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.     

On Pins and Needles: Tracing the Evolution of Copper-base Alloying at Tepe Yahya, Iran, via ICP-MS Analysis of Common-place Items

From 1967 to 1975 a team of archaeologists excavated the site of Tepe Yahya in southeastern Iran under the direction of C. C. Lamberg-Karlovsky. Although there are two forthcoming “final reports” (Hiebert (in progress), and Magee (in press); see also Lamberg-Karlovsky & Potts, 2001), analysis of the materials continues as opportunities allow. Metal artefacts, most especially those made of copper and its alloys, are found at this site from the late Neolithic through the Iron Age. Archaeometallurgical analysis, radiocarbon chronologies, and archaeological interpretation allow one to state when and how a type of metal or a style of object was invented, its use as a trade item, and its function and value to an ancient community. In the hopes of establishing a framework for future archaeometallurgical studies, most of the metal artefacts from Tepe Yahya, Iran, stored in the Peabody Museum of Harvard University, were analysed for elemental composition to complement stylistic and metallographic data.     

The Effect of State Economic Development Incentives on Employment Growth of Establishments

This paper examines the effects of state economic development incentives on the growth of 366 Ohio manufacturing and nonmanufacturing establishments that launched major expansions between 1993 and 1995. Growth is measured as the actual employment change that occurred in these establishments and as the employment growth announced when expansions were launched. Empirical findings indicate that incentives have very little (or even a negative) effect on actual growth and they have a substantial positive effect on announced growth. Findings also suggest that establishments that received incentives overestimated their announced employment targets more than establishments that did not receive incentives.     

Transmission electron microscopy (TEM) applied to ancient pottery

A comparative study of ancient pottery has been carried out, which utilized X‐ray diffraction, optics and scanning and transmission electron microscopy (SEM and TEM). Samples came from three prehistoric sites in northern Spain (La Rioja). Transmission electron microscope techniques, which use intact ion‐milled samples, allow minerals and glass to be imaged in situ, providing data on textures, crystal structures and composition. TEM provided detailed characterization of both source‐characteristic raw materials and products of the firing process, and revealed the range of intermediate phases, most of which had sizes beyond that of resolution by SEM. More importantly, TEM provided definition of the reaction processes, from starting materials through glass and new crystalline phases, providing data on both temperature and duration of firing.     

Morphological taphonomic transformations of fossil bones in continental environments,and repercussions on their chemical composition

The aim of this paper is to provide a summary of structural or surface modifications of vertebrate bone remains in continental palaeoenvironments that may have repercussions on their chemical composition. Both before and after burial, a different set of physical, chemical and biological agencies may produce modifications of the bone morphological structure and/or bone chemical composition. Several of these morphological modifications are diagnostic of particular agents, which otherwise may not be noticed or identified in a fossil association. In order to understand diagenesis, those events that occurred before final burial have to be considered, as they may strongly modify the bone morphological structure and influence post–burial changes.     

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.