Stratigraphy of ODP Leg 117 sites

Monsoonal-induced upwelling appears to have been initiated during the Miocene. On the Oman Margin, the effect of upwelling on the microplankton was established by the middle Miocene.

However, the effects of upwelling on the Owen Ridge region were not realized until later, in the early late Miocene. A transition in the upwelling regime took place between the Pliocene and Pleistocene. While the Miocene and Pliocene sediments are dominated by the siliceous component, the Pleistocene sediments seem to be dominated by the calcareous component.