Episodic fluid flow within continental rift basins: some insights from field data and mathematical models of the Rhinegraben

Vitrinite reflectance data from a petroleum exploration well in the northern Upper Rhinegraben show an unusual vertical maturity trend. Above and below a 500 m thick marl layer the vitrinite reflectance levels are consistent with modern, conductive, geothermal gradients. Between about 1000 and 1500 m depth, however, vitrinite reflectance levels are significantly elevated (about 0.6%Ro). This anomaly cannot be explained with one‐dimensional conductive or conductive–convective heat transfer models, and thermal effects of sedimentation or igneous intrusion seem implausible for this geological setting. The thermal anomaly that formed this maturation anomaly must have been hydrothermal in origin, two‐dimensional in nature, and persisted long enough to elevate the vitrinite reflectance values within this marl unit, yet it must have dissipated before the thermal perturbation would have altered the organic matter below and above the unit. In this study, we propose that the vitrinite reflectance anomalies were caused by a transient thermal inversion induced by episodic, lateral flow of hot (130–160°C) groundwater along conductive fractures and bedding planes. Heat flow constraints suggest that fluids must have moved rapidly up a vertical feeder fault from a depth of at least 3.6 km before migrating laterally. To test this hypothesis, we present a suite of simple, idealized mathematical models of groundwater flow, heat transfer, thermal degradation of kerogen and vitrinite systematics to explore the episodic flow that could have produced the observed thermal anomaly. In these simulations, a single, horizontal aquifer is sandwiched between two less permeable units: the total dimensions of the vertical section model are 4 km thick by 10 km long. The top of the aquifer coincides with the position of the observed thermal maturity anomaly in the Rhinegraben. Boundary conditions along the left edge of this aquifer were varied through time to allow for the migration of hot fluids out into the basin. Inflow temperature, horizontal velocity, duration and frequency of flow and thickness of the aquifer were varied. We found that a thermal maturity anomaly could only be produced by a rather restrictive set of hydrothermal conditions. It was possible to produce the observed vitrinite reflectance anomaly by a single hydrothermal flow event of 130°C fluid migrating laterally into the aquifer at a rate of 1 m a^?1 for about 10 000 years. The anomaly is spatially confined to near the left edge of the basin, near the feeder fault. If the flow event lasted longer than 100 000 years, then the maturation anomaly disappeared as the lower confining unit approached steady‐state thermal conditions. It is possible that such an event occurred about 5 million years ago in response to increases in fault permeability associated with far field Alpine tectonism.     

The Effect of Accelerated Alteration on the Discrimination between Baltic and Romanian Amber

Ten geological samples (five from each source—Romanian amber and Baltic amber) in duplicate for five different media (air, water, saline, acid and basic) were subjected to thermal alteration at 80 ± 2°C for 12 weeks, in the dark. The samples were analysed before and after the accelerated alteration experiment by Fourier transform infrared spectroscopy, both in transmittance and reflectance mode, and the acquired spectra were statistically processed by multivariate data analysis, mainly using principal component analysis. The results of the experiment are useful in giving a better picture of how to discriminate between archaeological amber artefacts.     

The use of reflectance values for the interpretation of natural and anthropogenic charcoal assemblages

Charcoal assemblages occur in both natural and archaeological settings. Cell wall reflectance values of charcoal in polished blocks under oil provide a proxy for temperature of formation. This paper aims to (1) determine whether wildfire charcoals and anthropological charcoals from various pyrotechnical activities can be distinguished using reflectance data and (2) establish if re-charring (i.e. use of charcoal fuel) can be recognised in the archaeological record through analysis of laboratory-produced re-charred charcoals and charcoals from an experimental iron smelt and traditional bronze casting which utilised charcoal fuel. Reflectance frequency data from assemblages representing burning of charcoal, in this case of iron smelting and bronze casting, indicates temperatures from above the mean value of charcoal production (>475°C) up to the maximum temperature reached in the subsequent process (i.e. >475 to >1,100°C). In contrast, wildfire charcoals showed a range of values including material with barely measurable reflectance (minimum values from 0.06% to 0.56%Ro) to maximum reflectance values varying from 1.65%Ro (Tilford) to 3.8%Ro (Zacca). The mean wildfire reflectance indicated temperatures in the range 325–400°C, which can therefore clearly be distinguished from that of the charcoal burning processes. The laboratory-produced re-charred charcoals take on the reflectance value of the highest temperatures experienced; reflectance values were not constrained by the original temperature of formation. High temperatures are most easily achievable by the burning of charcoal fuel, and hence high reflectance charcoals are likely to represent re-charred charcoal. Therefore, this quantitative reflectance method can be used in archaeology to determine the minimum temperature of formation of charcoals in anthropological processes which involve fire, can indicate the likelihood of use of charcoal or wood as fuel and can distinguish between an assemblage of high temperature anthropogenic charcoals and charcoals formed from natural wildfire.     

How the Romans got themselves into hot water: temperatures and fuel types used in firing a hypocaust

Abstract

The remains of hypocausts are noted as being widespread throughout the Roman Empire but, whereas the structure of hypocaust systems has been widely documented, primary knowledge of operating temperatures is limited. The petrographic technique of reflectance microscopy is used here to quantify cell wall reflectance values for charcoals from the hypocaust furnace of a bath suite forming part of small Romano-British villa complex at Groundwell Ridge near Swindon (Wiltshire, UK). The technique utilises material of archaeological origin to infer operating temperatures of the hypocaust furnace using established calibrations. The charcoals recovered from the furnace were identified as being predominantly Quercus (Oak) with some Populus/Salix (poplar/willow). Mean random reflectance of the samples indicated furnace-operating temperatures of 330–410°C. These temperatures fall below that of charcoal fuel production and hence suggest that it was wood that was used to fuel the hypocaust at Groundwell Ridge and not charcoal. Knowledge of the operating temperature of the furnace is a starting point in further calculations to understand, using primary evidence, the operating temperatures throughout the hypocaust system.     

Spectrochemical Characterization of Red Pigments Used in Classic Period Maya Funerary Practices

We studied the composition, colour chromaticity and form of application of red pigments in human bone samples from seven Classic period Lowland Maya sites. The samples were analysed by X‐ray diffraction, scanning electron microscopy (SEM) and X‐ray energy‐dispersive spectroscopy (EDS). Colour was measured using conventional colour identification standards (Munsell) and reflectance spectroscopy. Cinnabar and hematite were identified as the pigments used. We conclude that the reflectance method has advantages over conventional visual results, as it provides precise, objective and quantifiable optical data to distinguish the chromaticity, colour saturation and brightness of the pigments.     

Migration of metamorphic CO2 into a coal seam: a natural analog study to assess the long‐term fate of CO2 in Coal Bed Carbon Capture,Utilization, and Storage Projects

This study assesses the displacement of coalbed methane by CO₂ migration along a fault into the coal seam in the Yaojie coalfield. Coal and gas samples were collected continuously at various distances in NO.2 coal seam from F19 fault. Vitrinite reflectance, maceral, and pore distributions and proximate analysis of fourteen coal samples were performed. Gas components, concentrations, carbon isotopes of 28 gas samples were determined. We examined the coal–gas trace characteristics of coalbed methane displaced away from the fault by CO₂ injection after geological ages. From east to west, away from the F19 fault, the CO₂ concentration decreased, whereas the CH₄ concentration increased gradually. The δ¹³C values for CO₂ varied between ?9.94‰ and 1.12‰, suggesting a metamorphic origin. A wider range of values (from ?9.94‰ to 20‰) was associated with the mixing of microbial carbon dioxide, isotopic fractionation during CO₂ migration through the microporous structures of coals, and/or carbon isotope fractionation during gas–water exchange and dissolution of CO₂. Away from the F19 fault, the volumes of micropores, mesopores and macropores decrease gradually. The Dubinin–Radushkevich (DR) micropore volume decreased from 0.0059 to 0.0037 cm³ g^‐1, and the mesopore and macropore volumes decreased from 0.066 to 0.026 cm³ g^‐1. The CO₂ injection can mobilize aromatic hydrocarbons and mineral matter from coal matrix, resulting in the decrease in the absorption peak intensity for coal samples after supercritical CO₂ treatment, which indicates that chemical reactions occur between coal and CO₂, not only physical adsorption.     

Two Byzantine Albanian icons: a non-destructive archaeometric study

The present work is part of a project aimed at studying the pigments and painting techniques used by Albanian iconographers to produce Byzantine and post-Byzantine icons dating from the fourteenth to the nineteenth centuries; the state of conservation of these icons was also explored. Inorganic pigments are identified by means of X-ray fluorescence, reflectance spectrophotometry and UV fluorescence analysis. These analysis techniques were performed to discriminate between pigments on the basis of their typical features. Moreover, the study of the optical properties of paintings is of fundamental importance for correct restoration. This work enabled us to recognise the palette used in two artworks by anonymous painters of the fourteenth and fifteenth centuries. Only three small samples were taken from the edge and the back of the wooden tables in order to achieve information on preparatory layers. Twelve to fourteen non-destructive measurements were made to characterise the palette used by the two anonymous painters.     

Non-destructive provenance study of chert using infrared reflectance microspectroscopy

In this paper we explore the potential of non-destructive Infrared reflectance microspectroscopy (IRRMS) for the characterization of chert samples from 10 different geological outcrops in North America with emphasis on the Midcontinent. A principle objective of the project is to determine whether IRRMS analysis can provide a mineral-based signature for bedrock sources of chert artifacts. The technique utilizes a Bio-Rad Digilab FTS-40 Infrared spectroscope and microscope attachment that reflects an infrared beam off a chert specimen. Our findings indicate that spectral features from the molecules constituting minor and trace minerals in chert may provide sufficient characterization for chert sourcing.     

Lead isotope ratios: Tracking the migration of European‐Americans to Grafton,Illinois in the 19th century

Lead isotope analysis was conducted using inductively coupled plasma mass spectrometer (ICP‐MS) instruments on local soil samples and human premolar tooth enamel from a 19th century population from Grafton, Illinois, USA. The goal of the study was to determine if lead isotope analysis could be used to infer place of birth and patterns of 19th century migration into the city of Grafton. Five soil core samples from a location near Grafton, Illinois, five grave soil samples from the city cemetery and the tooth enamel of 19 human premolars were analysed. The results of the soil core analysis indicated that the lead isotopic signature of Grafton differs significantly from isotope ratios of other geographic areas associated with recorded places of birth of 19th century Jersey County residents. Elemental and isotope analysis of the soil samples indicated that diagenesis was not a factor in the analysis of lead isotopic signatures of enamel. From the lead isotope analysis of human premolars, the geographic origin of 13 of the remaining 15 individuals could be inferred. The inferred geographic origin was supplemented by an analysis of 1860 mortality and census records and demonstrated the utility of using lead isotope analysis in bio‐archaeological investigations. Copyright © 2010 John Wiley & Sons, Ltd.     

FTIR and statistical studies on amber artefacts from three Romanian archaeological sites

In the present study Fourier transform infrared spectroscopy in the reflectance mode (FTIR-reflectance) – was performed on well preserved archaeological amber, originating from three Romanian archaeological sites of Roman and Byzantine cultures, which did not allow sampling material. Resulting spectra were subjected to multivariate data analysis (MDA) using Principal Components Analysis (PCA). In the light of the FTIR-reflectance bands of archaeological samples from the region 1275 to 1155 cm⁻¹ and 900–600 cm⁻¹ we could conclude that the samples from first two locations, Ro?ia Montan? and Nuf?ru, are made from amber of Baltic origin. In the case of the third location, Isaccea, we take into account the possibility of a mixture of raw materials, both Baltic and Romanian amber. These assertions are supported by statistical analysis and the historical context. Besides the FTIR spectra comparison or other analytical data, it is very important to correlate any information about the material (colour, conservation status, historical context, connections with other artefacts) and the statistical analysis in order to favour safe conclusions.     

The multivariate statistical analysis and XRD analysis of pottery at Xigongqiao site

A series of pottery samples excavated from the Xigongqiao site in Tengzhou city of Shandong province was determined using inductively coupled plasma atomic emission spectrometry. Together with excavation data and archaeological analysis, the potential for provenance and technology of unearthed ancient pottery was studied by using multivariate statistical analysis and X-ray powder diffraction pattern (XRD) analysis. In order to characterize and classify these earthenware samples, the major and minor/trace element concentrations were studied with both cluster analysis and principal component analysis. The results showed that there were three different groups in cluster analysis dendrogram in good correlation with their colors. This indicated that the potteries were made from clays of different composition. These results were in agreement with the results of principal component analysis. XRD analysis further assessed the validity of multivariate statistical analysis.     

MOLECULAR AND ISOTOPIC DEMONSTRATION OF THE PROCESSING OF AQUATIC PRODUCTS IN NORTHERN EUROPEAN PREHISTORIC POTTERY*

A number of charred surface residues, adhering to ceramic containers, were obtained from various coastal and inland sites in north‐west Europe dating from the sixth to the fourth millennium cal bc . In order to investigate the use of these vessels and in particular to identify any marine products, the residues were subjected to carbon and nitrogen stable isotope analysis. Variation in carbon isotope ratios between different samples indicated that some vessels may have been used to process marine products. This analysis was corroborated by specific identification of aquatic products following structural and isotopic characterization of lipids extracted from selected samples.     

On the post-mortem accumulation of lead by skeletal tissues

Lead concentrations in a number of bones and soil samples taken from the same graves at the site of Bordesley Abbey were significantly correlated. Statistical analysis of the results indicated that 59% of the variation in the bone lead concentrations was due to contamination from the soil.A study of the distribution of lead in a tooth from the Romano-British site at Cirencester by fast particle activation analysis indicated that virtually all the lead was on the external surface, indicating post-mortem absorption.These results strongly suggest that lead is absorbed by skeletal tissue after death even in soils which have an alkaline pH. In the light of these findings, suggestions are made for the strategies which might be adopted for further research in this area.     

SCIENTIFIC ANALYSIS OF SEVENTH‐CENTURY GLASS FRAGMENTS FROM THE CRYPTA BALBI IN ROME*

Inductively coupled plasma emission spectroscopy, reflectance spectroscopy and X‐ray diffraction were used to study seventh‐century AD glass fragments from the Crypta Balbi in Rome. All the samples were found to be silica‐soda‐lime glasses. Iron determines the colour of blue‐green, green and yellow‐green transparent glasses; chemical composition suggests deliberate addition of iron and/or manganese in about half the samples. Copper was found as the main colourant in red, pale blue and blue‐green opaque fragments; elemental copper acts as an opacifier in red glass, and calcium antimonate in white, pale blue and blue‐green glasses. Detection of antimony in transparent fragments suggests recycling of opaque mosaic tesserae.     

Subsistence and mobility strategies in the Epipalaeolithic: a stable isotope analysis of human and faunal remains at 'Uyun al-Hammam,northern Jordan

This paper investigates evidence for subsistence and settlement activities in the Levantine Middle Epipalaeolithic through the application of stable isotope analysis to human and non-human remains from the site of 'Uyun al-Hammam, northern Jordan. In general, bone from the site suffers a high degree of diagenesis and collagen could not be extracted for analysis here. Carbon and oxygen isotopic values from human tooth enamel samples were variable, but within expected values for the Middle Epipalaeolithic, whereas animal carbon and oxygen isotopic values varied widely, most likely due to hydrological and climatological factors. Carbon and isotopic values for the human samples indicated a predominantly C₃ plant dietary input, while animal samples appeared to have varying amounts of C₄ inputs into their diet. This is the first isotopic analysis conducted on material from the Middle Epipalaeolithic of the southern Levant and, as such, even results constrained by temporal and climatological variants within the region contribute to the overall knowledge of settlement and subsistence strategies during this cultural period.     

Scientific study of the pigments and binders used in mural painting from the 16th-century ce St Mary's Church of Cheriapally,Kottyam, Kerala,and its relevance to conservation

The aim of this investigation was to analyze the materials and techniques of the paintings in the 16th-century ce St Mary's Church, to evaluate deterioration of the paintings, and to propose a suitable conservation treatment for their preservation. The material analysis of ground, pigments, binders, and plasters was undertaken using binocular microscopy, field emission scanning electron microscopy (SEM)–energy dispersive X-ray spectroscopy, X-ray fluorescence, Fourier transform infrared spectroscopy in reflectance (KBr) and transmittance mode (attenuated total reflection), thin-film X-ray diffraction, and micro-Raman spectroscopy. Gas chromatography–mass spectrometry (GC-MS) was used for identifying proteinaceous and lipidic materials extracted from the micro-samples. The study generated data on two different red and green pigments used as decorative materials. The red pigments were identified as cinnabar along with traces of hematite and clay minerals, and green as malachite and the minor presence of other minerals. SEM analysis identified cotton fiber embedded in the coarse plaster layer that provided better strength to the plaster. Plant oils and proteins found as the binder in the pigment samples suggested that the painting technique was executed as tempera. Lead white and gypsum materials were used in previous restoration works.     

The salt chimney effect: delay of thermal evolution of deep hydrocarbon source rocks due to high thermal conductivity of evaporites

Half of the topseals to the world's largest oilfields are evaporites. Rock salt has a thermal conductivity two to four times greater than that of other sedimentary rocks found in oil‐ and gas‐bearing basins. Strong heat conduction through evaporites can increase the geothermal gradient above evaporite deposits, resulting in a positive thermal anomaly and above‐average temperature while simultaneously decreasing the geothermal gradient below evaporites, resulting in a negative thermal anomaly. Most Triassic–Jurassic hydrocarbon source rocks in the Kuqa Basin, western China, are overlain by ~1500‐m‐thick Tertiary evaporites with underlying Cretaceous sandstones and mudstones. Directly measured strata temperatures indicate an obvious break in the steepness of the geothermal gradient above and below Paleogene evaporites, with a significantly steeper geothermal gradient above the evaporites. Simulations of the thermal evolution of source rocks based on data collected from well Kela‐2 indicate that if the thickness of evaporites (mainly rock salt and anhydrite rock) in overlying rocks above source rocks increases compared with the thickness of siliciclastic rocks in the overlying rocks, then strata temperatures and vitrinite reflectance in Jurassic source rocks will decrease accordingly. Our thermal simulations based on the thickness and thermal conductivity of evaporites accurately coincide with previous studies based on homogenization temperatures, hydrocarbon–water contact retrospection, and carbon isotope results from natural gases. The gas generation center located in the Kalasu Tectonic Belt today is also sealed in an evaporite‐related structural trap that formed at this time. Therefore, the speculated natural gas generation times not only correlate with the evaporite‐related structural trap formation, but the calculated maturity of deep source rocks below the evaporites also coincides with current gas reserves. And our studies can help to find the deep oils and gases under thick evaporites.     

Preservation potential of charcoal in alkaline environments: an experimental approach and implications for the archaeological record

Charcoalified plant material (usually wood) has been described as being inert with a high preservation potential. Although usually black on both the outside and inside, the physical and chemical properties differ as a function of temperature and time of exposure to a heat source. Post-depositional processes however may exert additional affects on charcoalified material and introduce bias into the archaeological record. This work explores the influence of alkaline conditions, often encountered in the soil environment, on the preservation potential of charcoalified material. Charcoal, experimentally produced at different temperatures, was exposed to a number of solutions of potassium hydroxide and calcium hydroxide with different pHs, to simulate exposure to alkaline soil conditions. Under these conditions chemically mediated physical interactions occur resulting in fragmentation of the charcoal samples into (very) small pieces the size of which depends upon the initial temperature of charcoalification. Moreover further interactions result in a decrease in reflectance relative to samples not exposed to alkaline conditions. Although experimentally driven the potential for physical loss of charcoal from a particular site coupled with the reduction in (expected) reflectance of any resident material, has important implications for any conclusions drawn regarding the archaeological record.     

Developing FTIR Microspectroscopy for the Analysis of Animal-Tissue Residues on Stone Tools

The analysis of microscopic residues on stone tools provides one of the most direct ways to reconstruct the functions of such artifacts. However, new methods are needed to strengthen residue identifications based upon visible-light microscopy. In this work, we establish that reflectance Fourier-transform infrared microspectroscopy (FTIRM) can be used to document IR spectra of animal-tissue residues on experimental stone tools. First, we present a set of reflectance FTIRM standards for the most commonly identified animal-tissue residues on stone tools: skin, meat, fat, hair, blood, feather barbules, fish scales, and bone. We provide spectral peak assignments for each residue and demonstrate that high-quality reflectance FTIRM spectra can be generated under ideal circumstances. Second, we document the spectra for these residues when they are located on a stone substrate such as flint or obsidian. We discuss procedures for correcting spectra that are affected by specular reflection and explain the effects of spectral interference from the stone. Our results show that reflectance FTIRM is sensitive to small intra-sample differences in composition. This means that it will record the effects of decomposition in ancient residues. The methodological developments we present here will help lithic residue analysts incorporate in situ reflectance FTIRM into their analysis protocols to strengthen identifications.     

Coal used for Fuel at Two Prehistoric Sites in Southern France: Les Canalettes (Mousterian) and Les Usclades (Mesolithic)

Charcoal analysis—the study of charcoal from archaeological contexts—is designed to reconstruct palaeoenvironment and human use of wood. At two prehistoric sites in the Causse du Larzac (France)—Les Canalettes (Mousterian) and Les Usclades (Mesolithic)—charcoal analysis has revealed specimens whose anatomical structure was abnormally compressed in transverse section. The authors conducted experiments to determine how the compression could have occurred. The result was the first evidence for lignite in Palaeolithic settlements. Lignite fragments in a hearth suggest local Palaeolithic people used it for fuel. The lignite could have come from major coal outcrops within 7 to 15 km of the sites. Coal use is otherwise unknown for Palaeolithic cultures in France, and its use at Les Canalettes during the last glacial is the oldest recorded instance. Coal may have been used for fuel primarily because wood became scarce during the last glacial.