Anta Formation (Miocene), Metán Subgroup (Orán Group), in río Piedras, Salta Province: Palynological data

Abstract

Deposition of the Salta Group (Cretaceous-Paleogene) terminated in the mid Eocene - Inca Diastrophic Phase. Following a compressive tectonic event in the Central Andes, this was succeeded by deposition of Metán Subgroup, divisible into Río Seco, Anta and Jesús María formations. The Anta Formation (300m thick) in Río Piedras is characterised by claystone, oolitic limestone and tuff deposited in shallow lakes or on a muddy plain. A comparative palynological analysis between Santa Bárbara Subgroup and Anta Formation (Metán Subgroup) shows that the transitional forest flora of the Anta Formation was more impoverished than that of the Santa Bárbara Subgroup, with higher percentages of Ulmaceae. The presence of Rhoipites sp. A (Rutaceae, cf. Ruta) in relative high percentages with Podocarpaceae and Anacardiaceae suggests a higher altitude (montane) palaeocommunity. Based on the palynological and sedimentological results the analised profile corresponds to a saline lake. These results indicate the first expansion of the steppe in a relatively dry climate in the NW of Argentina are also corroborated by fungal records.