Cenozoic Regional Erosion of the Abyssal Sea Floor Off South Africa
The Cape, Agulhas, and Mozambique basins off South Africa have a well-defined and mostly continuous erosional zone along their perimeters between 4 and 5 km (2.5 and 3.1 mi) water depth. This zone lies beneath a deep boundary current of Antarctic Bottom Water. However, current speeds are generally less than 15 to 20 cm/sec (5.9 to 7.9 in/sec) and part of the erosional zone is armored by authigenic manganese deposits, so that only limited erosion is presently occurring. Erosion and corrosion of sea-floor sediments by abyssal currents probably are in dynamic equilibrium with sediment supply. The present erosional zone is largely a relict feature inherited from late Miocene time when strongly increased glaciation of West Antarctica produced large volumes of bottom water that scoured the sea floor. A deeper unconformity dating to the early Oligocene marks the onset of significant abyssal circulation in the basins, and current-controlled deposition of sediments is well defined above this unconformity. In contrast, an underlying basal Eocene unconformity shows no marked effects of control by abyssal circulation, although erosion/corrosion by weak, deep currents could have occurred. The unconformity formed primarily because of reduced sediment supply, caused by elevated sea level and probably low productivity in surface waters.
Figures & Tables
The result of a session at the 1981 AAPG Annual Meeting, this volume attempts to document global age and magnitude of sea-level shifts, and ultimately, the cause of the short-term shifts. Twelve individual papers were published on topics such as: comparative anatomy of cratonic unconformities; relation of unconformities, tectonics, and sea-level change; outcrop features and origin of basin margin unconformities; significant unconformities and the hiatuses represented by them; regional unconformities and depositional cycles; relative sea-level changes during the Middle and Late Cretaceous; Late Oligocene-Pliocene transgressive-regressive cycles of sedimentation; oxygen-isotope record of ice-volume history; oceanic ridge volumes and sea-level change; Jurassic unconformities, chronostratigraphy, and sea-level changes; Cenozoic regional arosion of the Abyssal sea floor; and depositional sequences and stratigraphic gaps on submerged United States Atlantic margin.