Iron Concretions Research Articles

Backbeach Deflation Aprons: Morphology and Sedimentology

Backbeach deflation aprons are heterogeneous, coarse clastic deposits associated with active transverse dune fields. The apron comprises variously angular, rounded, fractured, cracked, polished, and ventifacted clasts of bedrock (local and exotic), beachrock, and bioherm fragments (coral and worm reef). Terrestrial and anthropogenic clasts (from archeological sites, deflated dunes, flotsam, and shipwrecks) are also present. The unit forms as a lag deposit on top of a gently sloping (ca. 0.008), planar sandy deflation surface and is typically only one clast thick. It is up to 100 m wide and extends for tens of kilometers along the coast. It is replaced landward by a steep (ca. 0.1) deflated soil surface armored with a layer of iron concretions. Backbeach deflation aprons are compound deposits that result from marine storm, eolian, and human activity since the mid- Holocene. The depositional model proposed involves periodic storm deposition of coarse clasts (of beachrock, bedrock, and biogenic origin) and flotsam (shipwreck and other floating debris) on the backbeach or dunes. Some clasts are deposited directly into interdune depressions and enter the deflation plain immediately. Others are deposited initially on dune surfaces. Dune migration results in winnowing of the storm-deposited coarse clasts (together with rhizoliths and any other coarse material in the dune) until they come to rest on the deflation surface. The lag deposit is subsequently buried and uncovered multiple times by dune migration, during which time it is exposed to polishing and subaerial weathering. Consequently, the lag comprises a variety of materials that reflect both storm and eolian processes. The clasts exhibit variable degrees of rounding, polishing, and ventification according to how long they have been in the deposit.Backbeach deflation aprons are characteristic of sandy beaches along approximately 475 km (. 10% of the total length) of the South African east coast. They develop in association with large-scale transverse dunefields on the backbeach, which in turn depend on reversing shore-parallel winds and high sediment abundance. The variable degree of polishing and weathering, planar surface, low elevation, and back-beach location along extensive shoreline distances distinguish backbeach deflation aprons from tsunami or marine storm deposits.

Pedogenic, lithogenic – or anthropogenic origin of Cr, Ni and V in soils near a petrochemical facility in Southeast Mexico

Abstract Large Cr, V and Ni contents were found in soils near Cd. Pemex in Tabasco, Mexico. Their origin was hypothesized to be either anthropogenic, derived from emissions of a petrochemical facility, or lithogenic, from the volcanic ash deposited by the “El Chichon” volcano, or accumulated residually by pedogenesis. We proved these possible origins by analyzing composite samples taken from the soil surface at different distances from the facility as well as samples from two soil profiles located close and far away from the facility within the same land unit, i.e. Acrisols developed on Miocene marine terraces. The sites located far away from the facility were closer to the volcano, and therefore supposedly more affected by the ash deposition. All samples were analyzed for their total metal content and profile samples for their different metal fractions. Additionally the soil microstructure, mineralogy and elemental composition of particular pedogenic features were studied in thin sections from the different soil horizons. Results evidenced that the emissions from the petrochemical facility do not contribute significantly to the total concentration of Cr, Ni and V in the adjacent soils. Nickel was found in the soil in concentrations between 39 and 318 mg kg− 1; particularly large contents of this element were associated to volcanic ash additions visualized in the thin sections. Micromorphological analyses of nodule like pebbles found in both profiles evidenced that these features are laterite fragments transported from preexisting soil. The matrix of these fragments is enriched with Cr and V (3000–7000 mg kg− 1 of Cr, and 1000–3000 mg kg− 1 V), and these elements are actually translocated into relatively newly formed iron concretions found within these laterites and reaching concentrations of up to 10,000–17,000 mg kg− 1 Cr. The fractionation showed that Cr and V were dominantly associated to crystalline iron oxides and to the residual fraction; water extractable, exchangeable and EDTA extractable fractions were below detection limits ( We conclude that the studied elements are of lithogenic and pedogenic origin; they were enriched dominantly through residual accumulation by lateritization, probably of mesozoic ultramafic rocks from the margins of the Caribbean plate, and later fragmented and transported by water to the present location; only Ni was also partly added by the recent volcanic activity.

Biomineralization and magnetic and thermal properties of the iron concretion from the laterite bauxite deposit of Bao Lok, South Vietnam

Biomineralization and magnetic and thermal properties of the iron concretion from the laterite bauxite deposit of Bao Lok, South Vietnam

Enrichment processes of arsenic in oxidic sedimentary rocks – From geochemical and genetic characterization to potential mobility

Sedimentary marine iron ores of Jurassic age and Tertiary marine sandy sediments containing iron hydroxides concretions have been sampled from boreholes and outcrops in two study areas in Germany to examine iron and arsenic accumulation processes. Samples were analyzed for bulk rock geochemistry (INAA/ICP-OES), quantitative mineralogy (XRD with Rietveld analysis), element distribution (electron microprobe) and arsenic fractionation (sequential extraction). Bulk Jurassic ores contain an average arsenic content of 123 μg g −1 hosted in mainly goethite ooids which slowly formed in times of condensed sedimentation. Enrichment occurred syndepositionally and is therefore characterized as primary. Iron concretions in Tertiary sediments mainly consist of goethite and yield arsenic up to 1860 μg g −1. The accumulation process is secondary as it took place in the course of oxidation of the originally reduced marine sediments under terrestrial conditions, leading to element redistribution and local enrichment in the near-surface part. The scale of enrichment was assessed calculating Enrichment Factors, indicating that arsenic accumulation was favoured over other potential contaminants. In spite of higher bulk arsenic contents in the oxidic rocks, the mainly pyrite-hosted As pool within the reduced deeper part of the Tertiary sediments is shown to have a higher potential for remobilization and creation of elevated arsenic concentrations in groundwater.

Magnetic susceptibility in surface sediments in the southern South China Sea and its implication for sub-sea methane venting

In order to understand the characteristics of magnetic variability and their possible implication for sub-sea methane venting, magnetic susceptibility (MS) of 145 surface sediment samples from the southern South China Sea (SCS) was investigated. Magnetic particles extracted from 20 representative samples were also examined for their mineral, chemical compositions and micromorphology. Results indicate that MS values range between -7.73x10(-8) and 45.06x10(-8) m(3)/kg. The high MS zones occur at some hydrocarbon-bearing basins and along main tectonic zones, and low ones are distributed mainly within the river delta or along continental shelves. Iron concretions and manganese concretions are not main contributors for high MS values in sediments, while authigenic iron sulphide minerals are possibly responsible for the MS enhancement. This phenomenon is suspected to be produced by the reducing environment where the high upward venting methane beneath the seafloor reacts with seawater sulfate, resulting in seep precipitation of highly susceptible intermediate mineral pyrrhotite, greigite and paramagnetic pyrite. It suggests that MS variability is possibly one of the geochemical indicators for mapping sub-sea zones of methane venting in the southern SCS.

Mechanism of arsenic sorption onto laterite iron concretions

We investigated arsenic sorption mechanisms onto laterite iron concretions (LIC) using electrophoretic mobility (EM) measurements, attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and surface complexation modeling. Competitive sorption experiments were also conducted in the presence of phosphate and sulfate, as these compounds may interfere with arsenic sorption in waters from sulfide mining waste and ore stock piles. Electrophoretic mobility measurement results indicate that arsenic sorption lowered the point of zero charge of the LIC at pH 3–10. This observation implies both As (III) and As (V) form inner-sphere complexes on the LIC. The FTIR studies suggest that both As (III) and As (V) also form inner-sphere complexes with LIC. Arsenic sorption onto LIC was modeled by surface complexation modeling using the generalized composite approach. The model assumes that all mineral phases contributing to sorption are represented by one type of surface group. Adsorption edge experimental data was used to verify model performance. Arsenic (III) sorption onto LIC, which is markedly reduced by increasing ionic strength, was modeled using the triple-layer model, while As (V) sorption onto LIC was modeled using both the diffuse and the triple-layer models. The presence of phosphate reduces the amount of both As (V) and As (III) sorbed, while sulfate only reduces adsorption of As (III).

Aeolian activity at a giant sandstone weathering pit in arid south-central Utah

Aeolian abrasional, depositional and deflational features indicate exceptionally strong southwesterly winds in a giant sandstone weathering pit in Grand Staircase Escalante Monument, about 22 km southeast of Escalante, Utah. The 60 m wide, 5–20 m deep pit has developed near the summit of a broad, barren 160-m-high dome on the Lower Jurassic Navajo Sandstone. Unlike other giant weathering pits (10–30 m diameter) in the region, the bedrock floor of this pit is undulatory, and there is a cylindrical, 10-m-high rock pedestal in the centre of the pit. An active dune surrounds the central pedestal and at times has as much as 8 m of local relief. The dune shifts considerably over brief (<1 year) periods of time. Fine-grained (<250 µm) dunal sand on the pit floor is periodically removed by deflation, leaving coarser sand (>250 µm) trapped in the pit. Dunal sand is typically derived from external sources (other than the pit walls and floor). Centimetre to metre-scale abrasional features such as grooves, flutes and dedos occur on the bedrock walls and floor of the pit. These dedos and other streamlined aeolian sculpted host-rock features occur in clusters and typically form in the lee of iron concretions. The dedos are similar to the controversial stalked blueberries on Mars. Above the western rim of the pit there is a 29-m-long, 5-m-wide aeolian groove with a fluted bedrock floor. A 1·2-km-long bedrock valley descends to the southwest from the pit and groove, amplifying southwesterly winds. Data from hand-held anemometers suggest that southwesterly winds can be accelerated 200–300 per cent or more by local topography. Copyright © 2008 John Wiley and Sons, Ltd.

Mechanism of arsenic sorption onto laterite iron concretions from Prestea, Ghana

Mechanism of arsenic sorption onto laterite iron concretions from Prestea, Ghana

Snowbeds on Silicate Rocks in the Upper Engadine (Central Alps, Switzerland)—Pedogenesis and Interactions among Soil, Vegetation, and Snow Cover

The pedogenesis and interactions among soil, vegetation, and snow cover of four alpine snowbeds on silicate rocks in the Upper Engadine (Central Alps, Switzerland) were investigated. The long-lasting snow cover of snowbeds causes differences in pedogenesis and soil properties compared to adjacent alpine sward. Because of the drainage characteristics of the silicate parent material, pedogenesis of snowbeds varies. On well-drained parent material, percolating meltwater favors podzolization during snowmelt. On less permeable parent material, meltwater causes temporarily water-logged conditions. Thus, the snowbed soils show redoximorphic features such as iron concretions. Snowbed soils are classified as Inceptisols or Entisols. A more detailed differentiation is only possible at the soil family level. Outside the snowbeds, moder humus forms (Rhizic Leptomoder, Rhizic Mullmoder) are common, whereas inside the snowbeds, mull humus forms (Rhizomull) as well as moder humus forms (Leptomoder) occur.

CHARACTERIZATION AND MICROMORPHOLOGICAL OBSERVATIONS OF Fe/Mn AND SILICATE MINERALS IN OKINAWAN AND BRAZILIAN SOILS

The study was conducted to characterize Fe/Mn, layer silicate minerals in the concretions of Okinawan and Brazilian soils and investigated their micromorphological features. Concretions and soil samples of Okinawa (Luvisol) and Miyako (Cambisol) Islands were developed from Ryukyus limestone, while Brazilian samples of Cambisol and Ferralsol were originated from sandstone rock. Fe/Mn minerals in both experimental sites were characterized using the successive selective dissolution procedure followed by the treatments of sodium hydroxide, hydroxylamine hydrochloride (HAHC) at 25°C and 60°C and dithionite-citrate-bicarbonate (DCB) in combination with X-ray diffraction technique (XRD). Elemental composition and micromorphological information on Fe/Mn minerals and their associated layer silicates were investigated using inductive coupled plasma atomic emission spectrometry (ICP-AES) and scanning electron microscopic (SEM) techniques respectively. XRD and SEM techniques were successfully able to investigate and distinguish the major minerals in Okinawan and Brazilianl samples were kaolinite (Ka), gibbsite (Gb), illite, quartz, and goethite (Ge), while the rear natural minerals of birnessite and smectite were investigated from the samples of Cambisol in Miyako and Luvisol in Okinawa respectively. Elemental analysis also confirmed that Brazilian samples did not contain any Mn oxide minerals. Detailed micromorphology of minerals exhibited that poorly crystalline birnessite has a blade or plate-like habit, which forms globular aggregates inside veins and cavities and widely spread smectite mineral in Okinawan samples showed a honeycombed polygonal pattern. Well-developed hexagonal kaolinite and gibbsite crystallites were also observed in Okinawan samples, while the book-like structure of kaolinite crystals with beveled edges in Brazilian samples imbedded inside concretions. Goethite crystals in Brazil samples are acicular and consist of several domains within the crystals along the needle axis and these acicular crystals arranged into stars, while cloudy shape of hematite crystals aggregated with kaolinite and imbedded inside silicate minerals to produce hard iron concretions.

Caracterização micromorfológica e considerações sobre a gênese de solos de tabuleiro do semi-árido do Brasil

Detalhadas investigações macro e, especialmente, micromorfológicas foram realizadas em dois perfis de Argissolo Amarelo e um de Planossolo de uma superfície geomorfológica tabular, pertencente aos Tabuleiros Sertanejos (Interioranos) na bacia hidrográfica do médio São Francisco em Petrolina, Pernambuco. O objetivo do estudo foi caracterizar micromorfologicamente os solos, procurando fornecer subsídios para o entendimento da pedogênese, como uma forma de entender a diversidade dos solos na paisagem. Os resultados indicam que os três perfis foram derivados de sedimentos pós-cretáceos, em intensa mistura com resíduos de rochas cristalinas do Pré-Cambriano, provavelmente, ainda, influenciados por materiais de antigos terraços fluviais do rio São Francisco. As diferenciações entre os três perfis estão relacionadas com a heterogeneidade resultante da mistura desses materiais de origem, mas, principalmente, com o posicionamento dos solos no relevo, gerando condições diferenciadas de drenagem. Concreções de ferro herdadas do material de origem, sofreram degradações e se transfomaram em mosqueamentos plínticos, e, posteriormente, foram dissipadas no solo, eluviação/iluviação, ou perdas do sistema, parece ser um dos processos envolvidos na pedogênese.

Characterization of Soils of Navegaon National Park (Maharashtra)

A soil vegetation study was carried out in the Navegaon National Park (Maharashtra). Six soil profiles were excavated under the three plant communities. Physico-chemical and morphological properties of soils were studied and they are classified accordingly. The soils under the plant community Tectona – Pterocarpus – Buchanania are very deep and dark brown to yellowish brown in colour with abundance of silica and iron concretion. These are moderately drained soils with silty loam to loamy in texture. They are classified as loamy, skeletal, mixed hyperthermic family of Typic Ustorthent and Udic Haplustoll. The soils under the plant community Cleistanthus – Ougeinia – Tectona are shallow to medium in depth and dark yellowish brown to dark reddish brown in colour and silty clay loam in texture. These arer classified as loamy, mixed, hyperthermic and loamy, skeletal, mixed hyperthermic family of Udic Haplustoll and paralithic vertic Haplustoll. The soils under the plant community Cleistanthus – Terminalia – Lagerstroemia are deep silty loam in texture and dark brown in colour, acidic to neutral. These are classified as loamy, mixed, hyperthermic family of Udic Argiustoll and Udic Haplustoll.

Stabilisation of lateritic soils as a raw material for building blocks

Some lateritic soils derived from different parent rocks in the Akure area of Nigeria were studied. The laboratory investigations indicated that most of these tropical soils, which were erroneously referred to as lateritic clays, actually contained very low proportions of clay particles. Migmatite-derived soils were found to respond better to stabilisation than those derived from charnockite. Firing was found to be the most important way of improving the durability of lateritic soil blocks as sintering takes place within the soil grain interstices. Iron concretions may be deleterious as they serve as focal points for sample failure.

Towards systematic image analysis in the study of soil micromorphology

Operational laboratories for quantitative image analysis of soil thin sections are now possible. This paper describes the evolving methodology at the University of Guelph, Ontario, Canada, and its application in selected Canadian soils. The paper deals with the collection of data under transmitted, reflected and circularly polarized illumination. The perfect registration of all data is achieved simply by not moving the thin section. The protocol for analysis of differentiation of voids, organic matrix, clay coatings, carbonate and iron concretions is presented. The storage and retrieval of data from CD-ROMs for analysis and sharing is also outlined. Once the digital imagery is stored it is easily useable for more studies as a greater understanding of the value of data is recognized. The paper makes the case for much greater use of the soil thin sections that already exist in the laboratories around the world.

Genesis of the Hussainiyat ironstone deposit, Western Desert, Iraq

The Hussainiyat ironstone deposit (Jurassic) is mainly pisolitic, intraclastic and concretionary in texture, associated with kaolinite mudstones and/or with quartzose sandstone. The ironstone consists mainly of goethite, hematite, kaolinite and quartz. The deposits were derived from a variety of parent rocks that included low- and medium-rank metamorphics, intermediate igneous rocks and pre-existing sediments of the Nubio-Arabian Shield. The source rocks suffered deep chemical weathering in the hinterland, and the products (Fe-oxyhydroxides, kaolinite and quartz) were later transported by rivers to the depositional site. Iron was mostly carried in association with the clay fraction and organic matter. Several genetic processes were involved in the ironstone formation. Iron concretions were mostly formed by bacterial build-up in swamps and marshes, and were subsequently embedded in kaolinitic mud. Large-scale development of groundwater laterite blanket (ferricrete) occurred later in the overbanks and floors of wadis, under oxidizing pedogenic conditions. During this stage iron was mobilized from the kaolinitic deposits and migrated upward in dry seasons and, to a lesser extent, downward in wet seasons. Pisolites and oolites grew in situ in the kaolinitic soil at the upper limit of the fluctuating water table. This ferricrete blanket had a wide and continuous extension within an elongated paleodepression. Seasonal heavy rain periods resulted in the flow of ephemeral streams and rivers, where major parts of this ferricrete was reworked and deposited with quartz sand and mud clasts as channel deposits. The original pisolitic-colloform ironstone was reworked continuously to form a semi-continuous sheet. In such wet seasons, additional Fe-enrichment took place as cementing materials or overgrowths.

The fossil fauna of Mazon Creek

Review of: Richardson’s Guide to the Fossil Fauna of Mazon Creek, edited by Charles W. Shabica & Andrew A. Hay. Northeastern Illinois University, Chicago, Illinois, 1997: XVIII + 308 pp., 385 figs., 4 tables, 1 faunal list; $75.00 (hard cover) ISBN 0-925065-21-8. Since the last century, the area around Mazon Creek in northern Illinois, about 100 km southwest of Chicago, has been known for its Pennsylvanian fossils. Mainly plant fossils were found along Mazon Creek and in the open coal pits of that area until the 1950s. Langford (1958, 1963) was the first to give a compilation of the flora and fauna of Mazon Creek. He listed and figured 60 genera including 71 species of animal fossils. As the coal mining moved farther south, and Pit 11 was opened in the 1950s, the relationship between plant and animal fossils in the iron concretions drastically changed. In this new book, the number of animal genera recorded has increased three times over that of Langford (1963), omitting about another 130 insect genera.

Effect of bentonite on the strength of fired lateritic soil blocks

Lateritic soils derived from migmatite and charnockite were subjected to stabilization using bentonite as an ideal clay. Moulded blocks were fired at 800 °C for strength improvement. It was observed that migmatite-derived lateritic soils respond better to stabilization as the average unconfined compressive strength peaked at 8244 kPa compared to charnockite-derived ones of 2936 kPa strength, both with 6% additive. The differing results are attributed to thermal sintering and pivotal positioning of iron concretions in the respective soils. Plastering may not be required for protection as the water absorption has been reduced to almost zero by the thermal binding effect on the soil grains. Aesthetically, the soils yield attractive reddish brown and deep brown colourations respectively on firing.

Effects of residue mulch and tillage on soil moisture conservation

The effects of selected soil management practices (conventional tillage, tied ridges and crop residue mulching) on soil moisture conservation in a semi-arid area of Kenya were studied during the short rains period, 1988, and long rains period, 1989. Three treatments, mulching, tied ridges and conventional tillage with three replications of each practice under a completely randomized block design, were used in the study. Nine experimental plots, each 4 m × 10 m were set up on a slope of 2%. During the study period, soil moisture was monitored on a weekly basis using the neutron probe at predetermined depths to a maximum depth of 120 cm. Calibration of the neutron probe was done for the soil at two depth ranges: 0–90 cm and 90–120 cm. The need to calibrate the probe for the 90–120 cm depth arose due to the presence of iron concretions within this depth range. The results obtained from this study showed that overall, crop residue mulching did result in more moisture down the profile throughout the two seasons within 2 years than the other two tillage practices. The tied ridged plots had the lowest amount of soil moisture in the soil profile during the two seasons. Thus the application of surface crop residue mulch seems to be the best soil management practice for increased soil moisture conservation and improved crop performance in rainfall marginal areas of Kenya.

Siderophilic bodies associated with hemosiderosis and atypical mycobacterial infection in an island siamang (Hylobates syndactylus)

Laminated iron concretions were noted in the liver of an aged siamang (Hylobates syndactylus) that had granulomatous enteritis and hepatitis due to Mycobacterium avium intracellulare infection. Preexisting hepatic siderosis, iron sequestration in macrophages, and compromised macrophage function due to mycobacterial infection are proposed as the basis for the abundance and size of the concretions. Similar siderophilic bodies and concomitant siderosis occurred in other siamangs. The concretions are similar to Schumann bodies and Michaelis-Gutmann bodies associated with granulomatous disease in other species.

Ferrolysis in Arundian alluvial palaeosols: evidence of a shift in the early Carboniferous monsoonal system

An unusual clay mineral assemblage from early Carboniferous (Arundian) palaeosols in South Wales contains a three component kaolinite/(chlorite-like material)/smectite mixed-layer clay. This is interpreted as the product of ferrolysis, a complex process involving dissolution of clays a d the subsequent production of interlayered varieties from the repetitive reduction and reoxidation of iron compounds in seasonally waterlogged, surface-water grey soils. Support for this interpretation comes from the distribution of iron species, iron concretions and vertic features in the palaeosol profile, which indicate formation under strongly seasonal, dry/hydromorphic conditions. The appearance of the ferrolytic pa- Iaeosol indicates a shi from a ‘dry’ to a ‘wet-type’ monsoonal regime in late Arundian times.