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Jurassic U-Pb geochronology of Cañadón Asfalto Basin, Argentina

From: Ben Creisler

A new online paper:

Rubén Cúneo, Jahandar Ramezani, Roberto Scasso, Diego Pol, Ignacio
Escapa, Ana M. Zavattieri & Samuel A. Bowring (2013)
High-precision U-Pb geochronology and a new chronostratigraphy for the
Cañadón Asfalto Basin, Chubut, central Patagonia: Implications for
terrestrial faunal and floral evolution in Jurassic.
Gondwana Research (advance online publication)

The fluvial, lacustrine and tuffaceous sedimentary succession of the
Cañadón Asfalto continental basin exposed in the Argentinean Chubut
Province of central Patagonia preserve an extraordinary record of
Jurassic fauna and flora that marks key events in the evolution of
Dinosauria, early mammals and major South American plant groups.
However, basin-wide correlation of the fossiliferous units is
complicated by fault displacements, unconformities and repetitive
lithofacies. New U-Pb analyses of zircon (CA-TIMS method) from five
primary tuff beds interstratified with the lacustrine strata establish
a new chronostratigraphic framework for the sedimentary and volcanic
units of Cañadón Asfalto Basin, constraining ca. 33 m.y. of
depositional history and biotic evolution that spans nearly all three
epochs of the Jurassic. Five major vertebrate- and plant-rich
stratigraphic intervals have been identified, and are being actively
investigated, that range in age from Pliensbachian to Kimmeridgian (or
younger). Our combined biostratigraphic and high-precision
geochronologic results indicate that the major faunal turnover of the
sauropodomorph dinosaurs which led to the rise of the eusauropods took
place in the Early Jurassic, earlier than previously recognized.
Similarly, the first successful radiation of the ornithischian
dinosaurs (heterodontosaurids), as well as the evolutionary
diversifications of the araucarian conifers and the osmundaceous
ferns, all occurred before the end of the Early Jurassic. The diverse
palynofloral assemblage of the Cañadón Calcáreo Formation that was
once considered to be early Cretaceous in age, is now entirely
constrained to the Late Jurassic.