The early Neogene continental rise off the eastern United States

Single and multichannel seismic data were used to investigate depositional components comprising the late Oligocene-middle Miocene constructional phase of the United States Atlantic continental rise in the Georges Bank-Blake Plateau region. The seismic sequence studied was bounded by the Eocene-Oligocene age Horizon A u unconformity at the base and a newly defined late middle Miocene age Horizon G at the top. Late Oligocene-middle Miocene accretion, onlapping the paleocontinental slope and downlapping onto Horizon A u basinward, was derived primarily from erosion of the uplifted central Appalachian Mountains. This accretion, up to 3.2 km thick, was characterized by seven depocenters. The lower paleocontinental slope-upper rise depocenters, situated off southern New England and the Delmarva Peninsula, were interpreted as deep-sea fan complexes or a broadly overlapping series of sedimentary blankets a a Schlee and Hinz (1987). , whereas the closely associated Oceanographer and Wilmington depocenters were inferred to be levee complexes. Immediately north of the developing Blake-Bahama Outer Ridge, two N-NE-oriented sediment ridges, that were probably built by Gulf Stream flow during an early Miocene sea level lowstand, were observed. On the lower continental rise, the proto-Hatteras and Mytilus outer ridges (from 0.4 to 0.8 km thick) were probably formed from the Wilmington and Oceanographer levee complexes in early-middle Miocene time through the interaction of the growing levee complex with the SW-moving abyssal current. Late middle Miocene (12-11.5 Ma) bottom-current erosion created the Horizon G unconformity and brought to an end this initial stage of continental rise construction. Nevertheless, the basic morphological framework that controlled late Neogene and Quaternary continental rise evolution was now in place.