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Lateritic formation kaolinites dating on the Rio Negro Basin: importance on the geomorphological evolution of central Amazonia - Brazil


Although widely studied, little is known about the ages of lateritic formations. The study of its genesis and evolution has as limitation the difficulty of dating, since such formations are always devoid of geocronômetros. The Amazon basin lateritic formations are no exception to this rule. The ages proposed for these mantles result from inferences as there are no techniques for precise and absolute dating of soils and alterites. The lateritic formations are good examples, since they cannot be satisfactorily dated considering the succession of climates. This scientific problem is the core of the project that is now presented and that will be developed in the central Amazon basin. The project brings a unique method of dating: the dating of lateritic profiles based on irradiation defects that accumulate in kaolinite. This method requires field studies, mineralogical analyses, and also specifically spectroscopic analyses and of artificial irradiation. In order to check the dating of the kaolinite, we propose also the study of sedimentary formations, themselves containing kaolinite and dating by cosmogenic isotopes. Simultaneously, the isotope ratio analyzes will be conducted to characterize paleoenvironments (transitions from forest vegetation on lateritic soils, to open vegetation formations - campinarana, caatinga amazônica and campina - on podzols and hydromorphic soil of Içá Formation. The isotopic fractioning will be held also in sediments containing remains of leaves, seeds and stem fragments in sedimentary layer supposedly of Içá Formation. Such analyzes will add elements to the discussion on paleoclimates. (AU)

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