Additional estimates of continental surface Precambrian shield composition in Canada

New trace element analyses have been made on the composite Canadian Precambrian shield samples reported in 1967.The overall mean abundance of Cr has been revised to 35 ppm (from 99). New abundances similar to 1967 values are (in ppm): Ni, 19; Co, 12; Cu, 14; Zr, 300; Sr, 315; Ba, 1070; Rb, 110: individual 1967 Rb values were erroneous.Elements not previously determined have the following overall mean values (in ppm): Zn, 52; Sc, 7.0; Nb, 26; Hf, 6.9; La, 32; Ce, 65; Nd, 26; Sm, 4.5; Eu, 0.94; Gd, 2.8; Tb, 0.48; Ho, 0.62; Yb, 1.5; Lu, 0.23; Y, 21; Pb, 17; values in ppb are: Ir, 0.02; Au, 1.8; Tl, 520.Clear positive correlations among Mg-Cr-Ni-Ir-Au appear for all rock-types, marble and quartzite as well as mafic igneous. Regional differences are apparent for several elements: e.g. higher Au, Ir, Cr, Ni in Baffin Island and Northern Quebec composites, compared with Saskatchewan and Southwestern Quebec; high Ti, Zn, Nb, Zr, Hf, REE, Y, Sr, K/T1 abundances and negative Eu anomalies in Southwestern Quebec.The overall REE abundances (omitting Southwestern Quebec) differ from other surface continental crustal rock estimates.     

Evolution of gold-bearing veins in dykes of the Woods Point dyke swarm,Victoria

The Woods Point dyke swarm comprises hundreds of narrow, subparallel igneous dykes and dozens of pipe-shaped dyke bulges within strongly deformed early Palaeozoic turbidites of the Melbourne trough. Porpylitic alteration accompanied dyke emplacement and was followed by microfracturing induced by high fluid pressures, involving CO₂ of magmatic origin, as the dykes solidified. Further stress caused through-going faults having ladder and other patterns. Isotopic studies suggest that metamorphically or geothermally-derived solutions filled the faults and other fractures with quartz and carbonate and altered immediately adjacent dyke rock. However earlier-formed vein and wall rock carbonates retained their magmatic isotopic composition. Fluid inclusions indicate vein deposition began at approximately 400°C with salinities up to 9 weight percent NaCl. Nine sulfide minerals and gold were deposited in the veins after ankerite, sericite and albite, while quartz deposition continued through all stages. Sulfur isotopic determinations indicate the vein sulfur could not have been derived from adjacent sedimentary rocks, nor exclusively from the dykes. Metamorphic waters of marine origin is a viable source for sulfur. Saline and CO₂-rich alkaline solutions reacted with the dyke wall rocks and probably evolved chemically prior to deposition of gold. Vug carbonates deposited by meteoric water that leached vein carbonates mark the end of vein formation.Present Adress: 631 Station Street, North Carlton 3054, Victoria, Australia     

Sorption of radium-226 from oil-production brine by sediments and soils

The sorption of²²⁶Ra from oil-production brine by soils and sediments was investigated. Sorption was rapid, and the percentage sorbed increased with brine dilution. Greatest removals of²²⁶Ra from sediments in the laboratory occurred with alkaline DTPA, HCl, and BaCl₂, with lesser removals using CaCl₂ and NaCl solutions. Digestion of sediments with NaOCl indicates that most of the native and sorbed²²⁶Ra is associated with the mineral rather than organic fraction of the sediments. Correlation analysis based on 14 soils indicates that the retention of²²⁶Ra may involve precipitation reactions associated with sulfate-bearing minerals, as well as ion-exchange reactions with the clay mineral fractions of surficial earth materials. Oceanographer, Naval Ocean Research and Development Activity, Code 334; NSTL Station, Mississippi 39529 NORDA Contribution #83:334:01.     

Macrophysiology of Calanus finmarchicus in the North Atlantic Ocean

Copepods represent the major part of the dry weight of the mesozooplankton in pelagic ecosystems and therefore have a central role in the secondary production of the North Atlantic Ocean. The calanoid copepod species Calanus finmarchicus is the main large copepod in subarctic waters of the North Atlantic, dominating the dry weight of the mesozooplankton in regions such as the northern North Sea and the Norwegian Sea. The objective of this work was to investigate the relationships between both the fundamental and realised niches of C. finmarchicus in order to better understand the future influence of global climate change on the abundance, the spatial distribution and the phenology of this key-structural species. Based on standardised Principal Component Analyses (PCAs), a macroecological approach was applied to determine factors affecting the spatial distribution of C. finmarchicus and to characterise its realised niche. Second, an ecophysiological model was used to calculate the Potential Egg Production Rate (PEPR) of C. finmarchicus and the centre of its fundamental niche. Relationships between the two niches were then investigated by correlation analysis. We found a close relationship between the fundamental and realised niches of C. finmarchicus at spatial, monthly and decadal scales. While the species is at the centre of its niche in the subarctic gyre, our joint macroecological and macrophysiological analyses show that it is at the edge of its niche in the North Sea, making the species in this region more vulnerable to temperature changes.     

Rates of fluvial sedimentation: Implications for archaeological variability

Rates of fluvial sedimentation exhibit spatial and temporal variability that is important with respect to the study of prehistoric archaeological sites. Sedimentation rates within fluvial basins vary in response to internal dynamics, geomorphic controls, and external factors including climate and tectonics. Fluvial rates of sedimentation may be estimated using sedimentary, pedogenic, biogenic, and radiometric evidence. Holocene rates of sedimentation vary by three orders of magnitude, as shown by radiometric data from numerous localities in North America. Sedimentation rates define rates of matrix accumulation in archaeological sites. These act as controls on site construction and site modification. Artifact densities, spatial patterning, and preservation are all conditioned by rates of matrix accumulation. These dimensions of prehistoric sites are critical to the evaluation of variability within and between archaeological sites and to the study of past settlement/subsistence systems.