[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Age of the Barun Goyot, Djadoktha and Nemegt Formations



Tim Donovan (uwrk2@yahoo.com) wrote:

> >   So the distinct geologies must span several
> > million years and not be rapid
> > and short-interval formations for ... what reason
> > again?
> > 
> 
<Faunal turnover e.g. Pinacosaurus-Saichania-Tarchia. The presence of
Saurolophus and a tyrannosaur closest to Tyrannosaurus in the Nemegt argues for
a younger age than that of the Djadokhta. The latter is late Campanian but
Russell and Jerzykiewicz considered the Nemegt mid Maastrichtian.>

  Okay, you missed my question by going into specific arbitrary taxonomy-based
biostrat hypotheses. I'm talking about proving taxonomic correllation of
stratigraphy. And how even such simple things as biological refugia and false
taxonomy, a MAJOR debate here, can be use to support several different ideas
about stratigraphy. Maybe we should stick to pollen? Or perhaps ostracods? Or
bryozoans? Or arthropods? Even pollen is likely to survive in a single region
past the extinction of all other types of its kind, such as monkey puzzles in
South America (which were once MUCH more widespread), and this very
inconsistency leads to problems in using taxa has strat markers. So far, all I
see is trying to use turtles and dinosaurs to constrain formations and
excessive use of "land vertebrate ages", which suffer MASSIVE problems of
taxonomic lumping/splitting effects.

  Incidentally, there are species of extant avian, insect and "genera" (not to
mention many other taxa) that go back into the Pleistocene and Oligocene, and
some into the Miocene. So how long can the ghost lineage of *Tyrannosaurus*
extend? How different must two different animals be to not mandate their
formations of recovery are the same age? What evidence makes anyone think that
if the same or very similar taxon appears in two different formations, they are
the same age? Using just the Santonian-Maastrichtian of Mongolia, for example,
we have lizards (just using lizards) that are spread in either Djadokhta or
Nemegt, some in Djadokhta and Baruun Goyot, and some in Baruun Goyot and Nemegt
formations, exclusively, sans finding specimens otherwise. The same is true of
small mammals. Yet no one argues each of these formations is the same age. I
HAVE seen some mention that parts of the Djadochta and Baruun Goyot are
equivalent in time, with marginal overlapping of strata and taxa, but this
recalls to me only similar situations with the Two Medicince Formation and the
Bearpaw Shale showing regressions and advances and thus intermingling in the
same time.

  I think armchair geologists need to stop thinking that stratigraphy is such a
narrow and simple process of absolute layers where species only occur in
absolute spans of time in a formation or age....

  Cheers,
> 
> 
>               
> __________________________________ 
> Yahoo! Mail - PC Magazine Editors' Choice 2005 
> http://mail.yahoo.com
> 


Jaime A. Headden

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


                
__________________________________ 
Yahoo! Mail - PC Magazine Editors' Choice 2005 
http://mail.yahoo.com