J.M. Flexor

Hauts niveaux marins pléistocènes du littoral brésilien

Abstract The high sea-level, corresponding to the last Pleistocene interglacial stade, left the most important records represented by extensive beach-ridge plains along the central and southern coasts of Brazil. During the maximum level, which was dated at 123,000 yr B.P. by coral samples, the relative sea-level was situated 8 ± 2 m above present level. Four generations of Quaternary marine sandy deposits have been described in southern Brazil (State of Rio Grande do Sul), where they are known as Barrier I, II, III and IV. The Barrier IV, about 4 m high, corresponds to the last great transgressive-regressive phase, whose maximum occurred about 5100 yr B.P. The Barrier III, with a height of about 8–10 m, corresponds to the penultimate transgressive-regressive period, whose maximum was produced about 123,000 yr B.P. The Barrier II, about 13–15 m high, and the Barrier I, about 20–25 m high, situated at inner positions in relation to the previous ones, have been formed during high sea-levels older than 123,000 years. Along the coastal plains of the States of Sergipe and Bahia, the high sea-level older than 123,000 years is represented only by one phase through cliffs carved within the Barreiras Formation. On the other side, along the coastalp plains of Sao Paulo, Parana and Santa Catarina, there are marine terraces with a minimum height of 13 m above present sea-level, which are certainly older than the Barrier III, and are probably recording the transgressive-regressive period of the Barrier II (middle Pleistocene?).

Vibrotestemunhador leve: construção, utilização e potencialidades

Undisturbed or minimally disturbed cores are very hardly obtainable from soft sedimentary deposits, mostly of Quatemary age. On the other hand, details of primary structures must be preserved making possible to reconstruct, as perfect as possible, their sedimentary environments. A very light and cheap vibracorer, suitably used for coring clayey-sandy organic sediments, like bay-bottom, lacustrine or lagoonal deposits, is here described.

Uranium and thorium series disequilibrium in quaternary carbonate deposits from the Serra da Bodoquena and Pantanal do Miranda, Mato Grosso do Sul State, central Brazil

Activities of gamma-ray emitting members of the uranium (238U) and thorium (232Th) series were measured in a quaternary limestone deposit that outcrops in the southeastern Pantanal Matogrossense Basin and in quaternary tufas deposited at the drainage of the Serra da Bodoquena. It is a first step in a study of the mobilization of uranium and thorium series and its relation to surface hydrology, in a region where carbonate deposits are being continuously dissolved and reprecipitated. The obtained results show that all these deposits are characterized by very low concentrations of uranium and thorium. The 238U/226Ra and 228Th/228Ra activity ratios are significantly different than 1.0, indicating that both series are in radioactive disequilibrium. Although the Serra da Bodoquena deposits seem to be very recent, their very fine granulation and high porosity suggest that they behave as open systems for geochemical exchanges of uranium and thorium series members. The Pantanal do Miranda limestone has a radiocarbon age of 3900 yr BP. Since the thorium series is in disequilibrium it is also concluded that this deposit behaves as an open system for geochemical exchanges.