ALBERT

Description: Soils of Arctic Canada were sampled during the Tundra Northwest Expedition 1999 (TNW-99) at 17 sites that cover the ecological regions of the High, Mid and Low Arctic zones. Almost all locations consisted of a mesic and a dry habitat and are described with respect to their ecological function. Analyses on soil characteristics were performed for soil morphology, texture and chemistry. The data showed a wide variability due to local aspects. Statistical evidence did not indicate that larger-than-local ecological regions could be defined in most cases by either soil chemical characteristics or vegetation patterns. Soil classification according to the World Reference Base of Soils (WRB) showed the dominance of different Cryosols, but also Gelic Cambisols and Gelic Regosols were found; according to US Soil Taxonomy, they could be classified as different Orthels, Turbels and Histels. Low temperature, high stone content and low nutrient availability were noted as factors hampering plant growth and soil activity.

Description: Geotechnical properties of Quaternary sediments from the middle and lower regions of the Mississippi Fan show that the sediments are normally to overly consolidated to a depth of 40 to 50 m below the seafloor. Below that depth, the sediments become highly underconsolidated and exhibit high excess pore-water pressures. The state of underconsolidation is attributed to the rapid rates of sediment accumulation and the low permeability of smectite-rich clays.

Description: Geotechnical examination of 180 m of core recovered in Pigmy Basin at Site 619 in the Gulf of Mexico indicates that excess pore-water pressures are present in the lower section of the hole. Shear strength-vertical effective stress relationships and consolidation testing (oedometer) indicate that the sediments are normally consolidated in the upper 30 m and underconsolidated below. The presence of gas within the pore waters greatly affected the measurements of shear strength, water content, and porosity in the interval between 80 and 160 m sub-bottom.

Description: In weakly indurated, nannofossil-rich, deep-sea carbonates compressional wave velocity is up to twice as fast parallel to bedding than normal to it. It has been suggested that this anisotropy is due to alignment of calcite c-axes perpendicular to the shields of coccoliths and shield deposition parallel to bedding. This hypothesis was tested by measuring the preferred orientation (fabric) of calcite c-axes in acoustic anisotropic, calcareous DSDP sediment samples by X-ray goniometry, and it was found that the maximum c-axis concentrations are by far too low to explain the anisotropies. The X-ray method is subject to a number of uncertainties due to preparatory and technical shortcomings in weakly indurated rocks. The most serious weaknesses are: sample preparation, volume of measured sample (fraction of a mm3), beam defocusing and background intensity corrections, combination of incomplete pole figures, and necessity of recalculation of the c-axis orientations from other crystallographic directions. Goniometry using thermal neutrons overcomes most of these difficulties, but it is time consuming. We test the interferences made about velocity anisotropy by X-ray studies about the concentration of c-axes in deep-sea carbonates by employing neutron texture goniometry to eight DSDP samples comprising mostly nannofossil material. Fabric and sonic velocity were determined directly on the core specimens, thus from the same rock volume and requiring no preparation. The c-axis orientation is obtained directly from the [0006] calcite diffraction peak without corrections. The fabrics are clearly defined, but weak (1.1 to 1.86 times uniform) with the maximum about normal to bedding. They have crudely orthorhombic symmetry, but are not axisymmetric around the bedding normal. The observed c-axis intensities, although higher than determined by the X-ray method on other samples, are by far too low to explain the observed acoustic anisotropies.