The Lower-Middle Devonian transition in the Argentine Precordillera Basin: First palynological evidences from the Punta Negra Formation

Abstract

This study presents the first palynological evidence of the Lower–Middle Devonian transition in the Argentine Precordillera Basin, based on a new stratigraphic section of the Punta Negra Formation at the southern Loma de Los Piojos locality. Thirty-three samples were analyzed, yielding low-diversity, poorly preserved palynomorph assemblages dominated by terrestrial taxa. The occurrence of the key trilete spore taxa Dibolisporites farraginis, Acinosporites macrospinosus, Cymbosporites catillus, and Chelinospora timanica indicates an Eifelian age for the upper part of the unit, representing the first reliable record of the Middle Devonian in the basin. Integration with previous palynological data from nearby sections suggests that the Emsian–Eifelian transition is located between 400 and 480 m above the base of the formation. The presence of marine fauna between 550 and 700 m, correlated with this interval, constitutes the earliest Eifelian marine record in Argentina and one of the southernmost in South America. These results refine the chronostratigraphic framework of the Punta Negra Formation and provide new insights into the evolution of the Precordillera Basin during the Early–Middle Devonian transition.