Abstract

Seventy-live samples from the Freda sandstone (1050 Ma old) have been drilled from the same slab in order to investigate the best method of sample preparation and to optimize procedures for chemical demagnetization of red sandstones, Expanding on the chemical demagnetization procedures used by Park, several variables have been tested. These include: multicoring or slotting of samples to permit access of the acid, temperature and normality of the acid, zero-magnetic field during leaching, and vacuum conditions before leaching steps. Through proper sample preparation and leaching procedures, it is possible to separate the solubility spectra and associate the components of magnetization with particular magnetic carriers.Visual inspection of cores sectioned during progressive chemical demagnetization has allowed the comparison of the solubility spectra to the blocking temperature spectra of thermal demagnetizations. This comparison has linked the coarser-grained specularite to the highest blocking temperatures, and the fine-grained hematilic cement to intermediate blocking temperatures. There exists a component of magnetization which appears to be insoluble lo the leaching process. It has been shown to be carried by detrital titanomagnetite. Through the combined use of chemical, thermal, and alternating field demagnetization a magnetic history involving deposition. lithilication. and later overprinting has been unraveled from this slab of Freda.

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