Sedimentation Rates and Pacific Plate Motion Calculated Using Seismic Cross-Sections of the Neogene Equatorial Sediment Bulge

The EW9709 cruise of the R/V Maurice Ewing surveyed two separate seismic reflection transects in the central Pacific: one from the equator to about 17°N on crust of ~40 Ma (late middle Eocene) age and the other from the equator to 26°N on crust of ~56 Ma (late Paleocene) age. The two transects have been analyzed using piston cores taken on EW9709 to define ages of the uppermost reflectors and using previously defined Neogene seismic stratigraphy by Mayer, Shipley, et al. (1985) to pick specific, dated, regionally traceable sediment reflectors and define Neogene sediment packets. The ages of the specific reflectors were used to calculate sedimentation rates. In this way gross sedimentological changes of the equatorial bulge were studied during the Neogene. The Neogene interval is characterized by an equatorial bulge that extends only about 3-5 degrees to either side of the paleoequator, and with significantly higher sedimentation rates at the paleoequator. The broadest bulge appears in the oldest sections studied (between 16 and 20 Ma). The highest rate of sedimentation occurs in the Middle Miocene (between 14 and 16 Ma). Neogene Pacific plate motion is calculated using the bulge apex as the location of the paleoequator. When compared to calculations of equator location based on the Hawaii-Emperor Seamount hot spot model, there is disagreement. The sediment bulge data consistently lie to the south of the hot spot model prediction for data older than 8 Ma. If hot spot plume motion is to account for the discrepancy, the plume is moving with some component of northern motion