Formation of vivianite in holocene clay sediments

Concretions of vivianite attaining 0.5 g occur in the upper 4 m of the bottom sediments of the Åsrum lake, Vestfold, S. Norway. The vivianite-bearing zone is of lacustrine origin. Vivianite is absent in the underlying lagunal and marine sediments. Electro-chemical and chemical data are given for the interstitial water and the clay.

Solubility product of vivianite is determined. The equilibrium constant is K = 10⁻⁴⁰ for the reaction 3 Fe⁺⁺ + 2 HPO₄⁻ + 2 OH⁻ = vivianite. The concretions grew by diffusion from a slightly supersaturated interstitial water phase. The degree of supersaturation is calculated. The stability relations of vivianite and hydroxyl apatite are discussed.     

Optical absorption spectra of iron ions in vivianite

Absorption bands are determined in polarized optical spectra of vivianite Fe₃(PO₄)₂·8H₂O, recorded at room and low temperatures. These bands are caused by spin-allowed d-d transitions in structurally nonequivalent Fe _A ²⁺ (～11000 cm^-1 (γ-polarization) (and) ～12000 cm^-1 (β-polarization)) (and) Fe _B ²⁺ (～8400 cm^-1 (γ, α-polarization) and ～11200 cm^-1 (α-polarization)) ions. A charge transfer band (CTB) Fe _B ²⁺ +Fe _B ³⁺ →Fe _B ²⁺ +Fe _B ²⁺ (～15000 cm^-1) also determined, has polarizing features giving evidence of a change in the Fe _B ²⁺ -Fe _B ³⁺ bond direction, when compared with Fe _B ²⁺ -Fe _B ²⁺ . Bands of exchange-coupled Fe³⁺-Fe³⁺ pairs (～19400, ～20400, ～21300 and ～21700 cm^-1) which appear on oxidation of Fe²⁺ in paired Fe _B octahedra are also characterized.     

Characterization of vivianite from Catavi,Llallagua Bolivia

Summary Vivianite from Catavi Mine, Llallagua, Bolivia, has a near ideal composition with traces of Mg, Zn and Mn. Total rare-earth elements are < 1,gmg/g. Mössbauer spectroscopy shows Fe^III/(Fe^II + Fe^III) is approximately 0.04.a = 10.030Å,b = 13.434Å,c = 4.714Å, = 102.73dg. The middle-infrared powder spectrum shows H₂O-related bands at 3490, 3290, 3130 cm^–1 (stretch), 1618 cm^–1 (bend), 825 cm^–1 (rock), and at 665 cm^–1 a possible M-OH₂ twist. P0₄ bands occur at 1045-940 cm^–1 (stretch) and 570-450 cm^–1 (bend). Corresponding laser Raman microprobe bands occur at 1051 (ms), 986 (m), 948 (vs), 867 (mw), 828 (w), 568, 532, 453 (m), 442 (mw). Weak Raman bands at about 342, 303, 270 (w), 235 (ms), 227 (sh, ms), 196 (ms), 187 (sh, m), 162 (mw), and 126 (m) may arise from lattice vibrations. Differential thermal responses include a major endotherm from 115–235°C with a shoulder at 170°C and a maximum at 210°C resulting from loss of structural water combined with oxidation of Fe²⁺, and two small exotherms with maxima at 605 and 780°C related to structural transformations.

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Charakterisierung des Vivianits von Catavi, Llallagua, Bolivien

Zusammenfassung Vivianit von der Catavi Mine, Llallagua, Bolivien zeigt annähernd ideale Zusammensetzung mit Spuren von Mg, Zn und Mn. Der gesamte Gehalt an seltenen EvolElementen ist < 1 ppm. Die Mössbauer Spektroskopie liefert ein Fe³⁺/(Fe²⁺ + Fe³⁺) Verhältnis von ungefähr 0.04.a = 10.030,b = 13.434,c = 4.714 Å, = 102.73°. Das Infrarot-Pulverspektrum zeigt dem H₂0 zuzuordnende Banden bei 3490, 3290, 3130 cm^–1 (Streckschwingungen), 1618 cm^–1 (Deformationsschwingung), 825 cm^–1 (Schaukelschwingung) und eine mögliche M-OH₂ Torsionsschwingung bei 665 cm^–1. PO₄ Banden liegen bei 1045-940 cm^–1 (Streckschwingung) und 570-450 cm^–1 (Deformations-schwingung). Entsprechende Banden der Laser Raman Mikrosonde liegen bei 1051 (mst), 986 (m), 948 (sst) 867 (mschw), 828 (schw), 568, 532, 453 (m), 442 (mschw). Raman Banden bei etwa 342, 303, 270 (schw), 235 (mst), 227 (Schulter, mst), 196 (mst), 187 (Schulter, m), 162 (mschw) und 126 (m) können auf Gitterschwingungen zurückgeführt werden. Differential-thermoanalytische Untersuchungen zeigen einen endothermen Bereich von 115–235°C mit einer Schulter bei 170 und einem Maximum bei 210°C, was auf den Verlust von strukturellem Wasser, das an eine Oxidation des Fe²⁺ gebunden ist, zurückzuführen ist; zwei auf strukturelle Transformationen zurückzuführende exotherme Maxima liegen bei 605 und 780°C.

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Rare earth elements in vivianite from Lake Åstrum

The rare carth elements are determined in vivianite concretions and surrounding clay sediments. Approximately 3/4 of the rare earth elements in the clay is present in adsorbed state. The concentration of REE in the pore water is calculated from the composition of the vivianite, assuming a diffusion model for the formation of the concretions and lower solubility of the rare earth elements above the concretions than in the pore water at some distance from the concretions. The concentrations thus calculated are similar to published values for ocean water.     

Electronic and magnetic structure of vivianite: cluster molecular orbital calculations

The electronic and magnetic structure of the octahydrophosphate vivianite, Fe₃(PO₄)₂·8H₂O, has been investigated by cluster molecular orbital calculations in local spin density approximation. Optical and Mössbauer spectra are well reproduced by the calculations, and the differences between the two iron sites can be correlated with differences in the geometrical structure of the first coordination sphere. The spin structure within the crystallographic ac plane is derived and explained on the basis of different superexchange pathways via edges of the phosphate tetrahedra. The calculations demonstrate that quite large clusters (up to 118 atoms) are necessary to arrive at reliable results.     

Redistribution of archaeological assemblages in plowzones

Archaeological surface surveys have located open‐air sites on cropland in the Sierra de Atapuerca (Burgos, Spain). To what degree agricultural disturbances have impacted archaeological site integrity is poorly defined and may greatly affect interpretations of prehistoric land use. This paper presents the results of three experiments concerned with the effects of tillage on artifact distribution, focusing specifically on lateral and vertical artifact displacement. We demonstrate highly variable horizontal displacement of artifacts by plowing and overall downward movement of lithic materials within the soil. This results in an expansion of site boundaries and reduction of surface artifact density, yielding a biased and unrepresentative picture of past human activity. More experimental studies are needed to better define agricultural disturbances to surface archaeological assemblages. © 2008 Wiley Periodicals, Inc.     

The occurrence and research potential of microfossils in inorganic archaeological materials

The microscopic remains of organisms, or “microfossils,” can occur within or attached to a range of different inorganic archaeological materials. Because of their small size, these inconspicuous phenomena can be easily overlooked. However, as this paper illustrates, the detailed biological and palaeontological analysis of microfossils in such contexts may be an important source of archaeological data. By critically reviewing a range of specialized cross‐disciplinary analyses, it is shown how microfossils can be used to provenance inorganic artifacts, reconstruct aspects of their manufacturing technology, and infer their function. © 2008 Wiley Periodicals, Inc.     

Assessing lithologic discontinuities and parent material uniformity within the Texas sandy mantle and implications for archaeological burial and preservation potential in upland settings

Alfisols within the Texas Gulf Coast Plain commonly exhibit textural contrasts between sandy, artifact-bearing A–E horizons (i.e., sandy mantle), and artifact-sterile clay-rich Bt (argillic) horizons. This has invoked debate about parent material uniformity and pedogenic versus geomorphic sandy mantle origins, which has implications for the scientific value of buried archaeological sites. To improve our understanding of archaeological burial in upland settings, we evaluated parent material uniformity within five pedons to distinguish pedogenically derived textural changes from geomorphologically created lithologic discontinuities. Depth trends in clay-free particle size classes and stable/immobile Ti and Zr constituents failed to reveal lithologic discontinuities between the sandy mantle and Bt horizons, and the observed textural differences are interpreted to have resulted from pedogenic processes. This interpretation is supported by clay skins, fine clay increases in Bt horizons, and micromorphological observations. Consequently, artifacts buried in upland summits have likely moved down the soil profile due to biomantle processes. Deep sandy mantle sites, non-parallel contacts between the sandy mantle and Bt horizons, and paleogullies incised into Eocene bedrock are better explained by colluvial/soil creep processes adjacent to summits, where archaeological materials may exhibit preservation potential. No single explanation can account for sandy mantle origins, and we advocate a case-by-case approach.     

Products of abiotic U(VI) reduction by biogenic magnetite and vivianite

Reductive immobilization of uranium by the stimulation of dissimilatory metal-reducing bacteria (DMRB) has been investigated as a remediation strategy for subsurface U(VI) contamination. In those environments, DMRB may utilize a variety of electron acceptors, such as ferric iron which can lead to the formation of reactive biogenic Fe(II) phases. These biogenic phases could potentially mediate abiotic U(VI) reduction. In this work, the DMRB Shewanella putrefaciens strain CN32 was used to synthesize two biogenic Fe(II)-bearing minerals: magnetite (a mixed Fe(II)-Fe(III) oxide) and vivianite (an Fe(II)-phosphate). Analysis of abiotic redox interactions between these biogenic minerals and U(VI) showed that both biogenic minerals reduced U(VI) completely. XAS analysis indicates significant differences in speciation of the reduced uranium after reaction with the two biogenic Fe(II)-bearing minerals. While biogenic magnetite favored the formation of structurally ordered, crystalline UO₂, biogenic vivianite led to the formation of a monomeric U(IV) species lacking U-U associations in the corresponding EXAFS spectrum. To investigate the role of phosphate in the formation of monomeric U(IV) such as sorbed U(IV) species complexed by mineral surfaces, versus a U(IV) mineral, uranium was reduced by biogenic magnetite that was pre-sorbed with phosphate. XAS analysis of this sample also revealed the formation of monomeric U(IV) species suggesting that the presence of phosphate hinders formation of UO₂. This work shows that U(VI) reduction products formed during in situ biostimulation can be influenced by the mineralogical and geochemical composition of the surrounding environment, as well as by the interfacial solute-solid chemistry of the solid-phase reductant.     

The Topaz Basin archaeological obsidian source in the transition zone of central Arizona

The Classic Period Migration Project involves the analysis of archaeological sites at Perry Mesa in central Arizona and resulted in the discovery of several small marekanite1 obsidian artifacts that signaled a previously unlocated source. The source was eventually located in the Topaz Basin area of the upper Cienega Creek stream basin, southwest of Camp Verde, Arizona.² While this locality solves the “unknown” sources in the Perry Mesa archaeological assemblage, it has not appeared in the archaeological record of Arizona with any frequency. The glass itself is an excellent medium for tool production, so its near absence in the archaeological record is likely attributable to social/territorial causes as well as limited secondary deposition, and along with other “minor” sources points to the archaeological utility of understanding these smaller sources. © 2009 Wiley Periodicals, Inc.     

The role of armadillos in the movement of archaeological materials: An experimental approach

Armadillos are medium‐sized animals whose burrowing behavior can be significant in archaeological settings ranging from South America to the central United States. Although archaeologists are well aware that these animals can move archaeological materials across stratigraphic layers, few data are available about the magnitude of mixing, number of burrows per individual, dimension of burrows, and their impact on archaeological sites. This paper addresses the problem from an experimental perspective. Specifically, we monitored the action of the yellow armadillo (Euphractus sexcintus) in translocating cultural materials. Our results suggest that: (1) the vertical movement of artifacts has no preferential direction; (2) cultural horizons at least 20 cm apart can be mixed; (3) the animal's activity leaves some distinct traces that can be recognized during an excavation; and (4) there is no significant correlation between size, shape, or weight of artifacts and amount of displacement. © 2003 Wiley Periodicals, Inc.     

Tsunamis in the New Zealand archaeological record

Historical and geological records both indicate tsunami inundation of New Zealand in the 700 years since the first human settlement. In addition, Maori oral traditions refer to unusual waves that might have been tsunami waves, although the accounts are open to other interpretations. Tsunami evidence has rarely been proposed from archaeological sites, primarily because of a limited understanding of the requisite evidence and environmental context. We list a criteria suggesting possible tsunami inundation of archaeological sites based upon geoarchaeological data, and use them in a case study from the Archaic Maori occupation site at Wairau Bar. The list is possibly incomplete, but indicates that archaeological investigations can gain from assessments of changing environmental conditions through time at any individual site. Our intention is not to prove tsunami inundation; rather, it is to point to archaeological sites as possible sources of information. We highlight the potential of the Wairau Bar site for further investigation.     

The chronology, palaeogeography and archaeological significance of the marine quaternary record of the West Sussex coastal plain, Southern England, U.K.

The Quaternary sediments of the West Sussex Coastal Plain have produced a wide range of floral, faunal and archaeological remains. These sediments consist of marine sands and gravels exhibiting transgressive and regressive trends which occur from present day sea-level to c. +43.0 m O.D. and are overlain by terrestrial silts and cold climate periglacial sediments. At the present day coastline, channel fill deposits occur below modern beach levels. New field observations, coupled with a re-investigation of old sites and literature, suggest that five discrete high stands of sea-level may be preserved in the area of the West Sussex Coastal Plain. Age estimates for these deposits suggest that they span large parts of the Middle and Upper Pleistocene (Oxygen Isotope Stages 13 to 5). Conformable relationships between many of the marine and terrestrial sediments suggest that the potential exists within the area to correlate the marine and terrestrial Quaternary stratigraphic records. In addition sediments associated with two of these high sea-level stands are associated with extensive buried landsurfaces covering large areas of the coastal plain. At some locations these intact landsurfaces are associated with evidence for human activity and represent stratigraphic and cultural resources of international importance.     

Dating the course of the lower red river in Louisiana: The archaeological evidence

Archaeological data from the lower Red River in Louisiana indicate that the modern course of the river is 1200 years older than previously suggested. Geologists claim a diversion of Red River through Moncla Gap approximately 500 to 1000 years ago. Marksville period occupations dating prior to A.D. 200 are identified at archaeological sites adjacent to the river below Moncla Gap. The position of these sites on Red River levees demonstrate that they post-date the river's occupancy of the area. Extensive Marksville and later prehistoric occupations in the Moncla Gap area are seen as a direct result of the development of riverine environments resulting from this diversion.     

Inverted clast stratigraphy in an eolian archaeological environment

Understanding the geomorphic history of eolian basins is important in interpreting the archaeological record and human responses to past environments. One hundred forty soil profiles were excavated and described in southern New Mexico and West Texas. Seven major late Quaternary stratigraphic units were found: La Mesa, eolian Jornada (I, II), eolian Isaacks' Ranch, eolian Organ (I, II, and III), Historical Blowsand, and the playa deposits of Petts Tank and Lake Tank. Each unit represents a period of landscape instability, eolian erosion, and concurrent deposition, followed by landscape stability and soil formation. Eolian erosion can form local surficial lag deposits if materials larger than the competence of the wind are present. However, erosional processes alone cannot explain the presence of older clasts at the surface with intact, younger deposits underneath. We propose a combination of processes: deflation in eolian windows, followed by lateral movement of clasts over areas that have not been deflated. The effects of these processes on artifact stratigraphy and archaeological interpretations could be significant. © 2002 Wiley Periodicals, Inc.     

Differential diagenesis of strontium in archaeological human dental tissues

The investigation of prehistoric human migration from the measurement of Sr-isotope ratios within preserved tissue is critically dependent on the preservation of biogenic Sr. A number of recent studies have involved isotope ratio measurements on samples of archaeological tooth and bone, but doubt remains as to the extent of diagenesis in various skeletal tissues and the effectiveness of procedures designed to decontaminate them. The authors have compared Sr abundance and isotope ratios in enamel and dentine from archaeological teeth in order to assess the integrity of the biogenic Sr signal preserved within the respective tissues. It is concluded that enamel appears, in most cases, to be a reliable reservoir of biogenic Sr, but that dentine, and by implication bone, is not. The diagenesis of dentine is highly variable even between burials within a single site. For the majority of teeth, dentine diagenesis was not simply by addition of soil-derived Sr, but involved substantial, sometimes complete, turnover of the original biogenic material. It is suggested that, for most of the samples investigated, current decontamination techniques may not have been effective in isolating biogenic Sr from dentine. Similar considerations are likely to apply to archaeological and fossil bone, but the possibility arises to use dentine and enamel measurements to assess the effectiveness of decontamination procedures which may then be used for bone.