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Re: The dinosaurs did not die in fire, from the latest Geology
"James R. Cunningham" <firstname.lastname@example.org> writes:
> Thomas R. Holtz, Jr. wrote:
[from the _Geology_ abstract]:
> > Tertiary sedimentary rocks of six non marine sequences (Colorado
> > Saskatchewan) contain no charcoal or below-background levels of
> charcoal and
> > a significant quantity of noncharred organic materials, revealing
> that there
> > was no distinctive wildfire across the North American continent
> related to
> > the K-T event.
The question is, did the latest research results *successfully* falsify
the earlier hypothesis of Wolbach, Anders and others? I would say,
"possibly" (with some quantifications). Their highest quality data came
from those sites where there is a big iridium spike AND a lack of soot.
Their "worst" data came from those boundary sites where both the iridium
spike and soot concentration are only slightly above background. And if
there is a lack of both components in the boundary zone, then the data
tells the researcher nothing.
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.
But I needn't remind the group that sampling as little as a few feet
above a known iridium spike layer will tell the researcher nothing,
because the results cannot be time-correlated with the impact event.
That sample could be used as a control, however.
Unfortunately, control samples can bite you in the butt. Modern wildfire
analogs reveal a major problem when one tries to chose control samples.
Modern soils can exist for a thousand+ years, and they can collect the
soot from tens (if not hundreds) of wildfires. One stratigraphic inch of
modern soil may represent 100 years of accumulation, and it may contain
soot from 3 wildfires separated by 30 years. Similarly, if we pick a
randomly chosen paleosol layer in the middle to bottom part of the Hell
Creek Formation, what are the chances that that particular paleosol
contains soot from one or more non-impact related wildfires? I'd say the
chances are pretty good. Therefore, if the control samples from the Hell
Creek formation paleosols usually record wildfires, then it makes sense
that soot present in the K-T boundary layer would also be in "background"
concentrations even though a fire might have occurred during the
deposition of the K-T boundary layer.
The biggest problem encountered in sampling is that of preservation. Not
all time-equivalent deposits are preserved in the stratigraphic record,
and this applies particularly to the thin air-fall layers deposited in
non-marine environments. Can we still identify the Mount Saint Helens
ash *layer* in a cow-trampled field in Ellensburg, WA?
The presence or absence of impact air-fall deposits at any given boundary
site strongly depends on local K-T erosion (or lack there-of) and on the
degree of K-T and post-K-T bioturbation (if any). Intraformational
erosion can strip the evidence away, and bioturbation can dilute the
evidence (sometimes down to background levels). The corollary to this is
that we are lucky to have ANY preserved K-T boundary air-fall impact
deposits. To expect air-fall deposits to be found in all K-T boundary
layers world-wide is naive. "Absence of evidence is not evidence of
I think the latest research goes a long way toward addressing the
question of whether world-wide K-T wildfires scorched our planet. But I
doubt that it will be the last word on the subject.
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