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Re: "Lazarus" Dinosaurs in the Paleocene!!?
Thanks for the link:
>>Revised ages for the global, geomagnetic time scale indicate that the age
of the Cretaceous-Tertiary boundary is 65.5 Ma (as determined by
Strange, because the Chicxulub crater is 64.98 +- 0.05 Ma, based on U/Pb in
zircons = the most precise method available. The author explicitely accepts
the association of crater, extinction and K-T boundary in the preceding
paragraph: >>thus some dinosaurs survived the asteroid-impact "extinction"
event that is generally accepted as marking the end of the Cretaceous Period
throughout the world<<. So does he jumble up his own chronology?
>>The boundary is in magnetochron C29r.<<
To be precise, in a very short (50,000 years) normal polarity subchron of
C29r. This subchron was used to show that there's no hiatus in the Hell
Creek Formation. Just forgot the ref :-]
>>Published data from the Hunter Wash area of the southern San Juan Basin
(where most of the Lazarus dinosaurs have been discovered) show that the
lower (dinosaur-bearing) part of the Paleocene Ojo Alamo Sandstone contains
a thin interval of reversed polarity, identified<<
How? The following sounds like the relative thickness of the layers was
>>as the uppermost part of magnetic-polarity chron (magnetochron) C29r,
overlain by a thicker interval of normal magnetic polarity, magnetochron
C29n, The thin interval of C29r at the base of the Ojo Alamo, is estimated
to represent about 0.170 m.y. Published estimates give the duration of
magnetochron C29n as 0.769 m.y., thus, the duration of the Alamoan Lazarus
dinosaur fauna would have been about 0.939 m.y. - virtually 1 million
years - and the time of extinction of this Paleocene dinosaur fauna would
have been about 64.5 Ma (Obradovich time scale).<<
Well, I'm still not convinced that this is reliably Paleocene. What if the
formation begins with C30r instead? Or if they identified such a subchron as
a normal chron?