The Early Cretaceous megaflora of the Springhill Formation, Patagonia. Paleofloristic and Paleonvironmental inferences

Abstract

The Springhill Formation (Lower Cretaceous) is considered as one of the most important oil producer units within the Austral Basin in Argentina. However, knowledge regarding this formation's plant community composition is still very scarce. In this work a thorough survey of the outcrops of the Springhill Formation was conducted regarding both geological and palaeobotanical aspects. Abundant fossil plant material was collected at the Estancia El Salitral and Río Correntoso localities in Santa Cruz Province, Argentina, consisting primarily of compressions of leafy shoots with several branching orders, completely to partially preserved fronds, simple to pinnate leaves and fertile scales. Analysis of these materials made it possible to describe 20 new taxa which add to the already known flora of the Springhill Formation; nine of these taxa were found in Estancia El Salitral, and the remaining 11 were found in Río Correntoso. The floristic diversity of the unit has increased through the discovery of the first megafossils of ginkgophytes (Baiera sp. 1 and Baiera? sp. 2), whereas new taxa have been described within the divisions of Pteridophyta, Pteridospermophyta, Cycadophyta and Pinophyta. Analysis of the vegetative and reproductive epidermal structures of the various groups included within this megaflora has been demonstrated to be a valuable tool for the recognition and differentiation of species. Analysis has also made it possible to suggest paleoenvironmental inferences. Finally, the megaflora from the Springhill Formation was compared to other relevant plant assemblages from the Lower Cretaceous of Western Gondwana. The megaflora was determined to be most similar to that of the well-known Patagonian Anfiteatro de Tico Formation and most different from that of the Brazilian Crato Formation.