Sediment transport time measured with U-series isotopes: Results from ODP North Atlantic drift site 984

DePaolo, Donald J.; Maher, Kate; Christensen, John N.; McManus, Jerry F

doi:10.1016/j.epsl.2006.06.004

Cited by 162 publications

(175 citation statements)

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“…Lower values of average 234 U/ 238 U activity ratio in the green siltstones (0.92) (see Table 1) can be explained by the fact that these deposits have reached a steady state of the 234 U/ 238 U activity ratio that depends only on their size (the average grain size d p ≈ 30 µm) [38], because they were under reducing conditions over 1 Ma. A significantly higher content of uranium in them compared to red siltstones shows a considerable variability in the permeability values of the aquifer, whereby they were away from the paths of groundwater filtration and have retained uranium.…”

Section: Resultsmentioning

confidence: 99%

Evolution of Uranium Isotopic Compositions of the Groundwater and Rock in a Sandy-Clayey Aquifer

Малов

2017

Water

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Uranium isotopes have been used as mechanistic or time scale tracers of natural processes. This paper describes the occurrence and redistribution of U in the Vendian aquifer of a paleo-valley in NW Russia. Forty-four rock samples were collected from nine boreholes with depths up to 160 m, and 25 groundwater samples were collected from 23 boreholes with depths up to 300 m. The U, Fe concentration, and 234 U/ 238 U activity ratio were determined in the samples. Estimations were made of the 14 C and 234 U-238 U residence time of groundwater in the aquifer. It has been established that the processes of chemical weathering of Vendian deposits led to the formation of a strong oxidation zone, developed above 250 m.b.s.l. The inverse correlation between the concentrations of uranium and iron is a result of removal of U from paleo-valley slopes in oxidizing conditions, accumulation of U at the bottom of the paleo-valley in reducing conditions, and accumulation of Fe on the slopes and removal from the bottom of the paleo-valley. Almost all U on the slopes has been replaced by a newly formed hydrogenic U with a higher 234 U/ 238 U activity ratio. After, dissolution and desorption of hydrogenic U occurred from the slopes during periods with no glaciations and marine transgressions. Elevated concentrations of U are preserved in reduced lenses at the paleo-valley bottom. In these areas, the most dangerous aspect is the flow of groundwater from the underlying horizons, since during the operation of water supply wells it can lead to the creation of local zones of oxidizing conditions in the perforated screens zone and the transition of uranium into solution. For groundwater under oxidizing conditions, an increase in the concentration of uranium is characteristic of an increase in the residence time (age) of water in the aquifer. Also, the 234 U/ 238 U activity ratio increases with increasing radioactivity of groundwater. Therefore, the most rational approach is to use groundwater for drinking water supply from the slopes of the Northern Dvina basin.

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Section: Resultsmentioning

confidence: 99%

Evolution of Uranium Isotopic Compositions of the Groundwater and Rock in a Sandy-Clayey Aquifer

Малов

2017

Water

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“…Even slight variations in estimated f a values can significantly affect inferences about weathering rates and comminution ages (e.g., DePaolo et al, 2006;Lee et al, 2010). Several approaches have been be used to estimate f a , and these are summarised in Maher et al (2006) and Lee et al (2010).…”

Section: Recoil Loss Factor F Amentioning

confidence: 99%

“…The 'comminution age' dating model of DePaolo et al (2006) hypothesises that measured disequilibria between U-series nuclides ( 234 U and 238 U) in fine-grained continental (detrital) sediments can be used to calculate the time elapsed since mechanical weathering of a grain to the threshold size ($50 lm). When 238 U undergoes alpha decay to 234 Th, the associated release of energy results in the physical displacement (recoil) of the 234 Th nuclide from the original position of 238 U.…”

Section: Conceptmentioning

confidence: 99%

“…Quantification of such rates is crucial to improve our understanding of the relationship between climate change, tectonics and landscape evolution throughout the Quaternary. Recent studies (e.g., DePaolo et al, 2006;Dosseto et al, 2010;Lee et al, 2010) of the fractionation between 234 U and 238 U in fine-grained sediment have demonstrated the potential in constraining the comminution age of continentally-derived sediments, that is, the time elapsed since physical weathering of the source rock into fine-grained (<$50 lm) particles Fig. 1).…”

Section: Introductionmentioning

confidence: 99%

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Sediment residence times constrained by uranium-series isotopes: A critical appraisal of the comminution approach

Handley

Turner

Afonso

et al. 2013

Geochimica et Cosmochimica Acta

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Cohen, T. (2013). Sediment residence times constrained by uranium-series isotopes: a critical appraisal of the comminution approach. Geochimica et Cosmochimica Acta, 103 (N/A), 245-262. Sediment residence times constrained by uranium-series isotopes: a critical appraisal of the comminution approach AbstractQuantifying the rates of landscape evolution in response to climate change is inhibited by the difficulty of dating the formation of continental detrital sediments. We present uranium isotope data for Cooper Creek palaeochannel sediments from the Lake Eyre Basin in semi-arid South Australia in order to attempt to determine the formation ages and hence residence times of the sediments. To calculate the amount of recoil loss of 234U, a key input parameter used in the comminution approach, we use two suggested methods (weighted geometric and surface area measurement with an incorporated fractal correction) and typical assumed input parameter values found in the literature. The calculated recoil loss factors and comminution ages are highly dependent on the method of recoil loss factor determination used and the chosen assumptions. To appraise the ramifications of the assumptions inherent in the comminution age approach and determine individual and combined comminution age uncertainties associated to each variable, Monte Carlo simulations were conducted for a synthetic sediment sample. Using a reasonable associated uncertainty for each input factor and including variations in the source rock and measured (234U/238U) ratios, the total combined uncertainty on comminution age in our simulation (for both methods of recoil loss factor estimation) can amount to ±220-280 ka. The modelling shows that small changes in assumed input values translate into large effects on absolute comminution age. To improve the accuracy of the technique and provide meaningful absolute comminution ages, much tighter constraints are required on the assumptions for input factors such as the fraction of α-recoil lost 234Th and the initial (234U/238U) ratio of the source material. In order to be able to directly compare calculated comminution ages produced by different research groups, the standardisation of pre-treatment procedures, recoil loss factor estimation and assumed input parameter values is required. We suggest a set of input parameter values for such a purpose. Additional considerations for calculating comminution ages of sediments deposited within large, semi-arid drainage basins are discussed. AbstractQuantifying the rates of landscape evolution in response to climate change is inhibited by the difficulty of dating the formation of continental detrital sediments. We present uranium isotope data for Cooper Creek palaeochannel sediments from the Lake Eyre Basin in semi-arid South Australia in order to attempt to determine the formation ages and hence residence times of the sediments. To calculate the amount of recoil loss of 234 U, a key input parameter used in the comminution approach, we use two suggested methods (weighted geome...

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“…Accumulation rates vary, reaching maximum values over 30 cm/ka, and averaging ~14 cm/ka for the study interval of MIS 9, allowing centennial-scale resolution of oceanographic and climatic conditions at this location. The quality and quantity of accumulating sediments at this oceanographically sensitive location have yielded valuable insights in a number of previous studies Schrag et al 2002;Raymo et al 2004;DePaolo et al 2006;Came et al 2007;Praetorius et al 2008;Mollenhauer et al 2011;Thornalley et al 2013;Mokeddem et al 2014;Mokeddem and McManus 2016).…”

Section: Site Location and Oceanic Settingmentioning

confidence: 99%

Insights into North Atlantic deep water formation during the peak interglacial interval of Marine Isotope Stage 9 (MIS 9)

Mokeddem

McManus

2017

Clim Dyn

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Sediment transport time measured with U-series isotopes: Results from ODP North Atlantic drift site 984

Cited by 162 publications

References 65 publications

Evolution of Uranium Isotopic Compositions of the Groundwater and Rock in a Sandy-Clayey Aquifer

Evolution of Uranium Isotopic Compositions of the Groundwater and Rock in a Sandy-Clayey Aquifer

Sediment residence times constrained by uranium-series isotopes: A critical appraisal of the comminution approach

Insights into North Atlantic deep water formation during the peak interglacial interval of Marine Isotope Stage 9 (MIS 9)

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