By Saulo Rodrigues-Filho
Mineralogical-sedimentological and geochemical investigations together with pollen info of a 12.7-m-long dated sediment center from Lake Silvana, SE Brazil, enable the reconstruction of the climatic background during the last 10,000 years. The lowermost part (I) displays a rough paleosol-type sediment with plentiful plant particles and rootlets; pollen shows grassland crops. part II represents fine-grained lake sediments; pollen shows a savanna-like crops. part III represents a pollen-free, coarse-grained allogenic sediment deposited less 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). different sediment sections convey a reference to erosional stages 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)
93%. Samples of the <20 pm fraction are composed of kaolinite (60%), gibbsite (10%), goethite (I0%), siderite (8%), muscovite (5%) and quartz (5%). It is interesting to note the occurrence of siderite and gibbsite contrasting with zone I (Figs. 3). Trace element analyses of the <20 /am fraction gave elevated concentrations of Mn and Hg, and reduced Cr, Pb and Cu relative to zone I (Figs. 5). P. The finely laminated and well-sorted sediments also indicate an environment of lacustrine sedimentation.
1997). The pollen assemblage in zone IV gave a conspicuous increase in arboreal elements (up to 85%) that represent the present-day vegetation with widespread semideciduous forest (Fig. 5). This vegetation change indicates a transition to semihumid climate with a dry season of 4-5 months that occurred shortly before 8000 + 50 yr. P. according to AMS radiocarbon dating obtained from a wellpreserved leaf (Fig. 7). 7 Photograph of the core section (340 cm) showing a well-preserved, radiocarbon-dated leaf (core-section diameter = 4 cm).
The term laterite has a broad usage and includes bauxites, ferricretes, iron and aluminium duricrusts, mottled horizons, pisolite - or nodule - bearing materials 25 and is extended to the formations or horizons that are parts of red or yellow ferralitic soils, tropical ferruginous soils and other kaolinitic formations (Tardy, 1992). , 1979). Dissolution of soluble minerals and geochemical reactions within the pedologic mantle is mainly controlled by hydrolysis, which in turn is climate-dependent (Chesworth, 1992).
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) by Saulo Rodrigues-Filho