Abstract
Absolute dating methods have been used in chronological studies of geological processes and sedimentary units of Quaternary age in Central Amazonia, Brazil. Although radiocarbon dating has been very useful in archaeological research and soil studies, the temporal interval of this method is inefficient in evaluating the sedimentation aspects and geological events from the beginning of the Quaternary in the Amazon basin. The use of crystal luminescence dating has been one of the most promising tool for determining the absolute dating of Quaternary deposits in the Amazonian region. Optically stimulated luminescence (OSL) dating, following the MAR and SAR protocols, in a tectonic-sedimentary study of Quaternary fluvial deposits in the confluence area of the Negro and Solimões rivers, indicated ages from 1.3 (Holocene) to about 67.4 kyears (Late Pleistocene) for these sediments. Low radioactive isotope concentrations were found about 2ppm for 235U and 238U; 5ppm for 232Th; and the 40K concentrations were almost zero. A comparison was made between MAR and SAR protocols taking into account the fluvial depositional process.
Highlights
The stratigraphy of Cretaceous and Cenozoic deposits in the Amazon basin has not yet been completely established due to the lack of geochronological dating
The use of radiocarbon dating for Amazonian fluvial deposits is still limited (Latrubesse and Franzinelli 1998, 2002, Rossetti et al 2005), and many records remain poorly understood
In the Optically stimulated luminescence (OSL) method, concentrations of radioactive material, which surround the periphery of the grains, are considered to remain constant over the time
Summary
The stratigraphy of Cretaceous and Cenozoic deposits in the Amazon basin has not yet been completely established due to the lack of geochronological dating. The lack of sedimentary and stratigraphic studies has avoided the means by which to adequately analyze inter and intra-basin correlations among Quaternary deposits These deposits are relatively thick, reaching tens of meters, and have become homogenized due to weathering. The use of radiocarbon dating for Amazonian fluvial deposits is still limited (Latrubesse and Franzinelli 1998, 2002, Rossetti et al 2005), and many records remain poorly understood. In part, this is due to a lack of organic material, especially in reference to the older alluvial deposits, which have been intensely weathered. TATUMI and CLAUDIO RICCOMINI the radiocarbon dating method, which is inefficient for records older than 40,000 years
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