INTRODUCTION

The Paleocene/Eocene (P/E) boundary, sometimes referred to as the Paleocene/Eocene Thermal Maximum, at ~55 Ma, was a warm period in the Earth's history marked by several unusual excursions recorded in marine sediments. Oxygen isotopes (¹⁸O) and carbon isotopes (¹³C) at this boundary dropped 2–3 in <10,000 yr, implying a warming of bottom waters by 4°–8°C and a significant change in the carbon cycle (Kennett and Stott, 1991; Bralower et al., 1995; Thomas and Shackleton, 1996; Schmitz et al., 1996).

The initiation of the P/E boundary event is marked by the extinction of 35%–50% of cosmopolitan benthic foraminifers, the largest extinction in the Cenozoic (Thomas and Shackleton, 1996; Norris and Röhl, 1999; Katz et al., 1999). The benthic extinction event that defines the P/E boundary is found at Site 1221 (Section 199-1221C-11X-3, 91 cm) (Lyle, Wilson, Janecek, et al., 2002).

The P/E boundary is characterized by a sediment interval low in CaCO₃. Calcium carbonate concentration as low as 10 wt% in sections recovered from Ocean Drilling Program (ODP) Legs 171, 189, and 198. Typical CaCO₃ concentrations, ranging 1.5–10.0 wt%, were found at all Leg 199 sites where the P/E boundary was recovered (Lyle, Wilson, Janecek, et al., 2002).