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Triassic Chinle Formation climate evidence from fossil pollen



From: Ben Creisler
bcreisler@gmail.com


A new paper that may be of interest:



Tammo Reichgelt, William G. Parker, Jeffrey W. Martz, John G. Conran,
Johanna H.A. van Konijnenburg-van Cittert, Wolfram M. Kürschner (2012)
The palynology of the Sonsela member (Late Triassic, Norian) at
Petrified Forest National Park, Arizona, USA.
Review of Palaeobotany and Palynology (advance online publication)
http://dx.doi.org/10.1016/j.revpalbo.2012.11.001
http://www.sciencedirect.com/science/article/pii/S0034666712003004


Recent palaeontological investigations and lithostratigraphic
revisions reveal a marked biotic turnover zone within the continental
deposits of the Sonsela member of the Chinle Formation (Late Triassic,
Norian) at Petrified Forest National Park, USA.

Within the Sonsela member we found three pollen assemblage biozones:
Zone II (90.5–94 m above the Mesa Redondo member) contains a
relatively diverse palynological assemblage, with a mix of
pteridosperms, voltzialean and some Mesozoic conifers. Following a 2.3
m hiatus, Zone IIIa (96–97.5 m) is characterized by a decrease in
pteridosperms and Mesozoic conifers and a drop in voltzialean conifer
diversity. The alleged voltzialean conifer pollen Klausipollenites
gouldii was dominant in this part of the assemblage and a significant
rise in spores and cycad pollen was also evident. In Zone IIIb
(97.5–98.5 m) diversity increases and several taxa, which were absent
in Zone IIIa reappear, although K. gouldii remained the most abundant
taxon. The transition between the palynological assemblages Zones II
and IIIa coincides approximately (within a ~ 2.5 m interval) with a
documented faunal turnover.

The floristic assemblages suggest that the climate of the
south-western United States during the Norian was most likely
semi-arid and highly seasonal, despite being located at tropical
latitudes, with aridification occurring towards the end-Triassic as
the continent drifted northwards and global volcanism increased. The
gymnosperm-dominated palynofloral assemblage as opposed to the fern-
and horsetail-dominated macrofossil record of the Sonsela member of
the Chinle Formation, conforms to a semi-arid upland environment
alternated by riparian, swampy lowland.

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Highlights


► Palynology investigated of Sonsela Member at Petrified Forest
National Park ► Distinctive palynofloral turnover occurs within the
Sonsela Member ► Palynofloral turnover occurs within a 2.5 meter
interval of a tetrapod fauna turnover ► Gymnosperm dominated
assemblage concurrent with semi-arid environment of the Late Triassic
(Norian) of the southwestern USA