|
|||||
|
|
Effects of weathering on single-domain magnetite in Early Pliocene marine marls |
|
| Authors: | A J van Velzen J D A Zijderveld |
| Institution: | Paleomagnetic Laboratory 'Fort Hoofddijk'. Institute of Earth Sciences, Utrecht University, Budapestlaan 17, 3584 CD Utrecht, Netherlands |
| Abstract: | Rock magnetic parameters are often used to recognize variations in the original magnetic mineralogy and for normalizing purposes in palaeointensity studies. Incipient weathering, however, is shown to have a profound but partly reversible influence on the rock magnetic properties of the marls of the Early Pliocene Trubi formation in southern Sicily (Italy). The remanence in the marls resides in single-domain (SD) magnetite grains, but the remanent coercive force (H The enhanced coercivities are attributed to stress in the magnetite grains induced by surface oxidation at low temperature. Upon heating to 150 °C a reduction of coercivities occurs that can be explained by a stress reduction as a result of a reduction of Fe Another effect of heating the marl samples to 150 °C is a substantial reduction of the coercivities of the secondary overprint in the natural remanent magnetization. After heating. separation of the secondary and primary components by alternating-field demagnetization is more efficient. The usual difficulties of thermal demagnetization above 300 °C may thus be avoided by a combination of moderate heating to 150 °C and subsequent alternating-field demagnetization. |
| Keywords: | marine sediments magnetite rock magnetism |