ABSTRACT Recently, a set of mercury (Hg) anomalies in Valanginian sediments recovered from European sections demonstrated that an important magmatic pulse occurred at the onset of the Weissert episode. In this study, we report the distribution of Hg contents near the onset of the Weissert episode from localities outside of Europe, in the proto–Atlantic Ocean (Blake Bahama and Cap Hatteras Basins, Deep Sea Drilling Project [DSDP] Holes 534A and 603B) and southern Tethys Ocean (Argo Abyssal Plain, Ocean Drilling Program [ODP] Hole 765C), in order to evaluate the global impact of volcanism during the Valanginian. In addition, we also reinvestigated the Orpierre and Angles sections of the Vocontian Basin at a very high time resolution, to examine the potential impact of regional volcanic activity during that time interval. The onset of the Weissert episode in the proto-Atlantic and in the southern Tethyan cores is marked by significant increases in Hg contents. The persistence of the Hg anomaly in Hg/total organic carbon and Hg/Al ratios suggests that Hg enrichments were not primarily controlled by runoff processes and/or redox conditions, but instead indicate an increase in volcanic activity. The Hg enrichments recorded from localities outside of Europe at different latitudes were correlated to those previously observed in European sections, thereby confirming the presence of a global Hg peak at the onset of the Weissert episode. This peak was probably related to the emplacement of the Paraná-Etendeka large igneous province, suggesting a key role for volcanic activity during the Valanginian global environmental perturbations. In coeval intervals in the Vocontian Basin, Hg records show abrupt and short-lived enrichments, which correspond in the sedimentary successions to a goethite-rich ocher-colored layer. Two regional processes could explain Hg deposition and sequestration in this region: increased Hg sequestration by organic matter production in an oxygen-depleted environment, and/or the presence of regional volcanic activity, which is also indicated by the occurrence of a distal volcanic ash layer.

ABSTRACT The Vaca Muerta Formation deposited in a retro-arc setting, favored by an under filled depocenter and uplifted peripheral zones. The onset of the deposition corresponds to a rapid flooding of oceanic water penetrated through sudden ruptures along the incipient Andean arc, as a consequence of the Late Jurassic extension during the thermal subsidence stage. The Vaca Muerta Formation forms part of the Lower Mendoza Subgroup, and is defined as the organic-rich calcareous mudstone (av. 5% TOC) deposited above the sharp contact of the continental Tordillo and the Quebrada del Sapo formations; the upper contact with the Quintuco Formation is gradational and diachronous. The Vaca Muerta Formation spans the early Tithonian Virgatosphinctes andesensis to the early Valanginian Lissonia riveroi ammonite Zones. In association with classical stratigraphic characteristics of this unit, this chapter presents a cyclostratigraphic and magnetostratigraphic study displaying an unprecedented accurate time scale for the Vaca Muerta deposition, which took place from Chron M22 to Chron M15 in a timespan of ~10 My (4.86 My within the Tithonian and 5.27 My within the Berriasian).