LARGE VOLUME TURBIDITE DEPOSITION ON CONTINENTAL MARGINS IN A GREENHOUSE WORLD: THE EARLY EOCENE CLIMATIC OPTIMUM (EECO)

We evaluate the hypothesis that during a prolonged eustatic highstand, deep ocean passive margin basins can accumulate substantial volumes of turbidity current deposits. To test this hypothesis we compiled an inventory (97 locations) of the global distribution of deep ocean siliciclastic turbidites that accumulated during the Early Eocene Climatic Optimum (EECO) or bounding time intervals. The EECO is a prolonged interval characterized by minimal glaciation and exceptionally high atmospheric and ocean temperatures. Eustatic sea level was abnormally high and, apart from possible Milankovich effects, relatively stable for approximately 6 Ma. Consequently, the EECO would have been a particularly unfavorable time for continental margin turbidite deposition if falling sea level is a prerequisite for transporting substantial volumes of terrestrial sediment into the deep ocean.

We find that turbidites are common and abundant along tectonically active margins during the EECO and also present on the passive margins of multiple continents. The presence of significant volumes of turbidites in passive continental margin deep ocean basins during the EECO argues in favor of the importance of mechanisms other than falling relative sea level to supply abundant siliciclastic sediments beyond the shelf edge. Most likely, abundant turbidites on passive margins resulted from voluminous sediment supplied by large integrated fluvial drainage systems.