Chloride ion concentrations during the compression of rocks to extract pore water

Pore water needs to be extracted from rocks with low permeabilities to allow the major ion concentrations in the pore water to be estimated. Compressing a rock is the most widely used method of extracting the pore water. However, ion concentrations have been found to change during compression in previous studies, and the mechanisms involved in such ion concentration changes have not yet been fully assessed. In this study, two natural rocks and four artificially prepared samples were compressed, and changes in the chloride ion (Cl^?) concentrations as the compression pressure increased were investigated. Mechanisms that could have caused the changes observed were then assessed. The Cl^? concentrations in squeezed water decreased as the pressure increased if the sample contained a significant amount of smectite. The strong dependence of Cl^? concentration on the amount of smectite indicated that smectite played an important role in decreasing the Cl^? concentration. The dilution of the pore water with interlayer water from the smectite appeared to be the dominant mechanism involved in the decrease in Cl^? concentration found in a Kunigel‐V1 sample, because dilution of the pore water with interlayer water quantitatively explained the decrease in the Cl^? concentration. The filter effect caused by the anion exclusion effect did not appear to be a dominant mechanisms in our case. However, Cl^? concentration decrease found in natural rocks could not be fully explained by dilution with interlayer water, so other mechanisms must be involved the phenomenon in natural rocks.     

Long‐term chemical evolution and modification of continental basement brines – a field study from the Schwarzwald,SW Germany

Highly saline, deep‐seated basement brines are of major importance for ore‐forming processes, but their genesis is controversial. Based on studies of fluid inclusions from hydrothermal veins of various ages, we reconstruct the temporal evolution of continental basement fluids from the Variscan Schwarzwald (Germany). During the Carboniferous (vein type i), quartz–tourmaline veins precipitated from low‐salinity (<4.5wt% NaCl + CaCl₂), high‐temperature (≤390°C) H₂O‐NaCl‐(CO₂‐CH₄) fluids with Cl/Br mass ratios = 50–146. In the Permian (vein type ii), cooling of H₂O‐NaCl‐(KCl‐CaCl₂) metamorphic fluids (T ≤ 310°C, 2–4.5wt% NaCl + CaCl₂, Cl/Br mass ratios = 90) leads to the precipitation of quartz‐Sb‐Au veins. Around the Triassic–Jurassic boundary (vein type iii), quartz–haematite veins formed from two distinct fluids: a low‐salinity fluid (similar to (ii)) and a high‐salinity fluid (T = 100–320°C, >20wt% NaCl + CaCl₂, Cl/Br mass ratios = 60–110). Both fluids types were present during vein formation but did not mix with each other (because of hydrogeological reasons). Jurassic–Cretaceous veins (vein type iv) record fluid mixing between an older bittern brine (Cl/Br mass ratios ~80) and a younger halite dissolution brine (Cl/Br mass ratios >1000) of similar salinity, resulting in a mixed H₂O‐NaCl‐CaCl₂ brine (50–140°C, 23–26wt% NaCl + CaCl₂, Cl/Br mass ratios = 80–520). During post‐Cretaceous times (vein type v), the opening of the Upper Rhine Graben and the concomitant juxtaposition of various aquifers, which enabled mixing of high‐ and low‐salinity fluids and resulted in vein formation (multicomponent fluid H₂O‐NaCl‐CaCl₂‐(SO₄‐HCO₃), 70–190°C, 5–25wt% NaCl‐CaCl₂ and Cl/Br mass ratios = 2–140). The first occurrence of highly saline brines is recorded in veins that formed shortly after deposition of halite in the Muschelkalk Ocean above the basement, suggesting an external source of the brine's salinity. Hence, today's brines in the European basement probably developed from inherited evaporitic bittern brines. These were afterwards extensively modified by fluid–rock interaction on their migration paths through the crystalline basement and later by mixing with younger meteoric fluids and halite dissolution brines.     

Freezing and melting behaviors of H2O‐NaCl‐CaCl2 solutions in fused silica capillaries and glass‐sandwiched films: implications for fluid inclusion studies

Fluid inclusions of the H₂O‐NaCl‐CaCl₂ system are notorious for their metastable behavior during cooling and heating processes, which can render microthermometric measurement impossible or difficult and interpretation of the results ambiguous. This study addresses these problems through detailed microscopic examination of synthetic solutions during cooling and warming runs, development of methods to enhance nucleation of hydrates, and comparison of microthermometric results with different degrees of metastability with values predicted for stable conditions. Synthetic H₂O‐NaCl‐CaCl₂ solutions with different NaCl/(NaCl + CaCl₂) ratios were prepared and loaded in fused silica capillaries and glass‐sandwiched films for microthermometric studies; pure solutions were used with the capillaries to simulate fluid inclusions, whereas alumina powder was added in the solutions to facilitate ice and hydrate crystallization in the sandwiched samples. The phase changes observed and the microthermometric data obtained in this study have led to the following conclusions that have important implications for fluid inclusion studies: (i) most H₂O‐NaCl‐CaCl₂ inclusions that appear to be completely frozen in the first cooling run to ?185°C actually contain large amounts of residual solution, as also reported in some previous studies; (ii) inability of H₂O‐NaCl‐CaCl₂ inclusions to freeze completely may be related to their composition (low NaCl/(NaCl + CaCl₂) ratios) and lack of solid particles; (iii) crystallization of hydrates, which is important for cryogenic Raman spectroscopic studies of fluid inclusion composition, can be greatly enhanced by finding an optimum combination of cooling and warming rates and temperatures; and (iv) even if an inclusion is not completely frozen, the melting temperatures of hydrohalite and ice are still valid for estimating the fluid composition.     

Immaculate Consumption: A Critique of the “Shop till you drop” School of Human Behavior

Consumer behavior and choice models have assumed a major role in historical archaeology. Recent interest in consumption is an honest attempt to move beyond an emphasis on production. Consumer models have clear material referents, making them useful in historical archaeology. These models, however, separate production from consumption, and privilege the autonomous individual as the preferred unit of analysis. They also reinforce and validate ideologies that obscure inequalities and power relations in modern society. For us the important issue is how people reproduce themselves as social beings. Focusing on social reproduction integrates both production and consumption.     

ANALYTICAL INVESTIGATION OF ARCHAEOLOGICAL POWDERS FROM GÖLTEPE (TURKEY)*

Nine powder samples originating from the archaeometallurgical she in Göltepe, southern central Turkey, have been analysed. Bulk analyses, using X-ray fluorescence and X-ruy photoelectron spectroscopy, and single particle analyses, using electron probe X-ray microanalysis, were carried out. The analyses were focused on determining the inorganic elemental composition of the samples and the distribution of particle types in the nine powder samples. In addition, the powder samples were classified on the basis of their elemental composition using multivariate techniques. The objective of this study was to characterize the powder samples and to establish an association with archaeological data from the site     

OPTICAL DATING OF SINGLE AND MULTIPLE GRAINS OF QUARTZ FROM JINMIUM ROCK SHELTER,NORTHERN AUSTRALIA: PART I,EXPERIMENTAL DESIGN AND STATISTICAL MODELS*

Jinmium rock shelter is famous for the claims made by Fullagar et al. (1996) for the early human colonization and ancient rock art of northern Australia. These claims were based on thermo-luminescence ages obtained for the artefact-bearing quartz sediments that form the floor deposit at the site. In this paper, we outline the background to the optical dating programme at Jinmium, and describe the experimental design and statistical methods used to obtain optical ages from single grains of quartz sand. The results, interpretations, and implications of this dating programme are reported in a companion paper (Roberts et al. 7999, this volume).     

Policy Interaction in the Provision of Unemployment Insurance and Low-Income Assistance by State Governments

In this paper we investigate empirical relationships between Unemployment Insurance (UI) and welfare policies using a unique database covering 48 states annually from 1973 through 1989. We first document substantial variation across states in UI program outcomes. Having established that UI is so variable, we explore the simultaneous interaction between UI and Aid to Families with Dependent Children (AFDC), Medicaid, and total state and local welfare spending. Our econometric results indicate substitution between the two cash assistance programs, AFDC and UI, by state governments. On the other hand, states that operate relatively generous UI programs also tend to allocate more resources to Medicaid and other in-kind, low-income assistance programs.