The plant community of the Apeleg Formation (Lower Cretaceous), Patagonia. Diversity and its comparison with coetaneous megafloras of Western Gondwana

MARTÍN A. CARRIZO; MAITEN A. LAFUENTE DIAZ; GEORGINA M. DEL FUEYO; ORLANDO CÁRDENAS

Salvador

Congreso; XIV International Palynological Congress - X International Organisation of Palaeobotany Conference; 2016

The Lower Cretaceous has proved to be a period of great diversification and development of plant communities all across Western Gondwana. This is demonstrated by the abundant plant fossils found in different litostratigraphic units such as those of the Springhill, Anfiteatro de Ticó and Kachaike formations in Santa Cruz Province (Argentine), the Cerro Negro Formation in Antarctica and the Crato Formation in Brazil. However, other plant assemblages are merely mentioned as part of old geological studies and stratigraphical works without a complete analysis of their floras, as it is the case of the megaflora from the Apeleg Formation (Hauterivian/Barremian) in the Chubut Province of Argentine. This unit is part of the sedimentary sequence that comprises the region between the Apeleg Village, the Alto Río Senguerr city and the Lago Fontana area in the Patagonian Cordillera. It is described as deposits of transition from a marine to a continental paleoenvironment overlaying the Katterfeld Formation deposits. The outcrops of the Apeleg Formation are typically composed by levels of dark grey massive sandstones intercalated with layers of consolidated black lutites. The knowledge regarding the plant community composition of this unit is very limited, only one paleobotany study was made with descriptions and illustrations of the flora found at the proximities of the Estancia Victoria locality and includes impressions of fronds of Scleropteris sp., Cladophlebis sp., Taeniopteris dissecta Baldoni et De Vera, Ptilophyllum aff. antarcticum and Ptilophyllum sp.. In this work, fossil plants found in new fossiliferous deposits of the Apeleg Formation outcropping in the same locality are described. The new materials consist of numerous impressions of fronds and branches that belong to Baiera (Braun) Florin (Ginkgoales), Brachyphyllum (Lindley et Hutton) Harrris, Elatocladus Halle (Coniferales) and bract-scale complex most probable attributable to Araucariaceae. These findings increment the diversity and richness of the Apeleg Formation megaflora. However in comparison with the other Lower Cretaceous plant communities mentioned above from Western Gondwana, the plant assemblage of the Apeleg Formation is the less diverse of all. This low-diversity is probably related to a lack of preservation due to the high grade of metamorphosis of the strata in which the fossils were found. The metamorphosis is commonly linked to the several intrusive bodies generated by the igneous volcanic activity that affected the deposits of the Apeleg Formation during the Lower Cretaceous.