Aeolian Abrasion Research Articles

The Original Shapes of Quartz Sand Grains

ABSTRACT The basic underlying assumption of grain-shape studies of sediment sources is that the shapes of quartz grains from a given source reflect the genesis or lithology of that source and are distinct from the shapes of quartz grains from other sources. However, this critical assumption has never been tested and thus is a source of doubt about the results of past grain-shape studies. Therefore, a study of the original shapes of quartz sand grains that are released from crystalline and sedimentary rocks was conducted. The study shows that this critical assumption is true for quartz grains that are released from crystalline rocks, wind-transported sedimentary rocks, and quartz-cemented sedimentary rocks. These quartz grains were subjectd to varied mechanical and chemical processes during the genesis of these sources, and these processes have imprinted the grains with unique, source-indicative shapes. Quartz grains from crystalline rocks have highly nonspherical, angular outlines and numerous crystalline nodes, grain embayments, and fractures which are the products of crystallization and deformation at elevated temperatures and pressures. Quartz grains from wind-transported sedimentary rocks have highly rounded outlines and abraded grain surfaces which are the products of eolian abrasion. Lastly, qua tz grains from quartz-cemented sedimentary rocks have moderately angular outlines and well-defined quartz overgrowths which are the products of quartz cementation in deep-burial settings. However, the results also show that this critical assumption is false for quartz sand grains that are released from water-transported sedimentary rocks with no secondary quartz. The shapes of quartz sand grains from such sediment sources are relict--that is, they are inherited from the sources of the water-transported sedimentary rocks; they do not reflect the genesis or lithology of their present souces; and they are commonly indistinguishable from quartz grains from other sources.

Aeolian abrasion of quartz particles and the production of silt-size fragments: preliminary results

Summary Experimental abrasion of quartz sand in an air stream shows that particles with initially high angularity are progressively rounded by the chipping of edges and corners. Grains closely resemble dune sand grains from deserts with respect to rounding and microscopic surface textures after 48 hours of abrasion. Results show an initially high weight loss from the original grains (primarily by edge chipping), compared with subsequent abrasion. High percentages of coarse and medium silt are produced but there is a gradual increase in the percentage of fine silt as rounding increases and the quantity of fines generated declines. Silica extraction from the fines using water shows concentrations of several hundred ppm. Implications for loess production and silcrete formation are suggested.

Individual particles and Martian aeolian action—A review

Evidence for aeolian activity on Mars is presented. Sand-sized particles of quartz and basalt were abraded in the laboratory under characteristic Earth and Martian velocity and pressure conditions, and the types of surface features (relief) were studied with the scanning electron microscope. In addition, silt and clay produced under these conditions was examined with both scanning and transmission electron microscopy. During the experiments, electrostatic aggregates of clay and fine silt were produced; electrostatic charging by mechanical abrasion seems to have occurred, and may be related to the presence of aggregates on Mars. Abrasion appears to be more vigorous under Martian than Earth conditions given the same mineralogy and particle sizes on the two planets. This is probably due to the higher velocities required for Martian aeolian activity. Electrical charging due to particle breakage may be important on Mars as deduced from simulation experiments and the data from the Viking orbiters and landers. Additionally, experiments with basalt at high abrasion velocities suggests that mineral surfaces on Mars may be structurally deformed. Thus weathering might be more rapid, if water were present in the atmosphere and regolith. Finally, during laboratory aeolian abrasion, submicron-sized quartz particles were produced, but material of this type is not found in sediments on Earth. Fine-grained sediments should be reexamined to look for these fine particles, as the production of clay-sized material has important consequences both for erosion and weathering on Earth and Mars.

The Effects of Eolian Sorting and Abrasion Upon the Shapes of Fine Quartz Sand Grains

ABSTRACT Grain-shape and surface-texture analyses were conducted on fine quartz sand grains from North Padre Island and the South Texas eolian sand sheet. The purpose was to determine the effects of eolian shape sorting and abrasion upon the shapes of eolian sand grains. Two conclusions are reached. The first is that the wind preferentially transports spherical, rounded sand grains, and this can result in the isolation and accumulation of such grains in an eolian deposit after a relatively short transport distance. The second is that eolian abrasion can greatly increase the roundness of sand grains during their transport over a distance of less than 160 km. Abrasion does not, however, produce any regular downwind change in sand-grain sphericity.

Wind as a Geological Process on Earth, Mars, Venus and Titan

This book gives an account of geological aspects of windblown material. Aeolian processes play an important role in modifying the surface of the Earth, and they are also active on Mars. Additionally, they are thought to occur on Venus and possibly Titan as well. The authors describe the following aspects: wind as a geological process, the aeolian environment, physics of particle motion, aeolian abrasion and erosion; aeolian sand deposits and bedforms, interaction of wind and topography and windblown dust. A particular strength of the book is that it deals with aeolian processes in a planetary context, rather than as a purely terrestrial phenomenon. In so doing, the authors ably demonstrate how we can gain better understanding of the Earth through comparative planetology. This paperback reissue will enable the book to be used as a text for advanced students in planetary science. Special terms are defined when they are first used. There is a glossary and an exhaustive bibliography.

Observations on the composition and mineralogy of an algerian duricrust complex

Duricrusts from the northern margin of the Plateau du Tademait are examined using a variety of techniques including: optical and scanning electron microscopy, X-ray diffraction, differential thermal analysis and infra-red spectroscopy. The escarpment edge is capped by a dolomitic limestone containing fibrous palygorskite. Two “older” duricrusts are recognised, a relatively pure limestone found only as isolated blocks on the plateau surface and a banded silcrete on top of and within the dolomatic limestone. The latter resembles silcretes described from elsewhere in western Algeria and ascribed to a period of Villafranchien silicification. Finally, two superficial duricrusts are described: a vesicular calcrete which occurs in pockets on the plateau surface and a friable gypcrete on the escarpment. Both contain quartz and feldspar grains which exhibit evidence of limited aeolian abrasion and chemical weathering, it is suggested that they are Holocene in age.

Rate of wind abrasion on Mars

Estimation of the rate of aeolian abrasion of rocks on Mars requires knowledge of (1) particle flux, (2) susceptibilities to abrasion of various rocks, and (3) wind frequencies on Mars. Fluxes and susceptibilities for a wide range of conditions were obtained in the laboratory and combined with wind data from the Viking meteorology experiment. Assuming an abundant supply of sand‐sized particles, estimated rates range up to 2.1×10−2 cm of abrasion per year in the vicinity of Viking Lander 1. This rate is orders of magnitude too great to be in agreement with the inferred age of the surface based on models of impact crater flux. The discrepancy in the estimated rate of abrasion and the presumed old age of the surface cannot be explained easily by changes in climate or exhumation of ancient surfaces.We consider the primary reason to be related to the agents of abrasion. Either windblown grains are in very short supply, or the grains are ineffective as agents of abrasion. At least some sand‐sized (∼100 μm) grains appear to be present, as inferred from both lander and orbiter observations. High rates of abrasion occur for all experimental cases involving sands of quartz, basalt, or ash. However, previous studies have shown that sand is quickly comminuted to silt‐ and clay‐sized grains in the martian aeolian regime. Experiments also show that these fine grains are electrostatically charged and bond together as sand‐sized aggregates. Laboratory simulations of wind abrasion involving aggregates show that at impact velocities capable of destroying sand, aggregates form a protective veneer on the target surface and can give rise to extremely low abrasion rates.

Transmission electron microscope study of quartz microstructures produced by aeolian bombardment

ABSTRACTThe near‐surface structure produced by laboratory aeolian bombardment of Brazilian quartz has been studied with transmission electron microscopy (TEM). Thin specimens of the abraded surface were prepared by a one‐sided ion etching technique, and control specimens of unabraded material were prepared by standard ion etching methods. The abraded sample exhibited a vastly larger number of defects than the unabraded specimen. The abraded sample contained areas with very little surface disruption, presumably where pieces of material up to several tens of microns in diameter had broken away. Other areas of the abraded surface were extremely disrupted, with open and closed microcracks spaced from a few tens of angstroms to a few microns apart. Electron diffraction indicated significant rotation among submicron blocks bounded by the fractures. These observations suggest that surface disruption occurs primarily by a mechanism involving brittle fracture, rather than plastic deformation.This study demonstrates the feasibility of studying the effects of abrasion on near‐surface structure with TEM. The degree and scale of fracturing also suggest a mechanism for forming submicron particles in quantity during aeolian abrasion.

Altered basaltic glass: A terrestrial analog to the soil of Mars

Analyses of Martian surface soil by Viking and Earth-based telescopes have been interpreted as indicating a regolith dominated by the weathering products of mafic or ultramafic rocks. Basaltic glass has previously been proposed as a more likely precursor than crystalline rock, given the low efficiency of surface weathering under present Martian conditions. On Earth large volumes of basaltic glass formed by quenching of magma by water. A similar interaction, between magma and ground ice, may have been a common occurrence on Mars. On the basis of this scenario palagonite, the alteration product of basaltic sideromelane glass, was studied as a possible analog to Martian soil. Samples from Iceland, Alaska, Antarctica, Hawaii, and the desert of New Mexico and Mexico were examined by optical and scanning electron microscopy, electron microprobe analysis, X-ray diffraction, spectrophotometry, and magnetic and thermogravimetric analysis. We suggest that palagonite is a good analog to the surface soil of Mars in chemical composition, particle size, spectral signature, and magnetic properties. Our model for the formation of fine-grained Martian surface soil begins with eruptions of basaltic magma through ground ice, forming deposits of glassy tuff. Individual glass shards are then altered by low-temperature hydrothermal systems to palagonitic material. Dehydration and aeolian abrasion strip the alteration rinds from the glass, and wind storms distribute the silt-sized palagonitic fragments in a planet-wide deposit.

Properties of electrostatic aggregates and their possible presence on Mars

Abstract Experiments indicate that at the high wind velocities characteristic of portions of the Martian surface, sand-sized particles will break down to silt and clay, which will then inevitably form sand-sized aggregates. Basalt and olivine aggregates held together by electrostatics were produced in an eolian abrasion device and their mass properties studied. It was difficult to examine aggregates after formation, as they separate and reform with very little handling, since electrostatic binding forces are quite weak. It is shown that aggregates range from 60 to more than 600 μm in diameter, that they generally are spheroidal in shape and become more elongate with increasing size, and that they tend to be layered with the inner portions more tightly bound than outer layers. After about one-and-one-half years, some aggregates lose their charge which is replaced with moisture; the aggregates retain their original sizes and shapes. None of the properties of electrostatic aggregates so far investigated are incompatible with the presence of these materials on Mars.

Eolian sedimentation on Earth and Mars: Some comparisons

Eolian sediments on Earth are mostly formed from quartz; they consist, in large part, of eolian sand deposits in deserts, silt and loess deposits in and adjoining present and former glaciated areas, and finally clay-sized particles carried in suspension for relatively long distances and deposited in oceanic areas by winds. The quartz particles in these regimes originally came from a granitic source; stresses in granitic rock formation, glacial action, and wind abrasion are largely responsible for making the particles available for the three kinds of eolian deposits. With respect to eolian sediments on Mars, it appears that an entirely different set of criteria must apply, but some critical parameters can usefully be compared. Evidence for free quartz on Mars is lacking and sand-sized particles are probably basaltic, although there does appear to be a deficit in the sand size range. Glacial action does not appear to be available as a large-scale particle producer but high-velocity winds could be efficient producers of very fine particles. Fine particles may aggregate in a similar way to that observed in the Australian regions where “parna” is seen; this could supply a silt mode on Mars. Impact experiments with basalt in eolian abrasion devices suggest that basalt sand-sized particles fragment rapidly to produce silt and clay-sized detritus. Cohesive forces must be more effective on Mars since the gravitational contribution to the bond/weight ratio ( R) is lowe; if R = 1 at about 100 μm on Earth, then R = 1 at about 140 μm on Mars and a much greater range of deposits will be stable. Compared to the terrestrial situation, both larger and smaller particles can be expected to make significant contributions to eolian sediments on Mars. The low gravity and the high speed of moving particles and the relatively weak rock material of which they are composed will allow large-scale fine particle production.

Sedimentology of cross-stratified sandstones in Arikaree group, Miocene, southeastern Wyoming

The Arikaree Sandstone of Early Miocene age in southeastern Wyoming contains large-scale cross-stratification thought by previous investigators to have formed in a fluvial environment. Detailed study of the cross-strata, however, suggests an aeolian origin. Average angle of dip of foreset beds is 24° with angles as high as 34°. Thickness of sets of cross-strata is commonly 3–4 m with 11 m measured in one location. Settling velocities in water of hornblende and quartz grains from these deposits yield cumulative curves indicative of deposition from aeolian suspension. Petrographic study of the suspected aeolian sandstones shows them to contain smaller percentages of volcanic air-fall shards than associated fluvial sediments. This probably reflects the high winnowing susceptibility of these very fine-grained, low-sphericity shards during aeolian transportation and deposition. Scanning electron microscopy revealed polygonal plate structures on the surfaces of quartz grains which are generally associated with aeolian abrasion. The evidence suggests that these cross-strata represent remnants of aeolian dunes, possibly barchan and transverse types, that migrated across the aggrading High Plains surface during the Early Miocene. They consequently became intercalated with fluvial sediments producing complex facies relationships.

Petrology, Provenance and Silica Diagenesis of the Penrith Sandstone (Lower Permian) of Northwest England

ABSTRACT The Penrith Sandstone (Lower Permian) of north west England is a continental red bed sandstone, deposited as barchan sand dunes in a hot, arid desert environment. The rock displays a high degree of mineralogical and textural maturity, being a coarse, well sorted orthoquartzite, composed of rounded unstrained, strained and polycrystalline quartz grains, with subordinate feldspar and rock fragments. Distinct petrographic features of the detrital grains suggest derivation from the Millstone Grit (Upper Carboniferous) sandstones of Yorkshire, and perhaps County Durham. In the southern part of the area non-silicified sandstones are interbedded with calcite cemented alluvial fan breccias (brockrams). This contrasts markedly with northern areas where brockrams are absent, in that the sandstones are tightly cemented with secondary quartz, occurring as overgrowths of optically continuous, bipyramidal quartz crystals around detrital grains. Many varieties of overgrowth are present, their structure being pre-determined by the internal structure of the detrital grains. Thus, unicrystaline unstrained and strained, and polycrystalline overgrowths can be recognised. Overgrowths of secondary feldspar occur occasionally on detrital orthoclase and microcline. It is suggested that the source of the secondary quartz is due to the solution of the siliceous dusts produced during aeolian abrasion of the quartz grains. Alkaline desert groundwaters are considered to be responsible for taking the siliceous dust into solution, which, upon evaporation, precipitated the silica as optically continuous quartz overgrowths around the detrital grains. The inverse relationship between silicification of the Penrith Sandstones and brockram distribution is attributed to differences in compositon of the groundwaters in the two facies.

Discussion

Mr B. Waugh said that for the past two years he had been examining by electron-microscopy the surface textures of sand grains, especially sand grains collected from modern desert and beach environments. The criteria used by the authors for distinguishing environments of deposition from distinctive surface textures were directly comparable with his results. In a study of the surface textures of sand grains from the Penrith Sandstone of the southern part of the Vale of Eden where the rock was poorly compacted, and from the Basal Yellow Sands of County Durham, electron micrographs showed the surface of the grains to be covered in conchoidal fractures, rounded abrasion-blocks, and percussion-marks (Waugh 1965, Proc. Yorks. geol. Soc. 35, 59–69). These were features of an aeolian abrasion process, and confirmed the accepted aeolian origin of these two deposits. Dr F unnell replied that it was gratifying to learn that Mr Waugh had found the suggested criteria applicable to his own results, and Mr Waugh’s confirmation of the mode of origin of the Permian occurrences by this means was most interesting. Mr W. B. H arland suggested that the evidence of glacial attrition of sand grains might not necessarily denote a glacial environment if a similar grinding process could also be shown to take place, for instance, in a mud-flow. On the other hand, it seemed that glacial action, in the sense of ice rafting, might well produce a till, possibly with little evidence of attrition of the sand grains in it unless most of

Experimental Abrasion 5. Frosting and Defrosting of Quartz Grains

Frosting of quartz grains is thought to be due in minor degree to mechanical action (1) by wind and (2) by water, but mainly to chemical action (3) by corrosive solutions and (4) by alternate solution and deposition of matter, especially in desert areas. Defrosting under water is likewise a physico-chemical process involving incipient crystal growth or solution. These physico-chemical actions, in contrast with mechanical attack, affect the whole surface of the grain equally, even in deep indentures. The typical circular markings of 3-10 μ diameter described by Cailleux as percussion cones are shown to be diffraction images of the light source. They can be observed also on the etched surface (e.g., by hydrofluoric acid) of crushed quartz, while electron micrographs of frosted grains fail to show any circular pattern of a few microns in diameter. Because of the diffraction effect, the resolution of the microscope is insufficient to distinguish chemical and mechanical action readily. True percussion cones occur on a minor proportion of well-rounded large quartz grains. Roughly speaking, the diameter is one-fifteenth or less of the long axis of the grain. On pebbles and cobbles this ratio is one-tenth. Experiments on wind abrasion and defrosting confirm these conclusions. On the one hand, mechanical aeolian abrasion is limited to corners and edges. It results in a coarser finish than natural chemical frost. On the other hand experimental fluviatile transport does not defrost but tends to frost polished grains on their protruding parts. Dry rolling in a bottle produces an ideal polish on protruding parts. The action of dew is invoked as the cause of desert frost by alternate solution and deposition. The chemical frost (noted by Sorby, Tricart, and others) is evidently a result of solution, possibly combined with deposition. The mechanical frost of aeolian action is somewhat suppressed in the desert by the healing over by dew action. Mechanical frost, both aqueous and aeolian, and chemical frost can be removed under water by solution or deposition according to the nature of the water involved. Experimental defrosting of sandpapered alum crystals in a saturated solution strongly supports the latter deduction. Experimental solution can lead to a polished finish and to rounding. The important solvent action of sea water will be treated in a later paper. A distinction is emphasized between reaction solution, in which case regrowth by evaporation is excluded, and non-reaction solution, in which case regrowth is possible. It would appear that the latter process produces smoothly rounded, polished surfaces, whereas the former tends to etch and cause frosted finish. In a short note (Kuenen and Perdok, 1961) the main points of the present paper were already recorded.

Experimental Abrasion 4: Eolian Action

Abrasion by eolian transport was studied in three different types of wind tunnel. Limestone, feldspar, and quartz were tested in the shape of cubes, crushed crystals, or natural grains. Abrasion increases with size, wind velocity, angularity and roughness of surface. Polished medium-sized quartz grains sustain no loss. Wind abrasion of quartz is 100 to 1,000 times more effective over the same distance than the mechanical action of a river. But eolian abrasion is slight for fine quartz sand and drops to zero at 0.05 mm. in diameter. No quartz particles are produced in the size range dominating in loess. Experimental abrasion of ventifacts indicates that these are cut slowly in scores of years by medium strong winds, but in a matter of days by storm winds, and in a matter of hours if the cutting sand is coarse and angular. These results must be looked upon as first approximations, for many factors in nature are either unknown or not reproduced in the experiments. Experiments on frosting and defrosting will be treated elsewhere.

Relation of the tide to property boundaries

Morphoscopy of sand grains from the Late Pleistocene loess–paleosol series exposed on the East European Plain along a longitudinal profile, from the southern limit of the Late Pleistocene ice sheet to the Azov Sea coasts is examined. The data presented refer to three main zones of the loess accumulation different in characteristics of the processes: the northern zone, including the vicinity of the Valdai ice sheet; the middle zone with the maximum sedimentation rate; and the southern zone adjoining seacoasts. The earlier part of the Valdai glacial epoch (before the Bryansk interstadial) was distinct for a rather moderate rate of subaerial processes without any noticeable spatial differentiation with respect to the latitudinal zones. In post-Bryansk time (after ∼24 ka BP) the most active dust accumulation is recorded in the middle zone. The maximum thickness of the Late Pleistocene loess has been recorded there, in the middle reaches of the Dnieper River. In the northern zone the rate of dust settling was not so high, presumably due to high speed of descending winds from the ice sheet. In the southern periglacial zone aeolian abrasion of sand grains was less pronounced as compared with areas farther to the north.

The Paleozoic Section of the Tomah and Sparta Quadrangles, Wisconsin

Previous articleNext article FreeThe Paleozoic Section of the Tomah and Sparta Quadrangles, WisconsinW. H. Twenhofel and F. T. ThwaitesW. H. Twenhofel Search for more articles by this author and F. T. Thwaites Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Journal of Geology Volume 27, Number 8Nov. - Dec., 1919 Article DOIhttps://doi.org/10.1086/622684 Views: 83Total views on this site Citations: 2Citations are reported from Crossref PDF download Crossref reports the following articles citing this article: R. H. Dott, Jr. The Importance of Eolian Abrasion in Supermature Quartz Sandstones and the Paradox of Weathering on Vegetation‐Free Landscapes R. H. Dott, Jr., The Journal of Geology 111, no.44 (Jul 2015): 387–405.https://doi.org/10.1086/375286R. H. DOTT JR, C. W. BYERS, G. W. FIELDER, S. R. STENZEL, K. E. WINFREE Aeolian to marine transition in Cambro-Ordovician cratonic sheet sandstones of the northern Mississippi valley, U.S.A., Sedimentology 33, no.33 (Jun 1986): 345–367.https://doi.org/10.1111/j.1365-3091.1986.tb00541.x