High-resolution magnetostratigraphy of four sediment cores from the Greenland Sea-II. Rock magnetic and relative palaeointensity data

Abstract

SUMMARY High-resolution magnetostratigraphic analysis of three sediment cores from the base of the volcanic seamount Vesteris Banken in the Greenland Basin and one from the Jan Mayen Fracture Zone revealed records of three pronounced geomagnetic events: the Mono Lake excursion (28–27 ka), the Laschamp event (37–33 ka) and the Biwa I*** Jamaica event (189–179 ka). Rock magnetic investigations, measurements of magnetic susceptibility, and ARM and IRM acquisition/demagnetization experiments show that only fine-grained (titano) magnetite (≤ 0.5 μm) is the dominant magnetic carrier mineral in the hemipelagic muds. There is no evidence for high amounts of high-coercivity minerals like haematite or goethite. Volcanic (basaltic) ash layers in sediments around Vesteris Banken seamount are characterized by extremely high values of magnetic susceptibility, reaching 16 000 times 10-6 (SI), as well as by low median destructive fields of the anhysteretic remanent magnetization (MDFARM), indicating magnetite of larger grain sizes (≥ 1 μm). Besides this, no significant variation in rock magnetic parameters across intervals of intermediate to reversed ChRM inclinations are observed. Therefore, these are interpreted as true records of geomagnetic field variations. The recovered sediments, characterized by only moderate fluctuations in concentration as well as grain-size-related rock magnetic parameters, provided good conditions for the reconstruction of the relative palaeointensity of the geomagnetic field. The recorded geomagnetic events are clearly linked to a drastic reduction in the relative palaeointensity of the field. The lowermost values were obtained for the time of the polarity transition with a trend to higher relative intensities in the course of the polarity events. Event ages and the relative palaeointensity variations, based on different methods, derived from the Greenland Sea sediments investigated are in good agreement with data published in the literature.