Application of Image Analysis for the Identification of Prehistoric Ceramic Production Technologies in the North Caucasus (Russia, Bronze/Iron Age)

The recent advances in microscopy and scanning techniques enabled the image analysis of archaeological objects in a high resolution. From the direct measurements in images, shapes and related parameters of the structural elements of interest can be derived. In this study, image analysis in 2D/3D is applied to archaeological ceramics, in order to obtain clues about the ceramic pastes, firing and shaping techniques. Images were acquired by the polarized light microscope, scanning electron microscopy (SEM) and 3D micro X-ray computed tomography (µ-CT) and segmented using Matlab. 70 ceramic sherds excavated at Ransyrt 1 (Middle-Late Bronze Age) and Kabardinka 2 (late Bronze–early Iron Age), located in in the North Caucasian mountains, Russia, were investigated. The size distribution, circularity and sphericity of sand grains in the ceramics show site specific difference as well as variations within a site. The sphericity, surface area, volume and Euler characteristic of pores show the existence of various pyrometamorphic states between the ceramics and within a ceramic. Using alignments of pores and grains, similar pottery shaping techniques are identified for both sites. These results show that the image analysis of archaeological ceramics can provide detailed information about the prehistoric ceramic production technologies with fast data availability

Titanian garnet in nepheline syenite from the Kaleybar area, East Azerbaijan Province, NW Iran

Abstract The Kaleybar nepheline syenite intrusion forms the largest silica undersaturated alkaline exposure in northwestern Iran. It consists of various rock types ranging from nepheline syenite to nepheline diorite that were emplaced during Eocene-Oligocene times, corresponding to the Alpine orogeny. The essential rock-forming minerals in nepheline syenite are plagioclase, K-feldspar, nepheline and amphibole. Clinopyroxene is the dominant phase in nepheline diorites. Titanian garnet occurs as an uncommon accessory phase forming reddish to deep brown individual grains. Chemically it is intermediate between Ti-andradite (67 to 78 mole %) and grossular (21 to 33 mole %) with TiO2 contents ranging from 1.5 to 5.0 wt %. Stoichiometry and R-mode factor analysis on garnet chemistry show that the dominant exchange vectors are Si-Ti and Al-Fe substitutions in the tetrahedral and octahedral crystal sites, respectively. A magmatic origin of the investigated Ti-garnet is suggested on the basis of mineralogical criteria and chemical properties

Pyrometamorphic process of ceramic composite materials in pottery production in the Bronze/Iron Age of the Northern Caucasus (Russia)

Pyrotechnology for the prehistoric pottery has been an important subject for the study of ancient production technology and technological styles. However, heterogeneous characteristics in chemical and mineralogical compositions and massive amounts of ceramic sherds at most archaeological sites make it difficult to identify production technologies. In this study, SEM-EDS/WDS, XRD and transmittance and reflectance FT-IR techniques were employed step by step, in order to overcome these limitations. The serial combination of each method covers a macro-, meso- and micro-scale and it enabled us to identify the relationship between firing temperature, reducing or oxidizing atmosphere and thermally induced mobility of Ca and Fe. Numerous ceramic pottery sherds from two archaeological sites in the North Caucasus, Ransyrt 1 (Middle-Late Bronze Age) and Kabardinka 2 (Late Bronze/Early Iron Age) were investigated and compared to the ceramics found at Levinsadovka and Saf’janovo around the Sea of Azov, Russia (Late/Final Bronze Age) for this purpose. Morphological changes by sintering and transformation of indicator minerals such as calcite, hematite, spinel, gehlenite, quartz and cis/trans-vacant 1M illite provide temperature thresholds at 675, 700, 750, 950, 1050, 1100, 1300 °C. With the laboratory based FT-IR, vibrational changes in shape, wavenumber and intensity corresponding to Si-O stretching bands yield an order and classification of the ceramics with regard to firing conditions between the samples as well as the unraveling of temperature profiles within a single sample in a 100 µm scale. With this approach, the number of archaeological ceramics could be classified according to the pyrometamorphic transformation of heterogeneous ceramic composite materials. Combined with the archaeological contexts of each site, these results will contribute to the reconstruction of local technological styles

Orthopyroxene rim growth during reaction of (Co, Ni, Mn, Zn)-doped forsterite and quartz: Experimental constraints on element distribution and grain boundary diffusion

Mantle metasomatism is an important process in subduction zones in which fluids from the dehydrating oceanic slab interact with the overlying upper mantle resulting in a chemical alteration of the mantle. Consequently, this fluid-rock interaction may influence the mantle rock's physical properties such as the deformation behavior. In order to study element redistribution during mantle metasomatism in the laboratory, we used the simplified model reaction olivine + quartz = orthopyroxene, where olivine acts as representative for the upper mantle and quartz as proxy for the metasomatizing agent. We conducted piston-cylinder experiments at 1.5 GPa and 950 to 1400 °C, lasting between 48 and 288 h, on samples containing a mixture of quartz and one set of synthesized forsterite samples doped with either Co, Ni, Mn, or Zn. Additionally, we tested the influence of either nominally anhydrous or hydrous experimental conditions on the chemical distribution of the respective dopant element by using either crushable alumina or natural CaF2 as pressure medium. Results of the chemical analyses of the recovered samples show dopant specific partitioning between doped forsterite and orthopyroxene independent of the confining pressure medium; except for the runs in which Ni-doped forsterite samples were used. The observed Ni- and Co-enrichment in forsterite samples may be used to identify mantle rocks that underwent mantle metasomatism in nature

A Model Rock Biofilm Growing in Percolation Columns

Sub-aerial biofilms (SAB) are ubiquitous, self-sufficient microbial ecosystems found on mineral surfaces at all altitudes and latitudes. SABs, which are the principal causes of weathering on exposed terrestrial surfaces, are characterized by patchy growth dominated by associations of algae, cyanobacteria, fungi and heterotrophic bacteria. A recently developed in vitro system to study colonization of rocks exposed to air included two key SAB participants - the rock-inhabiting ascomycete Knufia petricola (CBS 123872) and the phototrophic cyanobacterium Nostoc punctiforme ATCC29133. Both partners are genetically tractable and we used them here to study weathering of granite, K-feldspar and plagioclase. Small fragments of the various rocks or minerals (1–6 mm) were packed into flow-through columns and incubated with 0.1% glucose and 10 μM thiamine-hydrochloride (90 μL min−1) to compare weathering with and without biofilms. Dissolution of the minerals was followed by: (i) analysing the degradation products in the effluent from the columns via Inductively Coupled Plasma Spectroscopy and (ii) by studying polished sections of the incubated mineral fragments/grains using scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray analyses. K. petricola/N. punctiforme stimulated release of Ca, Na, Mg and Mn. Analyses of the polished sections confirmed depletion of Ca, Na and K near the surface of the fragments. The abrupt decrease in Ca concentration observed in peripheral areas of plagioclase fragments favored a dissolution- reprecipitation mechanism. Percolation columns in combination with a model biofilm can thus be used to study weathering in closed systems. Columns can easily be filled with different minerals and biofilms, the effluent as well as grains can be collected after long-term exposure under axenic conditions and easily analyzed

Reconstruction of magma chamber processes preserved in olivine-phlogopite micro-ijolites from the Oldoinyo Lengai, Tanzania

A detailed petrographic and mineralogical investigation of olivine-phlogopite micro-ijolite xenoliths from Oldoinyo Lengai, Tanzania indicates a complex evolutional history. These xenoliths consist of diverse textural subdomains characterized by minerals ranging from early-formed olivine, through diopside-hosted perovskite and phlogopite, to evolved aegirine-augite and titanite. Thermometry and mineral compositions in the subdomains suggest crystallization temperatures from 1070–970 °C to 850–700 °C at plutonic pressures and SiO2-activities controlled by perovskite-titanite equilibria. Double coronas are a characteristic textural feature of the olivine-phlogopite micro-ijolite, consisting of olivine cores surrounded by an inner clinopyroxene corona and an outer phlogopite corona. These double coronas might have formed during early magma chamber processes, including magma movement to a subsequent chamber resulting in dissolution of olivine with subsequent crystallization and accumulation of diopside and phlogopite. Diopside−aegirine-augite compositional zonation indicates several magma injections followed by cooling periods, during the formation of micro-ijolite groundmass. Mg# (80–83) and Ca (0.1–0.3 in wt%) contents of olivine together with the presence of primary melt inclusions in clinopyroxene, phlogopite, and nepheline indicate a magmatic origin from a possible parental olivine-nephelinite melt. There is evidence for subsolidus, or near-solidus, re-equilibration processes as indicated by the reaction of olivine with titanite forming symplectitic textures of ilmenite and diopside with minor zirconolite. Ti-exchange between phlogopite phenocrysts and other Ti-bearing minerals (perovskite, titanite, magnetite) resulted in ∼750 °C equilibrium temperatures for phlogopite, which are much lower than mafic magmatic (>900 °C) conditions. Calculated subsolidus temperatures suggest crystallization of olivine-phlogopite micro-ijolites over a 10–20 km depth interval

Laboratory VIS–NIR reflectance measurements of heated Vesta regolith analogs: Unraveling the spectral properties of the pitted impact deposits on Vesta

Pitted impact deposits on Vesta show higher reflectance and pyroxene absorption band strengths compared to their immediate surroundings and other typical Vestan materials. We investigated whether heating to different temperatures for different durations of Vestan regolith analog materials can reproduce these spectral characteristics using mixtures of HEDs, the carbonaceous chondrite Murchison, and terrestrial analogs. We find no consistent spectral trend due merely to temperature increases, but observed that the interiors of many heated samples show both higher reflectance and pyroxene band I strength than their heated surfaces. With electron probe microanalysis, we additionally observe the formation of hematite, which could account for the higher reflectance. The presence of hematite indicates oxidation occurring in the sample interiors. In combination with heat, this might cause the increase of pyroxene band strengths through migration of iron cations. The effect grows larger with increasing temperature and duration, although temperature appears to play the more dominant role. A higher proportion of Murchison or the terrestrial carbonaceous chondrite analog within our mixtures also appears to facilitate the onset of oxidation. Our observations suggest that both the introduction of exogenic material on Vesta as well as the heating from impacts were necessary to enable the process (possibly oxidation) causing the observed spectral changes

Quantitative dual-energy CT as a nondestructive tool to identify indicators for fossilized bone in vertebrate paleontology

Dual-energy computed tomography (DECT) is an imaging technique that combines nondestructive morphological cross-sectional imaging of objects and the quantification of their chemical composition. However, its potential to assist investigations in paleontology has not yet been explored. This study investigates quantitative DECT for the nondestructive density- and element-based material decomposition of fossilized bones. Specifically, DECT was developed and validated for imaging-based calcium and fluorine quantification in bones of five fossil vertebrates from different geological time periods and of one extant vertebrate. The analysis shows that DECT material maps can differentiate bone from surrounding sediment and reveals fluorine as an imaging marker for fossilized bone and a reliable indicator of the age of terrestrial fossils. Moreover, the jaw bone mass of Tyrannosaurus rex showed areas of particularly high fluorine concentrations on DECT, while conventional CT imaging features supported the diagnosis of chronic osteomyelitis. These findings highlight the relevance of radiological imaging techniques in the natural sciences by introducing quantitative DECT imaging as a nondestructive approach for material decomposition in fossilized objects, thereby potentially adding to the toolbox of paleontological studies

Silica Colloid Ordering in a Dynamic Sedimentary Environment

The formation of ordered particle arrays plays an essential role in nanotechnology, biological systems, and inorganic photonic structures in the geosphere. Here, we show how ordered arrays of amorphous silica spheres form in deeply weathered lithologies of the Great Artesian Basin (central Australia). Our multi-method approach, using optical and scanning electron microscopy, X-ray microdiffraction, Raman spectroscopy, and electron probe microanalysis, reveals that particle morphologies trace the flow of opal-forming colloidal suspensions and document syn- and post-depositional deformation. The micromorphology of amorphous silica pseudomorphs suggests that the volume-preserving replacement of non-silicate minerals proceeds via an interface-coupled dissolution precipitation process. We conclude that colloid flow and post-depositional shearing create but also destroy natural photonic crystals. Contrary to previous studies, our results indicate that purely gravitational settling/ordering is the exception rather than the rule during the formation of three-dimensional periodic sphere arrays in the highly dynamic colloidal suspensions of chemically weathered clastic sediments