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| Fossilized fish piled one atop another, suggesting that they were flung ashore and died stranded together on a sand bar after the wave from the seiche withdrew. Photo credit: Robert DePalma |
66 million years ago, the world changed suddenly and without warning. The Cretaceous era ended, virtually instantaneously, and gave way to the Triassic.
The cause was a massive chunk of rock hurtling in from space, super-heating the atmosphere, and crashing into Earth, setting off a chain of events which exterminated the large dinosaurs and much else - and cleared the way ultimately for the rise of mammals and birds.
The asteroid impacted at Chicxulub on Mexico's Yucatán Peninsula. The earth and the asteroid turned liquid with the heat of the impact, exploding liquid glass spheroids high into the atmosphere to rain down again like red hot bullets. The impact set off a seismic shockwave with catastrophic tsunamis which surged up river valleys, destroying everything in their path. These surges of salt and fresh water are known to science as seiches.
And now scientists believe they have found the result of one site of devastation, some 3000 Km from the Chicxulub impact site, at the Tanis deposit in North Dakota, USA. They have found the fossilised, chaotic debris left by one such surge. The species in the jumble are of course only the species that were around at the time, including freshwater sturgeons, apparently suffocated by the glass beads that rained down, blocking their gills.
Fossilised fish are normally found lying parallel to the rock strata in which they became buried, having died and settled on the sea or lake bed to be covered by more sediment in due course. At the Tanis site, however, they are preserved haphazardly along with tree trunks. Some of them are near vertical, suggesting that they and the trees were caught up in a large volume of mud and sand that was deposited simultaneously, just as you would expect of a tsunami-like surge.
The team led by Robert A. DePalma published their findings in PNAS a few days ago.
Significance
The Chicxulub impact played a crucial role in the Cretaceous–Paleogene extinction. However the earliest postimpact effects, critical to fully decode the profound influence on Earth’s biota, are poorly understood due to a lack of high-temporal-resolution contemporaneous deposits. The Tanis site, which preserves a rapidly deposited, ejecta-bearing bed in the Hell Creek Formation, helps to resolve that long-standing deficit. Emplaced immediately (minutes to hours) after impact, Tanis provides a postimpact “snapshot,” including ejecta accretion and faunal mass death, advancing our understanding of the immediate effects of the Chicxulub impact. Moreover, we demonstrate that the depositional event, calculated to have coincided with the arrival of seismic waves from Chicxulub, likely resulted from a seismically coupled local seiche.
Abstract
The most immediate effects of the terminal-Cretaceous Chicxulub impact, essential to understanding the global-scale environmental and biotic collapses that mark the Cretaceous–Paleogene extinction, are poorly resolved despite extensive previous work. Here, we help to resolve this by describing a rapidly emplaced, high-energy onshore surge deposit from the terrestrial Hell Creek Formation in Montana. Associated ejecta and a cap of iridium-rich impactite reveal that its emplacement coincided with the Chicxulub event. Acipenseriform fish, densely packed in the deposit, contain ejecta spherules in their gills and were buried by an inland-directed surge that inundated a deeply incised river channel before accretion of the fine-grained impactite. Although this deposit displays all of the physical characteristics of a tsunami runup, the timing (<1 hour postimpact) is instead consistent with the arrival of strong seismic waves from the magnitude Mw ∼10 to 11 earthquake generated by the Chicxulub impact, identifying a seismically coupled seiche inundation as the likely cause. Our findings present high-resolution chronology of the immediate aftereffects of the Chicxulub impact event in the Western Interior, and report an impact-triggered onshore mix of marine and terrestrial sedimentation—potentially a significant advancement for eventually resolving both the complex dynamics of debris ejection and the full nature and extent of biotic disruptions that took place in the first moments postimpact.
Robert A. DePalma, Jan Smit, David A. Burnham, Klaudia Kuiper, Phillip L. Manning, Anton Oleinik, Peter Larson, Florentin J. Maurrasse, Johan Vellekoop, Mark A. Richards, Loren Gurche, Walter Alvarez
A seismically induced onshore surge deposit at the KPg boundary, North Dakota
Proceedings of the National Academy of Sciences Apr 2019, 201817407; DOI: 10.1073/pnas.1817407116
Copyright © 2019 the Author(s). Published by PNAS.
Open Access
Reprinted under the terms of a Creative Commons Attribution 4.0 International License 4.0 (CC BY).
In fairness, I should point out that not everyone agrees that the Tanis deposit was the result of the Chicxulub impact, just as not everyone agrees that the impact was the cause of the K-T extinction. Near simultaneous volcanic activity in what is now India could have been the primary cause, although the impact could have triggered the volcanic activity. A devastating tsunami could have been caused by other seismic activity of course. The glass beads associated with the Tanis deposit are difficult to explain unless they had been deposited earlier in the mud and sand the tsunami swept up.
But for a creationist, what actually caused the devastating flood with its jumble of fossils of trees and animals mixed up with mud and sand and lying haphazardly, is irrelevant. What they can see is what we would expect to see covering Earth to a dept of many metres is the biblical flood had actually happened. They can now look at the result of a mass extinction cause by a devastating flood and see what one would look like.
What they see might well have to be ignored by the creationist industry. We should see it everywhere, but we don't. If we see anything like it we see it locally and containing just the species that were alive at that moment in time. The results of a biblical flood on an Earth on which there had never been any evolution or plate tectonics, would be a higgledy-pig deposit containing not just a snapshot of local flora and fauna at that point in time, but species from all continents and all era.
There is no such deposit.
The one thing that would be the inevitable and unavoidable result of catastrophic global flood is missing. The one prediction that can be made with any certainty from the hypothetical global flood is falsified by simple observation. Tweet
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