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

Geosciences ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 390
Author(s):  
Johanna Anjar ◽  
Naki Akҫar ◽  
Eiliv A. Larsen ◽  
Astrid Lyså ◽  
Shasta Marrero ◽  
...  
Keyword(s):  
Large Scale ◽  
Good Evidence ◽  
Ice Age ◽  
Maximum Deviation ◽  
Glacial Sediments ◽  
Rock Formation ◽  
Exposure Dating ◽  
Exposure Age ◽  
Two Samples ◽  
Exposure 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.

scholarly journals Erosion during extreme flood events dominates Holocene canyon evolution in northeast Iceland

2015 ◽  
Vol 112 (8) ◽  
pp. 2355-2360 ◽  
Author(s):  
Edwin R. C. Baynes ◽  
Mikaël Attal ◽  
Samuel Niedermann ◽  
Linda A. Kirstein ◽  
Andrew J. Dugmore ◽  
...  
Keyword(s):  
Large Scale ◽  
Dominant Role ◽  
Flood Events ◽  
Topographic Analysis ◽  
Exposure Dating ◽  
Extreme Flood ◽  
Bedrock Erosion ◽  
The Impact ◽  
Exposure Ages

Extreme flood events have the potential to cause catastrophic landscape change in short periods of time (100 to 103 h). However, their impacts are rarely considered in studies of long-term landscape evolution (>103 y), because the mechanisms of erosion during such floods are poorly constrained. Here we use topographic analysis and cosmogenic 3He surface exposure dating of fluvially sculpted surfaces to determine the impact of extreme flood events within the Jökulsárgljúfur canyon (northeast Iceland) and to constrain the mechanisms of bedrock erosion during these events. Surface exposure ages allow identification of three periods of intense canyon cutting about 9 ka ago, 5 ka ago, and 2 ka ago during which multiple large knickpoints retreated large distances (>2 km). During these events, a threshold flow depth was exceeded, leading to the toppling and transportation of basalt lava columns. Despite continuing and comparatively large-scale (500 m3/s) discharge of sediment-rich glacial meltwater, there is no evidence for a transition to an abrasion-dominated erosion regime since the last erosive event because the vertical knickpoints have not diffused over time. We provide a model for the evolution of the Jökulsárgljúfur canyon through the reconstruction of the river profile and canyon morphology at different stages over the last 9 ka and highlight the dominant role played by extreme flood events in the shaping of this landscape during the Holocene.

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

2021 ◽  
Author(s):  
Florian Hofmann ◽  
Emily H. G. Cooperdock ◽  
A. Joshua West ◽  
Dominic Hildebrandt ◽  
Kathrin Strößner ◽  
...  
Keyword(s):  
Production Rate ◽  
Trace Element Analysis ◽  
Micro Computed Tomography ◽  
Element Analysis ◽  
Exposure Dating ◽  
Exposure Age ◽  
Accuracy And Precision ◽  
Microct Imaging ◽  
Exposure Ages

Abstract. 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.

Timing and Extent of Late Quaternary Glaciation in the Ahuriri River Valley, Southern Alps, New Zealand

2021 ◽  
Author(s):  
Levan Tielidze ◽  
Shaun Eaves ◽  
Kevin Norton ◽  
Andrew Mackintosh
Keyword(s):  
New Zealand ◽  
Large Scale ◽  
Late Quaternary ◽  
Southern Alps ◽  
River Valley ◽  
Entire Study ◽  
Geomorphological Mapping ◽  
Exposure Dating ◽  
Quaternary Glaciation ◽  
Exposure Ages

<p>Some valleys in South Island, New Zealand already have a number of well-dated glacier records. However, understanding of the precise timing of old glacial events in many valleys still remains poor. For this purpose, the cosmogenic <sup>10</sup>Be surface exposure dating technique was used to constrain the timing and extent of late Quaternary glaciation in the Ahuriri River valley, Southern Alps, New Zealand. The 33 <sup>10</sup>Be surface-exposure ages from two different moraine complexes range from 16.6±0.4 ka to 19.7±0.5 ka suggesting rapid glacier recession (~17 km) during the last deglaciation.</p><p>Field observation and geomorphological mapping were also used to investigate the extent and drivers of glaciation in this valley. For the final step, we created detail and comprehensive map of the glacial geomorphology in an area covered by palaeo Ahuriri Glacier, in the central Southern Alps. Geomorphological mapping from high-resolution aerial imagery, large scale topographical maps, average resolution DEM, and several field investigations allowed us to produce the 1:38,000 scale map for the entire study site covering an area of about 532 km<sup>2</sup>.</p><p>This newly created map along with the new <sup>10</sup>Be surface exposure dataset will help us in better understanding of past glacier-climate interactions in the Southern Alps and in the Southern Hemisphere in general.</p>

scholarly journals Exposure dating of detrital magnetite using <sup>3</sup>He enabled by microCT and calibration of the cosmogenic <sup>3</sup>He production rate in magnetite

Geochronology ◽  
2021 ◽  
Vol 3 (2) ◽  
pp. 395-414 ◽  
Author(s):  
Florian Hofmann ◽  
Emily H. G. Cooperdock ◽  
A. Joshua West ◽  
Dominic Hildebrandt ◽  
Kathrin Strößner ◽  
...  
Keyword(s):  
Production Rate ◽  
Micro Computed Tomography ◽  
Exposure Dating ◽  
San Andreas ◽  
Exposure Age ◽  
Mineral Phases ◽  
Accuracy And Precision ◽  
Microct Imaging ◽  
Exposure Ages

Abstract. 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.

scholarly journals 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

2021 ◽  
Vol 76 (4) ◽  
pp. 401-423
Author(s):  
Cristian Scapozza ◽  
Chantal Del Siro ◽  
Christophe Lambiel ◽  
Christian Ambrosi
Keyword(s):  
Swiss Alps ◽  
Age Dating ◽  
Ice Age ◽  
Schmidt Hammer ◽  
Value Analysis ◽  
Glacier Forefield ◽  
Exposure Age ◽  
R Value ◽  
Glacial Landforms ◽  
Exposure Ages

Abstract. 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.

scholarly journals Flipping the Script: Measuring Both Performance Validity and Cognitive Ability with the Forced Choice Recognition Trial of the RCFT

2021 ◽  
pp. 003151252110197
Author(s):  
Kaitlyn Abeare ◽  
Kristoffer Romero ◽  
Laura Cutler ◽  
Christina D. Sirianni ◽  
Laszlo A. Erdodi
Keyword(s):  
Cognitive Ability ◽  
Verbal Memory ◽  
Visual Memory ◽  
Large Scale ◽  
Clinical Sample ◽  
Neuropsychological Test ◽  
Forced Choice ◽  
Control Group ◽  
Performance Validity ◽  
Two Samples

In this study we attempted to replicate the classification accuracy of the newly introduced Forced Choice Recognition trial (FCR) of the Rey Complex Figure Test (RCFT) in a clinical sample. We administered the RCFT FCR and the earlier Yes/No Recognition trial from the RCFT to 52 clinically referred patients as part of a comprehensive neuropsychological test battery and incentivized a separate control group of 83 university students to perform well on these measures. We then computed the classification accuracies of both measures against criterion performance validity tests (PVTs) and compared results between the two samples. At previously published validity cutoffs (≤16 & ≤17), the RCFT FCR remained specific (.84–1.00) to psychometrically defined non-credible responding. Simultaneously, the RCFT FCR was more sensitive to examinees’ natural variability in visual-perceptual and verbal memory skills than the Yes/No Recognition trial. Even after being reduced to a seven-point scale (18-24) by the validity cutoffs, both RCFT recognition scores continued to provide clinically useful information on visual memory. This is the first study to validate the RCFT FCR as a PVT in a clinical sample. Our data also support its use for measuring cognitive ability. Replication studies with more diverse samples and different criterion measures are still needed before large-scale clinical application of this scale.

scholarly journals Condom Use During Last Sexual Contact and Last 30 Days in Two Samples of Caribbean Military Personnel

2011 ◽  
Vol 6 (2) ◽  
pp. 132-135 ◽  
Author(s):  
Rachel Hallum-Montes ◽  
Rohan D’Souza ◽  
Maria Isabel Tavarez ◽  
Russell Manzanero ◽  
Grace E. Dann ◽  
...  
Keyword(s):  
Condom Use ◽  
Large Scale ◽  
Monitoring And Evaluation ◽  
Armed Forces ◽  
Sexual Contact ◽  
Unprotected Sex ◽  
Sexually Transmitted ◽  
Populations At Risk ◽  
Two Samples ◽  
Biological And Behavioral Surveillance

Condom use during last sexual contact is a survey measure that may be used to inform monitoring and evaluation indicators of recent condom use in populations at risk for HIV infection and other sexually transmitted infections, such as the uniformed services. The authors tested for differences in condom use measures that were fielded within separate Biological and Behavioral Surveillance Surveys conducted in the armed forces of two separate nations: the Dominican Republic and Belize. Both surveys included measures of condom use during last sexual contact with specified partners and both surveys included the Risk Behavior Assessment (RBA), which measures specific sexual acts and condom use frequency during a specified time period. In both samples, more than 40% of respondents who reported condom use during last sexual contact with a regular partner also reported engaging in unprotected sex when screened with the RBA. Furthermore, more than 60% of respondents who reported condom use during last sexual encounter with a commercial sex worker also reported engaging in unprotected sex when screened with the RBA. The results carry implications for monitoring and evaluation indicators of large-scale HIV prevention programs. The authors recommend that, when feasible, more in-depth instruments such as the RBA be considered to measure recent condom use in populations of uniformed services personnel.

scholarly journals The history of settlement and agrarian land use in a boreal forest in Värmland, Sweden, new evidence from pollen analysis

2021 ◽  
Author(s):  
Sigrún Dögg Eddudóttir ◽  
Eva Svensson ◽  
Stefan Nilsson ◽  
Anneli Ekblom ◽  
Karl-Johan Lindholm ◽  
...  
Keyword(s):  
Land Use ◽  
Pollen Analysis ◽  
Large Scale ◽  
Pollen Grains ◽  
Ice Age ◽  
Valuable Insight ◽  
Archaeological Survey ◽  
History Of ◽  
New Evidence ◽  
Insight Into

AbstractShielings are the historically known form of transhumance in Scandinavia, where livestock were moved from the farmstead to sites in the outlands for summer grazing. Pollen analysis has provided a valuable insight into the history of shielings. This paper presents a vegetation reconstruction and archaeological survey from the shieling Kårebolssätern in northern Värmland, western Sweden, a renovated shieling that is still operating today. The first evidence of human activities in the area near Kårebolssätern are Hordeum- and Cannabis-type pollen grains occurring from ca. 100 bc. Further signs of human impact are charcoal and sporadic occurrences of apophyte pollen from ca. ad 250 and pollen indicating opening of the canopy ca. ad 570, probably a result of modification of the forest for grazing. A decrease in land use is seen between ad 1000 and 1250, possibly in response to a shift in emphasis towards large scale commodity production in the outlands. Emphasis on bloomery iron production and pitfall hunting may have caused a shift from agrarian shieling activity. The clearest changes in the pollen assemblage indicating grazing and cultivation occur from the mid-thirteenth century, coinciding with wetter climate at the beginning of the Little Ice Age. The earliest occurrences of anthropochores in the record predate those of other shieling sites in Sweden. The pollen analysis reveals evidence of land use that predates the results of the archaeological survey. The study highlights how pollen analysis can reveal vegetation changes where early archaeological remains are obscure.

A gas migration law study of a large-scale 3D physical similarity simulation with an adaptive Kalman filter algorithm

2022 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Yuyu Hao ◽  
Shugang Li ◽  
Tianjun Zhang
Keyword(s):  
Kalman Filter ◽  
Large Scale ◽  
Gas Migration ◽  
Adaptive Kalman Filter ◽  
Physical Similarity ◽  
Content Type ◽  
Gas Concentration ◽  
Rock Formation ◽  
Concentration Estimation ◽  
Migration Law

Purpose In this study, a physical similarity simulation plays a significant role in the study of crack evolution and the gas migration mechanism. A sensor is deployed inside a comparable artificial rock formation to assure the accuracy of the experiment results. During the building of the simulated rock formation, a huge volume of acidic gas is released, causing numerous sensor measurement mistakes. Additionally, the gas concentration estimation approach is subject to uncertainty because of the complex rock formation environment. As a result, the purpose of this study is to introduce an adaptive Kalman filter approach to reduce observation noise, increase the accuracy of the gas concentration estimation model and, finally, determine the gas migration law. Design/methodology/approach First, based on the process of gas floatation-diffusion and seepage, the gas migration model is established according to Fick’s second law, and a simplified modeling method using diffusion flux instead of gas concentration is presented. Second, an adaptive Kalman filter algorithm is introduced to establish a gas concentration estimation model, taking into account the model uncertainty and the unknown measurement noise. Finally, according to a large-scale physical similarity simulation platform, a thorough experiment about gas migration is carried out to extract gas concentration variation data with certain ventilation techniques and to create a gas chart of the time-changing trend. Findings This approach is used to determine the changing process of gas distribution for a certain ventilation mode. The results match the rock fissure distribution condition derived from the microseismic monitoring data, proving the effectiveness of the approach. Originality/value For the first time in large-scale three-dimensional physical similarity simulations, the adaptive Kalman filter data processing method based on the inverse Wishart probability density function is used to solve the problem of an inaccurate process and measurement noise, laying the groundwork for studying the gas migration law and determining the gas migration mechanism.

scholarly journals A simple conceptual model to interpret the 100 000 years dynamics of paleo-climate records

2010 ◽  
Vol 17 (5) ◽  
pp. 585-592 ◽  
Author(s):  
C. S. Quiroga Lombard ◽  
P. Balenzuela ◽  
H. Braun ◽  
D. R. Chialvo
Keyword(s):  
Large Scale ◽  
Power Spectra ◽  
Greenland Ice Sheet ◽  
Ice Age ◽  
Solar Cycles ◽  
The Holocene ◽  
De Vries ◽  
Last Ice Age ◽  
Paleoclimate Records ◽  
Dominant Frequencies

Abstract. Spectral analyses performed on records of cosmogenic nuclides reveal a group of dominant spectral components during the Holocene period. Only a few of them are related to known solar cycles, i.e., the De Vries/Suess, Gleissberg and Hallstatt cycles. The origin of the others remains uncertain. On the other hand, time series of North Atlantic atmospheric/sea surface temperatures during the last ice age display the existence of repeated large-scale warming events, called Dansgaard-Oeschger (DO) events, spaced around multiples of 1470 years. The De Vries/Suess and Gleissberg cycles with periods close to 1470/7 (~210) and 1470/17 (~86.5) years have been proposed to explain these observations. In this work we found that a conceptual bistable model forced with the De Vries/Suess and Gleissberg cycles plus noise displays a group of dominant frequencies similar to those obtained in the Fourier spectra from paleo-climate during the Holocene. Moreover, we show that simply changing the noise amplitude in the model we obtain similar power spectra to those corresponding to GISP2 δ18O (Greenland Ice Sheet Project 2) during the last ice age. These results give a general dynamical framework which allows us to interpret the main characteristic of paleoclimate records from the last 100 000 years.

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