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ARGILOMINERAIS DO PALEOLAGO TREMEMBÉ E SISTEMAS DEPOSICIONAIS RELACIONADOS (PALEÓGENO, RIFT CONTINENTAL DO SUDESTE DO BRASIL)

1996; Sociedade Brasileira de Geologia; Volume: 26; Issue: 3 Linguagem: Inglês

10.25249/0375-7536.1996167180

2177-4382

Cláudio Riccomini, Armando Márcio Coimbra, Lucy Gomes Sant’Anna, Max Brandt Neto, José Vicente Valarelli,

Paleontology and Stratigraphy of Fossils

BRAZIL) Study of the clay mineral content of Oligocene lacustrine sediments of the Tremembé Formation and laterally correlative deposits of a marginal system of distal alluvial fans of the Resende Formation has furnished important indicators of paleoenvironmental and paleoclimatic conditions during the génesis of these minerais within the context of the Paleogene evolution of the Continental Rift of Southeastern Brazil.X-ray diffraction and scanning electron microscopy revealed clay minerais of the smectite and kaolinite groups and, to a much lesser extent, members of the mica and chlorite groups.Detrital clay minerais in the Tremembé and Resende Formations are mainly represented by smectites, generated under generally arid conditions probably during the Eocene.Ancient soils developed upon Precambrian basement rocks acted as remarkable source-areas for the smectites, although the conditions for their genesis are still unresolved.Eodiagenetic halloysite in deltaic sandstones of the Tremembé Formation was derived by decomposition of feldspar and is indicative of pluvial seasonality during sedimentation.Worm-like kaolinite was formed during a later diagenetic stage, without the influence of the depositional environment.The presence of kaolinite in the meandering fluvial system of the São Paulo Formation suggests a significam climatic change to humid conditions during the Late Oligocene.It appears, therefore, that the paleoclimatic and paleoenvironmental changes inferred from the clay mineralogy of the sediments studied here are in general accord with the pattern of global changes for the Paleogene as deduced from other geological and paleoceanographic evidence.