Re: Everything you know about the Iren Dabasu age is wrong...

[Tim Donovan <uwrk2@yahoo.com>]

> --- "Thomas R. Holtz, Jr." <tholtz@geol.umd.edu
> wrote
>  
> > van Itterbeecka, J., D.J. Horne, P. Bultynck, and
> N.
> > Vandenbergh. 2005.
> >Four species of charophytes are described and
> > illustrated from the Iren Nor site, together with
> > eight species of ostracods,
> > one of which (Cypridea irennorensis sp. nov.) is
> > new. Contrary to the vertebrate data, both groups
> of
> > microfossils indicate a latest
> > Cretaceous age (Campanian?Maastrichtian) for the
> > Iren Dabasu Formation, and suggest a possible
> > correlation with the Nemegt
> > Formation,
> 
> 
>   What about gastropods? Is Mesolanistes present?


 The left coiled gastropods Mesolanistes are known rom
Maastrrichtian deposits of North America and China as
well as the Nemegt. If they aren't present at Iren
Dabasu, it's unlikely to be of Nemegtian age.

> And
> Nemegtian turtles like Mongolemys? Are they present
> at
> Iren Dabasu?
> 
> 
> 
> 
>  which would allow the age estimation to
> > be refined to latest Campanian?Early
> Maastrichtian.
> > 
> > Possible correlation with the Nemegt?!?
> 
> 
>  I don't believe it. There are radiometric dates
> indicating a late Campanian age for Djadokhtan beds.
> Russell and Jerzykiewicz  estimated the Nemegt was
> of
> mid Maastrichtian age. AFAIK the Iren Dabasu and the
> Nemegt have no large dinosaurs in common even though
> the distance between the two formations is not very
> great, and the Nemegt fauna  seems fairly
> widespread, i.e.
> not just in Omnogov.
> 
> > Yeah, I knew
> > the stratigraphy there was poorly understood, but
> > the Iren Dabasu and Nemegt
> > were traditionally considered as opposite ends of
> > the stack of dinosaur bearing Late K sediments.
> 
>  Note that one of the authors above, van
> Itterbeecka,is the same person who persuaded
> Godefroit
> that the Tsagayan, with all its primitive or
> Campanian
> aspect lambeosaurs, is late Maastrichtian in age
i.e.
> younger than the Nemegt, which like Maastrichtian
North American units, appears to document a major
decline in lambeosaurs. These age
> estimates for the Tsagayan and Iren Dabasu just
don't make sense.
> 
> > 
> > Ah, well...
> > 
> >             Thomas R. Holtz, Jr.
> >     Senior Lecturer, Vertebrate Paleontology
> > Department of Geology               Director, Earth, Life &
> Time
> > Program
> > University of Maryland              College Park Scholars
> >     Mailing Address:
> >             Building 237, Room 1117
> >             College Park, MD  20742
> > 
> > http://www.geol.umd.edu/~tholtz/
> > http://www.geol.umd.edu/~jmerck/eltsite
> > Phone:      301-405-4084    Email:  tholtz@geol.umd.edu
> > Fax (Geol):  301-314-9661   Fax (CPS-ELT):
> > 301-405-0796
> > 
> > 
> 
> 
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