ROCK MAGNETISM OF DEFORMED UPPER TRIASSIC LIMESTONES FROM THE LAGONEGRO BASIN (SOUTHERN APENNINES, ITALY)

The stable component of the natural. remanent magnetization (NRM) of the Upper Triassic ''Calcari con Selce'' limestone formation at Marsico Nuovo (Lagonegro Basin, Southern Italy) has an inclination which is about 45 degrees too steep for the expected paleogeographic position. In order to explain this abnormal magnetization direction, several rock magnetic properties such as the dependence of susceptibility on temperature and alternating field frequency, anisotropy of low field susceptibility, anisotropy of anhysteretic remanent magnetization (ARM) and characteristics of acquisition and thermal decay of isothermal remanent magnetization (IRM) have been investigated. Strong inverse fabrics of both susceptibility and ARM have been recognized, which are due to magnetite in the superparamagnetic state on the one hand and in the stable single domain grain size on the other hand. Although internal deformation in the investigated rocks has not been reported in the geological literature, this may be the cause of the observed anisotropies. The anisotropy is probably responsible for the anomalous NRM directions of these limestones.