Early Sinking History of Ninetyeast Ridge, Northeastern Indian Ocean

Three sites were drilled on Ninetyeast Ridge. They penetrated a sequence of pelagic calcareous oozes underlain by a shallow-water sequence whose ages are Paleocene at Site 214, late Maastrichtian at 216, and late Campanian at 217. At Site 214, the southernmost drilled, a nonmarine sequence that consists of volcaniclastic sediments and thin lignite beds of Paleocene age was penetrated above the basement rocks. At Site 216, volcaniclastic material in the basal sediments is mostly reworked. Both Sites 214 and 216 bottomed in probable subaerial lava flows. Site 217, the northernmost drilled, bottomed in a strongly dolomitized sequence interpreted as a lagoonal reef facies that was subjected periodically to hypersaline conditions and, sometimes, actual emergence.

There is excellent correlation between volcanic, sedimentary, and paleontological data: all evidence indicates rapid sinking. The diachronous facies change (older and deeper to the north) is consistent with the notion of rapid northward movement during sinking, and there is some biogeographic evidence to support this.