Diagenetie processes and remagnetization in Permo- Triassic reb beds

Palaeomagnetic methods of analysis have largely been concentrated on distinguishing between the relatively hard and soft components which make up the natural remanent magnetization (NRM) of sedimentary rocks. Ihis has been because of the widespread beliefthat, in general, the hard cornponents are primary in origin whule the soft components are secondary, having been acquired a long time afler deposition. Also it is generally assumed that the primary components originate from depositional processes rathcr than diagenetie (post-depositional) alteration. Magnetic components acquired by in situ alteration are usually altributed to chemical remanent magnetization (CRM) with no more specific reference to tSe processes of magnetization. Furthermore the general practice has been Lo assume that tSe magnetic components with higher blocking temperatures or coercivities faithfully record the ambient geomagnetie field at or near tSe time of deposition despite any direct geological evidence of the age of tSe components. Ihis simplistie view of palaeomagnetism arises from tSe Neel equation which relates relaxation time to coercive force, particle volume and temperature for an assembly of non-interacting single-domain grajos: