Zircon microstriators in the sand of auriferous Andean tills: fine tools and noble metals

Chemically inert and physically hard minerals, of which zircon is universally present and usually abundant, are minor but important components of glacial gold and tin placer deposits. Zircons and other much less common resistant minerals inflict major damage on light minerals, of which quartz is the dominant, chemically resistant member. Because of its sharpness inherited from a strong crystal morphology, and overall prismatic form, zircon is especially important as an abrasive mineral in glacial systems. Its chemically inert nature, its dominancc in terms of hardness over light minerals, and its abundance amongst other hard minerals makes it unique and important as a microstriator. Transported in a highly viscous glacial medium, it is capable of damaging other softer grains with aggressive crushing, chipping, striating, abrading and polishing processes. These occur in both coarse-grained gravelly sand and in fine-grained clayey silt matrices at the base of the icc. Zircon grains tend to serve many functions, initially as inclusion tools in larger feldspar grains and as 'studs' in quartzite grains. Wearing first on points, and later, following liberation, they assume a shape by honing, faceting and fracturing as tools and as grit that allows them to act as microstriators, inflicting damage on other particles in the basal ice. With a hardness of 7.5, lacking significant cleavage, and exhibiting strong crystal form. the finer-grained zircons appear to abrade and striate quartz (hardness 7.0). feldspars (hardness 6.0). garnets (hardness 6.5–7.5), and gold (hardness 2.5-3.0). A detailed study of Bolivian tills shows the dominant form of the zircon striator to be an elongate, pencil shape (euhedral polygonal prism with sharp, pyramidal terminations) that shows various degrees of abrasion, and ranges from wide grains with dull edges to narrow grains with sharp edges (typical pencil form).     

The potential of perennial cave ice in isotope palaeoclimatology

Perennial ice from caves on and to the east of the Canadian Great Divide yield δ¹⁸O and δD values, which are unusually high measurements when compared with the average precipitation for the region. Furthermore, these ice data fall below and along lines of lower slope than the Global Meteoric Water Line. To explain the observed relationships, we propose the following process. A vapour-ice isotopic fractionation mechanism operates on warm-season vapour when it precipitates as hoar ice on entering the caves. The subsequent fall of hoar to the cave floor through mechanical overloading, along with ice derived from ground-water seepage (with a mean annual isotopic composition), results in massive ice formation of a mixed composition. This mixed composition is what is observed in the characteristic relationships found here. Such findings suggest that a warm versus cold climate interpretation for ancient cave ice may be the opposite of that found in the more familiar polar and glacial ice cores.     

Detectives and geology in fiction - 1: Holmes and Thorndyke

In the early years - the so called 'Golden Age' - of mystery fiction, there were a number of towering figures - the 'great detectives'. However, only two of them included geology among their concerns. Their abilities and achievements are here compared and assessed.     

Assessing the completeness of the deglacial-marine stratigraphic record on west Spitsbergen by accelerator mass spectrometry radiocarbon dating

The record of Quaternary glaciations of coastal areas is frequently preserved as a raised deglacial-emergence sequence. Detailed radiocarbon dating of foraminifera and marine macrofossils from a representative deglacial sequence on west Spitsbergen document two periods of sedimentation at c . 11,400 BP and at 9500 BP that together span < 500 years. The incompleteness of this record (< 25%), the highly episodic nature of sedimentation, the dominance of local glacial and environmental effects and the presence of allochthonous foraminifera inhibits ascertaining the relation between deglaciation of Svalbard/Barents Sea and changes in thermohaline circulation in the Norwegian Sea. The Late Weichselian and older deglacial sequences on west Spitsbergen have a similar sedimentologic succession. Thus, one possibility is that older raised-marine deglacial sequences on Svalbard and other Arctic areas may represent similar brief intervals, potentially confounding correlations across the Arctic and with well established events (i.e. the Eemian Interglacial) at lower latitudes.     

Global cotton and local environmental management: the political ecology of rich and poor small-hold farmers in southern Mali

This study examines the hypothesis that poor households engage in less sustainable soil management practices than rich households in a similar socioeconomic environment. This broad objective is explored in Mali's southern cotton belt through three specific research questions. First, is there empirical evidence to support the claim that poor households engage in less sustainable soil management practices than rich households? Second, what local and extra-local factors influence household agricultural management approaches in southern Mali? Third, what broader scale political and economic processes are linked to the factors that influence local-level agricultural management approaches? The author reports that soil quality measures on the farms of rich and poor households are not significantly different, refuting the conventional wisdom that the wealthy are better managers of the environment. A variety of environmentally deleterious practices are associated with export-oriented cotton production, an activity more vigorously pursued by wealthy than poor farmers. Finally, the focus on poverty in international environment and development discourse has allowed the government of Mali to avoid a serious debate on the sustainability of cotton production. The study's findings are based on household interviews describing agricultural management practices, an analysis of farm field soil measures, and discussions with donors and national policymakers.