INIBIOMA   20415
INSTITUTO DE INVESTIGACIONES EN BIODIVERSIDAD Y MEDIOAMBIENTE
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Macrofloras in the Austral Basin, Argentina: A complete record of Late-Cretaceous Angiosperms
Autor/es:
ARI IGLESIAS; AUGUSTO VARELA; POIRE DANIEL; MARIEL LUENGO; SEBASTIÁN RICHIANO; PATRICIO SANTAMARINA
Lugar:
Mendoza
Reunión:
Congreso; 4th International Paleontological Congress; 2014
Institución organizadora:
IANIGLA, CCT CONICET Mendoza
Resumen:
We found several new and historical fossil localities
in mid-Cretaceous littoral and continental sediments in northern Austral Basin,
Santa Cruz Province, Southern Patagonia. Four localities comprise a new flora
at the highest levels of Piedra Clavada Formation (Albian), were ferns and
conifers dominate most macroflora. The upper fossiliferous level in this unit
shows an unusual diversity of thirteen angiosperms leaf forms. The age of
Piedra Clavada Formation base on ammonoids and pollen is lower Albian. The
above unit, Mata Amarilla Formation, has been dated by zircons in 96.23 ± 0.71
My, constraining the unit to the Cenomanian. Fifteen leaf angiosperm
morphotypes has been recorded, few of them founded across the Albian-Cenomanian
times and included in several fossiliferous levels. Podocarps have dominated
the forest canopy, and petrified trees preserved in life position in a huge
forced regression surface at the Mata Amarilla Formation allow us a more
complete reconstruction of the forest structure. Taxodiaceae and Araucariaceae
were also recorded on higher fossiliferous levels. Angiosperm seems to occupy
the forest understory and over banks with mostly small flowers and winged
seeds. Several insect injuries in leaves and woods were also noticed. The
uppermost littoral-marine unit in the area, La Anita Formation, posses a
complete different macroflora, although the precise age is more ambiguous
(Coniacian?-Campanian?). Leaves, flowers and fruits of angiosperms are abundant
at the lowermost section, but diversity decreases. A lower Maastrichtian flora
was recorded in the continental Cachorro Formation, although the palinoflora
and macroflora are located in a freshwater pond. Most leaf forms correspond to
simple broad leaves of entire margin physiognomy correlated with climate
interpretations of hydromorphic paleosols (gleysols) recorded in the Mata
Amarilla Formation. Grow ring analyses on petrified trunks also agree with the
paleosols interpretation of a marked seasonality by water supply. Tree ferns,
cycads and probable palms also certificate frost free environments at these
middle-high latitudes in southern Patagonia during mid-Cretaceous. These data
strengthen previous hypothesis based on palynofloras and establish a floristic
change characterized by a rapid diversification of angiosperms during
plant-favorable temperatures and humidity in the Albian-Cenomanian. The study
of these floras and the age certifications, state down that angiosperm
diversification and dominance occur early in time at high latitudes in Patagonia.