Secular Oscillations of the Geomagnetic Field Recorded by Sediments Deposited in Caves in the Mediterranean Region

Abstract

Summary The palaeomagnetism of a 2.4-m section of interior facies sediments from the Upper Dry Cave, Jeita, Lebanon, reveals inclination oscillations which can be correlated with those recorded 1000 km away in core 1474 from the Black Sea. The ' magnetic ' ages so obtained for the Jeita section are consistent with the age (0–16 000 BP) deduced from anthropological and palaeoclimatic evidence. Entrance facies sediments have been studied from a 3.4-m section in Arbreda Cave and from a 1.1-m section in Hermits' Cave, Catalonia, Spain. The age of the Arbreda section, deduced from anthropological and palaeoclimatic controls is between 35 000 BP and 50 000 BP and the Hermits' Cave section is Middle Palaeolithic. At Arbreda, declination oscillations are observed and abnormally low inclinations are recorded at two horizons one of which may correlate with a geomagnetic excursion reported in an Indian Ocean core at about 40 000 BP. The palaeomagnetic record from Hermits' Cave exhibits large amplitude swings. The overall pattern of the results obtained from this and other studies is discussed in terms of a model field in which the long period secular variations originate from oscillations of fixed radial dipoles located in the outer core in the positions computed by Alldredge & Hurwitz.