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

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

...or so it seems, from a forthcoming paper in Cretaceous Research.
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WD3-4H2PJ9Y-2&_user=961305&_handle=V-WA-A-W-AD-MsSAYZA-UUA-U-AAWEYDYDAB-A
AWDVCECAB-BCWECVBUB-AD-U&_fmt=summary&_coverDate=09%2F09%2F2005&_rdoc=9&_orig=browse&_srch=%23toc%236755%239999%23999999999%2399999!
&_cdi=6755&view=c&_acct=C000049425&_version=1&_urlVersion=0&_userid=961305&md5=bfaa09ef0fa8b7792612c097d9bb6291


van Itterbeecka, J., D.J. Horne, P. Bultynck, and N. Vandenbergh. 2005. 
Stratigraphy and palaeoenvironment of the dinosaur-bearing
Upper Cretaceous Iren Dabasu Formation, Inner Mongolia, People's Republic of 
China. Cretaceous Research, in press.

Abstract
New field observations and sedimentological analyses of the dinosaur-bearing 
Upper Cretaceous Iren Dabasu Formation in the Iren Nor
region of Inner Mongolia (People's Republic of China) have led to a better 
understanding of its palaeoenvironment. The fluvial
deposits represent a braided river that, due to the large amount of fines, does 
not fit the classical model for braided rivers. The
study area is divided into two parts: in the northern part, sediments of the 
main channel belt of the ancient braided river system
are exposed along a dry river valley on the northern edge of the Iren Nor salt 
lake, while in the southern part, comprising all
other studied exposures, different facies of the ancient floodplain are 
represented, including minor channels, temporary ponds, and
palaeosols. The difference between the northern and southern parts is also 
reflected in the fossil content; only the southern
exposures have yielded dinosaur remains. The ancient braided river had a broad, 
vegetated floodplain populated by a diverse dinosaur
fauna. 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, which would allow the age estimation to be refined to latest 
Campanian?Early Maastrichtian.

Possible correlation with the Nemegt?!? 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.

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