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

By Saulo Rodrigues-Filho

Mineralogical-sedimentological and geochemical investigations together with pollen info of a 12.7-m-long dated sediment middle from Lake Silvana, SE Brazil, allow the reconstruction of the climatic background over the last 10,000 years. The lowermost part (I) displays a rough paleosol-type sediment with considerable plant particles and rootlets; pollen exhibits grassland plants. part II represents fine-grained lake sediments; pollen shows 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 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, according to 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)

Sample text

High concentrations of Ti, Cr, Pb, Ni, Cu and Zn in the C1 and C2 horizons seem mainly influenced by the mineralogical composition of the parent rock. 20 ~tg/g) represents an increase to values 10 times higher than those observed in the saprolite. 83) exists between Hg and aqua-regia-soluble A1 in both weathering profiles (Fig. 17), while almost no correlation between Hg and Fe exists (Fig. 14). e 0 5 10 15 0 5 A! 17 Correlation between Hg and aqua-regia-soluble A1 in both weathering profiles and between aqua-regia-soluble A1 and AI (XRF) in lake sediments.

Grain-size distribution illustrates the general dominance of the <20 ~am fraction (75%) accompanied by smaller amounts of both the 20-63 lain fraction (18%) and the >63 lam fraction (7%). However, contrasting patterns were observed in some layers characterized by silty-sandy sediments, which are concentrated in the upper zone IV (Fig. 2). Between depths of 40 and 80 cm, the occurrence of sandy materials was grouped into zone IVA. 9%. Mineralogical composition reflects environmental changes towards lacustrine sedimentation and more reducing conditions.

C r (pglg) 100 0 Ti (%) 1200 ~ 17n ~ ~ 300 ~ = i ~ ~=- , 39o ; "== i ~ --- ~-- 420 ~' ~ ~ ~ P-"--' 480 ~. ~ ! , 550 ~" ~ ~ 1,5 ..... ~ , ~ ............ ~ ---J A oE~0 6T0 " " 700 ," J~ 740 ~' =,, m m m m i 77o; u ~800~ 830 b, 8~o ~ , i ~ i ~ ' ' m B i J 930 " 1140 i ' m m 1230 . . . . 4 Summary diagram of chemical stratigraphy and grain size >20 Hm. Paleoenvironmental zones I to IVA as described in the text'. ,. Pollen Diagram @ o,o,o,o,o,ooot°,),,o . . . 320 ~::z,m ~ : Fe(%) Mn (pg/g) Hg (pg/g) C(org) ,20pm(%) ,ooo "°ZTI~ 20 0 i "='=" 2200 0 i ~" 0,5 " L~TLml ' ..............

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