Early Devonian paleogeographic evolution of SW Gondwana (Precordillera Argentina). How can the record of plants help us?

Abstract

In this work we refer new fossil plant records and revise the systematics of previously described taxa. The finding of Sporogonites excellens and the analysis of its fossil record allows us to propose it as a Lower Devonian indicator. The finding of a leafy lycophyte remains allows us to identify Haskinsia sp. in Precordillera and confirms its presence since the Emsian. From the registry of the plants associations found and taking into account the good age control in the sections to the north of the San Juan river, we propose a Devonian age (pre-Emsian) for the southern region (Banchongo Farm and vicinity). In this way, the Precordillera basin would be separated by a positive structure in at least two depocentres at this time, developing the Talacasto Formation to the north and center of the basin while the deposits of the Punta Negra and Villavicencio Formations occurred simultaneously to the south. During the Emsian- Middle Devonian, the rise in sea level, higher rates of sediment inputs and a marked subsidence made possible the deposition of the Punta Negra formation throughout the basin. The above conclusions affirm the importance of biostratigraphy plant-based in successions that do not have the presence of other markers.