Environmental Reconstruction of the South-Western Part of the Maracujá River Basin, Brazil, Based on Palynological and Sedimentological Analysis and Carbonaceous-Layer Radiocarbon Dating
We used sedimentological, palynological, and stratigraphic analysis, as well as absolute dating of a carbonaceous layer, to characterize Quaternary sediments deposited in the south-western part of the Maracujá River Basin located in the Quadrilátero Ferrífero geological province (Minas Gerais state, Brazil). Based on the sedimentology at an outcrop section, we defined four facies and nine subfacies that depict energy pulse variations, reflecting distinct palaeoenvironmental conditions and transitions. Palynological assemblages through the section verify inferred climate changes. Radiocarbon dating of samples from the lowest, middle, and highest stratigraphic layers revealed ages of 4730 ± 40 yr BP, 12730 ± 50 yr BP, and 16260 ± 70 yr BP, respectively. The geochronological data reveal that older layers lie above younger layers, showing a reversed temporal sequence in the area. This was a result of the sediments having developed in a flood plain environment; subsequent gully-erosion processes in the region left a sequence of alluvial terrace deposits on the peripheries of the flood plains.
KeywordsDating climate changes Stratigraphic reversal Quaternary Brazil
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