3D alluvial aquifer reconstruction in polluted areas by means of GPR (Sabiñánigo,N Spain)

Assumptions of simple geometries for alluvial deposits (related to main rivers) can preclude determination of complexities that are revealed as fundamental controls in underground flow. Although subhorizontal contacts between alluvial and substratum materials are expected, previous sedimentary or erosional processes can result in irregular geometries, only accessible through detailed analysis. The studied case presents the 3D reconstruction of a Quaternary terrace in the proximities of Sabiñánigo (Southern Pyrenees, Northeastern Spain), lying on homogeneous Eocene marls. The studied area is located in an industrialized area supporting strongly pollutant chemical industry (chlorinated pesticides) for the past 50 years. The objective of the study was to constrain the groundwater pathway along the area to subsequently analyze leakage of chemicals to the water table. In order to reveal preferred flow paths, a detailed characterization of the internal structure of the alluvial deposits (0.5–13 m thick) and their relations with the Tertiary substratum was carried out by means of ground penetrating radar (GPR, 50 and 100 MHz antennas). The obtained models permit identifying several topographic highs in the alluvial/substratum contact, determining preferred pathways in water flow, favoring particular conditions associated with low levels of the water table. The presented results support the interest of application of GPR surveys in order to characterize the groundwater pathways in expected homogeneous areas and their importance in order to establish the contaminant surveillance network.     

Star count of the North Galactic Pole region in theUBV colour bands

Astrophysics and Space Science -     

Flow characteristics of Metresa: an Oligocene seismoturbidite in the Dukla Unit, Polish Carpathians

Metresa is a thick, distinctive turburdite within the Menilite Shales in the Carpathians of south-east Poland. It was deposited by a SE-flowing turbidity current derived from the Silesian cordillera and can be traced for 55 km downcurrent; it has a width of at least 15 km. The current contained roughly 3 km³ of sediment and conforms to the definition of a seismoturbidite. Grain-size analyses of samples from the nine localities where Metresa is exposed indicate average velocities decreasing from 2 m s^?1 to less than 1 m s^?1 over the 55 km. Massive divisions are poorly developed; instead, the turbidite, although graded, tends to be laminated throughout. Flat lamination predominates with intercalated cross-lamination and erosion structures at various levels. Small-scale cross-lamination, presumably associated with ripples, occurs at some upper levels. An exceptional feature is a large-scale wave-like structure somewhat resembling hummocky cross-stratification. The structures are not consistent with the inferred velocities. It is suggested that the stability fields relating structures to stream power (herein called the ‘Allen fields’) are displaced in respect to deposition from waning turbidity currents.     

General elastic analysis of piles and pile groups

This paper describes the development of a boundary element analysis for the behaviour of single piles and pile groups subjected to general three‐dimensional loading and to vertical and lateral ground movements. Each pile is discretized into a series of cylindrical elements, each of which is divided into several sub‐elements. Compatibility of vertical, lateral and rotational movements is imposed in order to obtain the necessary equations for the pile response. Via hierarchical structures, 12 non‐zero sub‐matrices in a global matrix are derived for the basic influence factors. Solutions are presented for a series of cases involving single piles and pile groups. In each case, the solutions are compared with those from more simplified existing pile analyses such as those developed by Randolph and by Poulos. It is shown that for direct loading effects (e.g. the settlement of piles due to vertical loading), the simplified analyses work well. However, for ‘off‐line’ response (such as the lateral movement due to vertical loading) the differences are greater, and it is believed that the present analysis gives more reliable estimates. Copyright © 2000 John Wiley & Sons, Ltd.     

New U–Pb isotopic data for detrital zircons from metasedimentary sequences of northwestern Taimyr

This work presents the U–Pb (LA–ICP–MS) data of detrital zircons from metasedimentary sequences of northwestern Taimyr. An analysis of the youngest populations of detrital zircons testifies to the wide distribution of Cambrian sequences in the study area, but not Precambrian sequences as was considered earlier, and the need for a substantial revision of the stratigraphic scheme of this area. The detrital zircon age distribution shows that the Timan margin of the Baltic paleocontinent was a major provenance area of the Cambrian sediments in northern and northwestern Taimyr, as well as the coeval sediments of the Severnaya Zemlya archipelago.