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A paleomagnetic and geochemical record of the upper Cochiti reversal and two subsequent precessional cycles from Southern Sicily (Italy)

By A.A.M. van Hoof, B.J.H. van Os, J.G. Rademakers, C.G. Langereis and G.J. de Lange


A detailed paleomagnetic and geochemical study of the upper Cochiti (N-R) reversal recorded in marine marls on\ud southern Sicily shows two consecutive and very rapid transitions (R-N and N-R) that coincide with distinct lithological\ud boundaries. A 'Fe-migration model' is presented in which magnetite is formed under different diagenetic conditions. During\ud sulphate reduction, originally formed ('primary') magnetite is preserved. This primary magnetite has recorded the\ud pre-transitional normal polarity. After burial, migration of ferrous iron occurs and subsequent oxidation produces\ud 'secondary magnetite', which records the post-transitional reversed polarity and produces the two apparent transitions. In\ud addition, low temperature (LT) and high temperature (HT) components record the reversal in a slightly different way: the\ud HT component being acquired with a delay. It is probable that both components reside in magnetite but have a different\ud origin and grain size distribution, giving different blocking temperature spectra. The actual upper Cochiti reversal occurs at\ud a level with an estimated astronomically calibrated age of 4.165 Ma

Topics: Aardwetenschappen
Year: 1993
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