FERRIMAGNETIC CR AND MN SPINELS IN SEDIMENTS - RESIDUAL MAGNETIC MINERALS AFTER DIAGENETIC DISSOLUTION

Ferrimagnetic Cr-Fe and Mn-Fe spinels are the dominant remanence carry ing phases in the late Triassic Lunde Formation. These have largely be en identified by magnetic mineral extraction from the sediments, combi ned with microscopy. The extensive removal of most of the originally d eposited magnetic Fe-Ti oxides during diagenesis has left the Cr-Fe an d Mn-Fe spinels as a mineral residue which is resistant to dissolution . The rock magnetic signature of these minerals is not sufficiently kn own, to be able to identify these minerals on the basis of their magne tic properties alone.