MAJOR, MINOR AND TRACE ELEMENT EVOLUTION OF PHANEROZOIC SEAWATER

Study of primary fluid inclusions trapped in marine halite and calcite from various Phanerozoic sedimentary basins will provide a better understanding of the chemical evolution of seawater. Absolute concentrations of 21 selected major, minor and trace elements in fluid inclusions using combined Laser ablation-inductively coupled plasma-mass spectrometry (LA ICP-MS) and scanning electron microscope coupled to an x-ray energy-dispersive system (SEM-EDS) were measured to resolve which major geochemical processes controlled the composition of Phanerozoic seawater. More than 1000 fluid inclusions were analyzed from a large suite of Neoproterozoic and Phanerozoic marine halites and the preliminary results show that variations in minor and trace elements are in phase with reported secular variations in major seawater ions. I hypothesize that conservative minor and trace elements are more sensitive to changes in marine geochemical processes than major elements, which may lead to new insights about the factors that controlled Phanerozoic seawater chemistry. Important micronutrient tracers like Fe, Cu and Zn could record their potential role in influencing global biogeochemical cycles in the oceans. Primary fluid inclusions in marine calcite cements have been identified from petrographic studies; they are large enough to be imaged and analyzed. LA ICP-MS analyses of unevaporated fluid inclusions in marine calcite cements have never been reported, and so would represent a breakthrough in our understanding of the chemistry of Phanerozoic seawater.