Coarse-grained mineral dust deposition in alpine lakes provide evidence of increased windspeeds associated with more intense cyclogenesis during warmer intervals of the late Holocene period in arid and semi-arid tracts of North America.

2020 ◽  
Author(s):  
Atreyee Bhattacharya ◽  
Anne Bennett ◽  
Thomas Marchitto ◽  
Elana Leithold
Keyword(s):  
Grain Size ◽  
North America ◽  
Late Holocene ◽  
Mineral Dust ◽  
Fine Fraction ◽  
Dust Deposition ◽  
Size Fractions ◽  
Grain Sizes ◽  
Dust Generation ◽  
Semi Arid

<p>Mineral dust accumulation is often causally associated with aridity, with higher dust deposition rates are assumed to reflect increasing magnitude of aridity. However, the relation between dust deposition and aridity is not straightforward; grain sizes play a crucial role in processes associated with mineral dust generation, transportation and deposition in sedimentary settings.</p><p>In this study, we apply grain-size analyses in six well-studied cores (spanning the late Holocene) previously collected from alpine lake sites distributed across the arid and semi-arid regions of west, southwest, and the Great Plains of North America. Previous work with these cores has demonstrated that the lake sediments are predominantly detrital, windblown particles and little to no impact of fluvial proceeses . We find that the most commonly occurring grain sizes are a fine fraction (typically <4 microns, which is easily lofted and transported long distances) and a coarse fraction (typically >25 microns and in some cases with a distinct peak at 100 microns, both of which are are too large to be carried long distances and suggest short distance transportation). We used grain size separation techniques to separate the two size fractions and geochemically fingerprinted those from three sites.</p><p>We find that more rapid accumulation of the coarser coarser-grain size fractions occurred during wetter intervals in the Holocene. Furthermore, the geochemistry of the coarse fractions indicates regional rather than local sourcing of the material from bedrock weathering. We do not find any clear relationships between the fine fraction and aridity patterns, nor a clear source region for this material.</p><p>We hypothesize that the increase in coarser dust deposition during wetter intervals is related to either intensification of land-use patterns associated with agriculture and/or to episodically strong winds. Warmer and wetter intervals in the areas under consideration have been associated with intensified cyclogenesis. Our study demonstrates the critical need to incorporate grain-size analysis as well as geochemical fingerprinting of the different size fractions in interpreting mineral dust record.</p><p> </p><p>Acknowledgement: James Sickman, Jason Neff (for sharing samples), Jacob Ashford, Tyler Vollmer, Audriana Pollen, Alejandra Pedrazza, (for assistance with analyses and archival visits), John Morton, Wendy Freeman (for assisting students in the laboratory), Aradhna Tripati and Juan Lora (for assisting with data interpretation).</p><p> </p>

Geochemical characterization of discrete grain size fractions within contemporary alpine dust, Uinta Mountains, Utah, USA

2020 ◽  
Author(s):  
Pratt Olson ◽  
Jeffrey Munroe
Keyword(s):  
Grain Size ◽  
Clay Minerals ◽  
Mineral Dust ◽  
Fine Fraction ◽  
Particle Diameter ◽  
Source Analysis ◽  
Dust Collector ◽  
Mountain Range ◽  
Uinta Mountains ◽  
Source Regions

<p>The contemporary aeolian system is poorly understood due in part to a scarcity of direct measurements of modern dust deposition. The Uinta Mountains of Northeastern Utah, USA are well-suited to the study of contemporary dust owing to their gently sloping, soil-mantled alpine zones and relatively inert, quartzite-dominated bedrock. Capitalizing on this unique setting, eight marble dust traps, as well as one active dust collector, have been installed throughout the mountain range. Previous study of samples from these collectors has supported the quantification of mineral dust inputs to alpine pedogenesis and identified isotopic fingerprints that link dust to potential source regions. This project focuses on dust emptied from these samplers in Fall 2019, representing two years of continuous dust accumulation. The mean dust flux for these years is 4.1 g/m<sup>2</sup>/y, which corresponds to historic flux measurements ranging from 2.7 g/m<sup>2</sup>/y to 4.4 g/m<sup>2</sup>/y. The relatively large dust mass of these multi-year samples allows for samples from each collector to be split into a coarse and fine fraction prior to further analysis. Before separation, the median grain size of 2019 dust samples is approximately 10 µm. After sample separation, carried out through timed settling following Stoke’s Law, the approximate median particle diameter is 6 µm for the fine fraction, and 20 µm for the coarse fraction. Coarse Uinta dust is more enriched in quartz and feldspar relative to fine dust, which is dominated by clay minerals. The coarse material is therefore more mineralogically similar to local bedrock, supporting the theory that larger particles are endogenous in origin. Clay minerals are less abundant in local bedrock, suggesting that fine mineral dust may have an exogenous source. Analysis of trace and major elemental abundances, as well as Sr and Nd isotopic fingerprinting will support additional interpretations about the nature and origin of modern dust in the Uintas. These results will contribute to ongoing efforts to better understand how specific dust source regions influence the properties of mineral aerosols arriving in remote alpine environments.</p>

scholarly journals Energy saving cement production by grain size optimisation of the raw meal

2009 ◽  
Vol 2 (2) ◽  
pp. 201-210
Author(s):  
B. Simons
Keyword(s):  
Grain Size ◽  
Energy Consumption ◽  
Lower Energy ◽  
Fine Fraction ◽  
Energy Resources ◽  
Cement Clinker ◽  
Cement Production ◽  
Grain Sizes ◽  
Natural Energy ◽  
Energy Consuming

The production of cement clinker is an energy consuming process. At about 50% of the energy is associated with grinding and milling of the raw meal, that normally is in the range 100% <200 μm with 90% <90 μm. Question: is it possible to use coarser components of the raw meal without reducing the clinker quality. With synthetic raw meals of various grain sizes the clinker formation was studied at static (1100 - 1450°C) and dynamic conditions (heating microscope). A routine to adjust the grain size of the components for industrial raw meals is developed. The fine fraction <90 μm should mainly contain the siliceous and argileous components, whereas the calcitic component can be milled separately to a grain size between 200-500 μm, resulting in lower energy consumption for milling. Considering the technical and economical realizability the relation fine/coarse should be roughly 1:1. The energy for milling can be reduced significantly, that in addition leads to the preservation of natural energy resources.

scholarly journals Investigation of sand in piping

2012 ◽  
pp. 115-128
Author(s):  
Laslo Nadj
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Solid Particles ◽  
Granular Soils ◽  
Volcanic Cone ◽  
Size Fractions ◽  
Grain Sizes ◽  
High Flood ◽  
Grain Size Fractions

For the investigation of the grain size distribution of the material washed out from the piping, we used 20 samples originating from different places on the Danube and the Tisza rivers. The grading characteristics of these samples were investigated based on selected grain sizes and the uniformity of gradients. Based on the investigations it has become possible to identify which grain size fractions are likely to be washed out, and how to characterize those fractions. Based on the grain size distribution curves it has been made possible to define the boundaries of the zone susceptible to piping. The zone limits of granular soils liquefied by earthquakes and the zone limits of the soil out washed from piping are very similar. This apparent correspondence already formerly raised the hypothetic question of whether piping occurring during high flood can be simulated by shape to similar surface liquefaction phenomena experienced during earthquakes, as in both cases a volcanic cone is formed through the crater of which water is constantly issuing, dragging away solid particles.

scholarly journals Geology datasets in North America, Greenland and surrounding areas for use with ice sheet models

2019 ◽  
Vol 11 (1) ◽  
pp. 375-391 ◽  
Author(s):  
Evan J. Gowan ◽  
Lu Niu ◽  
Gregor Knorr ◽  
Gerrit Lohmann
Keyword(s):  
Grain Size ◽  
North America ◽  
Fine Fraction ◽  
Ice Sheet ◽  
Friction Angle ◽  
Glacial Cycle ◽  
Sediment Grain Size ◽  
Glacial Sediments ◽  
Surrounding Areas ◽  
Ice Sheet Modelling

Abstract. The ice–substrate interface is an important boundary condition for ice sheet modelling. The substrate affects the ice sheet by allowing sliding through sediment deformation and accommodating the storage and drainage of subglacial water. We present three datasets on a 1 : 5 000 000 scale with different geological parameters for the region that was covered by the ice sheets in North America, including Greenland and Iceland. The first dataset includes the distribution of surficial sediments, which is separated into continuous, discontinuous and predominantly rock categories. The second dataset includes sediment grain size properties, which is divided into three classes: clay, silt and sand, based on the dominant grain size of the fine fraction of the glacial sediments. The third dataset is the generalized bedrock geology. We demonstrate the utility of these datasets for governing ice sheet dynamics by using an ice sheet model with a simulation that extends through the last glacial cycle. In order to demonstrate the importance of the basal boundary conditions for ice sheet modelling, we changed the shear friction angle to account for a weaker substrate and found changes up to 40 % in ice thickness compared to a reference run. Although incorporation of the ice–bed boundary remains model dependent, our dataset provides an observational baseline for improving a critical weakness in current ice sheet modelling (https://doi.org/10.1594/PANGAEA.895889, Gowan et al., 2018b).

scholarly journals 14 kyr of atmospheric mineral dust deposition in north-eastern China: A record of palaeoclimatic and palaeoenvironmental changes in the Chinese dust source regions

The Holocene ◽  
2019 ◽  
Vol 30 (4) ◽  
pp. 492-506 ◽  
Author(s):  
Steve Pratte ◽  
Kunshan Bao ◽  
Atindra Sapkota ◽  
Wenfang Zhang ◽  
Ji Shen ◽  
...  
Keyword(s):  
Late Holocene ◽  
Mineral Dust ◽  
East Asian ◽  
Eastern China ◽  
Dust Deposition ◽  
Dust Source ◽  
Principal Mechanism ◽  
Middle Holocene ◽  
Source Regions ◽  
North Eastern

A multi-proxy record of Holocene and late-Pleistocene aeolian mineral dust is reconstructed using a combination of geochemical (trace elements), mineralogical and grain-size analyses on cores from the Hani peatland in north-eastern (NE) China. The dust record displays a sharp increase in dust deposition during the late Holocene in comparison to the rest of the Holocene. This trend is in line with climatic records from the Chinese dust source regions and their downwind areas, which generally show an increase in aridity and aeolian activity during the late Holocene. The larger part of the Chinese dust source regions experienced a gradual increase in effective moisture and vegetation cover reaching maxima during the middle Holocene (6.0–8.0 kyr cal. BP) co-occurring with the minima in dust deposition in Hani. These changes in the dust source regions are likely to have been modulated by the variations in the East Asian summer monsoon (EASM), which is the principal mechanism controlling climate in the region. The intensified EASM during the middle Holocene is also likely to have resulted in a sediment recharge at the margin of the Chinese drylands providing additional material and enhancing the atmospheric dust load after the late-Holocene aridification of the region. Combined together, these changes promoted a remobilization of dust sources increasing the amount of material available for transport by the East Asian winter monsoon (EAWM) and the Westerlies. Human activities might also have played a role in the increased dust emissions during the late Holocene, but further research is needed to assess the extent of those impacts at a regional level.

Downstream evolution of grain size in extremely mobile post-earthquake debris flows, China

2021 ◽  
Author(s):  
Erin L. Harvey ◽  
Tristram C. Hales ◽  
Daniel E. J. Hobley ◽  
Xuanmei Fan ◽  
Jie Liu ◽  
...  
Keyword(s):  
Grain Size ◽  
Debris Flow ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Debris Flows ◽  
Fine Fraction ◽  
Excess Pore Pressure ◽  
Extreme Rainfall Event ◽  
2008 Wenchuan Earthquake ◽  
Grain Sizes

&lt;p&gt;Large, catchment transitioning debris flows are an important mechanism for transporting sediment from hillslopes into higher order channels. Extremely large flows can exceed volumes of 10&lt;sup&gt;9&lt;/sup&gt; m&lt;sup&gt;3&lt;/sup&gt;, however even flows with volumes of&amp;#160; ~10&lt;sup&gt;3&lt;/sup&gt; m&lt;sup&gt;3&lt;/sup&gt; can lead to fatalities and extensive damage. Few processes transport a wider range of grain sizes than debris flows, which can transport grains from clays to 10 m boulders. While the structure of debris flows can often be inferred by their deposits, the range of grain sizes presents a challenge for their interpretation. Debris flow grain size distributions can be used to constrain debris flow runout due to their effect on excess pore pressure dissipation. Currently, there is limited data available for the entire grain size distribution of debris flow deposits in the field.&lt;/p&gt;&lt;p&gt;We constrained the entire grain size distribution for two extremely large (&gt;1 km in length) post-earthquake debris flows in Sichuan Province, China. These debris flows were triggered in August 2019 after an extreme rainfall event occurred close to the epicentre of the 2008 Wenchuan earthquake. We sampled the debris flows in November 2019 at intervals of 200 m and 500 m, respectively. At each site, we used a combination of field and laboratory sieving to obtain the coarse and fine fraction for both the surface and subsurface. We dug 1 m x 1 m x 0.5 m pits, excavating each layer at 10 cm depth increments. We sieved these increments into five size fractions in the field, including &lt; 1 cm. We sieved 1 kg of the &lt;1 cm fraction in the laboratory to estimate the distribution of the finest grains. The coarse surface fraction was then independently constrained using photogrammetry. Preliminary results for one debris flow show that the distribution of fine grains (~&lt;4 mm) is consistent both laterally and vertically across the runout. This suggests that the processes occurring vertically and laterally during deposition result in the consistent distribution of fines.&lt;/p&gt;

Oxygen isotope abundance measurements in fine size fractions of Luna 16 and 20 soil

1977 ◽  
Vol 284 (1319) ◽  
pp. 131-136 ◽  
Keyword(s):  
Grain Size ◽  
Weighted Average ◽  
Lunar Soil ◽  
Heavy Isotope ◽  
Size Fractions ◽  
Grain Sizes ◽  
Fine Size ◽  
Impact Events ◽  
Fractional Evaporation

Determination of 8 18 O values in fine size fractions of Luna 16 and 20 soil appears to indicate that a simple monotonic increase in 18 O abundance with decreasing grain size does not exist. The weighted average 8 18 O values for Luna 16 and 20 soil are approximately + 6.33% and + 6.65% relative to the s.m.o.w. standard. These averages (within errors of about ± 0.2 %0) fall inside the range of 8 18 O values found by other workers for lunar soils. Three possible interpretations of the patterns of 18 O-enrichment with grain size are suggested. (1) The generally accepted explanation is that the heavy isotope enrichments reflect fractional evaporation and/or fractional condensation processes resulting from bombardment of the lunar soil by nuclear particles in the solar wind and/or micrometorites. Thus the fines at each locality could be a mixture of fractions with a specific range of grain sizes each with a different exposure history. The grain size fractions could each have been derived from impact events at specific distances from the Luna sample localities. (2) The low 8 18 O values ( ca , + 5.1%0, s.m.o.w.) obtained for two fractions are difficult to explain, but could indicate concentrations of minerals with low 18 O abundances, such as ilmenite or olivine, in these grain sizes. Similarly the relatively enriched values obtained for other fractions could indicate concentrations of phases enriched in 18 O and/or susceptible to 18 O-enrichment in these grain sizes. (3) At least some of the results obtained could be artefacts resulting from the exposure of the samples to the atmosphere of various laboratories.

Power, security, and exchange: Impacts of a Late Holocene volcanic eruption in Subarctic North America

2021 ◽  
pp. 019769312098682
Author(s):  
Todd J Kristensen ◽  
John W Ives ◽  
Kisha Supernant
Keyword(s):  
North America ◽  
Social Relationships ◽  
Cultural Change ◽  
Volcanic Eruption ◽  
Late Holocene ◽  
River Basins ◽  
Adaptive Responses ◽  
Major Event ◽  
Hunter Gatherers ◽  
Bow And Arrow

We synthesize environmental and cultural change following a volcanic eruption at A.D. 846–848 in Subarctic North America to demonstrate how social relationships shaped responses to natural disasters. Ethnohistoric accounts and archaeometric studies reveal differences in human adaptations in the Yukon and Mackenzie river basins that relate to exertions of power over contested resources versus affordances of security to intercept dispersed migrating animals. The ways that pre-contact hunter-gatherers maintained or redressed ecological imbalances influenced respective trajectories of resilience to a major event. Adaptive responses to a volcanic eruption affected the movement of bow and arrow technology and the proliferation of copper use in northwest North America.

scholarly journals Investigation of Movement of Nourishment Sand of Different Grain Sizes Using Model for Predicting Bathymetric and Grain Size Changes

2009 ◽  
Vol 65 (1) ◽  
pp. 691-695
Author(s):  
Yasuhito NOSHI ◽  
Akio KOBAYASHI ◽  
Takaaki UDA ◽  
Masumi SERIZAWA ◽  
Takayuki KUMADA
Keyword(s):  
Grain Size ◽  
Grain Sizes
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