Dynamics of the Laschamp geomagnetic excursion from Black Sea sediments.

Abstract

Investigated sediment cores from the southeastern Black Sea provide a high-resolution record from mid latitudes of the Laschamp geomagnetic polarity excursion. Age constraints are provided by 16 AMS 14C ages, identification of the Campanian Ignimbrite tephra (39.28±0.11 ka), and by detailed tuning of sedimentologic parameters of the Black Sea sediments to the oxygen isotope record from the Greenland NGRIP ice core. According to the derived age model, virtual geomagnetic pole (VGP) positions during the Laschamp excursion persisted in Antarctica for an estimated 440 yr, making the Laschamp excursion a short-lived event with fully reversed polarity directions. The reversed phase, centred at 41.0 ka, is associated with a significant field intensity recovery to 20% of the preceding strong field maximum at ~50 ka. Recorded field reversals of the Laschamp excursion, lasting only an estimated ~250 yr, are characterized by low relative paleointensities (5% relative to 50 ka). The central, fully reversed phase of the Laschamp excursion is bracketed by VGP excursions to the Sargasso Sea (~ 41.9 ka) and to the Labrador Sea (~ 39.6 ka). Paleomagnetic results from the Black Sea are in excellent agreement with VGP data from the French type locality which facilitates the chronological ordering of the non-superposed lavas that crop out at Laschamp-Olby. In addition, VGPs between 34 and 35 ka reach low northerly to equatorial latitudes during a clockwise loop, inferred to be the Mono lake excursion.