O QuaternÃrio do Parque Nacional Serra da Capivara, PiauÃ, Brasil: morfoestratigrafia, sedimentologia, geocronologia e paleoambientes

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

The Serra da Capivara National Park is internationally recognized because it houses the most important concentration of rock paintings and archeological sites in the American continent. Vestiges of human occupation are distributed in 1.000 archeological sites many times located in Quaternary sediments, with few researches realized until the moment. The objective of this dissertation is to present a morphostratigraphical, sedimentological and geochronological studies of the sedimentary deposits found in the National Park and of the neighboring municipalities (Brejo do PiauÃ, JoÃo Costa, Coronel Josà Dias and SÃo Raimundo Nonato) in the southeastern region of the state of Piauà (Brazil). The studies should aid on the understanding of the paleoenvironment and paleoclimate events which took place in this region during the Quarternary. The subject area is located in the border of the geological domains of the ParnaÃba Sedimentary Basin and of the Borborema Province (Riacho do Pontal belt). A 1:60,000 morphostructural map of the National Park was developed where three (03) units were identified and named Vale da Serra Branca, Reverso da cuesta and Patamares Estruturais. In the Vale da Serra Branca, the summit is 520m high and the valley is 400m, colluvial fans are generally found half way its extension and they are made of fine sands with intercalations of debris flows and fallen rock of the Serra Grande Group.The Reverso da cuesta has as a stratum the Itaim and Pimenteira geological formations, which has a flat morphology and heights varying from 520m to 600m. It is regularly covered by eluvial-colluvial holocene sands dated by luminescence. The Patamares Estruturais has as stratum the Itaim and Pimenteira geological formations and the Serra Grande Group, they show four levels in their south portion, they have quaternary sedimentation made by colluvial material which recover the last one third of the slope, made by sandy and gravelly. To the south part of the park, recovering the lower slope area of the serrotes, or the lapies and the caves of the Riacho do Pontal belt, it is possible to find quaternary colluvial deposits which are sandy, gravelly or muddy. In the same area of the Riacho do Pontal belt there are alluvial deposits of the Piauà river and its tributaries made by sands and gravels. The oldest of these, are a clayish deposit dating from 436.000  51.500 thousand years. They are sandy and gravelly bars and floodplains of the river in the territory belonging to SÃo Raimundo Nonato municipality. The most important quaternary sedimentation in the studied area is formed by colluvial fans and braided rivers alluvial deposits, what suggest a semi-arid climate. Taking into account seventeen (17) datings, it was possible to infer four (04) colluvial events, most likely associated to semi-arid climatic conditions and to torrential rains: event number one, the oldest, between 135.000  16.400 and 117.000  14.500 years; event number two, between 84.000  13.400 and 76.200  9.350 years; event number three between 36.000  4.900 and 21.770  3.610, and the last event between 15.800  1.900 and 11.500  1.730 years. Considering fourteen (14) alluvial datings is possible to suggest at least three (03) fluvial events: the oldest event between 133.000  16.500 and 92.050  11.200 years; the second event between 54.000  6.300 and 22.250 Â3.590 years and the last event between 15.600  1.900 and 7.600  940 years. Almost all colluviations process events coincide chronologically with the alluviations. The sedimentary record of environmental changes from the Middle Holocene comes from a core from the lake Lagoa Grande in the Brejo do Piauà area where palynologic analyses demonstrated that several oscillations in tree and bush concentrations have been occurring since 5,130 years b.p. and such suggests that the Caatinga experienced since the Middle Holocene until the Present by moments wetter and drier than the current climate

ASSUNTO(S)

morfoestratigrafia piauà quaternary serra da capivara serra da capivara sedimentology geociencias morphostratigraphy geocronologia quaternÃrio piauà sedimentologia geochronology

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