Tremendous Erosion of Continents

Receding waters

The Recessive Stage of the Flood

by Michael J. Oard

This article is from the peer reviewed technical “Journal of Creation”

The Recessive Stage of the Flood was a time of intense continental erosion. The erosional debris formed the continental margin—a continuous wedge of mostly compacted sediments surrounding the continents. If we can determine which part of this wedge is composed primarily of detritus eroded during the Recessive Stage, some later cementing to sedimentary rock, then estimating the volume of those sediments and rocks could provide a rough quantitative estimate of material eroded from the continents. At present, a total value is not possible, but such an estimate can be made for select areas, providing a methodology that can be expanded to other marginal areas. One such area is the central Appalachian Mountains of the United States and its downgradient continental margin. Research shows an approximate average of 6,000 m of erosion across the Blue Ridge and Piedmont provinces. Another area is the continental margin off south-western Africa. Estimates there show an average 2,400 m of rock eroded off the adjacent continent. Erosion was probably greater in the coastal mountains and plains. Evidence from inselbergs on the coastal plain indicates that this erosional event was as rapid as it was significant. If representative, these studies show that much more sedimentary rocks and sediments existed on the continents than the present average of 1,800 m. Since a large proportion (about 30% or more) of the margin sedimentary rocks are Cenozoic, the Flood/post-Flood boundary must be in the late Cenozoic, assuming the geological column is an accurate chronostratigraphic representation of the rock record.

The Recessive Stage of the Flood was a period of significant continental-scale erosion.1,2,3 It was likely composed of two phases, the Ablative or Sheet Flow Phase followed by the Dispersive or Channelized Flow Phase.4 Thus, channelized erosional features would be superimposed upon the sheet flow eroded features. This prediction is borne out in many places, including the south-west Colorado Plateau of the USA (figure 1), which shows large-scale planation, followed by dissection into canyons and valleys. The first type of erosion has been called the Great Denudation in which an average of about 3,000 m of sedimentary rock was eroded from the south-west Colorado Plateau, leaving behind a vast planation surface (figure 2).5 The eroded volume there is within the estimated 2,500 to 5,000 m of average erosion for the whole Colorado Plateau.6The second erosional event is called the Great Erosion with Grand Canyon and Zion Canyon, Utah, being examples of dissection, corresponding to the more channelized erosion late in the Flood.7 But this erosion was not limited to the Colorado Plateau. When Flood water flowed from the continents into the newly deepening ocean basins, the same kind of erosion probably occurred. Equally significant volumes of rock were eroded from other areas, as shown by: erosional remnants, such as Devils Tower;8 eroded anticlines, such as the San Rafael Swell9 on the north-west Colorado Plateau (figure 3); and great Coastal Escarpments, such as the 3,500-km-long escarpment that rings southern Africa.10 This escarpment is about 3,000 m high in south-eastern Africa, but only about 1,000 m high in south-western Africa.

The sediment eroded would have been transported downgradient, and deposited at places where the flow velocity dropped quickly, typically due to a major depth increase in the water—conditions met almost universally along the continental margins. The continental margin consists of the continental shelf, slope, and rise (figure 4), and is composed of a continuous wedge of mostly sediments around all the continents and even large islands. It is one of the most significant geomorphological features on our planet. The sediments in the continental shelf reach 20 km or more in thickness (about 30% of which is likely Cenozoic), but vary in both lateral extent and thickness, depending on the location. These sediments were most likely deposited by sheet flow off the land. Later, after the bulk of sediments had been deposited, channelized erosion was caused by strong currents that swept in wide channels across the sedimentary surface and eroded submarine canyons.11,12

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