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Re: Age of Gobi Formations



Tim Donovon (sirius531@yahoo.com) wrote:

<In the Nemegt basin there is a consistent pattern predicted long ago by
geological research: localities become progressively older in an E/NE direction.
Khulsan is definitely lower than Red Walls to the west, and overlies a
Djadokhtan locality farther east.>

  This is a valid observationb, but should not limit one to seeing how
formations further north and east must be younger. Nearly all these formations
and localities are correllated by their fauna. Have a little more caution in
identification, unless one should choose that this can only support a pet
theory.

<PIN 551-1 is estimated to have been 1.35m in life, whereas ZPAL MgD-I/4 is c
1.2m, so maybe the latter isn't a full adult.>

  Or the type is exceptionally old. An ontogenetic study is underway through
Hurum's work, as the Hurum and Sabath work is not considered to be the ultimate
conclusion of Hurum's research. Hurum has identified multiple adults based on
suture shape and fusion in the braincase and nasals, so i should hope this helps
in identifying adults, rather than just picking the largest specimen and going
along with 70's and 80s identifications of adult status when most specimens
noted here were recovered post the material studied that led to the Russian
identification of adult ages.

<The lower Djadokhtan horizons are fluvial or contain mudstones e.g. at Alag Teg
and Bayan Mandahu. This lower level is overlain by eolian deposits such as those
at Tugrikin Shire, Bayan Dzak and upper Alag Teg etc. The transition to fluvial
or wet to eolian occurs from the Arts Bogd area all the way to Bayan Mandahu.
"Chuluut Uul" falls well within this area. The beds of "Chuluut Uul", like those
of Alag Teg, yield hadrosaurs and Pinacosaurus. But whereas the lower level at
Alag Teg is visibly overlain by eolian deposits, "Chuluut Uul" consists entirely
of fluvial beds.>

  Indicating a fluvial episode, not that it must have been Nemegtian or
Djadokhtan.

<That indicates it is stratigraphically quite low in the Djadokhta formation,
far lower than the stratotype at Bayn Dzak, where the eolian beds exceed 70m.
Yet dating of the basalt at "Chuluut Uul" clearly indicates a late Campanian age
of c 73 Ma.>

  And as previously indicated, was identified from the _middle_ "Barungoyotian,"
not the _lower_ as stated below. This does not date an Upper Campanian age for
the Djadokhta, but a split between the Djadokhta and Barun Goyot unconformity
(where no contact between formations is indicated, however it may exist
elsewhere and undated there); similarly, this date is likely changeable, as
stated previously, and as Donovon attested to not just two days ago, using the
term "outdated."

<If the bottom of the Djadokhta formation is that young, the top of the
formation probably reaches the Campanian-Maastrichtian boundary.>

  See above to useage of using "Chuulut Uul," which can't seem to be reliably
indicated anywhere based on fauna, as a reference to the _lower_ Djadokhtan
rather than previous cites and quotations that indicate a _middle_
"Barungoyotian."

  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)