Distinctive acoustic reflectors have been identified and traced over hundreds of kilometers on both low-frequency (air gun) and high-frequency (3.5 kHz) seismic profiles from the region immediately to the north of the Clipperton Fracture Zone in the equatorial Pacific. The reflectors result from impedance contrasts between carbonate-rich layers (up to 90% CaCO3) and siliceous clays, and they represent sharp decreases in porosity, increases in wet bulk density, and decreases in sound velocity. The reflectors have northern limits which increase with increasing age: reflector R0 (late Pleistocene) occurs only south of ~5¿N, R1 (upper Miocene) occurs south of ~6¿N, and R2 (middle to lower Miocene) extends to at least 10¿N. Radiolarian biostratigraphy of the piston cores shows that the most extensive of the reflectors, R2, is clearly time transgressive within the middle and lower Miocene. The variable geographic extent and the time-transgressive nature of individual acoustic reflectors are in part a consequence of the northward component of motion of the Pacific plate during the Neogene, with carbonate sedimentation generally restricted to a narrow equatorial region south of ~5¿N. There are no detectable unconformities within core intervals corresponding to the three major reflectors; hence the reflectors apparently do not represent significant erosional episodes. Superimposed on the effect of plate motion may be an abrupt narrowing of the equatorial productivity belt during the middle Miocene at 11-12 m.y. B.P. This abrupt transition from carbonate-rich to carbonate-poor sedimentation occured over a widespread region (approximately 3¿ of latitude) and corresponds with reflector R2. Similar events may have been responsible for the shallower reflectors R0 and R1.