Precision and accuracy in glacial geology

However, the configuration and stability of the ice sheet during past interglacial periods remains uncertain. Here we present geomorphological evidence and multiple cosmogenic nuclide data from the southern Ellsworth Mountains to suggest that the divide of the WAIS has fluctuated only modestly in location and thickness for at least the last 1. Fluctuations during glacial—interglacial cycles appear superimposed on a long-term trajectory of ice-surface lowering relative to the mountains. This implies that as a minimum, a regional ice sheet centred on the Ellsworth-Whitmore uplands may have survived Pleistocene warm periods. If so, it constrains the WAIS contribution to global sea level rise during interglacials to about 3. The West Antarctic Ice Sheet WAIS is pinned on an archipelago with its central dome situated over subglacial uplands and bedrock basins, the latter more than 1, m below sea level Fig. For over four decades there has been a fear that this topography could lead to marine instability, since retreat of the ice margin into the basins would enhance ice calving and ice-mass loss, leading to loss of the WAIS and a rapid rise in global sea level of 3—5 m refs 1 , 2 , 3.

Cosmogenic dating of fluvial terraces, Fremont River, Utah

Citation formats Abstract The timing and extent of former glacial advances can demonstrate leads and lags during periods of climatic change and their forcing, but this requires robust glacial chronologies. In parts of southernmost Patagonia, dating pre-global Last Glacial Maximum gLGM ice limits has proven difficult due to post-deposition processes affecting the build-up of cosmogenic nuclides in moraine boulders.

Our approach uses cosmogenic 10Be and 26Al exposure dating, but targets glacial outwash associated with these limits and uses depth-profiles and surface cobble samples, thereby accounting for surface deflation and inheritance.

Beryllium dating of Mount Everest moraines indicates a strong sibility of CRN inheritance. Details of the sample preparation and calculation were given in Owen et al. (, a) (see footnote 1). RESULTS AND DISCUSSION Figure 2. Cosmogenic radionuclide (CRN) ages for moraines in Khumbu Himal south of Everest compared with other.

Irka Hajdas, Susan Ivy-Ochs 9: Geochemical dataset of the Rhone River delta Lake Geneva sediments — disentangling human impacts from climate change 9: Holocene seismic activity of the Yavansu fault, western Turkey 9: Landscape evolution of the northern Alpine Foreland: Holocene treeline changes in the Canadian Cordillera are controlled by climate and local topography Historical evolution of human land-use in the catchment of Lake Murten Surface exposure dating of Lateglacial and Holocene glacier extents in the Canton of Uri, Switzerland

Precision and accuracy in glacial geology

Abstract An ongoing study attempting to date boulders from Neoglacial moraines across the Sierra Nevada mountain range, CA using high precision cosmogenic radionuclide CRN exposure dating has yielded ages that contradict historical records and prior research in the range. To test whether these CRN ages have glacial significance or are merely a function of geomorphic processes that promote inheritance, I collected glaciolacustrine sediment cores to document independent glacier chronologies for the Lyell and Maclure glaciers in Yosemite National Park and the Price glaciers in the Desolation Wilderness.

No rock flour record is apparent from the Price sediment cores. Based on historical accounts, prior research, and glaciolacustrine records, I interpret CRN dating for the Lyell moraines represents true age of the glacier maximum. I propose that the disparate CRN ages from the Maclure glacier result from an ice-cored moraine, which can preserve exposure histories of prior glacial advances by moraine reincorporation rather than obliteration.

Cosmogenic nuclide depth-profiles are used to calculate the age of landforms, the rates at which erosion has affected them since their formation and, in case of deposits, the paleo-erosion rate in the source area. However, two difficulties are typically encountered: 1) old deposits or strongly affected by cosmogenic nuclide inheritance often appear to be saturated, and 2) a full propagation of.

Earth Surface Processes and Landforms 30,8 ; Link to original published article: Sequences of samples taken across valleys known to have been covered repeatedly by the Fermoscandian ice sheet revealed two primary patterns of erosion. At Ravtasvaggi, Dievssavaggi and Alisvaggi, exposure ages in the valley bottom contrast with apparent exposure ages two to four times older on the valley sides. The pattern and scale of erosion in these valleys indicates that glacial valley formation is a result of multiple glacial cycles rather than the result of topographic modification during a single glacial cycle.

Initial data comparing hanging valley and trunk valley sites do not show distinct differences in apparent exposure ages. Slightly older ages for samples from hanging valley bottoms may suggest nuclide inheritance indicating lower erosion than in trunk valley bottoms, as would be expected given the marked topographic step between hanging and trunk valleys.

Although quantifying the amount of erosion depends on the assumed cosmogenic nuclide inheritance prior to the onset of erosion, the pattern of erosion is independent of this.

Explicit treatment of inheritance in dating depositional … – GSA Journals

The 10Be TCN ages show considerable variance on individual surfaces. This suggests that the predominantly bedrock hillslopes erode very slowly and sediment is transferred very gradually in most regions within Death Valley. This disparity between dates determined by different dating methods and the large spread of TCN ages suggests that the cobbles and boulders have considerable inherited 10Be concentrations, suggesting that the clasts have been derived from older shorelines or associated landforms.

Cosmogenic exposure dating is a dependable technique in landscape evo- lution studies, as it can be used to deduce the exposure age of a landform surface (Gosse and Phillips, ).

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A postglacial chronology for some alluvial valleys in Wyoming. Geological Survey Water Supply Paper United States Government printing office, A robust feldspar luminescence dating method for Middle and Late Pleistocene sediments.

Precision and accuracy in glacial geology

At the time that Darwin’s On the Origin of Species was published, the earth was “scientifically” determined to be million years old. By , it was found to be 1. In , science firmly established that the earth was 3. Finally in , it was discovered that the earth is “really” 4. In these early studies the order of sedimentary rocks and structures were used to date geologic time periods and events in a relative way.

Dating faulted alluvial fans with cosmogenic 10Be in the Gurvan Bogd mountain range (Gobi-Altay, Mongolia): climatic and tectonic implications Riccardo Vassallo,1 Jean-Franc¸ois Ritz,1 Re´gis Braucher2 and Se´bastien Carretier3 1Laboratoire Dynamique de la Lithosphe`re, UMR Universite ´Montpellier II, Montpellier, France; 2CEREGE, Europole Mediterraneen.

Glacial landforms from the statistical distributions of cosmogenic exposure dates Responsibility: Glacial landforms, especially moraines, have long been used as indicators of decreased temperature or increased precipitation in the past. Cosmogenic exposure dating of moraine boulders provides a method for estimating moraine ages. However, geomorphic processes interfere with cosmogenic exposure dating. To improve the accuracy of the cosmogenic exposure dating method, quantitative methods for assessing the effects of geomorphic processes on cosmogenic exposure dating are needed.

To address this need, this dissertation describes models of two geomorphic processes and their effects on the cosmogenic exposure dating of moraines. These processes are moraine degradation and inheritance. Both models use Monte Carlo techniques to estimate the statistical distributions of exposure dates from moraine boulders, given specific assumptions about the histories of the boulders. The moraine degradation model is based on prior examples from the literature; the inheritance model is novel.

Some implications of this work for cosmogenic exposure dating of moraines follow. Different geomorphic processes give rise to different statistical distributions of cosmogenic exposure dates. Moraine degradation produces distributions that are skewed toward the young tail of the distribution, whereas inheritance produces distributions that are skewed toward the old tail of the distribution.

Simple procedures for estimating moraine ages from cosmogenic exposure dates perform well in some cases and poorly in others, sometimes producing moraine age estimates that are incorrect by thousands of years. Simple estimators tested here include the mean, the mean after discarding outliers, the youngest date, and the oldest date.

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High frequency Holocene glacier fluctuations in New Zealand differ from the northern signature. A 10Be chronology of late-glacial and Holocene mountain glaciation in the Scoresby Sund region, east Greenland: Implications for seasonality during late-glacial time.

The stochastic nature of burial depth and hence in nuclide production in these clasts during exhumation and fluvial transport, and during post-depositional stirring, results in great variability in clast nuclide concentrations. We present a method for dealing with the problem of pre-depositional inheritance of cosmogenic nuclides.

Can in-situ cosmogenic 14C be used to assess the influence of clast recycling on exposure dating of ice retreat in Antarctica?. Quaternary Geochronology, 6 , Abstract Cosmogenic nuclide exposure dating of glacial clasts is becoming a common and robust method for reconstructing the history of glaciers and ice sheets. In Antarctica, however, many samples exhibit cosmogenic nuclide ‘inheritance’ as a result of sediment recycling and exposure to cosmic radiation during previous ice free periods.

In-situ cosmogenic 14C, in combination with longer lived nuclides such as 10Be, can be used to detect inheritance because the relatively short half-life of 14C means that in-situ14C acquired in exposure during previous interglacials decays away while the sample locality is covered by ice during the subsequent glacial. Measurements of in-situ14C in clasts from the last deglaciation of the Framnes Mountains in East Antarctica provide deglaciation ages that are concordant with existing 26Al and 10Be ages, suggesting that in this area, the younger population of erratics contain limited inheritance.

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Magnitudes and rates of change under different environmental scenarios The past is the key to the future Sea level rise to Modified from the IPCC sea level rise estimates from Wikimedia Commons and using estimates from Bamber and Aspinall , assuming a uniform rate of sea level rise. By examining how ice sheets responded to change in the past, glaciologists hope to uncover details that will help them understand how they are likely to change in the future. By looking at how ice sheets changed over long timescales, they can extend the short observation period over the Antarctic Ice Sheet.

For example, ice streams in Antarctica have been observed to change, accelerate, switch off and recede.

Cosmogenic exposure dating is an elegant method for estimating the ages of moraines, but individual exposure dates are sometimes biased by geomorphic processes. Because exposure dates may be either “too young” or “too old,” there are a variety of methods for .

Cosmogenic Exposure Dating and the Age of the Earth Cosmogenic nuclides are nuclides formed by the interaction of ‘target’ atoms with cosmic radiation. Such nuclides are formed in space, in the atmosphere e. The accumulation of cosmogenic nuclides in minerals at or near the earth’s surface provides a basis for exposure ‘dating‘ of landforms, the quantification of erosion rates, and other geologic applications Bierman, ; Cerling and Craig, ; Gosse and Phillips, Independent evidence discussed below strongly suggests that production rates of these nuclides have remained constant or nearly so, validating their use in geochronometry.

This essay focuses on cosmogenic exposure dating, a method of dating rock surfaces which has been compared to using the redness of someone’s skin in order to estimate the duration of exposure to sunlight an analogy attributed to Edward Evenson; Gosse and Phillips, Cosmogenic Nuclide Production The earth is constantly being bombarded by so-called galactic cosmic radiation.

This radiation interacts with nuclei in the atmosphere to produce garden variety or ‘meteoric’ cosmogenic nuclides e. These interactions produce a cascade of secondary particles, primarily neutrons and muons, which interact with target nuclei within minerals such as quartz and olivine at the earth’s surface, producing terrestrial cosmogenic nuclides TCN. The primary nuclear processes by which cosmogenic nuclides are produced are spallation, muon capture, and neutron activation Bierman, p.

The cosmogenic nuclides most widely utilized for geologic applications are the radionuclides 10Be, 26Al, and 36Cl, and the stable nuclides 3He and 21Ne.