Journal articles on the topic 'Silt-sized grains'

Æolian dust deposits are known to be widespread in south-eastern Australia, with the dominant model being that of ‘parna’, an aggregated material comprising clay, calcium carbonate, and silt-sized quartz. Despite a general acceptance of the parna model, there is surprisingly little evidence of silt-sized clay aggregates remaining in parna profiles. To investigate a relatively pure æolian dust deposit within the proposed zone of parna distribution, we examined the various phases of 3 source-bordering sand dunes on the lower Lachlan River floodplain of south-western NSW. In each dune exists an upper-slope phase of coarse brown sand, a mid-slope layer of reddish, clay-enriched sand, and a lower-slope phase of coarse sand dominated by an accumulation of carbonate glaebules. Granulometric analyses of the clay-enriched phase(s) of each dune identified a conspicuous particle population in the 20–60 μm range, and another in the fine-silt/clay range (<10 μm). Mineralogical characterisation revealed an abundance of illite and kaolinite in the upper 2 dune phases, coupled with a minor amount of smectite, further suggesting an allochthonous æolian origin, as the surrounding floodplain is smectite-rich and relatively poor in illite. Micromorphological features within the clay-enriched phase, including abundant argillans and laminar bands of well-sorted fine quartz grains, indicate that this clay is a depositional feature, illuviated from surface horizons and re-deposited at depth. A similar illuvial origin is suggested by the fine crystalline nature of the calcium carbonate accumulation, ubiquitously coating the matrix mineral grains of the lower dune phase. No discrete clay aggregates were identified; however, all the assumed components of parna (silt-sized quartz grains, clay, and calcium carbonate) were identified, spatially separated within each dune. The consistency of these features among the 3 dunes indicates an analogous æolian dust accession, but it is not clear whether the clay component of this dust was transported as coatings on quartz grains, or as silt-sized clay aggregates accompanied by silt-sized quartz grains.

Investigation of a sequence of alternating sand and silt deposits formed in an ephemeral braided stream channel adjacent to the modem Caribou River, Yukon, revealed differences in the palynological spectra of the sediment types. Picea, Betula, Alnus, and Gramineae are more concentrated in the silt units, whereas Cyperaceae, Chenopodium, Lycopodium, and Ericaceae are preferentially concentrated in the sand strata. These distribution patterns reflect the hydrodynamic properties of the grains, in addition to environmental differences. Grains of Picea, Betula, and Alnus settle through still water at the same rates as silt-sized quartz particles and are therefore concentrated in the portion of the deposit derived from the stream's suspended load. Thus, increases in percentages of these palynomorphs with decreasing grain size may not reflect vegetation changes or climatic alterations but may be consequences of the hydrodynamic situation.

It is generally accepted that large areas of southern New South Wales (NSW) and northern Victoria are mantled by soils derived from clayey loess deposits called parna. These parna deposits are believed to have formed during arid phases of the Pleistocene and the mineral constituents are assumed to have been transported as silt- and fine sand-sized pellets of calcareous clay, with some companion quartz grains of a similar size. A common property of parna-derived soils is subplasticity, where the apparent field texture grade becomes more clayey with increasing mechanical working of the bolus. This propensity for subplastic behaviour suggests that parna-derived soils contain stable silt- and fine sand-sized pellets of clay, yet there has been little direct micromorphological evidence of these pellets ever published. In the present study, thin section samples from several parna type-sites in southern NSW were examined micromorphologically to reveal the presence of very well size-sorted quartz grain populations (companion grains) and identifiable prolate clay aggregations of a similar silt to fine sand size. These prolate pellets, comprised of quartz, illite, kaolinite and chlorite, have a very distinctive mosaic-speckled b-fabric and are more widely distributed throughout the soil than the similarly sized and shaped faunal faecal pellets. Where these pelletal aggregations are not evident, such as in the deeper parna deposits, abundant illuviation features suggest that clay particles deposited within the parna, whether as pellets or coatings on grains, have subsequently undergone considerable weathering and a range of pedogenic processes.

This paper presents a qualitative and quantitative study of the microstructure of a compacted silt, carried out using a scanning electron microscope and mercury intrusion pore size distribution measurements. Samples have been statically compacted at three water contents: on the dry side of the standard Proctor optimum water content, at the optimum, and on the wet side. The wet sample has a matrix type structure, with a clayey fraction filling the voids and adhering to the silt-sized grains, whereas the other samples display a structure characterized by a skeleton made of silt grain aggregates linked together by clayey bidges. The distribution of water and air within the microstructure of the compacted soil is described for each of the three compaction states. Key words: compacted soil, microstructure, scanning electron microscope, pore size distribution, mercury intrusion, clay hydration.

AbstractThe mechanical behavior and microstructural evolution of laboratory-prepared, particle-free fresh-water ice and ice with 1 wt.% (~0.43 vol.%) silt-sized particles were investigated under creep with a stress level of 1.45 MPa at −10°C. The particles were present both within the grains and along the grain boundaries. The creep rates of specimens with particles were always higher than those of particle-free ice. Dynamic recrystallization occurred for both sets of specimens, with new grains nucleating along grain boundaries in the early stages of creep. The ice with particles showed a higher nucleation rate. This resulted in a smaller average grain-size for the ice with particles after a given creep strain. Fabric studies indicated that ice with particles showed a more random orientation of c axes after creep to ~10% strain than the particle-free ice.

The partial bleach (R–Γ) procedure of thermoluminescence (TL) dating of unheated sediments has been applied to the 2–4 μm sized feldspar-dominated grains from two components of a 10–11 ka BP glaciolacustrine silt. A previous TL study of the 4–11 μm sized feldspars from a ~12 cm thick summer layer of this varved deposit did not produce the correct age. Here it is shown that the 2–4 μm feldspar grains from a contiguous, 5 mm thick clay-rich winter varve give a satisfactory TL apparent age of 14.2 ± 2.3 ka. On the other hand, and consistent with the previous results, the 2–4 μm feldspar grains from the thicker summer layer yield an incorrect high apparent age of 55 ± 13 ka. These results have implications for general TL dating of waterlaid sediments.

Residual Osl Signals from Modern Greenlandic River SedimentsRipple-laminated sandy deposits at shallow water depths in four rivers on Jameson Land, East Greenland were sampled for optically stimulated luminescence (OSL) dating. Silt-sized grains have significantly higher equivalent doses (~1.1 Gy) than sand grains (~0.1 Gy). This suggests that coarse grain-size fractions are better bleached and more suitable than fine grains for OSL dating of glaciofluvial/fluvial sediments. A sample from a sidebar deposited during the spring flood yielded 1.0 Gy (~500 years) while a subaerial deposit was completely zeroed. The spring flood deposit is considered to be most similar to deglacial conditions and incomplete bleaching of this amount (1 Gy) is generally not a significant source of error for sediments of Pleistocene age. Most samples have rather poor luminescence characteristics and are affected by thermal transfer if preheat temperatures at or above 260°C are used.

The nature of the Pleistocene-Holocene palaeosols in the Gaza Strip, PalestineThe Pleistocene to Holocene succession in the Gaza Strip, Palestine, consists of an alternation of calcareous sandstones and reddish fine-grained deposits (palaeosols). The palaeosols can be subdivided into two main groups based on the sand-sized versus clay- to silt-sized grains: (1) the sandy hamra palaeosols, and (2) the loess and loess-derived palaeosols. The hamra palaeosols can, in turn, also be subdivided into two main types according to their colour and grain size: (1) light brown loamy to sandy hamra palaeosols, and (2) dark brown sandy clay hamra palaeosols. The hamra palaeosols are polygenetic and originated in humid environments. Their red colour results from ferric oxides coating the sand grains, but also by illuviation. The various pedogenitic units and their gradual transition to loess palaeosols are due to different phases of dust accretion. Both groups of palaeosols developed during the last glacial. They are considered to represent different climate environments: hamra palaeosols represent humid climates, whereas the loess and loess-derived palaeosols represent dry and semi-dry climates.

Abstract. Human CO2 emissions may drive the Earth into a next greenhouse state. They can be mitigated by accelerating weathering of natural rock under the uptake of CO2. We disprove the paradigm that olivine weathering in nature would be a slow process, and show that it is not needed to mill olivine to very fine, 10 μm-size grains in order to arrive at a complete dissolution within 1–2 year. In high-energy shallow marine environments olivine grains and reaction products on the grain surfaces, that otherwise would greatly retard the reaction, are abraded so that the chemical reaction is much accelerated. When kept in motion even large olivine grains rubbing and bumping against each other quickly produce fine clay- and silt-sized olivine particles that show a fast chemical reaction. Spreading of olivine in the world's 2% most energetic shelf seas can compensate a year's global CO2 emissions and counteract ocean acidification against a price well below that of carbon credits.

AbstractSequences of quartz-rich coarse (20−63 μm) silt occur in many low- and midlatitude unglaciated arid and semiarid areas and have been termed “desert loess.” The processes by which these deposits are generated have been debated for decades. All hypotheses to explain their origin seek to provide mechanisms for the generation of silt-sized material without glacial grinding, which is the main process involved in the production of coarse silt at high latitudes. Possible mechanisms for the formation of coarse silt in arid regions include derivation from preexisting siltstones, mechanical weathering of silicate rocks, and abrasion of sand grains in active dune environments during intense transport events. Examination of the characteristics of desert loess and field and laboratory experiments to assess the role of dune areas as a source of coarse silt by abrasion and/or resuspension of residual fines suggests that many loess sequences are dominated by locally derived coarse silt. Improvements in the characterization of desert loess particle size, mineralogy, and geochemistry are needed, however, to identify sources and sinks of coarse silt, especially when combined with climatic back-trajectory analysis. Properly scaled experiments and modeling of particle collisions will also help to better quantify the effectiveness of abrasion in the generation of coarse silt in support of field observations.

AbstractGeomorphic features and Pleistocene deposits on Huangshan have been attributed to glaciation. Recent reassessment questions this interpretation. As part of the reassessment, quartz sand grains from deposits identified as glacial boulder clays (till composed of boulders in a clay or silt matrix) were analyzed by scanning electron microscope for evidence of their sedimentary history. Surface textures found on the boulder-clay grains were compared with those on grains with known sedimentary histories including glacial, grus, colluvial, and alluvial grains. The analysis shows that the grains lack typical glacial textures. The surface textures present indicate a complex history. Nonuniformly weathered grain surfaces point to chemical weathering of the source rock. This is supported by the deep weathering of the nonquartz clasts in the sand-sized fraction as well as in boulders at the outcrops. The close correspondence in surface-texture frequencies with those of the alluvial grains indicates an alluvial component to the grains’ history. The similarity with the colluvial grains and the outcrops’ structures suggest an alluvial/colluvial origin for the deposits. The history indicated by the surface textures agrees with the recent reassessment of the geomorphic features and points to warm climatic conditions in east-central China for at least part of the Pleistocene.

This study examines the physical and geochemical properties of near-surface sediments, as well as the geochemical and stable O–H–C isotope composition of (ground)surface waters in and around the Haughton impact structure region (Devon Island, Nunavut) to determine the types of weathering (mechanical, (bio)chemical) and their relative contribution in this polar desert environment. The surface sediments collected from the Allen Bay and Thumb Mountain formations surrounding the impact crater are dominated by sand-sized particles; whereas the impact melt breccias inside the crater have a greater abundance of silt-sized particles. The subsurface sediments in the Allen Bay formation show a near equal amount of sand- and silt-sized particles. However, the micromorphologies of the sand-sized particles collected at the surface revealed that these grains, irrespective of the local geology, were heavily fractured. By contrast, fractures and rounded pits are observed on the surface of the sand grains located within the active layer; whereas those located just above the permafrost table have only rounded cavities on their surface. The (ground)waters also show variations in their solute concentration with depth; the highest concentrations being found in the groundwaters near the top of permafrost. Taken together, these observations suggest that there is a progressive evolution from a mechanically dominated weathering regime near the surface, to increasing chemical weathering with depth. The transition from mechanical weathering near the surface to increasing chemical weathering with depth can be attributed to the decreasing frequency and intensity of mechanical weathering processes (i.e., frost action, wetting–drying, thermal dilation) with depth, and to the presence of permafrost, which allows a greater availability of water for chemical aqueous reactions at the base of the active layer.

We propose a 3D-shape preferred orientation (SPO) measurement method of rigid grains using synchrotron micro-computational tomography (μ-CT). The method includes oriented sampling, 3D μ-CT imaging, image filtering, ellipsoid fitting, and SPO measurement. After CT imaging, all processes are computerized, and the directions of thousands of rigid grains in 3D-space can be automatically measured. This method is optimized for estimating the orientation of the silt-sized rigid grains in fault gouge, which indicates P-shear direction in a fault system. This allows us to successfully deduce fault motion sense and quantify fault movement. Because this method requires a small amount of sample, it can be applied as an alternative to study fault systems, where the shear sense indicators are not distinct in the outcrop and the fault gouge is poorly developed. We applied the newly developed 3D-SPO method for a fault system in the Yangsan fault, one of the major faults in the southeastern Korean Peninsula, and observed the P-shear direction successfully.

This paper contains the results of CBR tests that performed on compacted samples of real dune sand (cohesionless sand grains) and pseudo dune sand which is a mixture of sand sized aggregate of clay and silt. The effect of compaction and soaking on the bearing values are included in this research. The results indicated that the compacted real dune sands have high strength and low sensitivity to soaking. The 5 mm penetration of CBR of this soil is higher than that of 2.5 mm. On the other hand, the loss of strength due to soaking can be quite considerable in compacted pseudo dune sands. The CBR values obtained at 2.5 mm and 5 mm penetration are approximately equal in pseudo dune sands.

AbstractThermoluminescence (TL) age estimates have been obtained on coarse-grained detrital feldspar from Eemian beach sand (substage 5e), early Weichselian dune sands (substages 5d and 5b), and pre-Eemian beach sand. The past radiation dose is obtained using the additive dose method. Even for the oldest samples, which date to 300,000 yr B.P. by other methods, the TL signal is not in saturation and can be doubled by the addition of laboratory radiation doses without saturation being achieved. This is contrasted with the behavior of polymineral, silt-sized grains from loess in the adjacent area. The TL age estimates are systematically underestimated by about 40% when compared with the expected geological ages. However, they are in correct stratigraphic order and demonstrate that stage 5 beach deposits can be distinguished from those resulting from earlier high sea levels using TL signals from potassium feldspars.

Along the Balikpapan Beach, there are abundant sand-sized sediment particles. Sand is one of the unconsolidated sediment grains based on fractions on the Wentworth Scale. Unconsolidated Sediment is defined as Loose Material and/or sedimentary rocks that is not yet solid. Balikpapan Beach, based on the Regional Geological Map of Balikpapan sheet, formed the Alluvium Formation (abbreviated as Qa) of the Holocene Epoch, Quaternary. Alluvium formation (Qa) has an arrangement of rocks in the form of pebbles, gravel, sand, and clay. Samples of Unconsolidated Sediment or loose material and sedimentary rocks that is not yet solid are determined for grain size variations using the Sieving method. The Seiving method or Sieve Test is a method for determining the size of the grains which will then be viewed on a scale and followed by the amount of grain size data that will be presented in graphical form to facilitate the type of grain size that dominates. The research focused on how the grain size on Balikpapan Beach based on the Wentworth Scale and Sorting data after the Sieve Test. Sieve Test results measured Mesh#10, Mesh#20, Mesh#40, Mesh#60, Mesh#120, Mesh#200 and Filter Analysis of the relationship between Filter Diameter and Retained Percentage as follows: Granule by 3.53%, Sand (Very Coarse Sand by 3.53%, Coarse Sand by 4.75%, Medium Sand by 13.26%, Fine Sand by 66.26%, Very Fine Sand by 5.15%) and Coarse Silt by 3.35%. Therefore, particles in the area of research with the Sieve Test were dominated by Fine Sand particles. Fine Sand with grain size 0.125 – 0.25 mm tested with a filter diameter of 0.125 mm got a Retained Weight of 331.29 gr, Retained Weight Precentage of 66.26%.

Along the Balikpapan Beach, there are abundant sand-sized sediment particles. Sand is one of the unconsolidated sediment grains based on fractions on the Wentworth Scale. Unconsolidated Sediment is defined as Loose Material and/or sedimentary rocks that is not yet solid. Balikpapan Beach, based on the Regional Geological Map of Balikpapan sheet, formed the Alluvium Formation (abbreviated as Qa) of the Holocene Epoch, Quaternary. Alluvium formation (Qa) has an arrangement of rocks in the form of pebbles, gravel, sand, and clay. Samples of Unconsolidated Sediment or loose material and sedimentary rocks that is not yet solid are determined for grain size variations using the Sieving method. The Seiving method or Sieve Test is a method for determining the size of the grains which will then be viewed on a scale and followed by the amount of grain size data that will be presented in graphical form to facilitate the type of grain size that dominates. The research focused on how the grain size on Balikpapan Beach based on the Wentworth Scale and Sorting data after the Sieve Test. Sieve Test results measured Mesh#10, Mesh#20, Mesh#40, Mesh#60, Mesh#120, Mesh#200 and Filter Analysis of the relationship between Filter Diameter and Retained Percentage as follows: Granule by 3.53%, Sand (Very Coarse Sand by 3.53%, Coarse Sand by 4.75%, Medium Sand by 13.26%, Fine Sand by 66.26%, Very Fine Sand by 5.15%) and Coarse Silt by 3.35%. Therefore, particles in the area of research with the Sieve Test were dominated by Fine Sand particles. Fine Sand with grain size 0.125 – 0.25 mm tested with a filter diameter of 0.125 mm got a Retained Weight of 331.29 gr, Retained Weight Precentage of 66.26%.

The Doig Phosphate Zone (DPZ) is a phosphate-bearing marine unit located at the base of the Doig Formation, in the Triassic section of the Western Canada Sedimentary Basin. The DPZ has a maximum thickness of 90 m and extends across northeastern British Columbia and west-central Alberta. In this study, we characterize the significance and interpret the origin of apatite in the DPZ through mineralogical and geochemical analyses, thin section study, and field emission scanning electron microscopy. The occurrence of apatite in the DPZ is not evenly distributed but restricted to discrete 10 to 20 cm thick beds, located near the base of the DPZ. Phosphorites are of two types: grainstones composed primarily of unconformity-bounded coated grains, and intraclastic phosphorites composed of detrital silt-sized grains and apatite coated grains in a cryptocrystalline phosphatic matrix. The phosphorite beds are records of stratigraphic condensation due to low detrital input during transgression. The erosionally truncated phosphatic coated grains and intraclasts are interpreted to be a result of various phases of phosphatization, exhumation, erosion, reworking, winnowing, and redeposition in alternating quiescence and storms or bottom currents. The abundance of pyrite and chalcophile trace elements, as well as the low concentration of proxy elements for organic matter productivity and preservation, are further evidence of stratigraphic condensation, with sulfidic pore water development and extensive organic recycling promoted by biological activity during the long exposure times. The phosphorites were formed under oxygenated water conditions, as suggested by the depletion in Ce and the presence of a diverse benthic fauna.

AbstractThe early Ordovician (∼385 Ma) Power Steps Formation, Newfoundland, Canada, exposes a well-preserved mudstone-dominated clinothem that serves as an excellent archive for understanding how mud has been produced, transported and converted into mudstone prior to the evolution of globally widespread, deep soil horizons. Sedimentological analysis of four sandstone and five mudstone facies, along the Ochre Cove clinothem, reveal that mud and sand were delivered by unidirectional currents and experienced episodic reworking by storm waves. Petrographic examination and X-ray diffraction from described mudstone facies reveal significant variability in the distribution of illite versus chlorite between the lower and upper part of the Ochre Cove clinothem. This research highlights that in the present-day clay mineral fraction, illite is often detrital whereas chlorite originated via the alteration of silt-sized, highly unstable, mafic (volcanoclastic?) grains. Throughout all sedimentologic facies, albeit in different proportions, these mafic lithic grains were diagenetically altered via in situ weathering before significant compaction occurred, resulting in the precipitation of significant volumes of pore-bridging, silica- and iron-rich chlorite cement. Compositional, diagenetic and textural attributes across the Ochre Cove mud clinothem vary as a function of starting composition, hydrodynamic sorting and grain density. Given that a significant proportion of clay minerals has been generated via in situ transformation of a mafic, non-stable precursor assemblage, we recommend future studies to incorporate detailed petrographic description along with X-ray diffraction analyses when aiming to employ trends in whole-rock clay mineral data as a proxy in provenance and palaeoclimate studies of very old (pre-Devonian) mudstones and sandstones.

The augite-olivine flows (5.3 Ma) capping Mount Nakobalevu, a few kilometres north-west of Suva, Fiji, have been subjected to rapid and deep weathering. The Nakobalevu K1 and K2 weathering profiles (at approximately 454 m altitude) show features of strong bauxitisation, and the attributes of a 'classical' lateritic profile. Aluminium and iron enrichment in the 2-3 m depth layers of the Nakobalevu weathering profiles is marked, with the presence of abundant gibbsite (as gravels and nodules, and in the silt and clay-sized fractions), goethite, kaolinite, haematite and magnetite (grains); the presence of fragmented (goethitic and gibbsitic) crustal materials in each of the studied horizons, and the distribution pattern of the Al2O3, Fe2O3 and SiO2, would infer the occurrence of several erosion and weathering cycles, some of which would have evolved under drier climatic regimes. Using Soil Taxonomy, the Nakobalevu Pedon (JBK-1) is a Typic Kandihumult, clayey, kaolinitic, isohyperthermic, which does not give any indication of the gibbsitic materials present.

A significant amount of information on sedimentary provenance is encoded in the heavy minerals of a sediment or sedimentary rock. This information is commonly assessed by optically determining the heavy-mineral assemblage, potentially followed by geochemical and/or geochronological analysis of specific heavy minerals. The proposed method of semi-automated heavy-mineral analysis by Raman spectroscopy (Raman-HMA) aims to combine the objective mineral identification capabilities of Raman spectroscopy with high-resolution geochemical techniques applied to single grains. The Raman-HMA method is an efficient and precise tool that significantly improves the comparability of heavy-mineral data with respect to both overall assemblages and individual compositions within solid solution series. Furthermore, the efficiency of subsequent analysis is increased due to identification and spatial referencing of the heavy minerals in the sample slide. The method is tested on modern sediments of the Fulda river (central Germany) draining two Miocene volcanic sources (Vogelsberg, Rhön) resting on top of Lower Triassic siliciclastic sediments. The downstream evolution of the volcanic detritus is documented and the capability to analyze silt-sized grains has revealed an additional eolian source. This capability also poses the possibility of systematically assessing the heavy-mineral assemblages of shales, which are often disregarded in sedimentary provenance studies.

Abstract. Physical weathering in permafrost landscapes contrasts to mid- and low latitude physical weathering in the way that quartz is less stable in freeze–thaw (F/T) cycles and breaks down to silt sized grains. F/T weathering also produces a distinct single quartz grain micromorphology such as microcracks and brittle textures of the surface. Both of these sediment-mineralogical features have been used for identifying intense permafrost conditions (i.e. intense F/T dynamics) around Lake El'gygytgyn in NE Eurasia using a Pliocene–Pleistocene sediment record from the centre of the lake. This lake provides the longest terrestrial palaeoenvironmental archive in the Arctic and has been a sediment trap for 3.6 Ma. Detritic material marked by F/T weathering becomes distinctive ~2.55 Ma ago and has been accumulating since then in the lake basin. This time marker coincides with the establishment of a perennial lake ice cover and corresponds with pollen assemblages indicating a significant cooling during that time. It matches fairly well the timing of the Plio-/Pleistocene cooling known from other marine and terrestrial evidence. The onset of intense quartz weathering is regarded as a first order age assessment for the beginning of persistent Quaternary permafrost conditions and which deepened into the ground since then in settings of high continentality in the non-glaciated NE Eurasian Arctic.

Effects of Feldspar Contamination on Equivalent dose and the Shape of Growth Curve for OSL of Silt-Sized Quartz Extracted from Chinese LoessThis study examines the effects of feldspar contamination of different extent (by fluorosilicic acid etching for different time periods and mixing pure quartz with different percentage of unetched grains) on blue-light stimulated luminescence (BLSL) of quartz (38-63 μm) for Chinese loess. In particular, the De values and the shape of growth curves will be examined. The results show that: (1) The De determined using feldspar in Chinese loess is obviously underestimated, and infra-red stimulated luminescence (IRSL) has a greater underestimation than BLSL. For aliquots with no fluorosilicic acid etching, an IRSL De underestimation of ∼30% is observed for a sample with an expected age of ∼22 ka, ∼19% underestimation for BLSL, and ∼10% for post-IR BLSL. For quartz BLSL, the contamination of feldspar, which has not dissolved by fluorosilicic acid etching, will inevitably lead to age underestimation. We suggest that the IR-checking should be performed for every single aliquot. An aliquot should be excluded from the final De calculation if obvious IRSL signal was observed. (2) For the sample under examination blue LED stimulation can reset both IRSL and BLSL signals of feldspars, while IR stimulation cannot reset the BLSL of feldspars. (3) For multiple-mineral aliquot the growth curve shape of the post-IR BLSL is different from that of the IRSL, and within 25 Gy it is identical to that of the pure quartz BLSL. The contamination of feldspars in quartz will change the shape of a growth curve for quartz BLSL.

We have carried out a paleomagnetic study of three piston cores collected from Lake Turkana. The goal is to recover a Holocene paleomagnetic secular variation (PSV) record for this lake and to correlate it with other Holocene PSV records from the East Africa Rift Valley (EARV). All three cores were sampled with u-channels and magnetic measurements of magnetic susceptibility, the natural remanence (NRM), and two artificial remanences, anhysteretic remanence (ARM) and saturation isothermal remanence (SIRM), were made on them. The remanences were routinely step-wise demagnetized and measured at 10 mT steps up to 60 mT. The NRMS had a simple pattern of demagnetization with a characteristic direction (ChRM) removed between 10 and 60 mT. ARM and SIRM demagnetization indicated that the magnetic grains were relatively soft with median destructive fields (MDF) less than 30 mT. We interpret the magnetic grains to be multi-domain (silt-sized) magnetite/titanomagnetite. The resulting magnetic records of all three cores could be correlated. A chronology for these cores was determined from four radiocarbon dates on core 4P. We also estimated the sediment ages by correlating the PSV to two other well-dated PSV records from the same region, Lakes Malawi and Victoria. PSV age estimation indicates that the radiocarbon dates are about 500 year too old; a correction for that offset causes three of the four radiocarbon ages to become consistent with the PSV age estimates. The final composite Lake Turkana PSV record for the last ~4000 years is the highest resolution directional record of PSV (~200 cm/ky) ever to be recovered from Africa.

SUMMARYSoil Organic Carbon (SOC) is a major indicator of soil fertility in the tropics and underlies variability in crop response to mineral fertilizers. Critical SOC concentrations that interact positively with N fertilizer for optimal crop yield are less understood. A study was conducted on a Ferralsol in sub-humid Uganda to explore the critical range of SOC concentrations and associated fractions for optimal maize (Zea maysL.) yield response to applied mineral N fertiliser. Maize grain yield response to N rates applied at 0, 25, 50 and 100 kg N ha−1in 30 fields of low fertility (SOC<1.2%), medium fertility (SOC = 1.2–1.7%) and high fertility (SOC>1.7%) was assessed. Soil was physically fractionated into sand-sized (63–2000 µm), silt-sized (2–63 µm) and clay-sized (<2 µm) particles and SOC content determined. Low fertility fields (<1.2% SOC) resulted in the lowest response to N application. Fields with >1.2% SOC registered the highest agronomic efficiency (AE) and grain yield. Non-linear regression models predicted critical SOC for optimal yields to be 2.204% at the 50 kg N ha−1rate. Overall, models predicted 1.9–2.2% SOC as the critical concentration range for high yields. The critical range of SOC concentrations corresponded to 3.5–5.0 g kg−1sand-sized C and 9–11 g kg−1for clay-sized C.

The grain-size distribution is commonly used for soil classification; however, there is also potential to use the grain-size distribution as a basis for estimating soil behaviour. For example, much emphasis has recently been placed on the estimation of the soil-water characteristic curve. Many methods proposed in the literature use the grain-size distribution as a starting point to estimate the soil-water characteristic curve. Two mathematical forms are presented to represent grain-size distribution curves, namely, a unimodal form and a bimodal form. The proposed equations provide methods for accurately representing uniform, well-graded soils, and gap-graded soils. The five-parameter unimodal equation provides a closer fit than previous two-parameter, log-normal equations used to fit uniform and well-graded soils. The unimodal equation also improves representation of the silt- and clay-sized portions of the grain-size distribution curve.Key words: grain-size distribution, sieve analysis, hydrometer analysis, soil classification, probability density function.

Kemerovo district coal power plant, Tom-Usinskaya district coal power plant and Belovo district coal power plant are the largest coal power plants in Kuzbass and during the combustion of coal they generate annually about 1600 tons of coal ash which consists of fly ash and bottom ash. Almost all the generated ash is disposed into ash dumps except a small quantity of fly ash (3.5%) that is effectively utilized. Therefore, secondary use of the bottom ash can be a sustainable solution for reducing its by-products and overcoming the scarcity of raw materials required for construction work. Therefore, the main aim of this research was to determine the chemical composition and granulometric properties of bottom ash to find out the possibility of using it as raw material for the building materials production. A series of laboratory experiments were conducted to determine basicity index, activity index, average grain density, bulk density, true density and grain size distribution. The experimental results reveal that the particle size of ash is predominantly sand-sized while containing some silt-sized and rubble-sized fractions as well. The studied bottom ash has a low basicity and activity index, respectively, does not have independent hydraulic activity. Thus, bottom ash of the largest Kuzbass coal power plants can be used as raw material for the building materials production.

AbstractThis paper shows how heavy minerals and single-grain varietal studies can be conducted on silt (representing c. 50% of world's sediments) sediments to obtain quantitative data as efficiently as for sand-sized sediments. The analytical workflows include heavy mineral separation using a wide grain-size window (15–355 μ) analysed through integrated optical analysis, Raman spectroscopy, QEMSCAN microscopy and U–Pb dating of detrital zircon. Upper Jurassic–Cretaceous silt-sized sediments from the Mandawa Basin of central-southern Tanzania have been selected for the scope of this research. Raman-aided heavy mineral analysis reveals garnet and apatite to be the most common minerals together with durable zircon, tourmaline and subordinate rutile. Accessory but diagnostic phases are titanite, staurolite, epidote and monazite. Etch pits on garnet and cockscomb features on staurolite document the significant effect of diagenesis on the pristine heavy mineral assemblage. Multivariate statistical analysis highlights a close association among durable minerals (zircon, tourmaline and rutile, ZTR) while garnet and apatite plot alone reflecting independence between the three groups of variables with garnet increasing in Jurassic samples. Raman data for garnet end-member analysis document different associations between Jurassic (richer in A, Bi and Bii types) and Cretaceous (dominant A, Ci and Cii types) samples. U–Pb dating of detrital zircon and their statistical integration with the above-mentioned datasets provide further insights into changes in provenance and/or drainage systems. Metamorphic rocks of the early and late Pan-African orogeny terranes of the Mozambique Belt and those of the Irumide Belt acted as main source of sediment during the Jurassic. Cretaceous sediments record a broadening of the drainage system reaching as far as the Usagran–Ubendian Belt and the Tanzanian Archean Craton.

Vertical Electrical Sounding (VES) was carried out in parts of Etche Local Government Area, Rivers State, Nigeria to investigate availability of groundwater. An ABEM SAS 1000 terrameter was used. Schlumberger configuration was adopted for the sounding to acquire a 4 point data, with the use of ID Interpex software in order to know the subsurface variations in resistivity with respect to depth. The investigation revealed the subsurface, thickness of lithology, prolific aquiferous zones, the resistivity curve portrays an overall increase in resistivity trend ranging from 228.7Ωm - 5872Ωm. The resistivity trend in the form of ρ1< ρ2< ρ3< ρ4< ρ5, indicates the presence of conductive materials present at a shallow depth of the point of survey. The highest resistivity value is observed in the fifth layer and it is believed to have gravely sized particles. A stratigraphic layer with gravely sized particles in this area revealed a good aquifer quality with reasonable quantity of aquifer fluid contained within the interconnected pore spaces. This zone of the studied area contains rock units from the geoelectric section such as silt, medium sand, coarse sand and gravel. The fifth layer is the prospect zone for aquifer delineation. A geoelectric section drawn from the resistivity data shows that the first layer is silt, the second layer is fine sand, the third layer is medium sand, the fourth layer is silty sand, the fifth layer is fine sand and the sixth layer is medium sand. The sixth layer is believed to be the prospect zone for aquifer characterization. A suitable data from drilled boreholes should be introduced to this study so as to have a profound knowledge and views about the grain size, sphericity, roundness and parking. These characteristics will be useful to determine the dominant grain size existing in these aquifers and characterize them appropriately.

Biomineralized and organic metazoan tubular skeletons are by far the most common in the fossil record. However, several groups of organisms are also able to agglutinate particles to construct more rigid structures. Here we present a novel type of agglutinated tube from the austral and endemic palaeobiota of the Malvinokaffric realm (Devonian, Brazil). This fossil is characterized by an agglutinated tube made of silt-sized particles forming an unusual flanged morphology that is not known from the fossil record. Besides being able to select specific particles, these organisms probably lived partially buried and were detritus/suspension feeders. Comparisons across different modern groups show that these fossils are strongly similar to tubes made by polychaetes, specifically from the family Maldanidae. If this interpretation is correct, then an early divergence of the Sedentaria clade may have occurred before the Devonian.

Abstract. Hydraulic conductivity (K) is one of the significant soil characteristics in terms of flow movement and solute transport. It has been recognized that K is statistically related to the grain-size distribution. Numerous models have been developed to reveal the relationship between K and the grain-size distribution of soil, but most of these are inappropriate for fine-grained media. Therefore, a new empirical model for estimating K of low permeability media was proposed in this study. In total, the values of K of 30 soil samples collected in the Jiangning District of Nanjing were measured using the single-ring infiltrometer method. The new model was developed using the percentages of sand, silt and clay-sized particles, and the first and the second rank moment of the grain-size through the moment method as predictor variables. Multivariate nonlinear regression analysis yielded a coefficient of determination (R2) of 0.75, indicating that this empirical model seems to provide a new approach for the indirect determination of hydraulic conductivity of low permeability media.

Magnetic susceptibility (MS) patterns have proven useful for regional stratigraphic correlations of zones within thick, oxidized Peoria and Roxana Silts along the Illinois and Central Mississippi River valleys for more than 350 km. Variations in MS of C horizon loess are controlled by silt-sized magnetite content and are interpreted to reflect changes in sediment provenance due to fluctuations of the Superior and Lake Michigan glacier lobes and the diversion of the Mississippi River to its present course. Grain size distributions and scanning electron microscopic observations indicate that stratigraphic changes in MS are not significantly influenced by eolian sorting or diagenetic dissolution, respectively. Three compositional zones (lower, middle, and upper) are delineated within Peoria Silt which usually can be traced in the field by MS, the occurrence of clay beds, interstadial soils, and/or subtle color changes. These zones can be correlated with, but are generally of more practical use than, previously studied dolomite zones (McKay, 1977) or clay mineral zones (Frye et al.,1968). However, mineralogical analyses can help to substantiate zone boundaries when in question. MS and compositional zones may indirectly record a climatic signal, primarily through the effect that global cooling has had on ice lobe fluctuations in the Upper Mississippi drainage basin.

The available measurements of the acoustic attenuation coefficient, α, in aqueous suspensions of glass beads and sand are investigated for [Formula: see text] (where k is the acoustic wavenumber and a the grain radius) and volume concentrations, [Formula: see text], up to 0.65. The data are found to collapse substantially when dividing by volume concentration, consistent with the expected first-order linear dependence. Equations of the form [Formula: see text], with ka-dependent coefficients, provide a prediction that is within a factor of 2 for low and intermediate values of ka.

Abstract Variability of suspended sediment grain size distribution in winter floods. The work presents the results of research concern variability of suspended sediment grain size, transported during the winter floods in agricultural catchment, in the period of hydrological years 2012-2015. The information about grain size distribution from nine winter flood events were collected over the study period, which allowed to analyze the variability of suspended sediment particle size during the various events. Grain size of sediment was determined using a laser particle size analyzer Mastersizer Microplus from Malvern Instruments Ltd. Variability of individual particle size classes were observed in each flood. Sand fraction dominated in seven of nine measured events. There was no significant increase of suspended sediment size in relation to the maximum of discharge. It can be explain by a relatively low discharge of recorded events. The percentage of material classified as clay (<4 μm) ranged from 0.08 to 1.01%, silt-sized material (>4 and <63 μm) ranged between 9.31 and 67.17% and sand-size material (>63 μm) ranged from 32.01 to 90.61%. The relationship between the particle size and the discharge requires further studies. The diameter d10, d50 and d90 and a standard deviation were calculated for each flood. Mean values of d50 for individual flood ranged between 41.05 and 191.32 μm with average value of 99.01 μm and average standard deviation of 32.57.

Abstract In discussions on loess, two types are often demarcated: glacial loess and desert loess. The origin of the idea of desert loess appears to lie with V.A. Obruchev who observed wind-carried silt on the Potanin expedition to Central Asia in 1895. It might be considered that desert loess would be defined as loess associated with deserts but it came to be thought of as loess produced in deserts. This led to some controversy as no mechanism for producing silt particles in deserts was readily available. Bruce Butler in Australia in particular cast doubt on the existence of desert-made loess. Butler indicated loess-like deposits in Australia which he called Parna; these are very like loess but the silt sized particles are actually clay mineral agglomerates of silt size- formed in dry lake regions. At the heart of the desert loess discussion is the problem of producing loess material in deserts. It has been suggested that there are no realistic mechanisms for forming large amounts of loess dust but there is a possibility that sand grain impact may produce particle shattering and lead to the formation of quartz silt. This would appear to be a reasonable mechanism for the African deposits of desert loess, but possibly inadequate for the huge deposits in China and Central Asia. The desert loess in China and Central Asia is loess associated with a desert. The material is formed in cold, high country and carried by rivers to the vicinity of deserts. It progresses then from deserts to loess deposit. Adobe ground may be defined as desert loess. Adobe occurs on the fringe of deserts, notably in the Sahelian region of Africa, and in SW USA. The use of adobe in construction represents the major utilization of desert loess in a social context. More understanding of adobe is required, in particular with respect to the adobe reaction, the low order chemical reaction which provides modest cementitious properties, and can be likened to the pozzolanic reactions in hydrating cement systems. The location of loess and loess-like ground on the peripheries of deserts is aided by the observation of the nesting sites of bee-eater birds. These birds have a determined preference for loess ground to dig their nesting tunnels; the presence of nest tunnels suggests the occurrence of desert loess, in desert fringe regions. We seek amalgamation and contrast: ten main topics are considered: words and terms, particles, parna, geotechnical, adobe, people, birds, Africa, Central Asia, Mars. The aim is some large generalizations which will benefit all aspects of desert loess investigation.

Abstract. The tropical storm, floodwater, and the floodplain-sediment layer of a 100-year recurrence flood are examined to better understand characteristics of large monsoon floods on medium-sized rivers in northern Thailand. Storms producing large floods in northern Thailand occur early or late in the summer rainy season (May–October). These storms are associated with tropical depressions evolving from typhoons in the South China Sea that travel westward across the Indochina Peninsula. In late September, 2005, the tropical depression from Typhoon Damrey swept across northern Thailand delivering 100–200 mm/day at stations in mountainous areas. Peak flow from the 6355-km2 drainage area of the Ping River upstream of the city of Chiang Mai was 867 m3s−1 (river-gage of height 4.93 m) and flow greater than 600 m3s−1 lasted for 2.5 days. Parts of the city of Chiang Mai and some parts of the floodplain in the intermontane Chiang Mai basin were flooded up to 1-km distant from the main channel. Suspended-sediment concentrations in the floodwater were measured and estimated to be 1000–1300 mg l−1. The mass of dry sediment (32.4 kg m-2), measured over a 0.32-km2 area of the floodplain is relatively high compared to reports from European and North American river floods. Average wet sediment thickness over the area was 3.3 cm. Sediment thicker than 8 cm covered 16 per cent of the area, and sediment thicker than 4 cm covered 44 per cent of the area. High suspended-sediment concentration in the floodwater, flow to the floodplain through a gap in the levee afforded by the mouth of a tributary stream as well as flow over levees, and floodwater depths of 1.2 m explain the relatively large amount of sediment in the measured area. Grain-size analyses and examination of the flood layer showed about 15-cm thickness of massive fine-sandy silt on the levee within 15-m of the main channel, sediment thicker than 6 cm within 200 m of the main channel containing a basal coarse silt, and massive clayey silt beyond 200 m. The massive clayey silt would not be discernable as a separate layer in section of similar deposits. The fine-sand content of the levee sediment and the basal coarse silt of sediment within 200 m of the main channel are sedimentological features that may be useful in identifying flood layers in a stratigraphic section of floodplain deposits.

AbstractThis study of peri-urban minerogenic topsoil on glacigenic or post-glacial deposits shows the influence of the site-classification approach on the differentiated median background (DMB) values of major elements and the potentially harmful elements (PHEs) Ba, Cr, Cu, Mn, Ni, Pb and Zn. Composite samples from forests and meadows were taken in 25 sites, each of which had five sub-sites. A fraction of <2 mm was used to determine the organic matter by loss on ignition (LOI), grain size by laser diffraction and the elemental contents by X-ray fluorescence. The following five site-classification approaches are compared: geochemical (G), using relative median contents of Al, K, Ti; textural (T), according to mean percentages of clay-sized fraction (CLF) and silt fraction (SIF); lithological (L), based on soil parent material texture from the soil database; soil type (S), presented in the soil database; and parent material (P), generalising the underlying Quaternary deposits. Sites were classified into four level groups in which the DMB values were estimated after eliminating anomalies. The average ranks of three scores according to SIF, CLF, LOI, Al, K, Ti, Fe, Mg, Ca and S in the respective groups revealed the highest value for the G approach. It better eliminates the CLF and SIF influences on the median assessment indices of PHEs in sites.

Seaspray Group carbonate sediments of Oligocene to Recent age overlie the main hydrocarbon producing Upper Cretaceous to Eocene Latrobe Group in the offshore Gippsland Basin. Their sonic complexity creates major difficulties for hydrocarbon exploration. Carbonate facies are divisible into three subgroups based on seismic character, sonic logs, velocity profiles, carbonate content, petrologic character and age. The oldest unit is the Angler Subgroup that consists of carbonate pelagic marls (CaC03 70%) with interbedded clastic-rich units.Zones of high velocity (>3,000m/s) are restricted to the deeply buried parts of the Albacore Subgroup, at TWT's greater than 0.8 seconds. The characteristics of this high velocity facies are: a composition of fine grained bioclast-rich packstones and wackestones with less than 10% silt sized quartz; the carbonate content exceeds 60%; the intervals are prone to cementation and are stylolitised; they are diachronous (i.e. cut across seismic boundaries); velocities progressively increase with depth; highest velocities occur where the unit is thickest towards the centre of the basin; velocity increases laterally with steepness of angle on downlap surfaces due to coarser grain sizes and inferred greater initial porosity; and velocities increase with stratigraphic age in the Albacore Subgroup. Regardless of burial depth the Angler and Hapuku Subgroups contain no significantly high velocity zones.An empirical relationship derived from this data set provides a basis for re-interpreting average velocity to the top of the Latrobe Group in areas underlying high velocity canyon-fill sediments.

AbstractThe St. Elias orogen and the Surveyor Fan in the adjacent Gulf of Alaska are a coupled source to sink system recording the interplay of tectonics and variable degrees of glaciation during the collision of the Yakutat terrane with the southern Alaska margin since the Miocene. The Miocene to Holocene sediments of the Surveyor Fan were drilled during IODP expedition 341. The recovered material is used to constrain information on changes in erosion centers during the last 10 Ma to study the impact of climatic and tectonic processes on orogen evolution. Point counting of sand- and silt-sized light framework components and geochemical single grain analysis of heavy mineral groups epidote and pyroxene is applied to analyze patterns of sedimentary provenance of two sites on the distal and proximal Surveyor Fan (Site U1417 and U1418, respectively). The studied sands and silts of Miocene to Pleistocene age are slightly enriched in feldspar (plag >> kf) at the proximal site, compositions at both sites do not show systematical changes with time of deposition. Framework component spectra uniformly reflect the expected active margin provenance. Epidote and pyroxene compositions are very consistent and show no change with time of deposition. Associations of epidote and pyroxene with albite, titanite and pumpellyite are in line with near-shore sources in the Chugach Metamorphic Complex and the metabasite belt at its southern border, and in units of recycled detritus exposed in the fold and thrust belt on the western Yakutat Terrane, respectively. Rock fragments indicate input from mainly metamorphic sources during the Miocene and Pliocene and an increase of input from low-grade metamorphic and sedimentary rocks in the Pleistocene, a finding also indicated by the abundance of epidote and pyroxene. This implies increasing erosion of the near-shore areas of the fold and thrust belt with advance of glaciers to the shore since the Miocene, being enhanced by the onset of the Northern Hemisphere glaciation at the beginning of the Pleistocene. Climate changes connected to the mid-Pleistocene transition did not result in appreciable changes in the petrographic compositions. Glaciers seem to have remained nested in their topographically predefined positions, continuously feeding material with uniform characteristics into the fan.

Abstract. Terrestrial sedimentation buries large amounts of organic carbon (OC) annually, contributing to the terrestrial carbon sink. The temporal significance of this sink will strongly depend on the attributes of the depositional environment, but also on the characteristics of the OC reaching these sites and its stability upon deposition. The goal of this study was to characterise the OC during transport and stored in the depositional settings of a medium-sized catchment (111 km2) in SE Spain, to better understand how soil erosion and sediment transport processes determine catchment-scale OC redistribution. Total organic carbon (TOC), mineral-associated organic carbon (MOC), particulate organic carbon (POC), total nitrogen (N) and particle size distributions were determined for soils (i), suspended sediments (ii) and sediments stored in a variety of sinks such as sediment wedges behind check dams (iii), channel bars (iv), a small delta in the conjunction of the channel and a reservoir downstream (v), and the reservoir at the outlet of the catchment (vi). The data show that the OC content of sediments was approximately half of that in soils (9.42 ± 9.01 g kg−1 versus 20.45 ± 7.71 g kg−1, respectively) with important variation between sediment deposits. Selectivity of mineral and organic material during transport and deposition increased in a downstream direction. The mineralisation, burial or in situ incorporation of OC in deposited sediments depended on their transport processes and on their post-sedimentary conditions. Upstream sediments (alluvial wedges) showed low OC contents because they were partially mobilised by non-selective erosion processes affecting deeper soil layers and with low selectivity of grain sizes (e.g. gully and bank erosion). We hypothesise that the relatively short transport distances, the effective preservation of OC in microaggregates and the burial of sediments in the alluvial wedges gave rise to low OC mineralisation, as is arguably indicated by C : N ratios similar to those in soils. Deposits in middle stream areas (fluvial bars) were enriched in sand, selected upon deposition and had low OC concentrations. Downstream, sediment transported over longer distances was more selected, poorly microaggregated, and with a prevalence of silt and clay fractions and MOC pool. Overall, the study shows that OC redistribution in the studied catchment is highly complex, and that the results obtained at finer scales cannot be extrapolated at catchment scale. Selectivity of particles during detachment and transport, and protection of OC during transport and deposition are key for the concentration and quality of OC found at different depositional settings. Hence, eco-geomorphological processes during the different phases of the erosion cycle have important consequences for the temporal stability and preservation of the buried OC and in turn for the OC budget.

CONTROLE DE EROSÃO EM ESTRADAS RURAIS NÃO PAVIMENTADAS, UTILIZANDO SISTEMA DE TERRACEAMENTO COM GRADIENTE ASSOCIADO A BACIAS DE CAPTAÇÃO Rui Donizete Casarin1; Eduardo Luiz de Oliveira21Faculdade de Ciências Agronômicas, Universidade Estadual Paulista, Botucatu, SP, ruicasarin@ig.com.br2Departamento de Engenharia Civil, Universidade Estadual Paulista, Bauru, SP 1 RESUMO As estradas rurais de terra são estruturas viárias importantes para o desenvolvimento rural econômico e social da nação, sendo que a erosão provocada pelas águas das chuvas no seu leito e margens esta intimamente relacionada à má drenagem, tornando-se um dos principais fatores para sua degradação. Para que o sistema de drenagem funcione de forma adequada é necessário o conhecimento da erodibilidade, capacidade de infiltração de água no solo e adoção de práticas mecânicas de abatimentos de taludes com elevação do greide e interceptação de águas por meio de dispositivos de drenagem e captação. Neste artigo apresenta-se um modelo de drenagem por meio da construção de terraços embutidos com gradiente associados à bacia de captação em solos do tipo Argissolo Vermelho distrófico abrúptico de textura arenosa a média, com base em técnicas de abatimentos de taludes, elevando seu leito transversalmente das estradas com desviadores de fluxo. As frações granulométricas (areia, silte, argila) e a estabilidade de agregados indicam que esse solo sob ação antrópica pode apresentar processos erosivos resultando em escoamento superficial com arrastamento de solos, assoreando mananciais e cursos d’água localizados abaixo das estradas proporcionando grandes impactos ambientais nos corpos hídricos. A redução destes problemas de erosão nestas estradas de terra está na adoção de medidas que intercepte águas do próprio escoamento do seu leito, bem como as águas pluviais vindas de áreas adjacentes da contribuição, que são coletadas e conduzidas para terraços embutidos e bacias de captação. UNITERMOS: erosão em estradas rurais, infiltração de água no solo, práticas mecânicas de conservação de solo, contenção de águas pluviais. CASARIN, R. D.; OLIVEIRA, E. L. CONTROL OF EROSION IN RURALUNPAVED ROADS UTILIZING A TERRACE SYSTEM WITH GRADIENT ASSOCIATED TO CAPITATION BASIN 2 ABSTRACT The agricultural unpaved roads are important road structures for the economic and social agricultural development of the Nation, and the erosion provoked by rain water in the road bed and sides are closely related to bad draining, one of the main factors for their degradation. In order to make the draining system adequate, it is necessary to know about erodibility, infiltration capacity of water in the ground and adoption of mechanical slope abatement with grid elevation and water interception. This study presents drainage model through the construction of terraces with gradient transversally associated to the capitation basin in abruptic red dystrophic argisol soils, medium sandy texture, based on slops abatement techniques, elevating the road bed and deviating flow. The grain sized fractions of this ground (sand, silt, clay) and the aggregate stability indicated that this ground, under anthropic action, presents erosive processes resulting in superficial draining with ground hauling, sanding sources and courses of water situation below roads, providing great environmental impacts in the hydric bodies. The reduction of erosion problems in these unpaved roads is in the adoption of measures that intercept waters from the draining of their stream bed itself, as well as pluvial waters comings from adjacent areas of contribution, that are collected and conducted to inlaid terraces and capitation basis. KEYWORDS: erosion in agricultural roads, water infiltration in the soil, mechanical soil conservation practices, pluvial water containment.

Abstract Context. - Many ferralsols and podzols from central Amazon were developed by a long-time pedogenesis over a sandy-clay Cretaceous sediment which mainly consists of kaolinite and quartz [Lucas et al., 1996]. The soils progressively range from clayey microaggregate ferralsols on the plateaux associated with tropical forests, to podzols at the bottom of thalwegs and in some small declivities of the largest plateaux associated with forests of smaller trees or open savannahs [Chauvel et al., 1987; Bravard, 1988; Lucas, 1989; Cornu, 1995]. Their moisture properties are different from those of temperate soils [Arruda et al., 1987; van den Berg et al., 1997; Tomasella et al., 2000]. Methods. - To quantify the moisture properties, mercury injection porosimetry (MIP) seems to be an adequate method [Vachier et al., 1979]. It is easy to use and enables accurate investigation of the major part of the porosity spectrum. We used a Carlo-Erba 2000 which enabled 12 to 20 measurements for pore entry radii from 4 nm to 0.1 mm. It requires dried (here, air-then oven-drying), centimetre-sized samples. The drying of the sample, the large pressures of Hg used, the different surface properties of soil components in presence of water or Hg, may induce discrepancies between MIP data and water desorption measurements, particularly if the organic matter (OM) is abundant. We compared MIP and water desorption data, and established pedotransfer functions to estimate the water desorption curve from MIP data and OM content. Water desorption was performed with a pressure membrane equipment, which allows us to investigate pores with entry radii from 0.1 μm to 0.5 mm [AFNOR, 1996a], on decimetric samples. We also used water desorption data obtained in situ in other studies from similar sites [Tomasella and Hodnett, 1996]. For some depths, drying under controlled atmosphere [AFNOR, 1996a] enabled us to investigate pores with entry radii down to 1.5 nm. The total pore volume was determined on the same dry or humid sample (volume 100 cm3) by cylinder measurement or using the paraffin method [AFNOR, 1996b], in order to determine the volume of large pores. Organic carbon mass ratio (C) data are from Bravard [1988] and Cornu [1995]; a C value of 1 % corresponds to a volume ratio of organic matter to solid soil of 4.8 to 6 %. Notations. - We classified each pore class from its pore size (r), deduced from pressure data with the Laplace law (r is the entry radius for cylindrical pore model or the entry width for slit-shaped pore model): - nanopores (r &lt; 4 nm) and cryptopores (4 nm &lt; r &lt; 0.1 μm) are residual pores, containing residual water that roots cannot extract. It moves by evaporation in dry conditions; - micropores (0.1 μm &lt; r &lt; 10 μm) contain bioavailable water; - mesopores (10 μm &lt; r &lt; 0.1 mm) and macropores (0.1 mm &lt; r) are determinant for hydraulic conductivity, from which water drain in some hours (mesopores) or seconds (macropores) after the rain. We described their abundance in terms of volume, in order to better quantify their geometrical structure, and took as a reference the volume of dry solid matter in the soil, because the total soil volume is not constant (it depends on moisture content). Then we used the partial void ratio (u) for MIP, the water ratio (n) or the air ratio (a) for water desorption, and the fluid ratio (e) for total porosity: \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[\mathit{u}=\frac{\mathit{V}_{\mathit{viod}}}{\mathit{V}_{\mathit{solid}}},\ \mathit{n}=\ \frac{\mathit{V}_{\mathit{w}}}{\mathit{V_{solid}}},\mathit{a}=\frac{\mathit{V_{air}}}{\mathit{V_{solid}}},\mathit{e_{humid}}=\ \frac{\mathit{V_{w}}+\mathit{V_{air}}}{\mathit{V_{solid}}}\ and\ \mathit{e_{dry}}=\ \frac{\mathit{V_{air}}}{\mathit{V_{solid}}}=\ \frac{\mathit{V_{void}}\ +\ \mathit{V_{Hg}}}{\mathit{V_{solid}}}\] \end{document} MIP and water desorption give directly the values of ucrypto, umicro, umeso, nres, nmicro, nmeso. Total pore volume measurements give ehumid and edry. We must be aware that the maximum water content remains below the fluid content, because of residual air: air bubbles trapped during wetting (we tried to minimize this effect by a progressive, two-week-long wetting), air linked to hydrophobic soil organic surfaces, and air in non-connected pores (not here). Residual air can thus be neglected for MIP, and for the water desorption of samples without organic matter. By subtraction, we obtain: \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \begin{eqnarray*}&&(\mathit{n_{macro}}\ +\ \mathit{a_{res}})\ =\ \mathit{e_{humide}}\ {-}\ \mathit{n_{res}}\ {-}\ \mathit{n_{micro}}\ {-}\ \mathit{n_{meso}}{\ }{\ }and\\&&(\mathit{u_{macro}}\ +\ \mathit{u_{nano}})\ =\ \mathit{e_{dry}}\ {-}\ \mathit{u_{crypto}}\ {-}\ \mathit{y_{micro}}\ {-}\ \mathit{u_{meso}}.\end{eqnarray*} \end{document} We can extrapolate the ratio of dry nanopores (unano) with reasonable accuracy because its value is anyway very low. For the ferralsols between 1.1 and 1.7 m depth, (umacro + unano) ≤0.03. We added a small triangle to the left of the porosity spectrum, in order to have unano = 0.01 at 1.4 m depth for the ferralsol. Then unano ranges from 0.002 for the podzol to 0.02 for the ferralsol above 0.7 m depth. All the porosity spectra we obtained had very few small micropores. Two porosity domains can thus be defined: textural porosity below 0.25 μm pore size, and structural porosity above. We described these two domains using their logarithmic average pore entry radii (rtext or rstruct) and their lobe width λ,. These parameters were defined by fitting an Ahuja and Schwartzendruber curve [1972] (often named a symmetric, m = 1, van Genuchten curve [van Genuchten, 1980]): \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathit{u}\ =\ \frac{\mathit{u_{text}}}{1+(\mathit{r_{text}}/\mathit{r})^{{\nu}_{\mathit{text}}}}\) \end{document} then \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathit{u}=\ \mathit{u_{text}}+\frac{\mathit{u_{struct}}}{1+(\mathit{r_{struct}}/\mathit{r})^{{\nu}_{\mathit{struct}}}}\) \end{document} and it is the same for n. [Log(rtext) − λtext;Log(rtext)+ λtext] is the interval gathering half of textural porosity, with λtext = Log3/νtext and it is the same for structural porosity. We set ustruct from e measurements, to give it a physical meaning, and introduced it as a value of associated with the 1mm pore size during the fitting, so that all curves approach their asymptotic value for about the same pore size. Results on porosity spectra. - The carbon content declines with depth, with a local maximum in the Bh horizon for the podzols (fig. 4). Ferralsols have a high residual porosity and average meso- and macroporosities (fig. 2 and 5), podzols have basically high meso- and macroporosities (figs 3 and 6), and transition soils are intermediate. For ferralsols and transition soils, named clayey soils here, all porosity classes have typical variations with depth: maximum at the surface; local minimum at a compacted horizon at 0.13 to 0.3 m (ferralsol) or 0.4 to 0.6 m (transition soil); local maximum for meso- and macroporosity, at the « termites’ horizon » at 0.4–0.6 m (ferralsol) or 0.8–1.2 m (transition soil); constant values for residual porosity below a depth of 1.2 m, and decreasing values for the other porosity classes. The average textural pore size increases vertically from the surface to the depth, with a local minimum at the compacted level, and laterally from ferralsols to podzols (fig. 7 and 10). Interpretation. - Residual porosity is correlated to clay content and textural pore size is correlated to the kaolinite particle size (unpublished work). The compacted level, named biological plough pan [Chauvel et al., 1987], may be due to a gravitational accumulation of the finest kaolinites from the above horizons, at the foot of the highly pedoturbated level. Low microporosity is linked to a very low silt and fine sand content, typical of tropical soils. Meso-and macroporosities are due to a clay microaggregation for clayey soils, and to the coarse sand fabric for the podzol. Microaggregation of clay is enhanced near the surface by root or ant pedoturbation, and at depth by termit pedoturbation, and maybe lateral water flows on the slope. Dispersion. - The dispersion of the values is low for a depth between 0.7 and 1.5 m, which is due to a homogeneous kaolinitic plasma. The dispersion increases with pore size, surface proximity for depth 0.7 m, or the increasing depth below 1.5 m. Near the topsoil, this is due to the heterogeneous biological activity, giving an heterogeneous soil structure. In horizons below 1.5 m, the causes are micronodules, localised water flows, and insufficient root pedoturbation. Therefore, we took more samples near the surface, we quantified soil shrinkage from the same sample before and after drying, we gave a higher statistical weight to data from 0.7 to 1.5 m depth in regressions, and smoothed values with depth (table IV). Comparison of results on dry or humid samples Total poral volume. - The shrinkage of the ferralsols samples decreases with depth. On the contrary, the shrinkage of podzol samples increases with depth (fig 5, 6 and table I). Residual porosity and microporosity. - OM presence is correlated to a decrease in the residual and micro- porosity given by MIP, compared to water desorption data. For soil samples with a low organic matter content, MIP gives a lower residual porosity especially for fine clays and a higher microporosity (table I). We could establish one pedotransfer function for all the soils studied here by taking into account the average textural pore size (table II and fig- 8). Meso- and macroporosity. — Through drying, mesoporosity increases for clayey soils and shrinks for podzol. These changes are more important for deep than for shallow horizons. Through drying, macroporosity increases, except for deep horizons of clayey soils (fig. 5,6; tables I, III). Textural porosity of ferralsols and transition soils. - The progressive vertical and lateral variation of MIP data gives reliability to a comparison with the two points where the textural porosity of humid samples was measured. MIP gives a higher pore size (roughly doubled, see table II) and a lower textural lobe width (roughly halved), compared to water desorption data. Structural porosity. - Our measurements on dry samples, compared to water desorption data, give simultaneous variations of three parameters, average structural pore size, structural lobe width, and macropores/mesopores volume ratio: an increase for the upper horizons of clayey soils or the deep horizons of podzol, a low change for the upper podzol horizons, and a decrease for the deeper horizons of clayey soils (fig. 9 and 10). However, the dispersion on these parameters is too high to predict them for humid samples from our data on dry samples. In order to parameterise the water desorption curve, we propose to apply equations of table I to subdivisions of micro- and mesoporosity, sharing out the organic matter influence between these subdivisions to get a precise water desorption curve, that can then be parameterised [Bastet, 1999]. Interpretation. - Hysteresis and pore geometry effects could not explain differences between water desorption and MIP, as in both cases the non-wetting fluid (air or Hg) enters pore space, and the same pore geometrical model was applied. The contact angle used in the Laplace law may change with the soil composition, especially with OM content for water desorption (hydrophobicity). Then we may have overestimated humid pore sizes at shallow horizons. Correcting this would enhance the discrepancies observed here. Some phenomena are not taken into account in the Laplace law: compression of porosity during MIP [Penumadu and Dean, 2000], or water physiosorption on mineral surfaces during water desorption [Tuller et al, 1999]. The first phenomenon causes the Laplace law to overestimate dry pore sizes (for r &lt; 2 μm), the second causes it to overestimate humid nanoporosity. Both explain that MIP gives a higher microporosity, a higher textural pore size, a lower residual porosity. The drying of samples causes porosity shrinkage, diminishing pore volumes and pore sizes. Then some macropores of clayey soils could turn into mesopores. However, the shrinkage at a given scale may cause the opening of the porosity at a higher scale, with cracking. Thus, the shrinkage of residual porosity can explain the increase of microporosity for all horizons, the increase of mesoporosity for clayey horizons, and the increase of macroporosity (eye-visible cracks), for shallow clayey horizons. The shrinkage of podzol mesoporosity can explain the increase of its macroporosity as well. The amount of shrinkage due to drying, or compression during MIP depends on soil OM content and type, soil structure and soil texture. Soil texture could explain a smaller shrinkage of total porosity for podzol than ferralsol, for shallow horizons: the lentil-shaped kaolinites, depending on their relative positions, are more likely to occupy a variable volume than the quartz grains, round-shaped with cavities. Soil structure is determined by its pedogenesis: eluviation/illuviation, pedoturbation. The unexpected large shrinkage for deep podzol seems to be due to a loose structure, inherited from eluviation of clay. Pedoturbation, together with OM presence, may either create porosity, or seal or compact porosity [Sokolowska and Sokolowski, 1998 ; Chauvel et al., 1999]. They may create a new porosity likely to shrink in clayey soils and on the contrary they may consolidate the loose structure of podzols. Conclusion. - We established pedotransfer functions to define the water desorption curve from MIP, organic carbon content, and bulk density (table I and II). These functions can be used for soils with the following characteristics, thus for most tropical soils: - negligible fine clay (&lt; 0.2 μm) content, in order to enable the extrapolation of nanopore volume from MIP, without needing nitrogen desorption [Bruand and Prost, 1987]; - soils mainly composed of kaolinite and quartz. The organic carbon content has little influence on the humic podzol studied here, so the equations established here are pertinent for other podzols. These pedotransfer functions give information on the structure of these soils : - residual and micro- porosities modify between MIP and water desorption, according to the organic carbon content and the texture of clay (given by the average textural pore size), with the same law for all soils; - mesoporosity changes according to two different types of structure : (1) clay microaggregates for clayey soils, (2) sandy fabric for podzol, loose at depth due to eluviation of parent clay, consolidated near the surface by pedoturbation; - total porosity follows, with an attenuation, the changes in the MO-linked porosity and in the porosity linked to soil structuring particles, that is the residual porosity for clayey soils, and the mesoporosity for podzols; - macroporosity, in reality as in the equations, compensates for the difference. This method could be tested on soils with other granulometry, mineralogy, or higher OM content. This work was supported by IRD and the PEGI and PROSE programs, we thank Max Sarrazin for his technical collaboration and the reviewers for their critical reading.

Twenty sabkha samples were chemically analyzed by XRF technique for determination of their major oxides concentrations. Six cores penetrated both the intertidal and supratidal flat zones developed in six wadis mouths in the coastal stretch of the Al-Dafna plateau, northeast Tobruk city. The significance distribution and concentration of the major oxides are discussed and interpreted. Elements in the raw material of the study area reflect important evidence of geochemical weathering processes that affecting parent rocks as well as conditions of sedimentation, and rate of deposition. Correlation coefficients have been used to illustrate the abundance and distribution of these elements. The distribution of major oxides are follows Si2O > CaO > LOI > Al2O3 > SO3 > MgO > Na2O > K2O. The vertical distribution of major elements is mainly controlled by the abundance and proportions of the clastics, carbonates and evaporite minerals. It was found that silica present in the form of detrital, subrounded to rounded silt- to sand-sized quartz grains, while the content of Al2O3 is associated with terrigenous argillaceous materials. On the other hand, the presence of Fe2O3 is related to the abundance of clastic materials in sabkha deposits. It was found that K2O and Na2O concentrations increase toward the sabkha surfaces.

River incision into bedrock drives landscape evolution and couples surface changes to climate and tectonics in uplands. Mechanistic bedrock erosion modeling has focused on plucking—the hydraulic removal of large loosened rock fragments—and on abrasion—the slower fracturing-driven removal of rock due to impacts of transported sediment—which produces sand- or silt-sized fragments at the mineral grain scale (i.e., wear). An abrasion subregime (macro-abrasion) has been hypothesized to exist under high impact energies typical of cobble or boulder transport in mountain rivers, in which larger bedrock fragments can be generated. We conducted dry impact abrasion experiments across a wide range of impact energies and found that gravel-sized fragments were generated when the impact energy divided by squared impactor diameter exceeded 1 kJ/m2. However, the total abraded volume followed the same kinetic-energy scaling regardless of fragment size, holding over 13 orders of magnitude in impact energy and supporting a general abrasion law. Application to natural bedrock rivers shows that many of them likely can generate large fragments, especially in steep mountain streams and during large floods, transporting boulders in excess of 0.6 m diameter. In this regime, even single impacts can cause changes in riverbed topography that may drive morphodynamic feedbacks.

This study determined the distribution of total Hg (Hg_T) among aggregate size fractions in the A, E, Bh and Bs horizons of a representative temperate forest podzol. The aggregate distribution was dominated by the coarse sand size fraction (average of 55%) followed by fine sand (29%), fine silt (10%), coarse silt (4%) and clay (2%). In general, Hg_T mean values increased as the aggregate size become smaller: clay (170 ng g^-1) &gt; fine silt (130 ng g^-1) &gt; coarse silt (80 ng g^-1) &gt; fine sand (32 ng g^-1) &gt; coarse sand (14 ng g^-1). Total Hg enrichment in clay-sized aggregates ranged from 2 to 11 times higher than the values shown by the bulk soil (&lt; 2 mm). The accumulation of Hg_T in the finer size aggregates was closely related to total organic C, Na-pyrophosphate extracted C, metal (Al, Fe)-humus complexes and Al and Fe oxyhydroxides. Indeed, these parameters varied significantly (<em>p </em>&lt; 0.05) with the aggregate size and their highest values were found in the finer fractions. This suggested the role of these soil compounds in the increase of the specific surface area per mass unit and negative charges in the smallest aggregates, favouring Hg retention. Mercury accumulation factor (Hg_AF) values reached up to 10.8 in the clay size aggregates, being close to 1 in sand size fractions. Regarding Hg enrichment factors (Hg_EF), they were &lt; 4 (“moderate pollution” category) in most of the horizons and aggregate sizes. Grain size mass loading (GSF_Hg) revealed that finer fractions had a higher Hg loading than their mass fractions, with a notable contribution of fine silt which made up &gt; 50% of Hg_T in Bh and Bs horizons. The potential ecological risk index (PERI_Hg) increased as the aggregate size decreased, with the highest values in the illuvial horizons (45-903) and lowest in the E horizon (3-363). Heterogeneous distribution of Hg in the soil aggregate size fractions must be considered for Hg determination for purposes such as critical loads, background values or environmental risk indices. In addition, Hg accumulation in finer aggregates could be of concern due to its potential mobility in forest soils, either transferred by leaching to groundwater and freshwaters or mobilized by runoff in surface horizons.