Postglacial alluvial fan dynamics in the Cordillera Oriental, Peru, and palaeoclimatic implications

AbstractAlluvial fans record climate-driven erosion and sediment-transport processes and allow reconstructing past environmental conditions. Here we investigate the sedimentation history of two alluvial fans located in formerly glaciated valleys of the Cordillera Oriental, Peru.10Be exposure ages from the fan surfaces and radiocarbon ages from the fan interiors constrain the final stages of fan formation. The10Be and14C ages cluster mainly between 13.3–9.3 ka and 11,500–9700 cal yr BP, respectively. Our age data set indicates that—after deglaciation—large amounts of fan sediment were deposited until ∼10 ka, when sedimentation rates declined rather abruptly. This pattern is supported by10Be erosion rates for the fan catchments, because under the assumption of constant erosion the time needed to erode the material stored in the fans significantly exceeds their age. Correlating our ages with regional climate records indicates that precipitation exerts the primary control on fan sedimentation. Two periods with elevated lake levels and increased precipitation between 18 and 14.5 ka and from 13 to 11.5 ka resulted in rapid deposition of large fan lobes. Subsequently, lower precipitation rates decreased erosion in the catchments and sediment delivery to the fans, which have remained largely inactive since ∼9.5 ka.

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Using Soil stratigraphic observations to constrain TCN depth profile ages of relict alluvial fan surfaces in the Sonoran Desert, USA

10.5194/egusphere-egu2020-10614 ◽

2020 ◽

Author(s):

Brad Sion ◽

Eric McDonald ◽

Janelle Bustarde

Keyword(s):

Depth Profile ◽

Sonoran Desert ◽

Surface Modifications ◽

Alluvial Fan ◽

Soil Profiles ◽

Surface Erosion ◽

Soil Thickness ◽

Erosion Rates ◽

Comparison Results ◽

Exposure Ages

Interpretations of surface exposure ages derived from the accumulation of cosmogenic isotopes commonly are hampered by a lack of field documentation that is necessary to identify and constrain if any post-depositional surface modifications have occurred (e.g. surface erosion, burial) that will impact age interpretations. Previous authors have discussed these issues, but the community still has not fully adopted the practice of interpreting surface exposure ages in conjunction with detailed soil stratigraphic observations. We employ this &#8220;novel&#8221; approach by documenting a soil chronosequence from the Gould wash alluvial fan sequence near Cibola, AZ to demonstrate how soil stratigraphy can provide constraints for the relative stability of depositional surfaces and can influence interpretations of TCN ages. The Cibola chronosequence represents a range of alluvial fan ages that extend well beyond those commonly observed in the desert southwestern US (typically <100 ka) and provides evidence for extended periods of surface stability. We identified seven different alluvial fan surfaces within the sequence, documented their soil morphological and chemical properties, and dated four of the fan surfaces with 36Cl depth profiles. Fan deposits largely consist of volcaniclastic alluvium derived from the local Trigo Peaks and distal Castle Dome mountain blocks and show both a reduction of bar-and-swale surface topography and an increasing expression of desert pavement with relative surface age. The soil profiles consist of Av-Bk-BCky-Cky-Ck vertical horizon sequences (~125-cm thick) in the youngest fan units to Avk-Btky-Bkym-Bky-BCky-Cky-C (~400-cm thick) in the oldest fan unit that reflect systematic changes in soil thickness, structure, rubification of B horizons, and relative accumulations of eolian derived silt, clay, and salts as a function of relative surface age. Chlorine-36 depth profile analysis yielded variable fan ages that are largely controlled by the magnitude of allowable erosion. Model results for which input data were parameterized to optimize unconstrained erosion rates indicate surface exposure ages of 46 (2A), 114 (2B), 268 (3A), and 386 (4A) ka. These are associated with best-fit erosion rates of 0-6 mm/kyr that indicate 0-136 cm net erosion. By comparison, results for which erosion rates were constrained to ~1 mm/kyr based on soil stratigraphic observations yielded exposure ages of 41 (2A), 114 (2B), 209 (3A), and 287 (4A) ka, resulting in differences of 10-25% of the unconstrained ages. The systematic morphological trends observed in the soil profiles do not support inferences of net erosion exceeding 30 cm and therefore cannot support the results from unconstrained parameter optimization. Although statistical optimization schemes provide better model fits to the data as indicated by chi-shared minimization routines, current models cannot account for field observations or for inferred constraints on surface modifications based on cosmogenic isotope concentrations alone. That task is better suited for and required by the sampling protocol to achieve more reliable surface exposure dates.

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Influence of Wildfire on Earth Surface Processes and Geomorphology

10.5194/egusphere-egu21-948 ◽

2021 ◽

Author(s):

Paul Santi ◽

Francis Rengers

Keyword(s):

Debris Flows ◽

Management Practices ◽

Mass Movement ◽

Soil Formation ◽

Alluvial Fan ◽

Water Repellent ◽

Alluvial Fans ◽

Stream Channels ◽

Sediment Delivery ◽

Recurrence Intervals

Wildfire is a global phenomenon that is expected to increase in extent and severity due to shifting land management practices and climate change. It removes vegetation, deposits ash, influences water-repellent soil formation, and physically weathers rock. These changes typically lead to increased erosion through sheetwash, rilling, rock spalling, and dry ravel, as well as increased mass movement in the form of floods, debris flows, rockfall, and landslides. Post-wildfire changes in these processes bring about landform changes as hillslopes are lowered and stream channels aggrade or incise at increased rates. Research has documented increases in erosion after wildfire ranging from 2-1000 times the pre-fire rates. Post-wildfire landscape lowering by erosion has been measured in the western U.S. at magnitudes of 2 mm per year, with sediment delivery at the mouths of canyons increased in the range of 160-1000% during the post-wildfire window of disturbance. Furthermore, post-wildfire sediment transport enhances the development of alluvial fans, debris fans, and talus cones. Debris-flow likelihood is increased following wildfire, such that modest rainstorms with <2 year recurrence intervals are typically sufficient to trigger debris flows with volumes much larger (270-540%) than at unburned sites. In the western U.S., as much as 25-50% of alluvial fan accumulation can be attributed to post-wildfire debris flows and other post-wildfire fluvial transport. The window of disturbance to the landscape caused by wildfire is typically on the order of three to four years, with some effects persisting up to 30 years. &#160;Consequently, wildfire is an important agent of geomorphic change.

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A 14.5 million-year geologic record of East Antarctic Ice Sheet fluctuations in the central Transantarctic Mountains, constrained with multiple cosmogenic nuclides

10.5194/egusphere-egu2020-19999 ◽

2020 ◽

Author(s):

Gordon Bromley ◽

Alexandra Balter ◽

Greg Balco ◽

Margaret Jackson

Keyword(s):

Ice Sheet ◽

Data Set ◽

Antarctic Ice Sheet ◽

Climate Conditions ◽

Current Configuration ◽

Erosion Rates ◽

Transantarctic Mountains ◽

Geologic Record ◽

Exposure Ages ◽

East Antarctic Ice Sheet

The distribution of relict moraines in the Transantarctic Mountains affords geologic constraint of past ice-marginal positions of the East Antarctic Ice Sheet (EAIS). We describe the directly dated glacial-geologic record from Roberts Massif, an ice-free area in the central Transantarctic Mountains, to provide a comprehensive record of ice sheet change at this site since the Miocene and to capture ice sheet response to warmer-than-present climate conditions. The record is constrained by cosmogenic 3He, 10Be, 21Ne, and 26Al surface-exposure ages from > 160 dolerite and sandstone erratics on well-preserved moraines and drift units. Our data set indicates that a cold-based EAIS was present, and similar to its current configuration, for long periods over the last ~14.5 Myr, including the mid-Miocene, Late Pliocene, and early-to-mid Pleistocene, with moraine ages increasing with distance from and elevation above the modern ice margin. We also report extremely low erosion rates over the duration of our record, reflecting long-term polar desert conditions at Roberts Massif. The age-elevation distribution of moraines at Roberts Massif is consistent with a persistent EAIS extent during glacial maxima, accompanied by slow, isostatic uplift of the massif due to subglacial erosion. Although our data are not a direct measure of ice volume, the Roberts Massif glacial record indicates that the EAIS was present and of similar extent to today during periods when global temperature was believed to be warmer and/or atmospheric CO2 concentrations were likely higher than today.

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Estimation of erosion model erodibility parameters from media properties

Soil Research ◽

10.1071/sr99041 ◽

2000 ◽

Vol 38 (2) ◽

pp. 265 ◽

Cited By ~ 17

Author(s):

G. J. Sheridan ◽

H. B. So ◽

R. J. Loch ◽

C. M. Walker

Keyword(s):

Overland Flow ◽

Prediction Models ◽

Field Capacity ◽

Stepwise Multiple Regression ◽

Organic Carbon Content ◽

Regression Equations ◽

Sediment Delivery ◽

Data Set ◽

Erosion Rates ◽

Erosion Processes

The aim of this research was to enable erodibility values for hillslope-scale erosion prediction models to be determined from easily measured media properties. Simulated rainfall and overland flow experiments were carried out on 34 soils and overburdens from 15 Queensland open-cut coal mines at The University of Queensland Erosion Processes Laboratory. Properties of the 34 media determined included aggregate stability, Atterberg limits, bulk density, cation exchange capacity, dispersion ratios, electrical conductivity, exchangeable sodium percentage, organic carbon content, pH, texture, and water content at field capacity and wilting point. Correlation and stepwise multiple regression procedures were used to determine those media properties that could best be used to predict rill and interill erodibility. Correlations between media properties and sediment delivery at each of 5, 10, 15, 20, and 30% slope revealed that different media properties were correlated with erosion rates at different slopes. A media property could show a strong correlation with erodibility at 30% slope, and a low correlation at 5% slope. Splitting the data set into soils only, and overburdens only, showed that properties that were positively correlated with erosion rates for one group could be negatively correlated for the other group. Therefore, in this study, erodibility could not be explicitly linked to one set of media properties for all medium types and erosive conditions. It was concluded that a single regression equation could not be used to predict erodibility under all conditions. Instead, 4 equations were developed to predict rill and interill erodibility, for soils and overburdens separately. The need for separate regression equations was attributed to the presence of different erosive sub-processes for specific combinations of medium type and slope gradient.

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Multiple cosmogenic nuclides document complex Pleistocene exposure history of glacial drifts in Terra Nova Bay (northern Victoria Land, Antarctica)

Quaternary Research ◽

10.1016/j.yqres.2008.07.004 ◽

2009 ◽

Vol 71 (1) ◽

pp. 83-92 ◽

Cited By ~ 33

Author(s):

Luigia Di Nicola ◽

Stefan Strasky ◽

Christian Schlüchter ◽

Maria Cristina Salvatore ◽

Naki Akçar ◽

...

Keyword(s):

Volcanic Field ◽

Glacial Cycles ◽

Erosion Rates ◽

Terra Nova Bay ◽

Geological Surveys ◽

Victoria Land ◽

History Of ◽

Terra Nova ◽

Exposure Ages ◽

The Last Glacial

AbstractGeomorphological and glacial geological surveys and multiple cosmogenic nuclide analyses (10Be, 26Al, and 21Ne) allowed us to reconstruct the chronology of variations prior to the last glacial maximum of the East Antarctic Ice Sheet (EAIS) and valley glaciers in the Terra Nova Bay region. Glacially scoured coastal piedmonts with round-topped mountains occur below the highest local erosional trimline. They represent relict landscape features eroded by extensive ice overriding the whole coastal area before at least 6 Ma (pre-dating the build-up of the Mt. Melbourne volcanic field). Since then, summit surfaces were continuously exposed and well preserved under polar condition with negligible erosion rates on the order of 17 cm/Ma. Complex older drifts rest on deglaciated areas above the younger late-Pleistocene glacial drift and below the previously overridden summits. The combination of stable and radionuclide isotopes documents complex exposure histories with substantial periods of burial combined with minimal erosion. The areas below rounded summits were repeatedly exposed and buried by ice from local and outlet glaciers. The exposure ages of the older drift(s) indicate multiple Pleistocene glacial cycles, which did not significantly modify the pre-existing landscape.

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Influence of Late Holocene climate on Lake Eggers hydrology, McMurdo Sound

Antarctic Science ◽

10.1017/s0954102021000018 ◽

2021 ◽

pp. 1-13

Author(s):

E.J. Chamberlain ◽

A.J. Christ ◽

R.W. Fulweiler

Keyword(s):

Late Holocene ◽

Ross Sea ◽

Regional Climate ◽

Ice Cores ◽

Lake Ice ◽

Mcmurdo Sound ◽

Ice Accumulation ◽

History Of ◽

Ground Penetrating ◽

Western Ross Sea

Abstract Ice-covered lakes in Antarctica preserve records of regional hydroclimate and harbour extreme ecosystems that may serve as terrestrial analogues for exobiotic environments. Here, we examine the impacts of hydroclimate and landscape on the formation history of Lake Eggers, a small ice-sealed lake, located in the coastal polar desert of McMurdo Sound, Antarctica (78°S). Using ground penetrating radar surveys and three lake ice cores we characterize the ice morphology and chemistry. Lake ice geochemistry indicates that Lake Eggers is fed primarily from local snowmelt that accreted onto the lake surface during runoff events. Radiocarbon ages of ice-encased algae suggest basal ice formed at least 735 ± 20 calibrated years before present (1215 C.E.). Persisting through the Late Holocene, Lake Eggers alternated between periods of ice accumulation and sublimation driven by regional climate variability in the western Ross Sea. For example, particulate organic matter displayed varying δ15N ratios with depth, corresponding to sea ice fluctuations in the western Ross Sea during the Late Holocene. These results suggest a strong climatic control on the hydrologic regime shifts shaping ice formation at Lake Eggers.

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Economics of respiratory disease in dairy replacement heifers

Animal Health Research Reviews ◽

10.1017/s1466252320000250 ◽

2020 ◽

Vol 21 (2) ◽

pp. 143-148

Author(s):

Michael W. Overton

Keyword(s):

Respiratory Disease ◽

Milk Production ◽

Incident Case ◽

Data Set ◽

Dairy Heifers ◽

The Usa ◽

History Of ◽

On Farm ◽

The Impact ◽

Selective Culling

AbstractBovine respiratory disease (BRD) is a frequent disease concern in dairy cattle and is most commonly diagnosed in young dairy heifers. The impact of BRD is highly variable, depending on the accuracy and completeness of detection, effectiveness of treatment, and on-farm culling practices. Consequences include decreased rate of weight gain, a higher culling risk either as heifers or as cows, delayed age at first service, delayed age at first calving, and in some cases, lower future milk production. In this data set of 104,100 dairy replacement heifers from across the USA, 36.6% had one or more cases diagnosed within the first 120 days of age with the highest risk of new cases occurring prior to weaning. Comparison of the raising cost for heifers with BRD and those without a recorded history of BRD resulted in an estimated cost per incident case occurring in the first 120 days of age of $252 or $282, depending upon whether anticipated future milk production differences were considered or not. Current market conditions contributed to a cost estimate that is significantly higher than previously published estimates, driven in part by the losses associated with selective culling of a subset of heifers that experienced BRD.

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Characteristics and Care of U.S. Nursing Home Residents with a History of Chronic Mental Illness

Canadian Journal on Aging / La Revue canadienne du vieillissement ◽

10.1017/s0714980800013866 ◽

2000 ◽

Vol 19 (S2) ◽

pp. 1-17 ◽

Cited By ~ 3

Author(s):

Charles D. Phillips ◽

Kathleen M. Spry

Keyword(s):

Nursing Home ◽

Nursing Home Residents ◽

Minimum Data Set ◽

Chronic Mental Illness ◽

Data Set ◽

Minimum Data ◽

Troubles Mentaux ◽

History Of ◽

Resident Assessment ◽

Medicaments Psychotropes

RÉSUMÉTrès peu de recherches ont été effectuées sur les pensionnaires des maisons de soins ayant manifestés des troubles mentaux chroniques sans démence avant leur entrée en institution. Les données du Minimum Data Set for Nursing Home Resident Assessment and Care Screening (MDS) de 1993 ont été utilisées pouranalyser les différences dans les caractéristiques et les soins se rapportant à ce type de pensionnaires par rapport aux autres pensionnaires. Cette enquête portait sur 70 000 pensionnaires du Kansas, du Maine, du Mississippi et du Dakota du Sud. Les caractéristiques des pensionnaires qui éprouvaient ce type de troubles mentaux chroniques étaient plus fréquemment les suivantes: sexe masculin, 65 ans et plus, bénéficiaires de Medicaid, moins médicalement inaptes et niveau plus élevé de problèmes de comportements. Ces pensionnaires reçoivent aussi davantage de médicaments psychotropes et suivant une thérapie, la prévalence de la thérapie étant cependant moins éleveé. Les informations recueillies pourraient laisser croire que les soins accordés à ces pensionnaires ne sont pas des plus appropriés.

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