Re: More on SVP/GSA

[cnedin@geology.adelaide.edu.au (Chris Nedin)]

Dave Schwimmer wrote:

>  Everyone presenting in the GSA meetings seemed to accept the
>reality of an impact around 65 M.y.  (Even Keller's group at
>Princeton and Mexican associates seemed to tacitly accept it).
>
>  -However, there were several workers who presented strong
>evidence that the "megatsunami" deposits proximal to Chicxulub
>are not such.  An additional talk showed that these same
>"tsunami" deposits are abundantly filled with syndepositional
>trace fossils. The upshot of these talks is that these deposits
>are probably unrelated to the impact effects.
>
> -further, several papers argued that the impact deposits are
>  of late Maastrichtian age (i.e., before the K/T boundary).

As Mayerhoff et al. suggested recently.

>  Anne Weill presented a paper arguing impressively (to me) that
>acid rain and acidification of terrestrial envgironments was not
>a likely killing mechanisms.  She used survivorship by amphibians
>across the K/T boundary as the basis for that.

More evidence for my Laid-Back-Aquatic hypothesis <tm> (LBA <tm>)

>  Archibald showed that taxa going extinct across the K/T
>boundary are almost precisely those one would predict to be
>most _unlikely_ killed off by postulated impact-generated
>outcomes (acids, darkness, cold, etc).  Dinosaurs, for example,
>had much wider latitudinal range (and, presumably cold-tolerance)
>than, say, crocodilians; yet, crocs passed the boundary almost
>intact whereas non-avian dinos bought the farm.  Ditto for many
>taxa.  He plumps for a marine regression-based extinction model.

Just as my LBA <tm> hypothesis suggests. All large creatures that are
unable to maintain a stable body temperature in a *rapidly* fluctuating
environment (e.g. excluding birds and mammals) would have trouble
surviving. However, those creatures with a low metabolic turnover and
living in an environment which resists rapid temperature fluctuations (i.e.
aquatic) would have a much better chance. Thus crocs and anphibians would
be expected to survive but the dinos's wouldn't. Especially as the marine
regression drained the vast inland seas and thus robbed the continents of
their ameliorating influence over climate.
:-)

>  And of course, there were a range of papers at SVP arguing
>details of the impact event as an unipeachable reality and cause
>of the  K/T extinctions.

It appears that it is becoming increasingly difficult to reconcile the
indiscriminate effects of a meteorite impact with the selectivity in
extinctions.

Chris