EVIDENCE FOR RADON TRANSPORT BY CARRIER GAS THROUGH FAULTED CLAYS IN ITALY

Extensive soil-gas surveys in sedimentary basins in Italy were perform ed to study the potential of some naturally occurring gases as indicat ors for concealed fracture zones, hydrocarbon and geothermal fluids. O ne conclusive result is a positive correlation between anomalously hig h values of radon and carbon dioxide in the soil-air over faults. The correlation coefficient for 1173 gas samples is 0.41. Statistically de rived contourlines of Rn and CO2 anomalies show similar locations, sha pes and directions. Fairly good Rn-CO2 coupling evidence appears even on a point-to-point analysis. Furthermore, it was recognized that the highest Rn values are in contrast to the low Ra content of the underly ing clayey rocks and that conventional Ru transportation mechanisms se em to be inadequate for the clay sequences. All these facts strongly s uggest that Rn is transported from the subsoil, through fault-linked p athways, by carrier gases of which CO2 could be one of the major compo nents. The theory of geogas microbubbles is a possible explanation of the observed results. The carrier effect of ascending microbubbles can explain both the origin of soil-gas Rn anomaly and the Rn-CO2 couplin g phenomenon.