RESULTS

A bulk sediment stable isotope record spanning the entire sedimentary sequence is presented with CaCO₃ MARs in Figure F2A.

The oxygen isotope record shows marked variations from –2.7 to 0.6 (Fig. F2). The fluctuations of ¹⁸O values show three major patterns:

1. An irregular but consistent long-term increase from –2.2 to 0.1 prior to 11.5 Ma,
2. A sudden decrease starting at ~11.5 Ma followed by two stepwise decreases reaching a nadir at ~10.0 Ma, and then
3. Swinging back and forth thereafter with a long-term increase.

Significant fluctuations are also present in the carbon isotope record, with a range from –1.4 to 2.8 (Fig. F2). ¹³C values are high and increase upsection just prior to 11.3 Ma, decrease sharply thereafter, recover somewhat from 11.1 to 11.7 Ma, decrease sharply again and remain low to the lowest point at ~8.5 Ma, and recover again thereafter. Two major negative excursions can be recognized at ~11.3 and ~10.7 Ma with a net reduction in ¹³C values over a range of ~1.7 and ~1.6, respectively. Carbon isotope values show little correlation with oxygen isotope records in the studied interval (Fig. F2B).

CaCO₃ MARs range from 0 to 7.06 g/cm² k.y. Variations in CaCO₃ MARs follow the trends in stable carbon isotopes prior to 5 Ma (correlation coefficient [R] = 0.87), but this positive correlation almost disappears thereafter (R = 0.42) (Fig. F2B).