By Saulo Rodrigues-Filho
Mineralogical-sedimentological and geochemical investigations together with pollen information of a 12.7-m-long dated sediment middle from Lake Silvana, SE Brazil, allow the reconstruction of the climatic background during 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 lower 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 accordance with 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)
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). A sharp decrease in Pb concentrations in zone IV, accompanied by slightly lower ones of Cr and Ti, is in accordance with the increasing abundance of authigenic materials relative to detrital sediments (Fig. 4). The same trend is demonstrated by elevated Fe and Mn concentrations (Fig. 5). In turn, the relatively constant values for Hg and Cu relative to the underlying unit point to the increasing mobility of both metals, probably as a result of organically mediated redox reactions (Figs.
1993) have observed that during lateritic weathering, pseudomorphic replacement of parent-rock silicates by kaolinite and AI and Fe oxides is systematically accompanied by dissolution voids in overlying parent minerals. , 1998; Tardy, 1992). The zone of alteration consists of coarse and fine saprolite, where the structure of the parent rock is roughly preserved. Fine saprolite is characterized by a complete or partial alteration of most of the primary minerals, while iron and aluminum remain almost immobile.
I ........... ~ ' " ~ .......... ' " ~ ............ r - - ~ ............ ~'"'"'~ ............. Lack of Pollen 9,430 10,1 +/. ~::~:ZLL~2:~:-I ,, 1270 .......................................... tm. , ~ '-" ! ~ - ~ i " I j . . . . 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%).