Schmidt hammer exposure-age dating of periglacial and glacial landforms in the Southern Swiss Alps based on <i>R</i>-value calibration using historical data

As a contribution to the palaeoenvironmental history reconstruction of the Alpine periglacial domain, this study focuses on the Schmidt hammer exposure-age dating (SHD) of (peri-)glacial landforms using rebound-value (R-value) calibrations for 10 stations in the Scaradra glacier forefield (north-eastern part of the Ticino Canton, Lepontine Alps) and for 13 stations in the Splügenpass region (located between Switzerland and Italy, Rhaetian Alps). Linear calibration based on the known age of several moraines of the Scaradra glacier assessed by historical cartography allowed the reconstruction of the glacier fluctuations around the end of the Little Ice Age. Timing of deglaciation and of rock glacier development was defined in the Splügenpass region using the calibration of exposure ages based on two mule tracks built in 300 CE and 1250 CE, respectively. Discussion on R-value analysis and calibration improves the knowledge on the potential use of SHD for numerical-age dating in Alpine geomorphological studies.

Cosmogenic Exposure Dating (36Cl) of Landforms on Jan Mayen, North Atlantic, and the Effects of Bedrock Formation Age Assumptions on 36Cl Ages

Jan Mayen is a small volcanic island situated 550 km north of Iceland. Glacial sediments and landforms are relatively common on the island but, so far, only a few of them have been dated. In this study, we present and discuss 89 36Cl dates of primarily glacial and volcanic events on Jan Mayen. Calculations of sample exposure ages were complicated by young exposure ages, young rock formation age, and high native Cl contents, leading to updates in CRONUScalc to enable accurate exposure age calculations. The samples provide good evidence against an equilibrium assumption when subtracting background production (e.g., 36Cl produced by neutron capture from fission of U or Th) for samples on young bedrock, with younger exposure ages most significantly affected. Exposure ages were calculated with a range of assumptions of bedrock formation ages appropriate for Jan Mayen, including the assumption that the rock formation age equaled the exposure age (i.e., the youngest age it could possibly have), and we found that although the effect on most of the ages was small, the calculated ages of 25 of the samples increased by more than 1 standard deviation from the age calculated assuming equilibrium background production, with a maximum deviation of 6.1 ka. Due to the very young bedrock on Jan Mayen, we consider the nonequilibrium ages to be the most reliable ages from the island and conclude that large-scale deglaciation on the south and central, lower-lying, parts of the island, started around 20 ka and lasted until ~7 ka. On northern Jan Mayen, the slopes of the 2277 m high stratovolcano Beerenberg are currently partly glaciated; however, outside of the Little Ice Age moraines, all but two samples give ages between 14 and 5.7 ka.

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Slope Failure in a Period of Increased Landslide Activity: Sennwald Rock Avalanche, Switzerland

The Säntis nappe is a complex fold-and-thrust structure in eastern Switzerland, consisting of numerous tectonic discontinuities and a range of hillslopes prone to landsliding and large slope failures that modify the topography irreversibly. A slope failure, namely the Sennwald rock avalanche, occurred in the southeast wall of this fold-and-thrust structure due to the rock failure of Lower Cretaceous Helvetic limestones along the Rhine River valley. In this research, this palaeolandslide is examined in a multidisciplinary approach for the first time with detection and mapping of avalanche deposits, dynamic run-out modelling and cosmogenic nuclide dating. During the rock failure, the avalanche deposits were transported down the hillslope in a spreading-deck fashion, roughly preserving the original stratigraphic sequence. The distribution of landslide deposits and surface exposure age of the rock failure support the hypothesis that the landslide was a single catastrophic event. The 36Cl surface exposure age of avalanche deposits indicates an age of 4.3 ± 0.5 ka. This time coincides with a notably wet climate period, noted as a conditioning factor for landslides across the Alps in the mid-Holocene. The contemporaneity of our event at its location in the Eastern Alps provide additional support for the contention of increased regional seismic activity in mid-Holocene.

Exposure dating of detrital magnetite using ³He enabled by microCT and calibration of the cosmogenic ³He production rate in magnetite

We test whether X-ray micro-computed tomography (microCT) imaging can be used as a tool for screening magnetite grains to improve the accuracy and precision of cosmogenic 3He exposure dating. We extracted detrital magnetite from a soil developed on a fanglomerate at Whitewater, California, which was offset by the Banning strand of the San Andreas Fault. This study shows that microCT screening can distinguish between inclusion-free magnetite and magnetite with fluid or common solid inclusions. Such inclusions can produce bulk 3He concentrations that are significantly in excess of the expected spallation production. We present Li concentrations, major and trace element analyses, and estimated magnetite (U–Th) / He cooling ages of samples in order to model the contribution from fissiogenic, nucleogenic, and cosmogenic thermal neutron production of 3He. We show that mineral inclusions in magnetite can produce 3He concentrations of up to 4 times that of the spallation component, leading to erroneous exposure ages. Therefore, grains with inclusions must be avoided in order to facilitate accurate and precise magnetite 3He exposure dating. Around 30 % of all grains were found to be without inclusions, as detectable by microCT, with the largest proportion of suitable grains in the grain size range of 400–800 µm. While grains with inclusions have 3He concentrations far in excess of the values expected from existing 10Be and 26Al data in quartz at the Whitewater site, magnetite grains without inclusions have concentrations close to the predicted depth profile. We measured 3He concentrations in aliquots without inclusions and corrected them for Li-produced components. By comparing these data to the known exposure age of 53.5 ± 2.2 ka, we calibrate a production rate for magnetite 3He at sea level and high latitude (SLHL) of 116 ± 13 at g−1 a−1. We suggest that this microCT screening approach can be used to improve the quality of cosmogenic 3He measurements of magnetite and other opaque mineral phases for exposure age and detrital studies.

Undernutrition when young and the risk of poor renal function in adulthood in women with diabetes in Shanghai, China

Objective To evaluate the effect of undernutrition when young on the risk of poor renal function in adulthood in women with diabetes mellitus. Methods We studied diabetic women born between 1921 and 1958 who were exposed to the 1959-to-1962 Chinese famine when they were 0 to 37 years old. Exposure age was classified as young adulthood (18 to 37 years), adolescence (10 to 17 years), or childhood (0 to 9 years). The Adolescence group, which was provided with the largest amount of food during the famine, was used as the control group, and variance and binary logistic regression analyses were performed. Results The prevalences of low estimated glomerular filtration rate (eGFR) in the Childhood, Adolescence, and Young adulthood groups were 5.26%, 22.39%, and 79.24%, respectively. The risk of low eGFR for the Young adulthood group (odds ratio [OR] 1.65, 95% confidence interval [CI] 1.10, 2.48), but not for the Childhood group (OR 1.10, 95% CI 0.68, 1.78), was higher than that for the Adolescence group after adjustment for potential confounders. Conclusions Undernutrition during young adulthood significantly increases the risk of renal dysfunction in adult women with diabetes. Therefore, the nutrition of less affluent young women should be improved.

Exposure dating of detrital magnetite using 3He enabled by microCT and calibration of the cosmogenic 3He production rate in magnetite

We test whether X-ray micro computed tomography (microCT) imaging can be used as a tool for screening magnetite grains to improve the accuracy and precision of cosmogenic 3He exposure dating. We extracted magnetite from a soil developed on a fanglomerate at Whitewater, California, which was offset by the Banning Strand of the San Andreas Fault. This study shows that microCT screening can distinguish between inclusion-free magnetite and magnetite with fluid or common solid inclusions. Such inclusions can produce bulk 3He concentrations that are significantly in excess of expected cosmogenic production. We present Li concentrations, major and trace element analysis, and magnetite (U-Th)/He cooling ages of samples in order to model the contribution from radiogenic, nucleogenic, and cosmogenic thermal neutron production of 3He. We show that mineral inclusions in magnetite can produce 3He concentrations of up to four times that of the cosmogenic 3He component, leading to erroneous exposure ages. Therefore, grains with inclusions must be avoided in order to facilitate accurate and precise magnetite 3He exposure dating. Around 30 % of all grains were found to be without inclusions, as detectable by microCT, with the largest proportion of suitable grains in the grain size range of 400–800 µm. While grains with inclusions have 3He concentrations far in excess of the values expected from existing 10Be and 26Al data in quartz at the Whitewater site, magnetite grains without inclusions have concentrations close to the predicted depth profile. We measured 3He concentrations in aliquots without inclusions and corrected them for Li-produced components. By comparing these data to the known exposure age of 53.5 ka, we calibrate a magnetite 3He SLHL production rate of 116 ± 13 at g−1 a−1. We suggest that the microCT screening approach can be used to improve the quality of cosmogenic 3He measurements of magnetite and other opaque mineral phases for exposure age and detrital studies.

Using 10Be dating to determine when the Cordilleran Ice Sheet stopped flowing over the Canadian Rocky Mountains

During the last glacial maximum the Cordilleran and Laurentide ice sheets coalesced east of the Rocky Mountains and geomorphological evidence indicates ice flowed over the main ridge of the Rocky Mountains between ~54–56°N. However, this ice flow has thus far remained unconstrained in time. Here we use in situ produced cosmogenic 10Be dating to determine when Cordilleran ice stopped flowing over the mountain range. We dated eight samples from two sites: one on the western side (Mount Morfee) and one on the eastern side (Mount Spieker) of the Rocky Mountains. At Mount Spieker, one sample is rejected as an outlier and the remaining three give an apparent weighted mean exposure age of 15.6 ± 0.6 ka. The four samples at Mount Morfee are well clustered in time and give an apparent weighted mean exposure age of 12.2 ± 0.4 ka. These ages indicate that Mount Spieker became ice free before the Bølling warming and that the western front of the Rocky Mountains (Mount Morfee) remained in contact with the Cordilleran Ice Sheet until the Younger Dryas.