Time-averaged fault slip-rates can be established by reliably dating the abandonment of an alluvial deposit that has been displaced by Quaternary movement along a cross-cutting fault. Unfortunately, many Quaternary dating techniques are hindered by uncertainties inherent to individual geo-chronometers. Such uncertainties can be minimised by combining multiple independent techniques. In this study, we combine Be-10 exposure dating of boulder tops and U-series dating of layered pedogenic carbonate cements accumulated on the underside of clasts from two separate alluvial surfaces. These surfaces are both displaced by the active Olgiy strike-slip fault in the Mongolian Altay Mountains. We date individual layers of pedogenic carbonate, and for the first time apply a Bayesian statistical analysis to the results to develop a history of carbonate accumulation. Our approach to the U-series dating provides an age of initiation of carbonate cement formation and avoids the problem of averaging contributions from younger layers within the carbonate. The U-series ages make it possible to distinguish Be-10 samples that have anomalously young exposure ages and have hence been subject to the effects of post-depositional erosion or exhumation. The combination of Be-10 and U-series dating methods provides better constrained age estimates than using either method in isolation and allows us to bracket the abandonment ages of the two surfaces as 18.0-28.1 kyr and 38.4-76.4 kyr. Our ages, combined with measurements of the displacement of the surfaces, yield a right-lateral slip-rate for the Olgiy fault of 0.3-1.3 mm yr(-1), showing that it is a relatively important structure within the active tectonics of Mongolia and that it constitutes a substantial hazard to local populations. (C) 2014 Elsevier B.V. All rights reserved.

The long-lived radionuclide Fe-60 has been detected at the tow energies of an EN tandem accelerator. At an energy of 60 MeV, the suppression of the stable isobar Ni-60 is the main problem. Spraying hydrogen gas onto the ion source target and extracting the metal single hydrides the nickel contamination in the beam can be reduced more than 500 fold. In the gas ionization detector another five orders of magnitude of suppression are obtained. The resulting background Fe-60/Fe ratio of about 10(-11) has enabled first measurements with the standard samples used earlier at Argonne National Laboratory, The results of the two facilities are in agreement.

Here we present the first reconstruction of vertical ice-sheet profile changes from any of the Southern Hemisphere's mid-latitude Pleistocene ice sheets. We use cosmogenic radio-nuclide (CRN) exposure analysis to record the decay of the former Patagonian Ice Sheet (PIS) from the Last Glacial Maximum (LGM) and into the late glacial. Our samples, from mountains along an east-west transect to the east of the present North Patagonian Icefield (NPI), serve as 'dipsticks' that allow us to reconstruct past changes in ice-sheet thickness and demonstrates that the former PIS remained extensive and close to its LGM extent in this region until ~19.0 ka. After this time rapid ice-sheet thinning, initiated at ~18.1 ka, saw ice at or near its present dimension by 15.5 ka. We argue this rapid thinning was triggered by a combination of the rapid southward migration of the precipitation bearing Southern Hemisphere (SH) westerlies and regional warming.

Cosmogenic Cl-36 analysis by accelerator mass spectrometry (AMS) is a valuable environmental and geological sciences research tool. Overcoming the stable nuclide S-36 isobar interfering with measurement is challenging, however. Traditionally this has required large accelerators, but following recent technical advances it is now possible with similar to 30 MeV ion energies. Consequently 5 MV or even smaller modern bespoke spectrometers are now Cl-36-capable, increasing accessibility and promoting wider and more varied Cl-36 use.However, the technical ability to identify Cl-36 ions is quite distinct from demonstrated high-performance AMS. Such is the theme of this paper. We present a systematic analysis of the accurate measurement of sample radioisotope relative to the stable chlorine, the normalisation of the measured ratio and correction for remaining S-36 interference, all combined with the use of stable-isotope dilution to determine sample Cl concentration to begin with. We conclude by showing that repeated analyses support our claims for routine 3% Cl-36-AMS data. Accordingly, the modest SUERC spectrometer well competes with the performance of larger longer-established instruments, and the results may be quite generic for modern bespoke instruments. (C) 2012 Elsevier B.V. All rights reserved.

Cosmogenic nuclide surface exposure ages are determined from in situ Be-10 and Cl-36 analysis of 38 rock surfaces found in different glacial landforms in Denmark. Dating of erratic boulders and adjacent ice-sculpted bedrock on the island of Bornholm in the western Baltic Sea reveals almost identical values. This suggests that little if any inherited nuclides are present in the sampled boulders. West of the Last Glacial Maximum (LGM) ice margin in Denmark ages reflect exposure from the Middle Weichselian. East of the LGM margin exposure ages from 35 samples show Late Weichselian ages in a range between 20.6-11.9 ka. To test to what extent these dates reflect the onset of deglaciation immediately after cessation of active glacier flow, surface exposure ages are evaluated against independent chronologies of Late Weichselian ice-sheet fluctuations in southwestern Scandinavia. The Bornholm dates agree with the independent age model, however, in the data set for eastern Denmark only less than half the surface exposure ages lie within the expected age envelope. This apparent mismatch is most likely due to post-glaciation shielding and delayed surface stabilisation compared to the timing of ice-margin retreat. Thus ages from boulders resting in dead-ice moraines and mass wasting landscapes underestimate deglaciation by 3-6 thousand years. The results quantify the impact of exhumation and landform stabilisation on cosmogenic surface exposure ages on millennial scales. We conclude, that interpretation of cosmogenic exposure ages should include careful evaluation of possible post-depositional landform transformation in attempts to fine tune ages of e.g. end moraine features. With reference to independent age models we critically evaluate glacier advance - retreat scenarios from regions around the southern Baltic that alone are based on weighted average ages of cosmogenic exposure dating. (C) 2012 Elsevier B.V. All rights reserved.

This study centers on the question: How sensitive are 231Pa/230Th and 10Be/230Th to sediment composition and redistribution? The natural radionuclides 231Pa, 230Th and 10Be recorded in deep sea sediments are tracers for water mass advection and particle fluxes. We investigate the influence of oceanic particle composition on the element adsorption in order to improve our understanding of sedimentary isotope records. We present new data on particle size specific 231Pa and 10Be concentrations. An additional separation step, based on settling velocities, led to the isolation of a very opal-rich phase. We find that opal-rich particles contain the highest 231Pa and 10Be concentrations, and higher 231Pa/230Th and 10Be/230Th isotope ratios than opal-poor particles. The fractionation relative to 230Th induced by the adsorption to opal-rich particles is more pronounced for 231Pa than for 10Be. We conclude that bulk 231Pa/230Th in Southern Ocean sediments is most suitable as a proxy for past opal fluxes. The comparison between two neighboring cores with rapid and slow accumulation rates reveals that these isotope ratios are not influenced significantly by the intensity of sediment focusing at these two study sites. However, a simulation shows that particle sorting by selective removal of sediment (winnowing) could change the isotope ratios. Consequently, 231Pa/230Th should not be used as paleocirculation proxy in cases where a strong loss of opal-rich material due to bottom currents occurred.

In 2003, a National Electrostatics Corporation (NEC) 5MV tandem accelerator mass spectrometer was installed at SUERC, providing the radiocarbon laboratory with 14 C measurements to 4–5‰ repeatability. In 2007, a 250kV single-stage accelerator mass spectrometer (SSAMS) was added to provide additional 14 C capability and is now the preferred system for 14 C analysis. Changes to the technology and to our operations are evident in our copious quality assurance data: typically, we now use the 134-position MC-SNICS source, which is filled to capacity. Measurement of standards shows that spectrometer running without the complication of on-line δ 13 C evaluation is a good operational compromise. Currently, 3‰ 14 C/ 13 C measurements are routinely achieved for samples up to nearly 3 half-lives old by consistent sample preparation and an automated data acquisition algorithm with sample random access for measurement repeats. Background and known-age standard data are presented for the period 2003–2008 for the 5MV system and 2007–2008 for the SSAMS, to demonstrate the improvements in data quality.

In 2003, a National Electrostatics Corporation (NEC) 5MV tandem accelerator mass spectrometer was installed at SUERC, providing the radiocarbon laboratory with 14C measurements to 4–5‰ repeatability. In 2007, a 250kV single-stage accelerator mass spectrometer (SSAMS) was added to provide additional 14C capability and is now the preferred system for 14C analysis. Changes to the technology and to our operations are evident in our copious quality assurance data: typically, we now use the 134-position MC-SNICS source, which is filled to capacity. Measurement of standards shows that spectrometer running without the complication of on-line δ13C evaluation is a good operational compromise. Currently, 3‰ 14C/13C measurements are routinely achieved for samples up to nearly 3 half-lives old by consistent sample preparation and an automated data acquisition algorithm with sample random access for measurement repeats. Background and known-age standard data are presented for the period 2003–2008 for the 5MV system and 2007–2008 for the SSAMS, to demonstrate the improvements in data quality.

Small changes to our ion source and gas ionization detector have significantly improved Cl measurement by reducing source memory and increasing interference rejection. Gas stripped low energy 30MeV 36Cl5+ ions are still efficiently transported to the detector but 36S vs. 36Cl separation is improved by an order of magnitude. Accordingly 36Cl/Cl background is <10−15 before additional interference correction that is also newly automated. 35Cl− currents have increased to 30μA and 36Cl/Cl inter-cathode repeatability is 3%.

Accurate determination of chlorine concentrations in terrestrial rocks is of importance for the interpretation of terrestrial in-situ cosmogenic (36)Cl. Neutron capture by (35)Cl, together with production from Ca and K, is one of the three major production pathways of (36)Cl in rocks. Here, we present an inter-comparison of chlorine determinations by two procedures. The first approach is an independent Cl determination by prompt-gamma (neutron) activation analysis (PGAA). The second method is isotope-dilution based on isotopically enriched stable chlorine carrier added during chemical sample preparation for accelerator mass spectrometry (ID-AMS). Twenty-six (26) whole rock samples have been processed for PGAA and ID-AMS analysis. This study constitutes the first published inter-comparison for concentrations below 100 mu gCl/g. Our results show no significant difference in Cl concentrations between methods. This agreement indicates good retention of chloride during the procedure we employ for whole rock sample dissolution. No significant loss of stable chlorine from either the spike or the sample occurs before isotopic equilibrium is reached, prior to AgCl precipitation. Uncertainties, which are <5% for both methods, affect the uncertainty of the total (36)Cl production rate less than 2% for our samples.The Cl concentration measured by PGAA can be used to calculate the amount of isotopically enriched spike for AMS-ID sample preparation with the aim to optimize (36)Cl analysis. Furthermore, PGAA offers an advance for the interpretation of (36)Cl measurements. It allows measurement of concentrations of major, minor and trace elements including the elements for (36)Cl production (Cl, K, Ca, Ti, and Fe), as well as of neutron absorbers and neutron moderators (H, B, Sm and Gd). These measurements are performed simultaneously and with a precision necessary for calculating the relative contributions to (36)Cl production from the different mechanisms. (C) 2009 Elsevier B.V. All rights reserved.

The 230Thxs-normalization method is a widely used tool for the calculation of vertical fluxes to marine sediments, correcting for the influence of lateral sediment transport. However, the strong particle surface reactivity of thorium may lead to a grain size specific distribution of 230Th. Lateral transport during particle settling might have a sorting effect on particles, thus affecting the sedimentary 230Th signal as well. In this study, the specific distribution pattern of 230Th within different particle classes is investigated in carbonate-rich sediments and opal-rich sediments from the Atlantic Ocean. Sediments were split into distinct particle classes by wet-sieving and settling. The results show a clear preference of 230Th for the smallest particle sizes. Both in carbonate-rich and opal-rich sediment, most of the 230Th is bound within the particle size class <20µm accounting for 60-77% and 90% of the total 230Th inventory, respectively, whereas this size fraction was only 45% and 72% of sediment mass, respectivley. In the opal-rich material, 230Th does not show any preference for opal or non-opaline material.We also compare similar neighbouring deep-sea sediment cores (PS1768-8 and PS1769-1). While the difference in sedimentation rates is a factor of 2-3, the grain-size distribution in the two cores, as well as the 230Th-distribution between the grain sizes, does not differ significantly. These results indicate that syndepositional sediment redistribution at the sea floor may be a process that does not necessarily have a major impact on the grain size distribution. In addition, results from 10Be and 231Pa measurements of the same size-fractionated sediment samples will be presented. In contrast to the 230Th, it is expected to find these isotopes preferentially adsorbed on biogenic substances (opal, carbonate). The isotope ratios 10Be/230Th and 231Pa/230Th are used as palaeoproductivity and palaeocirculation proxies. If 230Th, 10Be and 231Pa are bound to different particle types, lateral transport involving particle sorting might affect the isotope ratios.