Jump to content

Intriguing Finds at KPg boundary in North Dakota


Intrigued

Recommended Posts

If the Chicxulub crater is the smoking gun for the impact theory on the KPg extinction event, then these findings from North Dakota by DePalma and his colleagues are one of the ricochets. Here is the 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."

The full article is available here on PNAS.

 

Link to comment
Share on other sites

Thank you for presenting this.

It seems a fine example of all the hard work that goes into infilling our knowledge between major breakthroughs.
Most Science is actually like this, lacking the glamour of the big breakthrough but totally necessary supporting work.

 

I particularly like the colour pcitures, I'm glad to see they are finally making their way into papers.

Perhaps you have more of the same up your sleeve?

+1

Link to comment
Share on other sites

17 hours ago, studiot said:

It seems a fine example of all the hard work that goes into infilling our knowledge between major breakthroughs.
Most Science is actually like this, lacking the glamour of the big breakthrough but totally necessary supporting work.

For sure. I would break the routine work into two categories. The fisrt would be the confirmation and detailing work, following major breakthroughs, that you mention. The second is more purely observation, devoid of hypothesis,  that contributes to the next breakthrough. Unfortunately, publication is more likely if the observations are clearly associated with the current paradigm. I think this can lead to shoehorning a suite of observations into that paradigm, when a more accurate approach would be to say "Here's something we noticed, though we have no idea what caused it."

I am now quaking with fear that someone will ask me for a "for instance". To forestall this I suggest the Sudbury Igneous Complex that was long thought to be a conventional igneous intrusion, but is now recognised as an impact melt from a large bolide.

18 hours ago, studiot said:

I particularly like the colour pcitures, I'm glad to see they are finally making their way into papers.

I'm just glad that pictures, whether black or white, in current publications are clear and informative, rather than the washed out greys of poor quality photo copies.

 

18 hours ago, studiot said:

Perhaps you have more of the same up your sleeve?

The difficulty is in discerning what might interest others. Can you be more specific as to what might capture your interest?

 

3 hours ago, michel123456 said:

I am not sure that the flow direction is axial. If i remember correctly deposits of branches from a regular wave at the beach is mostly parallel to the shore, not axial. IOW maybe the flow is perpendicular and not axial. Simple guess.

I'm not quite following you Michel. Could you expand on that a little? I'm missing something. (Probably brain cells. :))

Link to comment
Share on other sites

5 hours ago, Intrigued said:

 

 

I'm not quite following you Michel. Could you expand on that a little? I'm missing something. (Probably brain cells. :))

I mean, a branch on a wave does not take the position of the surfer.

A surfer will go on its axis & ride the wave. But if you take a simple plank, or a branch, it will float in a parallel way to the wave and be let on the shore this way.

Have you made a small experience of how a tsunami would have let the dead fish on the shore? Would the fish be oriented (as you say) axially in the direction of the wave, or perpendicular to the direction?

Link to comment
Share on other sites

Cherry picking this picture in order to explain:

2053364069_ScreenShot04-03-19at01_52PM.JPG.312725ee4cb0f142e49dc91702d058c7.JPG

 

Of course there are other pictures showing more random distributions, but I couldn't spot any where the fish is oriented perpendicular to the shore.

Edited by michel123456
Link to comment
Share on other sites

Thank you for your picture Michel, here are my thoughts.

 

Firstly I have identified quite a few fish roughly perperndicular to the general trend, although I agree the preponderance is parallel to the shoreline.

 

fish1.jpg.6cf34a9aa4afd4d602409ffef0fa0f0f.jpg

 

Secondly this stretch of water is clealy not open. That is it is a narrow channel between two shores, perhaps an estuary.

Such narrow channels have currents and/or tidal streams that flow parallel to the shorelines so there will be a stronger parallel distributing mechanism as compared to a plain shore set against open water.

Even a plain shore will have curves and inlets that are again roughly perpendicular to the main trendline of the shore, thus providing opportunity for some fish to be distibuted nearly perpendicular to others. Such a promentory can be seen Above the E of my added wording.

 

The distribution mechanism and resulting orientation is an interesting point you have raised, but is there enough information in the study to draw any firm conclusion?

 

Edited by studiot
Link to comment
Share on other sites

3 hours ago, studiot said:

Thank you for your picture Michel, here are my thoughts.

 

Firstly I have identified quite a few fish roughly perperndicular to the general trend, although I agree the preponderance is parallel to the shoreline.

 

fish1.jpg.6cf34a9aa4afd4d602409ffef0fa0f0f.jpg

 

Secondly this stretch of water is clealy not open. That is it is a narrow channel between two shores, perhaps an estuary.

Such narrow channels have currents and/or tidal streams that flow parallel to the shorelines so there will be a stronger parallel distributing mechanism as compared to a plain shore set against open water.

Even a plain shore will have curves and inlets that are again roughly perpendicular to the main trendline of the shore, thus providing opportunity for some fish to be distibuted nearly perpendicular to others. Such a promentory can be seen Above the E of my added wording.

 

The distribution mechanism and resulting orientation is an interesting point you have raised, but is there enough information in the study to draw any firm conclusion?

 

I believe one interesting factor is the following: do the branch have the same orientations with the fish? If yes, then it would show that the fish were dead before being deposited by the sea. If not (a random or other disposition) it would show that the fish were alive, for example as the result of being hunted, disoriented or sick.

Or eventually the extraordinary event of the  Chicxulub impact would have produced an extraordinary deposit, and that makes sense too.

Edited by michel123456
Link to comment
Share on other sites

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.