Figure F78. A. Thermal demagnetization of Sample 183-1138A-81R-5, 27-29 cm, from basement Unit 7. The NRM is stable and has a single component. Most unblocking temperatures are above 500°C. The decay curve gives no indication of a second magnetic phase. The magnetic mineral is most likely magnetite, which has a Curie temperature of 580°C. B. Thermal demagnetization of Sample 183-1138A-79R-4, 115-117 cm, from basement Unit 3. Unblocking temperatures are ~580°and ~300°C, indicating that both magnetite and titanomaghemite are the magnetic minerals. The NRM is stable and has a single component. J₀ is the magnetization intensity before thermal treatment.