By Saulo Rodrigues-Filho
Mineralogical-sedimentological and geochemical investigations together with pollen info of a 12.7-m-long dated sediment center from Lake Silvana, SE Brazil, enable the reconstruction of the climatic historical past over the last 10,000 years. The lowermost part (I) displays a rough paleosol-type sediment with plentiful plant particles and rootlets; pollen exhibits grassland crops. part II represents fine-grained lake sediments; pollen shows a savanna-like crops. 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 plants (semideciduous forest). different sediment sections express 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 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)
Petrographically, the occurrence of Fe oxyhydroxides and poorly ordered kaolinite as pseudomorphs after biotite could be observed. The ordering degree of kaolinite was determined through X-ray diffractograms, which clearly show two different patterns for poorly and well ordered kaolinite (Fig. 15). The strong displacement of the b-axis in poorly ordered kaolinite appears related to the water activity, as its occurrence is restricted to the surface horizon (colluvial unit) and to the C2 horizon, located near the groundwater table.
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). This author indicated that all these factors being considered, it is likely that most of the ferricrete profiles in West Africa began to form at the end of the Tertiary. Similarly, McFarlane (1983) estimates a period required for the formation of lateritic profiles of 1-10 Ma.
Hermann Behling from the Center for Tropical Marine Ecology, Bremen, Germany. Samples of t cm 3 were taken at 20 cm intervals (in the lower core section intervals are shorter) along the profile. Samples were prepared using the standard treatment with sodium pyrophosphate and heavy liquid separation by bromoform (Faegri and Iversen, 1989). Pollen preparation included addition of exotic Lycopodium spores to determine the 31 pollen concentration (grains/cm3). Most of the samples were counted up to a minimum of 300 grains, excluding aquatic pollen and spores.
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