scholarly journals Very low inheritance in cosmogenic surface exposure ages of glacial deposits: A field experiment from two Norwegian glacier forelands

The Holocene ◽  
2017 ◽  
Vol 27 (9) ◽  
pp. 1406-1414 ◽  
Author(s):  
John A Matthews ◽  
Richard A Shakesby ◽  
Derek Fabel
Keyword(s):  
Field Experiment ◽  
Ice Sheets ◽  
Viable Alternative ◽  
Rock Fragments ◽  
Perceived Need ◽  
Cosmogenic Nuclide ◽  
Exposure Age ◽  
Cosmogenic Nuclide Dating ◽  
Southern Norway ◽  
Exposure Ages

Terrestrial cosmogenic nuclide dating has been widely used to estimate the surface exposure age of bedrock and boulder surfaces associated with deglaciation and Holocene glacier variations, but the effect of inherited age has been rarely directly addressed. In this study, small clasts, embedded in flute surfaces on two cirque glacier forelands in Jotunheimen, southern Norway and deposited within the last ~60 years, were used to test whether such clasts have the modern surface exposure age expected in the absence of inheritance. Two different approaches were taken involving dating of (1) a single clast of cobble size from the proglacial area of Austanbotnbreen, and (2) 75 clasts mostly of pebble size from the proglacial area of Storbreen crushed and treated as a single sample. 10Be surface exposure ages were 99 ± 98 and 368 ± 90 years, respectively, with 95% confidence (±2σ). It is concluded that (1) these small glaciers have eroded and deposited rock fragments with a cosmogenic zero or near-zero concentration, (2) the likelihood of inherited cosmogenic nuclide concentrations in similar rock fragments deposited by larger warm-based glaciers and ice sheets should be small, and (3) combining a large number of small rock particles into one sample rather than using single large clasts of boulder size may provide a viable alternative to the commonly perceived need for five or more independent estimates of exposure age per site.

Slow regolith degradation without creep determined by cosmogenic nuclide measurements in Arena Valley, Antarctica

2008 ◽  
Vol 69 (2) ◽  
pp. 242-249 ◽  
Author(s):  
Jaakko Putkonen ◽  
Greg Balco ◽  
Daniel Morgan
Keyword(s):  
Indirect Evidence ◽  
Soil Surface ◽  
Ice Cover ◽  
Surface Erosion ◽  
Dry Valleys ◽  
Cosmogenic Nuclide ◽  
Exposure Age ◽  
Excellent Preservation ◽  
Exposure Ages ◽  
Landslide Deposit

Estimates of regolith degradation in the McMurdo Dry Valleys of Antarctica are currently based on indirect evidence and ancient ashes at or near the soil surface that suggest excellent preservation of surfaces. On the other hand, the existing cosmogenic-nuclide surface exposure ages from many parts of the Dry Valleys are younger than the age of surface deposits inferred from stratigraphic relations. This suggests some combination of surface erosion or past ice cover, both of which would reduce the apparent exposure age. This paper quantifies the regolith degradation and/or past ice cover by measuring10Be and26Al from a landslide deposit that contains 11.3 Ma volcanic ash. The surface sample yields an apparent exposure age of only 0.4 Ma. However, measurements of the subsurface nuclide concentrations show that the deposit has not been shielded by ice, and that the age of the ash does not conflict with the apparent exposure age when slow degradation of the deposit (2 m Ma−1) is taken into account. Soil creep, which is a common degradational process in a wide variety of environments, is non-existent at this field site, which likely reflects the persistent lack of bio- and cryoturbation.

Synoptic analysis of globally-distributed data sets of cosmogenic-nuclide exposure ages

2021 ◽  
Author(s):  
Greg Balco
Keyword(s):  
Global Analysis ◽  
Glacier Change ◽  
Data Sets ◽  
Distributed Data ◽  
Data Set ◽  
Cosmogenic Nuclide ◽  
Synoptic Analysis ◽  
Exposure Age ◽  
Exposure Ages ◽  
Globally Distributed

<p>This abstract describes a project to make large data sets of cosmogenic-nuclide measurements useable for synoptic global analysis of paleoclimate, glacier change, and landscape change. It is based on the 'ICE-D' (Informal Cosmogenic-nuclide Exposure-age Database), a transparent-middle-layer infrastructure for compiling and storing cosmogenic-nuclide measurements and generating internally consistent exposure-age data. The prototype implementation of this project focuses on a global data set of exposure ages from glacial deposits that are, potentially, useful for synoptic analysis of glacier change and paleoclimate. The aim is to address a number of messy data-management and analysis problems associated with cosmogenic-nuclide data, thus making it possible to apply unbiased, automated quantitative analysis to the entire globally-distributed data set. The presentation will highlight (i) examples of error-tolerant hypothesis testing using this approach; (ii) means of quantifying the importance of the details of cosmogenic-nuclide production-rate calculations to global paleoclimate inferences, and (iii) likewise, approaches to understanding the importance of geomorphic processes and landform evolution to global paleoclimate inferences drawn from exposure-dated landforms.</p>

scholarly journals Exposure-age data from across Antarctica reveal mid-Miocene establishment of polar desert climate

Geology ◽  
2020 ◽  
Vol 49 (1) ◽  
pp. 91-95
Author(s):  
Perry Spector ◽  
Greg Balco
Keyword(s):  
Liquid Water ◽  
High Elevation ◽  
Polar Desert ◽  
Cosmogenic Nuclide ◽  
Erosion Processes ◽  
Exposure Age ◽  
Antarctic Continent ◽  
The Antarctic ◽  
Exposure Ages ◽  
Desert Climate

Abstract High-elevation rock surfaces in Antarctica have some of the oldest cosmogenic-nuclide exposure ages on Earth, dating back to the Miocene. A compilation of all available 3He, 10Be, and 21Ne exposure-age data from the Antarctic continent shows that exposure histories recorded by these surfaces extend back to, but not before, the mid-Miocene cooling at 14–15 Ma. At high elevation, this cooling entailed a transition between a climate in which liquid water and biota were present and could contribute to surface weathering and erosion, and a polar desert climate in which virtually all weathering and erosion processes had been shut off. This climate appears to have continued uninterrupted between the mid-Miocene and the present.

Importance of sampling across an assemblage of glacial landforms for interpreting cosmogenic ages of deglaciation

2011 ◽  
Vol 76 (1) ◽  
pp. 148-156 ◽  
Author(s):  
Arjen P. Stroeven ◽  
Derek Fabel ◽  
Jonathan M. Harbor ◽  
David Fink ◽  
Marc W. Caffee ◽  
...  
Keyword(s):  
Spatial Scales ◽  
Ice Sheets ◽  
Cosmogenic Nuclides ◽  
Age Dating ◽  
Widespread Occurrence ◽  
Last Glaciation ◽  
Exposure Age ◽  
A Site ◽  
Glacial Landforms ◽  
Exposure Ages

AbstractDeglaciation chronologies for some sectors of former ice sheets are relatively poorly constrained because of the paucity of features or materials traditionally used to constrain the timing of deglaciation. In areas without good deglaciation varve chronologies and/or without widespread occurrence of material that indicates the start of earliest organic radiocarbon accumulations suitable for radiocarbon dating, typically only general patterns and chronologies of deglaciation have been deduced. However, mid-latitude ice sheets that had warm-based conditions close to their margins often produced distinctive deglaciation landform assemblages, including eskers, deltas, meltwater channels and aligned lineation systems. Because these features were formed or significantly altered during the last glaciation, boulder or bedrock samples from them have the potential to yield reliable deglaciation ages using terrestrial cosmogenic nuclides (TCN) for exposure age dating. Here we present the results of a methodological study designed to examine the consistency of TCN-based deglaciation ages from a range of deglaciation landforms at a site in northern Norway. The strong coherence between exposure ages across several landforms indicates great potential for using TCN techniques on features such as eskers, deltas and meltwater channels to enhance the temporal resolution of ice-sheet deglaciation chronologies over a range of spatial scales.

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

Geosciences ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 331
Author(s):  
Selçuk Aksay ◽  
Susan Ivy-Ochs ◽  
Kristina Hippe ◽  
Lorenz Grämiger ◽  
Christof Vockenhuber
Keyword(s):  
Slope Failure ◽  
Rock Avalanche ◽  
Eastern Alps ◽  
Rock Failure ◽  
Rhine River ◽  
Stratigraphic Sequence ◽  
Exposure Age ◽  
Wet Climate ◽  
Cosmogenic Nuclide Dating ◽  
Additional Support

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.

scholarly journals Cosmogenic nuclide dating of cave sediments in the Eastern Alps and implications for erosion rates

2020 ◽  
Vol 49 (2) ◽  
pp. 107-118
Author(s):  
Philipp Häuselmann ◽  
◽  
Lukas Plan ◽  
Peter Pointner ◽  
Markus Fiebig ◽  
...  
Keyword(s):  
Late Quaternary ◽  
Eastern Alps ◽  
Western Alps ◽  
Valley Bottom ◽  
Cosmogenic Nuclide ◽  
Base Level ◽  
Multi Level ◽  
Slow Evolution ◽  
Karst Systems ◽  
Cosmogenic Nuclide Dating

Karstic caves are created by water eroding and corroding rocks that can be dissolved. Since both the spring areas of caves (normally at the valley bottom) as well as the recharge is controlled by superficial processes, the morphology of the cave bears strong links to these influences. Lowering of local base levels promotes the development of horizontal phreatic cave passages at progressively lower elevations, resulting in the formation of multi-level karst systems. Upon the next lowering of base level, these upper systems become fossilized, and sediment trapped within them may remain preserved for millions of years. Dating these sediments gives clues regarding the time when the passages were last active, and thus may yield age information for old valley floors. The present paper presents cosmogenic nuclide datings of twelve samples from eight caves in the central part of the Northern Calcareous Alps of Austria. Besides three samples that gave no results, most of the obtained ages are at the Mio-Pliocene boundary or within the Pliocene, as was expected before sampling. No multi-level caves could be sampled at different elevations, thus, the obtained valley deepening rates are averages between the age of sediment deposition and the present-day valley floor. However, the valley deepening rates of 0.12 to 0.21 km/Ma are in accordance to previous findings and corroborate a comparatively slow evolution of base level lowering in the Eastern Alps compared to the fast (Late Quaternary) evolution in the Central and Western Alps.

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