Reconstrução da paisagem pantaneira da região de Poconé durante o Holoceno

Abstract

The Quaternary is a period well-known for its climatic oscilations. In Brazil, sediments from the Pantanal Basin harbour archives of such paleoenvironments. This basin is located in midwestern Brazil, at the headwaters of the Paraguay River and has and area of 150,500 km2. It is filled with unconsolidated sediments of the Pantanal Formation with a maximum inferrred thickness of 550 meters. The basin’s origin is related to the Andean orogeny and interplate dynamic processes that took place during the upper Tertiary. The objective of this study is to present the palaeoenvironmental evolution of the Pantanal during the Holocene by means of palynology, geochemistry and geochronology. A sediment core was drilled in Poconé-Mato Grosso, north of Pantanal basin, geographical coordinates. 17°19'33.76"S and 56°48'2.99", reaching 10.20 m deep. Organic carbon is irregularly preserved in the studied core, with values ranging widely. Sediments are essentially silicose with alumnium replacement toward the top, in agreement with the fining upwards section. Anomalies of iron oxide suggest subaerial exposure or mobilization in a reducing environment. The carbon-sulfur ratio indicates an oxic environment throughout the section, thus anoxic conditions are not related to water column depth. Age of the studied core is between 13,420 and 13,555 cal. B.P. The sandy base has a predominance of C3 plants, the palynoflora is essentially arboreal in the dated portion of the profile, in agreement with a Cerradão physiognomy. The last 3,995 years cal. B.P. are characterized by na increase in base level, high abundance of aquatic plants, and isotopic fractionation indicating CAM plants, what suggests the occurrence of arid periods. However, the last 1,400 years B.P. are dominated by herbaceous, with subordinate arbroeal elements untill presente day.