Re: Chracoal & K/T Unconformity

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Soot and charcoal are two different things. Both soot and charcoal can be
the result of natural processes (as pointed out by Timothy Jones). As Tim
also pointed out, charcoal (and presumably soot) are by no means rare in
the stratigraphic record. If you are going to talk about a global soot (or
charcoal) anomaly that is linked to a single impact event you are going to
have to demonstrate (not assume) that the anomalous layers are synchronous
and that they occur in temporally complete successions.  This hasn't been
done.  In fact, the biostratigraphy of several of the sections Tom Lipka
mentions in his comment are demonstrably incomplete. Without a complete
section you don't know whether you are dealing with a true anomaly or an
artificial concentration.  However, if the anomaly doesn't show up in
sections that can be demonstrated to be complete, you're justified in being
a little suspicious.

This also goes for the d13C spike discussed by Ivany and Salawich.  The
deep-sea sections from which they recovered their d13C anomalies all have
biostratigraphically incomplete records (as Gerta Keller and I pointed out
in our comment on the Ivany and Salawich paper, see Geology, Dec. 1993).
Ivany and Salawitch tried to counter our comment by making some general
criticisms of graphic correlation which, in my opinion, are both incorrect
and irrelevant.  [Note: graphic correlation was not used to contruct our
estimates of the completeness of these deep sea sections.  However, the
MacLeod and Keller (1991) graphic correlation for Brazos River was recently
confirmed by Stein et al. (1994, AMOCO Field Trip Guidebook) using
independent evidence from several different microfossil groups.]  The fact
remains that none of the sections from which the Ivany and Salawitch data
come contain the lowermost Danian planktonic foraminiferal biozone or any
evidence for the lowermost part of the overlying Zone P1a (see Fig. 1 from
our comment).  Indeed, half of their sections don't even contain an Ir
anomaly (which some impact proponents use to locate the K-T boundary).
Prior to the Ivany and Salawich paper Barrera and Keller (1990:
Paleoceanography, v. 5) demonstrated that the d13C excursion was gradual
across the boundary at Brazos River. Subsequent work has confirmed this at
Nye Klov (Schmitz et al., 1992, P3; Keller et al., 1993, GSA Bulletin;).
These authors link the gradual change in d13C values throughout the
uppermost Maastrichtian-lowermost Danian interval to terrestrially-driven
climate changes, not with impact-induced wildfires. Both Brazos River and
Nye Klov show every indication of being temporally complete K-T boundary
sections (e.g., complete set of biostratigraphic zones, Ir anomaly, Ni-rich
spinel anomaly, etc.) whereas none of the deep-sea cores used by Ivany and
Salawich can be judged complete on independent evidence.

I'm not familiar with the detailed stratigraphy of the Turkmenistan
section, but I do know that Stvens Klint is another demonstrably incomplete
K-T succession (see Schmitz et al., 1993).  For a different
(non-catastrophic) interpretation of the pollen spike see Sweet et al.
1990, GSA Special Paper 247.




Norm MacLeod




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Norman MacLeod
Senior Scientific Officer
N.MacLeod@nhm.ac.uk (Internet)
N.MacLeod@uk.ac.nhm (Janet)

Address: Dept. of Palaeontology, The Natural History Museum,
         Cromwell Road, London, SW7 5BD

Office Phone: 071-938-9006
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