Activities of gamma emitting members of the uranium ( 238 U) and thorium ( 232 Th) series were measured in quaternary limestone deposits that outcrop in the southeastern Pantanal Mato-grossense basin and in quaternary tufas deposited at the drainage of the Serra da Bodoquena. Gamma activities were also measured in the Xaraiés Limestone that outcrop mainly at the foothill of the Urucum Massif, near the city of Corumbá (MS), Central Brazil. The results obtained show that all these samples are characterized by very low concentrations of uranium and thorium. In the Xaraiés Limestone the uranium and thorium series are in secular radioactive equilibrium up to 226 Ra. On the other hand, the 238 U/ 226 Ra is significantly different than one in most of the analyzed samples from the Serra da Bodoquena and Pantanal do Miranda. In these cases, 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 Limestones has radiocarbon ages of about 4,000 y BP. Since the thorium series is in disequilibrium, it is also concluded that this deposits behave as open systems for geochemical exchanges. The 210 Pb activity in excess to the 226 Ra activity and the 228 Ra/ 226 Ra activity ratios show little variation in almost all analyzed samples. The 210 Pb activity excess reflects the high permeability of the samples which allows an equilibrium between rock and surface waters, whereas the 228 Ra/ 226 Ra indicates that these deposits incorporate very small amounts of thorium series bearing detritic material.
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