High Resolution Timing of the Late Paleocene Thermal Maximum by Extraterrestrial 3He Implied Sedimentation Rates at ODP Site 690B

The Late Paleocene Thermal Maximum (LPTM) was a dramatic event at ~55 Ma characterized by major species extinctions as well as carbon and oxygen isotope excursions. Early magnetostratographic estimates indicated that the LPTM occurred with extreme rapidity, but a lack of reliable, proximate tie points demonstrated a need for improved time constraints, which were recently established by analyses of sediment chemistry from ODP Site 690B in the Weddell Sea. Presumed orbitally-induced cyclical variations in Fe and Ca content confirm the rapid progress of the event but provide limited detail within the event itself [1]. Here we present extraterrestrial ³He data to test and refine the age model derived from cyclostratigraphy. \ Sedimentation rates were calculated from the accumulation of interplanetary dust particles (see Farley et al., this volume) in ~150 samples over a 5 meter interval including the LPTM. These sedimentation rates largely agree with the cycle tuning approach for the early to middle LPTM: the sedimentation rate begins to drop before the carbon isotope excursion, and it drops to a minimum value nearly coincident with the carbon isotope excursion that is approximately a factor of 3 lower than the pre-event value. Late in the event, however, the extraterrestrial ³He reveals a very different picture than cyclostratigraphy suggests: we find a 10-fold increase in sedimentation rate for ~1 meter followed by a decrease at the close of the LPTM. At this point it is unclear how to reconcile the results from the two techniques. \ References: [1] Röhl, U., Bralower, T. J., Norris, R. D. & Wefer, G. New chronology for the late Paleocene thermal maximum and its environmental implications. Geology 28, 927-930 (2000).