Re: Age of Cloverly

[dis@gj.net]

Jerry D. Harris wrote:
> 
> Hi All -
> 
>         Can anyone tell me if there's a more recent (and detailed) dating
> scheme for the Cloverly Formation of the Western US?  Is Ostrom '70 still
> considered the definitive dating scheme?  All the references I can find
> simply say "late Aptian-early Albian," all based on Ostrom's 1970 report,
> but I'm wondering if there's a more recent publication on this subject,
> maybe based on something other than vertebrates (e.g., palynomorphs, etc.).
> Anyone know something I don't about this? 

Yes there is a very recent paper on Cloverly Fission Track dates (in my 
ming the least accurate method). It is

Chen, Z-Q. and Lubin, S., 1997, A fission-track study of the terrigenous 
sedimentary sequences of the Morrison and Cloverly Formations in the 
northeastern Bighorn Basin, Wyoming: The Mountain Geologist, v. 34, no. 
2, p.51-62.

        THey date the top of the Little Sheep Mudstone Member at 115 + 
or - 10 Mya. The Old Shell Diamictite dated at 129 = or - 16 mya. Way to 
 old by my way of thinking. Why they did not do Argon/Argon is probably 
cost and the fact that they could do this in their own lab. 

        I still think biostratigraphic correlations with the Trinity 
Group of Texas would be the most accurate. So in my mind, it is up to 
you guys at SMU, although Rich Cifelli at the OMNH could resample the 
Cloverly and get some Argon/Argon run.

Hope this helps.

Jim K.