1967, Phys. Earth Planet. Interiors 1, 35—43. North-Holland Publishing Company, Amsterdam PALAEOMAGNETLC STABILITY RESULTS OF A RECONNAISSANCE SURVEY OF RED SANDSTONES IN MOROCCO D. H. TARLING and D. H. SUTTON Department of Geophysics & Planetary Physics, The School of Physics, The University of Newcastle upon Tyne, England Received May 1967 Evidence on the stability of remanence is examined in 50 sites in data are too few for full interpretations in terms of polar wan- red sandstones and 2 sites in basaltic lavas ranging in age from dering or tectonic movements, but it is found that the majority PreCambrian to Quaternary. It is concluded that the stability is of sites are normally magnetized and of low inclination of re- variable although the tests often yield contradictory results. The manence. 1. Introduction (48 and 13) were in basaltic lava. Three separate cores were drilled, in the laboratory, from each hand sample Palaeomagnetic studies in Morocco are likely to be yielding nine specimens per site. The remanence direc- extremely fruitful in view of the tectonic history of this tion and intensity were measured with astatic magneto- part of Africa, and rocks which are usually suitable for meters (BLACKETT, 1952; COLLINSON et a!., 1957) and palaeomagnetic studies, red sandstones and lavas, the susceptibility was measured with a susceptibility occur through most of the geological column ranging bridge (C0LLINs0N et al., 1963). from PreCambrian to Recent. The area is currently of interest from the relationship of northwest Africa to The stability of remanence was determined for one Europe (e.g. MELVILLE, 1966), the possible extension pilot specimen, chosen at random for each site, by of the West African fold belt through Morocco (e.g. heating it in air in a non-magnetic furnace to succes- SOUGY, 1962) and possibly into North America as the sively incremented temperatures (IRvING eta!., 1961a); Appalachians, and in terms of the detailed behaviour the susceptibility, and the direction or intensity of tectonic blocks during the formation of mountain remanent magnetization being determined after each chains — Morocco having been subjected to at least increment. The pilot specimens from the two basaltic three major orogenic phases. sites were tested in incremented alternating magnetic In order to test the suitability of the red sandstones fields up to 750 (peak) oersteds (IRVING et a!., 1961b). for subsequent detailed palaeomagnetic research, a The stability index [SI = max (range+/circular standard reconnaissance survey was carried out in 1964 with the deviation) for three or more successibe observations of assistance of the Service de Ia Carte Géologique du the remanent vector between the maximum and mini- Maroc. This survey was designed to look at the sta- mum values (range) of temperature or field] was de- bility of red sandstones in Morocco over as great a termined for each pilot specimen (TARLING and range of time and area as possible; the results of this SYMONS, 1967). survey were, therefore, not intended to answer any of One specimen from each of the other two untouched the problems outlined above, but to determine if rele- samples per site were then heated to 300—335 °C vant information could be obtained at a future date. (yielding three heated specimens per site) in order to remove the less thermally stable components of natural 2. Methods and techniques remanence in the sandstones. The specimens from the Three oriented hand samples were obtained at each basaltic sites were all subjected to a peak field of of 50 sites (fig. 1) which were mostly in road cuttings either 169 or 225 oersteds in order to reduce the effect through cross-bedded red sandstones. Two other sites of low coercivity components. 35