Mercury anomalies in upper Aptian-lower Albian sediments from the Tethys realm

The upper Aptian-lower Albian stratigraphic interval documents important perturbations in the carbon cycle associated with the Oceanic Anoxic Event 1b (OAE 1b) tentatively connected with pulses in volcanic activity and the formation of the southern Kerguelen Plateau. However, uncertainties in existing age models for this interval preclude a robust and definitely convincing cause-effect connection between these two events. A sedimentary record from the Poggio le Guaine section, Umbria-Marche Basin, shows anomalously high levels of mercury during the upper Aptian-lower Albian interval. The persistence of the anomalies of [Hg] after normalization against TOC, Al, and Fe suggests that chemical and physical processes related to organic-matter scavenging, adsorption onto clay minerals, hydrous iron oxides and sulphur only played a secondary role as mechanisms for Hg accumulation in the sediments. In agreement with previous studies in which anomalous enrichments of Hg in sedimentary records were interpreted as monitors of enhanced volcanic activity, we speculate that the Hg enrichments documented in the Poggio le Guaine section reflect a rapid increase in atmospheric Hg content associated with a massive release of volcanic Hg, and possibly suggest a multi-phase emplacement of the southern Kerguelen Plateau (SKP) as a realistic source. Nonetheless, comparison of Hg profiles and micropalaeontological data from the Poggio le Guaine section reasonably excludes the possibility that the global biotic turnover horizon documented in the upper Aptian could be directly attributed to the volcanic pulses of the SKP emplacement.