Toward a chronostratigraphy of the Paleocene-Eocene sedimentary record in northwestern Argentina

Abstract

The Santa Bárbara Subgroup of the Salta Group in northwestern Argentina represents a key sedimentary record to understand the geological, biological, and climatological changes that occurred in South America during the Paleogene. However, the lack of absolute ages in these non-marine successions have prevented conclusive interpretations and correlations at a regional-scale. In this contribution, we present an integrative study based on sedimentological and stratigraphic approaches, a paleontological review, and, for the first time, an absolute age from a tuff level in the upper section of the Mealla Formation. We propose the following scenario: 1) Cycles of low and high accommodation stages that can be tracked at basin-scale providing a criterion to regional correlations; 2) An U–Pb zircon age of 58 Ma, which combined with previously estimated ages for Santa Bárbara Subgroup indicate that this unit is constrained between 61 and 49? Ma; 3) On view of this new age the fossil-bearing levels of the Mealla Formation fill a hiatus of more than 4 Myr in the South American vertebrate record for the middle to late Paleocene, reshaping our understanding of the early evolutionary stages of this fauna. Our results represent a robust first step to achieve reliable regional correlations and an integrative comprehension of the evolution of the Salta Basin and its fossil biota.