Aeolian Sand Grains Research Articles

AEOLIAN SANDS IN NORTH AFRICA AND THE SOUTHWEST OF THE ARABIAN PENINSULA

Background. The majority of the world’s deserts were formed within the valleys and coasts of ancient alluvial rivers and lakes. The material carried across many hundreds and thousands of kilometres by the wind was mixing with sediments of various genetic types. In addition, due to the similar physical nature of the wind and water transport of sediments, the recognition of the aeolian environment can be problematic. Aim. Using innovative research approaches, to provide a qualitative structural description of sands; to identify and characterize factors contributing to the formation and preservation of a ferruginous film on grains; to establish the genesis of the transferred sediments, as well as the relationship with the parent rocks. Materials and methods. Samples for analysis were collected from aeolian deposits in three deserts: Rub al Khali (United Arab Emirates), Nubian desert (Egypt) and Grand Erg Oriental (Algeria). Particle size analysis was used to characterize samples in terms of three parameters (length, width, thickness). X-ray diffraction analysis was carried out using an ARL X’tra diffractometer (Switzerland). The collected samples were also studied using a binocular microscope in reflected light and a scanning electron microscope. Results. The mineral composition of the sands under study was examined. The graphs (histograms) of the size distribution of quartz grains (being the most common sand mineral in terms of size and frequency of occurrence) were plotted. The shape and nature of the grain surface were analysed. Conclusion. The frosting on aeolian sand grains can result not only from micro-cracking as the most common sign of wind transfer, but also from the presence of a calcite film on grains. Factors contributing to the formation and preservation of a ferruginous film (desert varnish) were identified. The conditions for the formation of aeolian sands, as well as the genesis of such sand sediments, were established.

Rounded boulders on Itokawa as clues to geological processes in the early solar system

Large rounded boulders on Itokawa are a surprising find and may be evidence of forceful inter-boulder collisions occurring over protracted periods of time. Surface textures of some boulders are reminiscent of those on terrestrial aeolian sand grains despite five orders of magnitude difference in scale. Using Hertzian analysis and fracture strength data, we calculate that the maximum collisional velocities involved in the comminution process are ~6–7m/s. We hypothesise that boulder rounding could be a product of collisions in a gravitationally stable orbiting debris field in which boulders acquire collisional energy from YORP spin. Collisional paths may be instigated by Yarkovsky drift and gyroscopic effects of rotation. Collisional energy is dissipated by elastic damping, but rapidly renewed by YORP spinup that takes only hundreds to thousands of years to regenerate comminution-strength collisions. The rounded boulders on Itokawa are found amongst angular, unworn material which suggests a mixed origin for Itokawa׳s regolith.

Studying the Morphologic Maturation of Aeolian Sand Grains During Transportation Process of Wind Erosion (Case study: Khartouran Erg)

Wind, in the duration of its erosional process, affects considerable changes in a grain's morphologyfrom its removal (detachment) step to sedimentation. In other word, a grain undergoes its gradualevolution during the transit process. In this project, the maturation of Aeolian sand grains had beenstudied upon as based on texture maturity indicator which includes: sorting, mean size grain, roundness aswell as abrasion coefficient parameters. The study area is the transport region of Khartouran Ergsediments, which founded on the basis of ground of wind erosion. According to these indicators,the direction of prevailing strong winds is notably mentioned. In a later step, four transects are selectedin different area in alignment with wind direction. Samples of sediment grains are taken at varieddistances in any one of the transects. The samples were taken from the windward slope of Rebdoulandform. The samples were evaluated to using granulometry and morphoscopy techniques. Grain sizeanalysis of was done using dry sieve analysis while morphoscopy of grains carried out by studying thequartz grains of 150 to 300 μm diameter by using binocular microscope. Results indicate a gradualmaturity (evolution) in sediment texture in all transects starting from the upper parts (near sand source)toward the lower parts (in transportation area).Also, results indicate that from among the four indicatorsof grain maturity namely: sorting, grain size, roundness and abrasion coefficient the respective factors ofeither abrasion coefficient index or roundness in the first value and then sorting and finallygrain’s mean size index are the ones accounted for validation for determination of maturity.

Bio-sedimentary structures evolving from the interaction of microbial mats, burrowing beetles and the physical environment of Tunisian coastal sabkhas

Microbial mats are widespread biotic systems in Tunisian coastal sabkhas. In these environments, staphilinid beetles are important bioturbators, making vertical burrows and depositing characteristic hillocks of excavation pellets on the mat surface. The intimate interplay between microbial and beetle activities results in a structured sedimentary surface. Small photosynthetic domes or bulges develop which in turn become microbially overgrown and gypsum-encrusted. Other examples are mat expansion domes above vertical burrows, and excavation pellets overgrown by biofilms trapping aeolian sand grains. In many cases the structures are too complex to explain clearly their formation. Since modern microbial mat-related surface structures form the base for interpretation of fossil record, it is essential to decipher what is contributed by the different structuie-forming factors.

The Provenance of the Varzaneh Aeolian Sand Field Regarding to Lithology and Texture, SW Esfahan, Iran

The main mineralogical/lithological composition of the Varzaneh aeolian sands is sedimentary and igneous lithics. The minor one is metamorphic lithics and mineral grains (such as quartz, feldspar and heavy mineral grains) respectively. The origin of the sedimentary lithics (mainly carbonates) mostly is from sedimentary rocks exposed in the west and the southwest of the study area. These rocks belong to Cretaceous and Jurassic outcrops. The origin of the igneous lithic grains chiefly belongs to Tertiary highlands, located to the north and the northeast of the study area. The main origin of the metamorphic lithic grains is from the mountain ranges located in the north-western and the western part of the drainage basin of the Zayandeh river. Texture of the aeolian sand grains is similar to the Zayandeh river sediments. Concentration of the aeolian sands at the west of the Zayandeh river delta, variation of their mineralogical/lithological composition from north to south, and textural characterizations of sand grains indicate that the water laid sediments of the Zayandeh river, widespread to the north of the aeolian sands, are the main supply of the aeolian sands and sediments deposited by the two ephemeral streams in the south and the southwest of the sand dunes are minor one.

Discrimination of Aqueous and Aeolian Paleoenvironments by Atomic Force Microscopy— A Database for the Characterization of Martian Sediments

In the search for aqueous habitats on Mars direct proof of (ancient) flowing water is still lacking, although remote sensing has provided indications of young fluvial systems. To demonstrate that such proof can be given, we examined surface marks on recent terrestrial sand grains by atomic force microscopy (AFM) and applied a quantitative three-dimensional analysis that can numerically distinguish between aeolian and aquatic transport mechanisms in sedimentary deposits on Earth. The surfaces of natural quartz grains as well as olivine, feldspar pyroxene, and monazite sands of known origin were imaged, each image yielding a three-dimensional map of the mineral surface. A fully automated analysis of distribution patterns of the structural elements that constitute the grain surfaces shows that wind-transported quartz grains have short linear elements irregularly distributed on the surface. Linear elements on water-transported grains, however, are longer with orientations that reflect the mineral symmetry. Because the surface patterns found on aqueous grains are due to preferential etching, they can be used as diagnostic fingerprints for the existence of past or present aqueous transport systems. We used a cluster analysis of the cross-correlation distance of distribution patterns in the structures of aeolian and aquatic sand grains to build a phenogram that provides a map for the relationship of the various sediments found on earth. The analysis shows that the method is highly significant and that water and wind transport can clearly be differentiated. In particular, feldspar and olivine sands contributed even more to the discrimination than quartz grains, which indicated that the method is promising for its application on future missions to Mars. Assuming that martian aqueous sand grains exhibit similar erosional patterns to mineral grains on Earth, simple AFM experiments on a Mars lander would be capable of proving the activity of flowing water in modern runoff systems and of analyzing the paleoenvironments of Mars.

Optical dating of tufa via in situ aeolian sand grains: a case example from the Southern High Plains, USA

Precipitated carbonates (commonly termed tufas or travertines) maybe of considerable utility for palaeoenvironmental reconstruction. Their potential, however, for such reconstruction is commonly limited by difficulties associated with their absolute age control. Attempts to date such deposits via uranium series techniques have been complicated by their chemically open behaviour. Here we describe an alternative approach to date tufa deposits associated with ephemeral saline lake basins from the Southern High Plains, USA. We have optically dated sand grains of a mixed aeolian/fluvial (spring fed) origin as the integrating dosimeter. We assume that the grains are fully resetting prior to their incorporation into the tufa deposits and employ a time-dependent disequilibrium dosimetric model to account for the build-up of uranium series daughter products. The approach was applied to a set of four samples with known stratigraphic association. We obtained stratigraphically sensible optical ages ranging from 78±8 to 56±4 ka. These data are consistent with existing palaeoenvironmental models of regional recharge.

The source of raw materials for Roman pottery from Leptiminus, Tunisia

AbstractLeptiminus, a Roman port city on the west coast of Tunisia, North Africa, exported olive oil and a garum fish paste to Rome. Excavations have uncovered many facilities including kilns and a potter's workshop, indicating an extensive ceramic industry. The vessels, manufactured at Leptiminus, included African red‐slip fineware, coarseware, and amphorae. A petrographic study of pottery sherds showed them to contain very similar temper, rounded aeolian sand grains and limestone, but varying in proportions to produce different textures. An investigation of the source of raw materials for the pottery found three distinct types of clay within a 50 km radius of Leptiminus: grey Miocene, brown Pliocene, and green Late Pliocene clay. Statistical analysis of trace element compositions, using induced neutron activation, of clays and sherds showed that the Pliocene brown clay was used to create all types of pottery. The specific clay horizon, used in Roman times, has apparently been removed by quarrying. However, a lateral continuation of this bed was found 7 m beneath the Leptiminus site 290. © 2002 Wiley Periodicals, Inc.

Palaeomagnetic constraints on the age of the Red Arch Formation and associated sandstone dykes (Northern Ireland)

The Red Arch Formation is a continental red bed succession of uncertain age exposed on the northeast coast of Ireland. There are lithological similarities with the Old Red Sandstone of the Highland Border region, although unconformities within the succession, the presence of reworked aeolian sand grains and variations in the induration of the rocks have prompted earlier workers to suggest that the upper part of the succession may be Triassic in age. This paper reports palaeomagnetic results from the Red Arch Formation. The characteristic magnetizations (ChRMs) are exclusively of reversed polarity and the palaeomagnetic pole position for the sequence bears close comparison with other results from the Old Red Sandstone in Scotland and southern Britain. These poles are regarded as magnetic overprints formed during the Kiaman Superchron because they fall in the Permo‐Carboniferous segment of the apparent polar wander path. Sandstone dykes that cut the Red Arch Formation on a NNE–SSW and NNW–SSE trend have also been studied palaeomagnetically. The dykes show more steeply inclined ChRMs predominantly of normal polarity. The dykes are therefore interpreted to be post‐Kiaman in age, a conclusion consistent with our structural observations. The age of the dykes cannot be determined precisely because they have also been, at least partially, remagnetized. Lithological and regional geological considerations suggest the dykes are Triassic in age and formed in an extensional stress regime prior to the opening of the North Atlantic. They were remagnetized in Tertiary times, possibly associated with uplift and emplacement of the British Tertiary Igneous Province.

The last glacial stratigraphic sequence, depositional environment and climatic fluctuations from the aeolian sand dune in Hongguang, Pengze, Jiangxi (China)

The Hongguang sand hill is located along the south bank of the Yangtze River in Pengze County, Jiangxi Province, China, rising more than 50 m above the ground. It consists of aeolian sand beds interbedded with 11 relatively thin palaeosols. The aeolian sand beds include dune-deposited cross-stratified sand beds and interdune-deposited horizontally-stratified sand beds, both being well sorted. The 11 palaeosols are numbered as Z 1 to Z 11 from bottom to top in chronological order. Among them, 10 palaeosols (Z 2 to Z 11) are dark brown soils while Z 1 includes black to very dark grey lenses of peaty soil, which change laterally into dark brown soil. A hierarchy of bounding surfaces, as summarized by Kocurek (1988), can be recognized in the sand hill — including super surfaces (namely palaeosols), first- and third-order bounding surfaces. The formation of palaeosols represents hiatuses between aeolian sand depositions and suggests a climatic change from arid to more humid conditions. 14C dates show that the sequence from Z 1 to Z 7 was formed between about 26,000 and 20,000 BP, indicating that each cycle from the aeolian sands to palaeosol, that is, each arid-to-humid climatic shift, spent an average term of about 1000 a. Analysis of sedimentary features of the sand hill shows that the aeolian sand grains were mainly from the Palaeo-Yangtze River, which was probably an intermittent river during the dune development. Discussion is also made on the possible palaeoclimatic linkage between the Hongguang area and the North Atlantic region during the last glaciation.

Origin of pore-lining chlorite in the aeolian Rotliegend of northern Germany

AbstractPore-lining chlorite is common in Rotliegend lake shoreline aeolian sandstones from northern Germany and preserves abnormally high primary intergranular porosity. In the north of the study area, in a basinward direction, the chlorites are Mg-rich while towards the south they become Fe-rich over a distance of about 15 km. All are unusually rich in Mn. Magnesium-rich examples tend to be more abundant than illite, while Fe-rich examples cover framework grains less continuously and are admixed with more abundant illite. Oxygen isotope analysis of 30 chlorites in the 2–6 µm fraction gave δ18O (SMOW) values of 7 to 12‰ (mean 9.8‰). These data show no obvious trend across the study area, nor in relation to changes in chlorite composition, or burial depth.The honeycomb arrangement of chlorite crystals suggests chlorite formation via the sequence smectite-corrensite-chlorite. Chlorite distribution and the systematic changes in its composition suggest that formation of a precursor was related to lateral migration of Mg-rich fluids from basinal shales and/or evaporites during shallow burial. Interaction of these fluids with early formed oxyhydroxide coatings on the aeolian sand grains provided a source of Fe and the Mn. The isotope data suggest that the eventual formation of chlorite during deep burial occurred from waters with positive δ18O values, comparable to those present during the deep burial formation of illite.

Lithostratigraphical subdivision of the Triassic Sherwood Sandstone Group in west Cumbria

SUMMARY The subdivisions of the Sherwood Sandstone Group, previously recognized on geophysical and lithological criteria in boreholes offshore in the East Irish Sea Basin, can be identified in the onshore exposures and boreholes of west Cumbria. The term St Bees Sandstone Formation is here restricted to the lower, fluvial, fine-grained sandstone, with claystone and siltstone partings, exposed around St Bees. This formation is sharply overlain by softer and coarser grained, aeolian and subordinate fluvial sandstone, which contains abundant, well-rounded aeolian sand grains, referred to the newly defined Calder Sandstone Formation. Higher sandstone has been separated from the Calder Sandstone Formation by its finer grain size and by geophysical log signatures. This is referred to the Ormskirk Sandstone and is dominantly aeolian in origin. Similar divisions of the Sherwood Sandstone Group can be recognized in the Carlisle Basin, and may also be present in other onshore areas, but await formal definition.

Provenance and sand budget of the arid frontier of Rajasthan, India

The aeolian sand spread in the Cis-Aravalli region has a provenance which is not that of the Trans-Aravalli Thar Desert. The textural parameters and mineralogenic population of the colluvial sand from the Cis-Aravalli area were studied. The size, roundness, sphericity and shape of the aeolian sand grains and the sand fraction of the colluvial deposits derived from Delhi metamorphics exhibit good correlation. The mineralogenic population of the QFO modes of the colluvial sand of the Cis-Aravalli area and aeolian sand from the arid frontier of Rajasthan (Ajmer-Jaipur region) indicate a Cis-Aravalli provenance for the sand of the arid frontier. The sand spread in the arid frontier (Ajmer-Jaipur-Bharatpur) region is similar to that of the dirty rubble of the Cis-Aravalli region, and appears to be endemic to the area. The sand budget of the arid frontier was estimated through daily recording of sand drift at Jobher over a period of one year. The average annual sand drift per 1 m 2 at Jobner has been computed as 0·16 m 3 and rate of average sand creep at Jobner has been estimated at 14·46 cm/year.

The roundness of aeolian quartz sand grains

The roundness of aeolian quartz sand grains

The formation of silt from quartz dune sand by salt-weathering processes in deserts

Recent discussions on the origin of silt-sized quartz particles in hot deserts, and previous experiments on salt weathering of rocks, prompted an experiment to test the hypothesis that salt-weathering processes might generate silt-sized particles. The experiment involved treating aeolian sand grains daily with saturated solutions of Na2SO4 in a climatic cabinet programmed to simulate a hot desert environment. Results indicate that (a) silt-sized particles are produced under these conditions, (b) the particles are angular (compared with the rounded aeolian grains) and (c) salt-crystal growth in cracks and other lines of weakness in the original particles may be responsible for the disintegration. It is suggested that salt-weathering processes in deserts—especially in coastal and playa areas where saline groundwater may be close to the surface—may provide an indigenous mechanism for the production of silt particles in hot deserts.

Long Distance Transport of Foraminiferal Tests by Wind in the Thar Desert, Northwest India

ABSTRACT In the Thar Desert, northwest India, aeolian sand grains were sampled from late Pleistocene dunes and the presence of marine Foraminifera was noted. The frequency of Foraminifera declines in a progressive fashion with distance from the sea, but they are found at least up to 800 km from the nearest point downwind on the coast. This indicates that Foraminifera have been susceptible to long distance transport by the wind, that the coast has been an important source area for the sands of the Thar Desert, and that the presence of Foraminifera in aeolian sediments does not necessarily imply former close proximity to the sea.

The Chemistry of World Calcrete Deposits

Over 300 published and unpublished analyses of calcrete (caliche), together with additional data generated by the author, have been processed to obtain an indication of the nature of world calcrete chemistry and the variability between major regions. Calcium carbonate, in the calcitic form, is the dominant constituent (over 79%), silica is second in importance, with its concentration varying inversely with that of the calcium carbonate, and magnesium carbonate is only exceptionally quantitatively important. Ses-quioxides, manganese, gypsum, and phosphates are locally important. The insoluble residue consists of aeolian sand grains in tropical deserts, silt and clay, particularly in subtropical examples, and amorphous silica in the form of opal, or chalcedony. Palygorskite (attapulgite) is often a major clay mineral. The data enable comparisons with recent analyses of American caliches, and particular reference is made to samples from the Kalahari of southern Africa, Libya, Cyprus, Kenya, and South-West Af...