Ponded Sediments of the Mid-Atlantic Ridge between 22° and 23° North Latitude
The numerous valleys of the flanks of the Slid-Atlantic Ridge, are partly filled with sediment. The petrology of sedirtients from two.such valleys (ponds) near 22– N. latitude shows f that the material has been deposited by turbidity currents. The material has betyi derived from Calcareous pelagic deposits which mahtle the surrounding hills. The turbidite sequences show peculiarities which can be explained by assuming that the currents rebounded repeatedly from thdporfd walls. A theoretical model fpr the flow of these currents agrees well with density,. thickness, and composition parameters that can be derived from the deposits and points to the occurrence of a hydraulic jump at the base of the slope. Adjacent valleys are separated by divides, and each valley contains an independent sedimentation unit. Good correlation exists between the volume of sediment in each valley and the size of the sufrpunaing hill area from which the - sediment was derived. Removal of 15 m of sediment from the entire region is required to account for the sediment that now fills the valleys. The oldest sediment outcropping in this region is upper Miocene, and the average sedimentation rate of the pelagic deposits can be estimated as approximately 3 mm/1000 years. In the ponds, the rate is much greater; more than 9 m of late Quaternary sediment have been found. Recently, the valleys have been faulted and partly uplifted. The accompanying earthquake activity may have initiated the turbidity currents responsible for the present rapid deposition on the valley floors.
Figures & Tables
Edited by Peter A. Roma and published in 1976, Mid-Atlantic Ridge contains a collection of related articles reprinted from other Geological Society of America publications as well as a brief review of exploration of the Mid-Atlantic Ridge from 1960 to 1975.