2019-11-072019-11-072013-04-08CUNHA, Lucas Noronha. Origem dos níveis de brechas da Formação Guia, Tangará da Serra, MT. Orientador: Joelson Lima Soares. 2013. 108 f. Trabalho de Curso (Bacharelado em Geologia) - Faculdade de Geologia, Instituto de Geociências, Universidade Federal do Pará, Belém, 2013. Disponível em: https://bdm.ufpa.br/jspui/handle/prefix/2422. Acesso em:.https://bdm.ufpa.br/jspui/handle/prefix/2422The Guia Formation (Araras Group) is constituted of thin bituminous limestone, shales and calcareous breccias, locally dolomitized which register deepwater environments, oversaturated with CaCO3. The base of this unit composes the carbonate cover related to the last Cryogenian glacial event (635 my) in Brazil. Breccia levels are commonly found on the limestones of the Guia Formation at the region of Tangará da Serra, state of Mato Grosso. Carbonate breccias are generally complicated regarding the interpretation of the generating processes. Tectonic events, gravity flows and subaerial exposure are the main breccia forming processes in carbonate rocks. To unveil the origin of the breccia levels in the study area is one of the main goals of this work. Petrographic and geochemical studies (SEM and X-Ray diffration) are some of the methods used to determine the diagenetic and/or depositional conditions that formed the breccias. In this work was done the description of the depositional composition (clasts and matrix) and diagenetic (cements and replacement) of two levels of breccias, and the interpretation of the processes that generated them. The first level was described next to the contact between the formations Mirassol d'Oeste (thin dolomites) and Guia, it consists of a carbonate breccia with open framework, forming discrete zones up to 3m thick, presents clasts of different lythotypes such as dolomites, limestones and sandstones. The clasts are angular, poorly selected and present themselves in a chaotic way with no preferential orientation. The matrix is composed of solid microcrystalline calcite in the red color. In this breccia level are also described: fibrous carbonate cement, dissolution features such as vug poros, iron-manganese concretions, gastropod shells and speleothems. The second level described is located in the central position of the Guia Formation and consists of intraformational carbonate breccias with open and closed frameworks up to 4m thick, their clasts correspond to argilite and limestone fragments belonging to the Guia Formation. The clasts are predominantly angular, poorly selected, rectangular and tabular, generally arranged in a chaotic way, nevertheless in the basal portion, next to the enclosing rock, the clasts present a parallel to the contact arrangement and tend to concentrate in larger abundance in the lower part of the level. The matrix is solid, red-colored and composed predominantly of calcite, present thick calcite crystals with features of baroque dolomite and calcite druses and undolomitized baroque dolomite. Locally, the breccia also shows carbonate cement composed of spatic calcite crystals and dolomite rombs among the clasts. The first level is interpreted as the result of karst processes associated with tectonic uplift movements. The presence of discrete deposits containing speleothems, iron-manganese concretions and dissolution pores inside within the layers of the carbonate rocks are commonly interpreted as features of subaerial exposure. The presence of unfossilized gastropod shells suggests that the cave formation processes occurred in the Holocene. The second level is interpreted as athe filling of neptunian dikes formed from fracturing and dilatation of limestones of the Guia Formation generated by seismicity. The occurrence of magnesian calcite cement suggests cementation in seawater while the presence of romboedric dolomite is probably a product of the substitution of the micritic matrix and the spatic calcite. Baroque dolomites indicate that the hydrothermal fluids affected the breccias during mesodiagenesis. Undolomitization processes can be associated to telodiagenesis conditions. These breccias that fill neptunian dikes are associated to a zone of folding and faulting between zones without deformation. Features that indicate subaerial exposure were not identified, therefore the formation of breccias in this level is probably associated to tectonic processes such as seismic events in buried environments.Acesso AbertoNeoproterozóicoFormação GuiaBrechas CarbonáticasCavernasDiques NeptunianosCNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIA::PETROLOGIATrabalho de Curso - Graduação - Monografia