Fracture-fill calcite as a record of microbial methanogenesis and fluid migration: a case study from the Devonian Antrim Shale, Michigan Basin

The Devonian Antrim Shale is an organic‐rich, naturally fractured black shale in the Michigan Basin that serves as both a source and reservoir for natural gas. A well‐developed network of major, through‐going vertical fractures controls reservoir‐scale permeability in the Antrim Shale. Many fractures are open, but some are partially sealed by calcite cements that retain isotopic evidence of widespread microbial methanogenesis. Fracture filling calcite displays an unusually broad spectrum of δ¹³C values (+34 to ?41‰ PDB), suggesting that both aerobic and anaerobic bacterial processes were active in the reservoir. Calcites with high δ¹³C values (>+15‰) record cementation of fractures from dissolved inorganic carbon (DIC) generated during bacterial methanogenesis. Calcites with low δ¹³C values (13C values between ?10 and ?30‰ can be attributed to variable organic matter oxidation pathways, methane oxidation, and carbonate rock buffering. Identification of ¹³C‐rich calcite provides unambiguous evidence of biogenic methane generation and may be used to identify gas deposits in other sedimentary basins. It is likely that repeated glacial advances and retreats exposed the Antrim Shale at the basin margin, enhanced meteoric recharge into the shallow part of the fractured reservoir, and initiated multiple episodes of bacterial methanogenesis and methanotrophic activity that were recorded in fracture‐fill cements. The δ¹⁸O values in both formation waters and calcite cements increase with depth in the basin (?12 to ?4‰ SMOW, and +21 to +27‰ PDB, respectively). Most fracture‐fill cements from outcrop samples have δ¹³C values between ?41 and ?15‰ PDB. In contrast, most cement in cores have δ¹³C values between +15 and +34‰ PDB. Radiocarbon and ²³⁰Th dating of fracture‐fill calcite indicates that the calcite formed between 33 and 390 ka, well within the Pleistocene Epoch.     

Big Game and Small Prey: Paleolithic and Epipaleolithic Economy from Valencia (Spain)

This study analyzes the faunal assemblages corresponding to the Middle and Upper Paleolithic and the Early Epipaleolithic for the central Spanish Mediterranean Region dated from between 135,000 and 9,000 B.P. To interpret these data, we employ a zooarchaeological and paleoeconomic perspective. Human large and small game hunting systems are analyzed through the identification of the origins of faunal assemblages, bone breackage patterns, and prey selection patterns. Our study shows that hunting systems changed significantly through time, which may be related to the characteristics of the Mediterranean ecosystem and, above all, to cultural changes.     

Teaching the Craft of Archaeology: Theory, Practice, and the Field School

Field schools are a rite of passage for archaeologists, the first experience of what for many is the defining activity of the discipline: fieldwork. While teaching competence in practical techniques is the minimum goal of any field school, this technical training must be situated within the broader goals that drive the fieldwork. The University of Denver Archaeological Field School provides the fieldwork for the Colorado Coal Field War Archaeological Project. This project is an experiment in archaeology as political action in the present. It explores the possibility of an emancipatory archaeology through engagement with contemporary audiences and struggles. In this paper we discuss some of the ways we try to link technical training with the admittedly unusual theoretical and political goals of the project, teaching not only skills but an awareness of the responsibilities these skills should bring.     

The transformation and future prospects of Europe's defence industry

Europe's defence industry has evolved by transforming itself from a collection of nationally oriented firms to one dominated by two giants. Stimuli external and internal to the European Union (EU) are responsible for this development. After describing the evolution of this sector since the end of the Cold War, the authors present four factors that played key roles: developments within the United States' defence industry; the impact of technology and defence economics; general economic restructuring within the EU together with nascent defence industrial policy; and progress towards the creation of a European Security and Defence Policy. While the evolution required all four factors, the EU played a critical and under–appreciated economic and political role in the changes that have transformed the European defence industry, and is now positioned to continue to shape this process.     

On the Rank-Size Distribution for Human Settlements

An explanation for the rank-size distribution for human settlements based on simple stochastic models of settlement formation and growth is presented. Not only does the analysis of the model explain the rank-size phenomenon in the upper tail, it also predicts a reverse rank-size phenomenon in the lower tail. Furthermore it yields a parametric form (the double Pareto-lognormal distribution) for the complete distribution of settlement sizes. Settlement-size data for four regions (two in Spain and two in the U.S.) are used as examples. For these regions the lower tail rank-size property is seen to hold and the double Pareto-lognormal distribution shown to provide an excellent fit, lending support to the model and to the explanation for the rank-size law.     

Bear dentine aspartic acid racemization analysis: a proxy for the dating of Pleistocene cave infills

A high correlation between chronometric determinations based on aspartic acid racemization ratios and radioactive dating methods is described from samples of cave bear (Ursus deningeri and Ursus spelaeus) dentine. For samples from a very restrictive environment, as deep cave bear sites are (in view of their highly stable geochemical and thermal history), an age calculation algorithm was obtained. It has been found that there is a very close relationship between collagen preservation, from total aspartic acid in the > 3500 D fraction, and the amino acid racemization.     

The Material Characterization of a Santamarian Ceremonial Axe

The characterization of a ceremonial bronze axe is described. The axe is assigned to the Santamarian culture of north‐west Argentina, c. 1000–1470 ad, and was selected to increase presently limited knowledge of prehistoric metallurgy in the Andean region of Argentina. The characterization methods used were electron probe microanalysis, gamma radiography, X‐ray diffraction, optical metallography and microhardness testing. The axe was well cast in a bivalve mould, with the only defects in the area of an ancient fracture. The analysis showed that it is made from a tin bronze with a, probably, accidental addition of lead. Arsenic was found as a surface contamination, probably deriving from arsenic in the water of the stream in which the axe was found. The axe shows that Santamarian craftsmen had the skill to decorate the axe in an artistic style with a strong local accent while providing a functional, annealed and cold‐worked cutting edge.     

An investigation of soil phosphorus distribution within occupation deposits from a Romano-British hut group

A simple scheme for soil sampling and subsequent analysis for total soil phosphorus using perchloric acid digestion is described and its application illustrated by samples from the native farmstead of the Roman period at Cefn Graeanog in North Wales. The floor deposits of three distinctive buildings were analysed, and the data obtained enhanced by Trend Surface Analysis to produce generalized maps of the phosphorus distribution, together with levels of significance of such distribution patterns. These were then used to clarify the details of the interpretation of the usage of the various types of building. Data for soil phosphorus concentration clearly reveal the pattern of erosion of constructed floors, the presence of features such as hearths and drains, and can be used to reveal patterns not otherwise discernible by excavation techniques.