Re: Age of the Djadok(ht)a, Barun Goyot and Nemegt Formations

["Jaime A. Headden" <qilongia@yahoo.com>]

  Now that I have some time, old mail:

Tim Donovan (uwrk2@yahoo.com) wrote:

<Mesolanistes. Shuvalov et al mentioned a variety of evidence.>

  Donovan loves going back to the oldies but goldies. New data enters the fray
and it must be applied as someone else applied it and in no other way. Because
they got it right? Shoehorning and strawmen. Indeed, we are still down to using
a single taxon as the primary reason for doubting the age of Iren Dabasu, not
attempting to assess the remainder of the data.

<Yes but "Djadoktha" was never used AFAIK.>

  It seems anal to me to quibble about a misspelling.

<As I pointed out repeatedly, radiometric dating of a Djadokhtan locality
indicates a late Campanian age. Recent work suggests the Baynshirenian ended by
the Campanian.>

  Which is fine since they are doubting referring the Iren Dabasu to an age
equivalent to Bayan Shiree and instead to an age equivalent to the Nemegt. The
locality dated, btw, Borzongiin Govi, was previously mentioned, and the ref
used (Shuvalov, 2000) does nto back up this statement, unless this is another
case of not providing a citation for claims. Let's review with a blast from the
past, over 2 years ago -- http://dml.cmnh.org/2003Sep/msg00171.html -- which
states (in part):

  "In addition K-Ar dates from basalts in the middle and upper parts of the
   Svita (in the gorge Borzongiin Gobi and others) are 78-80 MYR (Campanian). 
   Hence, we date the Baruungoyot Svita as Santonian-Campanian (Shuvalov and
   Nikolaeva, 1985)."

  This is hardly a "late Campanian" age, if this locality in fact derives from
the mainline Djadokhta as claimed, or from the Baruun Goyot, or from a similar
level.

<Basically I'm just repeating the conclusions of Shuvalov, Martinson, Osmolska,
Russell, Jerzykiewicz etc, concening the early-mid Maastrichtian age estimate
for the Nemegt. And this is NOT based on just taxa. The Nemegt couldn't be as
old as Campanian because far underlying beds are late Campanian. Again see
Shuvalov.>

  Which was cited above and apparently makes some of these formations even
younger. Since none of the hypotheses I've stated have required the formations
to be even Maastrichtian but allowed them to be Campanian, I have no problem
with the dates, as long as the data is accurate. This is always the problem
with dating non-clastic terrestrial formations, they must be compared with MUCH
less concise means, largely assumptions on taxonomic integrity and impressions
of speciation rates, which were estimates of a grand order that are being
slowly shown to be utter crap by actual molecular dating and detailed
osteological data of "species" and "genera" (which are similarly utterly crap
as they are arbitrary and subjective constructs).

<I replied by mentioning the discovery of Bactrosaurus from Bayshin Tsav; it is
also known from Iren Dabasu.>

  And *Bactrosaurus* can't be a genus that spanned a stage or two? Or maybe the
fossils they called *Bactrosaurus* at Bayshiin Tsab aren't really *B.
johnstoni* but a younger, more derived, more hadro-esque taxon? A different
species? Or maybe it's a new genus? Or maybe it's bad fossils that only LOOK
like they aren't *Gilmoreosaurus* because obviously, they must be either since
the formation IS the same age. See what I mean about strawmen?

  Cheers,

Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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