Rare earth elements,iron formations and sea water

Iron formations probably formed as chemical sediments when an Fe-rich solution entered the sedimentary environment. The REE patterns of such sediments are affected by the amount and type of precipitating and detrital phases, the REE pattern of the iron source solution, the REE pattern of the sea water into which the solution flows, and the mixing which takes place between input solution and sea water. What is known about the different types of iron formation suggests that all of these factors may vary from one type to another. Therefore, variations in REE patterns cannot be attributed solely to changes in sea water REE patterns. Comparison of the REE patterns of Archean and Ordovician iron formations of the Algoma type shows that similar iron formations have similar REE patterns regardless of age. This implies similar genetic histories.     

The development of montane arroyos and gullies

Field investigations in the Front Range of Colorado, U.S.A., confirm that the spatial distribution of vegetation in watersheds exerts strong control on the entrenchment of streams in the montane zone. When tractive force in channels exceeds threshold values of resistance on the valley floors, cutting of arroyos begins, producing forms that change allometrically. An algorithm based on the Cooke Method for discharge, the Manning Equation for depth of flow, and the DuBoys Equation for tractive force can be used to evaluate force for observed and experimental conditions. In small (<5 km²) basins in the Front Range of Colorado, forces for the 10-year discharge commonly range from 1 to 5 dynes, but the resistance offered by valley floors is usually unable to withstand forces from channel flows greater than 2 dynes. Biomass of vegetation on the valley floor exerts significant control on the trenching process, with threshold values of biomass commonly between 1.5 and 9 kg/m², the range of semi-arid vegetation cover. Thresholds exist in the montane erosion system for gradient, mean biomass in the basin, biomass on the valley floor, channel roughness, and channel width. Each threshold value, however, depends on the interrelationships among other variables in the system. Manipulation of the vegetation cover is the primary human impact on the montane channels, and management of the distribution of vegetation offers the most efficient method of maintaining the stability of channels.     

Investigations of intensities,aftershock statistics and the focal mechanism of Friuli earthquakes in 1975 and 1976

Isoseismal maps, derived from macroseismic observations in the epicentral region and in Switzerland for the Friuli earthquake of 6 May 1976, are presented. From these maps a focal depth ofh=8 km and a related attenuation factor of =0.001 can be estimated. An analysis of aftershocks reveals a slope ofp=0.85 for the logarithmic relationship between number of events and time. A firstmotion study for a preceding earthquake in Friuli on 24 March 1975, gives two possible fault plane solutions, both indicating a North-South direction of the axis of maximum shortening of the earth's crust.Contribution No. 146, Institute of Geophysics, Swiss Federal Institute of Technology, Zürich, Switzerland.     

Benthic-pelagic coupling in the Greenland-Norwegian Sea and its effect on the geological record

The sedimentation pattern of organic material in the Greenland-Norwegian Sea is reflected in the surface sediments, although less than 0.5% of the organic matter is buried in the sediment. Maximum fluxes and benthic responses are observed during June and/or August/September, following the pattern of export production in the pelagial zone. The annual remineralization rate on the Vøring Plateau is 3.0 g C m^–2 a ^–1 Freshly settled phytodetritus, as detected by chlorophyll measurements, is rapidly mixed into the sediment and decomposed. It stimulates the activity of benthic organisms, especially foraminifera. The mixing coefficient for this material is D _b=0.2 cm² d^–1, which is two to three orders of magnitude higher than that estimated from radiotracer methods. The effect on the geological record, however, is likely to be small. Chlorophyll-containing particles are at first very evenly distributed on the seafloor. After partial decomposition and resuspension, a secondary redistribution of particles occurs which can result in the formation of a high accumulation area, with an up to 80-fold increase in the sedimentation rate by lateral advection. This is mainly due to physical processes, because biodeposition mediated by benthic animals increases sedimentation by only a factor of two or three.     

Stable sulfur and nitrogen isotopic compositions of crude oil fractions from Southern Germany

Eleven samples of crude oil from the Molasse Basin of Southern Germany were fractionated and their contents of sulfur and nitrogen as well as the stable isotope compositions of these elements (${}^{34}\text{S}{}^{32}\text{S}$ and ${}^{15}\text{N}{}^{14}\text{N}$, resp.) investigated.According to the δ³⁴S determinations, all crude oils from the Tertiary base of the Western and Eastern Molasse belong to one oil family and differ significantly from the Triassic and Liassic oils in the Western Molasse.An enrichment of ³⁴S was observed with increasing polarity of crude oil fractions. The isotope distributions of sulfur in the polar constituents of the biodegraded oils from the sandstones of Ampfing, however, approach a homogeneous distribution.The nitrogen isotope distribution is rather uniform in Southern German oils. A regional differentiation can be recognized, although the overall isotopic variation is small. The δ¹⁵N values of the crudes and asphaltenes do not correlate.     

Hydrodynamics of the Lake of Geneva

Air-flow works on the lake's water body which results in winddriven water circulation and wind waves This is a summary of work done by LHYDREP on the physical limnological aspect of the Leman. General information on the basin of the Leman is given in chapter 1. Subsequently in chapter 2 the measuring programme is presented, discussing the measuring positions, the measuring installations and the instruments used of the three campaigns. The data obtained during these campaigns are subsequently interpreted. In chapter 3 the atmospheric dynamics over the lake is discussed. It deals mainly with the mechanical energy transfer process which is represented here (as usually) by the drog coefficient, C_y. It is shown that the airflow velocity, the fetch Reynolds number and the air stability play important roles. In chapter 4 the hydrodynamics of the lake is presented. Predictions of numerical hydrodynamical models of steady-state circulation (chapter 4.2), of storm surges and of seiches (chapter 4.3) and of inertial currents (chapter 4.4) are compared with available data of the Leman during the homogeneous season. In addition a preliminary study of wind waves (chapter 4.5) is given.     

Flood-related channel change in an arid-region river

A review of 112 years of change in the channel of the Salt River, central Arizona, U.S.A., shows that this arid-region river has a main-flow channel that has migrated laterally up to 1.6 km (1 mi) in response to floor events. Maps showing locational probabilities indicate that along the channel zones of relative locational stability alternate with zones of relative instability at a 3.2 km (2 mi) interval. Construction of upstream reservoirs has reduced sediment input into the main river but has not controlled floods. The channel width has not changed except for moderate fluctuations around mean values; the main-flow channel has incised approximately 6 m (20 ft) over most of the 48 km (30 mi) study reach during six recent floods. Gradient has remained unchanged. During floods bed material was mobilized to a depth below the original bed level that was greater than the height of the water surface above the original bed. Calculations based on tractive force indicate a threshold discharge of instability that is equal to the flow with a five-year return interval. The river exhibits remarkable stability with respect to gradient and sinuosity, irrespective of water and sediment discharges, but horizontal channel location exhibited selective instability. Over the record period of more than a century, the channel appears not to have been in equilibrium considering geometry, discharge, and sediment.     

Variable-density groundwater flow and solute transport in irregular 2D fracture networks

Numerical simulations of variable-density flow and solute transport have been conducted to investigate dense plume migration for various configurations of 2D fracture networks. For orthogonal fractures, simulations demonstrate that dispersive mixing in fractures with small aperture does not stabilize vertical plume migration in fractures with large aperture. Simulations in non-orthogonal 2D fracture networks indicate that convection cells form and that they overlap both the porous matrix and fractures. Thus, transport rates in convection cells depend on matrix and fracture flow properties. A series of simulations in statistically equivalent networks of fractures with irregular orientation show that the migration of a dense plume is highly sensitive to the geometry of the network. If fractures in a random network are connected equidistantly to the solute source, few equidistantly distributed fractures favor density-driven transport. On the other hand, numerous fractures have a stabilizing effect, especially if diffusive transport rates are high. A sensitivity analysis for a network with few equidistantly distributed fractures shows that low fracture aperture, low matrix permeability and high matrix porosity impede density-driven transport because these parameters reduce groundwater flow velocities in both the matrix and the fractures. Enhanced molecular diffusion slows down density-driven transport because it favors solute diffusion from the fractures into the low-permeability porous matrix where groundwater velocities are smaller. For the configurations tested, variable-density flow and solute transport are most sensitive to the permeability and porosity of the matrix, which are properties that can be determined more accurately than the geometry and hydraulic properties of the fracture network, which have a smaller impact on density-driven transport.     

Solar radio emission at 9.1 cm and sector boundaries

A possible connection between solar radio emission from 1.0 to 9.4 GHz and the interplanetary sector boundaries has been previously reported in the literature. The present research does not support the previous work as expected. The 9.1 cm activity appears to be organized around sector boundaries only in a very limited sense in that the distribution of very strong active regions peaks near the –/+ boundaries. However, this phenomenon is only observed during the most active part of the solar cycle. A peculiar asymmetry is found regarding the length of the positive and negative sectors.