Soil Micromorphology: Concepts, Techniques, and Applications

Vepraskas, M. J.; Wilson, Michael

doi:10.2136/sssabookser5.5.c7

Cited by 8 publications

(6 citation statements)

References 93 publications

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“…2. Although the third dimension could not be measured, the measured area % of iron (hydr)oxide grains approximates their total volume % because the relatively small iron (hydr)oxide grains were homogeneously distributed through the dust particles (Vepraskas and Wilson, 2008). The abundance of iron (hydr)oxide grains ranged widely, from high (e.g., 50 % in Fig.…”

Section: Iron (Hydr)oxidesmentioning

confidence: 99%

Mineralogical properties and internal structures of individual fine particles of Saharan dust

et al. 2016

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Abstract. Mineral dust interacts with incoming/outgoing radiation, gases, other aerosols, and clouds. The assessment of its optical and chemical impacts requires knowledge of the physical and chemical properties of bulk dust and single particles. Despite the existence of a large body of data from field measurements and laboratory analyses, the internal properties of single dust particles have not been defined precisely. Here, we report on the mineralogical organization and internal structures of individual fine ( <  5 µm) Saharan dust particles sampled at Tenerife, Canary Islands. The bulk of Tenerife dust was composed of clay minerals (81 %), followed by quartz (10 %), plagioclase (3 %), and K-feldspar (2 %). Cross-sectional slices of Saharan dust particles prepared by the focused ion beam technique were analyzed by transmission electron microscopy (TEM) to probe the particle interiors. TEM analysis showed that the most common particle type was clay-rich agglomerate, dominated by illite–smectite series clay minerals with subordinate kaolinite. Submicron grains of iron (hydr)oxides (goethite and hematite) were commonly dispersed through the clay-rich particles. The median total volume of the iron (hydr)oxide grains included in the dust particles was estimated to be about 1.5 % vol. The average iron content of clay minerals, assuming 14 wt % H2O, was determined to be 5.0 wt %. Coarse mineral cores, several micrometers in size, were coated with thin layers of clay-rich agglomerate. Overall, the dust particles were roughly ellipsoidal, with an average axial ratio of 1.4 : 1.0 : 0.5. The mineralogical and structural properties of single Saharan dust particles provide a basis for the modeling of dust radiative properties. Major iron-bearing minerals, such as illite–smectite series clay minerals and iron (hydr)oxides, were commonly submicron- to nano-sized, possibly enhancing their biogeochemical availability to remote marine ecosystems lacking micronutrients.

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Section: Iron (Hydr)oxidesmentioning

confidence: 99%

Mineralogical properties and internal structures of individual fine particles of Saharan dust

et al. 2016

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“…Prior to observation in the polarizing microscope, selected samples were prepared following standard protocols developed for fragile and friable materials (Vepraskas and Wilson, ). Samples were impregnated with polyester resin for thin‐section preparation.…”

Section: Methodsmentioning

confidence: 99%

Surface evolution of salt‐encrusted playas under extreme and continued dryness

Artieda

Dávila

Wierzchos

et al. 2015

Earth Surf Processes Landf

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Miocene continental saltpans are scattered in the Central Valley of the Atacama Desert, one of the driest regions on Earth. These evaporitic deposits are hydrologically inactive, and are detached from groundwater brines or aquifers. The surface of the saltpans, also known as salars, comprises desiccation polygons, commonly with nodular salt structures along their sides. The morphology and bulk mineralogy of salt polygons differs between and within salars, and the shape and internal structure of salt nodules varies between different polygon types. Based on field observation, and mineralogy and crystallography data, we generated a conceptual model for the genesis and evolution of these surface features, whereby rare rainfall events are responsible for the transformation of desiccation salt polygons and the initial formation of salt nodules along polygon borders. In addition, frequent, but less intense, deliquescence events further drive the evolution of salt nodules, resulting in a characteristic internal structure that includes laminations, and changes in porosity and crystal morphologies. As a result, and despite the extreme dryness, the surfaces of fossil salars are dynamic on timescales of several years to decades, in response to daily cycles in atmospheric moisture, and also to rare and meager rainfall events. We propose that fossil salars in the Atacama Desert represent an end stage in the evolution of evaporitic deposits under extreme and prolonged dryness.

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“…Micromorphology analysis follows established protocols and terminology (FitzPatrick, 1984;Stoops, 2003Stoops, , 2010Vepraskas and Wilson, 2008) with thin sections viewed through a polarizing microscope under plane polarized light (PPL), cross-polarized light (XPL), and oblique incident light (OIL). Thin section descriptions include compositional analysis of mineral grains through point counting within a 1 mm (horizontal) by 2 mm (vertical) grid system, similar to procedures suggested by FitzPatrick (1984, p. 104-106).…”

Section: Sedimentary and Stratigraphic Descriptionsmentioning

confidence: 99%

Geochronology and Depositional History of the Sandy Springs Aeolian Landscape in the Unglaciated Upper Ohio River Valley, United States

2019

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The study of active and stabilized late Quaternary aeolian landforms provides important proxies for past climate events and environmental transitions. Despite an overall increase in the study of aeolian landforms in previously glaciated and coastal settings in eastern North America, the history of aeolian sedimentation in many unglaciated inland alluvial settings remain poorly understood. This study reports on the geochronology and depositional history of aeolian landforms and sediments in the unglaciated upper Ohio Valley at the Sandy Springs site. Aeolian landforms and sediments include complex, linear, barchan-like, and climbing dunes; an interdune sand sheet; and sandy loess that blankets high valley surfaces. At Sandy Springs, aeolian dune sands and sandy loess are restricted to intermediate (S2) and higher (S3) geomorphic surfaces. Eight optically stimulated luminescence age estimates constrain the initiation of aeolian processes on the S2 surface to sometime after 17 ka and episodic deposition on the S2 and S3 surfaces between 11 and 1.4 ka. The distribution of aeolian sediments at Sandy Springs is influenced by several past factors including local wind fetch potential, sediment availability, and underlying alluvial topography. Sediment availability is interpreted as the primary factor controlling aeolian processes and appear linked to several pan-regional paleoclimate events. Sandy loess deposition at ca. 8.2 ka on the S3 surface may reflect hydrologic variability and cooling, associated with the final pulse of meltwater into the North Atlantic from the Laurentide Ice Sheet. Dune reactivation and erosion at ca. 4.5 ka on the S2 surface indicate enhanced sediment availability possibly associated with drought conditions. These results illustrate that the deciphering the coupled fluvialaeolian records in this catchment of the Ohio River provides new insight into the nature of changing surface processes against the backdrop of climate variability over the past ca. 20 ka.

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Soil Micromorphology: Concepts, Techniques, and Applications

Cited by 8 publications

References 93 publications

Mineralogical properties and internal structures of individual fine particles of Saharan dust

Mineralogical properties and internal structures of individual fine particles of Saharan dust

Surface evolution of salt‐encrusted playas under extreme and continued dryness

Geochronology and Depositional History of the Sandy Springs Aeolian Landscape in the Unglaciated Upper Ohio River Valley, United States

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