2015-02-272015-02-272013-03-06RABELO, Cleber Eduardo Neri. Paleoambiente da formação mosquito e a implantação do sistema desértico úmido da formação corda, jurássico superior, Centro-Oeste da Bacia do Parnaíba. 2013. 79 f. Dissertação (Mestrado) - Universidade Federal do Pará, Instituto de Geociências, Belém, 2013. Programa de Pós-Graduação em Geologia e Geoquímica.https://repositorio.ufpa.br/handle/2011/6359The Mesozoic was marked by significant geological changes, resulting of the Gondwana Orogeny uplifts, which propitiated the implantations of desertic systems concomitantly with expressive magmatic events. In the Parnaíba Basin, northeastern Brazil, these events are recorded in the Triassic Sambaiba Formation, and the Jurassic units, represented by basaltic flows, subordinated fluvial and eolian sandstones of Mosquito Formation and by fluvioaeolian deposits of Corda Formation. Outcrop- and core-based stratigraphic and facies analysis carried out in the Formosa da Serra Negra and Montes Altos regions, State of Maranhão, allowed the paleoenvironmental reconstitution of the Upper Mosquito and Corda formations. Additionally, we infer paleoclimate conditions for the westen-central portion of the Parnaíba Basin during the Jurassic. Were identified twenty sedimentary facies were grouped into five facies associations (FA) representing a volcanic plain deposits with sporadic fluvial and eolian sandstones (FA1- Mosquito Formation), succeeded by the installation of a wet desert system (AF2-AF5; Corda Formation). The volcanic plain (FA1) consists of basaltic flows interbedded with fine to coarse-grained sandstones (intertrap sandstones) composed of subangular to rounded grains of quartz, feldspars and volcanic glass fragments. The sandstones exhibit even parallel and low-angle cross stratifications, filling channel geometry or in tabular beds. Braided channel deposits (FA2) consist of polymictic conglomerates, with subrounded to angular pebbles and granules of basalt, and sandstone with massive bedding and trough cross-bedding. The sandy sheets (FA3) were divided into two architectural elements (AE), the first (AE1) is composed by thin and coarse grained sandstone whit adhesion lamination, adhesion warts, wind and water ripples marks, small-scale gutter cast and load cast structures. The dune field (FA4) is characterized by fine to medium-grained sandstone, with rounded grains, displaying small to medium-scale planar and tangential cross stratification of small to medium size, even parallel and cross laminations, even parallel stratification and subcritically climbing translatent strata. Fine to medium sandstone, moderately selected, beds with rip-up clast, curled mud flakes, flaser bedding and locally massive bedding, are organized in centimetric shallowing upward cycles. In the upper portion of cycles occur iron oxide/hydroxide mottled horizon, bioturbações, root marks and mud cracks interpreted as wet interdune deposits. Suspension lobes deposites (FA5) consist of fine grained sandstones and massive mudstones forming complex cross stratification with low angle and even parallel lamination, wavy and flaser beddings. Kaolinite and iron oxide hydroxide are abundant in FA1 and FA2, and characterize the subaqueous environments, while the abundance of smectite in paleosoils of FA4 indicates semi-arid climate. In the Jurassic, the central western region the Parnaíba Basin, was affected by extensional tectonics with recurrent eruptions of basic lava flow along of fissures system. During the intervals without magmatic activity, sediments supplied of ephemeral rivers were distributed in sheet flow or filled depressions on the volcanic plain. The end of magmatic event was succeeded by implantation of the Corda desert formed by dune field and ephemeral fluvial channels (wadi) that reworked partly the volcanic plain deposits and sandy sheet setting. The Jurassic desent of Corda Formation was wetter and smaller than to the Perm-Triassic ergs (Sambaíba Formation), preceding the extensive and warmer and coastal systems in the Cretaceous of the Parnaíba Basin.porAcesso AbertoGeologia estratigráfica - JurássicoSistema disértico úmidoFormação CordaFormação MosquitoArenitos intertrapBacia Hidrográfica do Rio ParnaíbaRegião Nordeste - BrasilDissertaçãoCNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIA::ESTRATIGRAFIA