Figure F39. A. Thermal demagnetization of Sample 183-1136A-16R-2, 116-118 cm, from basement Unit 1. 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 183-1136A-18R-5, 132-134 cm. Most unblocking temperatures are below 300°C. This indicates (titano)maghemite as the magnetic mineral. The increase of normalized susceptibility at 300°C indicates a change of minerals, probably from (titano)maghemite to magnetite. (Titano)maghemite results from low-temperature oxidation of basalt. C. Thermal demagnetization of Sample 183-1136A-17R-1, 22-24 cm. The constantly decreasing intensity of magnetization at all temperatures indicates both magnetite and titanomaghemite as the magnetic minerals. The NRM is a stable, single-component magnetization. Gradually increasing susceptibility after 300°C indicates a change from titanomaghemite to magnetite. J₀ is the magnetization intensity before thermal treatment.