New PDF release: A Holocene Sedimentary Record from Lake Silvana, Se Brazil:

By Saulo Rodrigues-Filho

ISBN-10: 3540662057

ISBN-13: 9783540662051

Mineralogical-sedimentological and geochemical investigations together with pollen info of a 12.7-m-long dated sediment center from Lake Silvana, SE Brazil, let the reconstruction of the climatic historical past during the last 10,000 years. The lowermost part (I) displays a rough paleosol-type sediment with considerable plant particles and rootlets; pollen exhibits grassland crops. 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 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, according 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)

Sample text

The mechanism of dismantling is thought to be related to the rehydration of hematite and kaolinite resulting in the formation of goethite and gibbsite at the top of the profiles (Nahon, 1986; Tardy, 1992). Bioclimatic changes may lead to significant transformations of pedologic systems. Transformation of original sequences is expressed by disorganization of upper horizons that are exposed to such changes. Nahon (1991 and references therein), based on studies of pedologic mantles in Senegal, have suggested that under drier climatic conditions, microaggregates of about 100 gm in diameter composed of kaolinite and iron oxyhydroxides undergo a process of segregation corresponding to a structural disorganization without major mineralogical changes.

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%).

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. 7%) and by the mineralogical composition of the <20 tam fraction, which gave as major constituents kaolinite (63%), gibbsite (15%), detrital goethite (10%), muscovite (5%) and less siderite (5%).

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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


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