The Floors of the Ocean: 1. The North Atlantic: Text to accompany the physiographic diagram of the North Atlantic — John Shaqi
The Floors of the Ocean: 1. The North Atlantic: Text to accompany the physiographic diagram of the North AtlanticHeezen, Bruce C.
Science
The Floors of the Ocean: 1. The North Atlantic: Text to accompany the physiographic diagram of the North Atlantic
Heezen, Bruce C.
Ocean bottom
Iberian Sector.--This sector was described by De Andrade (1937) on
the basis of a large number of discrete soundings by the Portuguese
Hydrographic Service. Relatively few echo-sounding profiles are
available for the area, and little more can be added to De Andrade's
description. The shelf in most places is less than 20 miles in width.
The few echo-sounding profiles available indicate several prominent
benches on the continental slope. Exceptionally large submarine
canyons occur off Cape St. Vincent, Setúbal, Lisbon (2), and Nazaré.
Preliminary investigations by the Lamont Geological Observatory
indicate that Tertiary sediments outcrop on the walls of Lisbon and
Setúbal canyons (Sutton _et al._, 1957). Tertiary sediments have also
been obtained by dredging and cable grappling along the continental
slope of northwest Iberia (Wiseman and Ovey, 1950).
Gibraltar Sector.--The continental margin in this sector is unique. The
straits cut through at about 200 fathoms so that profiles through the
straits show no continental shelf. A typical abrupt continental slope
is also absent since only locally do slope segments have gradients
exceeding 1:45. A series of prominent benches is seen in the sector
from profile E-7 to E-10.
The dominant bench levels in this sector are 300, 600, 850, 1300, 1700,
and 2100 fathoms. Insufficient profiles and dredgings are available
in this area to permit the correlation and dating of these benches.
Photographs in the area show sandy and rocky bottom, and thus dredging
in this area might yield rich rewards in ancient sediments. The benches
are so prominent that a detailed study of the topography should be
equally rewarding. Of particular interest is the manner in which the
broad benches in the Gibraltar area merge with the smaller benches
and breaks in slope of the steep continental slopes of Portugal and
Algeria. The topography in this sector most closely resembles that
of the northern Blake Plateau (profiles W-21, W-22) and the northern
part of the Anglo-French sector. In all these areas many benches are
developed, and steep slopes are only locally developed.
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