Diversity and bioactivity of actinomycetes from Signy Is- land terrestrial soils,maritime Antarctic

The Antarctic represents a largely untapped source for isolation of new microorganisms with potential to produce bio- active natural products. Actinomycetes are of special interest among such microorganisms as they are known to produce a large number of natural products, many of which have clinical, pharmaceutical or agricultural applications. We isolated, characterized and classified actinomycetes from soil samples collected from different locations on Signy Island, South Orkney Islands, in the maritime Antarctic. A total of 95 putative actinomyeete strains were isolated from eight soil samples using eight types of selective isolation media. The strains were dereplicated into 16 groups based on morphology and Amplified Ribosomal DNA Restriction Analysis （ARDRA） patterns. Analysis of 16S rRNA gene sequences of representatives from each group showed that streptomy- cetes were the dominant actinomycetes isolated from these soils; however, there were also several strains belonging to diverse and rare genera in the class Actinobacteria, including Demetria, Glaciibacter, Kocuria, Marmoricola, Nakamurella and Tsukamurella. In addition, screening for antibacterial activity and non-ribosomal peptide synthetase genes showed that many of the actinomycete strains have the potential to produce antibacterial compounds.     

Test of tectonic models by great circle Rayleigh waves

Summary. A large set of published great circle Rayleigh wave phase velocities in the period range 125–350s is used to compare three recent tectonic models (Okal, Lévêque, Jordan). Prior to any regionalization, the symmetry property of the great circle integrals is used to obtain a lower limit of the signal/noise ratio in the data. It turns out that the signal is responsible for at least 30 per cent of the data variance in the period range 175–300s.
A standard regression method is applied for computing the'pure path'velocities and the model efficiency is derived from a variance analysis. It is shown that, even at great depth, none of the three models explains more than 60 per cent of the energy due to the long-wavelength lateral heterogeneities (λ6500 km).
The three models have nearly the same efficiency for explaining the short-period data ( T ∼ 125s). Between 200 and 300s, the higher performance of Okal's model indicates that it is important to separate the subduction zones from the other orogenic zones. By perturbing the lateral extension of the subduction zones, it comes out that they constitute on both sides of the subducting slabs wider anomalies than often assumed, suggesting large downgoing flows. On the contrary, the effect of surface features such as marginal seas are restricted to a close region in front of the trenches.
Finally, the anomalous ellipticity values deduced directly from great circle data are partly explained by a coupling between tectonics and ellipticity.     

The Pb-Sr-Nd isotope geochemistry of some recent circum-Mediterranean granites

Pb, Sr and Nd isotopic compositions have been analyzed in recent granites from Northern Africa, Northern Italy and Greece. Lead isotope compositions of K-feldspars are rather homogeneous, and cluster close to the modern lead of Stacey and Kramers (1975) but with slightly higher²⁰⁷Pb/²⁰⁴Pb and²⁰⁸Pb/²⁰⁴Pb ratios. The Cyclades samples, however, have higher²⁰⁶Pb/²⁰⁴Pb ratios. Addition of mantle-derived lead was probably very limited, which supports a quasi-closed system evolution of this element in the continental crust. The Sr, Nd data fall in the enriched part of the¹⁴³Nd/¹⁴⁴Nd vs.⁸⁷Sr/⁸⁶Sr diagram and define a smooth hyperbolic mixing curve. Over a wide area, straddling different orogens, most granites may be accounted for by a binary mixture between a recycled crustal component and a depleted mantle-like component. No correlation is observed between either Pb and Sr or Nd isotopic ratios, or any isotopic ratio and major element contents. Quantitative modelling suggests that two cases fit the Sr and Nd characteristics of these granites: they both require anatexis of the crust on a scale large enough to average the isotopic properties of heterogeneous terranes. In the first case, the mantle-derived component may be represented by differentiated Island Arc-type magmas, and the granites result from mixing these magmas with anatectic melts. In the second case, mantle-derived igneous rocks, such as obducted ophiolites, are part of the crustal source and their variable involvement in the anatectic process causes isotopic variations.CRPG Contribution n 630.     

Chemical mass balance of calcrete genesis on the Toledo granite (Spain)

The chemical mass balance of calcrete genesis is studied on a typical sequence developed in granite, in the Toledo mountains, Central Spain.

Field evidence and petrographic observations indicate that the texture and the bulk volume of the parent rock are strictly preserved all along the studied calcrete profile.

Microscopic observations indicate that the calcitization process starts within the saprolite, superimposed on the usual mechanisms of granite weathering: the fresh rock is first weathered to secondary clays, mainly smectites, which are then pseudomorphically replaced by calcite. Based on this evidence, chemical mass transfers are calculated, assuming iso-volume transformation from the parent rock to the calcrete.

The mass balance results show the increasing loss of matter due to weathering of the primary phases, from the saprolite towards the calcrete layers higher in the sequence. Zr, Ti or Th, which are classically considered as immobile during weathering, are also depleted along the profile, especially in the calcrete layer. This results from the prevailing highly alkaline conditions, which could account for the simultaneous precipitation of CaCO₃ and silicate dissolution.

The calculated budget suggests that the elements exported from the weathering profile are provided dominantly by the weathering of plagioclase and biotite. We calculate that 8–42% of the original Ca remains in granitic relics, while only 15% of the authigenic Ca released by weathering is reincorporated in the calcite. This suggests that 373 kg/m² of calcium (i.e., three times the original amount) is imported into the calcrete from allochtonous sources, probably due to aeolian transport from distant limestone formations.