Molluscan Biozones, Event/Cycle Chronostratigraphy, and Sea Level History: A New Integrated Cretaceous Chronology for Northern South America

Abstract

The Cretaceous marine basins of northern South America, in their evolution, record a dynamic interplay between regional and plate tectonics, sealevel history, changing paleo-ocean/paleoclimate systems, and the rates/patterns of sedimentation driven by both allocyclic and autocyclic processes. Regional interpretation of these complex interactions; and the evolution of the South American passive margin, requires a high-resolution stratigraphic system of dating and correlation. Because short-term events and dynamic processes shape the stratigraphic record, this chronology must have a resolution of 2 Ma/biozone. New efforts to establish a more refined chronology for South America involve: (a) High-resolution (cm-scale) event/cycle chronostratigraphic analyses of key Colombian and Venezuelan sections; (b) search for datable ash/bentonite beds; (c) detailed paleontologic collecting to firmly establish biostratigraphic ranges of mollusks and microplankton with high biostratigraphic potential, and to formulate regional assemblage zones; and (d) integration of these diverse data through graphic correlation to provide a new chronologic standard for the region.more » Initial results are presented: Middle Cretaceous biozones are now resolved to <500 ka/zone; a fine-scale sequence stratigraphy and sealevel history has been determined; numerous regional physical and chemostratigraphic event beds are identified; and climate-driven cyclostratigraphy has been resolved to at least 50 ka within the passive margin sequences of Colombia and Venezuela.« less