| Calcareous nannofossils and stable isotopes were analyzed to determine the timing and causes of extensive Miocene debris flows and Oligocene slumps recovered by Ocean Drilling Program (ODP), cruise Leg 207 to Demerara Rise along French Guiana and Suriname. Five modes of emplacement are considered for the Oligocene and Miocene failures. These hypotheses include canyon incision and infilling, clathrate dissociation, sediment loading, current activity, and seismic triggering.; Calcareous nannofossil ages of the Miocene debris flows at Hole 1261A down to 351 mbsf indicate that the debris flow(s) were emplaced within the time period of Subzone NN11b (7.2--5.5 Ma). Hence, nannofossil biostratigraphy provides a time interval of 1.7 m.y.; Compared to previous drilling along the New Jersey Transect these results indicate the mass wasted deposits here are fundamentally different, i.e., not the result of canyon incision and infilling. Instead, this study suggests that the emplacement of the Miocene debris flows resulted from high mass accumulation rates combined with a seismic trigger. Paleocurrent reorganization and/or sea-level changes best account for the Oligocene slumps. |
