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Föllmi, Karl B.
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Föllmi, Karl B.
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- PublicationAccès libreThe transfer of Cadmium from rock to soil and the associated vegetation cover under natural conditions at the Swiss Jura Moutains(2010)
; ; ; Baize, DenisAs a result of soil-surveying studies conducted in the Swiss and French Jura Mountains during the early 1990's, anomalous cadmium (Cd) concentrations were identified in soils developed mostly on Bajocian and Oxfordian limestone. Measured Cd concentrations exceed in most of the cases the Swiss official tolerance guideline concentration for non-polluted soils established at 0.8 mg⋅kg-1. Several research works have confirmed the geogenic origin of Cd in soils derived mainly from the weathering of a Cd-rich carbonate substrata. Cd is a highly toxic trace element and the pedogenic / physicochemical conditions leading to its transfer from rocks to soils and its potential bioavailability to plants are in need of a detailed geochemical assessment. The aim of the present work is to complete the geochemical database by studying rock-soil-plant interactions with regard to this element under natural conditions in two specific sites. A first study of rock-soil interaction was carried out determining Cd-bearing phases in a soil developed on top of a road-cut section outcropping at the SW-facing slope of the Schleifenberg hill (canton Basel-Land, Switzerland). This section consisting of an oblique succession of Bajocian oolitic carbonate includes several horizons which are anomalously enriched in Cd (0.03–4.90 mg⋅kg-1). Cd contents in this soil are in the 0.3–2.0 mg⋅kg-1 range. Vertical pedogenetic processes (weathering of underlying bedrock) as well as lateral colluvial limestone (weathering of uphill carbonates) are responsible for the origin of Cd in the soil. Half of the Cd still resides in the carbonate fraction, while the Cd released from the weathered carbonates is associated either with organic matter (over 10%) or with Fe and Mn-oxyhydroxides (approximately 30%). Adsorption of a low percentage of Cd on clays is of less importance since Pb, Zn, Cu and Cr ions will compete with Cd to gain adsorbed sites on clays. No exchangeable Cd phase was found and this, together with the buffer capacity of this calcareous soil, suggests that the amount of mobile Cd is quite negligible, which also greatly reduce the amount of bioavailable Cd. Where developed on steep slopes, the soil will hardly accumulate and colluviums will constantly renew it. A second study regarding the transfer and distribution of geogenic Cd in the soil was conducted on six closely spaced soil profiles at the site called Le Gurnigel (canton Neuchâtel, Switzerland). The soils consist mainly of cambisols and cambic-neoluvisols showing an important allochthonous, aeolian fraction. Cd concentrations generally increase down the soil profiles, showing maxima (up to 16.3 mg⋅kg-1) near the soil-bedrock interface. Most Cd resides in the carbonate and organic fractions in topsoils, whereas the amorphous oxyhydroxides fraction becomes the most important Cd-bearing phase in the middle and in subsoils. Cd, Zn and Cr are positively correlated with comparable distributions in the soil profiles suggesting a common bearing phase such as Fe oxyhydroxides for these three elements. A complex transfer pattern of Cd starts with the release of Cd from the underlying bedrock, and then transferred into oxide, hydroxide, carbonate and organic phases. Additionally, the lateral advection of Cd-rich soils formed on steep slopes acts as a local allochthonous input of Cd to these soils, which in turn is transferred from the topsoil towards the deeper horizons by biological and pedogenic processes. The amount of readily exchangeable and therefore potentially bioavailable Cd is low in these soils (on average 0.2 mg⋅kg-1) provided that the pH remains above 5. Under stronger acidic and oxidizing conditions, Cd bound to organic matter may be mobilised and the bioavailability of Cd would range between 3.3–5.4 mg⋅kg-1 in cambisols and reach up to 1.7 mg⋅kg-1 in deeper cambic-neoluvisols. Soil-plant interactions were studied at the Le Gurnigel analyzing six local plants chosen for their ubiquity in the studied soil profiles. Cadmium accumulation was separately determined in roots and shoots. Three herbs, two graminoids and a tree were used for this purpose. They showed that the accumulation of Cd varies from one species to another and even between plants from the same family. Global levels of Cd in the selected vegetation are in the 2–6 mg·kg-1 range, thus exceeding the official limit value of Cd concentration tolerated in vegetal food for animals established at 1 mg·kg-1. The different behaviours were compared as a function of the variability of Cd in soils. A rise in the concentration of Cd in the soil progressively reduces the transport of Cd toward the shoots reducing also the yield production and increasing the accumulation of Cd in roots. Transfer coefficients from soil / rhizosphere to plant are inversely proportional to the total Cd concentration in soils and do not depend on species identity but instead on soil type. Sequential chemical extractions revealed that variations of Cd distribution between distant soil and rhzosperic soil occur mainly in the first three Cdbearing phases due principally to the incorporation of roots exudates that modify pH and redox conditions of the rizhosphere. High levels of Cd (up to 9 mg·kg-1) were found in shoots of three of the studied plants and may represent a mid-term hazard for animals and human health since these plants are used either for grazing of cattle or for medical purposes. The phenomenon of natural enrichment of soils with geogenic Cd and its progressive accumulation in vegetation covers is suspected to have a widespread occurrence elsewhere, as a function of frequent outcrops of Cd-enriched carbonates of Bajocian and Oxfordian age in western and southern Europe principally in France, Spain and Italy. - PublicationAccès libre
- PublicationAccès librePlatform-induced clay-mineral fractionation along a northern Tethyan basin-platform transect: implications for the interpretation of Early Cretaceous climate change (Late Hauterivian-Early Aptian)(2008)
; High-resolution clay-mineral analyses were performed on upper Hauterivian to lower Aptian sediments along a platform-to-basin transect through the northern Tethyan margin from the Neuchâtel area (Switzerland), to the Vocontian Trough (France) in order to investigate links between climate change, carbonate platform evolution, and fractionation patterns in clay minerals during their transport.
During the Hauterivian, the northern Tethyan carbonate platform developed in a heterozoan mode, and the associated ramp-like topography facilitated the export of detrital material into the adjacent basin, where clay-mineral assemblages are dominated by smectite and kaolinite is almost absent, thereby suggesting dry-seasonal conditions. During the Late Hauterivian Balearites balearis ammonite zone, a change to a more humid climate is documented by the appearance of kaolinite, which reaches up to 30% of the clay fraction in sediments in the Vocontian Trough. This prominent change just preceded the Faraoni Oceanic Anoxic Event and the onset of the demise of the Helvetic Carbonate Platform, which lasted to the late early Barremian.
From the Late Barremian onwards, the renewed growth of the northern Tethyan carbonate platform in a photozoan mode and the associated development of a marginally confined platform topography fractionated the clay-mineral assemblages exported into hemipelagic settings: kaolinite particles were preferentially retained in proximal, platform settings, due to their size and their relatively high specific weight. In the inner platform environment preserved in the Swiss Jura, an average of 32% of kaolinite in the clay fraction is observed during the latest Barremian–earliest Aptian, whereas clay-mineral assemblages of coeval sediments from deeper depositional settings are dominated by smectite and show only minor amounts of kaolinite.
This signifies that besides palaeoclimate conditions, the morphology and ecology of the carbonate platform had a significant effect on the distribution and composition of clay assemblages during the Late Hauterivian–Early Aptian along the northern Tethyan margin. - PublicationAccès libreDemise of the northern Tethyan Urgonian carbonate platform and subsequent transition towards pelagic conditions: The sedimentary record of the Col de la Plaine Morte area, central Switzerland(2008)
; Gainon, FrançoisThe sedimentary succession of the Col de la Plaine Morte area (Helvetic Alps, central Switzerland) documents the disappearance of the northern Tethyan Urgonian platform in unprecedented detail and suggests stepwise platform demise, with each drowning phase documented by erosion and phosphogenesis. The first identified drowning phase terminated Urgonian carbonate production in a predominantly photozoan mode. Using a correlation of the whole-rock δ13C record with the well-dated record from SE France, its age is inferred to as Middle Early Aptian (near the boundary between the weissi and deshayesi zones). A subsequent drowning phase is dated by ammonites and by a correlation of the whole-rock δ13C record as Late Early Aptian (late deshayesi to early furcata zone). A third drowning phase provides an ammonite-based age of Early Late Aptian (subnodosocostatum and melchioris zones) and is part of a widely recognized phase of sediment condensation and phosphogenesis, which is dated as latest Early to Middle Late Aptian (late furcata zone to near the boundary of the melchioris and nolani zones). The fourth and final drowning phase started in the latest Aptian (jacobi zone) as is also indicated by ammonite findings at the Col de la Plaine Morte. The phases of renewed platform-carbonate production intervening between the drowning phases were all in a heterozoan mode.
During the ultimate drowning phase, phosphogenesis continued until the Early Middle Albian, whereas condensation processes lasted until the Middle Turonian. Coverage of the external margin of the drowned Urgonian platform by a drape of pelagic carbonates started only in the Late Turonian. During the Santonian, the external part of the drowned platform underwent normal faulting and saw the re-exposure of already lithified Urgonian carbonates at the seafloor.
Based on the here-inferred ages, the first drowning phase just precedes oceanic anoxic episode 1a (OAE 1a or “selli event”) in time, and the second drowning phase partly overlaps with OAE 1a. The onset of the third drowning event slightly predates two further periods of increased organic-matter accumulation in the Vocontian Basin (Noir and Fallot levels), and the onset of the fourth and final drowning phase may coincide with two further periods of increased organic-matter accumulation in the Vocontian Basin (Jacob and Kilian levels, part of OAE 1b). These correlations indicate a relationship between the so-called anoxic episodes and the stepwise demise of the Urgonian platform, even if the onset of environmental change is registered earlier on the platform than in basinal sediments. - PublicationAccès libreCarbon cycle perturbation and stabilization in the wake of the Triassic-Jurassic boundary mass-extinction event(2008)
; Quan, T. M.The Triassic-Jurassic boundary mass-extinction event (T-J; 199.6 Ma) is associated with major perturbations in the carbon cycle recorded in stable carbon isotopes. Two rapid negative isotope excursions in bulk organic carbon (δ 13Corg) occur within the immediate boundary interval at multiple locations and have been linked to the outgassing of 12C-enriched CO2 from the Central Atlantic Magmatic Province. In British Columbia, a positive δ 13Corg excursion of +5‰ (Vienna Peedee belemnite (V-PDB)) spans part or all of the subsequent Hettangian stage. Here, we examine the significance of these carbon isotope excursions as records of global carbon cycle dynamics across the T-J boundary and test the link between carbon cycle perturbation-stabilization and biotic extinction-recovery patterns. A combination of δ 13Corg and palynological analyses from the Late Triassic to Early Jurassic in the Mingolsheim core (Germany) suggests that organic carbon isotope variations are best explained as the result of both compositional changes in terrestrial versus marine input and disturbance and recovery patterns of major terrestrial plant groups across the T-J boundary. A new high-resolution δ 13Ccarb record from the Val Adrara section in the Southern Alps (Italy) spanning from the uppermost Rhaetian through Lower Sinemurian does not exhibit a negative excursion at the T-J boundary but does record a large positive δ 13Ccarb excursion of +4‰ (V-PDB) in bulk carbonate that begins at the T-J boundary and reaches a local maximum at the Early Late Hettangian boundary. Values then gradually decrease reaching +0.5‰ at the Hettangian-Sinemurian boundary and remain relatively constant into the Early Sinemurian. Complementary δ 13Ccarb data from 4 more sections that span the Hettangian-Sinemurian boundary support carbon cycle stabilization within the Upper Hettangian. Our analyses suggest that isotope changes in organic carbon reservoirs do not necessarily require a shift in the global exogenic carbon reservoir and that the positive excursion in the carbonate carbon isotope record is best explained as the combined result of an increase in atmospheric pCO2 leading to accelerated carbon cycling, decreased skeletal carbonate production, and increased organic carbon burial lasting several hundred thousand years. The termination of the positive inorganic carbon isotope excursion coincides with the recovery of marine skeletal carbonate producers and coeval changes in terrestrial vegetation and reflects the gradual reduction in pCO2 and the stabilization of the global carbon cycle during the Sinemurian. - PublicationAccès libreOrganic carbon deposition and phosphorus accumulation during Oceanic Anoxic Event 2 in Tarfaya, Morocco(2008)
; ; - PublicationAccès libreThe Early Aptian Grünten Member : Description of a new lithostratigraphic unit of the helvetic Garschella Formation(2007)
- PublicationAccès libreThe Cenomanian/Turonian anoxic event at the Bonarelli Level in Italy and Spain: enhanced productivity and/or better preservation?(2007)
; ; - PublicationAccès libreEnrichment of redox-sensitive trace metals (U, V, Mo, As) associated with the late Hauterivian Faraoni oceanic anoxic event(2007)
; - PublicationAccès librePhosphorus and the roles of productivity and nutrient recycling during oceanic anoxic event 2(2007)
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