MAGNETOSTRATIGRAPHIC (RE)CALIBRATION OF THE PALEOCENE EOCENE BOUNDARYINTERVAL IN HOLE-550 AND HOLE-549, GOBAN SPUR, EASTERN NORTH-ATLANTIC/

A magnetostratigraphic reinvestigation of the Paleocene/Eocene boundar y intervals in DSDP Holes 550 and 549, Goban Spur, has removed uncerta inties associated with the previously published magnetostratigraphic i nformation for these chronostratigraphically important sections. In Ho le 550, levels assigned to nannoplankton zones NP4 and 5, previously c onsidered to be of normal polarity, carry a reverse polarity character istic magnetisation which is correlated with geomagnetic Chron C26r. U nconformably overlying these levels is a thin interval of reversely ma gnetised sediment which records the latter part of Chron C25r. Chron C 25n is redefined and its lower/upper boundaries are placed respectivel y at 425.08 and 422.12 mbsf in Hole 550. Chron C24r extends upwards si milar to 62.4 m. Respectively, the start and end of Chron C24n.3n are placed at 359.69 and 349.41 mbsf in this hole. Within Core 28, just ab ove C24n.3n, is a record of Chron C24n.2n as well as interval of indet erminate polarity within C24n.2r. The problematic issue of assigning n umerical ages to the various events associated with the Paleocene/Eoce ne transition in Hole 550 is then discussed. The remanence in Hole 549 is difficult to interpret because magnetic inclinations in the interv al previously assigned to Chrons C25n and C24r are typically <20 degre es compared with the similar to 60 degrees expected for the Paleogene sediments at this site. Acknowledging the complexities of this record, we have constructed the magnetostratigraphy for this hole, based on r esults from the present study and previous work [H.A. Townsend, The pa leomagnetism of sediments acquired from the Goban Spur on the Deep Sea Drilling Project Leg 80, in: P.C De Graciansky, C.W. Poag et al. (Eds .), Initial Reports DSDP 80 (1985) 389-410]. Contrary to the previous study, we are not able to fix the base of Chron C25n; it is located ei ther in the lower part of Core 18, where the core pieces are too small to be used reliably for paleomagnetic studies, or in the gap between Cores 18 and 19. The Chron C25n-24r boundary is blurred (similar to 35 1 to 353 mbsf) because of the shallow inclination problem. Chron C24n. 3n, which is characterised by inclinations of similar to 35 degrees, h as its lower/upper boundaries at similar to 318 and 307.62 mbsf respec tively. An apparent record of Chron C24n.2n, based on two samples, is present between 305.53 and 304.65 mbsf. (C) 1998 Elsevier Science B.V. All rights reserved.