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Parque Estadual Turistico do Alto Ribeira (PETAR) is located in the South‐western part of Sao Paulo State, in the Ribeira Valley. In this national state park a large number of caves are found, which are among the most visited of the country. These caves, located in a karstic zone, are characterized by the presence of carbonaceous rocks frequently fractured and collapsed. Although, carbonates (dolomites and calcitic rocks) usually have low U content, this element can be found in the structure of the surrounding rocks. This paper aims to determine 238U, 234U, 226Ra and 210Pb concentration in samples of rock, soil, river water and sediment, in Santana cave. The radionuclide 238U was determined by alpha spectrometry using a surface barrier detector. 226Ra and 210Pb were determined by measuring the gross alpha and beta activity on a gas flow proportional counter.

This paper presents a model for the dolomitization of carbonates in which the principal diagenetic processes in pore fluid flow. The results show that regional diagenesis can result from the slow movement of pore fluids and that the geometry and structure of the initial rock mass plays a critical role in the location and relative intensity of the alteration. (AIP)