Guest geology by David Middleton
Cenozoic Era: The Era of New Life
Who would have ever guessed that details about the first day of the Cenozoic Era might have been preserved the stratigraphic record?
Sep 09, 2019
Rocks at Asteroid Impact Site Record First Day of Dinosaur ExtinctionAUSTIN, Texas — When the asteroid that wiped out the dinosaurs slammed into the planet, the impact set wildfires, triggered tsunamis and blasted so much sulfur into the atmosphere that it blocked the sun, which caused the global cooling that ultimately doomed the dinos.
That’s the scenario scientists have hypothesized. Now, a new study led by The University of Texas at Austin has confirmed it by finding hard evidence in the hundreds of feet of rocks that filled the impact crater within the first 24 hours after impact.
The evidence includes bits of charcoal, jumbles of rock brought in by the tsunami’s backflow and conspicuously absent sulfur. They are all part of a rock record that offers the most detailed look yet into the aftermath of the catastrophe that ended the Age of Dinosaurs, said Sean Gulick, a research professor at the University of Texas Institute for Geophysics (UTIG) at the Jackson School of Geosciences.
“It’s an expanded record of events that we were able to recover from within ground zero,” said Gulick, who led the study and co-led the 2016 International Ocean Discovery Program scientific drilling mission that retrieved the rocks from the impact site offshore of the Yucatan Peninsula. “It tells us about impact processes from an eyewitness location.”
The research was published in the Proceedings of the National Academy of Sciences on Sept. 9 and builds on earlier work co-led and led by the Jackson School that described how the crater formed and how life quickly recovered at the impact site. An international team of more than two dozen scientists contributed to this study.
[…]
UT News
This bit is really interesting:
The evidence includes bits of charcoal, jumbles of rock brought in by the tsunami’s backflow and conspicuously absent sulfur.
While paleoclimatological evidence for a post-Chicxulub global cooling/darkening is limited (Vellekoop et al., 2014), the absence of sulfur-rich rocks in the crater backfill is a pretty good indication that the sulfur-rich evaporite rocks in the impact area were vaporized.
The first day of the Cenozoic
Abstract
PNAS
Highly expanded Cretaceous–Paleogene (K-Pg) boundary section from the Chicxulub peak ring, recovered by International Ocean Discovery Program (IODP)–International Continental Scientific Drilling Program (ICDP) Expedition 364, provides an unprecedented window into the immediate aftermath of the impact. Site M0077 includes ∼130 m of impact melt rock and suevite deposited the first day of the Cenozoic covered by <1 m of micrite-rich carbonate deposited over subsequent weeks to years. We present an interpreted series of events based on analyses of these drill cores. Within minutes of the impact, centrally uplifted basement rock collapsed outward to form a peak ring capped in melt rock. Within tens of minutes, the peak ring was covered in ∼40 m of brecciated impact melt rock and coarse-grained suevite, including clasts possibly generated by melt–water interactions during ocean resurge. Within an hour, resurge crested the peak ring, depositing a 10-m-thick layer of suevite with increased particle roundness and sorting. Within hours, the full resurge deposit formed through settling and seiches, resulting in an 80-m-thick fining-upward, sorted suevite in the flooded crater. Within a day, the reflected rim-wave tsunami reached the crater, depositing a cross-bedded sand-to-fine gravel layer enriched in polycyclic aromatic hydrocarbons overlain by charcoal fragments. Generation of a deep crater open to the ocean allowed rapid flooding and sediment accumulation rates among the highest known in the geologic record. The high-resolution section provides insight into the impact environmental effects, including charcoal as evidence for impact-induced wildfires and a paucity of sulfur-rich evaporites from the target supporting rapid global cooling and darkness as extinction mechanisms.
The very high sediment accumulation rate in the crater enables very detailed resolution of the events 65 million years ago. While the exact day of the impact can’t be identified, the events of that day and the following weeks can be reconstructed in great detail.
The paper is pay-walled; but it might just be worth $10. The SI includes this seismic profile, showing how their core ties into the crater.
Just 60 km away from the impact site, the Yaxcopoil-1 CSDP core encountered a thick evaporite sequence just below the layer of impact breccia:
Lithologies of units A, C, D and F are dominated by dolomites and anhydrites and indicate restricted interior carbonate platform environments (Fig. 2). Dolomites were likely deposited in very shallow
Stinnesbeck et al., 2004
subtidal to intertidal environments, as also indicated by the presence of mudstone lithologies, anhydrite nodules, laminated dolomite of likely stromatolitic origin, and the generally low abundance of megafossils (only rare bivalve fragments). Miliolids are often the only benthic
foraminifera recovered from these intervals and they are very rare. Alternating sequences of anhydrite and dolomite and massive anhydrite units are interpreted to indicate deposition in sabkha environments.
Anhydrite (CaSO4) is one of the most common evaporite minerals.
It’s been estimated that the Chicxulub impact may have injected far more sulfate aerosols into the upper atmosphere than any other known Phanerozoic Eon impact event.
[T]he total sulfur degassing from the evaporite-rich sediments in the Chicxulub impact site may have led to formation of 3.8 × 1018 to 1.3 × 1019 g sulfate aerosol, and global atmospheric mass loading from the sulfate aerosol alone is estimated to be of the order of 1–2.6 g cm−2.
Sigurdsson et al., 1992
To provide a frame of reference, Mount Pinatubo only injected about 20 million metric tons of sulfur dioxide into the stratosphere:
Several eruptions during the past century have caused a decline in the average temperature at the Earth’s surface of up to half a degree (Fahrenheit scale) for periods of one to three years. The climactic eruption of Mount Pinatubo on June 15, 1991, was one of the largest eruptions of the twentieth century and injected a 20-million ton (metric scale) sulfur dioxide cloud into the stratosphere at an altitude of more than 20 miles. The Pinatubo cloud was the largest sulfur dioxide cloud ever observed in the stratosphere since the beginning of such observations by satellites in 1978. It caused what is believed to be the largest aerosol disturbance of the stratosphere in the twentieth century, though probably smaller than the disturbances from eruptions of Krakatau in 1883 and Tambora in 1815. Consequently, it was a standout in its climate impact and cooled the Earth’s surface for three years following the eruption, by as much as 1.3 degrees F at the height of the impact.
USGS
In terms of sulfate aerosols, the Chicxulub impact could have been the equivalent of 190,000 to 1,900,000 Mount Pinatubos.
Had the impact occurred in an area devoid of sulfur-rich evaporites, the K-Pg extinction would have been far less severe.
Funny things
Mount Pinatubo injected about 20 million metric tons of sulfate aerosols into the stratosphere and caused about 0.7 °C of cooling, offsetting over 100 years of Gorebal warming for about three years. Pinatubo also injected about 50 million metric tons of CO2 into the atmosphere and caused no warming.
The Chicxulub impact put 190,000 to 1,900,000 Mount Pinatubos worth of sulfate aerosols into the upper atmosphere within a few days and left a big @$$ mark in the stratigraphic record. Humans have accounted for less than 1% of the cumulative CO2 emissions since 1751, yet we’re supposedly causing a “climate crisis” that rivals the PETM, Chicxulub impact and end-Permian extinction combined (Sarc?).
Did you ever wonder why past examples of volcanic greenhouse gas driven climate crises don’t seem to survive scrutiny?
While it has been proposed that intense volcanic release of carbon dioxide in the deep geologic past did cause global warming, and possibly some mass extinctions, this is a topic of scientific debate at present.
USGS
There is virtually no evidence that past volcanic releases of CO2 actually caused any discernible warming. Seawater pCO2 was higher before and after the oft-cited Paleocene-Eocene Thermal Maximum (PETM), which was sort of contemporaneous with the emplacement of the North Atlantic Large Igneous Province..
Note how the PETM (55 Ma) is about as far from a CO2 analog to modern times as it possibly could be… unless the PETM stomata data are correct, in which case AGW is even more insignificant than previously thought.
Regarding temperatures, the PETM is also about as far from being an analog to modern times as it possibly could be.
The Cretaceous and Paleogene Periods were warm. Whatever impact-related cooling that did occur, was of too short a duration to be resolved. But at least there’s some evidence for it. It has been postulated that the the initial effect of the Chicxulub impact was a sharp rise in temperature associated with the fireball and subsequent firestorms, followed by aerosol-induced cooling and then greenhouse warming (?)…
While there is evidence of the first two phases, the subsequent greenhouse warming is entirely speculative, based on recent assumptions about climate sensitivity to CO2. Assumptions that were largely scoffed at as recently as the late 1970’s.
Suggestion that changing carbon dioxide content of the atmosphere could be a major factor in climate change dates from 1861, when it was proposed by British physicist John Tyndall.
[…]
Unfortunately we cannot estimate accurately changes of past CO2 content of either atmosphere or oceans, nor is there any firm quantitative basis for estimating the the magnitude of drop in carbon dioxide content necessary to trigger glaciation. Moreover the entire concept of an atmospheric greenhouse effect is controversial, for the rate of ocean-atmosphere equalization is uncertain.
Dott & Batten, 1976
The same assumption, that the high CO2 levels can be directly related to increased volcanic activity during the mid-late Cretaceous Period, is not well-supported by any observations, present or past.
The highest Cretaceous CO2 levels preceded the 125-115 Ma peak in volcanic activity by 15 million years.
Nor is there a particularly good correlation between atmospheric CO2 and temperature…
If there was a clear relationship between volcanic activity, CO2 and temperature, we should see it in the rocks, particularly the basalt formations of the Columbia River Basalt Group (CRBG), the most recent, and best preserved flood basalt sequence.
According to Kashbohm & Schoene (2018)…
Flood basalts, the largest volcanic events in Earth history, are thought to drive global environmental change because they can emit large volumes of CO2 and SO2 over short geologic time scales. Eruption of the Columbia River Basalt Group (CRBG) has been linked to elevated atmospheric CO2 and global warming during the mid-Miocene climate optimum (MMCO) ~16 million years (Ma) ago. However, a causative relationship between volcanism and warming remains speculative, as the timing and tempo of CRBG eruptions is not well known. We use U-Pb geochronology on zircon-bearing volcanic ash beds intercalated within the basalt stratigraphy to build a high-resolution CRBG eruption record. Our data set shows that more than 95% of the CRBG erupted between 16.7 and 15.9 Ma, twice as fast as previous estimates. By suggesting a recalibration of the geomagnetic polarity time scale, these data indicate that the onset of flood volcanism is nearly contemporaneous with that of the MMCO.
Kashbohm & Schoene (2018)
It does appear that the timing of the vast majority CRBG eruptions can be fairly well tied down to a 700,000 to 900,000 year period coincident with the Mid-Miocene Climatic Optimum. However, even with the prodigious volume of CO2 associated with flood basalt eruptions, it’s not enough to significantly move the “climate needle”:
A statistic: It is estimated that an erupting basalt lava flow with a volume of 2000 km3 would release approximately 7 billion tonnes of carbon (or 26 billion tonnes of CO2).
This is about the same as the amount currently released by burning of fossil fuels – each year.
Saunders & Reichow
Armstrong McKay et al., 2014 estimated that the main phase of the CRBG eruptions, along with “cryptic degassing” of country rock, etc., emitted 4,090 to 5,670 billion tons of carbon over a 900,000 period. This only works out to 5-6 million tonnes of carbon per year… That’s an order of magnitude less than a rounding error. Our current 10 billion tonnes per year is only equivalent to 3% of the total annual sources in the Earth’s carbon budget. Self et al., 2005 found that CO2 emissions from flood basalt eruptions were insignificant relative to the mass of CO2 in the atmosphere and unlikely to have played a signifcant role in past episodes of “global warming.” Although they did note that the sulfur gas emissions may truly have been unprecedented.
While the impact of volcanic S gas release may be profound, the mass of CO2 directly released by individual flood lava eruptive events is tiny in comparison to the normal mass in the troposphere and stratosphere. The predicted increases in atmospheric concentration are a fraction of the current anthropogenic CO2 released from hydrocarbon burning (~25 Gt per year). Moreover, while the amount of CO2 in the atmosphere is currently ~3000 Gt, it was perhaps double this value during the late Cretaceous (i.e. ~6000 Gt). It is therefore unlikely that volcanic CO2 had a direct effect on mechanisms of global warming, supporting earlier findings by Caldeira and Rampino (1990). In addition, there would have been more than sufficient time for the extra mass of CO2 added to equilibrate, given that the lava-forming eruptive events must have been spaced at least hundreds, and probably thousands, of years apart. By contrast, SO2 emissions and the atmospheric burden of sulfate aerosols generated during flood basalt events appear to be unprecedented at any other time in Earth history. Acid rain may also have been widespread. What is less certain is whether affected biota would have had time to recover from the deleterious effects of sulfate aerosol clouds and acid rain, although quiescent intervals lasting millennia appear to offer ample time for the recovery of local biological and environmental systems (Jolley 1997).
Self et al., 2005
We can’t even be certain that the atmospheric concentration of CO2 during the Mid-Miocene Climatic Optimum was significantly elevated relative to the extremely low values of the Quaternary Period.
We can see that CO2 estimates for MMCO range from 250 to 500 ppm, rendering any efforts to draw conclusions about the CRBG and MMCO totally pointless. According to Pagani et al, 1999:
There is no evidence for either high pCO2 during the late early Miocene climatic optimum or a sharp pCO2 decreases associated with
Pagani et al., 1999
EAIS growth.
Pagani et al., suggest that changes in oceanic circulation driven by plate tectonics (opening of the Drake Passage) and the presence (or lack thereof) of a large polar ice sheet were the primary drivers of Miocene climate change, not volcanic activity. Same as it ever was…
FORECASTING THE FUTURE. We can now try to decide if we are now in an interglacial stage, with other glacials to follow, or if the world has finally emerged from the Cenozoic Ice Age. According to the Milankovitch theory, fluctuations of radiation of the type shown in Fig. 16-18 must continue and therefore future glacial stages will continue. According to the theory just described, as long as the North and South Poles retain their present thermally isolated locations, the polar latitudes will be frigid; and as the Arctic Ocean keeps oscillating between ice-free and ice-covered states, glacial-interglacial climates will continue.
Finally, regardless of which theory one subscribes to, as long as we see no fundamental change in the late Cenozoic climate trend, and the presence of ice on Greenland and Antarctica indicates that no change has occurred, we can expect that the fluctuations of the past million years will continue.
Donn, William L. Meteorology. 4th Edition. McGraw-Hill 1975. pp 463-464
Despite only having 12 years to solve the “climate crisis,” we are still living in an Ice Age, and will be so long as Antarctica remains isolated over the southern polar region, Greenland retains its ice sheet and the northern polar region retains at least seasonal ice cover.
The roughly 1.0 °C of warming since the coldest climatic period of the Holocene, the Little Ice Age, hasn’t budged us out of the Quaternary Period temperature “noise level.”
Another 0.5 to 1.0 ºC between now and the end of the century doesn’t even put us into Eemian climate territory, much less the Miocene or even the Pliocene. We will still be in the Quaternary Period noise level. Bear in mind that the instrumental temperature data are of much higher resolution than the δ18O derived temperatures. As such, the δ18O data reflect the bare minimum of dynamic amplitude range. Actual paleo temperatures would have reflected a far greater range of variability (higher highs and lower lows).
On the other hand, a Chicxulub-style impact could easily slap our rather cold climate back into Pleistocene glacial conditions faster than the Green New Deal could destroy our robust economy.
References
Armstrong McKay, David, Toby Tyrrell, Paul A. Wilson, & Gavin Foster. (2014). “Estimating the impact of the cryptic degassing of Large Igneous Provinces: A mid-Miocene case-study”. Earth and Planetary Science Letters. 403. 254–262. 10.1016/j.epsl.2014.06.040. Special thanks to David Armstrong McKay for kindly sending me a copy of his paper.
Berner, R.A. and Z. Kothavala, 2001. GEOCARB III: A Revised Model of Atmospheric CO2 over Phanerozoic Time, American Journal of Science, v.301, pp.182-204, February 2001.
Donn, William L. Meteorology. 4th Edition. McGraw-Hill 1975. pp 463-464
Dott, Robert H. & Roger L. Batten. Evolution of the Earth. McGraw-Hill, Inc. Second Edition 1976. p. 441.
Gulick, Sean P. S., et al. “The first day of the Cenozoic”. Proceedings of the National Academy of Sciences Sep 2019, 201909479; DOI: 10.1073/pnas.1909479116
Illis, B. 2009. “Searching the PaleoClimate Record for Estimated Correlations: Temperature, CO2 and Sea Level”. Watts Up With That?
Kasbohm, Jennifer, and Blair Schoene. “Rapid Eruption of the Columbia River Flood Basalt and Correlation with the Mid-Miocene Climate Optimum.” Science Advances, American Association for the Advancement of Science, 1 Sept. 2018, advances.sciencemag.org/content/4/9/eaat8223.
Pagani, Mark, Michael Arthur & Katherine Freeman. (1999). “Miocene evolution of atmospheric carbon dioxide”. Paleoceanography. 14. 273-292. 10.1029/1999PA900006.
Pearson, P. N. and Palmer, M. R.: Atmospheric carbon dioxide concentrations over the past 60 million years, Nature, 406, 695–699,https://doi.org/10.1038/35021000, 2000.
“Rate of Ocean Crust Production.” lect7-4, University of Leicester, www.le.ac.uk/gl/art/gl209/lecture7/lect7-4.html.
Royer, D. L., R. A. Berner, I. P. Montanez, N. J. Tabor and D. J. Beerling. “CO2 as a primary driver of Phanerozoic climate”. GSA Today, Vol. 14, No. 3. (2004), pp. 4-10
Self, Stephen & Thordarson, Thorvaldur & Widdowson, Mike. (2005). “Gas Fluxes from Flood Basalt Eruptions”. Elements. 1. 10.2113/gselements.1.5.283.
Sigurdsson, H., S. D’Hondt, S. Carey, “The impact of the Cretaceous/Tertiary bolide on evaporite terrane and generation of major sulfuric acid aerosol”.
Earth and Planetary Science Letters. Volume 109, Issues 3–4, 1992, Pages 543-559, ISSN 0012-821X,
https://doi.org/10.1016/0012-821X(92)90113-A.
Stinnesbeck, Wolfgang, et al. “Yaxcopoil-1 and the Chicxulub impact”. Int J Earth Sci (Geol Rundsch) (2004) 93: 1042–1065
DOI 10.1007/s00531-004-0431-6
Tripati, A.K., C.D. Roberts, and R.A. Eagle. 2009. “Coupling of CO2 and Ice Sheet Stability Over Major Climate Transitions of the Last 20 Million Years”. Science, Vol. 326, pp. 1394 1397, 4 December 2009. DOI: 10.1126/science.1178296
Vellekoop, Johan, et al. “Rapid short-term cooling at K–Pg boundary”. Proceedings of the National Academy of Sciences May 2014, 111 (21) 7537-7541; DOI: 10.1073/pnas.1319253111
Zachos, J. C., Pagani, M., Sloan, L. C., Thomas, E. & Billups, K. “Trends, rhythms, and aberrations in global climate 65 Ma to present”. Science 292, 686–-693 (2001).
An attempt to describe the event and the devastation caused by the ejecta. Some nice experiments used to illustrate the problem, including a high velocity impact cannon and a pizza oven…
2 hours, but entertaining. They got puppets!
Apocalyptical
Skip the first 19 minutes of not so funny comedy.
As, far as I can tell, all this brilliant and hipper official orthodox academic attempted explanation of Jurasic extinction, suffers in and by a single concept, or a conceptual condition;
Reversibility….
That extinction event seems to be a result of a non reversible natural condition.
The one academically considered thus far, does not offer that, and does not qualify as such…
as non reversible… it, happens to be reversible… over time.
Oh well, anything could be possible, pink unicorns have already got their own universe and an indisputable reality in what we keep calling science… or modern or post modern science.
cheers
Before discovery of the iridium layer, there was no good explanation for the end Cretaceous (not Jurassic) mass extinction event, which wiped out a lot more than just non-avian dinosaurs. An impact from space was then a radical idea. The hypothesis was confirmed by discovery of the Yucatan crater.
As I commented earlier, I’m hard-pressed to come up with a geological hypothesis that has been so consistently reinforced over time. Every discovery has built upon previous discoveries.
Yup. Reconfirmed from new finds with each passing year and decade.
Right up there with the once-denigrated “continental drift” and “Missoula floods”.
For that matter, ice ages were once doubted until repeatedly confirmed. Ditto Milankovitch cycles as an explanation thereof.
Same goes for the age of the earth.
The Cretaceous–Paleogene mass extinction event some 66.5 Ma suddenly wiped-out about 75% of the plant and animal species on Earth. With the exception of some ectothermic species such as the leatherback sea turtle and crocodiles, no tetrapods weighing more than 55 lb survived.
While the non-avian dinos get top billing, a wide range of species perished in the K–Pg extinction. It also destroyed a plethora of other terrestrial organisms, including some mammals, pterosaurs, birds (aka avian dinosaurs), lizards, insects and plants.
In the oceans, the end Cretaceous mass extinction killed off plesiosaurs and mosasaurs, giant marine lizards, and devastated fish, sharks, mollusks (especially ammonites, the entire subclass of which went extinct), and many species of plankton.
It does make you wonder though about some breakup into more than one impactor. Earth does not have the gravitation force of a Jupiter but still look at all those barbell meteors out there in observations of the solar system in recent years.
Maybe bits or pieces of it landed elsewhere, but it’s clear that an asteroid or other celestial body some seven to 50 miles in diameter, with a mass between 1.0×10^15 and 4.6×10^17 kg slammed into the Yucatan about 66.5 Ma, with serious consequences.
This amateur needs help!
Does anybody who knows this stuff tell me:
What does the fossil record show as the KT boundary is approached? Were the Dinosaurs in full bloom, the obvious dominant land vertebra like they say they were? Or , were their numbers decreasing?
There aren’t enough dinosaur fossils, nor is the distribution of fossils representative enough, to answer that. Dinosaurs were rarely preserved as fossils and only in specific types of depositional environments.
https://www.scientificamerican.com/article/what-are-the-odds-of-a-de/
The quote below comes from a article in 2010 where 41 experts confirmed that the asteroid killed off the Dinos in a few hours or weeks.
This is a caption of a picture showing a bright white line as the KT boundary.
The K-Pg boundary as exposed along the side of Interstate 25 near Raton Pass in southern Colorado. The obvious white layer is the K-Pg ejecta layer, says the University of Texas at Austin. It contains elevated levels of iridium and shocked mineral grains. Pollen and spores from Cretaceous plants are found immediately below this layer but not above it, a pattern that is seen from the southern United States all the way north to the Arctic Ocean. “This direct link between impact ejecta and plant extinction suggests a very strong cause and effect relationship between impact and extinction.”
My problem. NO mention of dinosaurs fossils. Does anybody know the answer to my question?
What are you expecting to see?
Most fossils are hard-shelled marine invertebrates. Land animals were rarely preserved as fossils. That’s why dinosaur fossils are so valuable. Outcrops of the K-Pg boundary are scattered all over the Earth, most are in marine depositional sequences. In most places, the boundary is not exposed or has been eroded away. While it is found all over the world, it is not continuous. It has been identified in scattered outcrops and cores.
Furthermore, dinosaurs didn’t cover the entire surface of the Earth. The odds of recognizable dinosaur fossils being present at any of the handful of K-Pg boundary outcrops are pretty slim. Although there have been a few…
https://www.sciencedaily.com/releases/2011/07/110712211016.htm
https://www.sciencedaily.com/releases/2019/03/190329144223.htm
Thank you for the references.
I was hoping that there would be evidence of a thriving dino population below and nada above the KT layer.
But, let’s forget dinos for a second. How about reptiles and mammals? How close beneath the KT boundary are their fossils found?
Mammals and reptiles are also poorly preserved as fossils. Mammal fossils become more abundant and diverse above the K-Pg boundary than below it. But the fossil record isn’t like a census.
Dinosaurs are reptiles. I suppose you mean other reptiles.
As David points out, the places where the Mesozoic/Cenozoic boundary is exposed on land are few. The odds of finding terrestrial tetrapod fossils above and below those scarce outcrops are thus low.
But please David’s links, especially that from this year, which discovery has previously been cited here. The site in ND contains the jumbled up remains of both marine and terrestrial organisms, assembled by the tsunami which flowed north from the Gulf of Mexico along the remnants of the Western Interior Seaway.
To wit:
“This unique, fossilized graveyard — fish stacked one atop another and mixed in with burned tree trunks, conifer branches, dead mammals, mosasaur bones, insects, the partial carcass of a Triceratops, marine microorganisms called dinoflagellates and snail-like marine cephalopods called ammonites — was unearthed by paleontologist Robert DePalma over the past six years in the Hell Creek Formation, not far from Bowman, North Dakota. The evidence confirms a suspicion that nagged at DePalma in his first digging season during the summer of 2013 — that this was a killing field laid down soon after the asteroid impact that eventually led to the extinction of all ground-dwelling dinosaurs. The impact at the end of the Cretaceous Period, the so-called K-T boundary, exterminated 75 percent of life on Earth.”
Plumage found at the Tanis site could have come from birds, but at least one big feather might be from a non-avian dinosaur.
https://www.sciencenews.org/article/new-fossils-north-dakota-dinosaur-killing-asteroid-impact
Perhaps more accurate to say seiche than tsunami, as the massive earthquakes produced sloshing. But global tsunamis also radiated out from the impact site.
I was thinking in the Western Inland Seaway. It’s uncertain whether or not it was still open to the Gulf of Mexico at he the time of the impact. If it wasn’t open, it would have been a seiche. Either way, it was catastrophic.
IMO what was left of the Seaway was very narrow in the Dakotas, and of course dry land north of there, but it was still open on the Gulf end.
http://www.elasmo.com/frameMe.html?file=paleo/texas/tx_maas.html&menu=bin/menu_fauna-alt.html
The mosasaurs and marine fish in the Tanis, ND jumbled mix also suggest that the flood, whatever it technically might have been, must have propagated from the Gulf up to the Dakotas.
Reconstructed end Cretaceous map of North America.
I’ve seen reconstructions that have it open and closed.
https://deeptimemaps.com/western-interior-seaway-thumbnails/
http://www.scotese.com/K/t.htm
DePalma describes is as “not presently known”…
https://www.pnas.org/content/pnas/116/17/8190.full.pdf
Tsunami or seiche, it was catastrophic.
The reconstruction I linked is more open, ie wider in the Dakotas, than others I’ve seen. But it appears that at least East TX was still covered by Gulf waters. How much of the rest of the Great Plains still lay under shallow seas is debatable.
The Tanis mosasaur could have come from far afield.
I’d say the last day of the Mesozoic Era rather than the first day of the Cenozoic.
That would be more accurate. The impact ended the Mesozoic.
Yup. The day started with Mesozoic species. By the end of it, they were dead or dying out.