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Re: craters and the k/t



Norm King wrote:

>I don't believe they found undisturbed Maastrichtian sediments within the 
>[Chicxulub] crater.

Actually, it was upper Campanian AND Maastrichtian sediments in the cores,
according to the Officer et al. data.

> One question is how to show sediments are really _undisturbed_.
>Others are how far "inside" is "inside", and what do you mean by 
>"inside"?

Some of the cores are tens of kilometers within the crater boundary.

> Sediments deposited over the top could now have settled into
>the crater by the eventual compaction of debris below them, so they now 
>lay opposite older Maastrichtian sediments in the crater wall.  Or, other 
>sediments may have slumped into the crater in large pieces that appear 
>undisturbed.  Yet another question is whether a K/T boundary as 
>identified on the basis of marine microfossils (as at Chicxulub) would 
>match a K/T boundary as identified on the basis of terrestrial fossils, 
>if it is the dinosaur's demise on land that we're ultimately intersted 
>in.  Still another question is, how did they date the Maastrichtian 
>sediments in the crater?  Could the biostratigraphic indices be reworked? 

Neither Officer et al. NOR the standard model folks have published plates of
the appropriate microfossils, the strat ranges in the sections, etc.
Officer et al. seem to imply that the upper Campanian and Maastrichtian
microfossils are in proper strat sequence.

>This is only the second meteorite ever recoverd in any DSDP or ODP core, 
>anywhere.  It came from the cm or so thick K/T layer in that downrange 
>core.  The question might be, "Is that just a coincidence?"  Might be, 
>but I don't like these one in a million coincidences.

Nevertheless, there are a lot of coincidences going on at the K/T.  Some
ultra-impactors reject the idea that the Deccan Traps or the Maastrichtian
Regression were going on before the impact, because "it is too much of a
coincidence".  Of course, this ignores the basic geological evidence, which
documents both these events as beginning well before the boundary.

>>> I don't know about the rest of you, but finally the number of
>>>observations that fit together so nicely in the impact scenario
>>>become so great that I find it impossible to believe that they are
>>>all coincidences.

See above.

Sherry wrote:

>>We also never have found an increase of fossils after the K-T that would 
>>suggest a sudden massive death event. Also, why would the effects of the 
>>impacts effect some animals and not others?

There is some good taphonomic work being done to show that a "bone spike"
would be unexpected by even this scale an impact.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661

"There are some who call me...  Tim."