Effect of mining and related activities on the sediment trace element geochemistry of lake coeur D'Alene,idaho, USA. Part I: Surface sediments

During the summer of 1989 surface sediment samples were collected in Lake Coeur d'Alene, the Coeur d'Alene River and the St Joe River, Idaho, at a density of approximately one sample per square kilometre. Additional samples were collected from the banks of the South Fork of the Coeur d'Alene and the Coeur d'Alene Rivers in 1991. All the samples were collected to determine trace element concentrations, partitioning and distribution patterns, and to relate them to mining, mining related and discharge operations that have occurred in the Coeur d'Alene district since the 1880s, some of which are ongoing. Most of the surface sediments in Lake Coeur d'Alene north of Conkling Point and Carey Bay are substantially enriched in Ag, As, Cu, Cd, Hg, Pb, Sb and Zn relative to unaffected sediments in the southern portion of the lake near the St Joe River. All the trace element enriched sediments are extremely fine grained (mean grain sizes « 63 μm). Most of the enriched trace elements, based on both the chemical analyses of separated heavy and light mineral fractions and a two step sequential extraction procedure, are associated with an operationally defined Fe oxide phase; much smaller percentages are associated either with operationally defined organics/sulphides or refractory phases. The presence, concentration and distribution of the Fe oxides and heavy minerals indicates that a substantial portion of the enriched trace elements are probably coming from the Coeur d'Alene River, which is serving as a point source. Within the lake, this relatively simple point source pattern is complicated by a combination of (1) the formation of trace element rich authigenic Fe oxides that appear to have reprecipitated from material solubilized from anoxic bed sediments and (2) physical remobilization by currents and wind driven waves. The processes that have caused the trace element enrichment in the surface sediments of Lake Coeur d'Alene are likely to continue for the foreseeable future.     

Burial-exhumation history of the central Apennines (Italy), from the foreland to the chain building: thermochronological and geological data

A clear correlation between regional unconformities and related exhumation events was documented by thermochronological and geological data in the central Apennines. This approach allowed: (i) two major exhumation episodes to be identified, corresponding to turning points in the long-term burial history, from rifting to convergent margin development, and (ii) a quantification of the amount of section removed during the two exhumation events. The first exhumation event was connected with the foreland buckling process associated with the coupling between the Alpine–Apennines system, the Dinarides chain and their common foreland. During the Neogene a thrust-system development, the superposition of an allochthonous unit is envisaged to explain the second palaeoheating event. The dismantling of this additional load in central Apennines has been related to the formation of the Middle Pliocene Unconformity, during the development of the Pliocene–Quaternary frontal thrust of the Apennine Chain.     

Trend-surface analysis of structure and thickness of Bulli Seam, Sydney Basin, New South Wales

Methods are presented which permit the analysis of structural and thickness variations of a stratigraphic interval into a number of components and testing of the components for relationship between structure and thickness. The methods are tested first in the axial region of the South Bulli Syncline area where the Bulli Seam is known to be thicker. Maps of the residual values from the structural and thickness first-degree trends are similar and there is a significant inverse relationship between the residuals. Data from the area where the Bulli Seam occurs also give seam structural and thickness residuals which have a significant inverse relationship. Local exceptions to this relationship are present but in most instances are due to laccolithic doming or changes in lithology of the Bulli Seam. A number of the trend components of structural and thickness variation also show an inverse relationship. It is postulated that most of the present structures defined at the Bulli Seam horizon were active during deposition of the Bulli Seam, and within the limit of the conditions suitable for peat accumulation, controlled thickness of the Bulli Seam. Thickness changes in overlying units suggest that a major part of the warping of the Bulli Seam horizon had occurred by the end of the Triassic Period.     

A British meta-anthracitic coal of Devonian age

Vitrinite from the Devonian Gramscatho Beds at Pendower in southwestern Cornwall displays optical properties which indicate an extremely high rank (meta-anthracite). Despite this high rank, wood structures are clearly evident in polished sections between crossed polars. Some coke is present and this feature, together with the optical properties of the main vitrinite mass, suggests that relatively high temperatures (probably in excess of 350°C), were associated with the metamorphism of the host rocks. Reflectivity measurements on oriented blocks show that the vitrinite is optically biaxial, which conflicts with the widely accepted view that vitrinites are negative uniaxial materials.