Specifically, it already treats an arbitrary number of sediment particle size classes, an arbitrary distribution of sediment fractions among those size classes, and an arbitrary number of vertical sublayers of user-defined thicknesses in the water column above the continent. Therefore, detailed treatment of bedload is already an available feature. Currently, the number of sediment classes is chosen to be three, with particle sizes of 0.063 mm, 0.25 mm, and 1.0 mm, and class fractions of 0.70, 0.20, and 0.10. Currently, there are eight layers in the water column, with the thickness of the bottommost layer of 1 cm. With these default choices, MABBUL’s current treatment of the 0.063 mm fine sand particles should be doing a respectable proxy job of representing behavior of flocculating clay and carbonate particles. A desirable future enhancement certainly would be to include suitable diagnostics to track and output formation of these rock species, including predicted the bedforms. Even so, MABBUL already accounts for these main aspects of turbulent transport and deposition of sediment particles at the small spatial scales. C. Megasequences—A new causal explanation As previously discussed, the fossil-bearing sediment record displays a structure consisting of six massive sediment layer packages known as megasequences separated from one another by global-scale erosional unconformities. This paper offers an explanation for this striking feature. The explanation relates to a crucial aspect of the CPT framework, namely, the imperative of rapid and extraordinary cooling of the newly forming ocean plates. The reason is that all the pre-Flood seafloor gets recycled into the mantle well before the continents reach their current locations. Without extra cooling of the newly forming ocean lithosphere, the runaway process would cease, and CPT would come to an abrupt halt. Since the first paper on CPT (Baumgardner 1986) it has been assumed that the enhanced cooling of the new oceanic lithosphere occurred at a steady and uniform rate. However, as discussed earlier, having this cooling instead occur in discrete episodes yields abrupt drops in global sea level and provides a simple means for explaining the erosional unconformities that bound the megasequences above and below. From its beginning the CPT framework already included one such episode to account for the runoff of water from the continents at the close of the Flood. The new approach includes six additional episodes. In quantitative terms, the amount of new ocean lithosphere generated by rapid seafloor spreading during the Flood, apart from any enhanced cooling, would produce some 5,400 m of cumulative sea bottom rise. The new approach assumes an episode of cooling sufficient to cause a 700 m drop in average sea bottom height and produce the erosional unconformity observed at the base of each of the six megasequences for a total of 4,200 m of cumulative sea bottom drop. A final episode of cooling at the top of the sixth megasequence results in an additional 1,200 m of sea bottom drop, corresponding to the runoff phase of the Flood. This final sea bottom drop therefore restores the global sea level to what it was before the onset of the cataclysm. Note that this final cooling episode brought the temperature profile of oceanic lithosphere quickly to what we observe it to be presently. The resulting drop in global sea level allowed the water that had covered the continent surfaces to drain rapidly back into the deepened ocean basins, which moved significant quantities of sediment from continent interiors to the continental shelves. Notably, this episode of lithospheric cooling also caused the earth’s outer shell of rock to become dramatically more rigid and less deformable. This, in turn, caused plate speeds to plummet and CPT to end. Before such abrupt sea bottom drops were incorporated into the MABBUL framework, the authors were uncertain whether the numerics would remain stable. We were pleased to find that MABBUL could accommodate 700 m drops in the mean sea bottom height, each during a time span of 24 hours, with no discernable negative consequences. As expected, a significant fraction of the water that had been on the continent surfaces drains back into the ocean following each episode of sea bottom drop. As of yet MABBUL does not have diagnostics to characterize the sedimentary signature of these episodes of dramatic sea level drop in a satisfactory manner. In the rock record a notable feature associated with some of the megasequence boundaries are extensive sandstone sheets just above those boundaries. Examples include the Tapeats Sandstone at the base of the Sauk megasequence and the St. Peter Sandstone at the base of the Tippecanoe megasequence. What MABBUL with its present diagnostics does show clearly, however, is that as the tsunami-driven pulses of sediment-laden water move inland, there is a progression in particle size deposition, with coarsest particles falling from suspension first and depositing closest to the coast and finer particles remaining in suspension longer and depositing further inland. Just how that sediment distribution is modified in MABBUL in response to an abrupt sea level drop followed by a steady sea level rise accompanied by repetitive tsunamis is a topic for future study. To the authors it will not be surprising if the result is a laterally extensive sandstone sheet extending inland from the continent margin. D. New possible trigger for runaway subduction Alongstanding enigma in the framework of catastrophic plate tectonics has been what initiated the peeling away of oceanic lithosphere at the earth’s surface and its sinking into the mantle in a runaway manner? The proposal that the cause for the erosional discontinuities that form the megasequence boundaries was sudden and extraordinary cooling of oceanic lithosphere resulting in an abrupt drop in global sea level logically brings with it a possible mechanism for the initiation the CPT cataclysm itself. In very brief terms, such an abrupt cooling of the rock layer beneath the ocean bottom increases its density appreciably and also makes it significantly more unstable to runaway sinking into the mantle below. Not only does the proposed cooling episode at the base of the Sauk megasequence appear to account for the spectacular megabreccia deposits along the western margin of North America (Sigler and Van Wingerden 1998; Van Wingerden 2003) and other evidences of extreme catastrophism at the stratigraphic discontinuity known as the Great Unconformity, it also provides a simple and yet plausible triggering mechanism for the runaway motions within the mantle that drive the entire ensuing cataclysm. This proposed trigger relies on no intermediate mechanisms or hypotheses but instead upon God’s direct supernatural intervention. VI. CONCLUSION Numerical simulation offers a means for investigating phenomena that are impossible, either because of their physical scale or the BAUMGARDNER AND NAVARRO Large tsunamis and Flood sediment record 2023 ICC 384
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