This article is from
Journal of Creation 35(2):3–4, August 2021

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Passive margins explained by Flood runoff

by Michael J. Oard

Passive margins are offshore continental margins not associated with an active plate margin. Instead, they are a shallow continental shelf that dips gently seaward to the drop-off of the continental slope, which becomes less steep on the continental rise.

Continental margin profiles in general are like deltas, except that the margins are basically continuous around all of the earth’s continents. This likely evinces sheet deposition during the Recessive Stage of the Flood.^1-3

According to plate tectonics, many passive margins formed on the edges of continents that rifted away from mid-oceanic ridges, thereby opening new oceans. Passive margins are found on both sides of the Atlantic Ocean and formed after spreading began. Coastal Great Escarpments, high cliffs or steep slopes close to the coast are found around many passive margins.⁴

Offshore areas subside, inland areas rise

The cause of passive margin uplift is unknown, since many mountain ranges in the plate tectonics paradigm are claimed to have uplifted by plate or continental convergence. Thus, many models have been suggested: “Even in the case of elevated continental margins such as in Scandinavia, Greenland, eastern Australia and southern Africa, various mechanisms are proposed.”⁵ Uniformitarian geologists propose the offshore area subsided due to thermal cooling after spreading and collected an enormous amount of sediment, while the onshore area rose, partly due to erosion and isostatic uplift. An escarpment formed on the continent and retreated inland. A planation surface formed early that is now above the escarpment, while another one formed below the scarp, supposedly over a long period of erosion.

The southern Africa passive margin

The story above is how uniformitarian geologists say the semi-continuous coastal Great Escarpment with its associated planation surfaces supposedly formed over 3,500 km around southern Africa (figure 1).⁶ The escarpment has retreated inland about 100–200 km, assuming it started at or near the coast as many believe. Yet, some think the scarp retreated little from its current position and mainly eroded downward. The planation surface above the escarpment is up to 3,000 m above sea level at the Drakensberg of southeast Africa.⁷ The coastal area is a dissected erosion surface.

The escarpment was formed on different rock types, with only local modification due to different rock types.⁸ As such, the erosion seems to have paid little attention to the hardness of the rocks, which runs counter to the normal expectations of the uniformitarian paradigm. Ollier and Marker state: “The geological relationships thus show that the Great Escarpment is essentially erosional in origin while structure is of secondary importance.”⁹

The escarpment crosses areas with a great variety of climates, ranging from warm humid to arid.¹⁰ However, it remains similar regardless of the current climate; the climate seems to have had no impact on the origin or erosion of the escarpment. This also is unexpected within the uniformitarian paradigm.

While southern Africa was rising, the adjacent offshore areas were sinking and collecting the sediments that had eroded off the continent. South African geomorphologist, Lester King, commented on the dip of the seismically imaged sediments eroded from the continent to the offshore margin of southeast South Africa, indicating uplift during sedimentation:

“We note that all the formations drilled dip offshore. The oldest and deepest formations dip at several degrees, the youngest and uppermost dip at less than one degree … . As the monoclinal tilting is always seaward, the land always moves up, the ocean floor always goes down [emphasis added].”¹¹

The latter statement is a clear statement of Psalm 104:8 by a uniformitarian geomorphologist! It confirms that the continents rose at the same time the ocean basins sank. The hinge line, which divides the rising land to the west in southeast Africa from the subsiding crust to the east, is close to the coast.

The Namibia passive margin

Drawn by Melanie Richard

The escarpment along the passive margin of southern Africa ends just north of Namibia. Many believe this passive margin formed 130 million years ago with the breakup of the Pangean supercontinent.¹² The coastal Great Escarpment in Namibia is about 100 km inland and about 800 m high, which separates the coastal plain from the African plateau that covers 25% of Africa. The origin of the abnormal elevation of the plateau or planation surface is debated, with the time of its rise estimated anywhere from the Triassic to the late Cenozoic.¹³ A coastal erosion surface is nearly flat with inselbergs, such as 600-m high Spitzkoppe. On the African plateau, several vast planation surfaces, separated by erosional scarps and dissected by rivers, are believed to exist. Apparently, the African plateau is not one continent-scale planation surface that was later faulted or folded to different elevations as some uniformitarian scientists believe.^14,15 Instead, it consists of several. Regardless, the origin of these planation surfaces is highly debated:

“The inner parts of the continents are largely shaped by planation surfaces; the genesis of these surfaces have [sic] generated numerous debates between geomorphologists for more than a century.”¹⁶

Several mechanisms for the Namibian passive margin uplift have been proposed, but some believe the deformation started only 10–20 Ma ago, 100 Ma after rifting. This conflicts with the assumption that the continental rifting caused the uplift. Another mechanism is ‘dynamic uplift’ caused by mantle flow. Picart et al. add their mechanism:

“Therefore, we propose that the upper Cenozoic deformation of the Namibian plateau resulted from two successive processes. Variations in the spreading rate at the end of the Eocene generated the bulging of the coastal domain. The steepening of the slopes increased erosion and the retreat of the scarp. The mass loss was compensated by isostasy which maintained the upward motion and propagated it slightly inland”¹⁷

The escarpment is believed to have retreated inland at a rate of 5–7.5 km/Ma.¹⁷ The mechanism for uplift and escarpment retreat seems unlikely. How can changes in spreading rates well out in the Atlantic affect the coastal uplift? Besides, steep slopes normally should become less steep with time due to mass wasting and rock fall.

Summary of uniformitarian difficulties

The above is evidence that uniformitarian scientists have a poor understanding of the cause of passive margin uplift, its erosion, the formation of planation surfaces, and origin of the Great Escarpment. There are four main difficulties. First, erosion should have been greater at higher elevations, and it is not.

Second, erosion should preferentially erode the softer rocks, but escarpment erosion affected similarly both soft and hard rocks.

Third, the escarpments still maintain steep slopes. If they were tens of millions of years old, they should have lost their steepness.¹⁸

Fourth, river valleys are generally perpendicular to the escarpments in the coastal sections. The river valleys have vertical walls and incomplete incision as though they have not yet adjusted to the uplift.⁸ The vast erosion of the escarpment, therefore, is more likely to be rapid and recent.

Noah’s Flood interpretation

The features of passive margins can better be explained by Noah’s Flood. The coastal Great Escarpments first formed by continental uplift while the ocean basins sank during the draining of the floodwater. Whatever the geomechanical reasons for this uplift (it is currently unknown), the pattern fits well with enormous continental erosion that took place during the Recessive Stage of the Flood. It is the type of erosion one would predict during a retreating ‘waterfall’ as water flowed off of the rising land toward the sinking ocean. But this waterfall would be hundreds to possibly thousands of kilometres long, which would place it during the Sheet Flow Phase of Noah’s Flood. Sheet erosion would have little concern for the hardness of the rocks or the present climate, and explains the large number of planation surfaces that take no notice of rock lithology or the present climate. Based on the volume of sediments offshore, the erosion over Namibia was immense. It appears that the average vertical erosion was about 2,400 m.¹⁹

Conclusion

Uniformitarian scientists have several difficulties explaining passive margin uplift. This is especially the case with the Great Escarpment that rims southern Africa. The erosional profile of the Great Escarpment does not fit uniformitarian expectations. However, it fits very well the catastrophic erosion of the Sheet Flow phase of the Recessive stage of the Flood.