ICELAND BASIN GEOMAGNETIC EXCURSION IN LAKE BAIKAL SEDIMENTS

The use of the geomagnetic polarity timescale (GPTS) to provide chronological control in a wide variety of geological settings is now universally accepted. It depends on the established sequence of major chrons and sub-chrons. One possibility towards increasing temporal resolution could be the use of brief intervals of divergent field directions and/or intensity fluctuations commonly, but not universally, known as geomagnetic excursions. A plethora of such features already exists in the literature, but the precise nature and timing of the most of them remains questionable. As part of an international collaborative project, magnetic remanence vectors of 1737 samples from the uppermost 100 m of Lake Baikal sediments have been determined along with continuous magnetic susceptibility profiles. Matching susceptibility variations to the oceanic oxygen isotope record and relative paleointensity variations to the global reference curve both imply an average deposition rate of 15 cm/kyr and a basal age of ~640 ka. Spectral analysis reveals the presence of Milankovitch cyclicities. Stable remanence vectors are almost all of normal polarity, but several short intervals of low and/or negative inclinations are found. The most prominent of these involves a systematic inclination swing and relative intensity low near a depth of 27 m. The main part of this excursion lasted ~5000 years, but the slow recovery to typical normal polarity inclinations may double this. Our chronology suggests that this feature represents the Iceland Basin Excursion. It also implies that the corresponding intensity low in the global intensity summary SINT-800 is incorrectly identified as the Jamaica/Pringle Falls Excursion and should now be re-assigned to the Iceland Basin Excursion.