 1000–20 000 years. As a result of the young ages, the deposits have not yet reached radioactive secular equilibrium and, therefore, yield very little gamma activity.The deposits formed from groundwaters that leached labile uranium from intermediate to felsic igneous rocks. Two accumulation mechanisms concentrate the uranium: evaporation, and adsorption onto organic matter.The uranium content and the activities of the various daughter nuclides are highly variable within and between the various deposits studied. Some of the variations can be explained in terms of the accumulation processes. In the evaporative process the highest value of uranium and daughter nuclides will be found at the surface, whereas in those deposits in which adsorption is the dominant mechanism these nuclides are found in association with buried organic matter. Under these circumstances, accumulations will be influenced by the flow of groundwater from different sources and also depend on whether daughter nuclides remain immobile or are leached after formation.


1985 ◽  
Vol 23 (1) ◽  
pp. 54-61 ◽  
Author(s):  
B. J. Szabo ◽  
J. I. Tracey ◽  
E. R. Goter

Drill cores of Enewetak Atoll, Marshall Islands, reveal six stratigraphic intervals, numbered in downward sequence, which represent vertical coral growth during Quaternary interglaciations. Radiocarbon dates indicate that the Holocene sea transgressed the emergent reef platform by about 8000 yr B.P. The reef grew rapidly upward (about 5 to 10 mm/yr) until about 6500 yr B.P. Afterward vertical growth slowed to about 0.5 mm/yr, then lateral development became dominant during the last several thousand years. The second interval is dated at 131,000 ± 3000 yr B.P. by uranium series. This unit correlates with oxygen-isotope substage 5e and with terrace VIIa of Huon Peninsula, New Guinea, and of Main Reef-2 terrace at Atauro Island. The third interval is not dated because corals were recrystallized and it is tentatively correlated with either oxygen-isotope stages 7 or 9. The age of the fourth interval is estimated at 454,000 ± 100,000 yr B.P. from measured 234U238U activity ratios. This unit is correlated with either oxygen-isotope stage 9, 11, or 13.


1990 ◽  
Vol 212 ◽  
Author(s):  
Robert Edis

ABSTRACTThe distribution of 238U, 234U, 230Th and 236Ra in rocks from the Koongarra uranium deposit has been examined. Alpha-spectrometry and ICP-MS were used to estimate elements in “accessible” and “inaccessible” phases, separated by a two-phase extraction scheme; and bulk analyses of visibly distinct zones were made using PIXE-PIGME, DNAA and XRF.The secondary U dispersion fan of the Koongarra site is characterised by 234U/238U, 230Th/234U and 236Ra/230Th activity ratios (ARs) below unity in the extractable (accessible) phases, and above unity in the non-extractable (inaccessible) phases. The patterns of the ARs suggest zones of different U deposition and leaching rates with the most rapid accumulation at the base of weathering, especially at the extremities of the dispersion fan.


2020 ◽  
Vol 290 ◽  
pp. 216-234
Author(s):  
Maude Thollon ◽  
Germain Bayon ◽  
Samuel Toucanne ◽  
Anne Trinquier ◽  
Yoan Germain ◽  
...  

1989 ◽  
Vol 176 ◽  
Author(s):  
T. Ohnuki ◽  
T. Murakami ◽  
K. Sekine ◽  
N. Yanase ◽  
H. Isobe ◽  
...  

ABSTRACTThe migration behavior of uranium series nuclides in an altered quartz-chlorite schist has been studied by utilizing data on the activity distributions of uranium series nuclides at Koongarra in the Northern Territory of Australia. The variation of 230Th/234U activity ratios (ARs) with distance along surface (2 m depth), intermediate (16 m) and deep (31 m) layers show different trends in the three layers parallel to the water flow. The relationship between the 234U/238U and 230Th/238U ARs reveals that the mobility of the uranium series nuclides is in order 238U, 234U and 230Th, and that the retardation factors oft 234U are greater than those of 238U by a factor of 1.1, 1.9 and 1.0 in the surface, intermediate and deep layers, respectively. X-ray diffraction patterns show different mineral assemblages, which are the alteration products of chlorite at the three layers. These results imply that the migration behavior of uranium series nuclides at each depth would be related to the alteration of chlorite.


1995 ◽  
Vol 412 ◽  
Author(s):  
R. J. Finch ◽  
J. Suksi ◽  
K. Rasilainen ◽  
R. C. Ewing

AbstractUranium-series activity ratios for U(VI) minerals from the Shinkolobwe mine in southern Zaire indicate that these minerals have not experienced significant preferential loss of uranium since their formation more than 100,000 years ago. The minerals examined include rutherfordine, UO2CO3, schoepite, [(UO2)8O2(OH)12]·12H2O, becquerelite, Ca[(UO2)6O4(OH)6]·8H2O, and uranophane, Ca[(UO2)2(SiO3OH)2]·5H2O. No correlation between mineral species and mineral age was evident. The oxidative dissolution of primary uraninite (UO2+x) has maintained ground waters supersaturated with respect to all of the secondary U(VI) minerals, providing an inexhaustible source of dissolved U6+ for mineral formation and growth. As long as uraninite persists in an oxidizing environment, the assemblage of secondary U(VI) phases is determined by local ground water chemistry (including transitory changes), but not necessarily a unidirectional reaction path towards equilibrium with U(VI) minerals of lower solubility. Thus the Shinkolobwe mine displays a complex assemblage of U(VI) minerals that reflects variations in the availability of dissolved elements besides U. Similarly, for a geologic repository exposed to oxidizing waters, the assemblage of corrosion products that will form during the corrosion of spent UO2 fuel is likely to be as complex as mineral assemblages found in natural uranium deposits under similar conditions.


2000 ◽  
Vol 663 ◽  
Author(s):  
Juhani Suksi ◽  
Kari Rasilainen

Abstract; Low 234U/238U activity ratios observed in rock and mineral samples were scrutinized. U isotope fractionation leading to 234U depletion (234U/238U<1) in rocks appears to be linked to changes in redox conditions. The fractionation takes place as selective chemical release dominates over direct physical μ recoil. This preferential 234U release depends on the valence contrast between the U isotopes, 238U occurring in +4 form and ingrown 234U, due to oxidizing microenvironment, in +6 form. Observed U isotopic fractionation combined with other uranium series disequilibrium measurements provides a tool for locating redox fronts formed as a result low temperature rock-groundwater interaction.


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