Influence of microstructure of loess on triaxial shear strength

Vicksburg loess is characterized by preferred orientation of constituent grains, which on the average dip 4° toward the west (N 80–85°W). This investigation was undertaken to study, quantitatively, the relationship between natural fabric anisotropies of Vicksburg loess and the orientation of applied stress distribution Results of the study indicate the fabric anisotropies in Vicksburg loess are reflected by definite variation in triaxial shear strength of dry and moist specimens.

In two series of triaxial tests, ultimate strength of the loess is maximum where σ₁ is perpendicular to grain orientation, and it is reduced where the principal stresses are 45° to the fabric plane. In this respect, Vicksburg loess may serve as a structural model for granular earth materials in illustrating the influence of fabric on ultimate strength. Moreover, the Mohr-Coulomb fracture line consists of two line segments, with an increase in slope at higher confining pressure. This characteristic suggests that poorly-cemented sands, or sandstones, and silts, or siltstones, may undergo two failures: one at small strains where cement bonds are disrupted and the other at larger strains where internal shearing resistance of granular components is exceeded.     

Agglutinated abyssal foraminifers of the equatorial pacific

The quantitative study of the distribution and taxonomic composition of recent living and dead (without plasma) benthic foraminifers revealed three foraminiferal assemblages in the bottom sediments of the Pacific Ocean at depths of 3350 to 4981 m. The assemblage dominated by the epibenthic Lagenammina difflugiformis, Reophax dentaliniformis, and Saccorhiza ramosa occupies the slopes of underwater hills. The assemblage with a high share of the infaunal Cribrostomoides subglobosum, C. nitidum, and Ammobaculites agglutinans is registered on the abyssal plateau. The assemblage with a significant proportion of the large Astrorhiza and Reophax species, which are characterized by an active way of life, populates gentle slopes and narrow depressions with potentially strong bottom currents.     

Cosmogenic nuclide measurements in southernmost South America and implications for landscape change

We measured in situ ¹⁰Be, ²⁶Al and³⁶Cl on glacial deposits as old as 1.1 Myr in the southernmost part of Patagonia and on northern Tierra del Fuego to understand boulder and moraine and, by inference, landscape changes. Nuclide concentrations indicate that surface boulders have been exposed for far less time than the ages of moraines they sit upon. The moraine ages are themselves constrained by previously obtained ⁴⁰Ar/³⁹Ar ages on interbedded lava flows or U-series and amino acid measurements on related (non-glacial) marine deposits. We suggest that a combination of boulder erosion and their exhumation from the moraine matrix could cause the erratics to have a large age variance and often short exposure histories, despite the fact that some moraine landforms are demonstrably 1 Myr old. We hypothesize that fast or episodic rates of landscape change occurred during glacial times or near the sea during interglacials. Comparison with boulder erosion rates and exhumation histories derived for the middle latitudes of semi-arid Patagonia imply different geomorphic processes operating in southernmost South America. We infer a faster rate of landscape degradation towards the higher latitudes where conditions have been colder and wetter.     

Statistical properties of aftershock rate decay: Implications for the assessment of continuing activity

Aftershock rates seem to follow a power law decay, but the assessment of the aftershock frequency immediately after an earthquake, as well as during the evolution of a seismic excitation remains a demand for the imminent seismic hazard. The purpose of this work is to study the temporal distribution of triggered earthquakes in short time scales following a strong event, and thus a multiple seismic sequence was chosen for this purpose. Statistical models are applied to the 1981 Corinth Gulf sequence, comprising three strong (M = 6.7, M = 6.5, and M = 6.3) events between 24 February and 4 March. The non-homogeneous Poisson process outperforms the simple Poisson process in order to model the aftershock sequence, whereas the Weibull process is more appropriate to capture the features of the short-term behavior, but not the most proper for describing the seismicity in long term. The aftershock data defines a smooth curve of the declining rate and a long-tail theoretical model is more appropriate to fit the data than a rapidly declining exponential function, as supported by the quantitative results derived from the survival function. An autoregressive model is also applied to the seismic sequence, shedding more light on the stationarity of the time series.     

Determination of solar wind elemental abundances from M/Q observations during three periods in 1980

Mass spectra in the range 2 ≦ M/Q ≦ 3 provided by a high resolution mode of the ISEE-3 Plasma Composition Experiment were evaluated for three selected periods during early 1980. The observed Ne/O ratios are compatible with estimated solar abundance ratios. In two of the three periods, the He/Ne-ratios agree with the Apollo foil results. Freezing-in temperatures for oxygen are similar to those obtained by other groups. Possible reasons for an unexpectedly high flux at M/Q = 2.4 are discussed.     

Quasi-Biennial Oscillations of Global Solar-Activity Indices

Quasi-biennial oscillations of solar activity are investigated using several global indices. The Singular Spectrum Analysis is used to separate out and study quasi-biennial oscillations; this method is one of the modifications of the main components method. The principal components of the solar cycle are stable 11-year, secular, and quasi-biennial variations. The periods and shapes of individual variations in each quasi-biennial train depend on the length and power of the particular 11-year cycle.     

Os Isotopes and the Origin of the Tasmanian Dolerites

New Os isotope data obtained for oxides separated from samplesof the Jurassic dolerites of Tasmania (Australia) are used toconstrain the petrogenesis of the Ferrar continental flood basaltprovince. It is proposed here that the unradiogenic initialOs ratio (¹⁸⁷Os/¹⁸⁸Os = 0·145 ± 0·049 2     

Environmental impact of salmon net-pen culture on marine benthic communities in Maine: A case study

The environmental impacts of salmon net-pen aquaculture on the benthic environment were investigated at a commercial fish farm located in coastal Maine waters. This site has a sandy mud bottom and low current velocities, is subjected to episodic sediment resuspension, and way in production for 3 yr prior to this study: We examined both the increase in carbon flux to the benthos caused by the net-pen and the effects of the elevated flux on sediment biogeochemistry and the microbenthic communities. The experimental design involved the establishment of two study sites, an ambient site ca. 100 m from the net-pen and a treatment site around the pen. Sediment traps deployed 1 m above the sediment-water interface indicated that carbon flux to the benthos was increased 1-fold to 6-fold (to a maximum of 5 g m^?2d^?1) at the edge of the net-pen with little or no increase in carbon flux 10 m from the pen. Unlike carbon flux rates, sediment organic matter inventories showed a complex pattern of change over time. Mineral surface area, organic carbon and nitrogen, digestible protein, and sterol content were initially (April 1991) lower beneath the pen than in ambient sediments. During 1991 ambient sediment accumulated organic matter until July after which it decreased, to a low during November. In contrast, organic matter inventories of sediment beneath the pen remained low until July and then increased to a high during November. These latter gains were associated with the development of bacterial mats at the sediment-water interface. Beneath the pen, microbial and macrofaunal communities were shifted toward those commonly associated with organic enrichment but seasonal trends and storm-related resuspension events also significantly affected these sediment communities. When abundant, most epibenthic organisms were more numerous near the pen than in adjacent ambient areas. These results suggest that net-pen aquaculture can alter the benthic ecosystem in Maine Coastal waters but indicate that the effects are spatially limited.     

Cadmium absorption and accumulation in different parts of kidney beans, radishes and pumpkins

This study is done to measure the absorption and distribution of cadmium in different parts of kidney beans, radishes and pumpkins. Three parts of a field was chosen. In one part 65 ppm of cadmium nitrate was added to water and in the other part 130 ppm, the last part was irrigated with normal water. Samples were digested by EPA 3050 method. Cadmium concentration was measured by Unicam 919 absorption unit. Beans accumulate cadmium mostly in root (70 ppm) and a little amount is mobilized through upper parts (12–16ppm), but kidneys did not accumulate a significant amount. In radishes the roots did not accumulate a significant amount of cadmium but stems had 4 ppm and leaves had 25 ppm. Cadmium concentration in soil does not affect its concentration in different parts of pumpkins and beside the stems and leaves (4 ppm) the other parts' concentrations were insignificant. In regard to the results of this study the cadmium concentrations in edible parts of the samples (kidney beans, radish roots and pumpkin fruit) were less than the U.S. EPA standards for agriculture and human beings.     

Rb-Sr whole-rock dating of late diagenetic to anchimetamorphic,palaeozoic sediments in southern France (Montagne Noire)

Rb-Sr whole-rock and mineral analyses are reported from Early Paleozoic sediments of the southern rim of the French Central Massif (Montagne Noire). The sediments—mainly pelites, silt- and sandstones—can be separated into three different zones (A, B, and C) according to their varying degrees of deformation and transformation, which took place during the Hercynian (= Variscan) orogeny (Carboniferous). For the least deformed, folded but not schistose, fossiliferous Lower Ordovician sediments (zone A), a scatter of the data points resulted, at least partly due to the varying amount of detrital muscovites, which did not equilibrate their Sr isotopes with those of the clay minerals. Fossiliferous Middle Cambrian sediments (zone B), however, are colinear in an isochron plot. The rocks are also folded, and show a beginning schistosity in the pelitic layers. The age of 333±16 m.y. therefore does not correspond to the time of sedimentation, as one would expect from most of the interpretations given in the literature. It is, however, in close agreement with the stratigraphically known time of folding and anchimetamorphism. The same result, within analytical error, of 326±17 m.y. was obtained for Lower Ordovician sediments (zone C), which show a schistosity not only in the pelites but also in some psammitic layers. As for the sediments of zone B, this result indicates open whole-rock systems for Rb and/or Sr during folding and anchimetamorphism. Minerals extracted from psammites of zones B and C gave the following results: albite coincides with the isochrons; detrital muscovites do not coincide and yield ages of about 650 m.y. (Cadomian orogeny) for both zone B and C sediments; detrital chlorites from zone B sediments seem to be only partly reset by anchimetamorphism and therefore plot closer to the whole-rock isochron. From this it must be concluded that an increasing amount of these detrital micas could significantly shift the position of the total-rock points, as might be the case for zone A sediments. From the whole-rock results of zone B and C sediments and the mineralogical and petrological changes during diagenesis and anchimetamorphism we conclude that many of the isochrons obtained from stratigraphically uncontrollable Precambrian sediments should be reinterpreted in favour of metamorphic and not sedimentary ages, especially if the metamorphism reached greenschist facies conditions. Devonian and Cambrian limestones intercalated between the pelites, silstones and sandstones contain Sr of a variable and slightly radiogenic isotopic composition in contrast to the expected ancient sea water Sr. This fact is interpreted again in favour of open whole-rock systems during the postdepositional history of the rock, rather than primary scatter of ancient, radiogenic sea water Sr.