Eastward Submarine Canyon and the Shaping of the Blake Nose

摘要

Eastward Canyon has formed along the north side of the Blake nose (30°10' N., 76°30' W.) and is part of the east edge of the Blake Plateau which lies off the southeast coast of the United States. The canyon has a length of about 40 mi and a maximum depth of about 500 m from the crest of the north side. The south wall of the canyon coincides with the north wall of the Blake nose and has a relief of over 2,000 m. The erosional processes which formed the canyon and which maintain the sharp declivity at the base of the escarpment have in effect eroded and shaped the Blake nose. Oölitic calcarenite with Early Cretaceous algae from the base of the Blake nose suggest it formed as a prograding sedimentary feature in a shallow-water environment, and may have extended much farther to the east before being eroded. Eastward Canyon has no extension onto the Blake Plateau and no river counterpart on land and therefore must have been formed by the deep western boundary undercurrent flowing south along the Blake Escarpment. The currents might gain considerable strength as they are deflected around the Blake nose. The extension of stratigraphic reflectors and JOIDES drill core dates from the Blake Outer Ridge suggest that present aspects of the canyon are largely Pleistocene in age. The lower end of the canyon merges into the Blake-Bahama abyssal plain at about 5,030 m, which implies that the solution of carbonate sediment is an important factor in erosion. Similar erosional processes may be important in maintaining the axis of maximum depth close to the Blake-Bahama escarpment farther to the south.