The behavior of trace elements in seawater, sedimentary pore water, and their incorporation into carbonate minerals: a review

Abstract

Trace elements are actively cycled in seawater, are essential components for marine life, and are transported to the seafloor where they can become enriched in marine sediments. Trace element enrichment in marine sediments depends on local hydrography, redox conditions, and biological activity. Most redox-sensitive trace elements partake in biological cycling in seawater and sedimentary pore waters, and their distribution in the rock record can help to constrain the dynamics and changes in environmental conditions on geologic timescales. Carbonate minerals including calcite, aragonite, and dolomite readily adsorb and/or incorporate trace elements during precipitation. Although experimental laboratory studies concerning incorporation of trace elements into carbonate minerals have not always yielded unambiguous results, they have generally confirmed a strong tendency of carbonate minerals to accumulate and retain certain trace elements. Because natural carbonate minerals can archive trace elements, they have attracted attention as sources of information on biogeochemical processes. Nonetheless, drawbacks of using trace element contents of marine carbonates as paleoproxies exist due to mineral alteration during early diagenesis, subsequent burial diagenesis, and meteoric diagenesis. These processes can affect trace element contents in marine carbonates to different degrees, possibly leading to alteration or even a complete loss of their original trace element composition. This review summarizes current knowledge on the behavior of trace elements in seawater and interstitial pore water by integrating trace element cycling in the water column, their transport to the seafloor, and their subsequent incorporation into carbonate minerals. This work provides a comprehensive overview for the carbonate sedimentologist, detailing the water column and early diagenetic processes that affect trace element patterns of unaltered or poorly altered carbonate rocks used as archives of paleoenvironmental change.