The new geological map of East Greenland

NE Greenland has seen epic polar exploration, bitter territorial disputes, scientific skulduggery but contains some of the world's most striking scenery and geology. It is now documented with a new geological map from 70°N to 82°N, which documents the architecture of the Caledonian mountain range over 1300km.     

Shallow bias of paleomagnetic inclinations in the Paleozoic and Precambrian

An updated analysis of the global paleomagnetic database shows that the frequency distributions of paleomagnetic inclinations for the Cenozoic and Mesozoic eras (younger than 250 Ma) are compatible with a random geographical sampling of a time-averaged geomagnetic field that closely resembles that of a geocentric axial dipole. In contrast, the frequency distributions of paleomagnetic inclinations for the Paleozoic and Precambrian eras (prior to 250 Ma) are over-represented by shallow inclinations. After discounting obvious secondary causes for the bias, such as from data averaging, sedimentary inclination error, inhomogeneous lithological distributions, and tropical remagnetization, we show that the anomalous inclination distributions for the Paleozoic and Precambrian can be explained by a geomagnetic field source model which includes a relatively modest (25%) contribution to the axial dipole from a zonal octupole field and an arbitrary zonal quadrupolar contribution. The apparent change by around 250 Ma to a much more axial dipolar field geometry might be due to the stabilization of the geodynamo from growth of the inner core to some critical threshold size, a gross speculation which would imply that either the threshold size was rather large or the inner core nucleated rather late in Earth history. Alternatively, if a geocentric axial dipole model is assumed or can eventually be demonstrated independently, the anomalous inclination distributions for the Paleozoic and Precambrian may reflect a tendency of continental lithosphere to be cycled into the equatorial belt, perhaps because geoid highs associated with long-term continental aggregates influence true polar wander.     

“Helping” or “Appropriating”? Gender Relations in Shea Nut Production in Northern Ghana

The potential for the development of shea industries to increase women’s incomes is the focus of a number of development interventions in rural West Africa. However, concerns have been voiced over the potential effects of increased commercialization on women’s rights over this resource. This study examines women’s participation and rights over shea production in a context of increasing commercialization in northern Ghana through a survey of 90 producers and eight oral histories. Although shea incomes are frequently described in the literature as falling under women’s control, joint spending decisions for shea income were reported by half of the married women surveyed. This does not appear to be an outcome of growing assertion of men’s rights over shea trees themselves but rather is explained, by women, largely in relation to their husbands’ involvement in nut production.     

Geomagnetic reversal frequency since the Late Cretaceous

Models of geomagnetic reversals as a stochastic or gamma renewal process have generally been tested for the Heirtzler et al. [1] magnetic polarity time scale which has subsequently been superseded. Examination of newer time scales shows that the mean reversal frequency is dominated in the Cenozoic and Late Cretaceous by a linearly increasing trend on which a rhythmic fluctuation is superposed. Subdivision into two periods of stationary behavior is no longer warranted. The distribution of polarity intervals is visibly not Poissonian but lacks short intervals. The LaBrecque et al. [2] polarity time scale shows the positions of 57 small-wavelength marine magnetic anomalies which may represent short polarity chrons. After adding these short events the distribution of all polarity intervals in the age range 0–40 Myr is stationary and does not differ significantly from a Poisson distribution. A strong asymmetry develops in which normal polarity chrons are Poisson distributed but reversed polarity chrons are gamma distributed with indexk = 2. This asymmetry is of opposite sense to previous suggestions and results from the unequal distribution of the short polarity chrons which are predominantly of positive polarity and concentrated in the Late Cenozoic. If short-wavelength anomalies arise from polarity chrons, the geomagnetic field may be more stable in one polarity than the other. Alternative explanations of the origin of short-wavelength marine magnetic anomalies cast doubt on the inclusion of them as polarity chrons, however. The observed behavior of reversal frequency suggests that core processes governing geomagnetic reversals possess a long-term memory.     

Some observations on the chemical weathering of the Dartmoor granite

The majority of geomorphological papers about Dartmoor have been essentially speculative, particularly when discussing weathering processes and the evolution of the Dartmoor landscape. In contrast, this article presents a synthesis of several experimental investigations aimed at studying the chemical weathering of Dartmoor granite through the systematic analysis of soil and water samples. This involved the computation of a geochemical budget to determine the amount of erosion in the catchment, as well as more detailed mineralogical investigations within a soil profile. The annual output of solutes due to weathering was 116 kg ha^?1 a^?1 of which the majority was silica (93 kg ha^?1 a^?1). From an examination of the soil mineralogy, it was calculated that these solutes were derived from the dissolution of approximately 200 kg ha^?1 a^?1 plagioclase, 90 kg ha^?1 a^?1 biotite, and 40 kg ha^?1 a^?1 orthoclase. As well as the weathering of granite, there was also the production of kaolinite (150 kg ha^?1 a^?1) and gibbsite (0.02 kg ha^?1 a^?1). Analysis of the soil water chemistry confirmed that kaolinite was the stable mineral phase in the regolith, although in areas where interflow was the dominant mode of water movement, the solute composition was in equilibrium with both kaolinite and gibbsite. Examination of the clay mineralogy confirmed these results. The microtexture of quartz grains was examined by the scanning electron microscope as another means of investigating the hydrochemical environment in the soil. Silica was found precipitated on all the grains examined but the maximum amount occurred in the Bs horizon. This evidence showed that, firstly, the dissolution of aluminosilicate minerals is greater than that calculated by the chemical budget and, secondly, that models of granite weathering must take localized weathering in the soil profile into account. The final part of the paper highlights the limitations of calculating denudation rates for an entire catchment and stresses the need to consider weathering as a highly localized phenomenon, particularly where there are high volumes of interflow at hill crest sites. Observations on granite decomposition in the future should be quantitative in approach and be related to the local site conditions.     

Polymer-stabilized emulsions and fine-particle recovery,II. The chalcopyrite-quartz system

The interaction between fine, generally ?2 μm chalcopyrite and polymer-stabilized oil droplets has been studied as a function of pH and weight percent solids in the pH range from 5 to 12. Oil droplets stabilized by partially esterified polymethacrylic acid and cellulose xanthate have been used as collectors. Chalcopyrite may be efficiently separated from fine quartz gangue at pH 11, using cellulose xanthate stabilized emulsions. Good recovery and grade may be obtained at pH 11 up to pulp densities of at least 5.1 wt.%. At other pH values, selectivity is poor due to Cu¹¹ species from chalcopyrite activating the quartz surface.     

Dredged basaltic rocks from the seaward extensions of the Reykjanes and Snaefellsnes volcanic zones,Iceland

Data for basaltic rocks dredged on the Reykjanes Ridge and Jökulbanki off the southwest coast of Iceland are presented. The rocks from the Reykjanes Ridge, which are identified as recent lavas, are olivine tholeiites and quartz tholeiites very similar to those formerly described from this region. The heterogeneous Jökulbanki dredges were identified as erratics.In the light of the present and other recent data on tholeiitic rocks from Iceland and the Reykjanes Ridge, a distinct chemical gradient, together with increased scatter across Iceland is demonstrated for certain incompatible elements. This is in accordance with the mantle plume theory.     

On the magnetic susceptibility anisotropy of deep-sea sediment

Susceptibility anisotropies in the form of vertically prolate ellipsoids have been reported in many deep-sea sediment cores. The results of the present investigation suggest that these anisotropies may not describe the original magnetic fabric of deep-sea sediment, but are more likely due to either a measurement effect or to deformation of the sediment during coring. Anisotropy measurements made on a spinner magnetometer sometimes were found to be greatly affected by the shape of the sample. This apparent “sample-shape effect” was not observed on a low-field torque meter. The anisotropy of samples taken near the base or the top of some piston cores often reflects sediment disturbance during the coring operation. Most samples of deep-sea sediment examined had weak anisotropies that could be interpreted as due to normal depositional processes, including bioturbation. The best-fitting susceptibility ellipsoids were usually oblate with near vertical minimum susceptibility axes.     

On the Age of Rhodesian Greenstone Belts

Deformation experiments have been carried out on a microgranodiorite under undrained conditions at a pressure of 0.448 GPa and temperatures up to 720 °C. The granodiorite contained a small amount of chlorite and amphibole minerals which decomposed at elevated temperatures, giving rise to a pore pressure. Evidence about the decomposition reaction was obtained from differential thermal analysis and optical microscopy. In some experiments small amounts of free water were enclosed with the sealed rock sample. The strength (at fracture or 2 per cent strain) fell to very low values (0.02 GPa) at 700 °C, and at temperatures of 670 °C and above there was evidence of partial melting which led to ductile behaviour. At somewhat lower temperatures the rock was relatively weak but brittle.