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Creation 39(4):41–44, October 2017

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Continental margins

Their rapid formation during Flood runoff

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continental-margins

During the last half of Noah’s Flood, the rising continents caused the Flood water to flow into the sinking ocean basins.1,2 These fast-moving, massive currents eroded vast amounts of sediment that had been laid earlier in the Flood, and carried it away. The water travelled so fast that little sediment was deposited on land. It wasn’t until the currents reached the oceans that they were able to slow enough to deposit their load.

The continental margin

All continents (and large islands) are surrounded by a continental margin, a continuous band of mostly sedimentary rock (figure 1). This makes up some 20% of the ocean floor; the rest is the deep ocean basins (abyssal plains).

Continental margins consist mainly of a continental shelf and a continental slope, although there is considerable variety (see box next page).

Continental shelf

NOAA
Figure 1. The continental margin shown in light blue (NOAA).
schematic-Atlantic
Figure 2. Schematic of an Atlantic type margin.

The continental shelf is relatively flat, dipping down very gently (less than 0.1°) as it extends out from the shoreline to the shelf break or shelf edge, which is where the continental slope begins (figures 2 and 3). Its width varies considerably from several kilometres (a few miles) to more than 400 km (250 miles); the average is 80 km (50 miles). At least one shelf is over 1,000 km (600 miles) wide.3 Very wide shelves are found along the Arctic Ocean, Bering Sea, and the Grand Banks, Newfoundland (figure 1).

Continental slope

At the edge of the continental shelf, at a consistent average depth of about 130 m (430 ft), the slope of the seafloor suddenly increases from nearly flat to about 4°, all the way down to depths of 1,500 to 3,500 m (4,900 to 11,500 ft). This is the continental slope, and if all the water were removed from the oceans, it would be the most conspicuous geomorphological boundary on Earth (figure 4).

In a few places on some continental margins the slope can be much steeper than average—up to 90°.

Margin sedimentary rocks

schematic-Pacific
Figure 3. Schematic of a Pacific type margin.

The sedimentary rocks within the continental margin can be extremely thick—over 20 km (12 miles) deep in places, especially in buried basins.4 The sedimentary units are generally sheet-like, thickening seaward with a slight dip (figure 5). This profile reinforces the evidence for a broad scale uplift of the adjacent continental area while the continental margin sank thousands of metres during its sedimentation.5 The ‘hinge line’ that separates inland uplift from offshore sinking is near the coast.

Geomorphologist Lester King sum-marized:

drop-off
Figure 4. The nearly flat continental shelf and the drop-off of the continental slope of the southeastern United States (NOAA). The drop-off is especially steep in the north where it descends down to the continental rise.
There have been repeated tectonic episodes: always in the same sense—the lands go up and the sea floor down… (emphasis mine).6

This is consistent with Psalm 104:8, describing the draining of the Flood water: “The mountains rose, the valleys sank down to the place that you appointed for them”.

The continental margin—a mysterious geomorphic feature

Although few scientists address this issue, the continental shelf and slope are very difficult to explain within the uniformitarian (slow and gradual) paradigm. Non-catastrophic processes would favour a gradual descent of sediments to the ocean depths. There really should be no continental shelf or slope (see dashed line on figure 6). King described the problem:

“Briefly the shelf is too wide, and towards the outer edge too deep, to have been controlled by normal wind-generated waves of the ocean surface” (emphasis mine).7

Present processes would not form such a profile. Hedberg also stated, “…there is considerable controversy as to the origin in detail of continental slopes. It seems evident that there is no unique answer.”8

The reason there should be a gradual descent to the deep sea is that most ocean currents are wind-generated. (Sinking of denser, salty water at high latitudes is only a minor factor, although some scientists think otherwise.)9 Because of the prevailing winds, ocean currents are commonly parallel to the coast, such as the Gulf Stream off the East Coast of the United States.10 A uniformitarian would thus expect sediments to spread out first and then slide down into the deep ocean.

seaward
Figure 5. Seaward thickening wedge of sedimentary rocks.
Atlantic-type-margin
Figure 6. The principal features of an Atlantic-type margin compared with the margin that should occur (dashed line) if formed by normal wind-driven currents in the ocean today. Vertical exaggeration is about 1/50.

The Genesis Flood formed the continental margin

Since continental shelves and slopes surround all of the continents, sheet deposition (which implies strong currents) seems the only reasonable way to explain their existence. This would correspond with the first half of the Retreating Stage of the Flood in Walker’s model11 when currents were very wide, possibly hundreds or even thousands of kilometres wide.

Sometimes, the dip of the sedimentary rocks in the continental margin increases seaward, forming what are called delta-like features. This indicates the depositional current was flowing offshore and not parallel to the shoreline as expected from wind-generated currents.

Hedberg states: “Reflection profiling has shown that many slopes in their present form are the result of prograding sedimentation.”8

Prograding means that the sediment was deposited by currents that moved perpendicularly away from the continents,12 unlike the typical parallel-to-shore currents we see today.

Today, when a flooding river enters a larger body of water, it deposits its sediment load in the form of a delta. By analogy this sheds light on the origin of the continental shelf and slope. The top of the delta would represent the continental shelf; the delta edge would correspond to the continental slope. Continental margins represent a global phenomenon that gives powerful evidence for the global Flood. This speaks strongly against the idea that the world’s sedimentary layers formed slowly over ‘millions of years’.

(1) The Atlantic type margin: this is generally seismically inactive—i.e. few earthquakes and volcanoes (figure 2).

(2) The Pacific type margin—seismically active (figure 3).1

In addition to the shelf and slope, Atlantic margins include the added feature of a continental rise. Pacific margins usually possess a deep-sea trench instead of a continental rise.

The profile of the Antarctica continental shelf differs from others because the weight of the ice sheet has not only pushed down the land but also the continental shelf.

  1. Kennett, J., Marine Geology, Prentice-Hall, Englewood Cliffs, NJ, pp. 23–30, 1982.

References and notes

  1. Oard, M.J., Massive erosion of continents demonstrates Flood runoff, Creation 35(3):44–47, 2013; creation.com/flood-runoff. Return to text.
  2. Oard, M.J., How did the waters of Noah’s Flood drain off the continents? Creation 37(3):28–31, 2015; creation.com/flood-drain. Return to text.
  3. Hedberg, H.D., Continental margins from viewpoint of the petroleum geologist, AAPG Bulletin 54(1):6–7, 1970. Return to text.
  4. Whittaker, J.M. et al., Global sediment thickness dataset updated for the Australian-Antarctic Southern Ocean, Geochemistry, Geophysics, Geosystems 14(8):3297–3305 | doi:10.1002/ggge.20181, 2013; ngdc.noaa.gov/mgg/sedthick/sedthick.html; The deepest sediments are in the northern Gulf of Mexico, off the east coast of North America, and in the Bay of Bengal. There is no data from the Arctic Ocean, but the sedimentary rocks are very thick along that margin. Return to text.
  5. Pazzaglia, F.J. and Gardner, T.W., Late Cenozoic flexural deformation of the middle U.S. Atlantic passive margin, J.Geophysical Research 99(B6):12,143–12,157, 1994 and Poag, C.W. and Sevon, W.D., A record of Appalachian denudation in postrift Mesozoic and Cenozoic sedimentary deposits of the U.S. middle Atlantic continental margin, Geomorphology 2(1–3):119–157, 1989. Return to text.
  6. King, L.C., Wandering Continents and Spreading Sea Floors on an Expanding Earth, John Wiley and Sons, New York, NY, p. 200, 1983. Return to text.
  7. King, ref. 6, p. 199. Return to text.
  8. Hedberg, ref. 3, p. 11. Return to text.
  9. Wunsch, C., An oceanographer charts the ebb and flow of opinion on ocean currents, Nature 439(7076):512–513, 2006. Return to text.
  10. Kennett, J., Marine Geology, Prentice-Hall, Englewood Cliffs, NJ, p. 241, 1982. Return to text.
  11. Walker, T., A Biblical geological model; in: Walsh, R.E. (Ed.), Proceedings of the Third International Conference on Creationism, technical symposium sessions, Creation Science Fellowship, Pittsburgh, PA, pp. 581–592, 1994; biblicalgeology.net. Return to text.
  12. Oard, M.J., Coastal Great escarpments caused by Flood runoff, Creation 37(4):46–48, 2015 has in its figure 6 a schematic of the Flood formation of the continental shelf. Return to text.

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