Palinofácies e evolução quaternária do ribeirão da Mata, município de Vespasiano, MG, Brasil

Abstract

PALYNOFACIES OF PRETA LAKE QUATERNARY SEDIMENTARY SEQUENCE, STATE PARK OF DOCE RIVER, MG, BRAZIL. This paper presents the results of a palynofacies study from a quaternary core of Preta Lake State Park of Doce River (PERD), MG, Brazil. Preta Lake is situated in the Doce River's Middle Valley lake complex, which consists of around 160 lakes. According to previous studies, the origin of the lake complex is linked mainly to local neotectonics, which can be divided into two phases. The first stage is characterized by E-W dextral transcurrent movements and occurred from the end of the Pleistocene. The second stage of tectonic movements occurred during the Middle Holocene and is characterized by NW-SE extensional regime, which was responsible for the generation of fault-block activity that promoted unevenness and tipping in beds of the tributary channels, acting as dams and thus creating the lakes. The analysis of palynofacies was carried out on 30 samples of a core of 200 cm, dated at the base at 6,620 ± 110 years BP. The core shows a sedimentary sequence that consists of three facies of clay varying in color: light gray clay at the base, dark gray clay and brown clay toward the top. From the characterization of the particulate organic matter components and the correlation between changes in their percentage, a palynofacies was identified with a predominance of amorphous organic matter-AOM (70-95%), fungal spores and opaque phytoclasts as subordinate elements. The palynofacies analysis allows us to conclude that: the sedimentary sequence of Preta Lake was deposited in anoxic-desoxic conditions, consistent with a shallow lake, deposited in a lake or paludal environment, due to large amount of AOM and substantial lack of algae and that Preta Lake has likely been in a filling process since 6,620 ± 110 years BP.