Essai de revue des concentrations métallifères dans le cycle sédimentaire

The author summarizes the main arguments in the debate between syngenetic and epigenetic deposits and then underlines the importance of the arguments which prove that the formation of the sediments and of the metalliferous concentrations which they bear are contemporaneous. This is strongly suggested by very early syn-sedimentary reworking of the mineralization. This approach leads to a consideration of metallogenesis of syngenetic sedimentary concentrations both as a supply of metal and a sedimentary trap. The exploitability of mineralized rocks is presently such that only the coincidence of an outstanding supply of metal and a receptive sedimentary environment will yield a workable ore deposit. Reviewing all metalliferous sources which could be contemporaneous with sedimentation (terrigenous, exhalative, marine and possibly also fluidogenic) the author stresses the geological and geochemical characteristic of the surrounding sediments. At the same time, the examination of traps in sandy, shaly and carbonate environments permits to the identification of the main characteristics of the concentration on the scale of the deposit and of the ore itself. The search for an understanding of metalliferous concentrations in the sedimentary cycle becomes a question of defining criteria for the quality of supplies and traps. On the level of the trap these would be the duration and the regulation of parameters which govern the efficiency of the concentrating system: the sedimentary features which result from these concentrating processes must be recognized within the lithologic column during tactical exploration. On the level of the metallogenetic province it is the purpose of strategic exploration to search among the available geological and geochemical data for features which favor each type of supply. These are the basic principles of the indirect method of exploration for sedimentary ore deposits.     

Circumstellar dust and variability of carbon stars

A sample of 35 variable carbon stars has been considered. The stellar temperatures, radii, absolute luminosities, masses, and mass loss rates have been estimated. Then the spherical circumstellar dust shells around the analysed stars are discussed and the differences in the infrared properties between semi-regular, irregular, and long-period variables are indicated.     

Surface temperature differences between minerals in crystalline rocks: Implications for granular disaggregation of granites through thermal fatigue

Thermal expansion differences between minerals within rocks under insolation have previously been assumed to drive breakdown by means of granular disaggregation. However, there have been no definitive demonstrations of the efficacy of this weathering mechanism. Different surface temperatures between minerals should magnify thermal expansion differences, and thus subject adjacent minerals to repeated stresses that might cause breakdown through fatigue failure. This work confirms the existence of surface temperature differences between minerals in granitic rocks under simulated short-term temperature fluctuations so as to discriminate their potential for initiating granular disaggregation. The influence of colour, as a surrogate for albedo, and crystal size, as a function of thermal mass are specifically identified because of their ease of quantification. Four rock types with a range of these properties were examined, and subjected to repeated short-term temperature cycles by radiative heating and cooling under laboratory conditions. Results show that while albedo is the main control for overall and individual maximum temperatures, crystal size is the main factor controlling higher temperature differences between minerals. Thus, stones with large differences of mineral sizes can undergo magnified stresses due to thermal expansion differences.     

Sediment yield and storage variations in the Négron River catchment (south western Parisian Basin,France) during the Holocene period

In the Négron River catchment area (162 km²), surface‐sediment stores are composed of periglacial calcareous ‘grèze’ (5 × 10⁶ t) and loess (21 × 10⁶ t), and Holocene alluvium (12·6 × 10⁶ t), peat (0·6 × 10⁶ t) and colluvium (18·5 × 10⁶ t). Seventy‐five per cent of the Holocene sediments is stored along the thalwegs. Present net sediment yield, calculated from solid discharge at the Négron outlet, is low (0·6 t km^?2 a^?1) due to the dominance of carbonate rocks in the catchment. Mean sediment yield during the Holocene period is 7·0 t km^?2 a^?1 from alluvium stores and 7·6 t km^?2 a^?1 from colluvium stores. Thus, the gross sediment yield during the Holocene period is about 18·7 t km^?2 a^?1 and the sediment delivery ratio 3 per cent. The yield considerably varies from one sub‐basin to another (3·9 to 24·5 t km^?2 a^?1) according to lithology: about 25 per cent and 50 per cent of initial stores of periglacial grèze and loess respectively were reworked during the Holocene period. Sediment yield has increased by a factor of 6 in the last 1000 years, due to the development of agriculture. The very high rate of sediment storage on the slope during that period (88 per cent of the yield) can be accounted for by the formation of cultivation steps (‘rideaux’). It is predicted that the current destruction of these steps will result in a sediment wave reaching the valley floors in the coming decades. Subboreal and Subatlantic sediments and pollen assemblages in the Taligny marsh, where one‐third of the alluvium is stored, show the predominant influence of human activity during these periods in the Négron catchment. Copyright © 2002 John Wiley & Sons, Ltd.     

CHANGES IN AGRICULTURAL PRODUCTION IN METROPOLITAN AREAS *

Different types of farming in metropolitan areas show both negative and positive responses to urban and nonurban forces of change. The variety of impacts has been neglected by most spatial intensity models and land use studies. This study examines census data from 1949 to 1982 in seven major U.S. metropolitan areas for six commodity types to detect regular patterns of changes in sales value, area harvested, number of animals, and intensity of production. Results show large declines in dairy farming, followed by poultry and fruit and nuts; some recent recovery in vegetable crops; and steady increases in both low value field crops and high value horticultural specialties. A trend toward polarization of metropolitan agriculture is indicated. Results also show differences between inner and outer urban fringe areas and a decline in the differential in intensity of production between metropolitan and non-metropolitan agriculture.     

Cuspidine‐bearing skarn from Chesney Vale,Victoria

The rare calc‐silicate minerals cuspidine, bultfonteinite, foshagite and xonotlite occur in a calcsilicate skarn zone near Chesney Vale, in northern Victoria. They are associated with andradite-grossular garnet, vesuvianite, diopside, wollastonite, prehnite, epidote, fluorite, calcite, perovskite,sphene and possibly tobermorite. The calc‐silicate skarn zone has formed in thermally meta‐morphosed, Ordovician, deep‐marine sediments adjacent to an Early Devonian aplitic granite pluton. The assemblages are estimated to have formed at low pressure (<100 MPa) at temperaturesnot exceeding 600°C in the presence of a low‐X_co2 fluorine‐bearing fluid. The occurrence is the firstrecord of bultfonteinite and foshagite in Australia and the first record of cuspidine and xonotlite inVictoria.     

Climatic factors controlling plant sensitivity to warming

Plant sensitivity to warming can be expressed as β or the number of days of advance in leafing or flowering events per 1 °C of Mean Annual Temperature (MAT) change. Many local studies demonstrate that β estimates for spring flowering species are usually larger than estimates for plants flowering in summer or fall. Until now, however, neither observational nor experimental estimates of this parameter were considered to be climate or geographically dependent. Here we question this paradigm through reanalysis of observational β estimates and mathematical modeling of the seasonal warming signal. Statistical analysis of a large number of bulk (averaged over species) estimates of β derived from the Pan European Phenology Data network (PEP725) revealed a positive spatial correlation with MAT, as well as a negative correlation with the Seasonal Temperature Range (STR). These spatial correlations of bulk β values as well as interseasonal variability in β were explained using a simple deterministic model of the Thermal Growing Season (TGS). More specifically, we found that the geographic distribution of bulk plant sensitivity to warming as well as the seasonal decline of β were controlled by the seasonal patterns in the warming signal and by average soil thermal properties. Thus, until recently, plants managed to keep pace with climate warming by shifting their leafing and flowering events by the same number of days as the length of the period of weather suitable for their growth. Our model predicts, however, an even greater increase in the TGS for subsequent increases in MAT. Depending on how they interact with other factors such as changes in precipitation and increased temperature variability, these longer thermal growing seasons may not be beneficial for plant growth.     

Changes in Habitat Availability for Multiple Life Stages of Diamondback Terrapins (<Emphasis Type="Italic">Malaclemys terrapin</Emphasis>) in Chesapeake Bay in Response to Sea Level Rise

Global sea level rise (SLR) will significantly alter coastal landscapes through inundation and erosion of low-lying areas. Animals that display area fidelity and rely on fringing coastal habitats during multiple life stages, such as diamondback terrapins (Malaclemys terrapin Schoepff 1793), are likely to be particularly vulnerable to SLR-induced changes. We used a combination of empirical nest survey data and results from a regional SLR model to explore the long-term availability of known nesting locations and the modeled availability of fringing coastal habitats under multiple SLR scenarios for diamondback terrapin in the MD portion of Chesapeake Bay and the MD coastal bays. All SLR scenarios projected the rapid inundation of historically used nesting locations of diamondback terrapins with 25%–55% loss within the next 10 years and over 80% loss by the end of the century. Model trajectories of habitat losses or gains depended on habitat type and location. A key foraging habitat, brackish marsh, was projected to decline 6%–94%, with projections varying spatially and among scenarios. Despite predicted losses of extant beach habitats, future gains in beach habitat due to erosion and overwash were projected to reach 40%–600%. These results demonstrate the potential vulnerability of diamondback terrapins to SLR in Chesapeake Bay and underscore the possibility of compounding negative effects of SLR on animals whose habitat requirements differ among life stages. More broadly, this study highlights the vulnerability of species dependent on fringing coastal habitats and emphasizes the need for a long-term perspective for coastal development in the face of SLR.