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The Morrison Formation: older than you think
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.
"This interpretation challenges previous stratigraphic correlations and has
implications for the ages of the ecosystems of the Morrison Fm. in
southeastern Wyoming as well as faunal and floral associations worldwide
that are thought to be contemporaneous with those of the Morrison Fm."