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All figures (15)
Fig. 12 (a–c) Results of RE analyses, HI—Hydrogen Index given in mg HC per g TOC, OI—Oxygen Index given in mg CO2 per g TOC, R400—Pyrolysis products <400°C issued from Flame Ionisation Detection (FID) given as percentage of total pyrolysis products <650°C
Fig. 4 (a–d) Unsupported 210Pb and (e–h) 137Cs profiles of sediment cores recovered in LGM from various water depths along the transect shown in Fig. 1 b, and of a sediment core from the centre of LPM. All activity data are given per dry substance and related to 1 September 1994. Insert diagram of (a) showing the semi-logarithmic plot of unsupported 210Pb (mBq/g) versus data for cumulative dry mass (mcum in g/cm2), mcum was calculated on
Fig. 3 (a–j) Selected water profiles demonstrating chemical stratification of LGM for two sampling dates in summer 1994. Data for surface water and deep-water composition of LPM are given inside the diagrams for comparison. Sulphate increase and Fe decrease between 22 August and 18 September 1994 document subsurface inflow of oxygen-bearing groundwater into LGM, slight Na and Cl increase in the surface water of LGM documents concentration increase due to evaporation. Increase of the Dissolved Salt Content (DSC) in the deep water is mainly contributed by DIC, Ca and NH4. There are no indications for incomplete seasonal mixing of the LGM water body
Fig. 13 FID heating curves of selected LGM sediments from various water depths, sediment depths and TOC contents of individual 3-cm samples are given inside the diagrams
Fig. 8 Sulphur in LGM and LPM sediments. (a) Normative sulphide-bound Fe in percent of Fetotal; pyrite as the only sulphide phase and absence of organic-bound sulphur is considered for the estimate. (b, c) Analytical determined elemental sulphur in percent of Stotal for LGM and LPM sediments. (d) Excess Fe in LPM sediments balanced for an assumed Fe/Al mass ratio of 0.75 for the siliciclastic debris. Littoral sediments of the modern LGM show slightly higher Stotal contents than the sediments from the lake centre (Fig. 5n), documenting overall higher H2S production in the shallow water area of LGM. Pore water dissolved H2S is fixed in the sediments mainly by reaction with reactive Fe or oxidation to elemental sulphur. The above mass balance estimates show that the sedimentary Fe inventory is most claimed in shallow water sediments of LGM. Pyrite genesis in the shallow water sediments is favoured by distinct seasonal change between oxic and anoxic conditions in the surface sediments. In LGM sediments from the 23 m sampling site and in sediments of the meromictic LPM a high proportion of elemental sulphur was detected in the freeze-dried samples. The real elemental sulphur contents may be overestimated due to oxidation of S2− to elemental sulphur during freeze-drying and sample handling
Fig. 7 Geochemical sediment profiles from the centre of LPM and from LGM cores. (a, b) Profiles, showing coincidence between Fetotal and Stotal peaks in the sediment cores 4 m and 6 m from the shallow water area. (c) Fe/Mn fractionation in LPM and LGM. In the steeply inclining sector of the LGM basin, Fe is distinctly enriched versus Mn by precipitation of Fe-oxihydroxides. The dissolved Fe concentrations in the monimolimnion of LPM exceeded 100 mg/l in 1995 (Chiodini et al. 1997); dissolved Fe is precipitated as FeS; formation of Fe(Mn,Ca)carbonates is prevented by pH-lowering associated with high CO2 concentrations in the deep water of the lake. (d, e) Ptotal and TOC/P profiles of LGM sediments document that the burial rate of P in the sediments from the lake centre is higher than that of littoral sediments
Fig. 9 (a–d) In situ pore water profiles of Ca, DIC, Sr, Ca/Sr of LGM sediments from various water depths at 1 cm resolution, sampling sites shown in Fig. 1b. Dialysis chambers were exposed between 23 August and 18 September 1994. Please note that each second data point is shown only for data presentation. Pore water profiles from the 12 m sampling site are exceptional. Relative enhanced post-depositional cation release from siliciclastic sediment components is mainly associated with differing diagenetic conditions in the steeply inclining sector of the LGM basin
Fig. 2 (a, b) Thermal stratification of LGM and Lago Piccolo di Monticchio (LPM) in summer 1994. (c–i) Selected water profiles of LGM for two sampling dates in 1994. Data for surface and deep water composition of LPM are given inside the diagrams for comparison; unique symbols for individual sampling dates are used throughout; data for deep water composition in LPM after Cioni et al. (2006) and references therein. Lowered Ca and Ca/Sr values in the surface water of LGM reflect the deposition of low-Sr autochthonous calcite. DIC was considered as HCO3 for the calculation of anion sums, distinct anion excess, particularly for 22 August, reflects high CO2 concentrations in the deep water of LGM. High Sr contents are typical for local springs
Table 1 Unsupported 210Pb data and derived 210Pb ages
Table 2 Mineral composition silt LGM 6 m, siliciclastic fraction
Fig. 10 (a–d) In situ pore water profiles of algae nutrients and SO4 for LGM sediments from various water depths. Note that SO4 pore water concentrations below 1.5 mg/l are not consumed, or possibly regenerated in the equilibrium with hauyne
Fig. 6 (a–c) Concentration of selected major and minor elements in deeper sections of the 8 m core versus their average concentration values in the upper 10.5 cm sediment; minor depletion or enrichment is recorded for Fe and Mn and trace elements that form oxy-anions that can be scavenged by Fe-oxidhydroxides; depletion shows systematic increase from light to heavy REEs. Trace elements marked by * and REEs were measured by ICPMS (Analyst: M. Zimmer, GFZ-Potsdam)
Fig. 1 (a) Location of Laghi di Monticchio. (b) Bathymetry of the maar lakes, map of Lago Grande di Monticchio showing sampling sites for short cores (○) and in situ pore water profiles (×); locations of piston core records (B, D, J, H, M, O, L) investigated in previous studies are marked inside. (c) Geological map re-drawn after Giannandrea et al. (2004) showing faults, the crater rim of the Monticchio unit and local springs (SA, S4, S5, S6) analyzed by Barbieri and Morotti (2003)
Fig. 11 (a1/2–f1/2) In situ pore water profiles of cations in LGM sediments from various water depths. Enhanced cation concentrations in the interstitial water of the steeply inclining sector of the LGM basin indicate high cation release by chemical alteration, which is also implied by the geochemical signatures of sediments from the 8 m site. The highest Fe concentrations are obtained in the pore water from 32 m; formation of authigenic Feminerals is inhibited by enhanced CO2 contents and SO4 depletion in the anoxic deep water of LGM
Fig. 5 Selected geochemical sediment profiles of sediment cores from LGM and LPM, respectively, sampling sites are shown in Fig. 1 b. Individual data points represent the middle of continuously sampled 3 cm sediment sections. (a, b) Compilation of TOC/N and TOC profiles demonstrating decreasing contributions of nonplanktonic organic matter towards the centre of the lake basin and overall higher contributions by terrestrial organic material for LPM sediments. (c–e) Profiles demonstrating decrease in net-accumulation of low-Sr autochthonous CaCO3 from the littoral to the profundal zone in LGM. (f) Estimate of the allochthonous
Journal Article
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DOI
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Laghi di Monticchio (Southern Italy, Region Basilicata): genesis of sediments—a geochemical study
[...]
Georg Schettler
,
Patrick Albéric
1
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Institutions (1)
University of Orléans
1
01 Jul 2008
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Journal of Paleolimnology