Reworking in Upper Mesozoic and Cenozoic central Pacific deep-sea sediments

Abstract

Data from deep-sea drilling cores from upper Mesozoic and Cenozoic central Pacific Ocean sediments have been used to estimate the frequency with which pelagic microfossils in sediments of different ages include species which have been displaced from older deposits. Intruding microfossils, which include planktonic foraminifera and calcareous nannofossils, and to a minor degree also radiolarians and diatoms, are most easily distinguished by not being contemporaneous with the sediments in which they are found. Presumably their occurrence arises from the mechanical reworking of oceanic sediments by bottom water currents. The data suggest that there were pulses of intensive reworking around 40 Myr BP, 30 Myr BP, 15 Myr BP, 5–10 Myr BP and during the Plio–Pleistocene; these pulses were interrupted by phases of only modest erosion on the Pacific Ocean floor. The absence of reworking of non-contemporaneous fossils in sediments older than 70 Myr suggests relatively sluggish deep-sea currents which were not able to erode deeply into the underlying Cretaceous and in certain areas Jurassic sediments.