High-resolution data of the Iceland Basin geomagnetic excursion from ODP sites 1063 and 983: Existence of intense flux patches during the excursion?

Peer Reviewed

Knudsen MF, Mac Niocaill C, & Henderson GM

Earth and Planetary Science Letters 251, Issue 1-1, pages 18-32, 2006, 10.1016/j.epsl.2006.08.016.

Based on discrete samples, we report new high-resolution records of the ∼ 185 kyr Iceland Basin (IB) geomagnetic excursion from Ocean Drilling Project (ODP) Site 1063 on the Bermuda Rise (sedimentation rate 32 cm kyr− 1) and from ODP Site 983 in the far North Atlantic (sedimentation rate 18 cm kyr− 1). Two records from Holes 1063A and 1063B are very consistent, and provide the highest resolution of the detailed field behaviour during the IB excursion obtained so far. Inclination records from Holes 983B and 983C in the far North Atlantic are also very consistent, whereas declination anomalies deviate more notably. The pseudo-Thellier (PT) technique was applied along with more conventional palaeointensity proxies (NRM/ARM and NRM/κ) to recover relative palaeointensity (RPI) estimates from Hole 1063A and Hole 983B. As expected, these proxies indicate that the field intensity generally dropped at both sites during the IB excursion, but also that the history of RPI from the two sites is different.

VGPs from Site 1063 indicate that the field at this location experienced some stop-and-go behaviour between patches of intense vertical flux over North America and the tip of South America, areas which coincide fairly well with patches of preferred transitional VGP clustering from reversals and zones of high seismic velocity in the lower mantle. Changes in RPI at this location were generally gradual, possibly due to the proximity of these flux patches, and the first period of VGP-clustering over North America was accompanied by a conspicuous increase in RPI. VGPs from Site 983 track along a different path, and the associated RPI changes are very abrupt and completely synchronous with the onset and termination of the excursion. The differing VGP paths from Sites 1063 and 983 indicate that the global field structure during the IB excursion was not dominated by a single dipole.

Keywords: Geomagnetic excursions, Iceland Basin excursion, Preferred VGP longitudes, Patches of vertical flux, Geomagnetic field structure
Categories: Arctic, Natural Science