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Re: The dinosaurs did not die in fire, from the latest Geology



"James R. Cunningham" <jrccea@bellsouth.net> writes:
> Phil Bigelow wrote:
> > And if
> > there is a lack of both components in the boundary zone, then the 
> data
> > tells the researcher nothing.
> 
> Doesn't it tell you that atmospheric circulation patterns were such 
> that
> fine particulate matter associated with the impact and/or fires 
> didn't
> reach that site in any quantity?  That's useful information re 
> seasonal
> flows and weather.


You raise a good point.  If there were global wild fires, then there
would be two sources for charcoal:  local soot (in abundance, assuming
that the paleolocality wasn't a desert); and air-fall soot that was blown
in from parts unknown.  Both soots contribute, but the local source would
contribute more, particularly if the sample site is a paleosol where a
lot of charcoal was created _in situ_.

I would venture a wild guess that the local source of soot would "swamp
out" the global soot's signature.  In any case, it doesn't matter,
because if enough good quality sample sites yield the same results, then
the individual contributions from local and world-wide sources become
irrelevant (although such a discrimination of soot types would be a
worthy scientific study in its own right). 

The big problem is in finding "good quality sample sites".  Using the
Hell Creek Formation as an example, the following types of paleo-terrain
can be identified:

- paleosols (ancient soils, usually inter layered with overbank mud)
- overbank deposits (mud from flooding, essentially)
- channel deposits
- point bar deposits
- stagnant water deposits (swamps and oxbows)
- lake deposits

The only environments that could be expected to preserve a reasonably
intact iridium signature are lakes and stagnant water environments. 
Unfortunately, these two environments are rare (accounting for maybe 2-5%
of the total volume of the Formation.  90+% of the Hell Creek Formation
is composed of overbank deposits which have been trampled and tunneled by
animals.  Thin chrono-layers become unrecognizable in these environments.

Note that research papers always give Lat./Long. coordinates for
terrestrial iridium sites, rather than providing the vertical distance
from the base of the Formation.  That's because the iridium "layer" is
always incomplete.

In order to get enough data points to make their research meaningful,
workers must resort to sampling less than ideal paleoenvironments (such
as overbank and paleosols).  This introduces a ton of ambiguity into the
results.  The author(s) know this.  It doesn't make their results
worthless, but it opens the door for reinterpretation by another worker.


> > Phrased another way:  The researchers' premise is that soot and
> > iridium-laden dust are both delicate atmospheric precipitates, and 
> if
> > both events occurred, and if one component is *preserved* at a 
> particular
> > K-T boundary layer site, then the other component *must* be 
> preserved
> > there as well.  Any anomaly from the expected result can be used 
> as
> > evidence for falsification of the world-wide wildfire hypothesis.  
> This
> > is a reasonable premise.


> This is not a reasonable premise. Original deposition of iridium 
> from
> impact detritus and de-orbiting of ejecta cannot be expected to be
> associated with fire initiation in a 1 to 1 correlation.


I may not have made my point very clear.  Two phenomena are in play here:

- Chronostratigraphic resolution (in other words, determining how long an
"event" took to deposit a thin layer, and;

- Stratigraphic integrity (in other words, have some components in the
layer been altered or removed?).

Regarding the first phenomenon, I think its safe to say that if a global
wild fire occurred, then both the air fall iridium and the air fall soot
were deposited *geolgically* simultaneously. With our current technology
we can't distinguish a few days of Cretaceous time from a few years of
Cretaceous time.  So "simultaneously" is used rather loosely here.

Regarding the second phenomenon: I am making an assumption (which may or
may not be true) that if the iridium-laden dust wasn't removed by
erosion, then the intermixed/overlying air fall soot (if any soot was
originally present) couldn't have been removed by erosion either.  In
other words, if subsequent flooding removed the iridium layer, then it
also would have removed the soot.  A somewhat sloppy analogy can be found
in the kitchen.  Mix wheat flour with corn flour.  Then try to figure out
how to remove one of the two components from the mix.  It ain't easy, and
I assume that Nature couldn't do a good job of separating them either. 
BTW:  neither iridium nor soot is soluble in water (even in highly acidic
water), so dissolution is not a consideration.

Of course, none of the above comments apply to _in situ_ charcoal
(charred roots, stumps, etc.).  There is still so much that we don't know
about the boundary zone that its ridiculous.

Thanks for letting me ramble.


<pb>
--








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