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Dating the Jiufotang and Jehol Biota



  R.-x. Zhu, Y. Pan, R. Shi, D. Li. 2004. New paleomagnetic and
  chronological constrains on the Jehol Fauna in northeastern China.
  _Geophysical Research_ (Abstracts) 6.

  Geophysical Research Abstracts, Vol. 6, 04890, 2004
  SRef-ID: 1607-7962/gra/EGU04-A-04890

Abstract:
  "In the past decade, much attention has been focused on the diverse
   fossil assemblages of the Jehol biota mainly discovered in western
   Liaoning Province in northeast China. Numerous vertebrate, invertebrate
   and plant fossils were excellently preserved in the lacustrine
deposits.
   We recently carried out a combination of Ar-Ar dating and paleomagnetic
   investigation on the Sihetun section in West Liaoning in purpose to
   attest the age of the famous fossil assemblage. The datings on the
lower
   and upper volcanic rocks yielded ages of 126.5+/-1.4 Ma and 124.5+/-1.5
   Ma, respectively. Detailed paleomagnetic investigation on the
   fossil-bearing lacustrine interval obtained a normal polarity. In
   combination of the new magnetic results with radiometric datings from
   both sediments and volcanic rocks, we concluded that the fossil-bearing
   lacustrine interval deposited during the normal polarity period of M3n
   (marine anomaly), of the early Cretaceous age. And, we proposed that it
   was a possibly strong volcanic-associated lake existed in a relatively
   short duration."

  He, H.-y., X.-l. Wang, Z.-h. Zhou, F. Wang, A. Boven, G.-h. Shi, and
  R.-x. Zhu (2004), Timing of the Jiufotang Formation (Jehol Group) in
  Liaoning, northeastern China, and its implications. _Geophysical
Research
  Letters_ 31: L12605 / doi:10.1029/2004GL019790.

Abstract:
  "The timing of the Jiufotang Formation remains speculative despite
recent
   progress in the study of the Jehol Biota. In this paper we contribute
to
   this topic with 40Ar/39Ar dating on K-feldspar (sanidine and
orthoclase)
   from tuffs interbedded within the fossil-bearing shales of the
Jiufotang
   Formation, from the upper part of the Jehol Group in Chaoyang,
Liaoning,
   northeastern China. 40Ar/39Ar step heating analyses of K-feldspar and
   the SHRIMP U-Pb zircon data indicate that tuffs at the Shangheshou
   section erupted at 120.3 ± 0.7 million years ago. This result confirms
   an Aptian age for the Jiufotang Formation that was mainly based on
   biostratigraphic evidence. It also places stringent controls on the age
   of the fossils from the formation, providing a minimum age (120 Ma) for
   the four-winged dinosaur, *Microraptor,* and the seed-eating bird,
   *Jeholornis.*"

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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