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

Abstract

Hole 690B, drilled on Maud Rise near Antarctica, provides one of the most important 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 major 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 issues, 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 magnetically 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 possible to construct a filtered magnetostratigraphy for the section. The result 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 associated with the Palaeocene/Eocene boundary, is considerably cleaner. It is not possible to define the upper and lower boundaries of this magnetochron, so we recommend that the dating of the events within this section be based on the biostratigraphy only.

Philippine Sea Plate motion history: Eocene-Recent record from ODP Site 1201, central West Philippine Basin

“…More than 90% of the 273 sediment samples yielded acceptable PCAs, with fits having an average maximum angular deviation (MAD) of 4.4 • (Supplement Table 1). Of these, 78 were discarded samples because they had unusually steep inclinations (>50 • ), which may have been due to an incompletely removed drill string overprint, which is commonly encountered in studies of ODP cores (e.g., Fuller et al, 1998;Ali et al, 2000;Fuller, 2002;Acton et al, 2002). Figs.…”

Orbital climate forcing of δ13C excursions in the late Paleocene–early Eocene (chrons C24n–C25n)

“…Interpreted magnetic polarity stratigraphies were taken from published reports for Sites 550 [ Ali and Hailwood , 1998; Townsend , 1985], 577 [ Bleil , 1985], and 690 [ Ali et al , 2000]. A preliminary magnetostratigraphic study for Site 1051 [ Ogg and Bardot , 2001] produced promising results, but only samples from Hole 1051A were progressively demagnetized and the sample spacing was coarse.…”

“…No scale is shown for sediment color data, which is plotted only in relative units. All data were generated for this study except the following: magnetic susceptibility logs for Site 1051 ([Shipboard Scientific Party, 1998]); magnetic polarity zonations for Sites 690 [Ali et al, 2000], 550 [Townsend, 1985;Ali and Hailwood, 1998], and 577 ; and nannofossil zonations for Sites 690 [Pospichal and Wise, 1990;Berggren and Aubry, 1996;Aubry et al, 1996], 550 [Muller, 1985;Berggren and Aubry, 1996;Aubry et al, 1996], and 577 [Monechi, 1985;Aubry, 1998]. See color version of this figure in the HTML.…”

The Paleocene-Eocene Thermal Maximum: New Data on Microfossil Turnover at the Zumaia Section, Spain

“…Baceta, V. Pujalte) Cyclostratigraphy has proved to be a valuable metronome to parse time in the geologic record and has recently been applied to the P/E transition interval from Ocean Drilling Program (ODP) Sites 1051 and 690 (Norris and Röhl, 1999, Röhl et al, 2000, Cramer, 2001) and in the Forada section (Agnini et al 2005). The polarity record of ODP Hole 690B is hampered by a strong drilling-induced overprint (Ali et al, 2000). However, apparent good magnetostratigraphic results from the upper part of chron C25r up to the lowermost Eocene chron C24r for ODP Site 1051 has enabled to propose a climatic orbital origin for the cycles observed in colour reflectance, magnetic susceptibility and Fe intensity counts (Norris and Röhl, 1999).…”