The drainage of Lake Ojibway in glaciolacustrine sediments of northern Ontario and Quebec,Canada

Physical evidence for the drainage of glacial lakes remains relatively rare in depositional records, giving rise to much debate on the location of outlets and discharge pathways, as well as on the climate impact of the attendant meltwater forcing. Lake Ojibway developed following the withdrawal of the Laurentide Ice Sheet in northern Ontario and Quebec, Canada. The late‐stage evolution of this large ice‐dammed lake was influenced by the complex dynamics of the retreating ice margin, which highly complicates the identification of the termination of Lake Ojibway in glaciolacustrine sediment records. Here, we document the composition of sections of rhythmites that contain in their upper part an anomalously thick and whitish bed (10–15 cm) that is in turn overlain by ～1 m of faintly bedded rhythmites. Grain‐size analyses showed that the thick whitish bed consists primarily of fine to coarse silt (2–63 μm), contrasting with the lower and upper rhythmites that are largely dominated by clay (<2 μm). The detrital carbonate content of the thick silt bed is characterized by consistently high values (2.5 to 2.8%), whereas the bounding rhythmites show lower and highly variable values. Oxygen isotope measurements further show a marked change going from typical glacial meltwater values (～ ?29.6 to ?27.7‰; VSMOW) for the lower rhythmites and the silt bed to modern‐like meteoric values (?18.4 to ?14.6‰) for the uppermost rhythmites. These data suggest that this marker bed may be associated with a major drawdown event that possibly corresponds to the final drainage of Lake Ojibway. AMS radiocarbon dating of ostracods extracted from the drainage bed also documents an important hardwater effect within the Ojibway basin.     

Processes controlling very low sedimentation rates on the continental slope of the Gonone-Orosei canyon system,NE Sardinia—terrestrial and oceanic significance

The narrow shelf and upper slope immediately above the Gonone canyon head off NE Sardinia represent areas of very low sedimentation rates. Along the sides of the canyon head (1,600 m water depth), the sediment deposits are homogeneous but show alternating light-grey intervals rich in carbonate and dark-grey ones rich in organic matter, possibly related to distal turbidite processes. Deposits older than 50,000 years are already encountered at core depths of 2.50 m, the sedimentation rates varying from 6–21 cm/10³ years in the lower parts of two cores and from 1.5–3 cm/10³ years in the upper parts. At about 35,000 years BP, both cores show a simultaneous drop in sedimentation rate by a factor of 3, probably in response to local mechanisms of channel avulsion. Lithological, mineralogical and geochemical properties reveal the environmental factors which are responsible for the extremely slow sediment accumulation. The southernmost sector of the coast, and partly also of the shelf, consists of Jurassic limestones which supply only small amounts of fine-grained material transported in suspension. During the last sea-level highstand, the accumulation of the Cedrino River pro-delta remained restricted to the coast, the low siliciclastic sediment yields resulting in poor shelf sediment trapping. The present morphology of the canyon head prevented the occurrence of gravity processes in the deeper part of the canyon system, including the coring sites. Accordingly, deposition was mainly fed by hemipelagic material of planktonic origin, together with only moderate terrigenous inputs. On a wider late Pleistocene timescale, seismic data indicate the occurrence of a coarse-grained, layered turbidite facies, implying a very different architecture of the canyon drainage system probably prior to 60,000 years BP.     

Interest of quality-based policies for Integrated Coastal Zone Management implementation: Lessons learnt from a French case study

This article shows how quality-based policies can support the effective implementation of Integrated Coastal Zone Management. It is based upon the analysis of the trial that is currently being conducted by the Marennes Oléron District on the Atlantic coast of France through the implementation of the Oléron Coastal Quality Action Plan. The author emphasizes three main aspects. At first, she exposes the general process that supported the emergence of the ICZM project of this district, highlighting the major role of early public participation, territorial planning and the design of operational action plans. She demonstrates that the implementation of coastal quality action plans can follow the integration building process of the ICZM iterative cycle, and thus support ICZM implementation. Then, she highlights the major role of science/management integration in the implementation of quality-based policies, showing in which way scientists can provide useful knowledge to practitioners at various stages of the decision-making process and contribute both to the development of public participation and success of these policies. At last, the author presents and discusses the lessons learnt from the follow up and analysis of the implementation of this action plan. She emphasizes its strengths and weaknesses by putting it into the perspective of other French ICZM projects, and shows in which way the resolution of the problems faced by stakeholders in it realization contributes to the strengthening of their management capacity. The main benefits of this process for a quality-based policy are outlined.     

High cadmium concentrations in Jurassic limestone as the cause for elevated cadmium levels in deriving soils: a case study in Lower Burgundy,France

Cadmium (Cd) is a highly toxic element and its presence in the environment needs to be closely monitored. Recent systematic surveys in French soils have revealed the existence of areas in eastern and central France, which show systematically high cadmium concentrations. It has been suggested that at least part of these anomalous levels are of natural origin. For the Lower Burgundy area in particular, a direct heritage from the Jurassic limestone bedrock is highly suspected. This potential relationship has been studied in several localities around Avallon and this study reports new evidence for a direct link between anomalously elevated cadmium contents of Bajocian and Oxfordian limestone and high cadmium concentrations in deriving soils. Soils in this area show cadmium concentrations generally above the average national population values, with contents frequently higher than the ‘upper whisker’ value of 0.8 μg g⁻¹ determined by statistical evaluation. In parallel, limestone rocks studied in the same area exhibit cadmium concentrations frequently exceeding the mean value of 0.030–0.065 μg g⁻¹ previously given for similar rocks by one order of magnitude, with a maximum of 2.6 μg g⁻¹. Mean ratios between the cadmium concentrations of limestone bedrock and deriving soils (Cd_soil/Cd_rock), calculated for different areas, range from 4.6 to 5.7. Calculations based on the analyses of both soils from a restricted area and fragments of bedrock sampled in the immediate vicinity of high-concentration soils are around 5.5–5.7. Cd_soil/Cd_rock is useful in determining the potential of soils in Lower Burgundy to reflect and exacerbate the high concentrations of cadmium present in parent bedrocks.     

Variability of precipitation intensity: sensitivity to treatment of moist convection in an RCM and a GCM

The present study investigates the sensitivity of the frequency distribution of precipitation rates to the closure employed in the penetrative mass flux cumulus parameterization of Zhang and McFarlane in the Canadian regional climate model (CRCM) and in the Canadian Centre for Climate Modelling and Analysis third generation global atmospheric general circulation model (AGCM3). The effects of an alternative prognostic closure for mass flux cumulus parameterization in place of the original diagnostic closure are investigated. A set of experiments is performed in which changes in the frequency distribution of precipitation rates and cloud base mass-flux are examined as a function of the parameters that define each closure scheme. The relationship between the frequency distribution of precipitation and cloud base mass flux is examined and a self-consistent relation is found when the depth of convection is taken into account. Experiments performed with the prognostic closure favor relatively strong cloud base mass-flux and deep penetrative convection with relatively more intense convective precipitation. The mean of the frequency distribution of convective precipitation is larger and the heavier events become more intense. Also, experiments performed with the prognostic closure favor less frequent convective activity. However these changes in the distribution of convective component of precipitation are generally offset by opposite changes in the distribution of the resolved large-scale component of precipitation, resulting in relatively smaller changes in total precipitation. The altered partition of precipitation between convective and large-scale components is found to alter the energy balance and the thermodynamic equilibrium structure of the troposphere. The robustness found in the CRCM results regarding the sensitivity of the frequency distribution of precipitation to changes in the closure of the deep convection parameterization is investigated by performing a similar analysis of AGCM3 simulations. A remarkable similarity of AGCM3 and CRCM results is found suggesting that the closure sensitivity identified in this study is robust.     

Enrichment of redox-sensitive trace metals (U,V, Mo,As) associated with the late Hauterivian Faraoni oceanic anoxic event

The Faraoni Level is a short-lived oxygen-deficient event that took place during the latest Hauterivian. In order to improve our understanding of the palaeoenvironmental conditions that occurred during this event, we have analysed the contents of several redox-sensitive trace elements (U, V, Mo, As, Co, Cd, Cu, Zn, Ni, Pb, Cr) from bulk limestone samples of late Hauterivian–early Barremian age from three reference sections. U, V, Mo and As show consistent and significant enrichments during the Faraoni event whereas the other redox-sensitive trace elements analysed here are not systematically enriched. In order to explain this discrepant behaviour, we propose that the Faraoni Level was deposited during a period of anoxic conditions near the sediment–water interface. The distinctive peaks in U, V, Mo and As contents are traceable throughout the three studied sections and represent a good correlation tool which helps to identify the Faraoni Level and its equivalents in the western Tethyan realm and outside of the Tethys. For example, a peak in U contents in upper Hauterivian sediments of the northwestern Pacific realm (ODP leg 185, site 1149) may well be an expression of the Faraoni event in this particular basin.     

L'aspidolite fluorée : rôle des évaporites dans la genèse du rubis des marbres de Nangimali (Azad-Kashmir,Pakistan)

Ruby-bearing marbles from Nangimali, in the Azad-Kashmir, Pakistan, contain, besides phengite, different mica intergrowths: paragonite, phlogopite and aspidolite (sodium phlogopite). Both phlogopites, intimately linked and coexisting with paragonite, are fluorine rich, contrary to phengite and paragonite. F-enriched aspidolite is described for the first time. Phengite is either associated with phlogopite or could be isolated. The presence of aspidolite in the ruby-bearing marbles, together with other arguments such as salt solid inclusions and presence of anhydrite, suggest the implication of evaporites in the genesis of gem corundums. To cite this article: V. Garnier et al., C. R. Geoscience 336 (2004).     

Airborne microphysical measurements and radar reflectivity observations near a cold frontal rainband observed during the FRONTS 87 experiment

Airborne microphysical measurements and ground-based radar-reflectivity observations, collected at the near of a narrow cold frontal rainband during the FRONTS 87 experiment, are used to infer some characteristics of the precipitation: size-distribution, liquid or ice-water content, mass-weighted fallspeed, radar-reflectivity and relationships between pairs of these quantities. In the ice phase region, two different methods are proposed to calculate the radar reflectivity from the aircraft data. The influence of the choice of the ice particle type on the calculated quantities is discussed from the results of the first method. The second method is new: it is based upon the use of a roughness parameter estimated from the analysis of the two-dimensional particle images of ice precipitation. Although this method is tentative, it gives conclusive results for the two different flight levels studied here.     

Marble-hosted ruby deposits from Central and Southeast Asia: Towards a new genetic model

Marble-hosted ruby deposits represent the most important source of colored gemstones from Central and South East Asia. These deposits are located in the Himalayan mountain belt which developed during Tertiary collision of the Indian plate northward into the Eurasian plate. They are spatially related to granitoid intrusions and are contained in platform carbonates series that underwent high-grade metamorphism. All occurrences are located close to major tectonic features formed during Himalayan orogenesis, directly in suture zones in the Himalayas, or in shear zones that guided extrusion of the Indochina block after the collision in South East Asia. Ar–Ar dating of micas syngenetic with ruby and U–Pb dating of zircon included in ruby gives evidence that these deposits formed during Himalayan orogenesis, and the ages document the extensional tectonics that were active, from Afghanistan to Vietnam, between the Oligocene and the Pliocene.The petrography shows that ruby-bearing marbles formed in the amphibolite facies (T = 610 to 790 °C and P ~ 6 kbar). A fluid inclusion study defines the conditions of gem ruby formation during the retrograde metamorphic path (620 < T < 670 °C and 2.6 < P < 3.3 kbar) for the deposits of Jegdalek, Hunza and northern Vietnam.Whole rock analyses of non-ruby-bearing marbles indicate that they contain enough aluminum and chromiferous elements to produce all the ruby crystals that they contain. In addition, (C, O)-isotopic analyses of carbonates from the marbles lead to the conclusion that the marbles acted as a metamorphic closed fluid system that were not infiltrated by externally-derived fluids. The carbon isotopic composition of graphite in marbles reveals that it is of organic origin and that it exchanged C-isotopes with the carbonates during metamorphism. Moreover, the O-isotopic composition of ruby was buffered by metamorphic CO₂ released during devolatilisation of marble and the H-isotopic composition of mica is consistent with a metamorphic origin for water in equilibrium with the micas. The (C, O, H)-isotopic compositions of minerals associated with marble-hosted ruby are all in agreement with the hypothesis, drawn from the unusual chemistry of CO₂–H₂S–COS–S₈–AlO(OH)-bearing fluids contained in fluid inclusions, that gem ruby formed at P ~ 3 kbar and 620 < T < 670 °C, during thermal reduction of evaporite by organic matter, at high temperature-medium pressure metamorphism of platform carbonates during the Tertiary India–Asia collision. The carbonates were enriched in Al- and chromiferous-bearing detrital minerals, such as clay minerals that were deposited on the platform with the carbonates, and in organic matter. Ruby formed during the retrograde metamorphic path, mainly by destabilization of muscovite or spinel. The metamorphic fluid system was rich in CO₂ released from devolatilisation of carbonates, and in fluorine, chlorine and boron released by molten salts (NaCl, KCl, CaSO₄). Evaporites are key to explaining the formation of these deposits. Molten salts mobilized in situ Al and metal transition elements contained in marbles, leading to crystallization of ruby.