نتایج جستجو برای: grained sediments
تعداد نتایج: 51407 فیلتر نتایج به سال:
By improving numerical representations of coastal circulation, sediment properties, and waves, we seek to develop reliable estimates of sediment concentration, transport and deposition. Efforts to include sediment transport calculations within three-dimensional numerical hydrodynamic models can increase our ability to predict suspended sediment concentrations, water column turbidity, and seabed...
We describe the physical context of the Dinaledi Chamber within the Rising Star cave, South Africa, which contains the fossils of Homo naledi. Approximately 1550 specimens of hominin remains have been recovered from at least 15 individuals, representing a small portion of the total fossil content. Macro-vertebrate fossils are exclusively H. naledi, and occur within clay-rich sediments derived f...
The Mars Exploration Rover Opportunity has investigated the landing site in Eagle crater and the nearby plains within Meridiani Planum. The soils consist of fine-grained basaltic sand and a surface lag of hematite-rich spherules, spherule fragments, and other granules. Wind ripples are common. Underlying the thin soil layer, and exposed within small impact craters and troughs, are flat-lying se...
An analytical solution of the equilibrium distribution of suspended sediment concentrations (SSC) in an estuary along the longitudinal axis is extended to include variable width. A turbidity maximum is formed at the convergence of fluxes from freshwater discharge and (vertically well mixed) salinity gradients. Simple scaling relationships control the longitudinal distribution of SSC and depend ...
Carbonate mud is a major constituent of recent marine carbonate sediments and of ancient limestones, which contain unique records of changes in ocean chemistry and climate shifts in the geological past. However, the origin of carbonate mud is controversial and often problematic to resolve. Here we show that tropical marine fish produce and excrete various forms of precipitated (nonskeletal) cal...
Influence of benthic macroinvertebrates on mixing of profundal sediments in southeastern Lake Huron1
Vertical distributions of size classed benthic macroinvertebrates were investigated in centimeter-thick sections of twelve cores from each of two stations in southern Lake Huron. Stations were selected on the basis of radioactivity profiles indicating surf&e sediment mixing to 3 and 6 cm. The corresponding occurrence of major taxonomic groups (amphipods and oligochaetes) to 2 cm at the first st...
A microstructure consisting of ultrafine grained (UFG) ferrite with average grain size of ~ 0.7 µm and dispersed nano-sized carbides was produced by cold-rolling and tempering of the martensite starting microstructure in a low carbon steel. Subsequently, fine grained dual phase (DP) steel consisting of equiaxed ferrite grains with average size of ~ 5 µm and martensite islands with average size ...
Rapid sedimentation by fine-grained sediments on the upper slope of the New Jersey margin has generated nearly lithostatic fluid pressures. We use measured porosity from ODP Site 1073 to predict the in situ fluid pressures. We then simulate the pressure history with one-dimensional and two-dimensional sedimentation-compaction models. Two-dimensional models simulate a compaction-driven flow fiel...
Diamictites are poorly sorted sediments characteristically carrying coarse-grained clasts in a fine-grained matrix. They have generally been considered of glaciogenic or glaciomarine origin. Recently, however, it has been suggested that some massive tillite/diamictite layers could represent impact breccias. An earlier petrographic study of rock and mineral clasts from Dwyka Group diamictites re...
Subsurface sediments were recovered from a 52-m-deep borehole cored in the 300 Area of the Hanford Site in southeastern Washington State to assess the potential for biogeochemical transformation of radionuclide contaminants. Microbial analyses were made on 17 sediment samples traversing multiple geological units: the oxic coarse-grained Hanford formation (9 to 17.4 m), the oxic fine-grained upp...
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