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ESTRATIGRAFIA E EVOLUÇÃO PALEOGEOGRÁFICA DO GRUPO SANTA BÁRBARA (EDIACARANO) NA SUB-BACIA CAMAQUÃ OCIDENTAL, RIO GRANDE DO SUL, BRASIL

2006; Sociedade Brasileira de Geologia; Volume: 36; Issue: 3 Linguagem: Inglês

10.5327/rbg.v36i3.1244

2317-4889

Gélson Luís Fambrini, Renato Paes de Almeida, Antônio Romalino Santos Fragoso-Cesar,

Paleontology and Stratigraphy of Fossils

In the south and southeastern Brazil and in the south of Uruguay post-Brasiliano Cycle sedimentary and volcanogenic deposits of the Ediacaran-Early Paleozoic occur. In the state of Rio Grande do Sul the best exposures of these rock covers crop out and were related to the Camaqua Supergroup. The supergroup, with a thickness of over 8,000m, is formed by the following units, from base to top: (i) siliciclastic Marica Group; (ii) volcano-sedimentary Bom Jardim Group; (iii) volcanic Acampamento Velho Formation; (iv) siliciclastic Santa Barbara Group; (v) siliciclastic Guaritas Group; and (vi) Rodeio Velho intrusive suite. The Santa Barbara Group occur in three sub-basins NNE-SSW oriented, named Western, Central and Eastern Camaqua respectively and separated by the Cacapava do Sul and Serra das Encantadas basement highs. This work aims to play a paleogeographic evolution of the Western Camaqua Sub-Basin. The sedimentary units of the Western Camaqua Sub-Basin comprise, at the base, conglomerates and sandstones with subordinate siltstones and fine-grained sandstones of the Estância Santa Fe Formation. These deposits are interpreted to be alluvial fans dominated by sheet-floods processes, and channel deposits in braided rivers. Above these rhythmites in the arroio Seival and arroio Santa Barbara valleys occur, composing a progradational succession to shallow water tabular sandstones, with evidence of tide action, named Seival Formation. This unit is covered by braided rivers sandstones and subordinate conglomerates of the Serra dos Lanceiros Formation. The fluvial succession is interrupted by succession of lagoonal rhythmites and fine-sandstones with evidence of tide action comprising the Arroio Umbu Formation. Lagoonal siltstones and sandstones were overlaid by delta-front fine-to-medium sandstones representing the progradation of estuarine delta. Over the lagoonal deposits new progradation of fluvial sandstones followed by alluvial fans conglomerates occur, comprising the Pedra do Segredo Formation. Important event of reorganization is registered in the Pedra do Segredo Formation through the uplift of the Cacapava do Sul High. The contribution of detritus by the basement high of the Cacapava do Sul and the presence of alluvial fans suggest that tectonic isolation of the Western Camaqua Sub-Basin occurred only at late stages of evolution of the group, by the progradation of alluvial facies over the lagoonal and estuarine environments.