Deep-ocean paleo-seafloor erosion in the northwestern Pacific identified by high-resolution seismic images

The deposition and diagenesis of pelagic marine sediments together play important roles in global geochemical cycles by returning elements, such as silica, from the hydrosphere to the geosphere and stably sequestering them within deep-ocean sedimentary sections around the world. Here, we present new, high-resolution (vertical resolution 2–5 m) seismic reflection data from the northwestern Pacific that we interpret to indicate a period of erosional activity that has returned silica to the hydrosphere and thus represents a departure from uniform sequestration by pelagic sediment deposition. The interpreted erosional features are observed as a ~ 200- to 300-m-wide horizontal variation in reflection character within the ~20-m interval overlying the regional chert/porcellanite layer. This reflection character variation is not consistent with uniform pelagic sedimentation, and it has not previously been noted in the northwestern Pacific, where most seismic data are lower-resolution. Erosion of seafloor sediments may have been caused by bottom-current activity, but the geometry of the observed features suggests that fluid-expulsion erosion from diagenesis of primarily siliceous sediment played some role in driving this mass transfer. This period of erosional activity occurred after this portion of the Pacific plate left the equatorial zone of high biological productivity ~75 Ma, and ended between approximately 35 and 55 Ma. Regardless of the details of the process, erosion of deep-ocean seafloor sediments represents a return of silica and other chemicals from the sediment to the bottom water and, if pervasive in the oceans, these processes should be accounted for in models of global geochemical cycles.