Abstract:
Five sections drilled in multiple holes over a depth transect of more than 2200m at the Walvis Ridge (SE Atlantic) during Ocean Drilling Program (ODP) Leg 208 resulted in the first complete Paleogene deep-sea record with relatively high sedimentation rates (1 to 3 cm/kyr). Here, we present a approximately 4.3 million year long interval that spans the late Paleocene to early Eocene (Magnetochrons C24r, C25n, upper C25r) containing the Paleocene-Eocene thermal maximum (PETM) and recently identified new warming events (ELMO layer; Lourens et al. 2005; Nature; "X" event; Roehl et al., this meeting). We have developed a detailed chronology by using records of elemental concentrations obtained by an X-ray fluorescence (XRF) Core scanner (Sites 1262, 1263) and non-destructive core logging data (magnetic susceptibility, color data) (Sites 1262, 1263, 1265, 1267). To define a complete time series of the investigated interval new revised composite depth records have been constructed for Sites 1263, 1267, and Site 1051 drilled during Leg 171B. Extensive spectral analysis and the computation of evolutive spectra using wavelet analysis of multiple proxies in the depth domain suggests that at Walvis Ridge the dominant sedimentary cycles are related to Milankovitch orbital forcing. All sites reveal almost perfect precession cycles modulated by the short (100-kyr) and long (405-kyr) eccentricity cycle. Direct counting of precession cycles in the iron (Fe) concentrations as well as the redness over greenness ratio (a*) of the color data at multiple sites results in revised estimates for the age and duration of magnetochrons C24r and C25n. The developed relative time scale spanning 4.263 Ma (203 precession cycles) is now accurate to the level of one precession cycle. Comparison of the amplitude modulation of the precession cycle in the geological data with current astronomical computations of the short and long eccentricity cycle suggests that the Paleocene-Eocene thermal maximum (PETM) and the ELMO layer are related to 100-kyr, but not to 405-kyr eccentricity maxima. We now can also give better estimates of the age of the PETM and the ELMO-layer using the amplitude modulation of the precession cycle in combination with cycle counting.