Depositional history of the Sulu Sea from ODP Sites 768, 769 AND 771

Abstract

Holes were drilled at three Sites in the Sulu Sea on Ocean Drilling Program Leg 124. Site 768 lies in the deeper part of the SE sub‐basin and Sites 769 and 771 lie on the flanks of the Cagayan ridge. The results indicate that the Sulu Basin originated in the late early Miocene (c.18.8 Ma) in a backarc setting. The Cagayan Ridge was a site of early to early middle Miocene arc volcanism with the deposition of a thick sequence of andesitic to basaltic volcaniclastic deposits. In the basin center an early Miocene pelagic sequence is interrupted by a thick unit of rhyolitic to dacitic pyroclastic flows. Middle to late Miocene sedimentation is more continental in character with thick quartz‐rich turbidites in the basin center. Only the hemipelagic claystone related to these terrigenous turbidites were deposited on the Cagayan Ridge. A decrease in the supply of clastic detritus from arc and continental sources and a change in the level of the carbonate compensation depth in the upper Pliocene resulted in pelagic carbonate deposition throughout the late Pliocene and Pleistocene.