Re: Charcoal & K/T Unconformity (from T. Jones)

[N.MacLeod@xxxxxxxxx (N. MacLeod)]

Fossil charcoal (commonly referred to as 'fusain') is possibly the most
ubiquitous of fossils. Once you start looking for it you find it almost
everywhere; marine, non-marine, clays, sands, limestones, even in lava
flows - and loads of it. And not only wood, all sorts of plant
organs/parts are preserved as charcoal - even flowers (trust me, I did my
Ph.D. on fossil charcoal). Therefore, the occurrence of charcoal cannot be
used as 'strong' evidence for an impact - it just adds to the story.

The deposition of charcoal after 'catastrophic' events is also
problematic. Nichols and Jones, 1992, Fusain in Carboniferous shallow
marine sediments; Donegal Ireland: the sedimentological effects of
wildfire. SEDIMENTOLOGY, 39, 487-502. describe a sequence where an
established shallow marine/estuarine sedimentological regime is disrupted
(by an enormous fire or series of fires), resulting in a very distinctive
and charcoal-packed horizon. On the other hand, researchers taking shallow
marine cores in Kalimantan, just off-shore and directly by the main
drainage river for a huge area which was devastated by fires in 1982-3 (an
area equivalent to Belgium, Luxembourg and Holland combined), didn't find
a trace of charcoal in any of their cores (collected just a few years
after the event) ???

Cheers  TIM JONES

On Sun, 16 Jul 1995, N. MacLeod wrote:

> I'm with Henry Barwood in thinking that the absence of charcoal, and (even
> more importantly) the absence of a thick sediment layer, in terrestrial
> basins that were supposedly denuded by an impact-related fireball is mighty
> peculiar.  Years ago Keith Rigby pointed out that in the Raton Basin the
> Cretaceous coals are capped by a thin K/T clay layer (termed by some the
> "fireball layer" that contains the shocked quartz and the Ir anomaly).
> Then it's right back into coal-rich fluvial deposits.  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?
>
> Also, with respect to Tom Lipka's posting about the erosional unconformity
> along the eastern seaboard of the U.S., most stratigraphers familiar with
> that region feel that the uppermost Maastrichtian eustatic sea-level fall
> is responsible for the interruption in sediment accumulation.  Once again,
> the problem is where did the sediment go?  A tsunami will resuspend
> sediment that is already deposited, but it can't remove sediment completely
> from an area thousands of miles in extent.  The unconformity along the
> eastern seaboard resulted in a gap that spans an unknown interval in the
> uppermost Maastrichtian and 1-2 planktonic foraminiferal biozones in the
> Danian.  This is a pretty long interval of time (approx. .25-.50 m.y.). I
> don't see any way for a tsunami to hit that area at the K-T boundary and
> produce that kind of record, whereas I can easily envision a global
> sea-level regression doing so.  Another way of looking at it is to compare
> the New Jersey record to Brazos River, Texas where the so-called tsunami
> deposit reaches thicknesses of tens of centimeters.  The duration of that
> hiatus is completely confined to the uppermost Maastrichtian (a fact that
> also has interesting implications for the timing of the so-called tsunami
> and it's alternative interpretation as a lowstand deposit). Since the
> energy of the K-T tsunami would fall off rapidly with distance I would
> expect a smaller scour surface and a smaller hiatus in New Jersey than in
> Texas if a tsunami was really the cause.
>
>
> Norm MacLeod
>
>
>
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> Norman MacLeod
> Senior Scientific Officer
> N.MacLeod@nhm.ac.uk (Internet)
> N.MacLeod@uk.ac.nhm (Janet)
>
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