Boron in chert and Precambrian siliceous iron formations

In order to assess the importance of siliceous sediments as a sink for oceanic B and to determine the effect of diagenesis on the mobilization of B, samples were analysed from chert nodules, bedded cherts, and siliceous banded iron formations from a variety of sedimentary environments and geologic ages. Boron analyses on bulk samples were made by prompt gamma neutron activation analysis. The distribution of B in rocks was mapped using α-track methods.Nodular Phanerozoic cherts typically contain 50–150 ppm B, and bedded cherts somewhat less. The B is initially concentrated in tests of silica-secreting organisms, but some is lost in early diagenesis as silica progressively recrystallises to quartz.Banded iron formation silica of Archean and Proterozoic age usually contains < 2 ppm B. This conforms with the view that such silica is not of biogenic origin but, since many iron formations are undoubtedly of marine origin, raises the question whether Precambrian oceans were impoverished in B. Analyses of Precambrian marine argillaceous sediments, averaging 70 ppm B, do not resolve this question.     

Observations and theoretical reconstruction of the green flash

Summary The phenomenon of the green flash at sunset (or sunrise) is reviewed. Several possible mechanisms that have been put forth to explain the green flash are discussed. A quantitative model for the phenomenon is then described, which includes parameters that are representative for a polar atmosphere (low humidity and small aerosol optical depth). It is supposed that the primary mechanism responsible for causing the green flash are natural molecular disperion, and, the filtering action imposed by the atmosphere for low elevation angles. Results from the model indicate that a green rim of vertical extent 0.15 milliradians would appear at the upper limb of the sun during sunset or sunrise. The theoretical results are compared with observations of a green flash made at wintertime in interior Alaska.     

Partition coefficient of thallium compared with rubidium

Analyses of 31 minerals (biotite, potash feldspar and plagioclase), occurring in 12 acidic volcanic rocks and 5 granodiorites from a Tuscan igneous series, gave the following mineral-groundmass (l) partition coefficients (D-values) for Tl: D^Kf-l, 0.75; D^bio-l, 1.82; D^pl-l, 0.13.Values for Rb (previously published) are similar for D^Kf-l but smaller for D^bio-l. Model calculations for crystallizing acid magma, using obtained D-values, confirm the observed trends of increased abundances of Tl, Rb in residual liquids and indicate and expected increase in Rb/Tl.In acid plutonic rocks, most of the Tl is in biotite; in equivalent lavas it is in the groundmass.     

Geochemistry of sporopollenin

Chemical studies of various modern and fossil spore walls of gymnosperms, angiosperms, pteridosperms, fungi and algae show the majority to contain sporopollenin now known to be derived from carotenoid esters by an oxidative polymerisation process. Chemical studies on microfossil walls and associated insoluble organic matter (kerogen) present in sediments up to 3,400 to 3,700 m.y. old suggest that these may have a common identity with sporopollenin of modern spore exines.     

High-temperature metamorphic imprint on calc-silicate granulites of Rayagada,Eastern Ghats,India: implication for the isobaric cooling path

 Calc-silicate granulites from Rayagada, north-central sector of Eastern Ghats granulite belt show a wide range of mineral assemblages and chemical compositions, which can be grouped as Gr. I (grossular- rich garnet-wollastonite-scapolite-calcite-clinopyroxene), Gr. II (andradite-rich garnet-scapolite-calcite-clinopyr- oxene), and Gr. III (scapolite-calcite-clinopyroxene-plagioclase) assemblages. Petrographic features suggest the following several reactions in the CaO–Al₂O₃–SiO₂-vapor system: Mei+4Wo+Cal=3Grs+Qtz +2CO₂, Mei+3Wo+2Cal=3Grs+CO₂, Mei= 3An+Cal, Wo+CO₂=Cal+Qtz, Mei+5Wo =3Grs+2Qtz+CO₂, An+Wo=Grs+Qtz, Mei+ 5Cal+3Qtz=3Grs+6CO₂, and the following reactions in the CaO–FeO–MgO–Al₂O₃–SiO₂-vapor system: Cpx_ss+Scp+Wo=Grt_ss+Qtz+CO₂, 4Hd+ 2Cal+O₂=2Adr+2Qtz+2CO₂, Cpx_ss+Scp= Grt_ss+Cal+Qtz. These reactions have been used to estimate peak T-X _CO2 condition for these granulites. A maximum temperature of ∼920 °C has been calculated at an estimated pressure of 9 kbar. A T-X _CO2 diagram shows an isobaric cooling from ∼920 °C to ∼815 °C. A range of X _CO2 (0.50 at 920 °C to 0.25 at 815 °C) has been observed for Gr. I calc-silicate granulites based on the reaction sequences including coronal garnet-forming reactions. This sequence is suggestive of internal fluid buffering rather than external fluid influx and the differences in X _CO2 conditions has been thought to be due to local buffering of fluid phases. Group II and Gr. III calc-silicate granulites, on the other hand, exhibit relatively lower temperature conditions. Received: 11 September 1995/Accepted: 20 June 1996     

Behaviour of boron in the generation of an anatectic complex: The Pen˜a Negra complex, central Spain

The Pe˜na Negra anatectic complex (central Spain) was formed from a pelitic protolith low in boron (3–80 ppm), by dehydration reactions, melting and fluid loss, which expelled much of the boron; residual B is present in sillimanite and muscovite. Migmatite melanosomes and restites (sillimanite + biotite + ilmenite) are relatively richer in B (mean 29 ppm), while the leucosomes are poorer (13 ppm). Late shears, fractures and zones of retrograde alteration have permitted some reintroduction of B. Experiments demonstrated that B cannot be removed from these rocks by heating or by leaching, indicating that very little is present in superficial adsorption and that the element occurs in mineral structures.     

Low-cost airlines in Europe: Reconciling liberalization and sustainability

This paper addresses the contradictions inherent in the interconnections between air transport liberalization and the economic and environmental dimensions to sustainability from the particular perspective of the dynamic expansion of European low-cost carriers and their networks. The argument considers the incompatibility of environmental sustainability with a business model that promotes rapid growth in air travel without meeting its external costs, but, simultaneously, claims to be socially and geographically inclusive. Moreover, that growth is perceived to be advantageous to strategies promoting national and regional economic growth and, consequently, the provision of low-cost airline services is being promoted by an array of national and local government agencies throughout the European Union. The paper concludes that the low-cost model does not account for its externalities despite air transport being the most environmentally damaging form of transport per passenger-kilometer but is clearly important to economic development at a variety of scales.