Seismic Stratigraphy and Geologic History of Blake Plateau and Adjacent Western Atlantic Continental Margin

Abstract

A multifold seismic reflection profile across the Atlantic continental margin from the shelf off Jacksonville, Florida, northeast across the Blake Plateau, northern Blake basin, Blake Outer Ridge, and lower continental rise shows in some detail the structure, stratigraphy, and geologic history of this passive margin since the Late Triassic(?)--Early Jurassic. A seismic stratigraphic framework divides the sedimentary section into seismic intervals, each representing depositional sequences and having distinct acoustic-stratigraphic characteristics. Interval velocities calculated from 64 reflection velocity analyses were used in the geologic interpretation and to construct a geologic depth section along the seismic profile. Dipping reflectors 7 to 10 km beneath the eastern margin of the Blake Plateau probably represent the eastern edge of the rifted North American continental basement. Up to 8 km of Jurassic(?) through Cretaceous sediments overlie the regional post-breakup unconformity beneath the Blake Plateau. Shallow-water carbonate sedimentation persisted through most of the Cretaceous. In the Late Cretaceous the shelf margin shifted from the Blake Escarpment landward to approximately its present location as a result of continued subsidence and a Late Cretaceous overall rise in sea level. An abbreviated section of deeper water carbonate sediments followed on the plateau during the Tertiary owing to many changes in sea level and currents sweeping the plateau. Subsidence of the plateau appears to be in response mainly to sediment loading. Up to 2 km of Neocomian and older sediments were deposited in the deep sea adjacent to the Blake Plateau. Widespread seafloor erosion and the localization of depositional regimes began in the middle Cretaceous. During the Tertiary enormous quantities of mainly terrigenous material were deposited along the deep-sea continental margin as a large wedge up to 4 km thick. Currents following the seafloor contours influenced sedimentation throughout the Tertiary.