More Dating of the Chicxulub Impact

Evidence found at the spectacular fossil bed at ‘Tanis’ has been trickling out for several years now.  This site has remains that appear to be the result of a gigantic tsunami that was produce by the Chicxulub impact.  The initial evidence was consistent with earlier findings that the impact was probably in the springtime.

This winter, two studies document the evidence of the springtime impact.

One study focusses on examination of the bones of the fish, which have seasonal growth rings not unlike tree rings [4]. The other study has a second indicator of growth, and also includes evidence that insects were spawning, which would presumably happen in spring [3]. Together, there is strong evidence that the animals were (a) alive at the time of the impact and (b) it was springtime.

Kewl!

One implication of this finding is that if it was springtime, then animals and plants might have been more vulnerable in the northern hemisphere than the south.  South of the equator, animals would be entering fall dormancy.  If the animals were in winter burrows, they might have been more protected from the immediate impact.  Up north of the equator, animals and plants would have been in critical breeding periods, and possibly more vulnerable.

“It is therefore plausible that this phenomenon predisposed an asymmetric pattern of extinction between the northern and southern hemispheres.”

([4], p. 6)

“We postulate that the timing of the Chicxulub impact in boreal spring and austral autumn was a major influence on selective biotic survival across the Cretaceous–Palaeogene boundary.”

([3], p. 91)

Given earlier studies that indicated these same general conclusions, I was pleased but not surprised by these findings.

But I was surprised that the popular reports reported this seasonal dating as and “exciting new finding” [1, 2] (here, here).  Sigh.  Exciting?  Yes.  New? Not really.

Anyway, this site is giving us incredibly and detailed picture of that day.

One thing that has not been reported, as far as I know, is what they have found of dinosaurs.  Early comments suggest that there may be direct evidence that dinosaurs were among the casualties.  This would finally end any question of whether dinosaurs were extinct before the impact.

There may also be evidence for activity immediately after the disaster, such as scavenging, or the blooming of plants. This would tell us something about what might have survived the impact, and how the aftermath unfolded.

As Jonathan Amos puts it, “If you haven’t yet heard of Tanis, you’re going to – a lot – over the next few years.”

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1. Jonathan Amos, ‘Dinosaur asteroid’ wrought springtime devastation, in BBC News – Science & Environment, February 24, 2022. https://www.bbc.com/news/science-environment-60495951
2. Kenneth Chang, The Dinosaur Age May Have Ended in Springtime, in New York Times. 2022. https://www.nytimes.com/2022/02/23/science/dinosaur-extinction-spring.html
3. Robert A. DePalma, Anton A. Oleinik, Loren P. Gurche, David A. Burnham, Jeremy J. Klingler, Curtis J. McKinney, Frederick P. Cichocki, Peter L. Larson, Victoria M. Egerton, Roy A. Wogelius, Nicholas P. Edwards, Uwe Bergmann, and Phillip L. Manning, Seasonal calibration of the end-cretaceous Chicxulub impact event. Scientific Reports, 11 (1):23704, 2021/12/08 2021. https://doi.org/10.1038/s41598-021-03232-9
4. Melanie A. D. During, Jan Smit, Dennis F. A. E. Voeten, Camille Berruyer, Paul Tafforeau, Sophie Sanchez, Koen H. W. Stein, Suzan J. A. Verdegaal-Warmerdam, and Jeroen H. J. L. van der Lubbe, The Mesozoic terminated in boreal spring. Nature,   2022/02/23 2022. https://doi.org/10.1038/s41586-022-04446-1

Evidence of Fallout from the Chicxulub Impact?

There is quite a bit of news about the first reports of a fossil bed that appears to record a massive die out due to falling debris—right at about the time of the Chicxulub impact.  This could be a snapshot of the actual event, showing the devastation hundreds of kilometers from the crater.

The first official paper describing the site is just published [1].  There is also a popular article in The New Yorker, published simultaneously (“The Day the Earth Died” [2]). The latter gives us the Hollywood version, which is romantic, if not totally convincing.

But let’s look at the scientific paper.

The finds are in the Hell’s Creek area, which is one of the richest fossil beds, particularly for Cretaceous dinosaurs.  At the time of the deposits, it was the northern end of a sea that extended from the Gulf of Mexico.  The deposit has been tagged ‘Tanis’ (more Hollywood), and is reported to lie between known Cretaceous and Paleocene strata—right where traces of Chicxulub are found world wide.

“the Cretaceous and Paleogene strata are separated by the Event Deposit” ([1], p. 3)

However, this deposit isn’t a centimeter thin layer of distinctive fallout as found all over the world. It is a thick and complicated jumble, 1.3m deep.  The deposits seem to be multiple, violent surges and retreats, which carried live and recently dead animals and plants. Much of the material is charred, indicating it was burned or burning at the time of deposit.

There are also many ejecta characteristic of a meteor strike.  These range in size up to a centimeter or so. These  molten blobsresemble the Chicxulub ejecta found elsewhere, and the size distribution varies over the depth as would be expected from heavier particles falling first. There are also spherules captured in amber which were preserved in original form, and also some found in the gills of fish.  The latter suggests that the fish were alive during the fallout.

The jumbled remains include many plants and animals in incredibly complete preservation.  This is interpreted as indicating that they were killed in a massive flood, or series of floods, rather than deposited after death.  In any case, the materials described are incredibly, absurdly, insanely rich!

The researchers speculate that this represents flooding caused by the Chicxulub impact, which likely caused magnitude 11 earthquakes, as well as the rain of hot molten rock that set fire to forests.  They hypothesize a time line that puts these events within the first hours after the impact—making it a picture of the actual event as it happened.  Which is, like wow!  The greatest find since Schliemann at Troy!

they also suggest that the well preserved carcasses on the top surface show no signs of scavengers, suggesting that there weren’t any animals alive.

“The absence of scavenging despite the shallow burial of plentiful, large carcasses and the lack of root traces along the upper surface of the Event Deposit may suggest a depleted local biodiversity after deposition ” ([1], p.8)

This paper is mainly describing the deposit and the overall picture.  This paper has very little information about the plants and animals found, and the evidence of the ecology at the time of the event.

One of the questions not answered yet is the presence of dinosaurs, and generally what was living at the time of the disaster.  The popular article indicates that one dinosaur bone was found, at the top of the deposit [2].  This might be evidence that the dinosaurs were, indeed, still around at the moment of the impact, which would settle a long-standing controversy as to whether the dinosaurs were actually wiped out by the strike, or were already dying out from other causes.

There are said to be more papers in the pipeline, which will presumably fill in these details

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This is clearly a spectacular site. It seems too good to be true, which is why people are being cautious.  The swashbuckling backstory also raises worries about overly optimistic interpretation.  This is a fascinating site, though it might not be exactly what De Palma et al. think it is at this time.

It is good to see that considerable expertise has already been brought in (the coauthors are a solid group), and we can expect a lot more careful attention now that they are finally publishing.

As they note, there is so much material here, it will take decades to sift through it.  I think we’re all eager for more.

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1. 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, and Walter Alvarez, A seismically induced onshore surge deposit at the KPg boundary, North Dakota. Proceedings of the National Academy of Sciences:201817407, 2019. http://www.pnas.org/content/early/2019/03/27/1817407116.abstract
2. Douglas Preston, The Day the Earth Died, in The New Yorker. 2019. p. 52-65. https://www.newyorker.com/magazine/2019/04/08/the-day-the-dinosaurs-died

Another great name for a band:

Chicxulub ejecta