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, let the reconstruction of the climatic background over the last 10,000 years. The lowermost part (I) displays a rough paleosol-type sediment with plentiful plant particles and rootlets; pollen shows grassland plants. part II represents fine-grained lake sediments; pollen shows a savanna-like plants. 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 head, has a pollen spectrum of present-day crops (semideciduous forest). the several sediment sections exhibit 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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Additional 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)
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. 1). Accelerator mass spectrometer (AMS) radiocarbon dating from the upper and the lower segments of this zone gave ages of 9430 _+ 60 and 10,120 + 50 yr. , respectively. Similarly, Ybert et al. P. 4-m-long sediment core from Lake Dom Helvecio, situated ca. 30 km to the south.
This preservation procedure is indicated to avoid losses of dissolved metals due to their adsorption on suspended sediments, on precipitates and on the container walls (Fletcher, 1980). The possible effect of increasing apparent dissolved metal concentrations as a result of the increased acidity, could be estimated from the total suspended solids (5-20 rag/l) and the average Fe and Mn concentration in surface sediments - 10% and 600 lag/g, respectively. Considering an unlikely total metal extraction from suspended sediments during storage, even so the contribution from the suspended load to the measured concentration of dissolved Fe and Mn would not be higher than 20% and 15%, respectively.
Stratigraphy, zones palynological I to IVA data as described and grain in the text. 8 m. The sedimentary sequence consists of alternate thin layers (ca. 5 mm) of well stratified clayey and silty-sandy reddish sediments. Grain-size distribution points to the deposition of this unit during a period characterized by high transportation energy, as reflected by an increase in both the sandy fraction (average of 18%) and the 20-63 lam fraction (average of 42%). Seasonal fluctuations in the rainfall regime are likely to explain the formation of alternate clayey and silty-sandy thin layers.
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