PALINOFÁCIES E EVOLUÇÃO QUATERNÁRIA DO RIBEIRÃO DA MATA, MUNICÍPIO DE VESPASIANO, MG, BRASIL

PALYNOFACIES AND QUATERNARY EVOLUTION OF RIBEIRAO DA MATA, VESPASIANO CITY, MG, BRAZIL. This study presents two palynofacies associated with floodplains of Ribeirao da Mata, a river in the northwest of the municipality of Vespasiano, Minas Gerais State, southearstern Brazil. In these fluvial deposits, ten profiles designated as P1 to P10, as well as C 14 dating, were determined. The C 14 method yielded ages between 7,258 and 4,956 years BP for the thicker deposits of the floodplains. The profiles exhibited the following sedimentary sequence. At the base, coarse sand was found with small cross bedding, indicating deposition in fluvial channels. This facies is overlain by packages of clay containing silt and fine sand, parallel laminations representing deposits in floodplains. Toward the top, there are coarser sediments characterizing paleochannels often with indication of paleocurrents in different directions. The youngest topmost facies is a package of silt and fine sand with ferruginous concretions related to a more recent fluvial system. The identification of the organic components yielded two palynofacies, designated here as A and B, that indicate different subenvironments within the floodplain. The samples RM-04 and RM-06 of palynofacies A revealed 60% amorphous organic material (AOM), about 20% opaque biostructured phytoclasts and less than 10% non-opaque phytoclasts characterizing areas of deeper water, whereas desoxic-anoxic pertain to the shallow floodplains. This palynofacies represents at profile P6 the sediments deposited between 7,258 and 5,529 years BP. In contrast the samples RM-01, RM-02 and RM- 05 revealed opaque biostructured phytoclasts (36-50%) and AOM, and/or non-opaque phytoclasts, besides fungal spores. Palynofacies B in profile P5 represents a depositional environment of areas bordering a floodplain and indicates an age of 5,529 years BP for the deposits in this floodplain.