U-Pb Age Constraints on the Jurassic Succession and Paleoflora of Mount
Flora, Antarctic Peninsula
R.A. Scasso1, J. Ramezani2, I.
Escapa3, A. Elgorriaga3, I.
Capelli1
1Instituto de Geociencias Básicas, Aplicadas y
Ambientales de Buenos Aires (IGeBA) -Departamento de Cs. Geológicas,
Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires,
Int. Guiraldes 2160, Ciudad Universitaria, Pab. II, C1428EHA - CABA,
Argentina
(rscasso@gl.fcen.uba.ar;
igan.capelli@gmail.com)
2Earth, Atmospheric and Planetary Sciences,
Massachusetts Institute of Technology, Cambridge, MA 02139, USA
(ramezani@mit.edu)
3Museo Paleontológico Egidio Feruglio, Av. Fontana
140, 9100 Trelew, Chubut, Argentina
(iescapa@mef.org.ar;
aelgorriaga@mef.org.ar)
.
Corresponding author: Roberto A. Scasso (rscasso@yahoo.com.ar)
†Additional author notes should be indicated with symbols (current
addresses, for example).
Key Points:
- Precise U-Pb zircon ages from the Mount Flora Formation in Antarctic
Peninsula constrain its classic fossil flora to late Middle Jurassic
- Similar but distinctly older Early Jurassic plant associations in
Patagonia suggest paleoenvironmental control on geographic
distribution
- Magmatic arc development, tectonic extension and continental break up
dominated the evolution of southern Gondwana in the Middle Jurassic
Abstract
The spectacular fossil plant assemblage preserved in the non-marine
Mount Flora Formation of the northern Antarctic Peninsula represents the
diverse Jurassic flora that once covered the Gondwanan continents at
high paleolatitudes. The depositional facies of the formation plays a
key role in the tectonic interpretations and basin evolution models that
attempt to reconcile large igneous province magmatism, continental break
up, and magmatic arc development throughout the Jurassic and Cretaceous.
Limited U-Pb in situ geochronology reported from the Mount Flora
Formation and adjacent units lack the necessary resolution to overcome
ambiguous correlations and biostratigraphic discrepancies. We present
two high-precision U-Pb zircon ages (CA-ID-TIMS method) from a distinct
tuffaceous interval of the Mount Flora Formation at Hope Bay, which
document a terminal Middle Jurassic age (Callovian Stage) for the
formation and its paleoflora. In excess of 1400 new collected fossil
plant specimens exhibit a highly diverse Jurassic plant association that
dominated the Antarctic Peninsula nearly 17 million years after its
disappearance from northern Patagonia. This suggests similar
paleoecological conditions were established diachronously throughout
basins of southern Gondwana, possibly facilitating floral migrations in
response to local climate change. The depositional facies of the Mount
Flora Formation, its age proximity to the marine Nordenskjöld Formation
in the Antarctic Larsen Basin, and its coincidence with a regional
unconformity in the northern Patagonia point out to a complex interplay
among magmatic arc development, tectonic extension and continental break
up that dominated the geologic and paleoenvironmental evolution of
southern Gondwana near the end of the Middle Jurassic.