Magnetostratigraphic reinvestigation of the Palaeocene/Eocene boundary interval in Hole 690B, Maud Rise, Antarctica

Hole 690B, drilled on Maud Rise near Antarctica, provides one of the most i mportant Palaeocene/Eocene boundary interval sections. Magnetostratigraphy plays a key role in dating Palaeocene/Eocene boundary events, but there are two problems with the published scheme in Hole 690B, The first concerns ma jor mismatches of several magnetozones and biozones in the succession, The second is an unexplained pervasive declination cluster, which should not be present in these azimuthally unoriented piston cores. To resolve these iss ues, a palaeomagnetic reinvestigation was carried out on 98 specimens from 12 cores through the upper Palaeocene-middle Eocene section in Hole 690B. The bulk of the samples carry an approximately uniformly directed magnetica lly hard component resulting in a declination cluster effectively identical to that of the earlier study. The spurious magnetization can be explained either as an 'inward-radial magnetization' or as a 'core-split overprint'. By estimating the extent of the overprint within each sample, it has been p ossible to construct a filtered magnetostratigraphy for the section. The re sult is that many of the magnetozone-biozone mismatches are eliminated, and the record of the 2.5 Myr Chron C24r, which brackets the various events as sociated with the Palaeocene/Eocene boundary, is considerably cleaner. It i s not possible to define the upper and lower boundaries of this magnetochro n, so we recommend that the dating of the events within this section be bas ed on the biostratigraphy only.