A MULTI-BASIN SEDIMENTARY MERCURY ANALYSIS OF THE MIOCENE MONTEREY FORMATION

Sedimentary mercury (Hg) contents have recently been used as a novel tool to track ancient volcanic activity. Mercury emitted from volcanoes is thought to be directly preserved in the sedimentary environment and, therefore, the sedimentary record. Mercury is transported from land to oceans by rock weathering and soil erosion by rivers, and biomass burning, so these factors must be considered when determining the controls on sedimentary Hg anomalies. Furthermore, Hg is a redox-sensitive element, and its accumulation can be controlled by the local redox potential of the water column and sediments. All ancient Hg records come from sedimentary successions that display lithologic variations and most likely have corresponding changes in local redox conditions. It is therefore necessary to constrain the local redox conditions of the basin in which Hg records are generated to provide context and normalize during data interpretation. Here, we will assess the various controls on sedimentary Hg contents from three basins from the eastern Pacific Ocean during the Miocene.

The Monterey Formation is a siliceous, organic matter-rich succession that was deposited in marginal marine basins off the California coast between 18 and 6 Ma. The local redox history for a similar portion of the formation has been constrained in three basins of the Monterey Formation using a multi-proxy approach (iron speciation and trace metal contents). The San Joaquin, Santa Barbara, and Santa Maria basins provide an opportunity to test the Hg proxy in environments with variable redox conditions and also across a range of terrigenous accumulation rates and provenances. Discrete ash beds are found throughout the sections due to synsedimentary volcanic activity; volcanogenic material is likely admixed through much of the apparently hemipelagic sediment, as well. Previous work suggests suboxic to euxinic conditions during the studied interval, which is ideal for resolving potential relationships between Hg and local redox fluctuations. Combining these data will result in a more nuanced understanding of Hg cycling in relation to fluctuating redox, distance from land, and other factors that may lead to increased sedimentary Hg accumulations.