28. Carbonate Sedimentation in the Sulu Sea Linked to the Onset of Northern Hemisphere Glaciation, 2.4 Ma

Pliocene and Pleistocene sediments from Sulu Sea ODP Sites 768 and 769 contain high-resolution records of pelagic sedimentation in a deep marine silled basin. Carbonate analyses reveal that both sites are free of pelagic carbonate up until 2.4 Ma, at which time carbonate becomes a major component of the pelagic marl sedimentation. The timing of this increase in calcium carbonate accumulation is precisely constrained by the position of the Gauss/Matuyama paleomagnetic reversal 2.47 Ma. The rapid increase in carbonate accumulation at both sites coincides with the onset of Northern Hemisphere glaciation 2.4 Ma, suggesting that conditions associated with expanded Northern Hemisphere ice sheets affected the western tropical Pacific. The results of this preliminary study do not allow determination of whether the increase in calcium carbonate accumulation 2.4 Ma is due to productivity changes, preservation changes, or some combination of the two.