| Previous studies have documented that global climate cooled in the late Eocene at the million-year time scale. However, the precise details and timing of this cooling remain unresolved. This study proposes that the late Eocene million-year time scale cooling trend was punctuated by precessional Milankovitch cyclicity and that the cooling trend was interrupted by a warm pulse during the latest Eocene. The late Eocene paleoclimate was studied on the New Jersey Continental Margin from slope sediments recovered during Leg 150 of the Ocean Drilling Program. A multiproxy approach that included the following analyses was used: (1) grain size, (2) bulk mineralogy, (3) petrographic thin sections, (4) stable oxygen isotopes from planktonic foraminifera Globigerina spp., (5) geophysical FMS logs (Formation Microscanner; measuring conductivity), (6) spectral analysis, and (7) comparison to global records from previously published work.;A general cooling trend from the middle to the late Eocene is indicated by an increase in siliciclastic sediment, decrease in calcium carbonate, and grain size coarsening. These lithologic changes document the transition from carbonate to siliclastic sedimentation that accompanied the paleoclimatic cooling and was previously documented for this margin. An increase in global ice volume through the late Eocene is also documented by stable oxygen isotopes obtained from the tests of Globigerina spp. Low resolution sampling at a 40 ka resolution showed delta18O values increasing from -3.67 per mil up to -2.83 per mil over a span of 1,050,000 years between 35.3 Ma and 34.25 Ma. High resolution sampling, one sample every 5 ka, over the interval from 34.75 Ma to 34.25 Ma show delta18O values ranging at -3.0 per mil and is interpreted as warming. These delta 18O values and interpretation are consistent with global composite stable isotope records and interpretations that document a warm period at the close of the late Eocene just before a dramatic short term global cooling in the early Oligocene. This cooling period lasted only a few hundred thousand years.;Orbital forcing of paleoclimate in the late Eocene is shown at high resolution by spectral analysis. Strong spectral peaks were found at intervals of 23.8 years and 19.2 years, which are very close to the Milankovitch precessional frequencies of 23ka and 19ka. Strong spectral peaks were also found at intervals of 23.4ka, and 18.7ka for the middle Eocene. The silica diagenesis found in the middle Eocene carbonates is thought to be the cause of the slight deviations in cyclicity. Precession within the late Eocene is also manifested by increases and decreases in planktonic foraminiferal productivity, measured directly by grain size analysis, and correlated to the oxygen isotope data. |
