Re: Chracoal & K/T Unconformity (from T.R. Lipka)

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Date
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From: Tompaleo@aol.com
Date: Sun, 16 Jul 1995 23:31:08 -0400
To: paleonet-owner@nhm.ac.uk
Subject: Re: Chracoal & K/T Unconformity
Status: O



inking that the absence of charcoal, and (even
> If a K/T fireball
>burned away everything in that area (as has been suggested by many
>impact-extinction proponents) one would expect severe mass wasting.  That's
>what happens after the landscape is denuded by forest fires today and those
>are highly localized. Where are these sediments?

Ah but these sediments do exist! Referring to the Melosh et a (1990)l paper I
cited last week, the authors cite soot layers (p.253) at sites in Denmark,
Spain, New Zealand and New Mexico and suggest that their model of ballistic
emplacement of impact ejecta  causing wildfires explains the amount of soot
observed at these sites. This and the nuclear weapon-style effects of thermal
radiation resulting from a large bolide striking a shallow carbonate platform
at 20-30 Km/s.

And a paper by Ivany and Salawich  (1993), cite a "breakdown and reversal" of
the normal surface water to deep water 13C/12C gradient at and just after the
K-T boundary.  A global weighted average of the negative anomalies from the
North /South Atlantic, Pacific and Antarctic Oceans is -1.8 delta 13C. They
suggest that a combustion of nearly 25% of the above ground biomass is
nescessary to produce the anomaly,  and that the cessation of primary
productivity in the oceans is insufficient to account for the effect. There
is also 87Sr/86 Sr isotopic (Meisel et al) evidence that seems to concur at
least  indirectly that continental weathering increased dramaticallly at the
boundary ( duriing a major eustatic sea level regression by as much as 100m
by some estimates?)

Sources:
Melosh, H. J., et al.  18 Jan. 1990. Ignition of Global Wildfires at the
Cretaceous/Tertiary Boundary. Nature, vol. 243.  p.251-254 (and references
cited therein for the loactions of soot deposits)

Ivany, L. S., and Salawich, R. J., 1993. Carbon Isotopic Evidence for Biomass
Burning at the K-T Boundary. Geology, v.21, no.6,  p. 487-490

Meisel, T.,  Krahenbuhl U., Nazarov, M. A., 1995. Combined Osmium and
Strontium Isotopic Study of the Cretaceous-Tertiary Boundary at Sumbar,
Turkmenistan: A Test for an impact vs. A Volcanic Hypothesis.
Authors present still more  isotpic evidence for an impact and large scale
continental denudation of sediments (during that regression) possibly caused
by acid rain or a tsunami.

About tsunamis, while I do not have the references handy, I do believe that
due to the magnitude of the imapactor in a <2Km deep carbonate platform,  the
resulting tsunami may have attained a height of 1-2 Km and that the tidal
waves would have reverberated several times around the globe and possibly
over the course of many days/weeks . Of course I do not imply at they
remained at the same intensity but merely point out the pulsing megawaves
crashing on near shore environments could cause some strange effects.  A
hiatus may  explain the initia/final l erosional uncomformity on the K-T east
coast but it's timing with the impact generated tsunami may have widened the
microfauna gap more than the hiatus itself can explain.

Then there's the puzzling extraterrestrial amino acid AIB found in
association with Ir at the Stvens Klint locality and the "pollen spike" at
the K-T in the western US. Any thoughts on yet another geochemical and
 biological anomaly?

                                                                     Regards,
                                                                     Thomas
R. Lipka




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