Figure F80. A. Thermal demagnetization of Sample 183-1137A-40R-4, 50-52 cm, from basement Unit 8. The NRM is a stable, single-component magnetization. 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 183-1137A-29R-4, 56-58 cm, from basement Unit 4. The unblocking temperatures are ~580° and ~300°C and indicate that both magnetite and titanomaghemite are the magnetic minerals. The NRM is a stable, single-component magnetization. J₀ is the magnetization intensity before thermal treatment.