 |
| Titel |
Phytological patterns during the rise of dinosaurs in the Chinle Formation of northern New Mexico, U.S.A. |
| VerfasserIn |
Randall B. Irmis, Sofie Lindström, Roland Mundil |
| Konferenz |
EGU General Assembly 2010
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250043655
|
|
|
|
|
|
| Zusammenfassung |
| In the Upper Triassic Chinle Formation of northern New Mexico a diverse suite of basal
dinosauromorphs and dinosaurs co-existed for many millions of years. Faunas with both
these basal forms and dinosaurs, and basal archosaurs have so far only been recovered from
the Petrified Forest Member, whereas assemblages from the younger “siltstone” member
include only dinosaurs and basal archosaurs.
New palynological data from the Poleo Sandstone, and the overlying Petrified Forest and
“siltstone” members of the Chinle Formation indicate major changes in the vegetation over
this interval. In general all the spore-pollen assemblages are dominated by bisaccate
gymnospermous pollen, mainly Alisporites and Protodiploxypinus. However, in the Petrified
Forest Member monosaccate conifer pollen assigned to Enzonalasporites become dominant,
and this probably indicates dryer conditions. Within that same member the enigmatic
palynomorph Froelichsporites traversei is abundant. The circumpolloid conifer pollen
Camerosporites appears to be restricted to the Poleo Sandstone and the Petrified Forest
Member. Within the overlying “siltstone” member the Enzonalasporites decrease in
abundance, and ferns and fern allies for the first time become common components
of the palynoflora; this may indicate the on-set of more humid conditions in the
area.
A single crystal U-Pb IDTIMS date of 213.1 ± 0.4 Ma based on 16 zircon analyses from a
redeposited sandstone within the lower part of the Petrified Forest Member places most of
the Chinle Formation in New Mexico within the Norian, and indicates that basal
dinosauromorphs and dinosaurs co-existed for at least 15 million years. In addition, it
provides better constraints on the ranges of key Late Triassic palynomorph taxa, indicating
that “Carnian” palynomorph assemblages from the Chinle Formation are actually Norian in
age. |
|
|
|
|
|
|