Fine Sand Fraction Research Articles

Pelagic-benthic coupling on the shelf of the northern Bering and Chukchi Seas. II. Benthic community structure

Benthic fauna abundance, biomass and diversity were investigated in the northern Bering and Chukchi Seas to determine factors influencing faunal distribution in this polar region. The hypothesis tested whether sebmen t grain size and water mass charactenstics, such as organic carbon supply to the benthos and temperature, are regulating factors in benthic community structure. Benthic communities under the cold, highly productive (-250 to 300 g C m-2 yr-') Bering Shelf-Anadyr Water (BSAW) are dominated by a high biomass of amphipods (F. Ampeliscidae and F. Isaeidae) and bivalves (F. Nuculidae and F. T e l l ~ n ~ d a e ) . A diverse, low biomass fauna exists in benthic communities under the warmer, less productive (-50 g C m-' yr-l) Alaska Coastal Water (ACW), includ~ng amphipods (F. Isaeidae and F. Ampeliscidae), bivalves (F Tellinidae and F. Thyasiridae), polychaetes (F. Maldanidae and Nephtyidae), and sand dollars (F. Echinarachniidae). Faunal diversities are lowest for stations under BSAW, characterized by high food supply and moderately homogeneous (well-sorted), sandy sediments. Highest diversities occur at stations in ACW, which is characterized by low food supply and a more heterogeneous (poorly-sorted) mixture of silt and clay, sand and gravel sediments. Faunal diversity also increased to the north in the Chukchi Sea, where food availability in the bottom water and surface sediments was greater and more heterogeneous, finer-grain sediments occur. The findings indicate that sediment heterogeneity, silt and clay fractions, and temperature are major regulating factors on benthic community structure, with each positively influencing faunal diversity. Lower diversity was correlated to an increase in fine sand fractions. Food supply, both in the bottom water and surface sediments, has a more variable Influence on benthic community structure, although i t has a direct posit~ve influence on benthic biomass.

Major benthic communities of the south-west lagoon of New Caledonia

A quantitative survey of the macrobenthos in the south-west lagoon of New Caledonia was carried out at 35 stations, sampled both with a grab and by diving. The stations were classified by multivariate analysis on the basis of their floral and faunal composition and three major communities, corresponding to muddy bottoms, grey sand bottoms and white sand bottoms, were identified. At the same time, grain-size analysis performed on sediment samples at each station enabled us to identify the most discriminating grain-size parameters for each type of bottom. Classification of stations with respect to the mud fraction and the very fine + fine sand fraction reproduced the groups identified on the basis of purely taxonomic criteria. Application of these results to the available sedimentological data allowed the main benthic communities in the investigation area to be mapped.

Potential for Buffering of Acidic Precipitation by Mineral Weathering in a Forested Entisol

AbstractBulk precipitation, soil‐water, and groundwater chemistry were monitored at Round Lake, a small, forested catchment receiving acidic precipitation (pH 4.6) in northwestern Wisconsin. The groundwater basin retained H ion and released nonhydrolyzable cations (NHC = Ca, Mg, Na, K) and Si. The percentages of plagioclase feldspar, hornblende, olivine, and augite increased with depth in soils from the catchment; quartz, orthoclase feldspar, and weathered mica decreased with depth. Thermodynamic stability indices estimated from water‐quality and mineralogic data, and from the WATEQF chemical speciation model indicate that the soil‐water and groundwater are undersaturated with respect to hornblende, chlorite, olivine, augite, plagioclase, and orthoclase feldspars and that these minerals may be undergoing dissolution. Minimally disturbed soil cores were leached with dilute H2SO4 and distilled water (pH 3.0 to 5.7). When the pH of the extracting solution was ≥4.5, Ca was released in the greatest amounts, followed by Si, Mg, K, Na, and Al. This ranking is similar to that for cations in groundwater. Leaching with a pH 3.0 solution released Si in the greatest amounts from the C horizon, followed by the Bw2, Bw1, and A + B/E horizons. This trend parallels the depth distribution of weatherable minerals in the very fine sand fraction. Results from the laboratory leaching study confirm the chemical modeling studies, indicating that mineral weathering (hydrolysis) can contribute to buffering within the groundwater basin at Round Lake.

Penetration resistance of fine sandy apedal soils as affected by relative bulk density, water content and texture

The major physical properties that control the penetration resistance of soils are the degree of soil compaction, water content and particle size distribution. Sandy soils with well-sorted particle size distributions and low cohesivity compact and consolidate easily under pressure. Six soil samples with predominantly fine sand fractions and clay contents varying between 8 and 20% silt plus clay were selected to determine the relationships among penetration resistance, relative bulk density and water content. Penetration resistance was measured using a constant-rate penetrometer. The relative bulk density given by the ratio between bulk density and maximum ASTM bulk density was used as the parameter representing the level of compaction. Curves relating penetration resistance to water content at different relative bulk densities and to relative bulk density at different water contents were determined for each soil. All the variables were incorporated into a multiple regression equation. This equation can be...

Landscape Position and Particle‐size Effects on Soil Phosphorus Distributions

AbstractThe objectives of this study were to investigate the effects of pedogenesis and landscape position on (i) the association of total P with particle‐size content and with various particle‐size separates, (ii) relative abundance of different forms of P, and (iii) P distributions between horizons and soils representing five landscape positions on an Ultisol hillslope in northwest Florida. Total‐P content in soil seemed to be directly associated with the amount of clay in the lower landscape positions. This association may be the result of the activity of the mineralogy dominant in the clay fraction. Total P in the clay and P‐fraction values indicated that some P had been redistributed between horizons and possibly between soils on the landscape. Coarser sands commonly had more total P than finer sand fractions. The sand fractions were composed primarily of quartz and ironstone. The amount of ironstone in the sand fraction was probably responsible for the amount of total P. Among P fractions, a large portion of P was in the residual form, especially in lower horizons, implying that the soils are intensely weathered or developed from parent materials that contained considerable residual‐P, which was occluded in sesquioxides prior to deposition of the sediments. The P forms were present in the order of decreasing abundance as residual‐P, Fe‐P, Al‐P, and Ca‐P. Water‐soluble P was not detected in any of the soils.

Sand‐sized Kaolinized Feldspar Pseudomorphs in a California Humult

AbstractDeeply weathered soils forming on andesitic mudflows are common in the foothills of the Sierra Nevada of California. Many of these soils (Humults) have oxidic mineralogy based on extractable Fe and gibbsite detected by x‐ray diffraction and differential thermal analysis. Thermal analysis and differential thermal analysis of whole soil samples reveal kaolin and gibbsite percentages greater than clay percentages obtained by particle‐size analysis. X‐ray diffractometry of the fine (0.1–0.25 mm) and coarse (0.5–1.0 mm) sands shows fractions dominated by kaolin throughout the profile. Halloysite predominates in the saprolite; kaolinite increases in abundance toward the soil surface. Gibbsite is present in the surface and upper argillic horizons. Observation of the fine sand fraction with a polarizing light microscope reveals highly weathered feldspar grains with very low birefringence. Scanning electron micrographs of coarse and fine sands show pseudomorphic replacement of feldspar by halloysite resulting in discrete sand‐sized grains wherein simple albite twins are preserved. Energy dispersive analysis by x‐ray of unweathered feldspars produces Si/Al count ratios of 6:1 and indicates the presence of K and Ca in the feldspar structure. Analysis of the surfaces and interiors of kaolinized feldspar grains shows Si/Al count ratios of 2:1 and an absence of K and Ca, demonstrating that the feldspars are completely altered to kaolin by desilication and loss of hydrolyzable cations. The alteration appears to be crystallographically controlled because the original feldspar crystal morphology is preserved.

Soil Genesis in a Developmental Sequence of Soils Formed in Sillimanite Mica Schist Residuum

AbstractDystochrepts formed in mica schist residuum occur on steeply sloping sideslopes, whereas associated Hapludults are found on gently sloping ridgetops in the Piedmont province of Georgia. In this study, morphological, physical, chemical, and mineralogical properties of Dystrochrepts and associated Hapludults were examined to determine the influence of weathering intensity differences within the pedon and across the Dystrochrept → Hapludult developmental sequence. More intense weathering at the soil surface has resulted in higher exchangeable Al contents, lower pH values, and a relative accumulation of total Si, quartz, sillimanite, opaque minerals, and clay‐sized mica and vermiculite. In contrast, biotite was more abundant at depth. Total Al was closely related to clay distribution within the pedon. Less intense weathering in the Dystrochrepts, apparently related to shorter development time, has led to coarser textured sola with higher base saturations, higher total Mg, K, and Na contents, and a greater abundance of fine sand‐sized biotite and K‐feldspar. Quartz in the fine sand fraction was concentrated in the Hapludult. Kaolinite was the dominant clay mineral in the Hapludult. Regularly interstratified mica‐vermiculite was identified in subsurface horizons of the Dystrochrept and is believed to be a transitory intermediate in the transformation of mica to vermiculite.

累積火山灰断面腐植層中の植物けい酸体による年代推定法 Ｉ 蓄積年率からの推定

Plant opals (PO) contained in the buried humic soils of volcanic ash profile are known to be mainly derived from grass. Thus, if we assume that PO in the soils is supplied at a constant rate from the grass and estimate the rate, then we can determine the ages of the soils from PO contents divided by the yearly supply or the accumulating rate of PO. The age here used does not mean the time passed since the soil formation but the period needed just for the formation of the soil itself.1. Two methods for determining PO content in the soil were examined:(1) Direct isolation of PO from the silt and fine sand fractions of the soil by floatation on a heavy liquid (2.2-2.3 sp. gr.). (2) Counting PO particles in the fine sand fraction under the microscope and changing the count % into the weight % by a previously determined exchange rate.2. Three methods for determining the accumulation rate of PO were compared:(1) Direct isolation of PO from plant tissues by wet or dry ashing followed by separation with a sedimentation method. (2) Counting PO particles in a weighed ash under microscope and changing the count % to the weight % of the ash by a preliminarily determined exchange rate. Methods (1) and (2) should be connected with the estimation of the annual production of grass species which can be obtained from ecological studies. (3) Determining the PO content in soil of known age by method 1-(1). The PO content divided by the age gives a mean annual PO accumulation rate.The values of the accumulation rates deduced by the three methods were concentrated in a narrow range of 0.36-0.47mg/cm2/yr when a few anomalous values were excluded.3. In two profiles, Yubunebara and Tanukiko at the foot of Mt. Fuji, both being composed of alternation of tephras and buried humic soils, the ages of the soils were determined using the method 1-(1) and accumulation rates of PO, 0.36 and 0.47mg/cm2/yr. If we assume that the ages thus obtained could approximately show the periods during the formation of the soils in the past and that the period of deposition of tephras was extremely shorter than the time needed for the formation of the whole profile, then the sum of the ages of the soils should roughly be equal to the age of the whole profile. Comparison of the former with the latter obtained by 14C dating showed that the coincidence was good in the period of less than 5, 000-6, 000y.B.P.

Latossolos da bacia do ribeirão do lobo (Brotas - Itirapina, SP): II. Mineralogia

Quatro perfis de Latossolos distróficos da bacia do ribeirão do Lobo, localizada entre os municípios de Brotas, Itirapina, São Carlos, foram amostrados e estudados através da fração areia muito fina: mineralogia do resíduo pesado e arredondamento da fração leve. A finalidade do trabalho foi estabelecer parâmetros para estudo da gênese dos solos, uniformidade do material de origem e semelhança entre perfis, constatadas previamente pela morfologia. Quantitativamente, os quatro perfis se assemelham exibindo composição mineralógica simples que, aliada á estabilidade química dos minerais, confere aos solos um caráter de elevada maturidade mineralógica, indicando esgotamento total das reservas de nutrientes minerais das plantas. Quantitativamente, um dos perfis distinguiu-se pelo maior teor de minerais pesados, 3 a 4 vezes superior aos demais. Na sua grande maioria, são minerais opacos, indicando uma importante contribuição de basaltos que afloram próximo a este perfil. A composição mineralógica denuncia os arenitos da Formação Botucatu e basaltos da Formação Serra Geral ambos do Jurássico-cretáceo, como material de origem, retrabalhados, para formar esses latossolos. A relação zirconita/turmalina mostra grande variação em dois perfis. Entretanto outros parâmetros como arredondamento, granulometria e variações nos tipos de zirconita e turmalina não confirmam nem sugerem a presença de descontinuídades litológicas, mas uma grande uniformidade dos perfis.

Relationship Between Exchangeable and Total Magnesium in Pennsylvania Soils

AbstractThe particle size distribution, total and exchangeable Mg, and mineralogical compositions were determined on eight well-drained, noncultivated subsoils from Pennsylvania. No correlation was found between the clay content and total Mg (r =.29), or between the clay content and exchangeable Mg (r =.35). Serpentine, talc, and hypersthene were found in the very fine sand and silt fractions of soils having relatively high exchangeable Mg. Mica and 14-Å clay minerals were the only Mg-bearing minerals noted in the same fractions of soils having relatively low exchangeable Mg. Of the Mg-bearing clay minerals found in the clay fractions (smectite, vermiculite, chlorite, illite, and interstratified chlorite/vermiculite), only smectite decreased as the exchangeable Mg in the soils decreased. Two distinctly different distribution patterns of Mg were found for soils having relatively high and low exchangeable Mg. The former soils showed a decreasing Mg content as the particle size decreased, and the latter soils showed the opposite. Exchangeable Mg correlated significantly with the amount of Mg in whole soil, sand, and silt, but not with the amount of Mg in the clay, an indication that sand and silt but not clay were the important sources of exchangeable Mg in these soils.

ZINC FIXING CAPACITY OF RICE SOILS.

An incubation study with labelled 65Zn was conducted to study the pattern of release and fixation of added 65Zn in 15 representative rice soils of Tamil Nadu at 10 levels of added 65Zn viz., 0. 2.5, 5.0. 7.5, 10, 20, 30, 40, 50 and 100/u/g of soil. The result showed that the DTPA extractable 65Zn was a function of added 65Zn and the rate of extractability was more in coarse textured soils than in clayey solls. The rate of extractability of added 65za had positive correlations with fine and coarse sand fractions and negative relationships with clay and organic carbon content of the soils. The Zn, fixing capacity revealed an exactly opposite trend to that of Zn extractability indicating higher Zn fixing capacity in clayey soils than the sandy loam soils.

Estimating relative ages from iron-oxide/total-iron ratios of soils in the western Po Valley, Italy

Nineteen samples were collected from deeper layers of as many terraces forming agesequences in five basins. Most samples were collected at depths of 1 m or more, with some below 3 m. Soils at the sample sites were tentatively identified as Alfisols, Entisols or Inceptisols. Total amounts of iron and the amounts extractable by dithionite and by oxalate were determined for the 19 samples. Redness ratings were calculated from sample colors and related to amounts of extractable iron by regression. Mineralogies of the fine sand, silt and clay fractions were also determined. The percentage of the total iron (Fe t) extracted by dithionite (Fe d) minus the amount extracted by oxalate (Fe o) increased gradually with ages of the terraces, which range from early Middle Pleistocene to Upper Pleistocene-Holocene. These percentages are independent of the total amounts of iron in the samples and of the general lithology of a basin. Such ratios thus promise to be useful in estimating relative ages, especially where time-sequences exist. Mineralogies of the samples were consistent with relative ages of terraces as estimated from the ratios of iron in different forms. So were the redness ratings. The regression of extracted iron on redness ratings suggests that colors can be used as preliminary field indicators of relative ages of terraces without time-sequences.

Properties of Australian fly ashes relevant to their agronomic utilization

Of the 13 fly ashes from Australian power stations, all were dominated by both amorphous and crystalline aluminosilicates and quartz, and these were associated with minor amounts of Fe oxides, lesser amounts of Ca, Mg, Na, K, Ti and P oxides, and variable levels of incompletely combusted C. The ashes consisted of particles predominantly in the silt plus fine sand fraction (67-98%), and electron microscopy revealed that ash matrices consisted of glassy spherical particles and less regularly shaped spongy particles. The available water capacity was high and varied from 27 to 105% with 11 of the 13 samples having values > 40%. Twelve of the 13 ashes were alkaline to strongly alkaline (pH range 8.0-12.8). Soluble salt levels were related to the coal source, and electrical conductivity of the saturation extracts (ECse) varied from 0.63 to 7.0 mS cm -1 for 11 of the samples; two ashes produced from brown coal had ECse values of 46.0 and 55.0 mS cm-1. The nutritional status of the ashes was assessed on samples leached with water to reduce the soluble salts to equilibrium levels. The ashes contained negligible amounts of N, but their P status was variable. The amounts of NH4OAc-extractable Ca and Mg were generally high in most samples and were considered more than adequate for most plant species; however, NH4OAc-extractable K values were generally low. Adequate levels of sulfate-S existed in 12 of the 13 samples, and levels of DTPAextractable Cu, Zn, Mn and Fe were high when compared with published critical values. Most of the unleached samples contained potentially toxic levels of B. The results are discussed with reference to the establishment of vegetation on ash dumps and to the use of fly ash in ameliorating the properties of soils.

Mineralogy, Genesis, and Sources of Surficial Sediments in the Kuwait Marine Environment, Northern Arabian Gulf

ABSTRACT This article shows the results of a detailed mineralogical investigation of the Recent bottom of the Arabian Gulf bordering Kuwait. The main objective of this study is to determine the sources of the study area and to define their relative importance. Heavy and light minerals in the very fine sand and coarse silt fractions were estimated microscopically. These size fractions were selected for heavy mineral analysis because they represent a large proportion of the total budget and their results will be readily comparable with the published results of the potential sources (wind-bore and river-bore sediments). X-ray diffraction was utilized to determine the mineralogical composition of the whole sediment and the mineral constituents of the clay-size fraction The light minerals are chiefly composed of carbonates, quartz, and feldspars with lesser quantities of chert, gypsum, and mica. Dolomite was found to be the most common heavy mineral followed by amphiboles, pyroxenes, mica, opaques, and epidotes. Aragonite, garnet, zircon, and tourmaline were recorded in lesser quantities. The gross mineralogy is biased toward carbonates, clay minerals, and a small amount of quartz and feldspars. Carbonates are represented by low-Mg calcite, dolomite, high-Mg calcite, and aragonite. Low-Mg calcite and dolomite were found to be the most common carbonate species. They are thought to be of detrital origin carried into the study area primarily as dust fallout. Clay minerals are composed of illite, palygorskite, an illite-montmorillonite mixed layer, kaolinite, and chlorite. Illite and palygorskite are the most important clay minerals, forming more than 70% of the clay-size fraction. It is suggested the palygorskite is most probably developed as a diagenetic mineral in the lower Mesopotamian plain and transported to the study area by eolian processes. Other clay minerals are thought to be of detrital origin derived from many sources. The results show that the dust storms which originate in southern Iraq and Kuwait by the prevailing northwestern wind are a major contributor to the total budget, particularly with respect to dolomite, palygorskite, and low-Mg calcite. Other sources which have impact upon the study area are local coastal sediment, direct precipitation from Gulf water, Shatt-al-'Arab river sediments, and the submerged ancient off Kuwait.

Provenance of the Plio-Pleistocene sediments in the East Turkana Basin, northern Kenya

The fossiliferous Plio-Pleistocene fluvio-lacustrine sediments in the East Turkana Basin of northern Kenya were derived from two major source areas: (1) Ethiopian plutonic igneous and metamorphic rocks of the Precambrian basement and (2) Kenyan Cenozoic volcanic rocks. Interpretations of provenance are based on heavy mineral analyses of 123 sandstone samples and data collected during stratigraphic studies. Thirty heavy minerals have been identified in the East Turkana Basin and commonly compose 5–20% of the fine sand fraction which is compositionally representative of the entire heavy fraction. Morphological properties of the grains, geometric form, roundness and surface textures indicate that the mineral distribution primarily reflects source rocks lithology. Seven distinct heavy mineral associations have been distinguished which are grouped into two suites: a plutonic suite dominated by blue-green hornblende, apatite, sphene, garnet and clinozoisite-epidote and a volcanic suite dominated by augite and opaque minerals. Both suites form mappable heavy mineral provinces. Plutonic provinces occur throughout the basin interior, and volcanic provinces are distributed along the basin margin in association with alluvial fan deposits. Sedimentation began in the Pliocene following formation of the Turkana half-graben and the Chew Bahir (Stefanie) graben. The sediments are predominantly first cycle with limited reworking in fluvial and lacustrine environments. Two perennial stream systems transported plutonic detritus to the basin interior from basement rocks of high relief exposed to the northeast in the Chew Bahir basin and eastern Omo valley. Short ephemeral streams transported volcanic detritus to alluvial fans along the basin margins from volcanic rocks of low relief which border the basin to the east and south.

Origin of Red Clay over Dolomite in the Loess‐Covered Wisconsin Driftless Uplands

AbstractRed clays associated with Prairie du Chien and Sinnipee (Galena) dolomites and loess were studied stratigraphically and geomorphically at 10 locations. The clay content (< 2 µm, 82 ± 9.1%; < 0.2 µm, 70 ± 10.4%, n = 15) relative to the overlying loess (< 2 µm, 28 ± 4.4%; < 0.2 µm, 16 ± 4.9, n = 4) and the dolomite insolubles (< 2 µm, 47 ± 11%; < 0.2 µm, 34 ± 9.6%, n = 7) indicate fine clay enrichment. Smectite‐rich oriented clay coatings on dolomite sands suggest illuviation. Undisturbed chertlines from dolomite through red clay bodies necessitate a volume‐for‐volume replacement. Periglacial activity during the Wisconsinan frequently produced loess (i), over a mixed zone of loess and red clay (ii), over in‐situ red clay (iii), and dolomite (iv). For the 1‐to 10µm quartz; euhedral grains indicated by x‐ray diffraction I(100)/(101) = 0.23, 0.54, 1.02, 0.70, respectively; nine trace element contents = 2.15 ± 0.40, 1.61 ± 0.18, 0.78 ± 0.10 relative to dolomite (1.0); and oxygen isotopes expressed as δ18O = 18.6, 19.7, 26.9, 26.4%. The values for the mixed zone (ii) fall between those for the loess (i) and insitu red clay (iii). Optical data for the morphology of the fine sand fractions (50–250 µm) were corroborative. The silt and sand of in‐situ red clay (protected in karst depressions and by chert lag gravels) are from the dolomite.

The Influence of Local Bedrock: An Important Consideration in the Interpretation of Textural and Mineralogic Analyses of Till

ABSTRACT Bedrock produces variations in texture and composition of tills not only on a regional scale but also on a local one. Bedrock influence is evident in Wisconsinan tills in an area as small as a township in the Allegheny Plateau of northeastern Ohio. Generally till sheets of the Plateau fine upward with decreasing age. Within the Mogadore and Northampton tills, samples from borings terminating in sandstone bedrock on the upland contain significantly more sand and have higher quartz-feldspar ratios than those from the same tills overlying lacustrine silts and clays in the valley. On the upland samples from the Northampton till, overlying sandstone contains slightly more sand than that from the same till overlying shale and siltstone. However, quartz-feldspar ratios increase down ice from sandstone bedrock highs. A few kilometers of transport may have been required for ice to crush plucked sandstone fragments which added more quartz to the fine sand fraction of the Northampton till. Geologists mapping tills using soil associations should be aware of textural and lithological variations produced by local bedrock.

A study of the sorptive properties of surface sediments in a landfill project region

Surface sediment samples were collected from 3 regions of a river island (a landfill area, a foreshore zone and a swamp segment) and the adsorptive properties of the - 180 μm and “clay” fractions were examined by studying the effects of concentration, pH and complex formation on the uptake of copper or zinc ions. The fine sand fraction contained basic material which raised the pH of aqueous suspensions to ∼8, at which value near total precipitation of added metal ions occurred. Uptake by the clay fractions (at pH 5) conformed to a Langmuir type adsorption isotherm, yielding parameters of similar order to values reported for soil clays and clay minerals. Using constant initial concentrations the amount of Cu or Zn adsorbed increased with pH until the threshold for precipitation ( ∼7) was exceeded. Both uptake and precipitation were inhibited in the presence of ligands which formed stable anionic complexes (e.g. NTA, EDTA, citric acid). The foreshore and swamp samples contained organic matter which retained part of the added metal ion as a solute in alkaline media. Treatment of these clay fractions with hydrogen peroxide did not destroy all the organic content, but it did change adsorptive behaviour. Extraction studies with 0.01 M nitric acid, 0.1 M oxalic acid, 0.1 M ammonium acetate, and 0.01 M EDTA showed that both the clay fractions and fine sands contained measurable amounts (0.05–40 mmol kg −1) of the metal ions Pb, Cd, Cu and Zn, but because of the basic nature of the sediments, adjacent waters had solution levels which remain well within acceptable limits. The overall results have been used to predict factors likely to promote formation of high leachate levels.

Mineralogy of the Recent intertidal muddy sediments of Kuwait — Arabian Gulf

The coast of the State of Kuwait is characterized by a relatively wide intertidal flat area. At the north, where it is close to Shatt-al-Arab estuary, the intertidal sediments are mainly fluviomarine, while open marine sediments dominate the southern intertidal flat area. Samples were examined from the intertidal zone of deposition from the fluviomarine and open marine environments. The sediments consist mainly of carbonate minerals (low-Mg calcite, high-Mg calcite, aragonite and dolomite), quartz, feldspars, clay minerals and heavy minerals. The mineralogy of the clay fractions of the sediments is dominated by illite, mixed-layer illite—montmorillonite, montmorillonite, chlorite, kaolinite and palygorskite with only minor amounts of quartz. Heavy minerals are concentrated in the very fine sand fraction and are dominated by opaque minerals, amphiboles, pyroxenes, epidotes, garnet, kyanite and sillimanite. Zircon, tourmaline, andalusite, staurolite and rutile are present in subordinate amounts. Three main sources are suggested for the intertidal sediments of Kuwait: (a) Shatt-al-Arab fluviatile deposits, (b) aeolian dust fallout, and (c) direct chemical and biogenic precipitation from the Gulf water.

Sediment dispersal from Vogelsberg Basalt, Hessen, West Germany

Volcanic detritus in sand size stream sediment spreading outward from Vogelsberg extrusive and hypabyssal rocks decreases in abundance from percentages exceeding 90 % to less than 5 % within 20 km of the source area. The rapid decrease results largely from dilution of the stream sediment resulting from disintegration of friable Bunter Sandstone on the plains surrounding the crystalline rocks. The effect is more pronounced in the fine sand fraction of the stream sediment because the Bunter sand is fine grained.