Carbon-14 production compared to oxygen isotope records from Camp Century,Greenland and Devon Island,Canada

Carbon-14 production rate variations that are not explainable by geomagnetic changes are thought to be in antiphase with solar activity and as such should be in antiphase with paleotemperature records or proxy temperature histories such as those obtainable from oxygen isotope analyses of ice cores. Oxygen isotope records from Camp Century, Greenland and Devon Island Ice Cap are in phase with each other over thousands of years and in antiphase to the ¹⁴C production rate residuals.     

Uranium abundance of the oceanic crust

Uranium contents of 67 oceanic basalts have been measured by fission track analysis. Average value for ridge and intraplate basalts is ~ 78 ppb, for the Easter Hot Line it is ~1600 ppb. Estimates of mantle concentrations derived from the ridge and intraplate samples are insufficient to account for the observed surface heat flow. The whole-Earth concentration of U is > 8 ppb. and < 33 ppb if all heat generated within the Earth reaches the surface.     

Comparison of 105 years of oxygen isotope and insoluble impurity profiles from the Devon Island and Camp Century ice cores

Oxygen-isotope profiles for the Devon Island ice cap and Camp Century Greenland are affected by a number of variables, some of which must have been the same for both sites. The two δ(¹⁸O) records spanning about 120,000 years are brought into relative alignment by comparison of major δ features, and subsequent verification that the insoluble particulate concentration records were also in phase for this alignment. The difference between the δ profiles is shown to be mainly a function of the altitude of the accumulation area for Camp Century. This altitude seems to have been higher than present for the last 100,000 years, suggesting the present flow line through the site has never been shorter. The maximum altitude for the Camp Century accumulation area is 1500 m above the present site and is almost synchronous with the maximum in particulate concentration that occurs at 16,000 yr B.P. The synchronism is likely due to the maximum sea-level lowering that exposed vast areas of continental shelf to wind erosion.     

Olivine-matrix reactions in thermally metamorphosed Apollo 14 breccias

Olivine clasts, which have mantles formed by reaction of the olivine with the breccia matrix, are present in the high-grade thermally metamorphosed Apollo 14 breccias. The mantled olivine clasts are most abundant in 14311, but they are also present in 14304 and 14319. Typically the mantles consist of two zones: an inner corona containing pyroxene, ilmenite and commonly plagioclase, and an outer light-colored halo where the matrix is depleted in ilmenite. The growth of the coronas involved matrix-to-corona diffusion of TiO₂ and corona-to-matrix diffusion of MgO and FeO. These diffusive fluxes can be attributed to chemical potential gradients developed between mineral assemblages in local equilibrium at the olivine-corona boundary and the matrix.     

Uranium content and radiogenic ages of hypersthene,bronzite, amphoterite and carbonaceous chondrites

U was measured by fission track analysis in 115 samples of hypersthene, bronzite, amphoterite and carbonaceous chondrites. On a weight basis the average values for the Cl carbonaceous and bronzite chondrites are similar to the “classic” value of 11 ppb, but the hypersthenes and amphoterites are ~50 per cent higher. Each class shows a well-determined peak in the U abundance distribution, allowing the calculation of radiogenic ages and comparison with other elements of interest.     

U/He ages as indicators of excess argon in deep sea basalts

U/He ages of deep sea basalts which show unequivocal evidence of excess Ar are generally higher than the corresponding K/Ar ages, suggesting that this result is diagnostic of the presence of excess rare gases. Concordant U/He and K/Ar ages are indicative of the validity of such ages. U/He ages lower than the corresponding K/Ar ages are not informative.     

The influence of pH on the kinetics, reversibility and mechanisms of Pb(II) sorption at the calcite-water interface

Pb(II) sorption experiments with calcite powders were conducted in suspensions equilibrated at atmospheric PCO_2(g) and ambient temperature at pH 7.3, 8.2 and 9.4. Pb fractional sorption was low at pH 7.3 and 9.4 relative to pH 8.2, and correlated well with PbCO₃⁰_(aq) speciation. Desorption experiments conducted for initial sorption times ranging from 0.5 h to 12 d reveal an almost completely reversible process at pH 8.2, attributed to the dominance of an adsorption mechanism, with slight and pronounced irreversibility at pH 7.3 and 9.4 respectively. Similarities in X-ray absorption near edge spectra (XANES) for 24 h and 12 d pH 7.3 and 9.4 sorption samples indicate no effect of initial sorption time. Results from linear combination (LC) fits of XANES spectra for samples sorbed at pH 9.4 confirm ∼75% adsorbed and ∼25% coprecipitated components. The coprecipitated fraction was attributed to the non-exchangeable metal observed in desorption experiments. At pH 7.3, ∼95% adsorbed and ∼5% coprecipitated components were obtained. A comparison of results from desorption experiments and LC-XANES alludes to an irreversibly bound adsorbed component for the pH 9.4 12 d sorption sample. Extended X-ray absorption fine structure spectroscopy (EXAFS) analysis of pH 7.3 and 9.4 12 d sorption samples confirms the presence of both adsorbed and coprecipitated metal. At pH 7.3 a first-shell Pb-O bond length of 2.38 Å is intermediate between that of adsorbed (2.34 Å) and coprecipitated (2.51 Å) Pb. At pH 9.4, two first-shell Pb-O distances at 2.35 Å and 2.51 Å were obtained, indicative of the occurrence of both adsorption and coprecipitation and a larger coprecipitated fraction relative to that at pH 7.3, consistent with LC-XANES results. We propose that the disparity in the fraction of coprecipitated metal with pH may be linked to the ability of sorbed Pb to inhibit near-surface dynamic exchange of Ca and CO₃ species, which dictates step advance and retreat. Less effective inhibition of step motion at pH 9.4, due to lower fractional sorption, combined with highest rates of dynamic exchange results in a significant fraction of coprecipitated Pb at this pH. At low pH, though fractional sorption is also low, lower rates of exchange prohibit significant coprecipitation. At pH 8.2, effective inhibition of surface processes due to higher fractional sorption and lower rates of exchange compared to pH 7.3 and 9.4 preclude detectable coprecipitation. Other factors such as changes in surface speciation and solubility of the Pb-Ca solid solution with pH may also come into play. Overall, this study presents evidence for the influence of pH on Pb sorption mechanisms, and addresses the efficiency of Pb immobilization in calcitic systems.     

The Potential for Rural Heritage Tourism in the Clarence Valley of Northern New South Wales

In the past, heritage tourism has been associated with urban sites but there is now an acceptance of the application of this concept to rural areas. In the Clarence Valley in northern New South Wales there is potential for an extension of agritourism associated with working dairy farms to include safari tours to clusters of dairy heritage sites which are scattered throughout the area. Remnants of the old dairy industry, which began in the Clarence River Valley of New South Wales in the late nineteenth century, are scattered throughout the landscape. Over 300 dairy milking bails remain—ghosts of the former thriving industry when over 2000 dairy farms were operating. Concrete foundations of some creameries built in the 1890s can still be found, and three factory buildings still stand. These relics are disappearing quite rapidly and if the importance of the industry is to be recognised by future generations then it seems that some heritage conservation is overdue. At the same time, in order to survive in a post-deregulated economic environment, the remaining 10 dairy farmers in the Clarence Valley are diversifying their activities, with one form of pluriactivity being agritourism. Currently few of these farmers have entered this field but most of them see its potential to broaden their income base. Associated with agritourism at the farm level, the local government authorities see heritage tourism as a way of increasing employment in the region.     

Local thickening of the Cascadia forearc crust and the origin of seismic reflectors in the uppermost mantle

Seismic reflection profiles from three different surveys of the Cascadia forearc are interpreted using P wave velocities and relocated hypocentres, which were both derived from the first arrival travel time inversion of wide-angle seismic data and local earthquakes. The subduction decollement, which is characterized beneath the continental shelf by a reflection of 0.5 s duration, can be traced landward into a large duplex structure in the lower forearc crust near southern Vancouver Island. Beneath Vancouver Island, the roof thrust of the duplex is revealed by a 5–12 km thick zone, identified previously as the E reflectors, and the floor thrust is defined by a short duration reflection from a < 2-km-thick interface at the top of the subducting plate. We show that another zone of reflectors exists east of Vancouver Island that is approximately 8 km thick, and identified as the D reflectors. These overlie the E reflectors; together the two zones define the landward part of the duplex. The combined zones reach depths as great as 50 km. The duplex structure extends for more than 120 km perpendicular to the margin, has an along-strike extent of 80 km, and at depths between 30 km and 50 km the duplex structure correlates with a region of anomalously deep seismicity, where velocities are less than 7000 m s^− 1. We suggest that these relatively low velocities indicate the presence of either crustal rocks from the oceanic plate that have been underplated to the continent or crustal rocks from the forearc that have been transported downward by subduction erosion. The absence of seismicity from within the E reflectors implies that they are significantly weaker than the overlying crust, and the reflectors may be a zone of active ductile shear. In contrast, seismicity in parts of the D reflectors can be interpreted to mean that ductile shearing no longer occurs in the landward part of the duplex. Merging of the D and E reflectors at 42–46 km depth creates reflectivity in the uppermost mantle with a vertical thickness of at least 15 km. We suggest that pervasive reflectivity in the upper mantle elsewhere beneath Puget Sound and the Strait of Georgia arises from similar shear zones.