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RE: The Morrison Formation: older than you think



David Marjanovic wrote:

Kelli Trujillo, Kevin Chamberlain & Ariel Strickland: Oxfordian Park: U/Pb ages from SHRIMP analysis for the Upper Jurassic Morrison Formation of southeastern Wyoming with implications for biostratigraphic correlations, SVP meeting abstracts 2006 (supplement to JVP 26(3)), p. 132A

The age of Quarry Nine at Como Bluff and two other sites is 156.3 +- 2 Ma, and that's (probably) in the Oxfordian. Not Tithonian, not Kimmeridgian.

If true... this has a domino effect for the entire stratigraphy of North America. If Como Bluff is re-dated to Oxfordian, then doesn't this push deeper Morrison sites back into the Callovian (at least)? How old would this make the Tidwell Member (which yielded _Dystrophaeus_), for example? Bathonian, or even Bajocian?


Cheers

Tim