Abstract: Pleistocene and Miocene Mass-Transport Deposits on the Continental Slope and Rise and their relationship to Sequence Boundaries: Initial results of the New Jersey Sea-Level Transect, ODP Leg 150

Cecilia M. G. McHugh, John E. Damuth, Gregory S. Mountain, Leg 150 Shipboard Scientific Party

Determining the relationship of sediment transport and erosion to eustatic sea-level change was a major drilling objective on the New Jersey continental slope and rise during ODP Leg 150. Pleistocene and Miocene mass-transport deposits were recovered from surfaces that can be traced

seismically to sequence boundaries on the adjacent continental shelf. Most Pleistocene mass-wasting deposits were of two types: (1) muddy slumps with soft-sediment deformation, isoclinal folds and other contorted and truncated bedding structures; and (2) matrix-supported debris-flows with mud clasts of various lithologies and ages (Pleistocene to Eocene). Several of these Pleistocene deposits have been correlated to the SPECMAP time scale and match known glacioeustatic lowerings. In contrast to other slope sites designed to recover the most complete section possible, Site 906 was drilled in the thalweg of a buried middle Miocene canyon. The floor of this feature can be traced to a major "Type I" sequence boundary at (approx.) 13.5 Ma on the shelf that may correlate with a glacio-eusta ic lowering. The fill of the canyon is composed of mud clast-supported conglomerates that grade upwards into sandy turbidites. Basal conglomerates contain fractures and faults and are interpreted as slide deposits derived from collapse of the canyon walls. Similar middle Miocene mass-transport deposits were recovered at Site 905, on the continental rise 55 km SE from Site 906. The clasts in these conglomerates are a variety of ages and lithologies derived from the slope. Clast and matrix deformation indicates that some deposits have been involved in multiple mass-wasting events. The absence of turbidites at this site indicates that gravity flow deposits are rarely preserved on the upper rise.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994