Abstract

The average direction of the remanent magnetization of the basalt layer at the bottom of hole EM 7 is inclined 36° above the horizontal, indicating that the layer is reversely magnetized. Detailed demagnetization experiments with alternating magnetic fields to 800 oersteds peak intensity indicate that the drilling operations did not remagnetize the basalts. The natural magnetization is extremely stable and is probably thermoremanent magnetization acquired as the basalt cooled through its Curie temperature, which is 355°C. The average intensity of the natural remanent magnetization is 0.0054 emu/cm3, and the intensity of the induced magnetization is less than 5 per cent that of the remanent. The ratio of remanent to induced magnetization, which is of importance in magnetic anomaly interpretations, decreases markedly with depth below the upper flow surface and emphasizes the danger of determining this ratio from material recovered only from the upper surfaces of submarine layers.