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 historical past over the last 10,000 years. The lowermost part (I) displays a rough paleosol-type sediment with ample plant particles and rootlets; pollen exhibits grassland crops. part II represents fine-grained lake sediments; pollen exhibits a savanna-like crops. part III represents a pollen-free, coarse-grained allogenic sediment deposited lower than excessive transportation power (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 plants (semideciduous forest). the several sediment sections express a reference to erosional levels within the catchment of the lake, in response to mineralogy and geochemistry, that are a reaction to weather improvement.
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Extra info 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)
I L I ) i -----" i 114o ~ : i ~ ~ i 1230 ~ 1260 ~ ; ~ I ! l~>63pm .................. 2 Summary diagram of mineral stratigraphy, distribution. Paleoenvironmental organic carbon and grain size zones I to IVA as described in the text. 3 Summary diagram of mineral stratigraphy and grain size distribution. Paleoenvironmental zones I to IVA as described in the text. e, ,~0"" 0 ~r~ns,z, C(org) (,/,) >20pm(%) 15 0 ° ~ - P b (pg/g) 1000 i ~ Cu (pg/g) 100 0 ~i ~ .
XRD analyses in the <20 ~m fraction of samples collected at regular core intervals revealed a dominance of poorly crystallized kaolinite, followed by goethite, muscovite and quartz. Varying contents of gibbsite and siderite occur since the transition from zone I to zone II. 1 Paleoenvironmental zone I (1270-1180 cm) The lowermost section of core SB1 differs from the overlying sections firstly in presenting no laminated structure, besides the occurence of abundant plant rootlets and carbonized plant debris (Fig.
It is interesting to note the relatively high Hg concentrations and gibbsite contents associated with very low Pb and Cr concentrations. Very similar features have been observed in the Amazonian lowlands, where ochre-coloured clays with different amounts of sand occur in the uppermost horizon above Precambrian shields and Palaeozoic sediments Orion, 1984). The ochre horizon is widely distributed over the Amazonian lowlands and contains poorly ordered kaolinite, in contrast to lower horizons, corroded quartz, gibbsite and goethite and exhibits a relative enrichment of Cr and Ti.