Download A Holocene Sedimentary Record from Lake Silvana, Se Brazil: by Saulo Rodrigues-Filho PDF

By Saulo Rodrigues-Filho

Mineralogical-sedimentological and geochemical investigations together with pollen facts of a 12.7-m-long dated sediment center from Lake Silvana, SE Brazil, enable the reconstruction of the climatic heritage over the last 10,000 years. The lowermost part (I) displays a rough paleosol-type sediment with ample plant particles and rootlets; pollen shows grassland plants. part II represents fine-grained lake sediments; pollen exhibits a savanna-like crops. part III represents a pollen-free, coarse-grained allogenic sediment deposited less than excessive transportation strength (increased precipitation). part IV, a greenish series with expanding C content material in the direction of the pinnacle, has a pollen spectrum of present-day crops (semideciduous forest). the various sediment sections exhibit a reference to erosional stages within the catchment of the lake, in keeping with mineralogy and geochemistry, that are a reaction to weather improvement.

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Extra resources for A Holocene Sedimentary Record from Lake Silvana, Se Brazil: Evidence for Paleoclimatic Changes from Mineral, Trace-Metal, and Pollen Data (Lecture Notes in Earth Sciences)

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5 32 73,5 113 EG 1/Co11. 2 . 15 8 26 14 35 75 EG1/ColI. 4 o - ┬░ . -- not measured A light increase in Fe, Ti and Cr concentrations were also observed in the colluvial unit relative to the B horizon. , 1979). Both the weathering degree and the composition of the parent rock are controlling the metal distribution within the weathering profile EG2, with the possible exception of Hg. The increase in gibbsite contents at the surface, in this case accompanied by elevated Hg concentrations, is a typical 55 picture of highly leached soils.

Plant fragments were separated from any sand, silt, or other foreign matter. Samples were then treated with hot diluted HC1 to remove any carbonates. After washing and drying, the cleaned charcoal was combusted and the carbon dioxide was recovered for analysis (Geochron report GX-23912). Granulometric distribution within the core was obtained by wet sieving, comprising the following grain size fractions: <20 ~m, 20-63 lam and >63 lam. Nylon sieves and distilled-deionizated water were used to avoid contamination.

Hg is also released to the atmosphere through anthropogenic emissions, among which gold mining and deforestation seem to be the most relevant in the Brazilian Amazon. Estimates of the Hg 57 emissions derived from gold mining in this region point to 200,000 to 260,000 tonnes Hg since the beginning of the European colonization (Malta, 1998; Lacerda, 1997). , 1994). As tropical ferralitic soils are thought to be as old as - 5 Ma. (Nahon, 1986; McFarlane, 1983), the long-term deposition of atmospheric Hg in soils rich in Fe and A1 hydroxides is likely to explain the widespread Hg accumulation in surficial ferralitic soils rather than a weatheringdriven accumulation process from the parent rock.

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