The first data on helium isotopy in a transitional clay layer at the cretaceous-paleogene boundary (Gams, Eastern Alps)

The paper presents preliminary results derived from the study of He isotopy in a transitional clay bed at the critical 65-Ma boundary in the Gams area (Eastern Alps). The ratio 3 He/ 4 He is shown to decrease from bottom to top of the transitional layer, and the difference between its values in the lower-and uppermost sublayers of the layer exceeds by more than ten times the measurement uncertainty (5%). The ratio 3 He/ 4 He is smallest in the upper part of the section, where all features of an impact event (spherules of pure nickel, diamonds, and awaruite) are established. The general inference of our study is that 3 He enrichment in the lower part of the Gams section is related not to cosmic matter but to a change in the conditions in the source area, most likely, to volcanic activity. The effect of the latter has been established, independent of He isotopic studies, from anomalous concentrations of As, Pb, Cu, and Zn and from the presence of particles of gold, copper, and titanomagnetite similar in composition to its basaltic varieties.