The chronology of a large ice-dammed lake and the Barents–Kara Ice Sheet advances, Northern Russia

Beach and shoreface sediments deposited in the more than 800-km long ice-dammed Lake Komi in northern European Russia have been investigated and dated. The lake flooded the lowland areas between the Barents–Kara Ice Sheet in the north and the continental drainage divide in the south. Shoreline facies have been dated by 18 optical stimulated luminescence (OSL) dates, most of which are closely grouped in the range 80–100 ka, with a mean of 88±3 ka. This implies that that the Barents–Kara Ice Sheet had its Late Pleistocene maximum extension during the Early Weichselian, probably in the cold interval (Rederstall) between the Brørup and Odderade interstadials of western Europe, correlated with marine isotope stage 5b. This is in strong contrast to the Scandinavian and North American ice sheets, which had their maxima in isotope stage 2, about 20 ka. Field and air photo interpretations suggest that Lake Komi was dammed by the ice advance, which formed the Harbei–Harmon–Sopkay Moraines. These has earlier been correlated with the Markhida moraine across the Pechora River Valley and its western extension. However, OSL dates on fluvial sediments below the Markhida moraine have yielded ages as young as 60 ka. This suggests that the Russian mainland was inundated by two major ice sheet advances from the Barents–Kara seas after the last interglacial: one during the Early Weichselian (about 90 ka) that dammed Lake Komi and one during the Middle Weichselian (about 60 ka). Normal fluvial drainage prevailed during the Late Weichselian, when the ice front was located offshore.     

Magnetic Reconnection and Extraplanar Diffuse Ionized Gas

Photoionization by stars cannot be the only cause for the diffuseionized gas component in the distant halos of galaxies.Quasistationary localized magnetic reconnection can efficientlycontribute to the ionization of the extraplanar halo gas. The gas isheated and re-ionized in numerous current filaments fast enough tocompensate recombination. The necessary magnetic energy is provided bythe disk activity.     

Mass flux and undertow in a surf zone

The mass of water carried shoreward by the breaking waves in a surf zone will, in a two-dimensional situation, be compensated by a seaward return flow, the undertow. It is shown that the undertow is driven by the local difference between radiation stress and the set-up pressure gradient which only balance each other in average over the depth. Turbulent shear stresses are required to maintain a steady situation. Comparison with measurements confirms the theoretical results.     

The dynamics of wave induced ship motions in shallow water

The analytical method developed by Svendsen (1968) for a forced heave motion is extended to the general problem of wave induced heave, roll and sway motions of a long ship at a depth of water which is only slightly larger than the draught of the ship. This corresponds, for example, to the situation of a fully loaded ship in a harbour area.After linearization of the problem, the water motion is considered for each of the three individual motions and for the wave reflection-transmission problem for a fixed ship. The ensuing results for the forces on the ship are then synthesized to form the equations of motion, which are presented with all coefficients given, including mooring forces.Analytical and numerical results are given for the three components of motion, for the associated resonance frequencies, and for the hydrodynamic masses and moments of inertia. Finally, the assumptions used are analyzed and evaluated by comparison with measurements and with other results for a special case.     

Formation of iron-containing colloids by the weathering of phyllite

The formation of colloids during the weathering of phyllite was investigated by exposing ground phyllite to Milli-Q water. Secondary mineral colloids of 10¹–10² nm were detected in significant concentrations. At pH of about 8.5, the solution concentration of these colloids reached up to 10 mg/L (however, acidification to pH 4.0 prevented the formation of the colloids). The mineralogical composition of the secondary mineral colloids is assumed to be a mixture of ferrihydrite, manganese oxyhydroxides, aluminosilicates, amorphous Al(OH)₃ and gibbsite with possible additions of iron silicates and␣iron-alumino silicates. The colloids were stable over longer periods of time (at least several weeks), even in the presence of suspended ground rock. Direct formation of iron-containing secondary mineral colloids at the rock–water interface by the weathering of rock material is an alternative to the well-known mechanism of iron colloid formation in the bulk of water bodies by mixing of different waters or by aeration of anoxic waters. This direct mechanism is of relevance for colloid production during the weathering of freshly crushed rock in the unsaturated zone as for instance crushed rock in mine waste rock piles. Colloids produced by this mechanism, too, can influence the transport of contaminants such as actinides because these colloids have a large specific surface area and a high sorption affinity.     

Accessibility Measures in Spatial Mismatch Models

Implicit in all spatial mismatch models is the concept of accessibility. However, there is an immense variety of measures utilized in the literature to index the concept, and it is not clear how much of the disparity in findings between studies is attributable to alternative measures. This research note attempts to provide some evidence on the impact of alternative measures of accessibility in employment probability models.     

Paleomagnetism of the Cretaceous Morelos and Mezcala Formations, southern Mexico

A paleomagnetic study of platform-facies carbonate rocks of the mid-Cretaceous Morelos Formation and deep-water carbonate rocks of the overlying Upper Cretaceous Mezcala Formation, sampled at Zopilote canyon, in Guerrero State, southern Mexico, indicates that their characteristic magnetization was acquired contemporaneously with folding of these rocks during the Late Cretaceous Laramide orogeny. The remanence carrier is interpreted to be magnetite, although other mineral phases of high coercivity carry recent secondary overprints. The overall mean is of Dec=323.1° and Inc=36.5° (k=162.7; α₉₅=2.7°; N=18 sites; 64% unfolding). Comparison with the North America reference direction indicates that this area has experienced a small, yet statistically significant, counterclockwise direction of 19.2±4.0°. Similar rotations are documented in other localities from southern Mexico; rotations are linked to mid-Tertiary deformation associated with the left-lateral strike-slip fault system that accommodated motion of the Chortis and Xolapa blocks.     

200 years of mining activities at La Paz/San Luis Potosí/Mexico - Consequences for environment and geochemical exploration

The Ag---Pb---Zn---Cu---Au mining district of Santa María de La Paz has been extensively exploited for approximately 200 years. Consequences of these activities are several deposits of tailings with high As and heavy metal concentrations, which are completely unstable. The climate is semiarid and as the dumps have no protective cover, material from the dumps is dispersed by strong winds. It is also washed out during seasonally heavy rainfalls. By these processes approximately 100 km² of surrounding have been contaminated by dump material. The As and heavy metal content of the soils was determined as well as their level in crops (Zea Maize) from agricultural lands in the vicinity of the dumps. In the direction of prevailing winds concentrations up to 1000 ppm Zn, 400 ppm Pb, 16 ppm Cd, 550 ppm Cu and 300 As have been detected in top soils. Using fuzzy cluster analysis the different contamination sources could be identified. Grains of corn from contaminated sites showed no critical concentrations, but leaves which are also used tor fodder, have As-concentrations up to 20 ppm.