Abstract
Previous geophysical investigations of the São Paulo plateau off southern Brazil have revealed that a large field of diapiric structures underlies the plateau. In April 1974, detailed geologic and geophysical surveys were conducted on two of these diapirs to determine whether the diapirs are composed of salt as previously speculated. Closely spaced multigrad measurements across the diapirs showed progressive increases in thermal gradient from the flanks to the centers. Values at the diapir centers were up to four times the regional thermal gradient measured for the plateau. Piston cores on the diapirs recovered sedimentary rocks as old as middle Eocene. Abnormally high salinities of 40 to 50 parts per thousand were measured in the interstitial waters of the Eocene sediments and indicate an underlying high concentration of salt. These data provide direct evidence that at least some of the diapiric structures beneath the SSo Paulo plateau are composed of salt.
