Reconstruction of palaeoenvironmental conditions of the Vaca Muerta formation in the southern part of the Neuquen Basin (Tithonian-Valanginian): Evidences of initial short-lived development of anoxia

The Vaca Muerta Formation is a famous source rock being largely present in Argentina. The formation was examined in the southern part of the Neuquen Basin through clay-mineral assemblage composition, as well as organic and inorganic geochemical characteristics. In total, 259 samples were analyzed on both sides of the Huincul Arch (major E-W structure that divided the southern part of the basin into two depocentres). South to this structure (Picun Leufu area), the total organic carbon content (TOC) can reach 20% but is generally ranging from 0.1 to 6%. To the north (Covunco area), average TOC does not exceed 0.5%. Clay-mineral assemblages indicate an evolution of the sources of elastic supply through time in response to evolving weathering/erosion at the regional scale. Redox-sensitive trace-element distribution shows that the particulate iron shuttle process operated, with an initially-euxinic depositional environment that evolved rapidly to oxygenated seawater and suboxic sediments. Our results suggest an episodically restricted circulation pattern that occurred at the beginning of the deposition of the Vaca Muerta Formation (highest TOC content).