Seismic stratigraphy of the Shatsky Rise sediment cap, northwest Pacific, and implications for pelagic sedimentation atop submarine plateaus

Abstract

Pelagic sediments accumulated atop Shatsky Rise since Early Cretaceous time provide a valuable record of Pacific paleoceanography. The accepted sedimentation model invokes relatively continuous pelagic sediment accumulation punctuated by four regional hiatuses caused by changes in oceanic chemistry. That framework was proposed more than two decades in the past and based on low-quality single channel seismic profiles. It was developed at the center of Tamu Massif, the main topographic high of Shatsky Rise, and extended to other highs with uncertainty owing to sparse data. The availability of high-quality seismic data and additional coring by the Ocean Drilling Program and Integrated Ocean Drilling Program allows a re-examination. Seismic and core data indicate that sedimentation atop Shatsky Rise has been complex, with regional and local variability. Four major hiatuses were previously defined and tentatively correlated to nearby topographic highs. These breaks occurred approximately during the Aptian-Barremian and Cenomanian-Coniacian ages of the Cretaceous and during the Paleocene and Oligocene epochs of the Cenozoic. They are of variable length and tend to be of shorter duration at the summit of Tamu Massif, but of longer durations elsewhere. All produced erosional unconformities that may be related to mass wasting of the sediment cap edges. Each hiatus is approximately correlated with global falls of sea level, suggesting a connection, perhaps to intensified bottom currents at those times. Local variability is observed in the form of discontinuous layering, non-uniform sedimentation, thinning of the sediment caps at their edges, and local erosion near topographic highs. These variations are likely the result of shifting bottom currents, possibly resulting from interactions of internal tides with topography. Shatsky Rise sedimentation is inherently punctuated and non-uniform and the sedimentary record includes significant lateral variability. Other large oceanic plateaus are likely to exhibit similar sedimentary cap complexities.