A palaeomagnetic investigation of a Permian redbed sequence from a mining drill core

Abstract

Summary Samples spanning 66 m of Permian redbeds were collected from a vertical, but azimuthally unoriented, drill core obtained during a uranium exploration programme in the Lodeve Basin of southern France. Inclinations are well grouped (?= - 6.5°, k= 121.5) and consistent with the known Permian palaeolatitude of Europe. Declinations have been estimated by using a sedimentological model involving tectonically-rotated cross-bed laminations. The results are very encouraging and suggest a pole at 151°E, 53°N (δp= 1°, δm = 2°, N= 43), which agrees well with the Eurasian apparent polar wander curve. The small polar discrepancy could well be due to secular variation, which is consistent with the small variance and presumed short time spanned by the sequence. Fully oriented surface samples confirm these findings, and support the validity of the orientation model. Temporal variations revealed by the stratigraphic ordering can be interpreted as slow dipole wobble, on a time-scale of 105 yr or more, on which is superimposed a more rapid nondipole secular variation. It appears that the core stores of the world could become - at least under favourable circumstances - an important source of palaeomagnetic information.