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Re: Dilcher et al., 1998



>From spatula@netaxs.com  Wed Dec  2 15:51:02 1998
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Josh smith wrote:

> Anyway, Dilcher and I talked at length about the quarry and the whole
> dating problem.  He said that he wasn't going to cite my work, because it
> didn't agree with what his co-authors wanted.

My apologies in advance, I've only read the abstract. My _Science_ issues
are borrowed- I'm only a poor little part time preparator :).

Josh, where are Dilcher and co. getting their dates from? Have they
performed their own radiometric tests that produce conflicting results? If
not, my rusty memory from Dinofest recalls that the site has many issues
that complicates dating.

Straighten me out, please!

        Sorry this reply took a while.  I JUST got home.


        Dilcher and co. (the title of this email is wrong, of course, it 
is actually Sun et al., 1998, not Dilcher et al., 1998) essentially just 
spit back out what Chen et al., 1998 said about the age of Sihetun in the 
_Sinosauropteryx_ description earlier this year.  They cited some other 
papers, but in effect, they said that although Smith et al., 1995 
produced Ar-Ar ages of ca. 122 Ma for the base of the Yixian, they felt 
that these ages were irrelevant because the rocks were obviously 
intrusives that were emplaced long after sedimentation in the lakes 
ceased and the lakes were gone.  They supported this assement with a 
bunch of biostratigraphic data (much of which represent endemic critters 
and plants and which are of course circular).  So, Sun et al., 1998 
didn't do any actual dating work of their own and didn't say much that 
Chen et al., 1998 didn't say in the spring.

        They didn't mention of course that Chen et al., 1998 offered 
absolutely no evidence to support their hypothesis that the rocks are 
intrusive....none.

(Haven't seen you since Dinofest Josh! *wave*)
-Sherry Michael
ANSP prep lab

Yeah, it is pretty pathetic that I haven't been across the river in 
several months.  How far is it?  6 blocks?  Sheesh.  Let me know the next 
time you are going to be there and I will pop over.

-Josh

-- 
__________________________
Josh Smith
University of Pennsylvania
Department of Earth and Environmental Science
471 Hayden Hall
240 South 33rd Street
Philadelphia, PA  19104-6316
(215) 898-5630 (Office)
(215) 898-0964 (FAX)
smithjb@sas.upenn.edu