Late Cenozoic Sedimentation and Erosion on the Rio Grande Rise

The Rio Grande Rise is capped by a thick sequence of pelagic carbonate and reefal sediments, ranging in age from upper Cretaceous to Recent. The north flank of the Rise is dissected by deep erosional canyons which expose the near-horizontally layered calcareous strata as outcrops on the canyon walls. Lithologic and stratigraphic studies of twenty-two piston cores from a small area ($~25 km^{2}$) on the north flank allow an interpretation of the depositional environment on the Rise during the late Cenozoic, and place constraints on the origin of the erosional canyons. A major unconformity of Pliocene age was penetrated by 12 of the cores. Sediments beneath the unconformity range in age from upper Eocene to lower Pliocene, and correspond approximately in depth with that of equivalent strata recovered at DSDP Site 357 nearby. Pliocene-Pleistocene sediments above the unconformity show systematic regional differences in rate of accumulation, extent of reworking, and the presence of stratigraphic gaps. On the f...