Re: age of formations

["Jonathan R. Wagner" <jonathan.r.wagner@mail.utexas.edu>]

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cc them when you post... assuming you *do* want a response from them. ;)

KELL00BELL@aol.com wrote:

     "stage of evolution?"
    This is considered bunk by most people... faunas do not have consistent,
reproducible "stages," and neither do their members... the taxonomic
composition of a fauna may have varied with age, but disparate faunas are
under no constraint to "evolve" in the same manner. If they do, then you've
got the makings of a paper (woo hoo!). but that shouldn't be the default
assumption.


"Considering that the Tsagayan lay between NA and Mongolia, which were
biogeographically linked in the Maastrichtian, and had more derived and
different faunas by then (fewer lambeosaurs) the Tsagayan hadrosaurs seem
too primitive and diverse for such a late age.  Godefroit said NE Asia was
completely isolated: "how, no one knows."  Is that credible?"
        Well, I think this depends partly on the age interpretation... As
for isolation mechanisms... well, there are profound differences in northern
and southern faunas of North America at about the same time, even though
exchange certainly *was* possible. Heck, there are differences between
Montana and Southern Alberta! So, I suppose it is credible, IMHO.


      "Nemegt age: Yes, Shuvalov included an IGEM figure of about 75 Ma for
the upper Barun Goyot, which suggests the overlying Nemegt is Edmontonian in
age.  But the margin of error is 7 Ma- an entire stage!  The top of the
Barun Goyot might be as young as mid-Maastrichtian."

    Eh? Well, I didn't remember that. Good catch! Anyway, I don't feel so
bad about it, since I'm not worried about the Horseshoe Canyon ages, and
Saurolophus angustirostris really may be S. osborni.


      "Regarding the Javelina: T. Lehman once wrote the K-T signature hasn't
been found, and the Puercan may be missing there, suggesting an
unconformity."

        Well, this could also mean that the "Puercan" is a regional
subdivision, and does not apply to the entire continent (which wouldn't
surprise me). Schiebout has reported Puercan mammals from the Black Peaks
Formation (overlying the Javelina). If there is an unconformity there, it's
a sneaky SOB. I've never seen any indication of it, and I've eaten lunch on
the K/T boundary at Big Bend must've been twenty times or more.
    For the record... not finding an iridium anomaly does not mean you
haven't found the K/T. This is science, we must always allow for the
possibility of sections with no iridium anomaly.


    Wagner


Jonathan R. Wagner
9617 Great Hills Trail #1414
Austin, TX 78759