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 heritage during the last 10,000 years. The lowermost part (I) displays a rough paleosol-type sediment with considerable plant particles and rootlets; pollen shows 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 head, has a pollen spectrum of present-day crops (semideciduous forest). the several sediment sections exhibit a reference to erosional stages within the catchment of the lake, according to mineralogy and geochemistry, that are a reaction to weather improvement.
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Additional 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)
1 Coring platform - core SB 1. 5 meters could be sampled. Sampling points within the weathering profile, which may reach a thickness of 30 meters, were selected according to changes in macroscopic features, such as color, texture and pedological and lithological structure. Water samples were collected at various depths above the core site SB 1 through a small pump and stored in polyethylene bottles. Three samples from selected 28 depths - surface, intermediate and bottom waters - were acidified with HNO 3 to pH 1 for determination of dissolved Fe and Mn, after filtering through cellulose membrane with pore size of ca.
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 ' .............. ~ l Cerrado Shrubs and Trees (%) , ~ Herbs (%) ............ ,i aTropic. Shrubs ! ',i and Trees (%) ! ~,,', ........... t:: , = ............ ~ = . ==. 7. ,=. z::~J ~. M,~ ....... ~= ................................... - - ............... i ........... ~ ' " ~ .......... ' " ~ ............ r - - ~ ............ ~'"'"'~ ............. Lack of Pollen 9,430 10,1 +/. ~::~:ZLL~2:~:-I ,, 1270 ..........................................
Ferricretes, or iron crusts, seem to be better preserved under seasonally contrasted tropical climates with a long dry season, as in humid regions they tend to break down (Nahon, 1986; Tardy and Roquin, 1992). Seasonally contrasted tropical climates are thought to be associated with the formation of iron crusts because alternating reducing and oxidizing conditions are required to allow successive small-scale redistribution of iron by leaching (Boulet, 1978 in Nahon, 1986). The formation of thick iron crusts may require more than 1 Ma, and certainly requires less than 6 Ma, depending on the nature of the parent rock, the intensity of climatic changes, the tectonic evolution, and other factors (Nahon, 1986).
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