Invasion of a karst aquifer by hydrothermal fluids: evidence from stable isotopic compositions of cave mineralization

Mineral deposits in the Cupp‐Coutunn/Promeszutochnaya cave system (Turkmenia, central Asia) record a phase of hydrothermal activity within a pre‐existing karstic groundwater conduit system. Hydrothermal fluids entered the caves through fault zones and deposited sulphate, sulphide and carbonate minerals under phreatic conditions. Locally, intense alteration of limestone wall rocks also occurred at this stage. Elsewhere in the region, similar faults contain economic quantities of galena and elemental sulphur mineralization. Comparisons between the Pb and S isotope compositions of minerals found in cave and ore deposits confirm the link between economic mineralization and hydrothermal activity at Cupp‐Coutunn. The predominance of sulphate mineralization in Cupp‐Coutunn implies that the fluids were more oxidized in the higher permeability zone associated with the karst aquifer. A slight increase in the δ³⁴S of sulphate minerals and a corresponding δ³⁴S decrease in sulphides suggest that partial isotopic equilibration occurred during oxidation. Carbonate minerals indicate that the hydrothermal fluid was enriched in ¹⁸O (δ¹⁸O_SMOW ～ + 10‰) relative to meteoric groundwater and seawater. Estimated values for δ¹³C_DIC (δ¹³C_PDB ～ ? 13‰) are consistent with compositions expected for dissolved inorganic carbon (DIC) derived from the products of thermal decomposition of organic matter and dissolution of marine carbonate. Values derived for δ¹³C_DIC and δ¹⁸O_water indicate that the hydrothermal fluid was of basinal brine origin, generated by extensive water–rock interaction. Following the hydrothermal phase, speleothemic minerals were precipitated under vadose conditions. Speleothemic sulphates show a bimodal sulphur isotope distribution. One group has compositions similar to the hydrothermal sulphates, whilst the second group is characterized by higher δ³⁴S values. This latter group may either record the effects of microbial sulphate reduction, or reflect the introduction of sulphate‐rich groundwater generated by the dissolution of overlying evaporites. Oxygen isotope compositions show that calcite speleothems were precipitated from nonthermal groundwater of meteoric origin. Carbonate speleothems are relatively enriched in ¹³C compared to most cave deposits, but can be explained by normal speleothem‐forming processes under thin, arid‐zone soils dominated by C4 vegetation. However, the presence of sulphate speleothems, with isotopic compositions indicative of the oxidation of hydrothermal sulphide, implies that CO₂ derived by reaction of limestone with sulphuric acid (‘condensation corrosion’) contributed to the formation of ¹³C‐enriched speleothem deposits.     

FT-IR measurements of petroleum fluid inclusions: methane, n-alkanes and carbon dioxide quantitative analysis

A recent advancement in petroleum geochemistry is to model fossil oil composition using microthermometric and volumetric data acquired from individual fluid inclusion analysis. Fourier transform infrared (FT‐IR) microspectroscopy can record compositional information related to gas (CH₄ and CO₂) and alkane contents of petroleum inclusions. In this study, a quantitative procedure for FT‐IR microspectrometry has been developed to obtain, from individual fluid inclusions, mol percentage concentrations of methane, alkanes and carbon dioxide as constraints to thermodynamic modelling. A petroleum inclusion in a sample from the Québec City Promontory nappe area was used as standard to record a reference spectrum of methane. The analytical procedure is based on the measurement of CH₄/alkane and CH₄/CO₂ band area ratios. CH₄/alkane infrared band area ratio is obtained after spectral subtraction of the reference methane spectrum. This area ratio, affected by absolute absorption intensities of methane, methyl and methylene, provides a molar CH₄/alkane ratio. Methyl/methylene ratio (CH₂/CH₃) ratio is obtained following procedures established in previous work. CO₂/CH₄ concentration ratio is estimated from relative absolute absorption intensities. Application to natural inclusions from different environments shows good correlation between FT‐IR quantification and PIT (petroleum inclusion thermodynamic) modelling.     

An unusual aperture in a child's calvaria from western Central Asia: differential diagnoses

The partial remains of a child's cranium were examined as part of a three‐year research project investigating the health and population movements of prehistoric communities in western Central Asia. Differential diagnoses are provided for an unusual aperture observed at the bregma. Possible aetiologies for the aperture include congenital and developmental defects, pathological alterations, surgical intervention, trauma and post‐mortem changes. The lesion presented in this article is interesting in terms of the contribution it makes to our understanding of the types of possible diseases that existed in the past, in this relatively understudied part of the world. Copyright © 2005 John Wiley & Sons, Ltd.     

LUMINESCENCE DATING OF POTTERY FROM LATER PREHISTORIC BRITAIN*

Dating of later prehistoric settlements relies heavily on potter; typologies in England and yet there has been little scientific dating in order to verify these typologies. In this work, luminescence dating techniques were applied directly to the pottery which forms the typological framework. Excellent agreement was obtained between the luminescence ages, and archaeological age ranges for known‐age pottery sherds with diagnostic form and surface decoration. A lower correlation, however, was found in several regions between the luminescence ages for undecorated body sherds and the archaeological assessment which was necessarily based solely on fabric, suggesting the need for reassessment of these fabric chronologies.     

THE CHALLENGE OF ‘TECHNOLOGICAL CHOICES’FOR MATERIALS SCIENCE APPROACHES IN ARCHAEOLOGY*

Recently several anthropological and sociological studies have interpreted technologies as cultural choices that are determined as much by local perceptions and the social context fly any material constraints or purely functional criteria. Using the example of ceramic technology we consider how materials science studies can contribute to and benefit from this understanding of technology as a social construct. Although we acknowledge some potential difficulties, it is our contention that both materials scientists and archaeologists have gained much and have much to gain by cooperating together to study ancient technologies, and that the concept of ‘technological choices’can facilitate a wider consideration of the factors shaping technological developments.     

NON‐DESTRUCTIVE PORTABLE GAMMA RAY SPECTROMETRY USED IN PROVENANCING ROMAN GRANITOID COLUMNS FROM LEPTIS MAGNA,NORTH AFRICA*

Portable gamma ray spectrometry (PGRS) provides a non destructive means to analyst quantitatively large artefacts, such as building stones, for the radioelements K. U and Th. Nine Raman granitoid columns at the Leptis Magna Ruins in Windsor Great Park, London, were measured in situ by PGRS. Corrections for the environmental background contribution to the gamma ray flux measured, and for the shape and size of the columns, are described Comparison of the PGRS data with a radioelement data base for Roman granite sources indicates that most of the columns originated in the Troad area of Turkey. Two columns could not be unambiguously provenanced using PGRS alone because there is insufficient difference between radioelement concentrations in certain sources. However, non‐destructive measurements of magnetic susceptibility, used in conjunction with PGRS data, suggest that these two columns originated in the Kozak Daǧ, also in Turkey.