Some ecological effects of the Venpet-Venoil collision

The effects of oil, released after the Venpet-Venoil collision in December 1977, on the intertidal fauna along the South Coast of South Africa have been monitored at monthly intervals since the incident. Localized areas, such as estuaries and sheltered coves, suffered the greatest damage due to the smothering effects of the oil. Damage to the remaining areas has been slight owing to the patchy distribution of the oil together with its physical and chemical characteristics.     

Heat flow anomalies and their interpretation

More than 10,000 heat flow determinations exist for the earth and the data set is growing steadily at about 450 observations per year. If heat flow is considered as a surface expression of geothermal processes at depth, the analysis of the data set should reveal properties of those thermal processes. They do, but on a variety of scales. For this review heat flow maps are classified by 4 different horizontal scales of 10ⁿ km (n = 1, 2, 3 and 4) and attention is focussed on the interpretation of anomalies which appear with characteristic dimensions of 10^{(n − 1)} km in the respective representations.The largest scale of 10⁴ km encompasses heat flow on a global scale. Global heat loss is 4 × 10¹³ W and the process of sea floor spreading is the principal agent in delivering much of this heat to the surface. Correspondingly, active ocean ridge systems produce the most prominent heat flow anomalies at this scale with characteristic widths of 10³ km. Shields, with similar dimensions, exhibit negative anomalies.The scale of 10³ km includes continent wide displays. Heat flow patterns at this scale mimic tectonic units which have dimensions of a few times 10² km, although the thermal boundaries between these units are sometimes sharp. Heat flow anomalies at this scale also result from plate tectonic processes, and are associated with arc volcanism, back arc basins, hot spot traces, and continental rifting. There are major controversies about the extent to which these surface thermal provinces reflect upper mantle thermal conditions, and also about the origin and evolution of the thermal state of continental lithosphere.Beginning with map dimensions of 10² km thermal anomalies of scale 10¹ km, which have a definite crustal origin, become apparent. The origin may be tectonic, geologic, or hydrologic. Ten kilometers is a common wavelength of topographic relief which drives many groundwater flow systems producing thermal anomalies. The largest recognized continental geothermal systems have thermal anomalies 10¹ km wide and are capable of producing hundreds of megawatts of thermal energy.The smallest scale addressed in this paper is 10¹ km. Worldwide interest in exploiting geothermal systems has been responsible for a recent accumulation of heat flow data on the smallest of scales considered here. The exploration nature of the surveys involve 10's of drillholes and reveal thermal anomalies having widths of 10⁰ km. These are almost certainly connected to surface and subsurface fluid discharge systems which, in spite of their restricted size, are typically delivering 10 MW of heat to the near surface environment.     

The influence of water table configuration on the near-surface thermal regime

Numerical solutions of the equations of fluid flow and heat transport are used to quantify the effects of groundwater flow on the subsurface thermal regime. Emphasis is placed on investigating the influence of water table geometry on the nature of the thermal disturbance to surface heat flow. Three different water table configurations are compared; with convex, linear, and concave geometries. Results indicate that knowledge of only the overall change in elevation of the water table between the highland and valley bottom is inadequate to determine the degree and character of the hydrologic disturbance in surface heat flow. The configuration of the water table exerts an important control on surface heat flow in advectively-disturbed cases.     

Reductive deposition of graphite at lithological margins in East Central Vermont: a Sr, C and O isotope study

O, Sr and C isotopes from east‐central Vermont are used to provide information on the timing and volume of metamorphic fluid flow. The results are then used to assess the evidence for redox transformations between C species. Oxygen profiles are homogenised on a metre scale; comparison with Sr isotopes suggest that O alteration may have occurred over a significantly larger timescale than that of Sr, possibly because O was modified during dewatering and diagenesis in addition to the high temperature alteration recorded by strontium. Sr isotope distributions are consistent with cross‐layer fluid fluxes of 10⁴?10⁶ moles m^?2; absolute values depend on the Sr fluid‐rock distribution coefficient which is poorly known; however, reaction progress constraints suggest that fluxes were towards the lower end of this range. High δ¹³C values observed at lithological boundaries cannot be explained by volume loss or closed system processes and are taken to indicate reductive precipitation of graphite as a result of mixing between CO₂ and CH₄‐bearing fluids. Mass balance calculations indicate that redox reactions occurring under metamorphic conditions convert a minimum of 10% of the CO₂ released from limestones into graphite, thus providing a potentially important control on the average residence time of C within the crust with implications for C cycling models.     

Ecotoxicology and pollution—Key issues

The following key issues in ecotoxicology, the integration of ecology and toxicology, are discussed: standardized tests and tests of specific hypotheses; future needs relative to ‘benchmarks’; exposure routes and reference comparisons; reproductive effects (e.g. for endocrine-disruptive chemicals) and non-standard data analyses; ‘acceptable’ variability; appropriate use of end-points (e.g. NOECs), biomarkers and bioindicators; external concentration effect vs internal dose response; setting testable hypotheses; integration and/or tiering with chemistry, physical and other variables; ‘validation’ vs proactivity. Ecotoxicology is proactive (e.g. directed testing, resulting in testable hypotheses) as opposed to reactive, the initial impetus for toxicology (determining the causes of observed effects). Ecotoxicology and policy must be integrated if the environment is to be protected.     

On the Evaluation of Rock Reference Materials -A “Five-Mode’ Approach*

The concentrations of numerous constituents must be evaluated in rock samples if they are to be used as reference materials. Because of varying degrees of specialized skills in earth-science laboratories, the collaboration of many institutions is required in order to establish reliable values. Analytical data reported in such operations are highly variable. The number of constituents reported per sample varies from one laboratory to another. The number of values reported varies from one constituent to another. The reported values for each constituent are generally incoherent, often displaying skewed distributions. The problem is then how to deduce the most probably “true’ concentration for each constituent. Various computation schemes, based on medians, means and related measures, are discussed. A new scheme, involving a combination of modes, is proposed.     

Strontium and oxygen isotope decoupling in the Hercynian Trois Seigneurs Massif,Pyrenees: evidence for fluid circulation in a brittle regime

Systematic shifts of oxygen isotopic compositions in the higher grade parts of the high temperature-low pressure Hercynian metamorphic sequence, exposed in the Trois Seigneurs Massif, have previously been explained as a result of an influx of surface-derived water during the prograde part of the metamorphic cycle. It has been suggested that this caused a regional lowering of ⁸⁷Sr/⁸⁶Sr in the metamorphic sequence. Mapping of strontium isotopic compositions across a 15 m meta-carbonate horizon in the higher grade pelite-psammite sequence shows that strontium isotopic compositions were homogenised over length scales of metres or less during the Hercynian metamorphism, which brought the carbonate and pelite-psammite to oxygen isotopic equilibrium with a common fluid. Comparison of model pre-Hercynian ⁸⁷Sr/⁸⁶Sr profiles across the carbonate (based on a depositional/diagenetic age of 450 Ma and initial ⁸⁷Sr/⁸⁶Sr ratio of 0.7086 given by 10 m length scale averaging) with the post-Hercynian ⁸⁷Sr/⁸⁶Sr profile (calculated from analysed ⁸⁷Sr/⁸⁶Sr and Rb/Sr compositions) implies strontium isotopic diffusion distances of ca. 0.4 m in the carbonate and ca. 7 m in the pelite-psammite. The limited Sr-isotopic diffusion distance of 0.4–0.7 m within the carbonate is compatible with pervasive oxygen-isotopic exchange over distances restricted to 4–15 m if fluid strontium concentrations were between 4 and 50 ppm. The strontium isotopic transport distances are not compatible with pervasive oxygen isotopic alteration over the observed 5 km regional scale. Either the flow was perfectly layer-parallel or, more probably, the regional-scale alteration of oxygen took place by fluid circulation in the brittle regime early in, or prior to, the Hercynian metamorphic event. Flow along cracks with incomplete diffusive exchange between fluid and wall rock would allow greater decoupling of oxygen and strontium isotopic transport than pervasive advective transport with local fluid-solid equilibrium.     

Robust Measures and the Estimator Limit

A new concept, the Estimator Limit, is proposed as a mean of overcoming discrepanices among the "robust'measures used in deducing "best values'from incoherent analytical data on proposed rock reference samples.
Un nouveau concept, l'"estimateur limite'est proposé pour surmonter les inconsistances entre les mesures "robustes'utilisées pour établir les "meilleures valeurs'à partir de données analytiques incohérentes (obtenues) sur des geostandards proposés.