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K/T acid rain, leached paleosols and the "barren zone" (Was: mammals over dinosaurs in...)



Dan Varner <Danvarner@aol.com> querried:

I hath scribed:
<< The presence of plant fossils and the
 rarity/absence of hydroxyfluorapatite-containing fossils could be
 explained as a result of acid leaching in the boundary zone ("Barren
 Zone" of Archibald, 1982). Retallack suspects that the leached paleosol

 is direct evidence of acid rain that was produced from the vaporization

 of sulfate target rocks from the impact bolide. >>

> Could you please give the Retallack reference?

I'll give a few, as there is a lot of interesting stuff in them
(including a few controversial issues, but interesting none-the-less).

A *very* good technical summary paper by Greg (and the one I recommend
the most) is:

1)  Retallack, G. J. 1996.  Acid Trauma at the Cretaceous-Tertiary
Boundary. G.S.A. Today 6(5):1-7.

Greg gives a good over-view of the research on the Hell Creek/Tullock
sections in Montana, and describes the boundary clay layer and it's
associated underlying leached zone.  A good color illustration of the
bounary clay is also shown.  Retallack divides this K/T boundary zone
into two distinctive units: a lower "boundary bed" that is composed of
leached soil (now kaolinite), and an overlying "impact bed", composed of
non-leached clay (smectite) with a strong iridium anomaly and shocked
quartz.  Overlying this is, of course, the requisite lignite bed.
The main points of the paper deal with the evidence that the Hell Creek
Fm. records a paleo-acid rain event at the K/T boundary.  I think most
of his evidence is quite strong, but a few points I take issue with
(minor details not worth mentioning here...geology-related).
As a footnote, I can't resist pointing out that the photo-caption for
the Bug Creek site on the first page is wrong!


2) Retallack, G.J., G.D. Leahy, and M.D. Spoon. 1987. Evidence from
paleosols for ecosystem changes across the Cretaceous-Tertiary boundary
in Montana. Geology 15: 1090-1093.


3) Prinn, R.G. and B. Fegley. 1987.  Bolide impacts, acid rain, and
biospheric trauma at the Cretaceous-Tertiary boundary. Earth and
Planetary Science Letters 83: 1-15.

One of the papers that started the raging K/T acid-rain debate!  (well,
what little debate there is of it).  A highly recommended read.



> Another feature of the K/T fossil plant zone (at least in North
Dakota) is
> the presence of very extant, active, and very large scorpions.

(!)  Well, I have been lucky so far.  A near-miss rattlesnake strike one
year, and a mild case of heat stroke another year.  Not bad for 10
years.  All were worth the risk as far as I'm concerned!   :-)

                                            <pb>