Mercury chemostratigraphy as a proxy of volcanic-driven environmental changes in the Aptian-Albian transition, Araripe Basin, northeastern Brazil

摘要

The stratigraphy of mercury (Hg) in sections of the Araripe Basin straddling the Aptian-Albian transition, encompassing the Romualdo, Ipubi, Crato and Barbalha (formerly Rio da Batateira)Formations showed positive excursions of Hg concentrations without correlation with organic carbon (C-org) contents. These incursions occurred during the deposition of the Barbalha Formation, which occurred in the Aptian under warm climate and high bio-productivity; in the Crato Formation, in the Albian, and also during the deposition of the Romualdo Formation. The Hg enrichments suggest external sources of Hg to the basin. The positive Hg excursion in the Ipubi Formation, unlike the others, was shown to be correlated with an increase in the deposition of C-org, suggesting internal processes as major river of Hg accumulation in sediments. The positive Hg excursions independent of C-org accumulation are concomitant to periods of intense volcanic activity in the Kerguelen Large Igneous Provinces (LIP). The excursion observed in the Ipubi Formation, however, seems associated with an event of anoxia, resulting in sediments rich in C-org, scavenging Hg from the water column. The Hg chemostratigraphy helps to understand of the paleoenvironmental changes in the Araripe basin, allowing understanding some of the drivers of such changes as the influence of volcanic activity and events of anoxia, as well as major biological crises.