Estratigrafia de sequências do grupo Cuiabá, faixa Paraguai Norte, Mato Grosso

Abstract

The Cuiabá Group represents a sedimentary deposited in a marginal basin installed in a passive limit SE of the Amazonian Craton during the Cryogenian/Neoproterozoic III, in low-grade metamorphosed and intensely deformed during Orogenic Cycle Brasiliano-Pan-African (<630mA), called in Zona Tectônica Interna da Faixa Paraguai. In the northern portion of Paraguai Belt, in Mato Grosso State the Cuiabá Group has about 4,000m of terrigenous deposits, with litte vulcanoclástic/chemical/organic contribuition and stratigraphic architeture was infuenced by the interplay of tectonic and climatic factors which put facies striking features in nature its stacking: (i) distensional tectonic during the breack-up of the Rodínia (<900 Ma), enabling the formation of tectonics lakes which accumulated great thicknesses of carbonaceous pelites, sandstones and lens of limestone (Campina de Pedra Formation), covered in conformity with sandstones, polymictic conglomerates and pelites (lower Acorizal Formation/Pindaival Member), (ii) glacial advance, documented by the interbedded of tilites, polymictic conglomerates, sandstones, pelites and thin layers of BIFs (Camadas de Transição/Acorizal Formation). The top of the succession marks the climax of the maximum advanced glacial in a basin, represented by thick horizon of diamictite (tillite) purplish gray in Acorizal/Jangada (Engenho Member), and sandy-pelitic rhythmites with dropstones, pelites, conglomerates and diamictites in the District of Cangas/Poconé in S-SW of the área (Cangas Member). (iii) glacio-isostatic uplift, responsible for reworking deposits previously accumulated in the margin of the basin and progradation of thick sedimentary prism (Coxipó Formation) consisting of subaqueous outwash fans forming metric finning-upward cycles of the quartz conglomerates, quartz sandstones and pelites (Pai Joaquim Member), covered by diamictites, pelites, sandstones, quartzites and limestone lenses (Marzagão and Guia Members and Mata-Mata Unit). From the stratigraphy sequences perspective the Cuiabá Group can be interpreted how a 1st order supersequence, with Climax of Rift (TSCR), Fill Rift (TSPR), Low-Stand (TSMB),Transgressive (TST) and High Stand (TSMA) Systems Tract. The basal and middle portion of Cuiabá Group (Campina de Pedra and Pindaival Member), were deposited in continental environment (lakes), with the influence of tectonics and the beginning of glaciation, corresponding to TSCR and TSPR. The Engenho Member represents the TSMB and Coxipó Formation corresponds to TST (Pai Joaquim Member) and TSMA (Marzagão, Guia Formations and Mata-Mata Unit), linked with deglaciation and glacio-isostatic rebound accumulation in marine sedimentary environments.