ALBERT

Description: SEDIMENT TRANSPORT AND DISTRIBUTION IN THE ARGENTINE BASIN. 4. BATHYMETRY OF THE CONTINENTAL MARGIN, ARGENTINE BASIN AND OTHER RELATED PROVINCES. CANYONS AND SOURCES OF SEDIMENTS1" By ALBERTO G. LONARDI* and MAURICE EWING ABSTRACT More than 152,500 km of precision sounding lines collected mostly by Lamont Geological Observatory up to February 1967 have been complemented with spaced soundings to construct a chart of the detailed submarine topography of the western South Atlantic, for the area located between 27°S and 57°S, and 28°W and 76°W. Seismic reflection data have been used to correlate the sediment distribution pattern and associated basement rock with the resulting configuration of the sea floor. On the basis of this comparative study the main physiographic provinces have been represented, defined and briefly described. Particular attention is given to the morphology of the Argentine continental margin and to its relation with other provinces. This study reveals that the Argentine Continental Slope and Rise are dissected by 70 submarine canyons, two of which, Ameghino Transverse Canyon and Almirante Brown Transverse Can- yon, trend parallel to the regional isohaths. The greatest regional erosion is found on the Continental Slope between 42°S and 46°S (Ameghino canyon system). Many of the 30 canyons identified in this region are tributaries of the Ameghino and Almirante Brown Transverse Canyons. Several submarine canyons are grouped off the Rio de la Plata, the major Argentine river, but are not as deeply incised as those of the Ameghino system. Topography of the group suggests that the axis of discharge of the Rio de la Plata during glacial stages was more to the south than at present and that the position of the river probably shifted with time. The genesis of all canyons studied along the continental margin can be reasonably related to Pleistocene glacial outwash drainages. The Polonio Fault, located off Uruguay, is the only evidence of major recent tectonism along the margin. Newly identified physiographic provinces include: the Lower Plateau off Brazil, the Malvinas Outer Basin, the Rio Grande Abyssal Plain, the North Georgia Abyssal Plain, the Eastern Enclosed Abyssal Plain, sedimentary ridges of regional extent and area covered by the giant ripples in the Argentine Oceanic Rise, and three major trenches with associated ridges in the Scotia Basin.

Description: Published

Description: The results of 57 seismic-refraction profiles recorded in the South Atlantic Ocean south of 47°S are used to describe the gross structure of the Scotia Sea basins, the Falkland plateau, and, to a lesser extent, the North Scotia and South Sandwich ridges. The Drake passage and Scotia Sea basins have normal or nearly normal oceanic crust. Their floors are covered by 300–1000 meters of sediment, except in a band in the western part, where the sediment cover is thin and nonuniform. There is direct correspondence between the position of the band of thin sediments and the position of a low oceanic ridge, as defined by morphology, seismic refractions, magnetic lineations, and earthquake epicenters; this correspondence suggests that the band may represent young oceanic crust produced by sea-floor spreading. Scouring or nondeposition due to strong bottom currents may also have reduced accumulation in this band. The Falkland plateau is a southward-tilted continental block capped by a thick wedge-shaped body of sediments, the top-most layers of which continue farther south to form the floor of the adjacent Falkland trough. The section beneath the Falkland trough is similar to a depressed or subsided oceanic crust overlain by 4 km of low-velocity sediments.

Description: Published