Single-grain zircon dating of the metamorphic and granitic rocks from the Biscayarhalvøya-Holtedahlfonna zone, north-west Spitsbergen

The Biscayarhalvøya-Holtedahlfonna zone (BHZ) in north-western Spitsbergen is a north-south trending, narrow horst, with crystalline basement rocks exposed under a Devonian unconformity. Previous K-Ar, ⁴⁰Ar/³⁹Ar and Rb-Sr analyses have confirmed the occurrence of Caledonian thermal events, and Grenvillian ages have been obtained by conventional zircon U-Pb and single-zircon Pb evaporation methods. A total of 55 zircon grains from three samples (an augen metagranite, a micaceous schist and a granitic neosome of migmatite) have been analysed by the single-zircon Pb evaporation method. The grains with the age range of ca. 950-1100 My (million years) are the major component in all three samples, suggesting tectono-thermal activity in that period. The detrital versus resorption orgin of the rounded shapes of these grains from the granitic neosome is not clear yet. Therefore, the ages of the migmatization and of the sedimentary protoliths are not concluded. The youngest presumed detrital grain from the granitic neosome is 1060 My old. The metagranite, cutting the Richarddalen unit, yielded grains with an age of ca. 950 Mya. A granite dyke with an age range of 955-968 My cuts the Biscayarhuken unit in the northern Liefdefjorden area. These indicate the sedimentary protoliths of the Richarddalen and Biscayarhuken units are pre-Neoproterozoic. The youngest detrital zircon ages of ca. 940 My indicate Neoproterozoic sedimentary protoliths of the Solanderfjellet micaceous schists. A significant population of zircon grains with an age range of 1600-1900 My in all three samples suggests a wide exposure of these rocks in the source areas during Meso- and Neoproterozoic times. Several Archean ages have also been obtained. The results are generally conformable with those obtained from north-western Spitsbergen.     

Seasonal variation of the soil seed bank of grasses in central Argentina as related to grazing and shrub cover

The objectives of this research were to (a) study seasonal variation of the seed bank of grasses in two areas with different grazing history, (b) analyse the effect of the presence of shrubs on the seed bank and (c) study seed viability and dormancy in buried seeds of Piptochaetium napostaense and Stipa tenuis. The seed density of grasses was in general low and showed seasonal variation. Most of the grasses showed maximum seed density in December when seed dispersal occurs. Shrub cover did not show a marked influence in seed accumulation. The relatively high number of damaged seeds suggests that predation may be an important factor in seed bank dynamics in the Caldenal. Seeds of dominant perennial forage grasses showed dormancy that could explain, at least in part, persistence of these species in spite of periodical disturbance.     

Hydrogeological Zoning of the Central Minusinsk Basin by the Conditions of Formation of Fresh Groundwater Resources

A detailed hydrogeological zoning of the central part of the Minusinsk artesian basin is performed. Local basins confined to smaller plicated structures, as well as hydrogeological massifs of local scale, are recognized within large block structures. Direction of subsurface streams and their role in the formation of groundwater resources and composition are discussed. Forecast resources of fresh groundwater are estimated for every recognized structure.     

Water Quality of Small Rivers in the Zone of Influence of Gold-Mining Facilities in Krasnoyarsk Region

Environmental and sanitary estimation of small-river water quality is made in the zone of influence of gold-mining facilities in Krasnoyarsk Region. The estimates are based on data on the hydrochemical regime and the characteristics of phytoplankton, microphyto-periphyton, macrozoobenthos, and ichthyofauna collected during the vegetation period of 2000.     

The Effect of Alongshore Protection Structures on Shore Dynamics

A mathematical model of the seashore dynamics is considered. The model describes the seashore protection against destruction by alongshore through structures, underwater trenches, and artificial islands. The results of model calculations are presented and correlated with the data of measurements made on hydraulic models.