Gold in “primitive” Archaean volcanics

Gold concentrations have been determined by neutron activation in sixteen samples of komatiites and related rocks from Barberton, South Africa. All the rocks give Au values in the ranges 1–1.5 ppb with no evidence for anomalously high values in such old primitive igneous types. As the rocks are extensively hydrated, it is possible that Au has been leached from the rocks during later hydration processes.     

The Ameralik dykes of West Greenland,the earliest known basaltic rocks intruding stable continental crust

The pre-3100 m.y. old Ameralik dykes from West Greenland show a range in primary composition from primitive low-K, low-Ti tholeiites virtually identical in composition to ridge basalts of modern ocean crust, to more differentiated basaltic rocks similar to some present-day continental tholeiites. Primary variations are distinguished from secondary metasomatism using REE patterns, Ni, Sr, Ti and Zr contents and Mg number as a guide to the stage of differentiation reached by a particular sample and comparing this to the amount of alkalis present. The chemistry of the dykes is compared to that of metabasalts from Archaean greenstone belts and the use of chemistry alone to distinguish the crustal environment under which Archaean basic rocks were formed is questioned.     

Aragonite dissolution on the Bermuda pedestal: Its depth and geochemical significance

The depth distribution of pteropod and planktonic foram tests, and fine-grained (<62 μm) aragonite, high-Mg calcite (12 mode mol.% MgCO₃), and low-Mg calcite has been determined for surface sediments of an area of the eastern slope of the Bermuda pedestal. Over the range 1800–3000 m, fine-grained aragonite and fine-grained high-Mg calcite gradually disappear relative to fine-grained low-Mg calcite, and pteropods gradually disappear relative to planktonic forams. This is interpreted as preferential dissolution of aragonite (and high-Mg calcite) relative to low-Mg calcite over this depth range. Coarse aragonitic debris derived from shallow-water organisms living on the Bermuda platform does not show consistent disappearance over the same depth zone. Chemical analyses of bottom water samples taken at the same time as some of the sediment samples indicate that the degree of saturation with respect to aragonite Ω_A over the zone of aragonite disappearance ranges from 0.55 to 0.85; i.e. major dissolution occurs only at Ω_A values distinctly less than one. These results lend credence to the hypothesis that CaCO₃ dissolution in the oceans, both as aragonite and as calcite, takes place mainly as a response to complex chemical kinetic phenomena and not as a result of the simple attainment of undersaturation (thermodynamic hypothesis) or the resuspension of bottom sediment (hydrodynamic hypothesis).     

Assessment of δ13C and C/N ratios in bulk organic matter as palaeosalinity indicators in Holocene and Lateglacial isolation basin sediments,northwest Scotland

Carbon isotopes (δ¹³C) and C/N ratios from bulk organic matter have recently been used as alternative proxies for relative sea‐level (RSL) reconstruction where there are problems associated with conventional biological indictors. A previous study on a single isolation basin (Upper Loch nan Eala) in northwest Scotland has shown a clear relationship between δ¹³C, C/N ratios and palaeosalinity from Younger Dryas and Holocene aged sediments. In this paper we present results of δ¹³C and C/N ratio analyses from other isolation basins in northwest Scotland over the Holocene and the Lateglacial period in order to validate this technique. The results from the Holocene sequences support the earlier findings that this technique can be used to identify RSL change from isolation basins over the Holocene in this region. The relationship between δ¹³C, C/N ratios and RSL change is not apparent in sediments of Lateglacial age. Other environmental variables such as atmospheric CO₂ concentration, poor vegetation development and temperature influence δ¹³C values during this period. Copyright © 2007 John Wiley & Sons, Ltd.     

A multiproxy climate record from a raised bog in County Fermanagh,Northern Ireland: a critical examination of the link between bog surface wetness and solar variability

A proxy climate record from a raised bog in County Fermanagh, Northern Ireland, is presented. The record spans the interval between 2850 cal. yr BC and cal. yr AD 1000 and chronological control is achieved through the use of tephrochronology and ¹⁴C dating, including a wiggle‐match on one section of the record. Palaeoclimatic inferences are based on a combination of a testate amoebae‐derived water table reconstruction, peat humification and plant macrofossil analyses. This multiproxy approach enables proxy‐specific effects to be identified. Major wet shifts are registered in the proxies at ca. 1510 cal. yr BC, 750 cal. yr BC and cal. yr AD 470. Smaller magnitude shifts to wetter conditions are also recorded at ca. 380 cal. yr BC, 150 cal. yr BC, cal. yr AD 180, and cal. yr AD 690. It is hypothesised that the wet shifts are not merely local events as they appear to be linked to wider climate deteriorations in northwest Europe. Harmonic analysis of the proxies illustrates statistically significant periodicities of 580, 423–373, 307 and 265 years that may be related to wider Holocene climate cycles. This paper illustrates how the timing of climate changes registered in peat profiles records can be precisely constrained using tephrochronology to examine possible climatic responses to solar forcing. Relying on interpolated chronologies with considerable dating uncertainty must be avoided if the climatic responses to forcing mechanisms are to be fully understood. Copyright © 2007 John Wiley & Sons, Ltd.     

Volcanic ash clouds affecting Northern Europe: the long view

The volcanic ash or ‘tephra’ cloud resulting from the relatively small (volume and VEI) eruption of the Icelandic volcano Eyjafjallajökull in 2010 caused major air travel disruption, at substantial global economic cost. On several occasions in the past few centuries, Icelandic eruptions have created ash and/or sulphur dioxide clouds which were detected over Europe (e.g. Hekla in 1947, Askja in 1875, and Laki in 1783). However, these historical observations do not represent a complete record of events serious enough to disrupt aviation in Europe. The only feasible evidence for this is within the geological tephra record. Ash layers are preserved in bogs and lakes where tephra deposited from the atmosphere is incorporated in the peat/mud. In this article we: 1, introduce the analysis of the Northern European sedimentary tephra record; 2, discuss our findings and modelling results; 3, highlight how these were misinterpreted by the popular media; and 4, use this experience to outline several existing problems with current tephra studies and suggest agendas for future research.     

A rare reflection effect eclipsing sdB+dM binary: 2M 1533+3759

In this paper, we report a rare reflection effect eclipsing sdB+dM binary, 2M?1533+3759. It is the seventh eclipsing sdB+dM binary that has been discovered to date. This system has an orbital period of 0.16177042 day and a velocity semi-amplitude of 71.1 km?s^?1. Using a grid of zero-metallicity NLTE model atmospheres, we derived T _eff=29250 K, log?g=5.58 and [He/H]=?2.37 from spectra taken near the reflection effection minimum. Lightcurve modeling resulted in a system mass ratio of 0.301 and an orbital inclination angle of 86.6°. The derived primary mass for 2M?1533+3759, 0.376±0.055 M _⊙, is significantly lower than the canonical mass (0.48 M _⊙) found for most previously investigated sdB stars. This implies an initial progenitor mass >1.8 M _⊙, at least a main sequence A star and perhaps even one massive enough to undergo non-degenerate helium ignition.     

Detecting infiltration and impacts of introduced water using strontium isotopes

Water introduced to surface drainages, such as agricultural and roadway runoff, mine drainage, or coalbed natural gas (CBNG)-produced water, potentially can be of environmental concern. In order to mitigate potential environmental effects, it may be important to be able to trace water discharged to the surface as it infiltrates and interacts with near-surface aquifers. We have chosen to study water withdrawn during CBNG production for isotope tracing in the hyporheic zone because it poses a variety of economic, environmental, and policy issues in the Rocky Mountain states. Ground water quality must be protected as CBNG water is added to semiarid ecosystems. Strontium (Sr) isotopes are effective fingerprints of the aquifer from which water originates. In this study, CBNG water was found to have a higher (87)Sr/(86)Sr ratio than the local alluvial aquifer water. This measurable difference allows the strontium isotope ratio and concentration to be used as tracers of CBNG water following its discharge to the surface. The dissolution and mobilization of salts from soil are an important contributor to ground water quality degradation. In the Powder River basin of Wyoming, the soils are calcium carbonate-buffered systems. The chemical similarity of strontium to calcium allows it to substitute into calcium minerals and enabled us to use strontium isotopes to identify calcium salts mobilized from the soil. Strontium isotopes are an effective monitor of the source of ions and the volume and direction of introduced water flow in the hyporheic zone.     

Interviewing landed elites in post-war Guatemala

This essay explores the methodological challenges of conducting ethnographic research among economic and managerial elites in Guatemala’s landed sector during the country’s post-war transition. Guatemala’s 34-year civil war ended with peace accords in 1996. From the mid 1990s through 2001, I conducted interviews with leading representatives of the private sector in Guatemala, including the owners and top managers of the country’s sugar plantations. The Guatemalan sugar elite describes itself as the new face of the private sector in Central America, implementing “corporate social responsibility” programs linked to the World Bank and other international agencies. Questions of access and interview dynamics are often discussed in relation to qualitative research on “elites.” Yet, I found the interview process to be less complicated than I anticipated. Of greater concern were the problems of research dissemination and praxis. The experience discussed here raises questions about whether research on particular elite groups can be sustained over long periods of time.