Damián A. Fernández
Museo Argentino de Cs. Naturales Bernardino Rivadavia, CONICET, Univ. Nacional de La Plata, Argentina [dafernandez@macn.gov.ar]
Paleofloristic analysis of the Río Turbio Formation (Eocene of the Santa Cruz Province) and its relation with global palaeoclimatic changes: spore-pollen evidences
It is presented a diverse and well preserved palynological assemblage from the Río Turbio Formation, mid-late Eocene, SW Santa Cruz Province. The region at the present time supports a low diverse southern beech forest dominated by Nothofagus antarctica (G. Forst.) Oerst. The palynological assemblage preserved in the Río Turbio Formation includes marine and continental palynomorphs. Spores of fungi and ferns, together with pollen of angiosperms and gymnosperms, were abundant and diverse. Within fern families Cyatheaceae/Dicksoniaceae/Schizaceae, Osmundaceae, and Gleicheniaceae were represented. Within angiosperms pollen from Nothofagaceae (Nothofagidites spp.), Myrtaceae (Myrtacidites spp.), and Proteaceae (Cranwellipollis sp., Propylipollis sp., Proteacidites sp.) were dominant in the assemblage. Pollen assigned to two pairs of -phylogenetically unrelated- genera (Nothofagus-Misodendrum and Prosopis-Tripodanthus) may trace back the host-parasite interaction between them to the Eocene. The gymnosperm record is dominated by Podocarpaceae, and specially, by pollen similar to extant Podocarpus (Podocarpidites rugulosus, P. elegans), Lagarostrobus (Lepidothamnus sp.) and Phyllocladus (Phyllocladidites mawsonii). Overall, the spore-pollen assemblage include more than 54 morphotypes (rarefied at a count of 300 specimens), suggesting a highly diverse paleoflora developed during mid-late Eocene times. This interval coincides with a period of pronounced global warming recorded at middle to high latitudes in both hemispheres. Fossil plants preserved at Río Turbio Formation are represented today by groups confined to temperate and subtropical-tropical rainforest in lower latitudes of South America as Ilex (Ilexpollenites sp.), Cupania (Cupanieidites sp.), and members of the Malpighiaceae (Perisyncolporites pokornyi), Bombacaceae (Bombacacidites sp.), and Arecaceae (Arecipites sp., Mauritiidites sp.), together with typical taxa of dry sclerophyll forest of northern Argentina as Prosopis sp.