44 Origin and Morphology of Ocean Margins
The tenus pelagic and neritic refer to marine organisms as well as sediments, and
mean open ocean and coastal, respectively. Littoral, etc. down to hadal, refer to
water depths. Littoral ist the same as intertidal, meaning between tides. Supralittoral
refers to the spray zone, sublittoral to offshore from the tidal area.
2.2 Margins Are Sediment Traps
The continental margins are the dumping site for the debris coming from the continents,
the terrigenous sediments. The margins are also the most fertile parts of the ocean, where
productivity is high. Thus, much organic matter becomes buried within the continental
debris. If contidions are right, over millions of years, this organic material can eventually
develop into petroleum. This happened, of course, in the Gulf Coast area, where oil is
found buried under immense masses of sediment (see Chap. 10).
Which margins are likely to have thick sediment wedges? It is reasonable to
expect that an ocean basin draining a large land area, per unit area of ocean (Table 2.2), is going to have a thick accumulation of sediment. Indeed, the margins of the
Atlantic Ocean have very thick wedges of sediment, up to 10 km and more. The
Atlantic also has the largest proportions of slope and continental rise areas of the
major ocean basins (Fig. 1.3). The reason for this is not only sediment supply, but
also the fact that the Atlantic margins are old "trailing edges" and have not been
disturbed by tectonic processes, other than sinking, for a long time.
Tabe 2.2. Land and ocean areas and drainage. (After H. W. Menard and S. M. Smith, 1966, J
Geophys Res 71 p 4305, and other sources)
Area
% of Earth
Drained
Ocean area
Average
(10 6 km 2 )
surface
land area b
land area
depth of water
(10 6 km 2 )
(km)
Asia
44.8
8.7
Europe
10.4
2.1
Africa
30.6
6.0
North America
22.0
4.3
South America
17.9
3.5
Antarctic
15.6
3.1
Australia
7.8
1.5
Pacific
181.3 a
35.4
18
10:1
4.0
(166.2)
(4.2)
Atlantic
106.6 a
20.8
67
1,6:1
3.3
(86.8)
(3.8)
Indian Ocean
74.la
14.5
17
4,3: 1
3.9
(73.4 )
(3.9)
a Including adjacent seas (Black sea, Mediterranean and Arctic included with Atlantic).
Numbers in parentheses: without adjacent seas.
b Excluding areas with interior drainage, and Antarctic.
The tenus pelagic and neritic refer to marine organisms as well as sediments, and
mean open ocean and coastal, respectively. Littoral, etc. down to hadal, refer to
water depths. Littoral ist the same as intertidal, meaning between tides. Supralittoral
refers to the spray zone, sublittoral to offshore from the tidal area.
2.2 Margins Are Sediment Traps
The continental margins are the dumping site for the debris coming from the continents,
the terrigenous sediments. The margins are also the most fertile parts of the ocean, where
productivity is high. Thus, much organic matter becomes buried within the continental
debris. If contidions are right, over millions of years, this organic material can eventually
develop into petroleum. This happened, of course, in the Gulf Coast area, where oil is
found buried under immense masses of sediment (see Chap. 10).
Which margins are likely to have thick sediment wedges? It is reasonable to
expect that an ocean basin draining a large land area, per unit area of ocean (Table 2.2), is going to have a thick accumulation of sediment. Indeed, the margins of the
Atlantic Ocean have very thick wedges of sediment, up to 10 km and more. The
Atlantic also has the largest proportions of slope and continental rise areas of the
major ocean basins (Fig. 1.3). The reason for this is not only sediment supply, but
also the fact that the Atlantic margins are old "trailing edges" and have not been
disturbed by tectonic processes, other than sinking, for a long time.
Tabe 2.2. Land and ocean areas and drainage. (After H. W. Menard and S. M. Smith, 1966, J
Geophys Res 71 p 4305, and other sources)
Area
% of Earth
Drained
Ocean area
Average
(10 6 km 2 )
surface
land area b
land area
depth of water
(10 6 km 2 )
(km)
Asia
44.8
8.7
Europe
10.4
2.1
Africa
30.6
6.0
North America
22.0
4.3
South America
17.9
3.5
Antarctic
15.6
3.1
Australia
7.8
1.5
Pacific
181.3 a
35.4
18
10:1
4.0
(166.2)
(4.2)
Atlantic
106.6 a
20.8
67
1,6:1
3.3
(86.8)
(3.8)
Indian Ocean
74.la
14.5
17
4,3: 1
3.9
(73.4 )
(3.9)
a Including adjacent seas (Black sea, Mediterranean and Arctic included with Atlantic).
Numbers in parentheses: without adjacent seas.
b Excluding areas with interior drainage, and Antarctic.